The Dalradian rocks of the Highland Border region of Scotland

The Highland Border region is defined here by the outcrop of the Southern Highland Group that lies north-west of the Highland Boundary Fault and runs from Stonehaven south-west to the Isle of Bute, and thence to the Campbeltown peninsula. The late-Neoproterozoic to early-Ordovician rocks of the Dalr...

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Bibliographic Details
Published in:Proceedings of the Geologists' Association 2013-01, Vol.124 (1-2), p.215-262
Main Authors: Tanner, P.W. Geoff, Thomas, Christopher W., Harris, Anthony L., Gould, David, Harte, Ben, Treagus, Jack E., Stephenson, David
Format: Article
Language:English
Subjects:
Dalradian Supergroup
Geological Conservation Review
Highland Border region
Lithostratigraphy
Metamorphism
Structural geology
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Summary:The Highland Border region is defined here by the outcrop of the Southern Highland Group that lies north-west of the Highland Boundary Fault and runs from Stonehaven south-west to the Isle of Bute, and thence to the Campbeltown peninsula. The late-Neoproterozoic to early-Ordovician rocks of the Dalradian Supergroup in this region form a stratigraphical and structural entity that encompasses the >300km-long surface traces of both the Tay Nappe (D1–D2) and the Highland Border Downbend (D4). The least deformed and metamorphosed Southern Highland Group rocks occur along the south-east margin of the region and are in continuity with the younger, newly recognized Trossachs Group, which has therefore been assigned to the Dalradian Supergroup. The earliest (D1) structures in the Dalradian rocks are dominant close to the Highland Boundary Fault but are successively overprinted northwards by D2, D3 and D4 structures and fabrics, here represented by a series of zones near-parallel to the Highland Boundary. Regional metamorphism increases progressively away from the Highland Boundary Fault and ranges from greenschist to upper amphibolite facies (sillimanite zone). Three fundamental features of deformed and regionally metamorphosed rocks worldwide were first recognized in this area: the ‘stretching lineation’ by Clough in 1897; the concept of regional metamorphic ‘Barrovian zones’ by Barrow in 1901; and the ‘facing direction’ of folds by Shackleton in 1958. The Highland Border region has acquired international recognition for research undertaken into the origin and mode of emplacement of the Tay Nappe, one of the largest recumbent folds known worldwide. This structure provides a framework for linking together most of the GCR sites in this paper.
ISSN:0016-7878
DOI:10.1016/j.pgeola.2012.07.013