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Seismic study of the transform-rifted margin in Davis Strait between Baffin Island (Canada) and Greenland: What happens when a plume meets a transform
Abstract
[ 1] The Davis Strait transform margin was studied using a 630-km-long wide-angle reflection/ refraction seismic transect extending from SE Baffin Island to Greenland. Dense airgun shots were recorded by 28 ocean bottom seismometers deployed along the line. A P wave velocity model was developed from forward and inverse modeling of the wide-angle data and incorporation of coincident deep multichannel reflection seismic data. Off Baffin Island in the Saglek Basin, 7 to 11-km-thick two-layered continental crust (5.8 - 6.6 km/s) is observed. Off Greenland, continental crust is divided into three layers (5.4 - 6.8 km/s) with a maximum thickness of 20 km. Farther offshore Greenland the crust thins to 7 - 12 km and the lower crust disappears. Between the continental blocks a 140-km-wide zone with oceanic crust ( layer 2 is 5.4 - 6.2 km/s and layer 3 is 6.7 - 7.0 km/s) is located. The western half of this zone is interpreted to be part of a volcanic margin with seaward dipping reflectors; the eastern part is associated with the Ungava fault zone (UFZ), the major transform fault in Davis Strait. The UFZ thus acted as leaky transform fault during phases of transtension. Southward flow of material from the Iceland plume created a 4 to 8-km-thick underplated layer (7.4 km/s) beneath the thinned portions of the continental crust and beneath previously emplaced oceanic crust. Plume related Paleogene volcanism is indicated by an up to 4-km thick layer (4.3 - 5.8 km/s) with basalts and interbedded sediments that can be traced from SE Baffin Island 400 km toward the east.
... The NCRM CTSE occupies parts of the east Canadian continental margin that are underlain by continental crust (Fig. 3). The latter can be up to c. 15-25 km thick below the pre-rift and syn-rift TSEs (Funck et al., 2007;Funck et al., 2012;Keen et al., 2018), and thins toward the oceanic domain (Fig. 4). The northern CTSE limit corresponds to the southern boundary of the Eurekan contractional deformation near 77° N, and the southern limit for the purpose of this volume is defined at 64° N. ...
... Seismic refraction data reveals deep crustal intrusions at the base of the crust characterized by high P-wave velocities (Vp > 7.0 km/s) and interpreted as underplated magmatic lower crustal bodies (LCB) (White et al., 1987;Holbrook et al., 2001) or highly intruded lower crust (White et al., 2008;Abdelmalak et al., 2017) (Fig. 5). The LCB is interpreted to be present beneath the thinned lithosphere (Funck et al., 2007;Dickie et al., 2011;Keen et al., 2012;Suckro et al., 2012;Suckro et al., 2013;Altenbernd et al., 2014Altenbernd et al., , 2015. ...
... The crustal structure is checked with available Receiver Function (RF) models (e.g., Dahl-Jensen et al., 2003;Kumar et al., 2007) and available seismic reflection data (Whittaker et al., 1997;Harrison et al., 2011;Gregersen et al., 2013). In the Labrador Sea, the C-C' conjugate crustal transect establishment is based on available published data (Chian and Louden, 1992;Funck and Louden, 1998;Hall et al., 2002;Funck et al., 2007;Gerlings et al., 2009; A C C E P T E D M A N U S C R I P T 2012; Keen et al., 2012). Note that the subject of this paper is the pre-rift and syn-rift deposits on the left (Canadian) side of the diagram, the subject of Gregersen et al. (2022) is the pre-rift and syn-rift deposits on the right (Greenland) side of the diagram, whereas the subject of the Knutz et al. (2022) inversion data was used where seismic reflection data is unavailable (e.g., Kimbell, 2013). ...
The Northeast Canada Rifted Margin (NCRM) Composite Tectono-Sedimentary Element (CTSE) developed during a long and complex history that produced two tectono-sedimentary elements (TSEs): (1) the pre-rift TSE of pre-Cretaceous age; and (2) the syn-rift TSE of Early Cretaceous-Paleocene age. The pre-rift TSE includes the oldest and most poorly known offshore sedimentary accumulations which mainly evolved in a cratonic setting. In contrast, Cretaceous-lower Paleocene sedimentary basins of the syn-rift TSE are known from several wells, seismic data, outcrops, and seabed samples, and their extent and distribution are mapped in most parts of the margin. The syn-rift TSE is the most prospective part of the margin and hydrocarbon shows have been documented in some wells and offshore seeps studies. This review provides insights into the Paleozoic-Cenozoic evolution of the NE Canada rifted margin in the Labrador Sea, Davis Strait, and Baffin Bay. In this context, we discuss structural inheritance and rift development, and account for confirmed and potential hydrocarbon systems and plays.
... In that year, the vessel CCGS Hudson acquired two lines (NUGGET-1 and -2) in southern Davis Strait (Funck et al., 2007;Gerlings et al., 2009). These lines were tied to four wells (Fig. 2) and relied on up to 28 ocean-bottom seismometers, through which the lateral resolution of the velocity models was significantly improved when compared to most of the previous experiments. ...
... In contrast, Chalmers and Pulvertaft (2001) concluded from seismic reflection records and the age of drilled sediments that there should be continental crust in the central part of Davis Strait. The first modern seismic refraction line was acquired in southern Davis Strait through Hekja O-71, Ralegh N-18, Gjoa G-37, and Qulleq-1 (NUGGET-line 1; Fig. 2, 10c), and here Funck et al. (2007) reported Figure 6. Magnetic-anomaly map compilation. ...
... The high-velocity lower crust (HVLC) in southern Davis Strait is restricted to the areas with thinned continental or igneous crust (Fig. 10c), but is not observed beneath the thicker crust off Greenland (Funck et al., 2007). To explain the distribution of the high-velocity lower crust, Funck et al. (2007) utilized the explanation presented by Nielsen et al. (2002), in which material related to the Iceland plume is guided by the relief at the base of the lithosphere. ...
... The Davis Strait, where many of the HVLC (high velocity lower crustal) bodies are concentrated, is a bathymetric high linking the Labrador Sea to Baffin Bay that is underlain by crust up to 20 km thick (Funck et al., 2007). The Davis Strait is thought to consist of continental lithosphere (Dalhoff et al., 2006) and hybrid/transitional crust, heavily intruded, as well as patches of exhumed mantle, likely accommodated by the "leaky" Ungava Transform Fault System (Funck et al., 2007;Suckro et al., 2013). ...
... The Davis Strait, where many of the HVLC (high velocity lower crustal) bodies are concentrated, is a bathymetric high linking the Labrador Sea to Baffin Bay that is underlain by crust up to 20 km thick (Funck et al., 2007). The Davis Strait is thought to consist of continental lithosphere (Dalhoff et al., 2006) and hybrid/transitional crust, heavily intruded, as well as patches of exhumed mantle, likely accommodated by the "leaky" Ungava Transform Fault System (Funck et al., 2007;Suckro et al., 2013). Furthermore, the Davis Strait appears to be the centre of Mesozoic-Cenozoic magmatism in the Northwest Atlantic (Funck et al., 2007;Funck et al., 2012;Hosseinpour et al., 2013;Suckro et al., 2013;Abdelmalak et al., 2019). ...
... The Davis Strait is thought to consist of continental lithosphere (Dalhoff et al., 2006) and hybrid/transitional crust, heavily intruded, as well as patches of exhumed mantle, likely accommodated by the "leaky" Ungava Transform Fault System (Funck et al., 2007;Suckro et al., 2013). Furthermore, the Davis Strait appears to be the centre of Mesozoic-Cenozoic magmatism in the Northwest Atlantic (Funck et al., 2007;Funck et al., 2012;Hosseinpour et al., 2013;Suckro et al., 2013;Abdelmalak et al., 2019). The Davis Strait underwent dextral transtension, but not breakup during the first stage of Labrador Sea-Baffin Bay formation (Wilson et al., 2006;Suckro et al., 2013), followed by further transpression during the second stage (Geoffroy et al., 2001;Suckro et al., 2013). ...
The Labrador Sea and Baffin Bay form an extinct Palaeogene oceanic spreading system, divided by a major continental transform, the Davis Strait, with the whole region defined as the Northwest Atlantic. The Davis Strait hosts the Ungava Fault Zone and is the central structural element of the Davis Strait Large Igneous Province (DSIP) that formed broadly coeval with continental breakup to its north and south. While constraints on the crustal structure in this region primarily exist in the offshore, crustal models are limited onshore, which makes an interpretation of regional structures as well as the extent, and therefore origin of the DSIP extremely difficult to ascertain. Here, we have collected all available teleseismic data from the Northwest Atlantic margins and applied a receiver function inversion to retrieve station-wise velocity models of the crust and uppermost mantle. We integrate the outcomes with published controlled-source seismic data and regional crustal models to make inferences about the crustal structure and evolution of the Northwest Atlantic. In particular, we focused on constraining the spatial extent and origin of high velocity lower crust (HVLC), and determining whether it is generically related to the Davis Strait Igneous Province, syn-rift exhumed and serpentinised mantle, or pre-existing lower crustal bodies such as metamorphosed lower crust or older serpentinised mantle rocks. The new results allow us to better spatially constrain the DSIP and show the possible spatial extent of igneous-type HVLC across Southwest Greenland, Northwest Greenland and Southeast Baffin Bay. Similarly, we are able to relate some HVLC bodies to possible fossil collision/subduction zones/terrane boundaries, and in some instances to exhumed and serpentinised mantle.
... The nature of the crust in this area has been difficult to interpret, in particular the possible occurrence of oceanic crust (Srivastava et al. 1982;Chalmers & Pulvertaft, 2001). Seismic studies in the northern Labrador Sea, Davis Strait and southern Baffin Bay have revealed the existence of extensive Palaeogene volcanic rocks (Whittaker, 1996;Skaarup, 2002;Skaarup et al. 2006;Sørensen, 2006;Funck et al. 2007Funck et al. , 2012Gregersen & Bidstrup, 2008;Gerlings et al. 2009;Keen et al. 2012Keen et al. , 2018aSuckro et al. 2012Suckro et al. , 2013Gregersen et al. 2019) and a magmatic underplate of several kilometres thickness, interpreted as plume-generated, beneath the thinned crust (Funck et al. 2007Gerlings et al. 2009;Keen et al. 2012;Suckro et al. 2013). Hosseinpour et al. (2013) presented a map with calculated thicknesses of igneous crust of up to 8 km in the Davis Strait area. ...
... The nature of the crust in this area has been difficult to interpret, in particular the possible occurrence of oceanic crust (Srivastava et al. 1982;Chalmers & Pulvertaft, 2001). Seismic studies in the northern Labrador Sea, Davis Strait and southern Baffin Bay have revealed the existence of extensive Palaeogene volcanic rocks (Whittaker, 1996;Skaarup, 2002;Skaarup et al. 2006;Sørensen, 2006;Funck et al. 2007Funck et al. , 2012Gregersen & Bidstrup, 2008;Gerlings et al. 2009;Keen et al. 2012Keen et al. , 2018aSuckro et al. 2012Suckro et al. , 2013Gregersen et al. 2019) and a magmatic underplate of several kilometres thickness, interpreted as plume-generated, beneath the thinned crust (Funck et al. 2007Gerlings et al. 2009;Keen et al. 2012;Suckro et al. 2013). Hosseinpour et al. (2013) presented a map with calculated thicknesses of igneous crust of up to 8 km in the Davis Strait area. ...
... Hosseinpour et al. (2013) presented a map with calculated thicknesses of igneous crust of up to 8 km in the Davis Strait area. Thin crust of oceanic character, but thicker than normal oceanic crust because of magmatic underplating, was identified in the southern part of the Ungava Fault Zone by Funck et al. (2007) and in the northern part, offshore Cape Dyer, by Suckro et al. (2013). Funck et al. (2012) noted a narrow gravity high that runs SSW-NNE throughout the entire Davis Strait, and concluded that it is composed of igneous crust along its entire length, formed along a leaky transform fault. ...
Volcanic rocks from the Davis Strait were studied to elucidate the tectonomagmatic processes during rifting and the start of seafloor spreading, and the formation of the Ungava transform zone between Canada and Greenland. The rocks are from the wells Hekja O-71, Gjoa G-37, Nukik-2 and Hellefisk-1, and from dredges on the northern Davis Strait High. Ages range from Danian to Thanetian (dinocyst palynozones P2 to P5, 62.5–57.2 Ma). The rocks are predominantly basaltic, but include picrites on the Davis Strait High. Calculated mantle potential temperatures for the Davis Strait High are c. 1500°C, suggesting the volume of magma generated was large; this is consistent with geophysical evidence for magmatic underplating in the region. The rare earth element patterns indicate residual mantle lithologies of spinel peridotite and, together with Sr–Nd isotopes, indicate melting beneath regionally extensive, depleted asthenosphere beneath a lithosphere of thickness similar to, or thinner than, beneath Baffin Island and distinctly thinner than beneath West Greenland. Some sites include basalts with more enriched compositions. Depleted and enriched basalts in the Hellefisk well show contemporaneous melting of depleted and enriched mantle components in the asthenosphere. The Hekja and Davis Strait High basalts and picrites have unique, ultradepleted compositions with (La/Sm) N < 0.5, (Tb/Lu) N < 1 and Nb/Zr = 0.013–0.027. We interpret these compositions as a product of the melting regime within the Ungava transform zone, where the melting column would be steep-sided in cross-section and not triangular as expected at normal spreading ridges. Magmatism along the transform stopped when the tectonic regime changed from transtension to transpression during earliest Eocene time.
... Propagation proceeded unhindered across the Grenville and Ketilidian orogens and through the North Atlantic craton but stalled at the junction of the Nagssugtoqidian and Rinkian orogens [Connelly et al., 2006;Grocott & McCaffrey, 2017;Peace et al., 2018;Peace et al., submitted]. There, the crust was locally thickened [Clarke & Beutel, 2018;Funck et al., 2007;Funck et al., 2012;Peace et al., 2017;St-Onge et al., 2009] and pre-existing mantle slabs may also have existed. Unique, ultra-depleted picrite cumulates erupted (Section 5.3) [Clarke & Beutel, 2018] and the Davis Strait NNE-SSW sinistral, right-stepping transtensional accommodation zone formed. ...
... Complex comprises ~ 8-km-thick oceanic crust underlain by an ~ 8 km thickness of HVLC with P-wave velocities up to 7.4-7.5 km/s [Chalmers & Pulvertaft, 2001;Funck et al., 2006;Funck et al., 2007;Srivastava et al., 1982] and a density of 2850 -3050 kg/m 3 [Suckro et al., A C C E P T E D M A N U S C R I P T 2013]. These values are similar to those of Icelandic-type lower crust. ...
... In these cases the area between the overlapping ridges shears in distributed "bookshelf" faulting mode [Perram et al., 1993]. zone [Funck et al., 2007]. ...
The breakup of Laurasia to form the Northeast Atlantic Realm disintegrated an inhomogeneous collage of cratons sutured by cross-cutting orogens. Volcanic rifted margins formed that are underlain by magma-inflated, extended continental crust. North of the Greenland-Iceland-Faroe Ridge a new rift–the Aegir Ridge–propagated south along the Caledonian suture. South of the Greenland-Iceland-Faroe Ridge the proto-Reykjanes Ridge propagated north through the North Atlantic Craton along an axis displaced ~150 km to the west of the rift to the north. Both propagators stalled where the confluence of the Nagssugtoqidian and Caledonian orogens formed an ~300-km-wide transverse barrier. Thereafter, the ~150 × 300-km block of continental crust between the rift tips–the Iceland Microcontinent–extended in a distributed, unstable manner along multiple axes of extension. These axes repeatedly migrated or jumped laterally with shearing occurring between them in diffuse transfer zones. This style of deformation continues to the present day in Iceland. It is the surface expression of underlying magma-assisted stretching of ductile continental crust that has flowed from the Iceland Microplate and flanking continental areas to form the lower crust of the Greenland-Iceland-Faroe Ridge. Icelandic-type crust which underlies the Greenland-Iceland-Faroe Ridge is thus not anomalously thick oceanic crust as is often assumed. Upper Icelandic-type crust comprises magma flows and dykes. Lower Icelandic-type crust comprises magma-inflated continental mid- and lower crust. Contemporary magma production in Iceland, equivalent to oceanic layers 2–3, corresponds to Icelandic-type upper crust plus intrusions in the lower crust, and has a total thickness of only 10–15 km. This is much less than the total maximum thickness of 42 km for Icelandic-type crust measured seismically in Iceland. The feasibility of the structure we propose is confirmed by numerical modeling that shows extension of the continental crust can continue for many tens of millions of years by lower-crustal ductile flow. A composition of Icelandic-type lower crust that is largely continental can account for multiple seismic observations along with gravity, bathymetric, topographic, petrological and geochemical data that are inconsistent with a gabbroic composition for Icelandic-type lower crust. It also offers a solution to difficulties in numerical models for melt-production by downward-revising the amount of melt needed. Unstable tectonics on the Greenland-Iceland-Faroe Ridge can account for long-term tectonic disequilibrium on the adjacent rifted margins, the southerly migrating rift propagators that build diachronous chevron ridges of thick crust about the Reykjanes Ridge, and the tectonic decoupling of the oceans to the north and south. A model of complex, discontinuous continental breakup influenced by crustal inhomogeneity that distributes continental material in growing oceans fits other regions including the Davis Strait, the South Atlantic and the West Indian Ocean.
... Their revision of previous plate kinematic models explains the Paleogene movement of the Greenland plate versus the North American plate with respect to the oceanic spreading system in Baffin Bay and associated fracture zones. This work agrees with regional seismic refraction studies (Funck et al., 2007) interpreting the emplacement of Paleocene oceanic crust within the elongated rift zone that underwent structural inversion during transpressive movement along the UFZ of almost 300 km during the Eocene. ...
... P-wave sonic velocities for basalts are typically in the range of 4.2-5.8 km/s through Davis Strait (Funck et al., 2007) but regions with even higher sonic velocities up to 7.4 km/s suggest magmatic underplating of the crust, which implies increased volcanic activity. ...
... The regional seismic refraction surveys done across Davis Strait shows this occurring in the middle regions between Baffin and Greenland (Funck et al., 2007;Gerlings et al., 2009). Velocity modelling from these studies also indicates the presence of transitional crust Fig. 1. ...
We present a compilation of the western Davis Strait region offshore southeastern Baffin Island, Nunavut, Canada with new subsurface geological structural details and observations regarding past hydrocarbon occurrences.
This consists of seismic mapping with archival data correlated with a filtered marine Bouguer anomaly gravity compilation and magnetic data sets covering northern Saglek Basin, the western part of the Lady Franklin Basin and the Ungava Fault Zone from south of Baffin Bay.
