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The origin of Georgia depression and the Coast Plutonic Complex/Insular Belt province boundary on Hardwicke and West Thurlow Islands, B. C.

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Title: The origin of Georgia depression and the Coast Plutonic Complex/Insular Belt province boundary on Hardwicke and West Thurlow Islands, B. C.
Author: Nelson, JoAnne Lee
Degree Master of Science - MSc
Program Geological Science
Copyright Date: 1976
Subject Keywords Geology -- B.C. -- Hardwicke Island; Geology -- B.C. -- West Thurlow Island
Abstract: Georgia Depression is a major northwest-trending structural trough that lies between the Coast Mountains and Vancouver Island, along the western boundary of the Coast Plutonic Complex. Field work on a part of this boundary on Hardwicke and West Thurlow Islands in Johnstone Strait established it as an intrusive contact between an Upper Jurassic quartz diorite and stratified rocks of the Vancouver Group. The Vancouver Group in the vicinity of the contact is broken by two major west-northwest trending preplutonic faults. Contact metamorphic conditions determined from basic and carbonate assemblages are P ,-3 kb. total and T . = (650 - 720°C . Post-plutonic fractures and dikes maximum trend northeast. The main result of the field study was to confirm for a particular area that the western margin of the Coast Plutonic Complex is essentially a magmatic front. Georgia Depression began to subside in the Upper Cretaceous as the Coast Plutonic Complex rose. It is proposed that the initial subsidence of Georgia Depression was complementary to the uplift of the Coast Mountains. Georgia Depression is part of the Coastal Trough of western North America, an elongate depression that lies between a series of colinear magmatic arcs (the Coast Plutonic Complex, the Cascades, and the Sierra Nevada) and the western margin of the North American plate. The various sub-basins of the Coastal Trough formed at different times, from the Upper Jurassic to the Late Tertiary, that correspond to the times of uplift of the adjacent igneous complexes. This coincidence suggests that the subsidence of the whole Coastal Trough, including Georgia Depression, was coupled to the uplift of the magmatic arcs of North America. The Coastal Trough may be analogous to the marginal synclines developed in Ramberg's (1967) diapir experiments.
URI: http://hdl.handle.net/2429/19795
Series/Report no. UBC Retrospective Theses Digitization Project [http://www.library.ubc.ca/archives/retro_theses/]

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