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Simplified geological map of Cape breton Island and adjacent parts of northern mainland Nova Scotia, New brunswick (Nb), and Prince edward Island (PeI) showing the location of the Isle Madame area (dashed box). Map is modified from reynolds et al. (2004). Abbreviations: AH, Antigonish Highlands; CF, Chedabucto Fault; CH, Cobequid Highlands; MFZ, Minas Fault Zone; rVF, roman Vally Fault; SMb, St. Marys basin. The Avalonian Mira terrane consists of volcanic-sedimentary-plutonic belts with ages of ca. 620 Ma, ca. 680 Ma (Stirling), and ca. 575–550 Ma (Coastal) (bevier et al. 1993). Asterisk in the Coastal belt indicates the location of Cambrian quartz sandstone sample SMb07-117 dated by barr et al. (2012).
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A quartz sandstone bed in a dominantly conglomeratic section in the central part of the Lower Carboniferous Horton Group on Petit-de-Grat Island, offshore southern Cape Breton Island, Nova Scotia, contains detrital zircon grains with ages ranging from mid-Devonian to Archean. The similarity of the Devonian and Neoproterozoic age spectrum to ages of...
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A new U-Pb (zircon) age of 357 ±1 Ma for the Wedgeport pluton in the Meguma terrane of southwestern Nova Scotia confirms that it is younger than other granitoid plutons of the Meguma terrane but not as young as the ca. 316 Ma age based on previous geochronological work. The pluton consists of mainly homogeneous biotite monzogranite characterized by...
Citations
... ,Murphy et al. (2004a, b),Pollock (2007),Satkoski et al. (2010),Dorais et al. (2012),Force & Barr (2012),Pollock et al. (2012),Thompson et al. (2012),Willner et al. (2013) andHenderson et al. (2016). Caledonian granite ages are from Ireland only and include various isotopic geochronological techniques. ...
... 'East' Avalonia data were taken fromCollins & Buchan (2004),Murphy et al. (2004b),Strachan et al. (2007),Linnemann et al. (2012) andWillner et al. (2013). Data from samples interpreted to be sourced from 'West' Avalonia are fromKeppie et al. (1998),Thompson & Bowring (2000),Barr et al. et al. (2012),Force & Barr (2012),Pollock et al. (2012), ...
The Lower Old Red Sandstone in southern Ireland is hosted in the Early Devonian Dingle Basin, which lies immediately south of the Iapetus Suture on the Dingle Peninsula, County Kerry. The basin developed as a post-Caledonian pull-apart structure prior to Acadian deformation, which in turn was followed by end-Carboniferous Variscan deformation. Detrital zircon U–Th–Pb geochronology is complemented by mica Ar–Ar and apatite U–Pb geochronology to gain a comprehensive understanding of the provenance of the Lower Devonian Lower Old Red Sandstone of the Dingle Basin and assess contributions of major tectonic components (e.g. Laurentia, Ganderia). Sedimentary rocks in the Lower Old Red Sandstone have similar detrital zircon age distributions, which are dominated by c. 1.2 Ga zircons as well as late Neoproterozoic grains. This indicates a dominant contribution of detritus of Laurentian affinity as well as contributions from westerly and southerly derived Ganderian detritus. Caledonian uplift of the area north of the Iapetus Suture would have facilitated a large contribution of (peri-)Laurentian material. The Upper Old Red Sandstone on the Dingle Peninsula has a distinctly different detrital zircon character including few late Neoproterozoic zircons and abundant zircons of c. 1.05 Ga age, indicating sediment derivation only from Laurentia and no recycling from the Lower Old Red Sandstone.
Supplementary material: The full detrital U–Pb zircon and apatite analytical dataset and the revised detrital mica age dataset are available at https://doi.org/10.6084/m9.figshare.c.3971862
... Leeder, 1982;Besly, 2009;Fraser and Gawthorpe, 1990). Extension affected Avalonia from the North American Atlantic Margin (Hamblin and Rust, 1989;Lynch and Tremblay, 1994;Martel and Gibling, 1996;Force and Barr, 2006;Gibling et al., 2008;Force and Barr, 2013;Force, 2014) ...
