Multi-chronometer dating of the Souter Head Complex: rapid exhumation terminates the Grampian Event of the Caledonian Orogeny

Mark, D. F. , Rice, C. M., Hole, M. and Condon, D. (2020) Multi-chronometer dating of the Souter Head Complex: rapid exhumation terminates the Grampian Event of the Caledonian Orogeny. Earth and Environmental Science Transactions of the Royal Society of Edinburgh, 111(2), pp. 95-108. (doi: 10.1017/S1755691020000043)

Abstract

The Souter Head sub-volcanic complex (Aberdeenshire, Scotland) intruded the high-grade metamorphic core of the Grampian Orogen at 469.1 ± 0.6 Ma (uranium-238–lead-206 (238U–206Pb) zircon). It follows closely peak metamorphism and deformation in the Grampian Terrane and tightly constrains the end of the Grampian Event of the Caledonian Orogeny. Temporally coincident U–Pb and argon/argon (40Ar/39Ar) data show the complex cooled quickly with temperatures decreasing from ca.800 °C to less than 200 °C within 1 Ma. Younger rhenium–osmium (Re–Os) ages are due to post-emplacement alteration of molybdenite to powellite. The U–Pb and Ar/Ar data combined with existing geochronological data show that D2/D3 deformation, peak metamorphism (Barrovian and Buchan style) and basic magmatism in NE Scotland were synchronous at ca.470 Ma and are associated with rapid uplift (5–10 km Ma−1) of the orogen, which, by ca.469 Ma, had removed the cover to the metamorphic pile. Rapid uplift resulted in decompressional melting and the generation of mafic and felsic magmatism. Shallow slab break-off (50–100 km) is invoked to explain the synchroneity of these events. This interpretation implies that peak metamorphism and D2/D3 ductile deformation were associated with extension. Similarities in the nature and timing of orogenic events in Connemara, western Ireland, with NE Scotland suggest that shallow slab break-off occurred in both localities.

• Item Type: Articles
• Additional Information: Scottish Universities Environmental Research Centre (SUERC) would like to thank NERC for continued funding of the NERC Argon Isotope Facility.
• Status: Published
• Refereed: Yes
• Glasgow Author(s) Enlighten ID: Mark, Professor Darren
• Authors: Mark, D. F., Rice, C. M., Hole, M., and Condon, D.
• College/School: College of Science and Engineering > Scottish Universities Environmental Research Centre
• Journal Name: Earth and Environmental Science Transactions of the Royal Society of Edinburgh
• Publisher: Cambridge University Press
• ISSN: 1755-6910
• ISSN (Online): 1755-6929
• Published Online: 08 July 2020
• Copyright Holders: Copyright © 2020 The Authors
• First Published: First published in Earth and Environmental Science Transactions of the Royal Society of Edinburgh 111(2):95 - 108
• Publisher Policy: Reproduced in accordance with the publisher copyright policy