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Anorogenic granite magma genesis: new isotopic data for the southern sector of the British Tertiary Igneous Province

Published online by Cambridge University Press:  03 November 2011

I. G. Meighan ,
A. E. Fallick  and
A. G. McCormick
I. G. Meighan
Affiliation:
I. G. Meighan and A. G. McCormick, Department of Geology, School of Geosciences,The Queen's University of Belfast, Belfast BT7 INN, Northern Ireland
A. E. Fallick
Affiliation:
A. E. Fallick, Isotope Geology Unit, Scottish Universities Research and Reactor Centre, East Kilbride, Glasgow G75 0QU, Scotland
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Abstract

It is now generally accepted that British Tertiary granites contain crustal and mantle components. Genesis principally by differentiation of crustally contaminated basaltic magmas is widely held and silicic melts with some remarkable trace element similarities were generated within different upper crust along the St Kilda/Skye - Carlingford zone.

New whole-rock (and mineral) O isotope data for the southern sector of the province (N Arran, Ailsa Craig, Mourne Mountains, Slieve Gullion, etc) reveal that δ18O lies in the range +5·1 to +9·7‰ for most of the analysed granites, meteoric water-rock interaction having been in general less intensive than at Skye and Mull. Nevertheless, highly 18O-depleted country rocks (with δ18O<0) exist adjacent to the N Arran and Mourne Mountains granite plutons. There is as yet no evidence for the existence of low -18O granitic melts in this southern sector where magmatic δ18O compositions (up to c. + 9·5‰) can be inferred for some of the intrusions.

New Nd (and Sr) isotope data indicate that although there is some similarity in initial 87Sr/86Sr ratios between the northern and southern sector granites, in northeastern Ireland initial εNd values for the analysed Tertiary acid major intrusions range from −3·9 to −4·5. This is in marked contrast to the Skye granites, some of which have values below −20, reflecting the involvement of different lithosphere.

Keywords

ArranMourne MountainsAilsa Craig plutonsA-typesbasaltic differentiationcrustal contaminationmeteoric water-rock interactionSr, Nd, O isotopestrace elements
Type
Research Article
Information
Earth and Environmental Science Transactions of The Royal Society of Edinburgh , Volume 83 , Issue 1-2: Second Hutton Symposium: The Origin of Granites and Related Rocks , 1992 , pp. 227 - 233
Copyright
Copyright © Royal Society of Edinburgh 1992

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