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Cryptic Sr and Nd isotopic variation across the Leinster Granite, southeast Ireland

Published online by Cambridge University Press:  01 May 2009

Peter Mohr
Peter Mohr
Affiliation:
Department of Geology, University College, Belfield, Dublin 4, Ireland
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Abstract

Rb–Sr isotope whole-rock data from the end-Caledonian Leinster Batholith define an errorchron age of 464±26 Ma, appreciably older than the accepted emplacement age of c. 405 Ma. This anomalously old age is the consequence of a highly variable initial Sr isotopic composition. Initial Nd ratios and TDM model ages also show a wide range of values. However, these isotopic variations are neither randomly distributed nor related to petrographic changes but instead reflect, in a simple way, geographic position about the axis of the batholith. The isotopic pattern revealed in the Leinster Batholith means that isochron ages obtained from S-type granites may be largely dependent on the sampling scheme adopted. The variable isotopic composition of the granite most likely resulted from either a heterogeneous metasedimentary source or hybridization of coeval, dominantly crustal melts.

Type
Articles
Information
Geological Magazine , Volume 128 , Issue 3 , May 1991 , pp. 251 - 256
Copyright
Copyright © Cambridge University Press 1991

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