A sulphur isotope study on selected Caledonian granites of Britain and Ireland
✍ Scribed by R. Laouar; A. J. Boyce; A. E. Fallick; B. E. Leake
- Publisher
- John Wiley and Sons
- Year
- 1990
- Tongue
- English
- Weight
- 656 KB
- Volume
- 25
- Category
- Article
- ISSN
- 0072-1050
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✦ Synopsis
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 614S in conjunction with 6"0, initial x7Sr/86Sr (Is,) and age; Group I have d 1 * 0 generally < + 10.5'%~, Is, in the range 0.703 to 0.708, and are younger than 435 Ma. 614S of this group ranges from -4.5'%,~, to +4.4'%~,: R = +0.7 f 2.6'%~) (n=40:la). Group I1 have 6I8O generally > + 10.5"/00, are generally older, I,, between 0.710 and 0.7208, with 614S in the range +6.2"/~ to +16"/00: R = +9.5 f 3 . 3 " / ~ (n = 13:la). The source region for group I1 granites contained a significant sedimentary component. Since sulphides in Lower and Middle Dalradian metasediments are characterized by unusually high JT4S values, between + 1 l'%,~, and + 17"/~, we suggest that group I1 granites contain a significant proportion of sulphur derived from these rocks.
KEY WORDS Caledonian granites S-type granites I-type granites Sulphur isotopes Dalradian