Despite reactivations during Variscan and Alpine orogenies and the opening of the Northern Atlantic, Avalonia is one of the few regions where the initial Mid-Paleozoic basin structure is still recognisable, largely intact, and well studied. Its kinematics and dynamics remain, however, largely unknown, in particular in view of the successive late Paleozoic to recent evolution of the basin. Consequently, the importance of the mid-Palaeozoic tectonic evolution and structural controls are often overlooked and poorly understood in basin studies. In this paper, we reassess the importance of Mid-Palaeozoic tectonics on subsequent sedimentary basin evolution of north-western Europe. To this end, we analyse the dynamics of early Variscan extension in Avalonia based on the integration and re-evaluation of available geophysical and geological data from lithosphere to basin scales. Based on a revised crustal map of the Thor suture zone, we present a new paleo-tectonic reconstruction and tectonic scenario for the Devonian-Carboniferous rifting. These findings are key for a better understanding of long-lived tectonic segmentation and post-rifting deformation phases. Our findings indicate that the structural grain of many crustal fault dominated sedimentary basin structures such as the North Sea Central Graben were created in the early Carboniferous. Consequently, the main basement structuration of northwest Europe was completed before the Variscan orogeny and successive post-Variscan extension and inversion phases reactivated the existing basement structures without creating major new fault groups. Incorporation of the Paleozoic structural grain allows for a consistent tectonic framework for the Mesozoic, contributing to fundamental understanding of basin evolution. From our tectonic framework analysis, Avalonia therefore stands out as a fine example of long lived lithosphere memory, spanning over 350 My of structural control in geodynamic evolution.
... A peak of lowermost Devonian to Upper Ordovician zircon ages was obtained for the magmatic rocks of the Oued Togba unit and their metamorphic equivalents . Such ages are also known from the Avalonian terrane assemblage Force and Barr, 2012;Linnemann et al., 2012), but are scarce in the Meguma terrane. A peak at about 600 Ma and the abundant occurrence of Tonian to Rhyacian zircons in the same unit further supports a possible connection with Avalonia (e.g. ...
... Global detrital zircon data (Cawood et al., 2013;Condie and Aster, 2013;Roberts, 2013;Roberts and Spencer, 2015; and references therein) also suggest major recycling of crust during this period. In addition, the new Hf data allow setting up the following hypotheses: Barr et al., 2000Barr et al., , 2003Barr et al., , 2011Barr et al., , 2012aBarr et al., , 2012bDoig et al., 1996;Dorais et al., 2012;Dunning et al., 2002;Escarraga et al., 2012;Force and Barr, 2012;Hamilton and Murphy, 2004;Keppie et al., 1998;Landing et al., 1998;Murphy et al., 1997Murphy et al., , 2004aMurphy et al., , 2008Murphy et al., , 2012Pollock, 2007;Pollock et al., 2009;Satkoski et al., 2010;Skipton et al., 2013;Thompson and Bowring, 2000;Thompson and Hermes, 2003;Thompson et al., 2007Thompson et al., , 2010Thompson et al., , 2012Tucker and McKerrow, 1995;Willner et al., 2013;Zartman and Hermes, 1987) and Meguma (Dostal et al., 2006;Keppie and Krogh, 1999 ...
The Adrar Souttouf Massif is located at the western margin of the West African Craton and consists of several NNE–SSW trending units. Of them, the two westernmost have been interpreted to be linked with the Avalonian terrane assemblage and Meguma, respectively. New Hf isotopic data corroborates the Avalon correlation but has no impact oneway or another on the possibleMeguma connection, as there is no Hf data available fromthe latter. The obtained pattern of εHf(t) values vs. zircon age of the likely Avalonia related Oued Togba unit is similar to publisheddata from Avalonia. Zircons of this unit show characteristic patterns of crustal mixing at 0.7 to 1.3 Ga and
1.75 to 2.25 Ga, while juvenile crust was likely formed around 0.6 to 0.75 Ga, from 1.2 to 2.2 Ga, and between 2.5 and 3.2 Ga. The zircons of the Sebkha Gezmayet unit reveal crustal mixing for the entire Palaeozoic and Neoproterozoic, from 2.05 to 2.11 Ga, and 2.8 to 2.9 Ga. Juvenile crust formation is interpreted to have occurred from 0.5 to 0.7 Ga, at around 2.1 Ga, and at ca. 2.9 Ga. As Mesoproterozoic zircons are abundant in the likely Avalonia-like Oued Togba unit, but uncommon at the West African Craton, their origin has to be found elsewhere. A comparison of available Hf data from Amazonia and Baltica, the two potential source cratons of Avalonia, shows similarities but is hampered by the lack of available data from Amazonia. Finally, a few grains from both units have Eoarchaean model ages. Among similar grains from other peri-Gondwanan terranes, they give indication of partial recycling of Eoarchaean crust in the vicinity of the northwestern West African Craton.