A regional seismic horizon for mapping basin architecture comes from the top of the Paleogene volcanic syn-magmatic zone, where pervasive volcanic flows and intrusions are intermingled with the sedimentary section. The seismic depth map to the top of the regional volcanic seismic horizon shows pre-rift sedimentary basins having maximum depths of approximately 6 to 7 km flanking the shallower Ungava Fault Zone. Correlation of Bouguer anomaly gravity and magnetic data interpretations with the seismic mapping, indicate that over some areas true crystalline basement is deeper than can be determined by reflection seismic, as the base of the syn-magmatic section is not resolvable for seismic mapping.
Extensive Paleogene mafic intrusives and extrusive basalts dominate the architecture of this volcanic rifted margin as seen by the dominant high amplitude magnetic anomalies associated with many deeper structures. The over 250 kilometer long Ungava Thrust Fault is recognised as the key structural element of the UFZ and valley complex. The adjoining Davis Strait High maps on seismic as a continuous structure running the length of Davis Strait plunging southwards to a Bouguer gravity high feature that terminates the western end of the extinct Eocene spreading zone south of Davis Strait. This horn shaped structural feature establishes the presence of an accommodation zone with multiple faults and localised thrust faulting as required to fit the non-simple mechanics for strike-slip motion that occurs along the south end of this transform fault system. The revised marine Bouguer anomaly gravity data set also reveals two new, near shore grabens east of Cumberland Sound, each extending over 100 km in length with sediment thicknesses of at least 5 km.
The southern Tariuk Basin and the northern Imaqpik Basin are both pre-rift basins and most likely originate from the Paleozoic based on seafloor dredge and nearby shallow drill cores from previous studies. The hydrocarbon charge of a previously unexplained petroliferous shallow marine drill core that is adjacent the eastern edge of the Tariut Basin is attributed to Paleozoic source rocks that have undergone enhanced thermal maturation from sill intrusion associated with rifting. The Imaqpik Basin shows strong evidence of a hydrocarbon system from the proximity of clustered sea surface oil slick features, interpreted from satellite radar images, and the a local zone of anomalously high dissolved methane measured within the water column that originates from the seafloor immediately east of Cape Dyer at the northern limit of that basin. The overlying Cape Dyer flood basalt field extends from limited onshore exposures into the offshore and maps with magnetic data over an area of approximately 13,000 km2. This extrusive feature and it’s implicit components are likely a key to understanding the enhanced thermal maturation of Paleozoic to Paleogene sedimentary source rocks in the pre-rift basins hosting this previously unrecognised unconventional petroleum system.
... Using geophysical data (seismic, gravity, and magnetic) Chalmers and Pulvertaft (2001) described the flank and structural high in Davis Strait as continental, while Srivastava et al. (1982) described the flank as oceanic. Several studies (Funck et al., 2007;2012;Keen et al., 2012;Suckro et al., 2013) propose that the Ungava Fault Zone in the Davis Strait acted as a leaky transform system where small amounts of oceanic crust may have been produced in the absence of a fully developed oceanic spreading center Funck et al., 2007). Funck et al. (2012) interpreted the northward extension of the Ungava Fault Zone as a continuation of the leaky transform fault where remnants of continental crust lay between this zone and the normal oceanic crust of the Baffin Bay Funck et al., 2012). ...
... Using geophysical data (seismic, gravity, and magnetic) Chalmers and Pulvertaft (2001) described the flank and structural high in Davis Strait as continental, while Srivastava et al. (1982) described the flank as oceanic. Several studies (Funck et al., 2007;2012;Keen et al., 2012;Suckro et al., 2013) propose that the Ungava Fault Zone in the Davis Strait acted as a leaky transform system where small amounts of oceanic crust may have been produced in the absence of a fully developed oceanic spreading center Funck et al., 2007). Funck et al. (2012) interpreted the northward extension of the Ungava Fault Zone as a continuation of the leaky transform fault where remnants of continental crust lay between this zone and the normal oceanic crust of the Baffin Bay Funck et al., 2012). ...
... Offshore, seismic reflection data in the northern Labrador Sea, Davis Strait, and Baffin Bay reveal extensive Palaeogene volcanic rocks (Whittaker et al., 1997;Skaarup et al., 2006;Gregersen and Bidstrup, 2008;Gregersen et al., 2013). Williamson et al. (2003) reported 40 (Funck et al., 2007;Dickie et al., 2011;Keen et al., 2012). ...
Passive margins are the locus of tectonic and magmatic processes leading to the formation of highly variable along-strike and conjugate margins structures. Using extensive new seismic, gravity, and magnetic datasets, complemented by seabed samples and field work, we investigate the tectonomagmatic evolution of the northwest (NW) Atlantic where breakup-related igneous rocks were emplaced during several Paleogene events associated with lithospheric stretching, continental breakup, and the formation of new oceanic basins. Interpretational methods include integrated seismic-gravity-magnetic (SGM) interpretation and seismic volcanostratigraphy. In addition, seabed and field samples were collected and analyzed to constrain the basin stratigraphy, hydrocarbon potential, and the geochronology and geochemistry of the volcanic sequences. Offshore, 2D seismic data reveal several Seaward Dipping Reflector (SDR) wedges and escarpments in the Labrador Sea, Davis Strait, and Baffin Bay. Onshore, eastward prograding foreset-bedded hyaloclastite delta deposits and overlying horizontal lava successions outcrop on Nuussuaq. These hyaloclastites and lava successions are world class analogues to the Lava Delta and Landward Flows volcanic seismic facies units identified offshore. Our mapping results document an aerial extent of the Paleogene breakup-related volcanics of 0.3 × 106 km2, with an estimated volume of 0.5–0.6 × 106 km3. Basalt samples recovered by dredging the Upernavik Escarpment have late Paleocene to/early Eocene ages, whereas the sedimentary samples provide an excellent seismic tie with the stratigraphy and the geology in this frontier area. From the integrated SGM interpretation, we identify a rapidly thinning crust and changes in top and intra-basement seismic reflection characteristics in the oceanic domain correlated with transition between different magnetic domains. The mapping results were subsequently integrated in a plate tectonic model. The plate tectonic reconstruction and basalt geochronology suggest that the majority of the volcanism in the NW Atlantic occurred between ~62 and ~58 Ma, associated with an increased spreading rate in the Labrador Sea, starting from the onset of the Selandian (~61.6 Ma). A change in the spreading direction during the Eocene (~56 Ma), synchronously with a shift of volcanic activity from the NW to the NE Atlantic, correspond to a northward drift of Greenland and the initiation of the Eurekan Orogeny. Finally, our interpretations reveal a complex rift configuration along the NW Atlantic conjugate margins both prior to and during breakup.
... Wells are open circles. The relationship of the study region to the Davis Strait and the Ungava Fracture Zone is shown, as well as the location of crustal-scale seismic data in the region (Funck et al., 2007; Nugget 1 line). FSC = Fylla Structural Complex off West Greenland (Døssing, 2011) and is conjugate to the southern part of our study region. ...
... Structures are complex with both NW-SE and NNE-SSW trends, as normal faults of late Early Cretaceous age were reactivated in Late Cretaceous time as transcurrent faults. This late Cretaceous trend is the same as that of the large-offset Ungava transform fault through Davis Strait (Figure 4; Funck et al., 2007;Oakey & Chalmers, 2012), suggesting the regional influence of shearing in the Fylla Bank region (Døssing, 2011). ...
... Deep crustal and sedimentary structure on both conjugate margins (Funck et al., 2007;Gerlings et al., 2009;Keen et al., 2012) has been used to recreate a cross section with oceanic crust younger than chron 27 removed (Danian time; Figure 7). This illustrates the considerable asymmetry across the margins, with a wider zone of thinned continental crust on the Greenland margin. ...
High-quality seismic reflection data from the offshore northern Labrador rifted margin allow imaging of the extended and rifted crust both along and across the continental margin and are described in conjunction with available seismic velocity and gravity data. The margin formed within cold, thick cratonic lithosphere. Both Archean continental basement and a discrete, undulating, high-amplitude, deep reflection about 10 km below basement are observed. The deeper reflection can be correlated with the crust-mantle boundary as measured on previous wide-angle seismic data in the region. This reflection, termed here the L-reflection, appears to be the equivalent to other top-mantle detachments found elsewhere on magma-poor rifted margins. However, normal mantle velocities have been observed to lie just below the reflection, suggesting that it may not be related to the formation of weak serpentinized mantle. A high-velocity and density zone occupies the outer shelf seaward of the L-reflection where basement is transparent, which may represent highly mafic crust or serpentinized mantle. A crustal reconstruction of this margin and its conjugate shows marked asymmetry, with a wider zone of crustal thinning on the Greenland margin. These crustal thinning profiles are comparable to those on other conjugate margins within cratonic lithosphere. While some of the attributes of this margin are those of a magma-poor system, at the ocean-continent transition, thick igneous crust created a magma-rich zone in Paleocene time when a hot spot was active in the Davis Strait to the north. Thus, this margin exhibits characteristics of both magma-rich and magma-poor systems.
... a) Line 1 through the southern portion of the western Davis Strait region intersecting all three of the exploration wells in the northern part of the Saglek Basin and near the Gjoa High. Pre-rift basement is locally seen in seismic data, but is primarily defined by refraction seismic from Funck et al. (2007). Seismic data courtesy of TGS. ...
... Along seismic refraction lines (e.g. Funck et al., 2007;Suckro et al., 2013), however, these relationships are clearer (see Keen et al., this volume). The landward limit of oceanic crust (black triangles) is shown in Figure 4 for the conjugate margins and the present study tentatively assigns oceanic crust between them, except where continental fragments are present (Fig. 4b, 7). ...
Western Davis Strait lies within the Labrador-Baffin Seaway rift system, which began forming in the Early Cretaceous as Greenland separated from North America. At chron C27n (Danian), regional seafloor spreading began, as well as significant magmatism. The opening direction changed from southeast-northwest to more north-south in the Thanetian-Ypresian between chrons C25n and C24n, resulting in significant strike-slip motion through the Davis Strait region until seafloor spreading ended at chron C13, near the Eocene-Oligocene boundary. This tectonism has influenced the stratigraphy preserved in basins within western Davis Strait, including confirmed Cretaceous successions in the Lady Franklin Basin and Cumberland Sound; however, regional overprinting of Paleocene-Eocene volcanic rocks obscures pre-rift basement and possible older strata over much of the region. Three industry wells and several seabed samples of bedrock help constrain the stratigraphic distribution of Cretaceous and Cenozoic strata based on the lithostratigraphy of the well sampled Labrador margin.
... Another volcanic margin, identified by Skaarup et al. (2006), is found east of Cape Dyer and is marked by seaward-dipping reflectors and thick inner flows, and is tentatively mapped farther north toward Home Bay ( Fig. 9; Dafoe, Dickie, and Williams, this volume; Keen et al., this volume). Through central Davis Strait is the Davis Strait High, composed of crystalline basement with a thin basalt cover (Funck et al., 2007;Suckro et al., 2013). It forms two main ridge systems which roughly parallel the southeast Baffin Island coastline, with nearby volcanic highs following a similar trend ( Fig. 9 ; Dafoe, DesRoches, and Williams, this volume). ...
... Units E and D are further subdivided by horizons E1, E2, D3, and D1A, which can be tied to wells in the northern part of the Saglek Basin (Fig. 6a); elsewhere these horizons can only be mapped locally. Refraction seismic data along profile 3 (Fig. 6a) constrains the presence of oceanic crust and depth to the top of continental basement (Funck et al., 2007;Keen et al., this volume). This is in contrast to the West Greenland margin where several wells constrain the Ev, E2, and E1 horizons (Gregersen et al., 2019, this volume). ...
... This implies that there could be some overlap with continental crust, but since intrusions are not included in this assessment, Hekja >1 km (interbedded); G37 Gjoa >1 km; 154/3-1-0.9 km (Funck et al., 2007(Funck et al., , 2008Klingelhöfer et al., 2005;Nelson et al., 2009 the isopachs will still provide a reasonable first order estimate for H. Average errors are ∼0.5 km for the basalt isopach (Figure 8c), ∼2 km for the lower igneous crust isopach ( Figure 8d) and 0.1 km/s for mean V p (Figure 8b), but they are highly dependent on model resolution of the individual refraction/wide-angle lines (Figures 1, 8, Figure S1 in Supporting Information S1). ...
... West Greenland is seismically poorly covered (Figure 1). However, off southwest Greenland, V p ∼ 7.4-7.5 km/s (Funck et al., 2007;Gerlings et al., 2009; Figure 8b) are slightly offset from the LIC isopach maximum (Figure 8d). ...
The North Atlantic Igneous Province (NAIP) has been the focus of numerous studies. However, a systematic integrated methodology to assess the NAIP, has so far been lacking. For this purpose, a synclinal oceanic rift approach is developed from the stratigraphic record. Mechanisms are addressed combining trace element and seismic velocity data as a proxy for excess mantle potential temperature (ΔTp), using simple mantle melting models. Unconformities play a major role in this assessment, providing evidence for a drop in ΔTp to ambient levels (≤50°C). Three phases can be delineated in the stratigraphic record: a (a) Pre‐; (b) Syn‐; and (c) Post‐breakup phase. The Syn‐breakup phase is bound at the base by the Breakup Unconformity and at the top by the Magmatic Unconformity. At breakup, magmatic crustal thickness (H) can be estimated from addition of basalt‐ and Lower Igneous Crust isopachs. These seismic estimations can be further constrained by observations on volcanic transport directions. This allows differentiation between hotspots and Volcanic Passive Margins (VPMs), where hotspots are characterized by continuous ΔTp amplitude variations, whereas VPMs only display declining or absent fluctuations post breakup. On Iceland and the Greenland‐Iceland‐Faroe Ridge, H is primary controlled by ΔTp fluctuations promoting ridge jumps and second, associated fluctuating active upwelling ratio (χ ∼ 2–4). Results suggest that there were at least three hotspots active at breakup. The West Greenland and proto‐Jan Mayen hotspots lost importance in the Oligocene, while Iceland remained and is currently the main hotspot in the North Atlantic.
... Judging from the magnetic data, the entire crustal section of the ridge is saturated by igneous bodies. The aeromagnetic survey materials [24] show a similarity between the magnetic field of the Alpha Ridge and magnetic anomalies of the Franz Josef Land archipelago and Greenland coast. ...
... The structure and velocity parameters of the crust of the Mendeleev Rise in the section of the Arktika-2000 profile generally indicate its continental nature. The substantial thickening of the lower crust with respect to the upper and their velocity characteristics make it possible to consider the continental margins of Ellesmere Island and Greenland as analogs of the Mendeleev Rise [24]. ...
... Magnetic anomalies, which are clearer in the south and more ambiguous in the north, have been the main tools with which the tectonic evolution and plate kinematics of the Labrador Sea and its margins have been deduced (Kristoffersen and Talwani, 1977;Srivastava, 1978;Roest and Srivastava, 1989). Targeted seismic reflection and refraction experiments have also been important, particularly in the identification of serpentinized mantle within the transitional zones Louden, 1992, 1994;Louden, 1992, 1995;Keen et al., 1994;Chian et al., 1995aChian et al., , 1995bReid, 1996;Funck and Louden, 1998, 1999, 2000Funck et al., 2001Funck et al., , 2007Funck et al., , 2008Gerlings et al., 2009). Combined, these geophysical data sets reveal complex fracturing within the Labrador Sea with four main fracture zones (Minna, Snorri, Hudson, and Ungava; Figure 2) offsetting magnetic anomalies 20-24 (Srivastava, 1978). ...
... The Labrador Sea and the Labrador offshore margin have been the focus of several crustal-scale seismic studies conducted by the Geological Survey of Canada (GSC) and also as part of the Lithoprobe Eastern Canadian Shield Onshore-Offshore Transect (Hall et al., 2002). The locations of these seismic lines are plotted in Figure 4 (901, 902, and 903 [Keen et al., 1994;Srivastava and Keen, 1995], F2 and F3 [Funck et al., 2001], F4 [Funck and Louden, 1998], F5 [Funck and Louden, 1999], F6 [Funck and Louden, 2000], F7 [Funck et al., 2008], N1 [Funck et al., 2007], N2 [Gerlings et al., 2009], O1 and O2 Louden, 1992, 1995], R1 and R2 [Chian et al., 1995b], and R96 [Reid, 1996]). Most recently, seismic refraction work has been undertaken across the Labrador Sea spreading center (D4 and D5 [Delescluse et al., 2015]). ...
A regional long-offset 2-D seismic reflection program undertaken along the Labrador margin of the Labrador Sea, Canada, and complemented by the acquisition of coincident gravity data, has provided an extensive dataset with which to image and model the sparsely investigated outer shelf, slope and deep water regions. Previous interpretation of the seismic data revealed the extent of Mesozoic and Cenozoic basins and resulted in the remapping of the basin configuration for the entire margin. In order to map the syn-rift package and improve understanding of the geometry and extent of these basins, we have undertaken joint seismic interpretation and gravity forward modelling to reduce uncertainty in the identification of pre-rift basement, which varies between Paleozoic shelfal deposits and Precambrian crystalline rocks, both with similar density characteristics. With this iterative approach, we have obtained new depth to basement constraints and have deduced further constraints on crustal thickness variations along the Labrador margin. At the crustal-scale, extreme, localized crustal thinning has been revealed along the southern and central portions of the Labrador margin while a broad, margin-parallel zone of thicker crust has been detected outboard of the continental shelf along the northern Labrador margin. Our final gravity models suggest that Late Cretaceous rift packages from further south extend along the entire Labrador margin and open the possibility of a Late Cretaceous source rock fairway extending into the Labrador basins.
... The last step began during the Maastrichtian (Kjennerud and Vergara, 2005;Ren et al., 1998) with magmatism, possibly related to this mantle exhumation. The Icelandic hotspot was first affecting the Labrador Sea (Funck et al., 2007;Keen et al., 2012Fig. 15Funck et al., 2007;Keen et al., 2012;Delescluse et al., 2015;Fig. ...
... The difference in rheology may explain this large-scale brittle behaviour, which has led to dramatic thinning of the crust and probably mantle exhumation. Data from Dinkelman et al. (2010), Funck et al. (2007), Oakey and Chalmers (2012), Saunders et al. (1998), Skaarup and Pulvertaft (2007), Sørensen (2006), Whittaker et al. (2011) and Keen et al. (2012), summarized in Fig. 15, do not support the categorisation (i.e. exhumation vs underplating) proposed by Lundin and Doré (2011) between the Laborador Sea and the NE Atlantic. ...
