Great Slave Lake Shear Zone, Canadian Shield: reconstructed vertical profile of a crustal-scale fault zone

The western Canadian Shield of northern Alberta is composed of a series of continental slivers that were accreted to the margin of the Archean Rae hinterland ca. 1.92.0 Ga., preserving a unique record of continental evolution for the interval 2.12.3 Ga. This part of Laurentia owes its preservation to the accretionary style of tectonic assembly south of the Great Slave Lake shear zone, which contrasts with indentationescape processes that dominate the Paleoproterozoic record farther north. The Buffalo Head and Chinchaga domains form the central core of this region, comprising a collage of ca. 23252045 Ma crustal elements formed on an Archean microcontinental edifice, and similar age crust is preserved as basement to the Taltson magmatic zone. The distribution of magmatic ages and inferred collision and subduction zone polarity are used to indicate closure of intervening oceanic basins that led to magmatism and emplacement of continental margin arc and collisional belts that formed from ca. 1998 to1900 Ma. Lithoprobe crustal seismic profiles complement the existing geochronologic and geologic databases for northern Alberta and elucidate the nature of late stages of the accretionary process. Crustal-scale imbrication occurred along shallow eastward-dipping shear zones, resulting in stacking of arc slivers that flanked the western Buffalo Head terrane. The seismic data suggest that strain is concentrated along the margins of these crustal slivers, with sparse evidence for internal penetrative deformation during assembly. Post-collisional mafic magmatism consisted of widespread intrusive sheets, spectacularly imaged as regionally continuous subhorizontal reflections, which are estimated to extend over a region of ca. 120 000 km2. The form of such mid-crustal magmatism, as subhorizontal sheets (versus vertical dykes), is interpreted to represent a style of magma emplacement within a confined block, for which a tectonic free face is unavailable.

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Paleomagnetism of the 1.1 Ga Lackner Lake Complex and tectonics of the Kapuskasing Structural Zone

Canadian Journal of Earth Sciences ◽

10.1139/e89-150 ◽

1989 ◽

Vol 26 (9) ◽

pp. 1778-1783 ◽

Cited By ~ 8

Author(s):

D. T. A. Symons

Keyword(s):

Fault Zone ◽

Canadian Shield ◽

Superior Province ◽

Thermal Demagnetization ◽

Abitibi Subprovince ◽

Reversed Polarity ◽

Middle Proterozoic

The Middle Proterozoic Lackner Lake Complex is a circular alkalic syenite–carbonatite stock with a diameter of about 5.5 km. It intrudes granulite-rank Archean gneisses in the Kapuskasing Structural Zone of the Wawa Subprovince in the Superior Province of the Canadian Shield. It adjoins the Ivanhoe Lake fault zone, which forms the boundary with the Abitibi Subprovince and is the probable locus of maximum motion between the subprovinces. Specimens from 18 sites in the complex were analyzed paleomagnetically by alternating-field and thermal demagnetization and by saturation isothermal remanence tests. Large, recent viscous remanence components required removal before a stable remanence with a mean direction of 305.4°, 64.1 °(α95 = 5.2°) was isolated. Its pole of 53.7°N, 156.5°W (dp = 6.7°, dm = 8.3°) indicates emplacement at 1108 ± 10 Ma during a brief normal interval in a predominantly reversed-polarity time. This study indicates that there has been no postintrusion tilting of the Kapuskasing Structural Zone and that postintrusion uplift by unroofing did not exceed about 8 km.

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Structure of the crust and upper mantle of the Great Slave Lake shear zone, northwestern Canada, from teleseismic analysis and gravity modelling

Canadian Journal of Earth Sciences ◽

10.1139/e03-038 ◽

2003 ◽

Vol 40 (9) ◽

pp. 1203-1218 ◽

Cited By ~ 17

Author(s):

David W Eaton ◽

Jacqueline Hope

Keyword(s):

Shear Zone ◽

Upper Mantle ◽

Receiver Function ◽

Function Analysis ◽

Crustal Material ◽

S Wave ◽

Crust And Upper Mantle ◽

Fast Axis ◽

Great Slave Lake ◽

Basic Features

The Great Slave Lake shear zone (GSLsz) exposes lower crustal rocks analogous to deep-seated segments of modern strike-slip fault zones, such as the San Andreas fault. Extending for 1300 km beneath the Western Canada Sedimentary Basin to the southern margin of the Slave Province, the GSLsz produces one of the most prominent linear magnetic anomalies in Canada. From May to October 1999, 13 three-component portable broadband seismograph stations were deployed in a 150-km profile across a buried segment of the shear zone to investigate its lithospheric structure. Splitting analysis of core-refracted teleseismic shear waves reveals an average fast-polarization direction (N49°E ± 19°) that is approximately parallel to the shear zone. Individual stations near the axis of the shear zone show more northerly splitting directions, which we attribute to interference between regional anisotropy in the upper mantle (fast axis ~N60°E) and crustal anisotropy within the shear zone (fast axis ~N30°E). At the location of our profile, the shear zone is characterized by a 10-mGal axial gravity high with a wavelength of 30 km, superimposed on a longer wavelength 12-mGal low. This gravity signature is consistent with the basic features of the crustal model derived from receiver-function analysis: a Moho that dips inward toward the shear-zone axis and a mid-crustal zone with high S-wave velocity (ΔVs = 0.6 ± 0.2 km/s). The axial gravity high may be related to uplift of deeper crustal material within the shear zone, or protolith-dependent compositional differences between the shear zone and surrounding wall rocks.

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