... A peak of lowermost Devonian to Upper Ordovician zircon ages was obtained for the magmatic rocks of the Oued Togba unit and their metamorphic equivalents (Gärtner et al., 2013). Such ages are also known from the Avalonian terrane assemblage (Barr et al., 2011; Force and Barr, 2012; Linnemann et al., 2012), but are scarce in the Meguma terrane. A peak at about 600 Ma and the abundant occurrence of Tonian to Rhyacian zircons in the same unit further supports a possible connection with Avalonia (e.g. ...
... Global detrital zircon data (Cawood et al., 2013; Condie and Aster, 2013; Roberts, 2013; Roberts and Spencer, 2015; and references therein) also suggest major recycling of crust during this period. In addition, the new Hf data allow setting up the following hypotheses:Archibald et al., 2013; Barr et al., 2000 Barr et al., , 2003 Barr et al., , 2011 Barr et al., , 2012a Barr et al., , 2012b Doig et al., 1996; Dorais et al., 2012; Dunning et al., 2002; Escarraga et al., 2012; Force and Barr, 2012; Hamilton and Murphy, 2004; Keppie et al., 1998; Landing et al., 1998; Murphy et al., 1997 Murphy et al., , 2004a Murphy et al., , 2008 Murphy et al., , 2012 Pollock, 2007; Pollock et al., 2009; Satkoski et al., 2010; Skipton et al., 2013; Thompson and Bowring, 2000; Thompson and Hermes, 2003; Thompson et al., 2007 Thompson et al., , 2010 Thompson et al., , 2012 Tucker and McKerrow, 1995; Willner et al., 2013; Zartman and Hermes, 1987) and Meguma (Dostal et al., 2006; Keppie and Krogh, 1999; MacDonald et al., 2002; MacLean et al., 2004; Murphy et al., 2004b; Waldron et al., 2009) in comparison to the zircon record of the (meta-) igneous rocks of the Oued Togba and Sebkha Gezmayet units of the Adrar Souttouf Massif (Gärtner et al., 2013). The sketch map of the current location of the West Avalonian and Meguma terranes was compiled from the literature cited in the text. ...
Upper Palaeozoic lacustrine basin deposits not only record local tectonism but are also an archive to evaluate global palaeoclimate changes linked to the Late Palaeozoic Gondwanan ice age. The Tournaisian Horton Group of Nova Scotia, south‐east Canada, accumulated in rift basins following the final accretion of peri‐Gondwanan terranes to the Appalachians. Sedimentology, mineralogy and geochemistry of the well‐exposed sandstones and shales at the classic Blue Beach section ( ca 353.5 to 352 Ma) reveal the interplay of local tectonism and global climatic controls on lacustrine sedimentation. The lacustrine depositional environment gradually transitioned from deep water offshore at the base of the section to wave‐dominated and fluvial‐dominated nearshore at the top. Multiple small transgressive‐regressive sedimentation cycles have an average 21 ka duration, likely related to Milankovitch cyclicity. Unusually abundant soft‐sediment deformation structures (SSDS) and landslides are the sedimentary responses to frequent earthquakes during the most active phase of rift subsidence. The overall succession shows changes from a shallowing‐up balanced‐filled to an overfilled lacustrine basin. The chemical weathering intensity index and the Th/K ratio show a longer‐term trend from dry and cool conditions low in the section to humid and warm conditions near the top, with rapid change in the transition period. The section records the peak of the global mid‐Tournaisian carbon isotope excursion and the corresponding cooling event (354 Ma to approximately 351 Ma). The sedimentary succession is a response to long‐ and short‐term climatic cycles influencing lake level and sediment supply during the time of maximum rift basin subsidence recorded by the soft‐sediment deformation structures.