The outer Vøring Basin, Norwegian Sea, is an abnormally deep and distal part of the Norwegian passive margin, known as “magma-rich”. Yet, the lastest borehole drilled in its northernmost part led to a drastic change in the interpretation of seismic reflection data. This update motivates a new model for the entire Mesozoic-Eocene rifting period. Here I evaluate the link between tectonics, serpentinization and magmatism in the Norwegian margin from the Ryazanian-Valanginian to the Palaeocene-Eocene magmatic breakup. Maps of the regional Nise sandstones and main regional unconformities specifically highlight the fundamental role of the Nyk-Vema Structure to understand the basin and to question the deformation timing related to deep structures. The top of partially serpentinized mantle is supported by high-amplitude reflectors clearly visible on certain seismic lines, known as “T-Reflector”, covered with gravity-driven pre-exhumation sediments and further deposits. A new structural scheme based on the interpretation of 2D and 3D seismic data shows the complex organization of fault networks and constrains a major deformation period between the Late Campanian and the Late Palaeocene. Ocean-scale complementary arguments are in good agreement with Lower-Cretaceous mantle exhumation. Before becoming a volcanic margin in the Palaeocene, this segment of the Norwegian margin appears as amagmatic until the Late Campanian, at least. I propose an integrated model since the onset of hyperextension in the end of the Jurassic until the cessation of activity of the Aegir Ridge in the Miocene. This model has implications regarding the context-dependent interpretation of lower-crustal bodies, the ubiquity of serpentinization and mantle exhumation worldwide, and on the hydrocarbon system.
... Судя по магнитным данным, весь разрез коры хребта насыщен магматическими телами. Материалы упомянутых выше аэромагнитных съёмок [24] показывают сходство магнитного поля хребта Альфа с однотипными магнитными аномалиями архипелага Земли Франца-Иосифа и побережья Гренландии. ...
... Структура и скоростные параметры земной коры поднятия Менделеева в сечении профиля «Арктика-2000» в общих чертах указывают на его континентальную природу. Существенное утолщение нижней коры относительно верхней и их скоростные характеристики позволяют рассматривать в качестве материковых аналогов поднятия Менделеева континентальные окраины островов Элсмир и Гренландии [24]. Рис. 7. Скоростная модель земной коры вдоль профиля ГСЗ «Арктика-2000» [13]. ...
Main positive morphostructures of the Amerasia Basin, the Lomonosov Ridge, Alpha Ridge, Mendeleev Rise, Chukchi Plateau and Northwind Ridge, have been considered from geomorphological, geological and geophysical aspects. Time and Depth seismic sections have been provided up to the Moho discontinuity from the Lomonosov Ridge and its junction with the Greenland and East-Siberian shelves. Time and Depth seismic sections of the Mendeleev-Alpha rises and Chukchi Plateau are presented too. The sections were set up based on seismic surveys: deep seismic sounding and multichannel seismic reflection. Some similarities have been reflected for the foregoing land structure depth sections and typical sections of the continental crust. Brief geological and geophysical data have been presented for the positive morphostructures of the Atlantic Ocean such as the Rockall and Vring plateaus, the continental nature of which is established beyond all doubt. Genesis of positive morphostructures in the northern Atlantic Ocean and the Arctic Ocean has been connected with processes of continental rifting and concomitant intraplate magmatism.
... It includes a large number of sedimentary basins underlain by continental crust (Figs 2, 3). The interpretation and extent of the oceanic crust and continental crust in the Baffin Bay, Davis Strait and northern Labrador Sea are discussed in several studies (Chian & Louden 1994;Chalmers & Pulvertaft 2001;Skaarup 2002;Dalhoff et al. 2006;Funck et al. 2006Funck et al. , 2007Funck et al. , 2012Gerlings et al. 2009;Damm 2010;Oakey & Chalmers 2012;Suckro et al. 2012;Hosseinpour et al. 2013;Altenbernd et al. 2014Altenbernd et al. , 2015Altenbernd et al. , 2016Keen et al. 2018). Most of the studies used seismic refraction data or magnetic data, gravity data and regional plate-tectonic reconstructions for determining the crustal type and to locate the boundary between the continental and oceanic crusts (COB). ...
... Thus, the crystalline basement of the West Greenland coast most likely continues westward below the thick sedimentary basins (Fig. 3). The offshore extension of the crystalline basement and continental crust is supported by refraction data that show P-wave velocities mostly >5 km/s below the sedimentary basins (Reid & Jackson 1997;Funck et al. 2006Funck et al. , 2007Funck et al. , 2012Altenbernd et al. 2014Altenbernd et al. , 2015Altenbernd et al. , 2016. ...
Large structural highs and sedimentary basins are identified from mapping of the West Greenland continental margin from the Labrador Sea to the Baffin Bay. We present a new tectonic elements map and a map of thickness from the seabed to the basement of the entire West Greenland margin. In addition, a new stratigraphic scheme of the main lithologies and tectonostratigraphy based on ties to all offshore exploration wells is presented together with seven interpreted seismic sections. The work is based on interpretation of more than 135 000 km of 2D seismic reflection data supported by other geophysical data, including gravity- and magnetic data and selected 3D seismic data, and is constrained by correlation to wells and seabed samples. Eight seismic mega-units (A–H) from the seabed to the basement, related to distinct tectonostratigraphic phases, were mapped. The oldest units include pre-rift basins that contain Proterozoic and Palaeozoic successions. Cretaceous syn-rift phases are characterised by development of large extensional fault blocks and basins with wedge-shaped units. The basin strata include Cretaceous and Palaeogene claystones, sandstones and conglomerates. During the latest Cretaceous, Paleocene and Eocene, crustal extension followed by oceanic crust formation took place, causing separation of the continental margins of Greenland and Canada with north-east to northward movement of Greenland. From Paleocene to Eocene, volcanic rocks dominated the central West Greenland continental margin and covered the Cretaceous basins. Development of the oceanic crust is associated with compressional tectonics and the development of strike-slip and thrust faults, pull-apart basins and inversion structures, most pronounced in the Davis Strait and Baffin Bay regions. During the late Cenozoic, tectonism diminished, though some intra-plate vertical adjustments occurred. The latest basin development was characterised by formation of thick Neogene to Quaternary marine successions including contourite drifts and glacial related shelf progradation towards the west and south-west.
... Gray lines show seismic-refraction and DSS profi les; type columns of the crust from seismic data are the same as in Table. 3 Normal oceanic crust (Type 1, fi g. 15), which includes normal oceanic crust of spreading basins (less then 10 km thick) and thickened crust of oceanic plateaus and hot zones (about 15-30 km thick, Type 2), is common in the Circumpolar Arctic, in the Norwegian-Greenland, Eurasian, and Baffi n-Labrador ocean basins [Bohnhoff & Makris 2004;Ljones et al. 2004;Funck et al. 2007]. It includes two oceanic layers overlain by thin sediments [Ljones et al. 2004, etc.]. ...
... In the Baffi n-Labrador ocean basin, the crust thickens to 15-17 km mainly due to magmatic underplating in the lower crust , where P-wave velocity reaches 7.4-7.6 km/s [Funck et al. 2007]. Thick (more than 20 km) crust of oceanic plateaus and hot zones also forms the Greenland-Iceland-Faroe Ridge [Bohnhoff & Makris 2004;Ljones et al. 2004], which apparently continues to the west of the southern Greenland via the Baffi n Bay and forms a single zone of thickened crust -the Baffi n Island-Greenland-Iceland-Faroe Islands Ridge . ...
This booklet is devoted to the Tectonic Map of the Arctic (TeMAr) that has been compiled
under the International project Atlas of Geological maps of the Circumpolar Arctic in scale
1:5 M. The project has been carried out since 2004 by Geological Surveys of the Arctic countries supported by the UNESCO Commission for the Geological Map of the World (CGMW) and national programs for scientifi c substantiation for the United Nations Commission for the Law of the Sea (UNCLOS).
The TeMAr working group coordinated by Russia (VSEGEI) includes leading scientists
from Geological Surveys, universities and national Academies of Sciences of Denmark, Sweden, Norway, Russia, Canada, the USA, France, Germany and Great Britain.
The Tectonic Map compilation activities were aimed at acquiring thorough understanding
of deep-water geological formations of the Arctic and Norwegian-Greenland basins, shelves of the marginal seas and the adjacent continental onshore areas of the oceans. The Tectonic Map is supplemented with a set of geophysical maps, schematic maps and sections that illustrate the deep structure of the Earth’s crust and upper mantle of the Circumpolar Arctic.
... Chalmers & Pulvertaft 2001;Torsvik et al. 2002). Central Baffin Bay and the Labrador Sea (BB, LS; Fig. 2) are underlain by oceanic crust, though the Davis Strait (DS; Fig. 2) between the two basins is thought to be underlain by thinned continental crust (Funck et al. 2007). ...
... Korenaga et al. 2000;Holbrook et al. 2001;Hopper et al. 2003;Schmidt-Aursch & Jokat 2005; Voss & Jokat 2007;Voss et al. 2009;Jackson & Dahl-Jensen 2010), and several refraction profiles have constrained crustal structure across the Davis Strait (e.g. Funck et al. 2007;Gerlings et al. 2009;Suckro et al. 2013), Baffin Bay (e.g. Funck et al. 2012;Suckro et al. 2012) and Nares Strait (e.g. ...
The Greenland landmass preserves ∼4 billion years of tectonic history, but much of the continent is inaccessible to geological study due to the extensive inland ice cap. We map out, for the first time, the 3-D crustal structure of Greenland and the NW Atlantic ocean, using Rayleigh wave anisotropic group velocity tomography, in the period range 10–80 s, from regional earthquakes and the ongoing GLATIS/GLISN seismograph networks. 1-D inversion gives a pseudo-3-D model of shear wave velocity structure to depths of ∼100 km with a horizontal resolution of ∼200 km. Crustal thickness across mainland Greenland ranges from ∼25 km to over 50 km, and the velocity structure shows considerable heterogeneity. The large sedimentary basins on the continental shelf are clearly visible as low velocities in the upper ∼5–15 km. Within the upper continental basement, velocities are systematically lower in northern Greenland than in the south, and exhibit a broadly NW–SE trend. The thinning of the crust at the continental margins is also clearly imaged. Upper-mantle velocities show a clear distinction between typical fast cratonic lithosphere (Vs ≥4.6 km s⁻¹) beneath Greenland and its NE margin and anomalously slow oceanic mantle (Vs ∼4.3–4.4 km s⁻¹) beneath the NW Atlantic. We do not observe any sign of pervasive lithospheric modification across Greenland in the regions associated with the presumed Iceland hotspot track, though the average crustal velocity in this region is higher than that of areas to the north and south. Crustal anisotropy beneath Greenland is strong and complex, likely reflecting numerous episodes of tectonic deformation. Beneath the North Atlantic and Baffin Bay, the dominant anisotropy directions are perpendicular to the active and extinct spreading centres. Anisotropy in the subcontinental lithosphere is weaker than that of the crust, but still significant, consistent with cratonic lithosphere worldwide.
... The deep basement along southwest Greenland consists of continental crust along most of the margin, flanked by a transitional zone and oceanic crust more centrally in the Labrador Sea (Fig. 7, 17;Oakey and Chalmers, 2012). A number of seismic refraction studies have also discussed and located the oceanic crust, transition zone, and continental crust (Chian and Louden, 1994;Funck et al., 2007;Gerlings et al., 2009). Additional detail discussing the crustal domains can be found in Keen et al. (this volume). ...
The chapter describes the stratigraphy and geological evolution of West Greenland continental margin, including the tectonostratigraphy, the seismic stratigraphy, the lithostratigraphy, and the biostratigraphy, with ties to all offshore wells on the margin, and with descriptions from selected onshore wells and outcrops.
... A synthesis of recent (Funck et al., 2007Suckro et al., 2012Suckro et al., , 2013Altenbernd et al., 2014Altenbernd et al., , 2015 and older seismic refraction results in Keen et al. (this volume) show a variety of structural styles, which can be distilled into two main types of rifted margin: 1) magma-poor margins with hyperextended zones, serpentinized, and possibly exhumed mantle, and proto-oceanic crust (e.g. Chian et al., 1995;Keen et al., 2018a); and 2) magma-rich margins with thick zones of igneous crust, possibly overlying older, magma-poor margins in some regions (Keen et al., 2012(Keen et al., , 2018b. ...
The papers contained in this bulletin provide a comprehensive summary and updated understanding of the onshore geology and evolution of Baffin Island, the Labrador-Baffin Seaway, and surrounding onshore regions. This introductory paper summarizes and links the geological and tectonic events that took place to develop the craton and subsequent Proterozoic to Cenozoic sedimentary basins. Specifically, the Precambrian and Paleozoic geology of Baffin Island and localized occurrences underlying the adjacent Labrador-Baffin Seaway, the Mesozoic to Cenozoic stratigraphy and rift history that records the opening and evolution of the Labrador-Baffin Seaway, the seismicity of the region, as well as both the mineral (Baffin Island) and hydrocarbon (onshore and offshore) resource potential are discussed.
... Принято считать, что мощность типичной океанической коры составляет 6-8 км, и она состоит из слоя рыхлых осадков мощностью не более одного километра со скоростями продольных волн 2-4 км/с; второго океанического слоя мощностью 2-3 км со скоростями Vp от 4 до 6 км/с, представленного вулканитами; третьего океанического слоя мощностью 4-5 км со скоростями Vp от 6.5 до 7.2 км/с. Однако немало примеров того, когда океаническая кора горячих точек и вулканических провинций имеет мощность более 20 км, и в ее нижней части выделяется слой со скоростями, промежуточными между корой и мантией (7.2-7.6 км/с) [Funck et al., 2007;McNutt et al., 2007;Fernàndez et al., 2010]. ...
В книге приведен обзор глубинных исследований земной коры континентов и океанов с использованием продольных и поперечных сейсмических волн. Показаны возможности многоволновой сейсморазведки для повышения
информативности глубинных исследований земной коры за счет использования значений параметра Vp/Vs и коэффициента Пуассона. Приведены результаты многоволновых сейсмических исследований Арктической зоны, северо-востока России и прилегающих акваторий.
The book introduces in deep studies overview of continental and oceanic Earthʼs crust using compression and shear seismic waves. Multiwave seismics opportunities using values of the Vp/Vs and Poissonʼs ratios for geological objectives solutions
are shown. Multiwave seismics studies of the Arctic and North-East regions of Russia and adjacent water areas are presented.
... Figure 11. Comparison of 1D P-wave velocity-depth structures in the crust at representative locations along MZ4 and MZ5 with oceanic crust models from previously published studies that have experienced varying amounts of magmatic activity (Funck et al., 2007;Hermann & Jokat, 2016;Kodaira et al., 1998;Sinha et al., 1981;Tréhu et al., 1989;Tsikalas et al., 2005). ...
A variety of structures results from the interplay of evolving far‐field forces, plate kinematics, and magmatic activity during continental break‐up. The east Limpopo transform margin, offshore northern Mozambique, formed as Africa and Antarctica separated during the mid‐Jurassic period break‐up of the Gondwana supercontinent. The nature of the crust onshore has been discussed for decades in an effort to resolve issues with plate kinematic models. Two seismic refraction profiles with coincident multichannel seismic reflection profiles allow us to interpret the seismic velocity structures across the margin, both onshore and offshore. These seismic profiles allow us to (a) delineate the major regional crustal domains; (b) identify widespread indications of magmatic activity; and (c) map crustal structure and geometry of this magma‐rich transform margin. Careful examination of the profiles allows us to make the following observations and interpretations: (a) on land, continental crust is overlain by a >10‐km thick volcano‐sedimentary wedge related to an early rifting stage, (b) offshore, thick oceanic crust formed due to intense magmatic activity, and between the two (c) a 50–60‐km wide transform zone where the crustal structures are affected by intense magmatic activity and faulting. The prominent presence of intrusive and extrusive igneous units may be attributed to the combination of a deep‐seated melting anomaly and a trans‐tensional fault zone running through thinned lithosphere that allowed melt to reach the surface. A comparison of the crustal thinning along other transform margins shows a probable dependence with the thermal and/or tectonic history of the lithosphere.
... The connection between Baffin Bay and the Arctic Ocean is subject to a long-standing debate centred on the magnitude of displacement along the Nares Strait lineament ('Wegener Transform Fault') (Taylor 1910;Dawes and Kerr 1982;Srivastava 1985). Recent studies suggest that the Precambrian igneous terrain on SE Ellesmere Island is part of the Greenland plate, with the Eurekan Frontal Thrust and its continuation into Jones Sound marking the plate boundary (Harrison 2006) (Fig. 1) The connection between Baffin Bay and the Labrador Sea has been addressed by multiple studies and several platekinematic reconstructions have been proposed (Johnson et al. 1982;Srivastava 1985;Roest and Srivastava 1989;Chalmers and Pulvertaft 2001;Sorensen 2006;Funck et al. 2007Funck et al. , 2012Oakey and Chalmers 2012;Suckro et al. 2013a). The current perception is that the Davis Strait region was undergoing south-west extension during the initial phase of seafloor spreading in Baffin Bay and the Labrador Sea (chrons C27-C24), and then developed into a transtensional system as NNE-oriented seafloor spreading ensued during the Eocene (Fig. 3). ...
Baffin Bay formed as a result of continental extension during the Cretaceous, which was followed by sea floor spreading and associated plate drift during the early to middle Cenozoic. Formation of an oceanic basin in the central part of Baffin Bay may have begun from about 62 Ma in tandem with Labrador Sea opening but the early spreading phase is controversial. Plate-kinematic models suggests that from Late Paleocene the direction of sea floor spreading changed to N-S generating strike-slip movements along the transform lineaments, e.g. the Ungava Fault Zone and the Bower Fracture Zone, and structural complexity along the margins of Baffin Bay. The Baffin Bay Composite Tectono-Sedimentary Element (CTSE) represents a 3-7 km thick Cenozoic sedimentary and volcanic succession that has deposited over oceanic and rifted continental crust since active seafloor spreading began. The CTSE is subdivided into 5 seismic mega-units that have been identified and mapped using a regional seismic grid tied to wells and core sites. Thick clastic wedges of likely Late Paleocene to Early Oligocene age (mega-units E and D2) were deposited within basins floored by newly formed oceanic crust, transitional crust, volcanic extrusives and former continental rift basins undergoing subsidence. The middle-late Cenozoic is characterized by fluvial-deltaic sedimentary systems, hemipelagic strata and aggradational sediment bodies deposited under the influenced of ocean currents (mega-units D1, C and B). The late Pliocene to Pleistocene interval (mega-unit A) displays major shelf margin progradation associated with ice-sheet advance-retreat cycles resulting in accumulation of trough-mouth fans and mass-wasting deposits products in the oceanic basin. The Baffin Bay CTSE has not produced discoveries although a hydrocarbon potential may be associated with Paleocene source rocks. Recent data have improved the geological understanding of Baffin Bay although large data and knowledge gaps remain.
... It remains open to question whether such settings might produce dateable linear magnetic reversal isochrons like those over thicker (~ 7 km) standard oceanic crust and, thus, whether published interpretations of the weak anomalies as reversal isochrons as old as C33 1,20 can be seen as reliable (~ 79 Ma; Fig. 2). Davis Strait connects the Labrador Sea and Ba n Bay regions, and is host to two large N-S trending transform faults (see, Fig. 3) which are thought to have acted as sheared continental margin segments during Paleocene and Eocene times [21][22][23][24][25] . The a nity of the crust in the oor of Davis Strait is uncertain 21,26,27 . ...
