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Gravitational collapse and extension along a mid-crustal detachment: the Lough Derg Slide, northwest Ireland

Published online by Cambridge University Press:  01 May 2009

G. I. Alsop
G. I. Alsop
Affiliation:
Department of Geological Sciences, University of Durham, Durham DH1 3LE, U.K.
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Abstract

Pre-Caledonian basement is juxtaposed with an inverted Upper Dalradian cover sequence along the Lough Derg Slide, in south Donegal, northwest Ireland. Shear-sense criteria indicate that the Dalradian Succession is translated via oblique dextral thrusting over high pressure granulite facies basement in the footwall. Crustal thickening induced by large scale folding associated with this ductile thrusting resulted in mid-amphibolite facies metamorphism adjacent to the sole of the Dalradian nappe. Subsequent to peak metamorphism, the overthickened Dalradian cover sequence suffered heterogenous deformation associated with ductile extension concentrated in the strain-softened mylonites of the hangingwall. The oblique ductile thrusts initiated during crystal thickening were reactivated in a normal sense. Pre-existing fold axes rotated towards the extensional transport direction, which is marked by a secondary stretching lineation with associated S–C fabrics. Ductile extension and hangingwall collapse are considered to be related to gravitational instability induced by the earlier crustal thickening episode.

Type
Articles
Information
Geological Magazine , Volume 128 , Issue 4 , July 1991 , pp. 345 - 354
Copyright
Copyright © Cambridge University Press 1991

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