| Title | Lithoprobe: new perspectives on crustal evolution |
| Author | Clowes, R M; Cook, F A; Green, A G; Keen, C E; Ludden, J N; Percival, J A; Quinlan, G M; West, G F |
| Source | Canadian Journal of Earth Sciences vol. 29, no. 9, 1992 p. 1813-1864, https://doi.org/10.1139/e92-145 (Open Access) |
| Year | 1992 |
| Alt Series | Geological Survey of Canada, Contribution Series 31992 |
| Alt Series | Lithoprobe Publication 300 |
| Publisher | Canadian Science Publishing |
| Document | serial |
| Lang. | English |
| Media | paper; on-line; digital |
| File format | pdf |
| Province | Eastern offshore region; British Columbia; Ontario; Quebec; Newfoundland and Labrador |
| NTS | 92; 82; 41; 40; 31; 42; 12; 11; 2; 1 |
| Lat/Long WENS | -128.0000 -48.0000 52.0000 42.0000 |
| Subjects | geophysics; igneous and metamorphic petrology; structural geology; tectonics; metamorphic rocks; crustal evolution; crustal models; crustal structure; crustal studies; continental crust; oceanic crust;
tectonic environments; tectonic evolution; tectonic elements; tectonic interpretations; tectonic models; tectonic setting; seismic reflection surveys; seismic interpretations; seismic profiles; seismic surveys, ground; seismic surveys, ship; seismic
surveys; geophysical interpretations; geophysical surveys; oxygen isotopes; isotopes; plutonic rocks; granitic rocks; igneous rocks; Archean; magnetic surveys, airborne; magnetic interpretations; magnetic surveys; geophysical interpretations;
sedimentary rocks; faults; faults, thrust; fault zones; structural interpretations; structural features; mohorovicic discontinuity; LITHOPROBE; Grenville Orogeny; Superior Province; Grenville Province; Kapuskasing Structural Zone; Cordilleran Orogen;
Insular Belt; Coast Belt; Intermontane Belt; Omineca Belt; Foreland Belt; Dunnage Zone; Avalon Zone; Humber Zone; Gander Zone; Southern Province; Keweenanwan Rift; Abitibi Belt; Precambrian; Proterozoic; Paleozoic |
| Illustrations | sketch maps; cross-sections; seismic profiles |
| Abstract | Lithoprobe is Canada's national, collaborative, multidisciplinary earth science research program directed toward an enhanced understanding of how the North American continent evolved. Research in its
eight transects or study areas, which span the country from Vancouver Island to Newfoundland and geological time from 4Ga to the present, is spearheaded by seismic reflection surveys. These, combined with many other studies, are providing new insight
into the varied tectonic processes that have been active in forming the continent. Results from the Southern Cordillera transect show that Mesozoic crustal growth occurred in the central and eastern Cordillera by the accretion and amalgamation of
exotic terranes, the collision of which resulted in the generation of crustal-scale antiforms and duplexes. After the principal periods of compression, this area was affected by a major episode of extension that led to the unroofing of the
metamorphic core complexes. Farther to the west, past and present subduction processes have eroded the lower lithosphere of accreted terranes and left underplated sediments and oceanic lithosphere. The Lithoprobe East transect, covering the Paleozoic
Newfoundland Appalachians and Mesozoic rifted Atlantic margin, reveals three lower crustal blocks, each with distinctive reflection signatures on marine seismic data. Structures of the geologically established tectono-stratigraphic domains, imaged
clearly by new onshore reflection data, sole at upper crustal to mid-crustal levels, suggesting that much of the surface stratigraphy is allochthonous to the lower crustal blocks. At the ocean-continent transition, interpretations suggest
underplating of thinned continental crust by basaltic melt during the rifting process.In Lake Superior, data from the Great Lakes International Multidisciplinary Program on Crustal Evolution (GLIMPCE) transect reveal the complex structures of the
late Middle Proterozoic Keweenawan rift, which is up to 35 km deep, that almost split North America. The GLIMPCE data in Lake Huron show a spectacular series of east-dipping crustal-scale reflections that coincide with the Grenville front tectonic
zone. These and other data have led to a two-stage model involving collision of an exotic terrane with the southern Superior cratonic margin in the late Early Proterozoic followed by stacking-crustal penetrating imbrication and ramping associated
with the Middle Proterozoic Grenvillian orogeny. The Archean Kapuskasing structural zone, a prominent northeast-trending feature that cuts obliquely across the dominant east-west structures of the Superior Province, is interpreted as a thin thrust
sheet, soled by a variably reflective décollement, above which about 70 km of crustal shortening has occurred to bring mid-crustal to lower crustal rocks to the surface, and below which the Moho deepens. The shortening may have been accomplished by
brittle faulting and erosion at levels above 20 km and ductile folding or faulting in the lower crust. Preliminary studies in the Archean Abitibi greenstone belt indicate that two major fault zones, the Larder Lake-Cadillac and Porcupine-Destor,
which host significant mineralization, were generated by crustal-scale thrust and (or) strike-slip tectonics. Archean crustal sections are as structurally diverse and complex as their Proterozoic and Phanerozoic counterparts. The reflection Moho has
highly variable characteristics as imaged within transects and among different transects. Crustal and Moho reflectivity observed in the various transects is caused by a wide range of features, including fault-shear zones, lithologic contacts,
compositional layering, fluids in zones of high porosity, and anisotropy. |
| GEOSCAN ID | 193231 |
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