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Pluton emplacement by wall-rock thrusting, hanging-wall translation and extensional collapse: latest Devonian plutons of the Cobequid fault zone, Nova Scotia, Canada

Published online by Cambridge University Press:  01 May 2009

I. Koukouvelas ,
G. Pe-Piper  and
D. J. W. Piper
I. Koukouvelas
Affiliation:
Department of Geology, University of Patras, Patras, Greece
G. Pe-Piper
Affiliation:
Department of Geology, Saint Mary's University, Halifax, N.S. B3H 3C3, Canada
D. J. W. Piper
Affiliation:
Atlantic Geoscience Centre, Geological Survey of Canada, Bedford Institute of Oceanography, P. O. Box 1006, Dartmouth, N.S. B2Y 4A2, Canada
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Abstract

Latest Devonian A-type granite-gabbro plutons, in part ductilely deformed, are spatially associated with the strike-slip Cobequid fault zone. The youngest intrusions are close to the Cobequid fault zone, which was the main conduit for magma. Two phases of deformation accompanying magma emplacement are recognized. Early magmas intruded ductile rocks during left-lateral oblique thrust movements. A second stage of right-lateral oblique slip normal faulting accommodated uplift of the plutons when coarse granite was emplaced in the crestal regions. Cross-cutting late stage porphyries, granitic clasts in marginal basins cut by granitic dykes, and superposition of brittle on ductile structures all indicate rapid uplift of the plutons. The geometry of the Cobequid fault zone shows that pluton emplacement was not the result of extension in releasing bends during transcurrent shear. Rather, flower-structure high-angle faults acted as magma conduits and space was created by two processes: translation of wall rocks along thrust faults at depth, developing space away from the master fault zone and backward collapse of the uplifted magma chamber creating space towards the fault zone.

Type
Articles
Information
Geological Magazine , Volume 133 , Issue 3 , May 1996 , pp. 285 - 298
Copyright
Copyright © Cambridge University Press 1996

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