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Map of Canada showing the locations of the major geological provinces and orogens, the 10 Lithoprobe transect areas (outlined areas), and the positions of seismic-refraction and seismic-reflection profiles (black lines). SNORCLE, Slave-Northern Cordillera Lithospheric Evolution; SCORD, Southern Cordillera; ABG, Abitibi-Grenville; ABT, Albert Basement Transect; ECSOOT, East Coast Seismic Onshore-Offshore Transect; GLIMPCE, Great Lakes International Multidisciplinary Program for Crustal Evolution; GSLsz, Great Slave Lake shear zone; KSZ, Kapuskasing Structural Zone; LE, Lithoprobe East; THOT, Trans-Hudson Orogen Transect; WSUP, Western Superior. Lines offshore west of SCORD are data recorded by the Geological Survey of Canada and incorporated into the SCORD interpretations. Inset map shows Canada in relation to the world.
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Application of regional geophysical and geological methods throughout two decades of Canada's Lithoprobe project provides new opportunities to analyze the Mohorovičić discontinuity (Moho) and crust-mantle transition. The transect format employed during Lithoprobe, in which 10 specified regions of Canada were targeted for approximately a decade each...
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... combined with seismic data from the Northwest Territories (Figs. 1-3), the results from Alberta and north- eastern British Columbia appear to display a consistently deeper Moho south of the GSLSZ when compared with re- 15c. (concluded). Map of the depth to refraction Moho in kilometres (includes P-wave receiver function data, as well as refraction lines 1 and 2;D. White, personal communication, 2008). The white lines represent the boundaries between domains shown in Fig. 15b. sults from north of the shear zone. Whether this transition occurs at the GSLSZ or whether it is more gradual is not known due to the sparse data. However, results from a tele- seismic study do not appear to indicate a substantial offset of the Moho at the GSLSZ ( Eaton and Hope ...
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... combined with seismic data from the Northwest Territories (Figs. 1-3), the results from Alberta and north- eastern British Columbia appear to display a consistently deeper Moho south of the GSLSZ when compared with re- 15c. (concluded). Map of the depth to refraction Moho in kilometres (includes P-wave receiver function data, as well as refraction lines 1 and 2;D. White, personal communication, 2008). The white lines represent the boundaries between domains shown in Fig. 15b. sults from north of the shear zone. Whether this transition occurs at the GSLSZ or whether it is more gradual is not known due to the sparse data. However, results from a tele- seismic study do not appear to indicate a substantial offset of the Moho at the GSLSZ ( Eaton and Hope ...
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... combined with seismic data from the Northwest Territories (Figs. 1-3), the results from Alberta and north- eastern British Columbia appear to display a consistently deeper Moho south of the GSLSZ when compared with re- 15c. (concluded). Map of the depth to refraction Moho in kilometres (includes P-wave receiver function data, as well as refraction lines 1 and 2;D. White, personal communication, 2008). The white lines represent the boundaries between domains shown in Fig. 15b. sults from north of the shear zone. Whether this transition occurs at the GSLSZ or whether it is more gradual is not known due to the sparse data. However, results from a tele- seismic study do not appear to indicate a substantial offset of the Moho at the GSLSZ ( Eaton and Hope ...
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... zones of the Appalachian Orogen in central and southern Newfoundland, taken from fig. 1 of Hall et al. (1998). Broken lines are layer boundaries taken from models of near-collinear wide-angle seismic profiles. Numbers indicate P-wave velocities in km/s. Section is at true scale for P-wave velocity of 6 km/s. Lower box shows lower crust and Moho at expanded scale. A, B, and C identify features described in text. For location, see Fig. 4. LE, Lithoprobe East transect. Wide-angle seismic-velocity model across the Torngat Orogen along lines 1N, 2N, and 3N, showing a 70 km wide, 10-15 km deep, crustal root below the orogen (redrawn from Funck and Louden 1999). For location, see Fig. 4b. LLC, Lac Lomier complex; TD, Tasiuyak domain. off the base of the section into the mantle. A fabric with si- milar mantle dip occurs immediately above S1 at the eastern end of the section (fabric S2, Fig. 10). There is no direct measurement of the depth to Moho at this end, except for a zone of horizontal reflectivity cutting through S1 at *14 s reflection time, and a base of strong deep reflections at 13 s reflection time (''Ml'', Fig. 10). Note that, in turn, S2 is truncated by the extensive and strong reflection fabric at ...
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... zones of the Appalachian Orogen in central and southern Newfoundland, taken from fig. 1 of Hall et al. (1998). Broken lines are layer boundaries taken from models of near-collinear wide-angle seismic profiles. Numbers indicate P-wave velocities in km/s. Section is at true scale for P-wave velocity of 6 km/s. Lower box shows lower crust and Moho at expanded scale. A, B, and C identify features described in text. For location, see Fig. 4. LE, Lithoprobe East transect. Wide-angle seismic-velocity model across the Torngat Orogen along lines 1N, 2N, and 3N, showing a 70 km wide, 10-15 km deep, crustal root below the orogen (redrawn from Funck and Louden 1999). For location, see Fig. 4b. LLC, Lac Lomier complex; TD, Tasiuyak domain. off the base of the section into the mantle. A fabric with si- milar mantle dip occurs immediately above S1 at the eastern end of the section (fabric S2, Fig. 10). There is no direct measurement of the depth to Moho at this end, except for a zone of horizontal reflectivity cutting through S1 at *14 s reflection time, and a base of strong deep reflections at 13 s reflection time (''Ml'', Fig. 10). Note that, in turn, S2 is truncated by the extensive and strong reflection fabric at ...
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... zones of the Appalachian Orogen in central and southern Newfoundland, taken from fig. 1 of Hall et al. (1998). Broken lines are layer boundaries taken from models of near-collinear wide-angle seismic profiles. Numbers indicate P-wave velocities in km/s. Section is at true scale for P-wave velocity of 6 km/s. Lower box shows lower crust and Moho at expanded scale. A, B, and C identify features described in text. For location, see Fig. 4. LE, Lithoprobe East transect. Wide-angle seismic-velocity model across the Torngat Orogen along lines 1N, 2N, and 3N, showing a 70 km wide, 10-15 km deep, crustal root below the orogen (redrawn from Funck and Louden 1999). For location, see Fig. 4b. LLC, Lac Lomier complex; TD, Tasiuyak domain. off the base of the section into the mantle. A fabric with si- milar mantle dip occurs immediately above S1 at the eastern end of the section (fabric S2, Fig. 10). There is no direct measurement of the depth to Moho at this end, except for a zone of horizontal reflectivity cutting through S1 at *14 s reflection time, and a base of strong deep reflections at 13 s reflection time (''Ml'', Fig. 10). Note that, in turn, S2 is truncated by the extensive and strong reflection fabric at ...
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... zones of the Appalachian Orogen in central and southern Newfoundland, taken from fig. 1 of Hall et al. (1998). Broken lines are layer boundaries taken from models of near-collinear wide-angle seismic profiles. Numbers indicate P-wave velocities in km/s. Section is at true scale for P-wave velocity of 6 km/s. Lower box shows lower crust and Moho at expanded scale. A, B, and C identify features described in text. For location, see Fig. 4. LE, Lithoprobe East transect. Wide-angle seismic-velocity model across the Torngat Orogen along lines 1N, 2N, and 3N, showing a 70 km wide, 10-15 km deep, crustal root below the orogen (redrawn from Funck and Louden 1999). For location, see Fig. 4b. LLC, Lac Lomier complex; TD, Tasiuyak domain. off the base of the section into the mantle. A fabric with si- milar mantle dip occurs immediately above S1 at the eastern end of the section (fabric S2, Fig. 10). There is no direct measurement of the depth to Moho at this end, except for a zone of horizontal reflectivity cutting through S1 at *14 s reflection time, and a base of strong deep reflections at 13 s reflection time (''Ml'', Fig. 10). Note that, in turn, S2 is truncated by the extensive and strong reflection fabric at ...