The processes that accommodated plate divergence between Greenland and North America are most confidently interpretable from a short-lived (61-42 Ma) sequence of magnetic isochrons in the Labrador Sea. Understanding of the preceding and following periods is impeded by the lack of clear isochrons in the basin’s continent-ocean transition and axial zones. By closing the regional plate circuit, we build and interpret a detailed plate motion model for Greenland and North America that is applicable in, but unaffected by data uncertainty from, the Labrador Sea, Davis Strait, and Baffin Bay. Among our findings, we show the Labrador Sea initially opened during a ~8.3-16.5 Myr-long period of focused extension culminating in continental breakup no earlier than 74-72 Ma, and experienced a ~80° change in spreading direction around 56 Ma. We describe some possible implications for the accommodation of strain prior to continental breakup and during extreme spreading obliquity.
... The tectonic evolution of the Labrador Sea -Davis Strait -Nuussuaq -Baffin Bay region is complex involving multiple phases of rifting related to the initial opening of the norther Atlantic, transpressional movements, counter-clockwise rotation of Greenland, causing Late Paleocene -Early Eocene compression and inversion followed by Neogene -late Neogene uplift of the margins (e.g. Chalmers et al. 1999;Chalmers & Pulvertaft 2001;Dam et al. 1998Dam et al. , 2009Funck et al. 2007;Gregersen et al. 2019;Japsen et al. 2005;Knutsen et al. 2012;Nielsen et al. 2011;Oakey & Chalmers 2012;Pedersen et al. 2018Pedersen et al. , 2019. During the late Cenozoic -present-day Post-drift Phase tectonism diminished, though some intra-plate vertical adjustments occurred and a series of uplift events took place along the passive margins. ...
play-based quantitative resource assessment of conventional hydrocarbons covering the entire Greenland continental shelf - Assessment Unit 1- Labrador Sea - Davis Strait
... The crustal structure in the inner Labrador Sea has recently been studied in a reflection/refraction seismic transect running WSW from the Qulleq-1 well to the Gjoa G-37 and Hekja 0-71 wells off eastern Canada. This new seismic line shows that oceanic crust is restricted to two narrow zones at or close to the Ungava Fracture Zone, a major transform zone that transferred sea-floor spreading through the Davis Straede (Davis Strait) into Baffin Bugt (Baffin Bay; Fig. 49A, B; Funck et al. 2007). Funck et al. believe that these zones of oceanic crust formed when phases of transtension along the fracture zone created gaps which were filled with melt that formed new oceanic crust. ...
The geological development of Greenland spans a period of nearly 4 Ga, from Eoarchaean to the Quaternary. Greenland is the largest island on Earth with a total area of 2 166 000 km2, but only c. 410 000 km2 are exposed bedrock, the remaining part being covered by a major ice sheet (the Inland Ice) reaching over 3 km in thickness. The adjacent offshore areas underlain by continental crust have an area of c. 825 000 km2. Greenland is dominated by crystalline rocks of the Precambrian shield, which formed during a succession of Archaean and Palaeoproterozoic orogenic events and stabilised as a part of the Laurentian shield about 1600 Ma ago. The shield area can be divided into three distinct types of basement provinces: (1) Archaean rocks (3200–2600 Ma old, with local older units up to> 3800 Ma) that were almost unaffected by Proterozoic or later orogenic activity; (2) Archaean terrains reworked during the Palaeoproterozoic around 1900–1750 Ma ago; and (3) terrains mainly composed of juvenile Palaeoproterozoic rocks (2000–1750 Ma in age). Subsequent geological developments mainly took place along the margins of the shield. During the Proterozoic and throughout the Phanerozoic major sedimentary basins formed, notably in North and North-East Greenland, in which sedimentary successions locally reaching 18 km in thickness were deposited. Palaeozoic orogenic activity affected parts of these successions in the Ellesmerian fold belt of North Greenland and the East Greenland Caledonides; the latter also incorporates reworked Precambrian crystalline basement complexes. Late Palaeozoic and Mesozoic sedimentary basins developed along the continent–ocean margins in North, East and West Greenland and are now preserved both onshore and offshore. Their development was closely related to continental break-up with formation of rift basins. Initial rifting in East Greenland in latest Devonian to earliest Carboniferous time and succeeding phases culminated with the opening of the North Atlantic Ocean in the late Paleocene. Sea-floor spreading was accompanied by extrusion of Palaeogene (early Tertiary) plateau basalts in both central West and central–southern East Greenland. During the Quaternary Greenland was almost completely covered by ice, and the present day Inland Ice is a relic from the Pleistocene ice ages. Vast amounts of glacially eroded detritus were deposited on the continental shelves around Greenland. Mineral exploitation in Greenland has so far encompassed cryolite, lead-zinc, gold, olivine and coal. Current prospecting activities in Greenland are concentrated on gold, base metals, platinum group elements, molybdenum, iron ore, diamonds and lead-zinc. Hydrocarbon potential is confined to the major Phanerozoic sedimentary basins, notably the large basins offshore North-East and West Greenland. While reserves of oil or gas have yet to be found, geophysical data combined with discoveries of oil seeps onshore have revealed a considerable potential for offshore oil and gas.
... For example, the Palaeoproterozoic Torngat-Nagssugtoqidian orogenic belt (van Gool et al. 2002;Grocott and McCaffrey 2017) could have formed a rheological barrier, preserving thicker, continental-affinity crust and lithosphere in the Davis Strait (Heron et al. 2019). The HVLC underlying Davis Strait (Funck et al. 2007 could represent remnants of pre-existing metamorphosed or metasomatised crust or mantle (Petersen and Schiffer 2016;Peace et al., 2017). ...
The North Atlantic, extending from the Charlie Gibbs Fracture Zone to the north Norway-Greenland-Svalbard margins, is regarded as both a classic case of structural inheritance and an exemplar for the Wilson-cycle concept. This paper examines different aspects of structural inheritance in the Circum-North Atlantic region: 1) as a function of rejuvenation from lithospheric to crustal scales, and 2) in terms of sequential rifting and opening of the ocean and its margins, including a series of failed rift systems. We summarise and evaluate the role of fundamental lithospheric structures such as mantle fabric and composition, lower crustal inhomogeneities, orogenic belts, and major strike-slip faults during breakup. We relate these to the development and shaping of the NE Atlantic rifted margins, localisation of magmatism, and microcontinent release. We show that, although inheritance is common on multiple scales, the Wilson Cycle is at best an imperfect model for the Circum-North Atlantic region. Observations from the NE Atlantic suggest depth dependency in inheritance (surface, crust, mantle) with selective rejuvenation depending on time-scales, stress field orientations and thermal regime. Specifically, post-Caledonian reactivation to form the North Atlantic rift systems essentially followed pre-existing orogenic crustal structures, while eventual breakup reflected a change in stress field and exploitation of a deeper-seated, lithospheric-scale shear fabrics. We infer that, although collapse of an orogenic belt and eventual transition to a new ocean does occur, it is by no means inevitable.
... Petrologically, NAIP igneous rocks are highly diverse and include tholeiitic and alkali basalts, nepheline-and quartz-syenites, nephelinites, and carbonatites (Holbrook et al., 2001). NAIP igneous rocks are also highly variable in structure and include dykes, and sills (Magee et al., 2014), seaward-dipping reflectors (SDRs) (Larsen and Saunders, 1998), high-velocity lower crustal bodies (Funck et al., 2007), seamounts (Jones et al., 1974), and subaerial flows (Wilkinson et al., 2017;Horni et al., 2017). ...
The breakup of Pangaea was accompanied by extensive, episodic, magmatic activity. Several Large Igneous Provinces (LIPs) formed, such as the Central Atlantic Magmatic Province (CAMP) and the North Atlantic Igneous Province (NAIP). Here, we review the chronology of Pangaea breakup and related large-scale magmatism. We review the Triassic formation of the Central Atlantic Ocean, the breakup between East and West Gondwana in the Middle Jurassic, the Early Cretaceous opening of the South Atlantic, the Cretaceous separation of India from Antarctica, and finally the formation of the North Atlantic in the Mesozoic-Cenozoic. We demonstrate that throughout the dispersal of Pangaea, major volcanism typically occurs distal from the locus of rift initiation and initial oceanic crust accretion. There is no location where extension propagates away from a newly formed LIP. Instead, LIPs are coincident with major lithosphere-scale shear movements, aborted rifts and splinters of continental crust rifted far out into the oceanic domain. These observations suggest that a fundamental reappraisal of the causes and consequences of breakup-related LIPs is in order.
... The Labrador continental margin formed through crustal extension between Labrador and Greenland beginning in the early Cretaceous. The initial rifting style was "non-volcanic" (Chalmers, 1997;Funck et al., 2007) in that the extension was largely accommodated by faulting and stretching of the crust rather than by emplacement of magma (White and McKenzie, 1989;Reston, 2009). The southern portion of the margin continued to develop in a non-volcanic environment (Chian et al., 1995;Keen et al. 2018a) until the cessation of seafloor spreading in the Labrador Sea in the Oligocene (Delescluse et al., 2015). ...
This report assesses the qualitative petroleum resource potential of offshore Labrador by a team of geoscientists at the Geological Survey of Canada. The team examined existing well data and seismic data, conducted basin analyses, mapped petroleum system elements to determine the potential of prospective regional conventional hydrocarbon plays on the margin.
... In our modeling, we have fixed the extension velocity and orientation for 15 Myr in order to approximate Phase 1 of the rift history ( Figure 4). Our modeled Davis Strait region is susceptible to rifting and indeed thins throughout the simulation, which is in keeping with geophysical interpretation of the region (Figure 9b; Funck et al., 2007;Suckro et al., 2013). If we allow our reference case Model M1 to deform for longer than 15 Myr, the modeled Davis Strait thins further before joining up to the north and south spreading zones after 19 Myr ( Figure S5). ...
Mesozoic‐Cenozoic rifting between Greenland and North America created the Labrador Sea and Baffin Bay, while leaving preserved continental lithosphere in the Davis Strait, which lies between them. Inherited crustal structures from a Palaeoproterozoic collision have been hypothesized to account for the tectonic features of this rift system. However, the role of mantle lithosphere heterogeneities in continental suturing has not been fully explored. Our study uses 3‐D numerical models to analyze the role of crustal and subcrustal heterogeneities in controlling deformation. We implement continental extension in the presence of mantle lithosphere suture zones and deformed crustal structures and present a suite of models analyzing the role of local inheritance related to the region. In particular, we investigate the respective roles of crust and mantle lithospheric scarring during an evolving stress regime in keeping with plate tectonic reconstructions of the Davis Strait. Numerical simulations, for the first time, can reproduce first‐order features that resemble the Labrador Sea, Davis Strait, Baffin Bay continental margins, and ocean basins. The positioning of a mantle lithosphere suture, hypothesized to exist from ancient orogenic activity, produces a more appropriate tectonic evolution of the region than the previously proposed crustal inheritance. Indeed, the obliquity of the continental mantle suture with respect to extension direction is shown here to be important in the preservation of the Davis Strait. Mantle lithosphere heterogeneities are often overlooked as a control of crustal‐scale deformation. Here, we highlight the subcrust as an avenue of exploration in the understanding of rift system evolution.
... Принято считать, что мощность типичной океанической коры составляет 6-8 км, и она состоит из слоя рыхлых осадков мощностью не более одного километра со скоростями продольных волн 2-4 км/с; второго океанического слоя мощностью 2-3 км со скоростями Vp от 4 до 6 км/с, представленного вулканитами; третьего океанического слоя мощностью 4-5 км со скоростями Vp от 6.5 до 7.2 км/с. Однако немало примеров того, когда океаническая кора горячих точек и вулканических провинций имеет мощность более 20 км, и в ее нижней части выделяется слой со скоростями, промежуточными между корой и мантией (7.2-7.6 км/с) [Funck et al., 2007;McNutt et al., 2007;Fernàndez et al., 2010]. ...
В книге на основе лучевого и полноволнового конечно-разностного математического моделирования и экспериментального материала рассмотрены возможности расширения типов и классов сейсмических волн, используемых в морской сейсморазведке. Даны рекомендации по идентификации поперечных и обменных волн при морских сейсмических исследованиях с автономными донными сейсмическими станциями, изложены подходы к обработке и интерпретации данных 3-компонентных наблюдений.
Приведены результаты многоволновых сейсмических исследований в акватории Охотского моря и в глубоководной части Северного Ледовитого океана. Показано, как за счет многоволновой интерпретации повышается информативность и достоверность геолого-геофизических построений, открываются дополнительные возможности по определению природы земной коры.
Книга предназначена для широкого круга геологов и геофизиков, занимающихся глубинными исследованиями земной коры и верхней мантии акваторий, и может быть полезна преподавателям, студентам и аспирантам геофизических и геологических специальностей.
(Based on numerical full-wave and ray-tracing modeling and experimental data this book considers possibilities of expanding the types and classes of seismic waves that are conventionally used in marine seismic studies. The book offers recommendations on identification of shear and converted wave phases in the marine seismic data acquired by ocean bottom seismometers and conveys approaches to processing and interpretation of the 3-component seismic observations.
The book presents some results of the multiwave seismic studies from the Sea of Okhotsk and the abyssal Arctic Ocean. It shows how the multiwave interpretation enhances information capability and reliability of the geophysical and geological models opening further possibilities for determining the nature of the crust.
The book might be of interest to geological and geophysical community involved in offshore seismic studies of the Earth’s crust and upper mantle, and may be useful for geophysics and geology teachers, students and post-graduate students.)
... Transforms would act as rift-propagation barriers and would enhance considerably the amount of syn-breakup magmatism at the tip of the propagating rift. Funck et al. (2007) demonstrated the occurrence of high velocity igneous lower crust 4 to 8 km-thick (7.4 km/s) beneath the Ungava fault zone itself. These authors considered that the Ungava leaky transform zone would have acted as a barrier guiding the migration of hot material towards both the adjacent northern Labrador Sea and southern Baffin Bay VPMs. ...
We question the timing of continental breakup and early oceanization in Baffin Bay, North-East Atlantic. North of the Ungava fault zone, the breakup was syn-magmatic and led to the development of conjugate volcanic passive margins (VPMs). We investigated the innermost part of the W-Greenland VPM where a remarkable inner-SDR is fully exposed in the Svartenhuk area. Our new radiometric ages and paleomagnetic data from syn-tectonic basaltic lavas indicate that continental stretching and thinning spanned the C26r to, at least, the C24r period, giving an Eocene lower boundary age for continental breakup in Baffin Bay. These results contradict the proposed flooring of Baffin Bay by a Paleocene oceanic crust older than C24n and also question the accretion of oceanic crust before C22. We confront our results to the dynamics of the northward oceanic-rift propagation across the Ungava transform fault system, and we suggest that plate breakup in Baffin Bay occurred ~8 m.y. later than in N-Labrador Sea as a result of the thermal and mechanical barrier effect induced by the Ungava transform zone.
... Paleocene basalts were sampled from the seabed over the Davis Strait High and south of the Hecla High, where additional Early Eocene basalts were recovered (Larsen & Dalhoff 2006). A refraction seismic study by Funck et al. (2007) also shows basalts in the western parts of the study area and farther west with a tie to the Canadian Gjoa G-37 well. This well includes basalts with thinner mudstones in a >1 km thick Danian to Thanetian interval (Nøhr-Hansen et al. 2016). ...
The West Greenland continental margin has been the subject of petroleum exploration by companies and research projects since the 1970s and many data have been acquired since. Licensing rounds issued by the Greenland authorities in 2002 and 2004 offshore southern West Greenland resulted in company licenses which led to data acquisition and three exploration wells. The extensive new data form a basis for updated mapping by means of data, new analyses of the subsurface geology and improved understanding of the stratigraphy and the geological development. The Geological Survey of Denmark and Greenland (GEUS) has recently completed a comprehensive mapping project of the subsurface in an area covering 116 000 km2 offshore southern West Greenland (Fig. 1). The results include maps displaying large structural highs and faults, Cretaceous sedimentary basins and volcanic areas, illustrated by cross-sections through the area. A new seismic stratigraphy with eight mega-units from the seabed to the basement was also defined. In addition, studies from wells of biostratigraphy and petrology were carried out that provide important new information. The new data include extensive 2D seismic data and eight wells including the three exploration wells AT2-1, AT7-1 and LF7-1 drilled in 2011 by Cairn Energy (Fig. 1). Key results of the work are summarised below.
... However, in the original Hosseinpour et al. (2013) model, true oceanic crust is said to occur after 61 Ma (i.e. a longer period of continental rifting than in the Labrador Sea). Furthermore, Hosseinpour et al. (2013) include oceanic crust in the Davis Strait where previous work suggests crust of predominantly continental affinity (Funck et al. 2007;Suckro et al. 2013). Despite these potential timing and crustal affinity issues with the Hosseinpour et al. (2013) model, it is used herein to provide a first-order estimate of crustal thickness through time as redefining these model inputs to address the issues outlined is far beyond the scope of this study. ...
Mesozoic to Cenozoic continental rifting, breakup and spreading between North America and Greenland led to the opening, from south to north, of the Labrador Sea and eventually Baffin Bay between Baffin Island, northeast Canada and northwest Greenland. Baffin Bay lies at the northern limit of this extinct rift, transform and spreading system and remains largely underexplored. With the sparsity of existing crustal-scale geophysical investigations of Baffin Bay, regional potential field methods and quantitative deformation assessments based on plate reconstructions provide two means of examining Baffin Bay at the regional scale and drawing conclusions about its crustal structure, its rifting history and the role of pre-existing structures in its evolution. Despite the identification of extinct spreading axes and fracture zones based on gravity data, insights into the nature and structure of the underlying crust have only been gleaned from limited deep seismic experiments, mostly concentrated in the north and east where the continental shelf is shallower and wider. Baffin Bay is partially underlain by oceanic crust with zones of variable width of extended continental crust along its margins. 3-D gravity inversions, constrained by bathymetric and depth to basement constraints, have generated a range of 3-D crustal density models that collectively reveal an asymmetric distribution of extended continental crust, approximately 25-30 km thick, along the margins of Baffin Bay, with a wider zone on the Greenland margin. A zone of 5-13 km thick crust lies at the centre of Baffin Bay, with the thinnest crust (5 km thick) clearly aligning with Eocene spreading centres. The resolved crustal thicknesses are generally in agreement with available seismic constraints, with discrepancies mostly corresponding to zones of higher density lower crust along the Greenland margin and Nares Strait. Deformation modelling from independent plate reconstructions using GPlates of the rifted margins of Baffin Bay was performed to gauge the influence of original crustal thickness and the width of the deformation zone on the crustal thicknesses obtained from the gravity inversions. These results show the best match with the results from the gravity inversions for an original unstretched crustal thickness of 34-36 km, consistent with present-day crustal thicknesses derived from teleseismic studies beyond the likely continentward limits of rifting around the margins of Baffin Bay. The width of the deformation zone has only a minimal influence on the modelled crustal thicknesses if the zone is of sufficient width that edge effects do not interfere with the main modelled domain.
