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The Tarskavaig Nappe of Skye, northwest Scotland: a re-examination of the fabrics and their kinematic significance

Published online by Cambridge University Press:  01 May 2009

R. D. Law  and
G. J. Potts
R. D. Law
Affiliation:
Department of Earth Sciences, The University, Leeds LS2 9JT, U.K.
G. J. Potts
Affiliation:
Department of Earth Sciences, University of Oxford, Parks Road, Oxford OX1 3PR, U.K.
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Abstract

Early petrofabric studies of quartz c axis preferred orientation within the Tarskavaig Nappe, located at the southern end of the Moine thrust zone, have been interpreted as indicating that structures within the nappe have been produced by tectonic movements acting at right angles to those responsible for formation of structures within the overlying, but immediately adjacent, Moine Nappe. Such a dramatic contrast in inferred transport direction has not been recognized within the rest of the thrust zone.

Re-examination of the microstructures and c axis fabrics within mylonitic metasediments from the western part of the Tarskavaig Nappe has revealed that these tectonites are characterized by maximum principal extension axes which trend sub-parallel to the WNW-trending Moine thrust zone transport direction. Later folding has reorientated and modified these structures within the eastern part of the nappe producing fabrics which have erroneously been taken to indicate a transport direction orientated sub-perpendicular to that of the rest of the Moine thrust zone.

WNW-trending maximum principal extension axes and WNW-directed overthrust senses are indicated by microstructures within schists from the adjacent Moine Nappe, suggesting that structures within both the Tarskavaig and Moine nappes may be associated with a common west-northwest transport direction.

Essentially coaxial (pure shear) strain paths (indicated by symmetrical c axis fabrics) dominate the internal parts of the Tarskavaig Nappe. Close to the base of the nappe, non-coaxial strain paths, originally associated with WNW-directed overthrusting, are indicated by asymmetrical c axis fabrics and oblique grain shape alignments. Strain compatibility considerations indicate that the lower kinematic domain (which must either be contemporaneous with, or later than, formation of the upper domain) must be characterized by a combination of pure and simple shear deformation.

Type
Articles
Information
Geological Magazine , Volume 124 , Issue 3 , May 1987 , pp. 231 - 248
Copyright
Copyright © Cambridge University Press 1987

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