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... southernmost Alberta, the crust deepens continuously from *45 km at Edmonton to *56-58 km at the United States -Canada border (Figs. 2, 3, 23). The deep Moho con- tinues southward into Montana and spatially correlates with the Archean Medicine Hat block in Canada and the Archean Wyoming Province in Montana ( Clowes et al. 2002). In addi- 16a. Interpretation of the two crossing seismic-refraction profiles as illustrated in Musacchio et al. (2004). Note the high-velocity lower crust in the southern part of line 1 (L2s) and the dipping zones within the mantle north of there. These characteristics have been interpreted to be associated with subducted oceanic crust ( Musacchio et al. 2004). tion, the crustal thickening is associated with a high-velocity (>7.5 km/s) layer that may be as much as 20 km thick in Montana (Fig. 23b). Although the deep Moho and high-ve- locity lower crust coincide with Archean rocks near the sur- face, Paleoproterozoic (ca. 1.74-1.82 Ga; Davis et al. 1995) ages of lower crustal xenoliths from within the high-velocity layer have led to interpretations that rely on Paleoprotero- zoic magmatic and (or) structural underplating ( Lemieux et al. 2000;Clowes et al. ...
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... the Cordillera of western Canada (Fig. 21), the geo- physical Moho displays both rapid and undulatory changes in depth. In the southeastern Cordillera, beneath the Fore- land thrust and fold belt, the Moho deepens to *50 km from *40 km beneath the WCSB (Figs. 2, 22). According to interpretations of both seismic-reflection (e.g., Cook 1995) and seismic-refraction profiles ( Clowes et al. 1995), the Moho then undergoes a rapid westward decrease in depth to *35 km (Figs. 2, 3). Whether this change is very nearly a step or whether it occurs as a relatively steep ramp is ...
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... Abitibi-Grenville transect region encompasses the Archean tectonic assemblages of the Abitibi Province, post- assembly modification of the Abitibi by Proterozoic tecton- ism, and the Mesoproterozic development of the Grenville Orogen (Fig. 11). The first Lithoprobe transect, the Kapus- kasing Structural Zone, and the Great Lakes International Multidisciplinary Program for Crustal Evolution (GLIMPCE) profiles are associated with the Abitibi- Grenville transect and are included here. The Abitibi- Opatica belts are part of the Superior craton but are consid- ered separately here from the Western Superior transect, as discussed later in the ...
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... underthrusting of the southern Abitibi belt rocks northward beneath the Opatica belt may be responsible for the apparent difference in character of the reflection Moho between the southern (Abitibi) and northern (Opatica) por- tions of the seismic profile in Fig. 13. Here, the reflection Moho of the Opatica belt is sharp and relatively flat, perhaps partly due to structural flattening in the lower crust. In con- trast, the reflection Moho beneath the southern (Abitibi belt) portion of the line is much less ...
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... crust is generally thinner within the Archean Abitibi portion of the Superior Province (32-40 km) than it is be- neath the Grenville Province (42-46 km) ( Seismic-reflection data were acquired across the Wawa gneiss of the Kapuskasing Structural Zone and indicated that the gneiss is highly reflective (e.g., Percival and West 1994). The listric character of the reflections in the Abitibi and Opatica reflection profiles (Fig. 13) is consistent with the orientation of structures in the Wawa gneiss of the Ka- puskasing Structural Zone; thus, it is likely that rock types similar to those in the Wawa gneiss are present beneath the northern Abitibi (Opatica). As a result, the lower crust of the Opatica belt is likely a result of north-directed underthrust- ing and tectonic underplating. Thus, the structures in the middle and lower crust are likely younger than those at the surface, and the surface features are structurally decoupled from those in the middle ...
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... the northern Cordillera, the Moho displays a similar westward decrease in depth (Fig. 24) to that observed be- neath the southern Rocky Mountain trench. In the north, however, the change occurs beneath the WCSB east of the 16b. (concluded). Interpretation of seismic-refraction profiles in the Western Superior transect illustrating an interpreted amphibolitic layer in the lower crust that may have originated as oceanic crust ( Musacchio et al. 2004). Fig. 17. Foldout 2. Seismic-reflection data along the north-south corridor in the Western Superior transect (modified from White et al. 2003; Van der Velden 2007). Note that the lower crust on the south is reflective and corresponds to the high-velocity layer observed in the refraction data and that reflections are observed dipping north- ward from the lower crust into the upper ...
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... the northern Cordillera, the Moho displays a similar westward decrease in depth (Fig. 24) to that observed be- neath the southern Rocky Mountain trench. In the north, however, the change occurs beneath the WCSB east of the 16b. (concluded). Interpretation of seismic-refraction profiles in the Western Superior transect illustrating an interpreted amphibolitic layer in the lower crust that may have originated as oceanic crust ( Musacchio et al. 2004). Fig. 17. Foldout 2. Seismic-reflection data along the north-south corridor in the Western Superior transect (modified from White et al. 2003; Van der Velden 2007). Note that the lower crust on the south is reflective and corresponds to the high-velocity layer observed in the refraction data and that reflections are observed dipping north- ward from the lower crust into the upper ...
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... and adjacent parts of the Midcontinent Rift, signifi- cant crustal thickness variations are documented by Lithop- robe studies. These variations generally correlate with large- scale tectonic belts but are not expressed by surface topogra- phy and are often poorly correlated with gravity anomalies. The thickest crust in the region (up to 55 km) is observed beneath the central graben of the 1.1 Ga Midcontinent Rift beneath Lake Superior ( Shay and Tréhu 1993). This zone of anomalous crustal thickness is flanked by much thinner crust (35-40 km) at the margins of the rift. Despite the extreme thickness of the crust, the rift is marked by a positive grav- ity signature that reflects the voluminous package of dense basaltic rocks that forms most of the crustal section (Mariano and Hinze 1994). To the east, the Grenville Front in southern Ontario marks a transition from thicker crust (up to 45 km) within the Mes- oproterozoic Grenville Orogen to significantly thinner crust (*35 km) in the Superior Craton ( Fig. 14; Winardhi and Mereu 1997; White et al. 2000). Unlike the unusually thick crust found beneath the Wyoming Craton of western North America ( Gorman et al. 2002), the zone of thickened crust in the Grenville does not appear to be associated with any high-velocity lower crustal layer (Winardhi and Mereu 1997); the Grenville Front has subsequently been observed using data from a Lithoprobe teleseismic profile (Rondenay et al. 2000) and more recently using a regional deployment of portable seismograph stations ( Eaton et al. 2006). The distribution of seismograph stations used in the latter inves- tigation showed that the region of thick crust near the Gren- ville Front constitutes a keel that strikes parallel to the Front. The crustal thickness variations here are far in excess of requirements for local isostatic equilibrium ( Eaton et al. 2006). This crustal root may be preserved as a result of processes that slowly reduce density contrast between the lower crust and upper mantle (Fischer ...
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... continental-scale database that was acquired within the Lithoprobe program ( Fig. 1) is unique in its magnitude and in its relative uniformity of parameters for data acquisi- tion and processing. Throughout the time frame of the proj- ect , efforts were made to maintain high standards of data quality, as technological advances occurred to allow comparative analyses of datasets from different re- gions and different vintages. Although most seismic and magnetotelluric data were recorded by contractors, the ac- quisition, processing, and initial interpretations were moni- tored and carried out by a relatively small group of individuals, within which consistent communication was ...
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... the western margin of the Cordillera, Moho depth ap- pears to change beneath the Coast Mountains ( Clowes et al. 1995;Hammer et al. 2000;Clowes et al. 2005). On the west 18. Map of the Trans-Hudson Orogen transect region showing the locations of the seismic-refraction (black) and seismic-reflection (red) profiles (Németh et al. 2005). SBZ, Superior Boundary Zone. coast in the northern Cordillera, the Moho shallows toward the Pacific Ocean (Hammer et al. 2000;Morozov et al. 2001). In the northern Cordillera, the crust may thin by as much as 10 km from the intermontane region to the Coast Mountains and thin further into the Pacific Ocean ( Hammer et al. 2000;Fig. 24). Thinned crust beneath the Coast Moun- tains in this area has been interpreted to result from postac- cretion extension (Hammer et al. ...