... However, in the original Hosseinpour et al. (2013) model, true oceanic crust is said to occur after 61 Ma (i.e., a longer period of continental rifting than in the Labrador Sea). Furthermore, Hosseinpour et al. (2013) include oceanic crust in the Davis Strait where previous work suggests crust of predominantly continental affinity (Funck et al., 2007;Suckro et al., 2013). Despite these potential timing and crustal affinity issues with the Hosseinpour et al. (2013) model, it is used herein to provide a first-order estimate of crustal thickness through time as redefining these model inputs to address the issues outlined is far beyond the scope of this study. ...
Mesozoic to Cenozoic continental rifting, breakup, and spreading between North America and Greenland led to the opening, from south to north, of the Labrador Sea and eventually Baf-fin Bay between Baffin Island, northeast Canada, and northwest Greenland. Baffin Bay lies at the northern limit of this extinct rift, transform, and spreading system and remains largely underexplored. With the sparsity of existing crustal-scale geophysical investigations of Baffin Bay, regional potential field methods and quantitative deformation assessments based on plate reconstructions provide two means of examining Baffin Bay at the regional scale and drawing conclusions about its crustal structure, its rifting history, and the role of pre-existing structures in its evolution. Despite the identification of extinct spreading axes and fracture zones based on gravity data, insights into the nature and structure of the underlying crust have only been gleaned from limited deep seismic experiments, mostly concentrated in the north and east where the continental shelf is shallower and wider. Baffin Bay is partially underlain by oceanic crust with zones of variable width of extended continental crust along its margins. 3-D gravity inversions, constrained by bathymetric and depth to basement constraints, have 2 J.K. Welford, A.L. Peace, M. Geng, S.A. Dehler and K. Dickie generated a range of 3-D crustal density models that collectively reveal an asymmetric distribution of extended continental crust, approximately 25-30 km thick, along the margins of Baffin Bay, with a wider zone on the Greenland margin. A zone of 5 to 13 km thick crust lies at the centre of Baffin Bay, with the thinnest crust (5 km thick) clearly aligning with Eocene spreading centres. The resolved crustal thicknesses are generally in agreement with available seismic constraints, with discrepancies mostly corresponding to zones of higher density lower crust along the Greenland margin and Nares Strait. Deformation modelling from independent plate reconstructions using GPlates of the rifted margins of Baffin Bay was performed to gauge the influence of original crustal thickness and the width of the deformation zone on the crustal thicknesses obtained from the gravity inversions. These results show the best match with the results from the gravity inversions for an original unstretched crustal thickness of 34-36 km, consistent with present-day crustal thicknesses derived from teleseismic studies beyond the likely continentward limits of rifting around the margins of Baffin Bay. The width of the deformation zone has only a minimal influence on the modelled crustal thicknesses if the zone is of sufficient width that edge effects do not interfere with the main modelled domain.
... A mantle plume (Morgan, 1971) has been proposed as the causal mechanism for continental breakup and magmatism between Greenland and Canada (e.g. Storey et al. 1998;Courtillot et al. 1999;Nielsen et al. 2002;Funck et al. 2007;Gerlings et al. 2009;Altenbernd et al. 2015). It is postulated that initial rifting was relatively amagmatic (Nielsen et al. 2002;Altenbernd et al. 2015) and that the arrival of a mantle plume at ca. 62-60 Ma led to the onset of seafloor spreading in the Labrador Sea (Gerlings et al., 2009) and widespread magmatism around the Davis Strait (Holm et al. 1993;Storey et al. 1998). ...
Breakup between Greenland and Canada resulted in oceanic spreading in the Labrador Sea and Baffin Bay. These ocean basins are connected through the Davis Strait, a bathymetric high comprising primarily continental lithosphere, and the focus of the West Greenland Tertiary volcanic province. It has been suggested that a mantle plume facilitated this breakup and generated the associated magmatism. Plume-driven breakup predicts that the earliest, most extensive rifting, magmatism and initial seafloor spreading starts in the same locality, where the postulated plume impinged. Observations from the Labrador Sea-Baffin Bay area do not accord with these predictions. Thus, the plume hypothesis is not confirmed at this locality unless major ad hoc variants are accepted. A model that fits the observations better involves a thick continental lithospheric keel of orogenic origin beneath the Davis Strait that blocked the northward-propagating Labrador Sea rift resulting in locally enhanced magmatism. The Davis Strait lithosphere was thicker and more resilient to rifting because the adjacent Paleoproterozoic Nagssugtoqidian and Torngat orogenic belts contain structures unfavourably orientated with respect to the extensional stress field at the time.
... The margins of the southern Labrador Sea are non-volcanic (Chian et al., 1995) however they are volcanic in the northern Labrador Sea, Davis Strait (Keen et al., 2012), and Baffin Bay (Suckro et al., 2012). The Davis Strait is classified as a volcanic passive margin (Chalmers, 1997) due to the presence of volumetrically extensive igneous rocks (Storey et al., 1998) and a 4-8 km thick high velocity underplated layer (Funck et al., 2007). ...
Continental breakup between Greenland and North America produced the small oceanic basins of the Labrador Sea and Baffin Bay, which are connected via the Davis Strait, a region mostly comprised of continental crust. This paper contributes to the debate regarding the role of pre-existing structures on rift development in this region using seismic reflection data from the Davis Strait data to produce a series of seismic surfaces, isochrons and a new offshore fault map from which three normal fault sets were identified as 1) NE-SW, 2) NNW-SSE and 3) NW-SE. These results were then integrated with plate reconstructions and onshore structural data allowing us to build a two stage conceptual model for the offshore fault evolution in which basin formation was primarily controlled by rejuvenation of various types of pre-existing structures. During the first phase of rifting between at least Chron 27 (ca. 62 Ma; Paleocene), but potentially earlier, and Chron 24 (ca. 54 Ma; Eocene) faulting was primarily controlled by pre-existing structures with oblique-normal reactivation of both the NE-SW and NW-SE structural sets in addition to normal reactivation of the NNW-SSE structural set. In the second rifting stage between Chron 24 (ca. 54 Ma; Eocene) and Chron 13 (ca. 35 Ma; Oligocene), the sinistral Ungava transform fault system developed due to the lateral offset between the Labrador Sea and Baffin Bay. This lateral offset was established in the first rift stage possibly due to the presence of the Nagssugtoqidian and Torngat terranes being less susceptible to rift propagation. Without the influence of pre-existing structures the manifestation of deformation cannot be easily explained during either of the rifting phases. While basement control diminished into the post-rift, the syn-rift basins from both rift stages continued to influence the location of sedimentation possibly due to differential compaction effects. Variable lithospheric strength through the rifting cycle may provide an explanation for the observed diminishing role of basement structures through time.
... This model is reinforced by the aforementioned high-density, lower-crustal layer thickening towards the MCR and the presence of synchronous dikes (and kimberlites) north of Lake Superior , which are typically believed to be the surface expression of underplated mafic rocks . Magmatic underplating (~5 km thick) is also observed in the Davis Strait off of SE Baffin Island (Funck et al., 2007) and to the north in Baffin Bay (Suckro et al., 2012) but has been interpreted as a more recent Paleogene feature associated with Icelandic plume activity. Whitmeyer and Karlstrom (2007) with geologic sub-terranes of the Superior Province outlined in black from . ...
Continental interiors are an underappreciated facet of plate tectonics due to the perception that they are often static over long timescales. Salient tectonic margins receive more attention, owing to their comparatively dynamic state during the creation and destruction of continents and ocean basins. I utilize low-temperature (U-Th)/He and 40Ar/39Ar thermochronology to address questions regarding the spatial and temporal thermal evolution, and by proxy, the exhumation and burial histories of these slowly-cooled terranes through deep time. Chapter One is focused on the topographic evolution of the Hangay Mountains of central Mongolia, where apatite (U-Th)/He data and thermal models suggest that the post-orogenic landscape experienced rapid relief loss of a few hundred meters in the mid-Mesozoic. The Hangay are now characterized by a relict landscape that has undergone slow exhumation on the order of ~10 m/Ma since the Cretaceous (~100 Ma), analogous to other old landscapes such as the Appalachians. The central Mongolian landscape remains in a state of topographic disequilibrium, while modest surface uplift since the Oligocene and recent glaciation have had little effect on erosion rates due to the fact that there has been minor tectonism and a very dry climate during the Cenozoic.
Chapter Two confronts the problem of dispersed apatite (U-Th)/He cooling ages that often afflict slowly-cooled terranes, such as the Hangay Mountains. Conventional total- gas analysis offers little explanation or remedy for He age scatter that has been typically attributed to many factors, such as isotopic zonation, crystal lattice defects, and radiation damage. Unlike conventional analysis, the continuous ramped heating (CRH) technique exploits incremental 4He release during a continuous, controlled heating rate under static extraction line conditions. This approach allows the measurement of the cumulative gas released from apatite grains and assessment of the characteristic sigmoidal release curve shape as a means to distinguish between expected (radiogenic) and anomalous volume- diffusion behavior. Screening results for multiple apatite suites show that the CRH method can discriminate between the simple, smooth release of apatites exhibiting expected behavior and well-replicated ages, and grains that do not replicate well with more complicated 4He release patterns – and offers a means to correct these ages.
Chapter Three is focused on understanding the assumed long-term stability of the southern Canadian Shield. Craton stability over billion-year timescales is often inferred due to the lack of geologic records to suggest otherwise. For the Proterozoic (2.5-0.54 Ga) there is little or no intermediate temperature thermal-history information for many locations, however K-feldspar 40Ar/39Ar MDD data and modeled thermal histories linked to published high- and low-temperature data from the Canadian Shield suggest the southern craton experienced unroofing delayed until ~1 Ga, coeval with the formation of the supercontinent Rodinia. K-feldspar data suggest a prolonged period of near- isothermal cooling of <0.5°C/Ma in the late Proterozoic where rocks were positioned at cratonic depths in the middle crust for up to ~500 million years at temperatures of ~150- 200°C and subsequently exhumed to the surface in the Neoproterozoic. Thermal history solutions and geophysical evidence of underplating and crustal thickening at the Mid- Continental Rift and adjacent regions suggest uplift and a previously unrecognized phase of cratonic unroofing that began in the Neoproterozoic, which ultimately contributed to the development of the Great Unconformity of North America.
... It is commonly accepted that thickness of typical oceanic crust is 6-8 km, and that it consists of a layer of loose sediments of about 1 km thick with P-wave velocities from 2 to 4 km/s, the oceanic layer 2 having the thickness from 2 to 3 km with Vp from 4 to 6 km/s represented by volcanic rocks, and the oceanic layer 3 from 4 to 5 km thick with Vp from 6.5 to 7.2 km/s (White et al., 1992). Although there are many examples where oceanic crust of hotspots and volcanic provinces has the thickness of N20 km, and has a layer with velocities intermediate between crust and mantle (7.2-7.6 km/s) in its lower part (Fernàndez et al., 2010;Funck et al., 2007;McNutt and Caress, 2007). ...
Deep seismic studies of the Sea of Okhotsk region started in late 1950s. Since that time, wide-angle reflection and refraction data on more than two dozen profiles were acquired. Only five of those profiles either crossed or entered the deep-water area of the South-Okhotsk Basin (also known as the Kuril Basin or the South-Okhotsk Deep-Water Trough). Only P-waves were used to develop velocity-interface models in all the early research. Thus, all seismic and geodynamic models of the Okhotsk region were based only on the information on compressional waves. Nevertheless, the use of Vp/Vs ratio in addition to P-wave velocity allows discriminating felsic and mafic crustal layers with similar Vp values. In 2007 the Russian seismic service company Sevmorgeo acquired multi-component data with ocean bottom seismometers (OBS) along the 1700-km-long north-south 2-DV-M Profile. Only P-wave information was used previously to develop models for the entire profile. In this study, a multi-wave processing, analysis, and interpretation of the OBS data are presented for the 550-km-long southern segment of this Profile that crosses the deep-water South-Okhotsk Basin. Within this segment 50 seismometers were deployed with nominal OBS station spacing of 10–12 km. Shot point spacing was 250 m. Not only primary P-waves and S-waves but also multiples and P-S, S-P converted waves were analyzed in this study to constrain velocity-interface models by means of travel time forward modelling. In offshore deep seismic studies, thick water layer hinders an estimation of velocities in the sedimentary cover and in the upper consolidated crust. Primarily, this is due to the fact that refracted waves propagating in low-velocity solid upper layers interfere with high-amplitude direct water wave. However, in multi-component measurements with ocean bottom seismometers, it is possible to use converted and multiple waves for velocity estimations in these layers. Consequently, one can obtain P- and S-waves velocity models of the sedimentary strata and the upper consolidated crust. Velocity values in the upper consolidated crust beneath the South-Okhotsk Basin (Vp = 5.50–5.80 km/s, Vp/Vs = 1.74–1.76) allow interpretation of this 2.5–3.5-km-thick layer to be consistent with a felsic (granodioritic) crust. These results suggest that the Earth's crust in this region can be considered continental in nature, rather than previously accepted oceanic crust. Even though, the crust is thinned and stretched at this location.
The Marvin Spur is a 450-km-long east–west trending escarpment along the northernmost periphery of the Alpha Ridge, starting about 500 km from the coasts of Ellesmere Island and Greenland off the Arctic Ocean margin of North America and running subparallel to the Amerasian margin of the continental Lomonosov Ridge. This region was investigated as part of the Canada-Sweden Polar Expedition in 2016, from which two seismic profiles are presented. The first is a 165-km-long line along the crest of the Marvin Spur. The second is a 221-km-long line extending southwestward from the spur to the northern flank of the Alpha Ridge within the Cretaceous High Arctic Large Igneous Province (HALIP). Multichannel seismic reflection data were acquired along both lines using a 100-m-long streamer, and the airgun shots were also recorded using 16 sonobuoys and 5 stations on the sea ice to calculate a velocity model for the crust from forward modelling of seismic travel times. The Marvin Spur profile reveals up to 1100 m of sedimentary rocks on top of a 1-km-thick series of basalts (4.5–5.1 km s−1). Upper and lower crust have velocities of 5.8–5.9 km s−1 and 6.2–6.3 km s−1, respectively, with the upper crust being 1–2 km thick compared to around 13 km for the lower crust. A wide-angle double seismic reflection manifests the top and base of a 6-km-thick lower crustal layer that we interpret as magmatic underplating beneath the continental crust of the Marvin Spur. We correlate a high-amplitude magnetic anomaly on Marvin Spur with a comparable anomaly on Lomonosov Ridge by invoking 110 km of dextral strike-slip motion. Assuming that HALIP-related magmatic deposits generate these anomalies, the strike-slip motion pre-dates the main phase of magmatism (latest Cretaceous, 78 Ma). On the northern Alpha Ridge, sediments are around 1-km-thick and cover a 700 to 1700-m-thick series of basalts with velocities of 4.4 to 4.8 km s−1. Below is a 3-km-thick layer with intermediate velocities of 5.6 km s−1 and a lower crust with a velocity of 6.8 km s−1. Moho depth is not resolved seismically, but gravity modelling indicates a total thickness of 13 or 18 km for the igneous crust except for the Fedotov Seamount where Moho deepens by about 5 km. Construction of the seamount occurred in multiple magmatic phases, including flow eruptions during deposition of the Cenozoic sedimentary succession post-dating the main HALIP magmatism.
The Icelandic plume, a major convective upwelling, has had a considerable influence on the geological evolution of the North Atlantic region. Direct manifestations of this major convective upwelling include positive residual depth anomalies and long wavelength free-air gravity anomalies, both of which reach from Baffin Island to Norway and from Newfoundland to Svalbard. Signifi cant shear wave velocity anomalies, observed in full-waveform tomographic models between 100 km and 200 km depth, show the Icelandic plume has a complex, irregular planform. These anomalies suggest about fi ve horizontal fi ngers radiate away from the central plume conduit. The best imaged fingers lie beneath the British Isles, southern Scandinavia and Greenland, extending ~1,000 km from the Icelandic plume. It is proposed that these radial miscible fi ngers develop due to the Saffman-Taylor instability, a fluid dynamical phenomenon which occurs when a less viscous fluid is injected into a more viscous fluid. Mobility ratio (i.e. the ratio of fluid viscosities), Peclet number (i.e. the ratio of advective and diffusive transport rates) and thickness of the horizontal layer into which the fluid is injected, together control the presence of fi ngering due to the Saffman-Taylor instability. Estimates for the Icelandic plume suggest the mobility ratio is at least 15, the Peclet number is ~ 2 x 10⁴, and the asthenospheric channel thickness is 100 ± 50 km. Appropriately scaled laboratory experiments play a key role in developing a quantitative understanding of the spatial and temporal evolution of mantle plume planforms. My results prove that the presence or absence of radial miscible fi ngering due to the Saffman-Taylor instability is controlled by changes in mobility ratio, Peclet number and horizontal layer thickness. At large horizontal thicknesses, gravity has an increasingly important influence and acts to damp the production of radial viscous miscible fi ngers. Observed values from the Icelandic plume suggest the fluid dynamics may be more complex than the Saffman-Taylor instability alone. Additional processes, such as interaction with the base of the lithospheric plate, along with the Saffman-Taylor instability, may be the origin of the fi ngers.
The continental Lomonosov Ridge spans across the Arctic Ocean and was the subject of a geophysical study in 2016 with two seismic reflection lines crossing the ridge in proximity to the North Pole, one of which continues across the continent-ocean transition zone into the Amundsen Basin. One seismic station and 15 sonobuoys were deployed along these two lines to record seismic wide-angle reflections and refractions for development of a crustal-scale velocity model. Its viability is checked using gravity data from the experiment which are also used to interpolate crustal structure in areas with poor seismic constraints. On the line extending into the Amundsen Basin, continental crust composed of two layers with velocities of 6.0 and 6.5 km/s is encountered beneath the Lomonosov Ridge where the Moho depth is 21 km based on gravity modelling. The crust is overlain by a 1-km-thick layer with velocities of 4.7 km/s coinciding with a zone of positive magnetic anomalies of up to 180 nT. This layer is interpreted to include extrusive volcanic rocks related to the Cretaceous High Arctic Large Igneous Province (HALIP). Within the Amundsen Basin, three distinct crustal domains can be distinguished. Closest to the ridge is a 40-km-wide zone with a crustal thickness around 5 km interpreted as thinned continental crust. Five distinctive faulted basement blocks display high-amplitude reflections along their crests with velocities of 4.6 km/s, representing the continuation of the magmatic rocks further upslope. Brozena et al. (2003) interpreted magnetic Chron C25 to be located in this zone but our data are not consistent with this being a seafloor spreading anomaly. In the adjacent crustal domain, heading basinward, the basement flattens and two layers with velocities of 5.2 and 6.8 km/s can be distinguished, where the upper and lower layer have a thickness of 1.5 and 2.0 km, respectively. The upper layer is interpreted as exhumed and highly serpentinized mantle while the lower layer may be less serpentinized mantle with some gabbroic intrusions. This may explain the high-amplitude reflections within the overlying sediments that are interpreted as sill intrusions. Continuing basinward, the last crustal domain represents 4-to 5-km-thick oceanic crust with a variable basement relief and velocities of 4.8 and 6.5 km/s at the top of oceanic layers 2 and 3, respectively. It is within this zone that the first true seafloor spreading anomaly Chron C24 is observed, which argues for a similar breakup age in the Eurasia Basin as in the Northeast Atlantic. On the other profile crossing the Lomonosov Ridge, a 60-km-wide intrusion into the lower crust is observed where velocities are increased to 6.9 km/s. Gravity modelling supports the interpretation of magmatic underplating beneath the intrusion. Seismic data in this region show that the crust is overlain by a 2-km-thick series of high-amplitude reflections with a velocity of 4.8 km/s in a 30-km-wide zone where strong magnetic anomalies (>800 nT) are observed, suggesting a composition of basalt flows. This part of the Lomonosov Ridge appears therefore to have a HALIP-related magmatic overprint at all crustal levels.
