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Structural evolution of Svecokarelian migmatites, southern Finland: a study of Proterozoic crustal development

Published online by Cambridge University Press:  03 November 2011

A. M. Hopgood
A. M. Hopgood
Affiliation:
Department of Geology, University of St Andrews, St Andrews, Fife KY16 9ST, Scotland.
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Abstract

Svecokarelian migmatites in the Jussarö area of the southern Finnish archipelago comprise tonalitic gneiss, amphibolite, metagabbro, microgranite, the metamorphosed derivatives of sediments, including carbonates and graded argillites, together with later-emplaced potassic granite, and basic and acidic pegmatites. The rock assemblage shows evidence of repeated deformation; a succession of 15 sets of folds (and fold-related structures) is identified and documented. There are two sets of early intraf oliai isoclinal folds (Faa and Fab), isoclinal folds (Fbr), recumbent folds (Fx), upright open folds (Fy), tight upright folds (Fbb), two sets of asymmetrical folds (Fc and Fd), ‘scar’ folds (Fb1, Fcb Fd1), slip folds Fb, conjugate shear folds (Fe), angular folds (Fn), open warps (Fw) and tight ductile shears (Fds). From isotopie evidence reported elsewhere, the evolution of this crustal segment of the Svecokarelides is known to have spread over a period of approximately 200 m.y. from c. 1900 m.y. to c. 1700 m.y.

Keywords

amphibolitegranitemetagabbrometasedimentneosomepegmatitepolyphase deformationsubduction
Type
Research Article
Information
Earth and Environmental Science Transactions of The Royal Society of Edinburgh , Volume 74 , Issue 4 , 1984 , pp. 229 - 264
Copyright
Copyright © Royal Society of Edinburgh 1984

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