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... the southwestern Grenville Province of Ontario and Fig. 10. Seismic-reflection profile 4S (Fig. 4b) across the Grenville Province (taken from fig. 4 of Hall et al. 2002), showing (in thin black lines) asymmetrical distribution of inward- dipping crustal fabrics, opposing dip in mantle reflections and no obvious reflection signal from the Moho. Broken line shows inferred location of Moho from wide-angle seismic- velocity models from profiles 2 and 1 (Fig. 4b). Column 2 on left side gives 1-D velocity values (km/s) from profile 2 after converting depths to two-way traveltimes. Mu, strong- reflection fabric above Moho; U, strong-reflection fabric above S2; S1, dipping fabric described in text; S2, dipping fabric truncated at Mu as described in ...
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... the east, the Grenville Front crustal root terminates 11. Map of the Abitibi-Grenville transect region with seismic-refraction lines (broken lines) and seismic-reflection lines (red lines; white circles indicate reflection line numbers) indicated (modified from Ludden and Hynes 2000). abruptly at the Ottawa-Bonnechere graben, which marks the western boundary of a region of relatively thin (30-35 km) crust and moderate seismicity ( Eaton et al. 2006). The Gren- ville Front crustal root reappears and thickens toward the east, where it is expressed as a regional gravity low in east- ern Quebec (Berry and Fuchs 1973;Eaton et al. 1995). In the Superior Craton north of the Front, northward-dipping mantle reflectors imaged by Lithoprobe reflection data are linked to a possible suture and have been interpreted as an upper mantle shear zone that was active during Archean subduction (Calvert et al. 1995). Despite the evidence for subduction, the Moho is relatively flat in the Superior Cra- ton, with the exception of local deepening near the Kapus- kasing structure (Boland and Ellis 1989;Darbyshire et al. ...
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... resulting maps of refraction depth and reflection times are presented in Figs. 2 and 3. It is to be expected that there are some general similarities between the two maps because, to some extent, the position of the reflection Moho depends on the location of the refraction Moho (i.e., it is the base of the deepest reflections from depths estimated from other geophysical methods). However, where coinci- dent refraction and reflection lines have been obtained (e.g., Western Superior, Lithoprobe East, SNORCLE), the position of the reflection Moho (if visible) and the refraction Moho are close (i.e., reflections are observed at appropriate reflec- tion travel times for depths to the refraction Moho), particu- larly for average crustal P-wave velocities of *6.2-6.5 km/s (e.g., Cook 2002). For example, both maps show that the Moho is regionally shallow beneath much of the Cordillera, beneath Canadian Shield north of the Great Slave Lake shear zone (GSLSZ; Fig. 1), and along the eastern seaboard. Elsewhere, the refraction Moho is generally deeper than *38 km, with travel times >*12.5 s, although some local variations are ...
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... western Superior Province was assembled during the interval 2.72-2.60 Ga by a sequence of at least five distinct large-scale accretionary events ( Percival et al. 2006) result- ing in the east-west trending ''belt-like'' pattern that charac- terizes the regional geology (Figs. 15a, 15b). The Moho and associated crust-mantle transition in the western Superior Province have been imaged by a variety of seismic methods, including near-vertical seismic-reflection profiling ( White et al. 2003;Calvert et al. 2004), travel time -amplitude inver- sion and direct imaging using refraction -wide-angle reflec- tion (R/WAR) data ( Musacchio et al. 2004 andKay et al. 1999, respectively), and P-and S-wave receiver functions ( Angus et al. 2008). The depth to Moho varies by *50% within the western Superior Province, ranging from 32 to >45 km (Fig. 15c). The thickest crust is observed in the south, to the north of the Midcontinent Rift system in Lake Superior (Fig. 15c), where it is associated with a northward- thinning, high-velocity lower crustal layer (V p = 7.4- 7.5 km/s). Crustal thickness decreases gradually northward toward the centre of the province where it flattens at *38 km depth. The thinnest crust (32 km) is found in the westernmost part of the province where Calvert et al. (2004) have proposed late crustal-scale extension. A local minimum of *36 km occurs beneath the Lake Nipigon re- gion, which may be related to Mesoproterozoic rifting ( Kay et al. 1999;Musacchio et al. 2004;Calvert et al. ...
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... western Superior Province was assembled during the interval 2.72-2.60 Ga by a sequence of at least five distinct large-scale accretionary events ( Percival et al. 2006) result- ing in the east-west trending ''belt-like'' pattern that charac- terizes the regional geology (Figs. 15a, 15b). The Moho and associated crust-mantle transition in the western Superior Province have been imaged by a variety of seismic methods, including near-vertical seismic-reflection profiling ( White et al. 2003;Calvert et al. 2004), travel time -amplitude inver- sion and direct imaging using refraction -wide-angle reflec- tion (R/WAR) data ( Musacchio et al. 2004 andKay et al. 1999, respectively), and P-and S-wave receiver functions ( Angus et al. 2008). The depth to Moho varies by *50% within the western Superior Province, ranging from 32 to >45 km (Fig. 15c). The thickest crust is observed in the south, to the north of the Midcontinent Rift system in Lake Superior (Fig. 15c), where it is associated with a northward- thinning, high-velocity lower crustal layer (V p = 7.4- 7.5 km/s). Crustal thickness decreases gradually northward toward the centre of the province where it flattens at *38 km depth. The thinnest crust (32 km) is found in the westernmost part of the province where Calvert et al. (2004) have proposed late crustal-scale extension. A local minimum of *36 km occurs beneath the Lake Nipigon re- gion, which may be related to Mesoproterozoic rifting ( Kay et al. 1999;Musacchio et al. 2004;Calvert et al. ...
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... western Superior Province was assembled during the interval 2.72-2.60 Ga by a sequence of at least five distinct large-scale accretionary events ( Percival et al. 2006) result- ing in the east-west trending ''belt-like'' pattern that charac- terizes the regional geology (Figs. 15a, 15b). The Moho and associated crust-mantle transition in the western Superior Province have been imaged by a variety of seismic methods, including near-vertical seismic-reflection profiling ( White et al. 2003;Calvert et al. 2004), travel time -amplitude inver- sion and direct imaging using refraction -wide-angle reflec- tion (R/WAR) data ( Musacchio et al. 2004 andKay et al. 1999, respectively), and P-and S-wave receiver functions ( Angus et al. 2008). The depth to Moho varies by *50% within the western Superior Province, ranging from 32 to >45 km (Fig. 15c). The thickest crust is observed in the south, to the north of the Midcontinent Rift system in Lake Superior (Fig. 15c), where it is associated with a northward- thinning, high-velocity lower crustal layer (V p = 7.4- 7.5 km/s). Crustal thickness decreases gradually northward toward the centre of the province where it flattens at *38 km depth. The thinnest crust (32 km) is found in the westernmost part of the province where Calvert et al. (2004) have proposed late crustal-scale extension. A local minimum of *36 km occurs beneath the Lake Nipigon re- gion, which may be related to Mesoproterozoic rifting ( Kay et al. 1999;Musacchio et al. 2004;Calvert et al. ...
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... within the Canadian Shield, there appears to be little correspondence between depth, or travel time, to the Moho and the age of the rocks on the surface (Figs. 1-3). Some of the greatest depths and longest travel times to the Moho are located in the Archean Superior Province and Medicine Hat block (southern Alberta), but comparable fea- ...
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... some regions, structural emplacement of oceanic rocks beneath older continental or arc crust may account for younger rocks at depth ( Davis et al. 1995), as well as lower crustal rocks with high velocities (Eaton et al. 2000;Clowes et al. 2002). If this occurs, either (1) the crust-mantle transi- tion of the old oceanic crust could remain as part of the lower continental crust and the subducted oceanic Moho could subsequently be identified as the continental Moho (Fig. 26a) as in the Lithoprobe East (Van der Velden et al. 2004), the Abitibi-Opatica (Fig. 13), the Western Superior (Fig. 16), and the SNORCLE ( Cook et al. 1999) transects; or (2) the subducted basaltic oceanic crust could undergo a phase change to eclogite, thus producing a new Moho (re- fraction Moho and perhaps also reflection Moho) above the eclogite. In this case, more felsic rocks above would be lower density and relatively weak, whereas the eclogite be- low would have geophysical characteristics that are appro- priate for upper mantle (Fig. 26a) and could be relatively strong (Cook ...
