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Structure and stratigraphy of the Morar Group in Knoydart, NW Highlands: implications for the history of the Moine Nappe and stratigraphic links between the Moine and Torridonian successions

Krabbendam, M.; Leslie, A.G.; Goodenough, K.M.. 2014 Structure and stratigraphy of the Morar Group in Knoydart, NW Highlands: implications for the history of the Moine Nappe and stratigraphic links between the Moine and Torridonian successions. Scottish Journal of Geology, 50 (2). 125-142. https://doi.org/10.1144/sjg2014-002

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Abstract/Summary

The Caledonian Orogen in northern Scotland comprises two major thrust nappes: the Moine and the Sgurr Beag Nappe. The Moine Nappe contains early Neoproterozoic Morar Group rocks (Moine Supergroup) and basement inliers. This paper describes the structure and stratigraphy of the Knoydart peninsula, a key area within the southern Moine Nappe. The geology of Knoydart is dominated by a thick internally coherent sequence of Morar Group rocks. This sequence is shown to be deformed by large-scale, west-vergent and west-facing Caledonian (early Palaeozoic) folds that represent D2 within the southern Moine Nappe. Subsequent D3 deformation led to refolding or tightening of F2 folds, so that the major Morar Antiform is, in essence, a composite F2/F3 fold. F2 and F3 folds are broadly co-axial, but F3 folds have steeper axial planes. The F2/F3 folds refold a regional-scale, originally recumbent, isoclinal F1 fold nappe of probable Knoydartian (mid-Neoproterozoic) age. The F1 fold nappe is cored by a thin sliver of basement gneiss; the lower limb comprises migmatitic Morar Group rocks, exposed in the Morar Window. The upper limb of the F1 fold nappe occupies most of Knoydart and is stratigraphically coherent and right-way-up. Within this sequence, the upper unit of the Lower Morar Psammite is barely deformed, preserving trough-cross-bedding and large-scale channels in thick beds. This suggests braided river deposition, similar to the Torridon Group west of the Moine Thrust and the Morar Group in the northern part of the Moine Nappe. On the basis of lithological similarity and stratigraphic disposition, it is suggested that the lowermost part of the Morar Group in Knoydart correlates with the Neoproterozoic Sleat Group on Skye.

Item Type: Publication - Article
Digital Object Identifier (DOI): https://doi.org/10.1144/sjg2014-002
ISSN: 0036-9276
Date made live: 13 Jan 2015 15:18 +0 (UTC)
URI: http://nora.nerc.ac.uk/id/eprint/509381

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