A play-based resource assessment of conventional hydrocarbons has been performed for the offshore areas of central West Greenland and the onshore Nuussuaq Basin (Assessment Unit 3, AU3). Four play levels have been assessed, with an estimated mean for the undiscovered resources of ~3,650 MMBOE risked recoverable. The known prospectivity includes 24 leads with Mean Case Risked Recoverable volumes of ~100 MMBOE. The unidentified prospectivity has Mean Case Risked Recoverable volumes of ~3,550 MMBOE resulting in an average area yield of ~27 MB/1000 km2 (risked).
The deep model of the Earth’s crust and upper mantle of the Arctic basin is represented by a series of velocity sections along the DSS profiles and a set of maps showing the thickness of the sedimentary cover, the thickness of the Earth’s crust as a whole and the distribution of the continental and oceanic types of the Earth’s crust in the Circumpolar Arctic. Crustal Thickness Map is based on results of deep seismic studies and gravity field anomalies in the Circumpolar Arctic. Over 300 profiles of total length of about 140,000 km and equations of correlation, which link the depth of the Moho discontinuity occurrence with Bouguer anomalies and the topography, were used for the map compilation. Correlation sketch map of crustal types, which differ in velocity and density parameters, structure, and total crust thickness, has been compiled based on the data of deep seismic studies on continents and in oceans. The sketch map of crustal types distribution, which was compiled based on seismic profiles in the Arctic, demonstrates the position of the oceanic and continental crust in the structures of the Circumpolar Arctic. Summary geotransect is composed of DSS seismic line fragments and supplemented with density modelling. The geotransect demonstrates structure of the Earth’s crust and upper mantle along the line 7600 km long, which crosses the continental crust of the East European Platform, Barents-Kara shelf seas, Eurasian Basin oceanic crust, reduced crust of the Central Arctic Submarine Elevations, shelf seas of Eurasia passive margin, and crust of the Chukotka-Kolyma folded area.
Elevated topography is evident across the continental margins of the Atlantic. The Cumberland Peninsula, Baffin Island, formed as the result of rifting along the Labrador–Baffin margins in the late Mesozoic and is dominated by low-relief high-elevation topography. Apatite fission-track (AFT) analysis of the landscape previously concluded that the area has experienced a differential protracted cooling regime since the Devonian; however, defined periods of cooling and the direct causes of exhumation were unresolved. This work combines the original AFT data with 98 apatite new (U–Th)/He (AHe) ages from 16 samples and applies the newly developed ‘broken crystals’ technique to provide a greater number of thermal constraints for thermal history modelling to better constrain the topographic evolution. The spatial distribution of AFT and AHe ages implies that exhumation has been significant toward the SE (Labrador) coastline, and results of thermal modelling outline three notable periods of cooling: in the pre-rift stage (460–200 Ma), from synrift stage to present (120–0 Ma) and within the post-rift stage (30–0 Ma). Pre-rift cooling is interpreted as the result of exhumation of Laurentia and synrift cooling as the result of rift-flank uplift to the SE and differential erosion of landscape, whereas the final post-rift period is probably an artefact of the modelling process. These results suggest that the source of the Cumberland Peninsula's modern-day elevated topography is uplift during rifting in the Cretaceous and the isostatic compensation following continuous Mesozoic and Cenozoic differential erosion. This work highlights how interaction of rift tectonics and isostasy can be the principal source for modern elevated continental margins, and also provides insight into the pre-rift exhumational history of central Laurentia.
Supplementary material: Thermal histories are available at: https://doi.org/10.6084/m9.figshare.c.4528409
During the final stage of continental rifting, stretching localizes in the future distal domain where lithospheric necking occurs resulting in continental breakup. In magma-poor margins, the lithospheric necking is accompanied by crustal hyperextension, serpentinization and exhumation of mantle lithosphere in the continent-ocean transition domain (COT). In magma-rich margins, the necking is accomplished by the emplacement of large amounts of volcanics in the COT, in the form of seaward dipping wedges of flood basalts (SDRs). This study examines the factors controlling the final crustal architecture observed in rifted margins and the magmatic budget during continental breakup, using observations from the Labrador Sea. The latter shows magma-rich breakup with SDRs documented in the north and magma-poor breakup with a wide domain of exhumed serpentinized mantle recorded in the south. The pre-rift strength of the lithosphere, defined by the inherited thermal structure, composition, and thickness of the lithospheric layers, controls the structural evolution during rifting. While variations in the magmatic budget associated with breakup are controlled primarily by the interaction between the pre-rift inheritance, the timing and the degree of mantle melting, in relation to lithospheric thinning and mantle hydration.
Voluminous, subaerial, ultra-depleted, 62 Ma, primary picritic lavas lie on conjugate volcanic margins on both sides of Davis Strait separating Baffin Island and West Greenland. Temporally, these picrites erupted just prior to, and coeval with, the initiation of sea-floor spreading in Labrador Sea and Baffin Bay. Petrogenetically, the chemical characteristics of these picrites (MgO = 18–21 wt%; K 2 O = 0.01–0.20 wt%; ⁸⁷ Sr/ ⁸⁶ Sr i ≈ 0.7030; εNd i ≈ +5.2–8.6; ³ He/ ⁴ He ≤ 49.5R A ) are those of D-MORBs that demand derivation only by partial melting of highly incompatible-element depleted subcontinental lithospheric mantle (SCLM) at a pressure of ~ 4 GPa, followed by rapid ascent to the surface, but do not necessarily require high temperatures or high degrees of partial melting. Tectonically, these picrites formed near Paleoproterozoic suture zones in the SCLM of thick Paleoproterozoic cratonic terranes during Paleogene rifting between Greenland and North America. Structurally, the picrites are related to the major intersection of a NNW-trending lithospheric thinning under Baffin Bay and the ~E-W-trending thickened lithosphere of the Paleoproterozoic Nagssugtoqidian Fold Belt. During the late Mesozoic, ENE extension that thinned the mantle lithosphere and created normal-faulted basins. Elastic finite-element models and present-day studies of crustal extension show that the thicker Nagssugtoqidian Fold Belt underwent less thinning and extension than the Baffin Bay lithosphere. These extensional disparities occurred at the orthogonal intersection of pre-existing ~E-W-trending strike-slip faults in the thicker Nagssugtoqidian Fold Belt with the incipient spreading under Baffin Bay, and likely resulted in the formation of one or more pull-apart basins. Because the strike-slip faults are ancient suture zones, trans-tension within these suture zones easily reached depths of ~120 km, not only creating adiabatic decompression melting in the SCLM, but also forming an open pathway for the picritic melts to rapidly reach the surface. This purely tectonic model requires no spatially or temporally improbable deep mantle plume for generation of the Paleocene picrites of Davis Strait.
New analyses of the palynological assemblages in 13 offshore wells on the Canadian margin and six on the West Greenland Margin, in conjunction with onshore data, have led to a new biostratigraphic framework for the Cretaceous–Cenozoic strata of the Labrador Sea – Davis Strait – Baffin Bay (Labrador–Baffin Seaway) region and the first broad biostratigraphic correlation of the Canadian and Greenland margins. This framework is based on 167 last occurrences and 18 local/regional peak/common-occurrence events for dinocysts, miospores, fungal spores and Azolla. Detailed biostratigraphic evidence has confirmed the following hiatuses: pre-Aptian in the Hopedale Basin; pre-Albian in the Saglek Basin; Albian–Turonian in some wells of the Hopedale Basin; Turonian–Santonian/Campanian in some areas; pre-Campanian and late Campanian – Thanetian on the Greenland Margin; late Maastrichtian and Danian in some wells of the Hopedale Basin and in the Saglek Basin; Selandian in part of the Hopedale Basin, in all the Saglek Basin wells and in two wells on the West Greenland Margin; late Ypresian and/or Lutetian on both sides; Oligocene to middle Miocene of considerable variability on both margins, with all of the Oligocene and the lower Miocene missing in all the West Greenland Margin wells; and middle to late Miocene on the western side. On the Canadian margin, the hiatuses can be partially matched with the five previously recognised regional unconformities; on the Greenland margin, however, the relationship to the five unconformities is more tenuous. Palynomorph assemblages show that most Aptian to Albian sediments were deposited in generally non-marine to marginal marine settings, interrupted by a short-lived shallow marine episode in the Aptian. A marine transgression started in the Cenomanian–Turonian and led to the most open-marine, oceanic conditions in the Campanian–Lutetian; shallowing probably started in the late Lutetian and continued into the Rupelian, when inner neritic and marginal marine palaeoenvironments predominated. Throughout the rest of the Cenozoic, inner neritic palaeoenvironments alternated with marginal marine conditions on the margins of the Labrador–Baffin Seaway. These observations broadly reflect the tectonic evolution of the seaway, with rift conditions prevailing from Aptian to Danian times, followed by drift through much of the Paleocene and Eocene, and post-drift from Oligocene to the present. Dinocysts
indicate that climatic conditions in the Labrador–Baffin Seaway region were relatively temperate in the Cretaceous, but varied dramatically through the Cenozoic. The Danian was a time of increasingly warmer climate, a thermal maximum being reached around the Paleocene–Eocene boundary reflecting the global thermal event at this time. Warm to hot conditions prevailed throughout the Ypresian, but the climate began to cool in the Lutetian, a trend that accelerated through the Priabonian and Rupelian. Throughout the Neogene, temperatures generally declined, culminating in the Quaternary.
Continental extension causes rifting and thinning of the lithosphere that may result in breakup and eventually the initiation of seafloor spreading and passive continental margin development. Ambiguity exists regarding the roles of magmatism and structural inheritance during rifting and continental breakup during this process. This study focuses on the importance of these controls on the Mesozoic-Cenozoic separation between West Greenland and Eastern Canada. It is important to improve our knowledge of the processes that influenced breakup as the current understanding of these processes is limited and also to reduce hydrocarbon exploration risk in this tectonic setting. During this study passive margin processes were investigated using a variety of methodologies at a range of scales from that of conjugate margin pairs (Chapters 4 and 5), through margin and basin scale studies (Chapter 6) to the smallest scale on individual igneous intrusions (Chapter 7). At the largest scale an assessment of the magmatic and structural asymmetry between the conjugate margins of the Labrador Sea based primarily on field data and subsequent analysis near Makkovik, Labrador, but also other large-scale geophysical datasets demonstrated that early rifting was dominated by simple shear rather than pure shear. In such a scenario Labrador would have been the lower plate margin to the upper plate southwest Greenland margin. Further analysis of field observations indicated that rifting of the Labrador Sea region may have been aided by a favourably orientated basement metamorphic fabric and that observable onshore brittle deformation structures may be related to Mesozoic rifting. Further north in the Davis Strait, seismic interpretation at the margin and basin scale allowed a series of seismic surfaces, isochrons and a new offshore fault map to be produced. The results of this analysis demonstrated that the geometry of rift basins was primarily controlled by pre-existing structures, an assertion supported by observations of reactivation onshore in West Greenland. Finally, at the smallest scale, results of numerical modelling offshore Newfoundland demonstrated that even on non- volcanic passive margins, intrusive magmatism can influence thermal evolution. In addition, the presence of widespread igneous rocks on passive margins may be indicative of regional-scale thermal perturbations that should be considered in source rock maturation studies. Overall, the conclusion of this project is that both magmatism and structural inheritance have profoundly influenced the continental breakup between West Greenland and Eastern Canada, and that interplay between these two complex groups of mechanisms may have also contributed to the geological evolution of this area.
Multichannel and wide-angle seismic data collected off Virginia during the 1990 EDGE Mid-Atlantic seismic experiment provide the most detailed image to date of the continent-ocean transition on the U.S. Atlantic margin. Multichannel data were acquired using a 10,800 cu inch (177 L) airgun array and 6-km-long streamer, and coincident wide-angle data were recorded by ten ocean bottom seismic instruments. A velocity model constructed by inversion of wide-angle and vertical-incidence travel times shows strong lateral changes in deep-crustal structure across the margin. Lower-crustal velocities are 6.8 km/s in rifted continental crust, increase to 7.5 km/s beneath the outer continental shelf, and decrease to 7.0 km/s in oceanic crust. Prominent seaward- dipping reflections comprise a 100-km-wide, 25-km-thick ocean- continent transition zone that consists almost entirely of mafic igneous material accreted to the margin during continental breakup. The boundary between rifted continental crust and this thick igneous crust is abrupt, occupying only about 20 km of the margin. Appalachian intracrustal reflectivity largely disappears across this boundary as velocity increases from 5.9 km/s to greater than 7.0 km/s, implying that the reflectivity is disrupted by massive intrusion and that very little continental crust persists seaward of the reflective crust persists seaward of the reflective crust. The thick igneous crust is spatially correlated with the East Coast magnetic anomaly, implying that the basalts and underlying intrusives cause the anomaly. The details of the seismic structure and lack of independent evidence for an appropriately located hotspot in the central Atlantic imply that nonplume processes are responsible for the igneous material.
Several recent models of crustal evolution are based on the belief that
the thickness of the continental crust is proportional to its age, with
ancient crust being the thickest. A worldwide review of seismic
structure contradicts this belief and falsifies these models, at least
for the Archean. Proterozoic crust has a thickness of 40-55 km and a
substantial high-velocity (greater than 7 km/s) layer at its base, while
Archean crust is only 27-40 km thick (except at the site of younger
rifts and collisional boundaries) and lacks the basal high-velocity
layer. Seismology also provides evidence that the lithosphere is
thickest beneath Archean cratons, while diamond ages show that this
lithospheric keel must have already existed in the Archean. Geochemical
data also indicate significant differences between Archean and
Proterozoic lithosphere. Major and trace element studies of sediments
show a change in upper crustal composition between the Archean and the
Proterozoic. The secular change in the crust-forming process is
attributed to a decline in mantle temperature, leading to a change in
the composition of the lithospheric mantle. The higher temperature of
the Archean mantle led to the eruption of komatiitic lavas, producing a
refractory lithospheric mantle which is ultradepleted in FeO and
volatiles. The resultant lithospheric keel is intrinsically less dense
than the surrounding mantle and thus not suceptible to delamination. In
contrast, Proterozoic crust developed above fertile mantle. The eruption
of continental flood basalts and underplating of basaltic sills is
attributed to subsequent heating and partial melting of the lithospheric
mantle. Consequently, Proterozoic crust is thickened and has a
high-velocity basal layer.
Regional reflection seismic profiles across the Labrador Sea originally acquired in 1977 have been reprocessed and reinterpreted. Zones of different structural style have been identified. The seismic interpretations have been used to constrain magnetic modelling and oceanic crust has been confirmed from magnetic anomaly 27N and seaward. However, all attempts to model the area landward of magnetic anomaly 27N as a series of remanent magnetizations of alternating polarity have failed. Interpretations which fit the magnetic and seismic data consist of a zone of block-faulted and subsided continental crust on both the Greenland and Canadian sides, which is separated from oceanic crust by zones of continental crust intruded by and in places overlain by magnetized igneous material. It is concluded that seafloor spreading started in the Labrador Sea in the Palaeocene (Chron 27N) and that large areas under deep water formerly thought to be underlain by oceanic crust should now be considered to be continental.
An onshore/offshore seismic wide-angle experiment was conducted in order to investigate the structure and composition of the Archean crust beneath the shelf of southwest Greenland parallel to the passive margin. A velocity/depth profile along the thinned continental or transitional crust was obtained so that constraints could be placed on the magmatic rifting history in the northern Labrador Sea. A high-velocity zone with P wave velocities of more than 7.2 km/s at the bottom of the transitional crust is indicated from the results of a 1D extremal inversion. A velocity/depth model containing midcrustal and lower crustal discontinuities between 12 and 25 km depth, and a Moho dipping northward at 30 to 42 km depth, is produced by combining 2D travel time forward modeling and inversion. Hot spot magmatism may explain magmatic underplating of the thinned continental or transitional crust of SW Greenland.
An interface corrugation with a relief of 10 km and a width of 30 km was successfully imaged in a test of the interface inversion. Velocity-depth curves derived for shot points 14-19 using the tau-sum method are similar to an average one-dimensional velocity model from forward modeling using travel time correlations from southern profiles 14-19. A two-dimensional velocity structure was derived by using the average one-dimensional velocities for the deeper crustal layers and formally inverting for depth to interfaces. The final inversion model is found to be consistent with previous refraction interpretations south of the Ouachita orogenic trend and concurrent interpretations of the PASSCAL data set. Inversion results for the central and southern portion of the PASSCAL profile indicate a depth of 10-12 km for a midcrustal layer which thins southward from approximately 10 km to about 4 km. A lower crustal layer with an average thickness of 12 km and a Moho depth of approximately 29.5 km are also determined. Interface depths are in agreement with a normal movement stack of the PASSCAL data set. In particular, the shallowing of the Moho to a depth of 30 km over the northern 50 km of the profile matches previous interpretations of the data set and has been interpreted here and in previous studies as the location of the Paleozoic continental margin. Geophysical studies of the modern Atlantic continental passive margin provide the simplest comparison to the crustal structure derived here. The lower crustal layer found south of the shallowing of the Moho to 30 km beneath the PASSCAL profile is analogous in thickness and position to rift stage lower crust.
A detailed refraction - wide-angle reflection seismic experiment was carried out in northern Labrador to determine the velocity structure of relatively unaltered Archean crust in the Nain Province. Six 3-component land seismometers were used to record an airgun source along a profile parallel to the coast. Forward modeling of traveltimes and amplitudes yields a P- and S-wave velocity model that shows two crustal blocks separated by a fault. Magnetic data suggest, but do not prove, that the fault is the offshore continuation of the Handy fault. A southwards thickening of the lower crust across the fault indicates that a transcurrent component might have been associated with the faulting. The total crustal thickness is 33 km to the north and 38 km to the south of the fault. The presence of PmS reflections imply a sharp transition at the Moho. Upper crustal velocities of 5.8-6.3 km/s and Poisson's ratios of 0.20 and 0.24, north and south of the fault respectively, are consistent with a gneissic composition, but suggest a higher quartz content in the northern block. Velocities in the middle crust increase to 6.5 km/s, where a discontinuity at a depth between 16 and 18 km marks the transition to the lower crust with velocities between 6.6 and 6.9 km/s. Poisson's ratios of 0.24 and 0.26 indicate, respectively, a felsic middle crust and an intermediate composition for the lower crust. The absence of a high-velocity basal layer is in accordance with other examples of Archean crust.