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... some regions, structural emplacement of oceanic rocks beneath older continental or arc crust may account for younger rocks at depth ( Davis et al. 1995), as well as lower crustal rocks with high velocities (Eaton et al. 2000;Clowes et al. 2002). If this occurs, either (1) the crust-mantle transi- tion of the old oceanic crust could remain as part of the lower continental crust and the subducted oceanic Moho could subsequently be identified as the continental Moho (Fig. 26a) as in the Lithoprobe East (Van der Velden et al. 2004), the Abitibi-Opatica (Fig. 13), the Western Superior (Fig. 16), and the SNORCLE ( Cook et al. 1999) transects; or (2) the subducted basaltic oceanic crust could undergo a phase change to eclogite, thus producing a new Moho (re- fraction Moho and perhaps also reflection Moho) above the eclogite. In this case, more felsic rocks above would be lower density and relatively weak, whereas the eclogite be- low would have geophysical characteristics that are appro- priate for upper mantle (Fig. 26a) and could be relatively strong (Cook ...
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... general, as in most other regions, the reflection Moho observed on near-vertical-incidence reflection profiles across the western Superior Province ( Fig. 17; White et al. 2003;Calvert et al. 2004; Van der Velden 2007) is defined by a relatively abrupt vertical transition from reflective lower crust to nonreflective upper mantle with or without an asso- ciated distinct reflection at the base of the reflective lower crust. Similarly, wide-angle reflection images show a prom- inent Moho reflection across the western Superior Province ( Kay et al. 1999). The reflection Moho varies smoothly with only a few exceptions where zones of dipping reflectiv- ity can be followed from the lower crust into the upper man- tle to sub-Moho depths of 5-10 km. In at least one instance, a vertical offset of the Moho by 2-3 km occurs across one of these zones. These zones have been interpreted as suture zones associated with the original cratonic assembly ( White et al. 2003) and can be traced to the middle or upper crust along low-angle ...
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... some areas, there are no clear reflection(s) from the crust-mantle transition, although there may be a diffuse tran- sition from reflective crust to transparent mantle. If diffuse arrivals are visible, the reflection Moho is delineated as the base of reflectivity. If the lower crust and upper mantle are both nonreflective, however, no reflection Moho can be de- fined. In these cases, converting the crustal depths from re- gional refraction profiles to reflection travel time can approximate the position of the crust-mantle transition. An example of complete lack of reflections (type Ia of Cook 2002) is visible in the Fort Simpson region along SNORCLE line 1 (Fig. 25a). Examples of fading of crustal reflectivity 21. Map of western Canada showing the Alberta Basement, Southern Cordillera (S. Cord), and SNORCLE transect regions (modified from Cook et al. 2005). Black lines show the locations of regional seismic-reflection profiles. In the Alberta Basement Transects, PRAISE is the Peace River Arch Industry Seismic Experiment, CAT is the central Alberta transect, and SALT is the Southern Alberta Lithosphere Transect. CH, Coppermine homocline; IP, Interior platform; Sfb, Skeena fold belt; TT, Tintina fault. ...
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... crustal properties and inferred rock compositions vary significantly across the western Superior Province. V p and V p /V s range from 6.7 to 7.5 km/s and 1.72 to 1.86, re- spectively ( Fig. 16a; Musacchio et al. 2004). An 8% azimu- thal anisotropy is invoked for a distinct lower crustal zone (V p = 7.4-7.5 km/s in the fast propagation direction, which is normal to the east-west regional geological strike; and V p /V s = 1.86) of inferred amphibolitic composition within the southern part of the province (Fig. 16b). The upper man- tle velocities immediately beneath the Moho are generally high ranging from 8.0 to 8.3 ...
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... crustal properties and inferred rock compositions vary significantly across the western Superior Province. V p and V p /V s range from 6.7 to 7.5 km/s and 1.72 to 1.86, re- spectively ( Fig. 16a; Musacchio et al. 2004). An 8% azimu- thal anisotropy is invoked for a distinct lower crustal zone (V p = 7.4-7.5 km/s in the fast propagation direction, which is normal to the east-west regional geological strike; and V p /V s = 1.86) of inferred amphibolitic composition within the southern part of the province (Fig. 16b). The upper man- tle velocities immediately beneath the Moho are generally high ranging from 8.0 to 8.3 ...
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... Trans-Hudson Orogen (THO) is part of a North American network of Paleoproterozoic orogenic belts formed by crustal accretion and collision of older Archean continental blocks ( Fig. 18; Hoffman 1988). However, it is the only component of the network that exposes a complete orogenic section characterized by a zone of Paleoproterozoic 12. Model of refraction velocities along profile MG (see Fig. 11 for location) as interpreted by Winardhi and Mereu (1997). GFTZ is the location of the Grenville Front Tectonic Zone that dips southward at this location. The elevated velocities in the lower crust to the south of GFTZ have been interpreted to be associated with eclogites (Eaton 2006). Vp, P-wave velocity. (ca. 1.9-1.8 Ga) juvenile rocks sandwiched between variably reworked Archean continental blocks -the Hearne Craton to the northwest and the Superior Craton to the southeast. Recognition of the THO as a major orogenic belt dates back to the late 1970s and early 1980s; the volume edited by Lewry and Stauffer (1990) provides a comprehensive summary. Until Lithoprobe, the prevailing view was that the Archean Superior Province extended beneath the THO. However, the 1991 reflection survey across the orogen 15a. Map of the Western Superior transect region illiustrating the locations of seismic-refraction profiles 1 and 2 (modified from Musacchio et al. 2004). KI, Keewenawan intrusive complex; QFZ, Quetico fault zone; SLF, Sydney Lake fault; SSGB, Savant-Sturgeon greenstone ...
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... Trans-Hudson Orogen (THO) is part of a North American network of Paleoproterozoic orogenic belts formed by crustal accretion and collision of older Archean continental blocks ( Fig. 18; Hoffman 1988). However, it is the only component of the network that exposes a complete orogenic section characterized by a zone of Paleoproterozoic 12. Model of refraction velocities along profile MG (see Fig. 11 for location) as interpreted by Winardhi and Mereu (1997). GFTZ is the location of the Grenville Front Tectonic Zone that dips southward at this location. The elevated velocities in the lower crust to the south of GFTZ have been interpreted to be associated with eclogites (Eaton 2006). Vp, P-wave velocity. (ca. 1.9-1.8 Ga) juvenile rocks sandwiched between variably reworked Archean continental blocks -the Hearne Craton to the northwest and the Superior Craton to the southeast. Recognition of the THO as a major orogenic belt dates back to the late 1970s and early 1980s; the volume edited by Lewry and Stauffer (1990) provides a comprehensive summary. Until Lithoprobe, the prevailing view was that the Archean Superior Province extended beneath the THO. However, the 1991 reflection survey across the orogen 15a. Map of the Western Superior transect region illiustrating the locations of seismic-refraction profiles 1 and 2 (modified from Musacchio et al. 2004). KI, Keewenawan intrusive complex; QFZ, Quetico fault zone; SLF, Sydney Lake fault; SSGB, Savant-Sturgeon greenstone ...
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... Trans-Hudson Orogen (THO) is part of a North American network of Paleoproterozoic orogenic belts formed by crustal accretion and collision of older Archean continental blocks ( Fig. 18; Hoffman 1988). However, it is the only component of the network that exposes a complete orogenic section characterized by a zone of Paleoproterozoic 12. Model of refraction velocities along profile MG (see Fig. 11 for location) as interpreted by Winardhi and Mereu (1997). GFTZ is the location of the Grenville Front Tectonic Zone that dips southward at this location. The elevated velocities in the lower crust to the south of GFTZ have been interpreted to be associated with eclogites (Eaton 2006). Vp, P-wave velocity. (ca. 1.9-1.8 Ga) juvenile rocks sandwiched between variably reworked Archean continental blocks -the Hearne Craton to the northwest and the Superior Craton to the southeast. Recognition of the THO as a major orogenic belt dates back to the late 1970s and early 1980s; the volume edited by Lewry and Stauffer (1990) provides a comprehensive summary. Until Lithoprobe, the prevailing view was that the Archean Superior Province extended beneath the THO. However, the 1991 reflection survey across the orogen 15a. Map of the Western Superior transect region illiustrating the locations of seismic-refraction profiles 1 and 2 (modified from Musacchio et al. 2004). KI, Keewenawan intrusive complex; QFZ, Quetico fault zone; SLF, Sydney Lake fault; SSGB, Savant-Sturgeon greenstone ...
