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Sm—Nd ages from the Ballantrae complex, SW Scotland

Published online by Cambridge University Press:  03 November 2011

P. J. Hamilton ,
B. J. Bluck  and
A. N. Halliday
P. J. Hamilton
Affiliation:
Isotope Geology Unit, Scottish Universities Research and Reactor Centre, East Kilbride, Glasgow G75 0QU, Scotland.
B. J. Bluck
Affiliation:
Department of Geology, University of Glasgow, Glasgow G12 8QQ, Scotland.
A. N. Halliday
Affiliation:
Isotope Geology Unit, Scottish Universities Research and Reactor Centre, East Kilbride, Glasgow G75 0QU, Scotland.
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Abstract

The Ballantrae complex has yielded its oldest yet determined age of 576 ± 32 Ma from an Sm–Nd internal isochron for a block ‘eclogite’ interpreted as being a component of the mélange-olistostrome unit at Knockormal. This unit is possibly older than the main ophiolitic part of the complex and the ‘eclogite’ block provides evidence for the existence of oceanic crust older than c. 575 Ma on the southern margin of the Laurentian shield.

An Sm–Nd internal isochron from a high-grade metapyroxenite in the metamorphic aureole beneath an obducted slab of mantle peridotite at Laigh Knocklaugh yields an age of 505 ± 11 Ma. This is interpreted as close to the age of metamorphism and is older than the K–Ar age of 478 ± 8 Ma determined for the amphibolites of the aureole which underlie the metapyroxenite. The metapyroxenite had a provenance deeper in the oceanic crust than the amphibolite and the former has been structurally detached and justaposed against the latter in this telescoped metamorphic sequence.

Keywords

Arenigeclogitemélangemetamorphic aureolemetapyroxeniteobductionolistostrometrondhjemite
Type
Midland Valley
Information
Earth and Environmental Science Transactions of The Royal Society of Edinburgh , Volume 75 , Issue 2: Deep Geology of the Midland Valley of Scotland and Adjacent Regions. Bicentenary Symposium , 1984 , pp. 183 - 187
Copyright
Copyright © Royal Society of Edinburgh 1984

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