Late- to post-Variscan structures on the coast between Penzance and Pentewan, south Cornwall
Proceedings of the Ussher Society
The occurrence of two generations (D1/D2) of folds and cleavage, compatible with a top to the north-north-west sense of shear during Variscan convergence is confirmed. A subsequent change in the stress regime (sigma(1) approximate to vertical, sigma(3) approximate to north-north-west-south-south-east) brought about the extensional reactivation of convergence-related features. The resultant D3 structures are diverse and include zones of distributed shear within the footwall of the Carrick Thrust, together with detachments and high angle brittle extensional faults within the hangingwall. D3 deformation probably initiated during the Stephanian, prior to lamprophyre intrusion, but persisted into the early Permian and was partially synchronous with granite emplacement and high temperature mineralization. Changes in the stress regime during the Permian (sigma(1) approximate to east-north-east-west-south-west, sigma(3) approximate to north-north-west-south-south-east to sigma(1) approximate to north-north-west-south-south-east, sigma(3) approximate to east-north-east-west-south-west) resulted in strike-slip faulting and the formation of steeply dipping cleavages. Triassic rift-related extension is also recognised (sigma(1) approximate to vertical, sigma(3) approximate to east-north-east-west-south-west). Low temperature base metal mineralization was in part synchronous with Permian and Triassic faulting. This study demonstrates that the Variscan basement in south Cornwall preserves a valuable record of the late Palaeozoic to Mesozoic tectonic evolution of the region.
Vol. 9 (1), pp. 72-78
Place of publication
DRAKE CIRCUS, ENGLAND