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... Trans-Hudson Orogen (THO) is part of a North American network of Paleoproterozoic orogenic belts formed by crustal accretion and collision of older Archean continental blocks ( Fig. 18; Hoffman 1988). However, it is the only component of the network that exposes a complete orogenic section characterized by a zone of Paleoproterozoic 12. Model of refraction velocities along profile MG (see Fig. 11 for location) as interpreted by Winardhi and Mereu (1997). GFTZ is the location of the Grenville Front Tectonic Zone that dips southward at this location. The elevated velocities in the lower crust to the south of GFTZ have been interpreted to be associated with eclogites (Eaton 2006). Vp, P-wave velocity. (ca. 1.9-1.8 Ga) juvenile rocks sandwiched between variably reworked Archean continental blocks -the Hearne Craton to the northwest and the Superior Craton to the southeast. Recognition of the THO as a major orogenic belt dates back to the late 1970s and early 1980s; the volume edited by Lewry and Stauffer (1990) provides a comprehensive summary. Until Lithoprobe, the prevailing view was that the Archean Superior Province extended beneath the THO. However, the 1991 reflection survey across the orogen 15a. Map of the Western Superior transect region illiustrating the locations of seismic-refraction profiles 1 and 2 (modified from Musacchio et al. 2004). KI, Keewenawan intrusive complex; QFZ, Quetico fault zone; SLF, Sydney Lake fault; SSGB, Savant-Sturgeon greenstone ...
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... seismic studies included a series of vibro- seis reflection profiles, totalling *2060 km, a coincident 200 km long east-west dynamite reflection profile in the western Reindeer zone and three long-range R/WAR lines, two *750 km and one 500 km long, across and along the orogen (Fig. 18). Moho reflections from the near-vertical re- flection data and the two phases, PmP and uppermost mantle refraction (Pn), from the wide-angle data demonstrated the existence of a crustal root within the Reindeer zone and en- abled compilation of a map of the surface of the Moho (Fig. 20). This map shows the substantial variation in Moho depth, presumably associated with the collisional and post- collisional development of the orogen ( Hajnal et al. 1996Hajnal et al. , 2005). The dynamite survey showed clearer Moho signatures than the vibroseis survey and included some dipping sub- Moho reflections that are likely related to collisional tecton- ics of the THO ( Bezdan and Hajnal 1996). Interpretations of the reflection data, combined with analyses of the potential 15b. (continued). Map of the Western Superior transect region showing the locations of regional seismic-reflection profiles (modified from Van der Velden ...
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... seismic studies included a series of vibro- seis reflection profiles, totalling *2060 km, a coincident 200 km long east-west dynamite reflection profile in the western Reindeer zone and three long-range R/WAR lines, two *750 km and one 500 km long, across and along the orogen (Fig. 18). Moho reflections from the near-vertical re- flection data and the two phases, PmP and uppermost mantle refraction (Pn), from the wide-angle data demonstrated the existence of a crustal root within the Reindeer zone and en- abled compilation of a map of the surface of the Moho (Fig. 20). This map shows the substantial variation in Moho depth, presumably associated with the collisional and post- collisional development of the orogen ( Hajnal et al. 1996Hajnal et al. , 2005). The dynamite survey showed clearer Moho signatures than the vibroseis survey and included some dipping sub- Moho reflections that are likely related to collisional tecton- ics of the THO ( Bezdan and Hajnal 1996). Interpretations of the reflection data, combined with analyses of the potential 15b. (continued). Map of the Western Superior transect region showing the locations of regional seismic-reflection profiles (modified from Van der Velden ...
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... reflection Moho is very well defined over profiles 89/6 and especially 89/9 in southern Newfoundland ( Fig. 6; ) and correlates well with the wide-angle Moho. The reflection Moho here links narrow zones of strong reflectivity, which extend laterally in 10-20 km segments (above ''A,'' Fig. 6), to a well-defined base of crustal reflectivity. The lower crust has a strong northwesterly dipping fabric that ap- pears to sole towards the Moho, though Van der Velden et al. (2004), from their reprocessed data, considered that the dip- ping fabric is more likely truncated by the reflection Moho. 3. Map of the travel times to the reflection Moho (contour interval = 0.33 s) for the same area as in Fig. 1. Locations of most reflection profiles recorded during the Lithoprobe program along with the addition of some related profiles are shown as black lines. The non- Lithoprobe profiles include the Mackenzie delta in northwest Canada ( Cook et al. 1987), the Ahbau Lake profile in central British Columbia (Mair and Lyons 1976), and several profiles in the offshore region of the Atlantic margin ( Marillier et al. 1994). The times are all related to sea level by calculating the static shift between the elevation datum of each profile and sea level. 4. (a) Geological map of the Lithoprobe East transect region ( Hall et al. 1998), showing the major geological provinces and locations of seismic-refraction (broken lines) and seismic-reflection (solid lines) profiles. Red lines are those shown in Figs. 5, 6, and 7. (b) Geologi- cal map of the ECSOOT region ( Hall et al. 2002), illustrating the major geological provinces and locations of seismic-refraction (red lines) and seismic-reflection (black lines) profiles. NMo Pn>Yiroao (3890 _2500 Ma) • 0IIIh000 _ _ an \,~, ! -...... 1-1 ="" These two interpretations lead to differing geological im- plications. Hall et al. (1998) suggested the fabrics relate to collisional compressional strains detaching at the Moho in a pattern familiar from numerical models of compressional or- ogens ( Quinlan et al. 1993). Van der Velden et al. (2004) proposed that the fabrics link to a northwest-dipping feature in the mantle farther to the west that might be a relict sub- duction zone. They also concluded that the truncation of the dipping fabric by the Moho reflection indicates that the lat- ter is a younger structure cutting across the earlier dips and perhaps related to the top of a zone of eclogitization of mafic crustal material now in the seismological ...
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... Moho below the Appalachians of Newfoundland and the adjacent seas shows some variability in character and depth and has varying relationships to reflection fabrics in lower crust and mantle. The depth of the Moho has been Map of the depth to the refraction Moho (contour interval = 2 km) for the same area as in Fig. 1. Locations of the seismic-refraction profiles recorded during the Lithoprobe program along with the addition of some related profiles are indicated by the black lines. The non- Lithoprobe profiles include the Mackenzie Delta in northwest Canada (O' Leary et al. 1995), the Peace River Arch experiment (Zelt and Ellis 1989), a regional east-west profile in Alberta ( Chandra and Cumming 1972), and several profiles in the offshore region of the Atlantic margin (e.g., Keen et al. 1986;Marillier et al. 1989). The map was constructed by picking refraction depths along each interpreted profile and then applying an automatic contouring program to produce the map. The map has a much higher spatial resolution than global models such as CRUST5.1 ( Mooney et al. 1998). It is more reliable for Canada than models such as CRUST2.0 ( Bassin et al. 2000), which do not utilize the Lithoprobe dataset, and it is similar to the recent LITH5.0 model, which included the Lithoprobe data and used spherical splines for interpolation (Perry et al. 2002). well defined from wide-angle seismic experiments (e.g., Hughes et al. 1994). It tends to be lower (shallower) within the orogen (*30-35 km) than within the Grenville Orogen to the northwest (*40-45 km) or the Avalon Zone to the southeast (*40 km), which is illustrated in Fig. 5. Depar- tures from this simple conclusion (thicker crust below the Magdalen basin in the Gulf of St. Lawrence and thinner crust offshore northeastern Newfoundland) have been attrib- uted to late Appalachian extension and magmatic underplat- ing in the ...
