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Structural evolution of the Skiddaw Group (English Lake District) on the northern margin of eastern Avalonia

Published online by Cambridge University Press:  01 May 2009

R. A. Hughes ,
A. H. Cooper  and
P. Stone
R. A. Hughes
Affiliation:
British Geological Survey, Windsor Court, Windsor Terrace, Newcastle upon Tyne NE2 4HB, U.K.
A. H. Cooper
Affiliation:
British Geological Survey, Windsor Court, Windsor Terrace, Newcastle upon Tyne NE2 4HB, U.K.
P. Stone
Affiliation:
British Geological Survey, Murchison House, West Mains Road, Edinburgh EH9 3LA, U.K.
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Abstract

The Skiddaw Group comprises a marine sedimentary sequence deposited on the northern margin of eastern Avalonia in Tremadoc to Llanvirn times. It is unconformably overlain by subduction-related volcanic rocks (the Eycott and Borrowdale Volcanic groups) of mid-Ordovician age, and foreland basin marine strata of late Ordovician and Silurian age. The Skiddaw Group has a complex deformation history. Syn-depositional deformation produced soft sediment folds and an olistostrome. Volcanism was preceded (in late Llanvirn to Llandeilo times) by regional uplift and tilting of the Skiddaw Group, probably caused by the generation of melts through subduction-related processes. The Acadian (late Caledonian) deformation event produced a northeast- to east-trending regional cleavage, axial planar to large scale folds, and a later set of southward-directed thrusts with associated minor folds and crenulation cleavages. This event affected the northern Lake District probably in the late Silurian and early Devonian. The Skiddaw Group structures contrast strongly with those formed during the same event in the younger rocks of the Lake District inlier. The contrasts are attributed to differing rheological responses to varying and possibly diachronous stresses, and to possible impedence of thrusting by the combined mass of the Borrowdale Volcanic Group and the Lake District batholith.

Type
Articles
Information
Geological Magazine , Volume 130 , Issue 5 , September 1993 , pp. 621 - 629
Copyright
Copyright © Cambridge University Press 1993

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