A method of seismic traveltime inversion for simultaneous determination of 2-D velocity and interface structure is presented that is applicable to any type of body-wave seismic data. The advantage of inversion, as opposed to trial-and-error forward modelling, is that it provides estimates of model parameter resolution, uncertainty and non-uniqueness, and an assurance that the data have been fit according to a specified norm. In addition, the time required to interpret data is significantly reduced. The inversion scheme is iterative and is based on a model parametrization and a method of ray tracing suited to the forward step of an inverse approach. The number and position of velocity and boundary nodes can be adapted to the shot-receiver geometry and subsurface ray coverage, and to the complexity of the near-surface. The model parametrization also allows ancillary amplitude information to be used to constrain model features not adequately resolved by the traveltime data alone. The method of ray tracing
We have interpreted all available single-channel and multichannel seismic reflection profiles to produce maps of structure contours on basement and isopachs of sediment thickness in the northwestern Atlantic Ocean, including the Labrador and Irminger basins. Where appropriate, we have modified and incorporated existing charts into the compilation. Contours are in meters, derived by applying velocity-regression equations based on sonobuoy results; this gives a more accurate representation of geologic relations than is possible in reflection-time mapping. Major structural relations and sediment distribution for the Mid-Atlantic Ridge, Mid-Labrador Sea Ridge, Davis Strait, and adjacent Greenland and eastern Canadian continental margins are clearly defined in the maps. Observ d basement structure is in good agreement with that expected from current plate-kinematic models of the region. The sediment-thickness patterns are controlled by interaction of such factors as age of underlying oceanic crust, crustal tectonic history, structural trends in basement, locations of sediment sources, and nature of the sedimentary processes delivering sediment to the basins.
A refraction and wide-angle reflection seismic study was carried out in southern Nares Strait (northernmost Baffin Bay) on a 378 km long profile running from Pituffik/Thule Air Base on Greenland into Makinson Inlet on Ellesmere Island, Canada. Eight ocean bottom seismometers and eight land stations were deployed to record the airgun shots along the line. A crustal velocity model was developed by forward and inverse modeling techniques. The Proterozoic Thule Basin can be correlated across Nares Strait as a continuous structure with a total thickness of 4-5 km. The basin is divided into three units. The upper unit has velocities of 4.5-5.0 km s-1 and a Poisson's ratio (σ) of 0.30, indicating a high content of carbonates. The middle unit is characterized by high velocities (6.1 km s-1) and a Poisson's ratio of 0.28. This unit is interpreted to correlate with the basaltic sills found in the Cape Combermere formation. The lower unit is a low-velocity zone and, hence, its velocities are unconstrained. The underlying crust is divided into three layers, upper crust (6.0-6.2 km s-1, σ = 0.25), middle crust (6.1-6.3 km s-1, a = 0.26) and lower crust (6.7-6.9 km s-1, σ = 0.26). These properties are consistent with a granitic/gneissic composition in the upper/middle crust and with granulites in the lower crust. Moho depth on either side of Nares Strait is 36 km, with some shallowing to 33 km in a 100 km wide zone. The Moho shallowing is related to local uplift at the Carey Islands just to the south of the line based on correlation with the gravity data. With only minor lateral changes of crustal velocities and Moho depth across southern Nares Strait, the eastern Archean/Proterozoic part of Ellesmere Island appears to be part of the same plate as Greenland with Thule Basin as intracratonic feature. No structures consistent with a strike-slip boundary could be resolved in southern Nares Strait.
Seismic reflection and refraction data from the SE Greenland margin
provide a detailed view of a volcanic rifted margin from Archean
continental crust to near-to-average oceanic crust over a spatial scale
of 400 km. The SIGMA III transect, located ˜600 km south of the
Greenland-Iceland Ridge and the presumed track of the Iceland hot spot,
shows that the continent-ocean transition is abrupt and only a small
amount of crustal thinning occurred prior to final breakup. Initially,
18.3 km thick crust accreted to the margin and the productivity
decreased through time until a steady state ridge system was established
that produced 8-10 km thick crust. Changes in the morphology of the
basaltic extrusives provide evidence for vertical motions of the ridge
system, which was close to sea level for at least 1 m.y. of subaerial
spreading despite a reduction in productivity from 17 to 13.5 km thick
crust over this time interval. This could be explained if a small
component of active upwelling associated with thermal buoyancy from a
modest thermal anomaly provided dynamic support to the rift system. The
thermal anomaly must be exhaustible, consistent with recent suggestions
that plume material was emplaced into a preexisting lithospheric thin
spot as a thin sheet. Exhaustion of the thin sheet led to rapid
subsidence of the spreading system and a change from subaerial, to
shallow marine, and finally to deep marine extrusion in ˜2 m.y. is
shown by the morphological changes. In addition, comparison to the
conjugate Hatton Bank shows a clear asymmetry in the early accretion
history of North Atlantic oceanic crust. Nearly double the volume of
material was emplaced on the Greenland margin compared to Hatton Bank
and may indicate east directed ridge migration during initial opening.
Many mantle plumes started with voluminous heads of hot material that ascended as diapirs through the mantle. Flood basalts, radial dike swarms, and frequently continental breakup are associated with the impingement of starting plume heads on the base of the lithosphere. The buoyant plume head material ponds at the base of the lithosphere and then flows laterally. Relief on the base of the lithosphere acts as an upside-down drainage pattern with enclosed catchments for this flow. That is, plume material preferentially collects beneath regions where the lithosphere is locally thin, such as thermally subsiding sedimentary basins. An example is uplift associated with the Iceland starting plume which inverted the Mesozoic Irish Sea basin. Additional relief at the base of the lithosphere is associated with rifting and seafloor spreading. In the case of the northern North Sea, material from the Iceland starting plume ponded beneath a basin with locally thin lithosphere. Rifting breached the enclosed catchment allowing the ponded plume material to drain across the new passive margin toward very thin lithosphere produced by seafloor spreading. Rifting also creates a conduit for the flow of plume material away from the region underlain by the starting plume head. An example is the volcanic passive margin off Nova Scotia which is 2000 km from the center of the Bahama starting plume head. Numerical and analytical calculations indicate that lateral flow of plume material consistent with this observation is expected if its viscosity is around 1018Pas.
The Labrador Sea is a small oceanic basin that developed when the North American and Greenland plates separated. An initial period of stretching in Early Cretaceous time formed sedimentary basins now preserved under the continental shelves and around the margins of the oceanic crust. The basins subsided thermally during Late Cretaceous time and a second episode of tectonism took place during latest Cretaceous and early Paleocene time, before the onset of sea-floor spreading in mid-Paleocene time. Around the northern Labrador Sea, Davis Strait and in southern Baffin Bay, voluminous picrites and basalts were erupted at and shortly after the commencement of sea-floor spreading. Volcanism occured again in early Eocene time at the same time as sea-floor spreading commenced in the northern North Atlantic. Farther southeast, along the Labrador and southern West Greenland margins, oceanic crust is separated from continental crust by highly stretched but non-magmatic transition zones which developed before sea-floor spreading. A complex transform zone, which developed during sea-floor spreading in late Paleocene and early Eocene time, separates continental and oceanic crust along the Baffin Island margin. The Greenland and Labrador ocean- continent transitions are asymmetric across the only available conjugate cross-sections. However, a cross-section through the Labrador margin farther north resembles the Greenland cross-section in the conjugate pair more than it does the Labrador cross-section of this pair. Consideration of the geological history of the area suggests that the non-magmatic transition zones may have formed by slow extension of a few millimetres per year through a period of 53 Ma during Cretaceous and early Paleocene time.
Sanidine crystals from two tuff layers at the base of the Palaeocene Eigg Lava Formation on the Isle of Muck, Inner Hebrides, yield step-wise Ar release plateau ages of 62.8+/-0.6 (2 sigma) and 62.4+/-0.6 Ma using the laser Ar-40/Ar-39 dating technique. These determinations, which are in accord with, but significantly more precise than earlier results, provide a definitive age for the inception of igneous activity in the Small Isles. From stratigraphical inferences, the Muck ages provide precise, maximum constraints on the possible age of Skye magmatism and possibly most of the British Tertiary Volcanic Province. The new ages significantly predate the oldest ages determined so far for Tertiary magmatism in NE Greenland but are similar to ages obtained from W Greenland and offshore SE Greenland and support the concept that the initiation of regional volcanism was primarily controlled by lithospheric thin spots. The Muck sanidine age appears to precisely date the first manifestation of the impingement of the Iceland mantle plume on the lithosphere beneath NW Scotland.
The southern part of the continental margin off southern West Greenland is an amagmatic margin that may have taken at least 30 and possibly more than 60 million years to form during the Cretaceous at an average extension rare of between 8.7 and 4.4 mm a(-1). To its northwest and east are volcanic continental margins formed in the Early Tertiary when sea-floor spreading started above the hot North Atlantic plume head. The survival of the amagmatic margin means that plume head material could never have been present under it and therefore the plume head could not have had the circularly symmetric shape commonly depicted in the literature.
The crust across each margin of the Labrador Sea, a conjugate rift margin pair, consists of three well-defined zones: thinned continental crust, 70 80-km-wide transitional crust, and oceanic crust. The transition zone is characterized by a low-velocity upper crust (4 5 km/s) underlain by a 6.4 7.7 km/s layer. We propose that the lower layer is serpentinized upper mantle; it is less likely to be gabbroic igneous lower crust. The low-velocity upper crust may be either an oceanic basaltic layer or very thin (
A refraction/wide-angle reflection seismic transect across the Labrador peninsula covers the Core Zone of the SE Churchill Province, the Paleoproterozoic Torngat Orogen, and the Archean Nain Province including a portion of the Labrador continental margin. An airgun array was used as source, and 11 ocean-bottom seismometers and 16 land stations recorded the shots. Forward modeling of travel times and amplitudes reveals a deep asymmetric crustal root beneath the Torngat Orogen, with a crustal thickness of >49 km and with P-wave velocities of 6.9-7.0 km/s. The geometry of the velocity model and the root can be best explained by either westward dipping subduction or westward underthrusting of the Nain crust. Gravity modeling suggests a correlation of the crustal root with a gravity low that extends ~100 km in an E-W direction and ~200 km from north to south. The preservation of the crustal root is attributed to the lack of postorogenic heating and ductile reworking consistent with the lack of abundant postcollisional magmatism in the SE Churchill Province. A discontinuity possibly cutting through the entire crust is interpreted as a zone of major transcurrent shearing associated with the main phase of deformation. West of the Torngat Orogen, the crustal thickness in the Core Zone of the Churchill Province varies between 35 and 38 km (P-wave velocities of 5.8-7.0 km/s). East of the orogen, the crystalline crust in the Nain Province is ~38 km thick (velocities from 5.8 to 6.9 km/s) but thins to 9 km in the shelf area of the Labrador margin, where it is covered with up to 8 km of sediments. No high-velocity zone was found beneath the thinned continental crust at the margin.
Wide-angle seismic studies have determined the detailed velocity structure along a 350-km-long profile across the Labrador margin. Combination of this model with a previously published cross section for the southwestern Greenland margin constitutes the first combined conjugate margin study based on seismic velocity structure. The results indicate three distinct zones across the Labrador margin, similar to the structure of the conjugate Greenland margin. Zone 1 represents 27 to 30-km-thick continental crust thinning gradually seaward over ~100 km distance. Farther seaward, zone 2 is 70-80 km wide, characterized by a distinct lower crust, 4-5 km thick, in which velocity increases with depth from 6.4 to 7.7 km/s. Interpretation for this lower crustal block favors an origin by serpentinized peridotite rather than by magmatic under-plating. Zone 3 represents two-layered, normal oceanic crust. The cross sections from both margins are reconstructed to an early drift stage at Chron 27. This demonstrates that the serpentinites in zone 2 are symmetrically distributed between previous identifications of Chrons 31 and 33 on both margins. Zone 1 shows a marked asymmetry, with a gradual thinning of continental crust off Labrador contrasted with a rapid thinning off Greenland. The abundant serpentinization of upper mantle peridotite in zone 2 and the asymmetric shape of zone 1 are both probably related to a very slow rate of continental rifting which produced little if any melt.
We present the results of a combined multichannel seismic reflection (MCS) and wide-angle, ocean bottom seismic profile collected in 1988 across the Carolina Trough on the U.S. Atlantic continental margin. Inversion of vertical-incidence and wide-angle travel time data has produced a velocity model of the entire crust across the continent-ocean transition. The margin consists of three structural elements: (1) rifted continental crust, comprising 1-4 km of post-rift sedimentary rocks overlying a 30-34 km thick subsedimentary crust, (2) transitional crust, a 70- to 80-km-wide zone comprising up to 12 km of postrift sedimentary rocks overlying a 10- to 24-km-thick subsedimentary crust, and (3) oceanic crust, comprising 8 km of sedimentary rocks overlying an 8-km-thick crystalline crust. The boundary between rifted continental and transitional crust, marked by the Brunswick magnetic anomaly, represents an abrupt change in physical properties, with strong lateral increases in seismic velocity, density, and magnetic susceptibility. The transitional crust contains mid-crustal seaward-dipping reflections observed on the MCS section and has seismic velocities of 6.5-6.9 km/s in the midcrust and 7.2-7.5 km/s in the lower crust. Modeling of potential field data shows that transitional crust also produces the prominent, margin-parallel gravity anomaly and the Brunswick and East Coast magnetic anomalies. These observations support the interpretation that the transitional crust was formed by magmatism during continental breakup. The prodigious thickness (up to 24 km) of igneous material rivals that interpreted on continental margins of the North Atlantic (e.g., Hatton Bank and Vøring Plateau), which formed in the vicinity of the Iceland hotspot. These observations, when combined with other transects across the margin, confirm previous suggestions that the U.S. Atlantic margin is strongly volcanic and further imply that the magmatism was not the result of a long-lived mantle plume.
This paper examines the complete crustal transition across the
nonvolcanic, southwest Greenland continental margin of the Labrador Sea
using wide-angle and coincident vertical-incidence seismic profiles. Six
ocean bottom seismometers and a sonobuoy record P and S wave first and
multiple arrivals from the crust and upper mantle, which are analyzed by
two-dimensional dynamic ray tracing and one-dimensional reflectivity
modeling. The resulting seismic velocity model requires that the
preexisting 30-km thick continental crust is thinned abruptly to
˜3 km across the continental slope, primarily by removal of the
lower crust. Farther seaward, the crust thickens to ˜6 km
primarily through the addition of a high-velocity (7.0-7.6 km/s) layer
in the lower crust. This lower crustal layer is 4-5 km thick, extends
for a horizontal distance of ˜80 km, and is interpreted as
partially serpentinized upper mantle. It is overlain by a low-velocity
(4.0-5.0 km/s), upper layer which is interpreted as highly fractured
upper continental crust. Our model suggests that seafloor spreading did
not start until chrons 27-28, 13 Ma younger than previously suggested.
This interpretation is supported by two-dimensional modeling of gravity
and magnetic data along the refraction line. Our results are consistent
with a simple shear mechanism for the initial rifting, with the SW
Greenland margin as the upper plate. However, a full characterization of
the rifting mechanism must await comparison with a seismic model for the
conjugate margin, east of Labrador.
A modeling methodology for obtaining two-dimensional (2-D) crustal structure from wide-angle seismic data is applied to data from the southeastern Grenville Province. The model of Grenville crustal structure is more detailed than a model obtained from a previous interpretation of the data and includes elements analogous to those imaged in a nearby deep reflection data. A crustal-scale zone of wide-angle reflectors with an average easterly apparent dip of 13° defines a major Grenvillian terrane boundary. -from Authors
During Ocean Drilling Program Leg 152, Sites 914 through 919 were drilled on the southeast Greenland Margin along a transect from the middle shelf into the adjacent deep-water Irminger Basin 500 km south of the Iceland hot-spot track (Iceland-Greenland Ridge). Sites 915 through 918 penetrated the entire cover of postrift sediments, and three of these four sites sampled the volcanic basement of the seward-dipping reflector sequences (SDRS). The landwater feather edge of the SDRS was drilled at the most landward site, Site 917, where a 779.5-m-thick, south to southeastward dipping volcanic section was found to overlie steeply dipping, marine pre-rift sediments of unknown, possibly Cretaceous, age. The more seaward Site 915 (later deepened by Site 990) recovered two lava flows that are stratigraphically lcoated above Site 917 and located within the oldest part of the main SDRS wedge. The central part of the SDRS wedge was penetrated at Site 918 in the Irminger Basin where a 120-m-thick lava section was recovered below 1189 m of postrift sediments. A few sills and dikes were sampled. All other igneous units recovered were subaerially erupted and deposited lavas, some of which may have flowed over wet ground or into shallow water. Lava at Site 917 display compositions ranging from picrite over olivine basalt to basalt, dacite, and acid tuffs. The younger lavas at Site 915 and Site 918 have a quite uniform composition similar to depleted Icelandic tholeiites. Two major successions are defined: the older Continental Succession and the younger Oceanic Succession. The Continental Succession comprises the Lower and Middle Series laveas at Site 917, and the Oceanic Succession comprises the Uppers Series lavas at Site 817 and the main SDRS series lavas at Site 915 (and Site 990) and Site 918.(See original for remainder of abstract).
The crustal velocity structure and the Moho depth of the Proterozoic Torngat Orogen, NE Canada, is determined by active seismic tomography using travel times of crustal turning rays and Moho reflections. The orogen developed during oblique convergence of the Archean Superior and Nain Provinces, which trapped an interior belt of Archean crust (Core Zone) between them, with the Torngat Orogen evolving between the Core Zone and the Nain Province. Beneath the central orogen a crustal root is found with a preserved depth of >52 km and a width of ~100 km. To the north, the root shallows to
Two detailed seismic refraction lines were shot in northern Baffin Bay in order to determine the crustal structure and so provide constraints on the complex geological and tectonic history of the area. An array of air guns provided the seismic source, with a total of 16 ocean bottom seismometers as receivers. The data were analyzed by iterative forward modeling of travel times and arrival amplitudes, and the crustal velocity structure obtained was interpreted in the light of previous seismic reflection and refraction results from this area, together with other available geological and geophysical information. Plate reconstructions suggest that the region was a single entity from the Archean until the late Mesozoic, when it underwent successive stages of extension, translation, and compression. On line 2, at 76°N, the continental crust thins between Greenland and Ellesmere Island, reaching to a minimum of about 10 km beneath a narrow, linear basin, which may delineate a former transform plate boundary. On line 4, on the northern margin of Baffin Bay, there is a marked change in velocity structure across the apparent continent-ocean boundary, with continental crust being replaced by a layer of intermediate seismic velocity that is believed to be serpentinized mantle, indicating that northern Baffin Bay was formed by amagmatic continental rifting and separation. A thick sedimentary sequence is the result of erosion of the Eurekan Orogen to the north, which was formed during the final, compressional tectonic motion. The seismic refraction results are consistent with the tectonic history inferred from plate kinematics.