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... of data quality, both in acquisition and processing, over the length of Lithoprobe have provided in- creasing numbers of observations of reflections projecting from the lower crust to beneath the reflection Moho (Cook 2002). In some cases, the dipping reflections appear as sim- ple, single reflections, as in the Abitibi-Opatica dataset (Fig. 13); whereas in others, they are multilayered, as along SNORCLE profile 1 (Fig. 25a). In a few examples, the crus- tal reflections appear to project through a subhorizontal re- flection Moho, as in central Alberta (Fig. ...
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... Alberta basement study (Fig. 21) consisted of three separate seismic-reflection transects (Peace River Arch in- dustry seismic experiment (PRAISE), the central Alberta transect (CAT), and the southern Alberta Lithoprobe transect (SALT)). Although each of these efforts had specific objec- tives, the overall purpose of the study was to establish the structure and tectonic evolution of the Canadian Shield Pre- cambrian basement beneath the Phanerozoic strata of the Western Canada Sedimentary Basin (WCSB; Ross ...
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... intersecting lower crustal and mantle reflec- tion fabrics characterize the southern margins of the south- eastern Grenville Province ( Fig. 10; Hall et al. 2002). Labradorian deformation mapped at surface indicates out- wardly verging thrust systems. The mid-crustal reflection fabrics confirm that such structures extend to the lower crust, in a pattern of crosscutting blocks. Very strong reflec- tion fabrics are observed in the deep crust and extend into the mantle. Fabric S1 (Fig. 10) runs from subhorizontal origins at the top of the lower crust, dips through the base of the crust (as estimated by extrapolation from wide-angle profile ECSOOT 2), and flattens at that level before dipping ...
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... intersecting lower crustal and mantle reflec- tion fabrics characterize the southern margins of the south- eastern Grenville Province ( Fig. 10; Hall et al. 2002). Labradorian deformation mapped at surface indicates out- wardly verging thrust systems. The mid-crustal reflection fabrics confirm that such structures extend to the lower crust, in a pattern of crosscutting blocks. Very strong reflec- tion fabrics are observed in the deep crust and extend into the mantle. Fabric S1 (Fig. 10) runs from subhorizontal origins at the top of the lower crust, dips through the base of the crust (as estimated by extrapolation from wide-angle profile ECSOOT 2), and flattens at that level before dipping ...
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Using seismic reflection and exploratory well data from the Jeanne d’Arc basin, offshore Newfoundland, we examined the link between unconformity generation and the onset of seafloor spreading between the central Grand Banks and Iberia. A prominent unconformity developed across the entire basin, previously interpreted as a ‘break-up’ unconformity, i...
Citations
... Further north and east, the seismograph data coverage is more heterogeneous, but a variety of studies carried out over the last 30-40 years provides a good indication of crustal thickness variations. The Lithoprobe project (Bostock et al., 2010;Cook et al., 2010;Hammer et al., 2010, and references therein) used seismic reflectionrefraction profiles, gravity modeling and receiver function analysis to investigate crustal structure in the southern Trans-Hudson orogen (transect THOT), the WS and Abitibi-Grenville regions (transect AG). Subsequent receiver function studies have added a substantial amount of information on Moho depth variations. ...
The Archean Superior craton was formed by the assemblage of continental and oceanic terranes at ∼2.6 Ga. The craton is surrounded by multiple Proterozoic mobile belts, including the Paleoproterozoic Trans‐Hudson Orogen which brought together the Superior and Rae/Hearne cratons at ∼1.9–1.8 Ga. Despite numerous studies on Precambrian lithospheric formation and evolution, the deep thermochemical structure of the Superior craton and its surroundings remains poorly understood. Here we investigate the upper mantle beneath the region from the surface to 400 km depth by jointly inverting Rayleigh wave phase velocity dispersion data, elevation, geoid height and surface heat flow, using a probabilistic inversion to obtain a (pseudo‐)3D model of composition, density and temperature. The lithospheric structure is dominated by thick cratonic roots (>300 km) beneath the eastern and western arms of the Superior craton, with a chemically depleted signature (Mg# > 92.5), consistent with independent results from mantle xenoliths. Beneath the surrounding Proterozoic and Phanerozoic orogens, the Mid‐continent Rift and Hudson Strait, we observe a relatively thinner lithosphere and more fertile composition, indicating that these regions have undergone lithospheric modification and erosion. Our model supports the hypothesis that the core of the Superior craton is well‐preserved and has evaded lithospheric destruction and refertilization. We propose three factors playing a critical role in the craton's stability: (a) the presence of a mid‐lithospheric discontinuity, (b) the correct isopycnic conditions to sustain a strength contrast between the craton and the surrounding mantle, and (c) the presence of weaker mobile belts around the craton.
... In the Northern Canadian Cordillera (NCC), a broad range of techniques have been employed in the investigation of the lithosphere and the Moho, exploiting the change in acoustic impedance (seismic velocity divided by density). These include Lithoprobe and Trans-Alaska Crustal Transect (TACT) seismic reflection and refraction experiments (e.g., Beaudoin et al. 1994;Welford et al. 2001;Cook et al. 2004Cook et al. , 2010Clowes et al. 2005;Creaser and Spence 2005;Fernández-Viejo et al. 2005;Fuis et al. 2008), passive seismic methods (e.g., Frederiksen et al. 1998;Dalton et al. 2011;Schaeffer and Lebedev 2014;Estève et al. 2021), receiver function analysis (e.g., Postlethwaite et al. 2014;Audet et al. 2020;Zhang et al. 2021), and joint models of seismic, gravity (e.g., Snyder et al. 2018) and mineral physics data (e.g., Tesauro et al. 2014aTesauro et al. , 2014b. ...
... Despite local perturbations, the Moho beneath the NCC and adjacent craton is broadly flat (Fig. 5c), aligned with the previous results (e.g., Beaudoin et al. 1994;Welford et al. 2001;Cook et al. 2004Cook et al. , 2010Clowes et al. 2005 Moho deepens beneath the St. Elias Mountains (Fig. 6a), suggesting the presence of crustal roots (i.e., airy isostacy). To the northeast, as far as the Great Bear magmatic zone, the Moho is broadly flat at a shallower depth of ∼32 km. ...
The geometry and depth of the Moho beneath the Northern Canadian Cordillera and adjacent North American craton are modeled through the application of both cokriging and 3-D inversion of gravity data, integrated with sparse seismic depth estimates. Models require a regional density correction, with lower densities beneath the Cordillera than the craton. The lower densities are primarily attributed to a reduction in upper mantle density, ascribed to thermal expansion under regionally higher temperatures. The eastern margin of this low-density zone is broadly aligned with the rapid westward shallowing of the lithospheric-asthenospheric boundary. From the Cordillera to the North American craton, the Moho is broadly flat at a depth of ~32 km. A zone of deeper Moho (up to ~38 km) beneath the Mistry Creek embayment has a modeled mantle density that is of a colder cratonic signature, akin to the Mackenzie craton, and is interpreted to represent the preserved remnants of an old rift basin, that is a local focus of the diffuse seismicity. Southeast of the Fort Norman structure, seismicity is broadly focussed along the eastern edge of the low-density zone. Major structures such as the Denali and Tintina faults, with 100’s km of right-lateral displacement, separate zones of higher and lower upper mantle density, supporting the interpretation of their continuation into the upper mantle. Within the North American craton upper mantle density steadily increases towards the Great Bear magmatic zone, but increases more rapidly beneath the Slave craton in tangent with a deepening of the Moho.
... Considering that the Zoige basin and the southern West Qinling orogen belong to the Yangtze craton and its western extension, the Songpan-Ganze terrane, and the two sets of north-dipping reflectors with a close distance may have experienced similar tectonic events; the initial condition of the collisional orogeny in the West Qinling orogen could be likely to be described by three convergent hypothetical models (Fig. 5): (1) a branch of Paleo-Tethys Mianlue ocean possibly developing in the late Paleozoic exists on the north of the Mianlue ocean; (2) the opening and subsequent northward subduction of the back-arc oceanic basin following the closure of the Paleo-Tethys Mianlue ocean in the Triassic; and (3) multistage continental subduction deriving from the subducting and dragging of the oceanic crust. Similar crustal structural characteristics have been documented by seismic reflection profiles in the Archean Superior Province of Canada by the Lithoprobe Project (Cook, 2002;Cook et al., 2010;Hammer et al., 2010) and the North China block . The first two models agree with one another in that there are two oceanic closure events during the collisional orogeny of the West Qinling orogen, while the third model requires only one ocean represented by the Mianlue ocean and closed by northward subduction. ...
