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Mylonitic mafic granulite in fault megabreccia at Clarke Head, Nova Scotia: a sample of Avalonian lower crust?

Published online by Cambridge University Press:  01 May 2009

Wes Gibbons  and
J. Brendan Murphy
Wes Gibbons
Affiliation:
Department of Earth Sciences, University of Wales, Cardiff, Wales CF1 3 YE, UK
J. Brendan Murphy
Affiliation:
Department of Geology, St Francis Xavier University, Nova Scotia B2G ICO, Canada
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Abstract

The Clarke Head fault megabreccia was produced within a major Late Palaeozoic transcurrent structure (the Minas fault system) which separates the displaced Meguma terrane of southern Nova Scotia from rocks more typical of the Avalon Superterrane. A large clast of anomalously high grade metabasite embedded in the clay matrix of the fault megabreccia displays a fresh granulite facies mineralogy (2-pyroxene + garnet + plagioclase) and mylonitic to ultramylonitic textures induced by anhydrous shearing deep in the roots of the fault zone. Whole rock geochemistry reveals the granulite protolith to have been a continental, within-plate mafic magma transitional between theoleiitic and alkaline. The original geochemical signature has survived strong dynamic recrystallization at granulite grade. Well-preserved REE abundances testify to a lack of metasomatic fractionation during high grade shearing under water-absent conditions. Sm—Nd data indicate that the basic granulite has a TDM age of c. 1 Ga. Isotopic comparisons with adjacent areas reveal similar TDM ages both north and south of the Minas fault system. The high grade clast may be typical of the lower crust in Nova Scotia and is thought to offer a rare window into the deep crust of the Avalon Superterrane in North America.

Type
Articles
Information
Geological Magazine , Volume 132 , Issue 1 , January 1995 , pp. 81 - 90
Copyright
Copyright © Cambridge University Press 1995

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