Seismic refraction results show that the igneous section of oceanic crust averages 7.1 [plus minus] 0.8 km thick away from anomalous regions such as fracture zones and hot-spots, with extremal bounds of 5.0-8.5 km. Rare earth element inversions of the melt distribution in the mantle source region suggest that sufficient melt is generated under normal oceanic spreading centers to produce an 8.3 [plus minus] 1.5 km thick igneous crust. The difference between the thickness estimates from seismics and from rare earth element inversions is not significant given the uncertainties in the mantle source composition. The inferred igneous thickness increases to 10.3 [plus minus] 1.7 km (seismic measurements) and 10.7 [plus minus] 1.6 km (rare earth element inversions) where spreading centers intersect the regions of hotter than normal mantle surrounding mantle plumes. This is consistent with melt generation by decompression of the hotter mantle as it rises beneath spreading centers. Maximum inferred melt volumes are found on aseismic ridges directly above the central rising cores of mantle plumes, and average 20 [plus minus] 1 and 18 [plus minus] 1 km for seismic profiles and rare earth element inversions respectively. Both seismic measurements and rare earth element inversions show evidence for variable local crustal thinning beneath fracture zones, though some basalts recovered from fracture zones are indistinguishable geochemically from those generated on normal ridge segments away from fracture zones. The authors attribute the decreased mantle melting on very slow-spreading ridges to the conductive heat loss that enables the mantle to cool as it rises beneath the rift.
Sea-floor spreading magnetic lineations 25 (59 Ma) and older have been
reidentified in the Labrador Sea by using previous magnetic compilations
and some recently acquired data. The higher density of these
identifications enabled the calculation of a new set of better
constrained rotation poles that describes the sea-floor spreading
history of the Labrador Sea and Baffin Bay in a way that is somewhat
different from previously published reconstructions. The most important
inference that emerges from this work is that the change in spreading
direction between Greenland and North America after anomaly 25 time is
larger than previously recognized. As a result, the position of
Greenland at the time of initial opening (92 Ma) may have been about 100
km farther south than obtained in earlier reconstructions.
Two densely sampled marine refraction lines were shot in northern Baffin Bay on the shelves of Devon and Ellesmere islands (North American plate) and Greenland (Greenland plate). A total of 11 ocean-bottom seismometers recorded the airgun signals. The processed data were analyzed by the use of ray tracing and amplitude modelling. Two-dimensional models were derived that reproduce the characteristics of the observed data. A 5 km deep sedimentary basin was identified on the south end of line 3. On both lines the crustal velocity has a range of 5.7–6.6 km/s. Midway along the line on the shelf of Devon and Ellesmere islands, the Moho shallows abruptly northward from 27 to 20 km. The thinned crust is not overlain by a sedimentary basin to compensate for the elevated Moho, suggesting this is not an extensional feature. The thickness of the crust adjacent to northwest Greenland increases from south (22 km) to north (37 km). The thickening occurs in two stages: a sharp increase in the depth to Moho northwest of the sedimentary basin followed by a gradual deepening to the end of the line. The thin crust on the shelf of Ellesmere Island is located adjacent to the thick crust of Greenland. Plate reconstructions based on regional magnetic anomalies and transform faults indicate that Greenland is a separate plate. The crustal structure revealed by seismic refraction and reflection profiles and the variations in the depth to Moho are consistent with the plate boundary occurring between the refraction lines.
Morgan, W.J., 1983. Hotspot tracks and the early rifting of the Atlantic. In: P. Morgan and B.H. Baker (Editors), Processes of Continental Rifting. Tectonophysics, 94: 123–139.
Sonobuoy and tape recording buoy seismic refraction measurements were carried out in Baffin Bay and Davis Strait to study the extent and tectonic development of the oceanic region and the structure of some of the major features of the surrounding continental shelves. Both the oceanic and continental shelf areas are occupied by thick sequences of sediment, 3–7 km, the sediment pile being thicker in the north. A refraction profile in Davis Strait shows that it is underlain by a crust similar to that beneath Iceland, with a total crustal thickness of over 20 km. The main difference is that a normal mantle velocity is measured beneath the Davis Strait. The results, supported by a seismic reflection profile in the region, suggest that Davis Strait may once have been the site of a hot spot or upwelling mantle plume. The main oceanic crustal layers, layers 2 and 3, under the central basin are thin. A total main crustal thickness of 4 km was measured (omitting the sediment, that is) compared with a mean thickness of 7 km for the major ocean basins. The crust is underlain by mantle rocks exhibiting normal mantle velocities, the mean being 8.0km s−1. Seven refraction lines distributed over the east-west extent of oceanic crust show no detectable median ridge. This accords well with models of the decrease of ridge topography after spreading has ceased as the thermal anomaly beneath decays and supports the hypothesis that the area has not been spreading for about 50 My. The anomalously thin crust can also be related to its age. Thin crust is found near the active mid-ocean ridges at distances corresponding to ages between 50 and 80 My. We postulate that the crust in Baffin Bay is not fully developed and in time a thicker crust will form. These results support the hypothesis that at least the lower part of layer 3 of the ocean basins is composed of altered mantle material.
Geophysical data collected from 1972 to 1975 during a systematic mapping program of the Labrador Sea have been analysed to investigate its geological history and evolution. The data have been used to establish the location of the ridge axis, the age of the ocean floor, and the direction of movement of Greenland relative to North America. Different poles of rotation for the Eurasian and Greenland plate relative to the North American plate in the Late Cretaceous have been derived in order to fit together satisfactorily the plate boundaries defined by the magnetic anomalies in the Labrador Sea and the North Atlantic. The analysis shows that active seafloor spreading commenced in the southern Labrador Sea during the Campanian (anomaly 32) and in the northern Labrador Sea during the Maastrichtian (anomaly 28), with little or no spreading in the Baffin Bay region during this period. With the commencement of active seafloor spreading in the Norwegian Sea during the lower Paleocene (anomaly 24), the direction of seafloor spreading changed in the Labrador Sea and spreading commenced in Baffin Bay. The spreading ceased in the Labrador Sea and Baffin Bay during the lower Oligocene (pre-anomaly 13) when Greenland started to move with the North American plate.Paleogeographic reconstruction of the three plates shows that Greenland moved north relative to North America during the first phase of opening of the Labrador Sea (75–60 Myr), giving rise to compressive forces between northern Greenland and the Canadian Arctic Islands. During the second phase of opening of the Labrador Sea (60–40 Myr) Greenland moved past Ellesmere Island in the left lateral sense along Nares Strait. Some compression is also inferred from these constructions between the margins of northeast Greenland and Svalbard. The poles of rotation obtained for the three plates show a different set of events which may have been responsible for the separation of Rockall Plateau from the British Isles during the early evolution of the North Atlantic.
We present new and reprocessed seismic reflection data from the area where the southeast and southwest Greenland margins intersected to form a triple junction south of Greenland in the early Tertiary. During breakup at 56 Ma, thick igneous crust was accreted along the entire 1300-km-long southeast Greenland margin from the Greenland Iceland Ridge to, and possibly ∼100 km beyond, the triple junction into the Labrador Sea. However, highly extended and thin crust 250 km to the west of the triple junction suggests that magmatically starved crustal formation occurred on the southwest Greenland margin at the same time. Thus, a transition from a volcanic to a non-volcanic margin over only 100–200 km is observed. Magmatism related to the impact of the Iceland plume below the North Atlantic around 61 Ma is known from central-west and southeast Greenland. The new seismic data also suggest the presence of a small volcanic plateau of similar age close to the triple junction. The extent of initial plume-related volcanism inferred from these observations is explained by a model of lateral flow of plume material that is guided by relief at the base of the lithosphere. Plume mantle is channelled to great distances provided that significant melting does not take place. Melting causes cooling and dehydration of the plume mantle. The associated viscosity increase acts against lateral flow and restricts plume material to its point of entry into an actively spreading rift. We further suggest that thick Archaean lithosphere blocked direct flow of plume material into the magma-starved southwest Greenland margin while the plume was free to flow into the central west and east Greenland margins. The model is consistent with a plume layer that is only moderately hotter, ∼100–200°C, than ambient mantle temperature, and has a thickness comparable to lithospheric thickness variations, ∼50–100 km. Lithospheric architecture, the timing of continental rifting and viscosity changes due to melting of the plume material are therefore critical parameters for understanding the distribution of magmatism.
The continental margin of Baffin Island was interpreted from a compilation of seismic reflection and potential field data. Based on these data, it was divided into volcanic and non-volcanic segments. In the northernmost area, coast-parallel grabens and continental basement highs are superseded beneath the slope by irregular basement topography. In combination with the velocities from refraction data and the lack of a magnetic slope anomaly, we propose a non-volcanic margin. In the central region, the seismic data show a limited region with a seaward dipping reflector sequence that may be intercalated with a sedimentary section. Both north and south of Cape Dyer extensive volcanic rocks are interpreted at and below seabed consistent with a volcanic margin. In the southern region, the depth to basement drops rapidly offshore. A thick prograding sedimentary wedge produces a high-amplitude long-wavelength free-air gravity anomaly that was previously confused with the continent–ocean boundary. Although some volcanic rocks are mapped in the region, this area is adjacent to the non-volcanic Labrador Sea margin and is interpreted to be of similar structure. Segmentation of the margin by major faults can explain the abrupt transitions from volcanic to non-volcanic margin segments. The continent–ocean boundary for the region is determined based on the potential field and seismic data. Along the Greenland plate in Davis Strait the continent–ocean boundary coincides with the Ungava Fault Zone. The continent–ocean boundary is used in conjunction with published poles of rotation to evaluate plate reconstructions at chrons 33n and 27n. The earlier reconstruction produces an extensive overlap of boundaries in the north. The later reconstruction shows a gap in the southern region. Thus, additional information is required to refine the reconstructions.
Paleocene volcanic rocks in West Greenland and Baffin Island were among the first products of the Iceland mantle plume, forming part of a larger igneous province that is now submerged beneath the northern Labrador Sea. A 40Ar/39Ar dating study shows that volcanism commenced in West Greenland between 60.9 and 61.3 Ma and that ∼80% of the Paleocene lava pile was erupted in 1 million years or less (weighted mean age of 60.5±0.4 Ma). Minimum estimates of magma production rates (1.3×10−4 km3 year−1 km−1) are similar to the present Iceland rift, except for the uppermost part of the Paleocene volcanic succession where the rate decreases to <0.7×10−4 km3 year−1 km−1 (rift). The timing of onset of volcanism in West Greenland coincides with the opening of the northern Labrador Sea and is also strikingly similar to the age of the oldest Tertiary volcanic rocks from offshore SE Greenland and the British–Irish province. This is interpreted as manifesting the impact and rapid (>1 m/year) lateral spreading of the Iceland plume head at the base of the Greenland lithosphere at ∼62 Ma. We suggest that the arrival, or at least a major increase in the flux, of the Iceland mantle plume beneath Greenland was a contributing factor in the initiation of seafloor spreading in the northern Labrador Sea. Our study has also revealed a previously unrecognised Early Eocene volcanic episode in West Greenland. This magmatism may be related to movement on the transform Ungava Fault System which transferred drifting from the Labrador Sea to Baffin Bay. A regional change in plate kinematics at ∼55 Ma, associated with the opening of the North Atlantic, would have caused net extension along parts of this fault. This would have resulted in decompression and partial melting of the underlying asthenosphere. The source of the melts for the Eocene magmatism may have been remnants of still anomalously hot Iceland plume mantle which were left stranded beneath the West Greenland lithosphere in the Early Paleocene.
Refraction results from the 1983 Canadian Expedition to Study the Alpha Ridge suggest a crustal model with many similarities to the region of Iceland. The overall character of the seismic sections, the derived velocity structure, the lateral dimensions of crustal transition zones and the general crustal thicknesses are comparable from the Arctic and Atlantic regions. Additional similarities are noted in the alkalic basalts, the subaerial to subaqueous, within-plate volcanic environment and the positive regional magnetic responses at satellite altitudes.Based on the geophysical semblances and the apparent evolutionary sequence of within-plate volcanism and tectonic events extending from the northern Ellesmere-Greenland area to Iceland, it is proposed that the Alpha Ridge and Iceland may have been affected by the same mantle plume.
Seismic reflection and refraction data acquired on four transects spanning the Southeast Greenland rifted margin and Greenland–Iceland Ridge (GIR) provide new constraints on mantle thermal structure and melting processes during continental breakup in the North Atlantic. Maximum igneous crustal thickness varies along the margin from >30 km in the near-hotspot zone (<500 km from the hotspot track) to ∼18 km in the distal zone (500–1100 km). Magmatic productivity on summed conjugate margins of the North Atlantic decreases through time from 1800±300 to 600±50 km3/km/Ma in the near-hotspot zone and from 700±200 to 300±50 km3/km/Ma in the distal zone. Comparison of our data with the British/Faeroe margins shows that both symmetric and asymmetric conjugate volcanic rifted margins exist. Joint consideration of crustal thickness and mean crustal seismic velocity suggests that along-margin changes in magmatism are principally controlled by variations in active upwelling rather than mantle temperature. The thermal anomaly (ΔT) at breakup was modest (∼100–125°C), varied little along the margin, and transient. Data along the GIR indicate that the potential temperature anomaly (125±50°C) and upwelling ratio (∼4 times passive) of the Iceland hotspot have remained roughly constant since 56 Ma. Our results are consistent with a plume–impact model, in which (1) a plume of radius ∼300 km and ΔT of ∼125°C impacted the margin around 61 Ma and delivered warm material to distal portions of the margin; (2) at breakup (56 Ma), the lower half of the plume head continued to feed actively upwelling mantle into the proximal portion of the margin; and (3) by 45 Ma, both the remaining plume head and the distal warm layer were exhausted, with excess magmatism thereafter largely confined to a narrow (<200 km radius) zone immediately above the Iceland plume stem. Alternatively, the warm upper mantle layer that fed excess magmatism in the distal portion of the margin may have been a pre-existing thermal anomaly unrelated to the plume.
Many hotspot tracks appear to become the locus of later rifting, as though the heat of the hotspot weakens the lithosphere and tens of millions of years later the continents are split along these weakened lines. Examples are the west coast of Greenland-east coast of Labrador (Madeira hotspot), the south coast of Mexico-north coast of Honduras (Guyana hotspot), and the south coast of West Africa-north coast of Brazil (St. Helena hotspot). A modern day analog of a possible future rift is the Snake River Plain, where the North American continent is being “pre-weakened” by the Yellowstone hotspot track.This conclusion is based on reconstructions of the motions of the continents over hotspots for the past 200 million years. The relative motions of the plates are determined from magnetic anomaly isochrons in the oceans and the motion of one plate is chosen ad hoc to best fit the motions of the plates over the hotspots. However, once the motion of this one plate is chosen, the motions of all the other plates are prescribed by the relative motion constraints.In addition to the correlation between the predicted tracks and sites of later continental breakup, exposed continental shields correlate with the tracks. Their exposure may be the result of hotspot induced uplift which has led to erosion of their former platform sediment cover.
Physiography Davis Strait region Canadian and Greenland Arctic Open File Rep. 3933B Geol. Surv. of Can
- G N S Oakey
- H R Ekholm
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Oakey, G. N., S. Ekholm, H. R. Jackson, and C. Marcussen (2001a), Physiography, Davis Strait region, Canadian and Greenland Arctic, Open File Rep. 3933B, Geol. Surv. of Can., Ottawa, Ontario, Canada
Gravity anomaly map, Bouguer on land, free air at sea, Davis Strait region, Canadian and Greenland Arctic, Open File Rep
- G N Oakey
- R Forsberg
- H R Jackson
Oakey, G. N., R. Forsberg, and H. R. Jackson (2001b), Gravity anomaly map, Bouguer on land, free air at sea, Davis Strait region, Canadian and Greenland Arctic, Open File Rep. 3934B, Geol. Surv. of Can., Ottawa, Ontario, Canada
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Escher, J. C., and T. C. R. Pulvertaft (1995), Geological map of Greenland, scale 1:2.500.000, Geol. Surv. of Greenland, Copenhagen, Denmark
Cruise report Hudson 2003-047 NUGGET (Nunavut to Greenland Geophysical Transect) Open File Rep. 1838 157 pp. Geol. Surv. of Can
- H R T Jackson
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- J Klingelhöfer
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- Jensen
Physiography, Davis Strait region Gravity anomaly map, Bouguer on land, free air at sea, Davis Strait region, Canadian and Greenland Arctic, Open File Rep
- G N Oakey
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- H R Jackson
Oakey, G. N., S. Ekholm, H. R. Jackson, and C. Marcussen (2001a), Physiography, Davis Strait region, Canadian and Greenland Arctic, Open File Rep. 3933B, Geol. Surv. of Can., Ottawa, Ontario, Canada. Oakey, G. N., R. Forsberg, and H. R. Jackson (2001b), Gravity anomaly map, Bouguer on land, free air at sea, Davis Strait region, Canadian and Greenland Arctic, Open File Rep. 3934B, Geol. Surv. of Can., Ottawa, Ontario, Canada. Oakey, G. N., W. Miles, and H. R. Jackson (2001c), Magnetic anomaly map, Davis Strait region, Canadian and Greenland Arctic, Open File Rep. 3935B, Geol. Surv. of Can., Ottawa, Ontario, Canada.
Margin segmentation of Baffin Bay/Davis Strait, eastern Canada based on seismic reflection and potential field data Lateral flow and ponding of starting plume material Regional correlation of Mesozoic-Palaeogene sequences across the Greenland-Canada boundary, Rep
- N Skaarup
- H R Jackson
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Davis Strait: structure and evolution as obtained from a systematic geo-physical survey
- S P Srivastava
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- R F Macnab
- H R Jackson
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(rujackson@nrcan.gc.ca) F. Klingelhö fer, Department of Geodynamciss and Geophysics
- H R Jackson
- P O Box
H. R. Jackson, Geological Survey of Canada (Atlantic), Bedford Institute
of Oceanography, P. O. Box 1006, Dartmouth, Nova Scotia, B2Y 4A2,
Canada. (rujackson@nrcan.gc.ca)
F. Klingelhö fer, Department of Geodynamciss and Geophysics,
IFREMER, Centre de Brest, BP 70, 29280 Plouzané, France. (klingelhoefer@
ifremer.fr)
K. E. Louden, Department of Oceanography, Dalhousie University,
Halifax, Nova Scotia, B3H 4J1, Canada. (keith.louden@dal.ca)
B04402
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