Although it is well known that the West Qinling orogen was created by the convergence and collision between the North China block (NCB) and the South China block (SCB), the process of the microplate convergence in the West Qinling orogen and its adjacent blocks remains poorly understood. Here we address this question by analyzing $ 400 km seismic-reflection-profile data to constrain the subsurface structure of the orogenic system. Our data reveal two north-dipping reflection sets sandwiched between a sub-horizontal Moho (16 s to 18 s, t.w.t.) and a decollement zone ($6 s, t.w.t.) that separates the upper and mid-lower crusts. In detail, two sets of north-dipping reflectors occur beneath the Zoige basin (CDP 3000-4500, NR-1) and the southern West Qinling orogen (CDP 7000-10500, NR-2), which correlate to south-directed thrusts and are best interpreted as the result of the closure of the Paleo-Tethys Mianlue ocean in the early Triassic. This interpretation is consistent with the presence of an ocean separating the southern West Qinling orogen (S-WQO) from the northern West Qinling orogen (N-WQO). The origin of the required ocean is likely to be a branch of the Paleo-Tethys Mianlue ocean. Ó
... Moreover, the high density of this unit (Fig. 12) excludes high degrees of serpentinization (Mével, 2003), which indicates a non-mantelic origin. The internal reflectivity, apparent in the GXT-2100 line drawing (Fig. 16), is also in favour of a crustal nature (Hammer and Clowes, 1997;Cook et al., 2010), and the reflection at the bottom of this layer may be a good candidate for the seismic Moho (Prodehl et al., 2013). ...
... Лаврентия, и по профилю МТ (линии 1-2, 3-4, 5-6 и 9), который пересекает остров Ньюфаундленд. Сейсмические образы коры и коро-мантийной границы заимствованы: по профилю Line 86/3 -из публикаций [Marillier et al., 1989;Cook et al., 2010], по траверсу 89 (Lines 1-2, 3-4, 5-6, 9) [Li et al., 2008]. Таким образом, согласно существующим геологическим и геодинамическим интерпретациям, начиная, по крайней мере с неоархея (2.7 млрд лет), и вплоть до настоящего времени континенты Лаврентия и Балтика, даже отправляясь в гипотетическое свободное плавание, находились вблизи один от другого. ...
... Исследования в пределах трансекта ECSOOT по линиям 3S и 4S [Hall et al., 2002;Cook et al., 2010] включали сейсморазведку отраженных волн МОВ (normal-incidence reflection profiles) и глубинные сейсмические зондирования в пологих лучах (wide-angle surveys) с использованием возбуждения в акватории и приемников в море и на суше. Линии 3S и 4S (375-725 км) размещены вдоль береговой линии Лабрадорского моря, которая ограничивает Гренвиллский сектор ГСНО. ...
... Морской сейсмический профиль программы FGP Геологической службы Канады по линии 86/3, пересекающий залив Св. Лаврентия [Marillier et al., 1989;Cook et al., 2010] и комплексный профиль трансекта Lithoprobe East (LE) по линиям 89/1, 2, 3, 4, 5, 6, 9 через остров Ньюфаундленд [Van Staal, Barr, 2012] являются естественным продолжением один другого (рис. 9). ...
Abstract. The purpose of this paper is to reconstruct the Grenville-Sweconorwegian orogen (GSNO) for a systematically presentation of the main structural-tectonic, igneous and metamorphic features of this Precambrian orogen, formed in the boundary zone between the North American and East European composite cratons. The article presents an interpretation of new geophysical data characterizing the deep structure of the Grenville sector of the GSNO (LITOPROBE Program, Canada). The study of the conditions and conditions for the emergence and evolution of the GOOS is of special interest due to the fact that it is territorially and, in a certain sense, “ideologically” located in the center of the Rodinia, a supposed Neoproterozoic supercontinent. The GSNO was formed in the Meso-Neoproterozoic in the interior of the Lauroscandia continent. At present, the synform tectonic structure of the GSNO is divided into two sectors: Grenville along the southeastern margin of the Canadian Shield, and Sveconorwegian in southwestern Scandinavia. There are two periods in the history of the formation of the GSNO: the first (“preparatory”) in the interval from ~1.9 to ~1.16 Ga and the second (the formation of the GSNO proper) in the interval from ~1.19 to ~0.9 Ga. Metamorphism at the base of the Allochthonous Belt corresponds to high-pressure granulite facies and, in some places, to high-temperature eclogite facies. The age of metamorphism in the rocks of the Paraautochthonous belt is 1.05-0.95 Ga, the level of metamorphism increases from the greenschist facies near the Grenville Front to the high-pressure amphibolite facies near the Allochthonian Boundary Thrust, demonstrating inverted metamorphic zonation. The Sveconorwegian sector is characterized by high-pressure
granulite metamorphism and locally, at the base of allochthonous and within paraautochthonous complexes, high-temperature eclogites are noted. The outstanding characteristic of the GSNO is the widespread occurrence of specific intrusive magmatism. The high-temperature nature of magmatism and metamorphism, the repeated repetition of thermal impulses, and the enormous volume of the crust that has undergone high-temperature transformations point to the mantle plume as the most adequate source of thermal energy. The GSNO intracontinental development model contradicts popular ideas about the origin of this orogen as a result of the collision and association of previously distant continents (Laurentia, Baltica and Amazonia), which are supposed to have completed the assembly of the Rodinia supercontinent. It is concluded that it is necessary to revise the ideas about the tectonic position and geodynamic evolution of the GSNO, which is not analogous to the Tibet-Himalayan orogen. The unity of the Lavroscandia in the Meso-Neoproterozoic was broken twice as a result of the formation of oceanic structures similar to the Atlantic Ocean. The integrity of the continent after some time was restored with the participation of the processes of subduction of the oceanic lithosphere, accretion and obduction of island-arc and oceanic terranes.
Cвеконорвежского орогена (ГСНО), чтобы систематически представить главные структурно-тектонические, магматические и метаморфические особенности этого докембрийского орогена, сформированного в пограничной зоне между Северо-Американ-ским и Восточно-Европейским композитными кратонами. В статье представлена интерпретация новых геофизических данных, характеризующих глубинное строение Гренвиллского сектора Гренвилл-Свеконор-вежского орогена (ГСНО) (Программа ЛИТОПРОБА, Канада). Исследование условий и обстановок возникно-вения и эволюции ГСНО представляет специальный интерес в связи с тем, что он территориально и в определенном смысле «идейно» размещен в центре Родинии-предполагаемого неопротерозойского супер-континента. ГСНО был сформирован в мезо-неопротерозое во внутренней области континента Лав-роскандия. В настоящее время синформная тектоническая структура ГСНО разделена на два сектора: Гренвиллский вдоль юго-восточной окраины Канадского щита, и Свеконорвежский на юго-западе Сканди-навии. В истории формирования ГСНО выделяются два периода: первый («подготовительный») в интер-вале от ~1.9 до ~1.16 млрд лет и второй (собственно формирование ГСНО)-в интервале от ~1.19 до ~0.9 млрд лет. Метаморфизм в основании Аллохтонного пояса соответствует гранулитовой фации повышен-ных давлений и в ряде мест-высокотемпературной эклогитовой фации. Возраст метаморфизма в поро-дах Параавтохтонного пояса равен 1.05-0.95 млрд лет, уровень метаморфизма возрастает от зеленослан-цевой фации близ Гренвиллского фронта до амфиболитовой фации повышенных давлений близ Погранич-ного надвига аллохтона, демонстрируя инвертированную метаморфическую зональность. Для Свеконор-вежского сектора характерен гранулитовый метаморфизм повышенных давлений и локально, в основании аллохтонных и в пределах параавтохтонного комплексов, отмечены высокотемпературные эклогиты. Выдающейся характеристикой ГСНО является широкое проявление специфического интрузивного магма-тизма. Высокотемпературный характер магматизма и метаморфизма, многократное повторение тер-мальных импульсов и грандиозный объем коры, подвергшейся высокотемпературным преобразованиям, указывают на мантийный плюм в качестве наиболее адекватного источника тепловой энергии. Модель внутриконтинентального развития ГСНО противоречит популярным представлениям о возникновении этого орогена в результате столкновения и объединения ранее удаленных континентов (Лаврентии, Бал-тики и Амазонии), которые, как предполагается, завершили сборку суперконтинента Родиния. Сделан вы-вод о необходимости пересмотра представлений о тектонической позиции и геодинамической эволюции ГСНО, который не является аналогом Тибет-Гималайского орогена. Единство Лавроскандии в мезо-неопро-терозое дважды нарушалось в результате формирования океанических структур, подобных Атлантическому океану. Целостность континента через некоторое время восстанавливалась при участии процессов субдукции океанической литосферы, аккреции и обдукции островодужных и океанических террейнов.
