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A sulphur isotope study on selected Caledonian granites of Britain and Ireland
Author(s) -
Laouar R.,
Boyce A. J.,
Fallick A. E.,
Leake B. E.
Publication year - 1990
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.3350250318
Subject(s) - dalradian , geology , geochemistry , protolith , pyrrhotite , group (periodic table) , pyrite , igneous rock , sedimentary rock , metamorphic rock , chemistry , organic chemistry
A sulphur isotope study was carried out to assess the value of such isotopic data in constraining the contributions of igneous and sedimentary protoliths for British and Irish Caledonian granites. Conventional separation techniques yielded sulphides from only 19 of the 50 selected granites, including both Newer and Older intrusions. These sulphides are dominated by pyrite, with lesser pyrrhotite, and rare chalcopyrite. Two groups emerge from consideration of δ 34 S in conjunction with δ 18 O, initial 87 Sr/ 86 Sr (I Sr ) and age; Group I have δ 18 O generally < + 10·5‰, I Sr in the range 0·703 to 0·708, and are younger than 435 Ma. δ 34 S of this group ranges from −4·5‰ to +4·4‰ x̄ = +0·7 ± 2·6‰ (n=40:1σ). Group II have δ 18 O generally > + 10·5‰, are generally older, I Sr between 0·710 and 0·7208, with δ 34 S in the range +6·2‰ to +16‰: x̄ = +9·5 ± 3·3% (n = 13:1σ). The source region for group II granites contained a significant sedimentary component. Since sulphides in Lower and Middle Dalradian metasediments are characterized by unusually high δ 34 S values, between +11‰ and +17‰. we suggest that group II granites contain a significant proportion of sulphur derived from these rocks.