Syn-rift strata in the Grand Banks of Atlantic Canada are the result of Late Triassic to Cretaceous extensional processes within the proximal domain of the Newfoundland margin. The precise timing of exhumation events in proximal domains and their significance to the stepwise, long-term development of magma-poor rift systems globally remains uncertain. We report new detrital zircon U–Pb (n = 518) and double-dating fission-track (FT) and U–Pb (n = 269) results from seven samples of syn-rift, Lower Cretaceous Hibernia Formation sandstone units from the Jeanne d’Arc basin to constrain the timing of proximal domain rift processes in the Grand Banks during the onset of hyperextension and outboard development of the necking and distal domains. Syn-depositional, Early Cretaceous U–Pb detrital zircon dates for Berriasian to Barremian strata of the Hibernia Formation indicate provenance from volcanic centers along the SW Grand Banks transform and are consistent with north-directed paleoflow into the southern Jeanne d’Arc basin. Hibernia Formation strata mostly yield Neoarchean to Paleozoic detrital zircon grains with Cryogenian to Paleozoic FT cooling populations that document the episodic exhumation of Appalachian basement and cover successions. The near-zero lag time between the ages of Early Cretaceous exhumation-related cooling and Berriasian to Barremian deposition are consistent with rapid exhumation along NNE-trending normal fault systems in the Avalon Uplift region and margins of the Jeanne d’Arc basin. Early Cretaceous FT cooling populations in Hibernia Formation strata support this rapid tectonic exhumation being coincident with the onset of hyperextension and mantle exhumation processes outboard of the Grand Banks and crustal breakup along SW Iberia that are more generally constrained by marine geophysical studies. Syn-rift strata in long-lived, proximal domain basins can therefore test the timing of exhumation processes that result from magma-poor rift development, including lithospheric thinning associated with the generation of outboard architectural elements.
Quantitative mineral and detrital zircon U–Pb-Hf isotope studies of syn-rift sandstone units in the Mizzen F-09 delineation well, northern Flemish Pass basin, were conducted to test competing models for Grand Banks paleogeography and Late Jurassic development of the Newfoundland-Iberia magma-poor rift system. Bodhrán formation (informal nomenclature) strata yield ca. 145–155 Ma detrital zircon grain populations that indicate a late Tithonian (146 ± 1 Ma) maximum depositional age for syn-rift fluvial to tide-modulated fluvial strata in Mizzen F-09 and evidence for Grand Banks rift magmatism to have occurred throughout the Late Jurassic. Late Tithonian tectonic subsidence and magmatism in the northern Flemish Pass basin region were coincident with the onset of necking processes and extreme crustal thinning within the Newfoundland-Iberia rift system. The chondritic to superchondritic Hf isotope compositions of Late Jurassic detrital zircon grains indicate repeated partial melting of lithospheric mantle during rift development, perhaps along master detachment faults or transfer zone systems. Bodhrán formation strata have chemically unstable minerals (plagioclase, potassium feldspar, garnet, muscovite, rutile, staurolite) and late Paleozoic to Paleoarchean detrital zircon age populations that together show provenance from Appalachian-Variscan basement and cover assemblages. A positive correlation between the abundance of metamorphic minerals and unique-aged, mid-Permian (ca. 271–280 Ma) detrital zircon grains from post-Variscan igneous rocks indicate Iberian provenance contributions to Bodhrán formation strata. The new results from Mizzen F-09 are consistent with models for WNW-directed fluvial discharge into the northern Flemish Pass basin and sediment derivation from upper Paleozoic foreland basin or cover assemblages located west of Variscan front, some which may have been stripped off Beothuk Knoll, Flemish Cap, or adjacent highlands.
Thick conglomerate-dominated sedimentary successions of the Horton and lower Windsor groups in the southern Isle Madame area show provenance variations with stratigraphic position, based on pebble counts, petrographic observations, and facies trends throughout the conglomeratic units. These coarse clastic sediments were deposited in a transtensional basin that formed south of a splay of the Minas Fault Zone, now repeated by younger faults in the study area. A stratigraphic section 1300 m thick that includes the base of the Horton Group was derived mostly, if not entirely, from units in the Avalonian Mira terrane to the east. Similar provenance indications continue stratigraphically upward in this section and elsewhere on Isle Madame through the thick lower and central parts of the Horton Group. In the upper part of the Horton Group, an influx of high- grade metamorphic and deformed plutonic clasts is recorded in the conglomerates, and the percentage of this material continues to increase above a dark fine-grained interval and into the overlying Windsor Group. The metamorphic clasts strongly resemble local basement rocks exposed as belts between conglomeratic domains in Isle Madame, indicating that these deeper crustal rocks were unroofed within the former basin in the late Tournaisian, resulting in redirected drainage patterns. Paleocurrent and facies information suggest that the Mira terrane sources were located to the northwest at the time of deposition. Hence, paleogeographic reconstruction for the area involves not only unroofing of the deeper crustal rocks, but also dextral transcurrent movement to place the appropriate parts of the Mira terrane at the northwestern corner of exposed parts of the basin. This movement was along a subsequently deformed part of the Minas Fault Zone.