... The crustal thickening is quite localised and so is likely to be missed unless sampling across the margin is quite dense. Studies in eastern Canada across the boundary between the Superior Craton and the Grenville Orogen show some similarities with localised zones of thickening adjacent to the transition(Cook et al. 2010, Darbyshire et al. 2017. ...
In recent years there has been a considerable expansion of deployments of portable seismic stations across Australia, which have been analysed by receiver function or autocorrelation methods to extract estimates of Moho depth. An ongoing program of full-crustal reflection profiles has now provided more than 25,000 km of reflection transects that have been interpreted for Moho structure. The Moho dataset is further augmented by extensive marine reflection results. These new data sources have been combined with earlier refraction and receiver function results to provide full continental coverage, though some desert areas remain with limited sampling. The dense sampling of the Moho indicates the presence of rapid changes in Moho depth and so the Moho surface has been constructed using an approach that allows different weighting and spatial influence depending on the nature of the estimate. The inclusion of Moho results from continental-wide gravity inversion with low weighting helps to resolve the continent-ocean transition and to provide additional control in the least sampled zones. The refined distribution indicates the presence of widespread smaller-scale variations in Moho structure. Strong lateral contrasts in crustal thickness remain, but some have become more subdued with improved sampling of critical areas. The main differences from earlier results lie in previously poorly sampled regions around the Lake Eyre Basin, where additional passive seismic results indicate somewhat thicker crust though still with a strong contrast in crustal thickness to the cratonic zone to the west.
... The crustal thickening is quite localized and so is likely to be missed unless sampling across the margin is quite dense. Studies in eastern Canada across the boundary between the Superior Craton and the Grenville Orogen show some similarities with localized zones of thickening adjacent to the transition (Cook et al. 2010, Darbyshire et al. 2017. ...
In recent years there has been a considerable expansion of deployments of portable seismic stations across Australia, which have been analysed by receiver function or autocorrelation methods to extract estimates of Moho depth. An ongoing program of full-crustal reflection profiles has now provided more than 25,000 km of reflection transects that have been interpreted for Moho structure. The Moho dataset is further augmented by extensive marine reflection results. These new data sources have been combined with earlier refraction and receiver function results to provide full continental coverage, though some desert areas remain with limited sampling. The dense sampling of the Moho indicates the presence of rapid changes in Moho depth and so the Moho surface has been constructed using an approach that allows different weighting and spatial influence depending on the nature of the estimate. The inclusion of Moho results from continental-wide gravity inversion with low weighting helps to resolve the continent-ocean transition and to provide additional control in the least sampled zones. The refined distribution indicates the presence of widespread smaller-scale variations in Moho structure. Strong lateral contrasts in crustal thickness remain, but some have become more subdued with improved sampling of critical areas. The main differences from earlier results lie in previously poorly sampled regions around the Lake Eyre Basin, where additional passive seismic results indicate somewhat thicker crust though still with a strong contrast in crustal thickness to the cratonic zone to the west.
... Moreover, the high density of this unit (Fig. 12) excludes high degrees of serpentinization (Mével 2003), which indicates a non-mantelic origin. The internal reflectivity, apparent in the GXT-2100 line drawing (Fig. 16), is also in favour of a crustal nature (Cook et al., 2010;Hammer and Clowes, 1997), and the reflection at the bottom of this layer may be a good candidate for the seismic Moho (Prodehl et 35 al., 2013). ...
... We perform this analysis for several overlapping depth ranges that are 10 km thick, from 5 to 50 km with a 5 km overlap. Previous studies suggest shallow Moho depths of ∼32 km over much of western BC (Cook et al., 2010;Tarayoun et al., 2017), and 18-26 km beneath Haida Gwaii (Gosselin et al., 2015). Our analysis investigates structure through the entire crust. ...
Coastal British Columbia (BC), Canada, has the highest seismic hazard in the country due to convergent and transpressive deformation at offshore plate boundaries between the Pacific, Juan de Fuca (JdF) and North American (NA) plates. Further landward, the crust of the NA plate is made up of several geologically unique exotic terranes and is unusually thin. Investigating the geophysical features in this area can help us better constrain its tectonic history and the geophysical processes that are currently underway. Here, we conduct an analysis of teleseismic body‐wave scattering data (i.e., receiver functions [RFs]) recorded at stations across western coastal BC including northern Vancouver Island and southeastern Alaska. Using these RFs, we perform a harmonic decomposition with respect to earthquake back‐azimuths to determine the orientation of seismic anisotropy over a series of depth ranges, attributable to either mineral alignment or dipping structures. We find a coherent pattern of margin‐parallel orientations at upper crustal depths that persist onto the mainland at distances 420 km from the margin. Furthermore, dominant receiver function orientations at depth are attributed to dipping faults and interfaces, and fabrics due to lower crustal shearing or inherited from tectonic assembly along the margin. This work supports models for the tectonic assembly of this region that involve a combination of plate subduction and transpressive motion along crustal scale faults that pervade a wide portion of the margin. This work also helps to constrain the current geometries of the subducting Pacific and JdF slabs.
... The mountainous elevations and upper-crustal thrust belts of many shortened Cordilleran systems have led to the assumption that the lower crust must thicken at depth to match the uppercrustal shortening. But seismic transects through several Cordilleran hinterlands (Clowes et al., 1995(Clowes et al., , 2005Fuis et al., 2008;Cook et al., 2010) have imaged relatively thin crust (Hasterok and Chapman, 2007). For example, crustal thicknesses in the Canadian Cordillera's backarc hinterland (30-35 km thick) are consistently thinner than crustal thicknesses in the craton to the east (40-45 km thick; Kao et al., 2014). ...
What causes previously stable continental crust in the forelands of Cordilleran orogenic systems to shorten during low-angle subduction? The National Science Foundation/EarthScope Bighorn Project combined seismic imaging of the crust and Moho with kinematic modeling of Laramide (Late Cretaceous–Paleogene) basement-involved deformation to address this question. In north-central Wyoming, asymmetrical ENE-verging upper-crustal folds are highly discordant with broader, N-trending warps in the Moho, indicating crustal detachment. Restorable cross sections of ENE-directed detachment at a depth of ~30 km, combined a smaller component of NNW–SSE shortening due to the east-narrowing shape of the crustal allochthon, can explain the anastomosing network of Laramide basement-cored arches without major deformation of the underlying mantle lithosphere.
Thrust-related fold geometries and west-to-east initiation of deformation in the Laramide and Sevier thrust belts point to Cordilleran end-loading from the west. Differences between Laramide (~N65E) and plate (~N25E) convergence directions, along with the fanning of Laramide shortening directions from nearly E–W to the south to NE–SW to the north, indicate slip partitioning during end-loading west of the Rockies.
Sub-horizontal detachment with a near-zero critical taper within cratonic crust suggests an extremely weak Laramide detachment zone during deformation. Analogous lower-crustal deformation in subduction forearcs is associated with slow earthquakes and slab dehydration. We hypothesize that low-angle subduction of the Farallon Plate suppressed fluid-consuming melting and corner-flow processes that characterize higher-angle subduction. This allowed subduction-generated fluids to escape upward into the overlying continental lithosphere, causing retrograde metamorphism and increased fluid pressure that facilitated crustal detachment. This hydration-based hypothesis predicts that crustal detachment will accompany major earthquakes in active analog orogens.
