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The structural age and possible origin of the Vagastie Bridge granite and associated intrusions, central Sutherland

Published online by Cambridge University Press:  01 May 2009

R. E. Holdsworth  and
R. A. Strachan
R. E. Holdsworth
Affiliation:
Department of Geological Sciences, University of Liverpool, Liverpool L69 3BX
R. A. Strachan
Affiliation:
Department of Geology, Oxford Polytechnic, Headington, Oxford OX3 0BP
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Abstract

The Vagastie Bridge granite, central Sutherland, belongs to a regional suite of igneous intrusions within Moine psammites adjacent to the base of the east Sutherland migmatite complex. An isotopic date of 405 ± 11 Ma, obtained using U–Pb determinations on zircon and sphene taken from the granite, has previously been interpreted as an intrusion age. However, a reassessment of the field relationships demonstrates that intrusion was syn-tectonic with respect to the later stages of ductile Caledonian deformation affecting the Moine rocks. It is suggested that the granite suite magmas originated at depth and that they were channelled into the still active Caledonian ductile thrust zone (the Naver Thrust) which forms the tectonic base of the Naver Nappe. On regional grounds, the interpretation of the c. 405 Ma date as an intrusion age is untenable, which implies that the isotope systematics of the Vagastie Bridge granite require re-investigation.

Type
Articles
Information
Geological Magazine , Volume 125 , Issue 6 , November 1988 , pp. 613 - 620
Copyright
Copyright © Cambridge University Press 1988

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