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Geology and geochemistry of the volcanic rocks of the Pioneer Formation, Bridge River area, southwestern British Columbia (Canada)

Published online by Cambridge University Press:  01 May 2009

J. Dostal  and
B. N. Church
J. Dostal
Affiliation:
Department of Geology, Saint Mary‘s University, Halifax, Nova Scotia B3H 3C3, Canada
B. N. Church
Affiliation:
Geological Survey Branch, B.C. Ministry of Energy, Mines and Petroleum Resources, Victoria, British Columbia V8V 1X4, Canada
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Abstract

The Pioneer Formation of southwestern British Columbia (Canada) is composed predominantly of middle to late Triassic pillow basalts. These rocks are an integral part of the Cadwallader and the Bridge River terranes that were delaminated from the oceanic lithosphere and stacked against the continental margin of the North American craton by middle Jurassic time. The basalts are underlain and locally intercalated with ribbon cherts and argillites that range in age from Mississippian to Triassic. The Triassic basalts are conformably overlain by clastic sediments containing late Carnian–Norian conodont fauna. The tholeiitic basalts have enriched and depleted REE patterns, and have been emplaced in an oceanic environment. The compositional variations of the basalts are attributed to dynamic partial melting of source rocks that are believed to have been part of the rising mantle diapir. According to our model, after initial melting in the garnet stability field, the mantle diapir rose up to the spinel stability field where it underwent subsequent melting. The reconstructed stratigraphy of the Bridge River area may be interpreted in terms of an oceanic plate moving over a mantle plume and into a trench where offscraping preserved tectonic lenses of the subducting plate in an accretionary prism.

Type
Articles
Information
Geological Magazine , Volume 131 , Issue 2 , March 1994 , pp. 243 - 253
Copyright
Copyright © Cambridge University Press 1994

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