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Rb‐Sr isochron study of the Thorr and Main Donegal Granites, Ireland
Author(s) -
O'Connor P. J.,
Long C. B.,
Kennan P. S.,
Halliday A. N.,
Max M. D.,
Roddick J. C.
Publication year - 1982
Publication title -
geological journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.721
H-Index - 54
eISSN - 1099-1034
pISSN - 0072-1050
DOI - 10.1002/gj.3350170403
Subject(s) - isochron , geology , dalradian , geochemistry , isochron dating , pluton , anatexis , devonian , isotope , partial melting , crust , paleontology , metamorphic rock , tectonics , physics , quantum mechanics
A Rb‐Sr whole‐rock isochron study indicates that the entire Donegal granite suite was emplaced into orthotectonic Caledonian (Dalradian) rocks over a short interval during mid‐Silurian to earliest‐Devonian times. The Thorr pluton, probably the earliest member of the suite, yields an age of 418 ± 26 Myr and initial 87 Sr/ 86 Sr ratio of 0·7055 ± 4, while the latest member, the Main Donegal pluton has an age of 407 ± 23 Myr and initial 87 Sr/ 86 Sr ratio of 0·7063 ± 5 (Λ 87 Rb = 1·42 ± 10 −11 yr −1 ). Errors on both the age and initial Sr isotope ratios incorporate both a priori and geological scatter components and are quoted at the 2‐sigma level. The low and restricted range of initial Sr isotope ratios suggests small but significant differences in the composition of the parental granitic magmas which were derived from a low Rb/Sr, low 87 Sr/ 86 Sr source.