International Geological Journal - Official Journal of the Carpathian-Balkan Geological Association

SULPHUR ISOTOPES OF SELECTED HERCYNIAN GRANITIC AND SURROUNDING ROCKS FROM THE WESTERN CARPATHIANS (SLOVAKIA)

Pages: 3 - 13

Authors: MILAN KOHUT, CLEMENTE RECIO

Abstract: A reconnaissance sulphur isotopic study has been carried out on selected Hercynian granites and related rocks to test the applicability of such data in constraining the relative contribution of igneous and sedimentary protoliths to the West-Carpathian granitic rocks. Chemical separation techniques yielded enough sulphide sulphur for analysis in 22 out of 26 selected whole rock samples. In general, more mafic rocks, showing higher whole-rock bulk sulphur content, yielded more sulphide for isotopic analysis than more felsic ones. The δ34S values obtained range from –0.9 to +5.7 ‰ (average +2.5 ± 2.3 ‰) for granites of S-type affinity, while results for I-type granites are lower, ranging between –2.9 and +2.3 ‰ (average –0.7 ± 1.9 ‰). Medium grade metamorphic rocks (gneisses ± mica schist) in the area gave values between –2.0 to +4.6 ‰ (average +0.8 ± 2.1 ‰) similar to S-type granites, while basic igneous rocks, and metamorphic rocks of obvious mantle affinity have a narrow span of values between –0.3 and +1.9 ‰ (averaging +0.7 ± 0.9 ‰). Despite the lithological variability implied above, the range of δ34S(CDT) values measured is rather narrow when compared with other granitic provinces elsewhere. The results presented here for the West-Carpathian granites fit better within a collisional orogenic setting than in a volcanic arc and/or oceanic subduction scenario. Sulphur isotopic results would be more easily explained within the frame of the I-/S-type model, while other data, such as magnetic susceptibility, could both fit the above and the magnetite-/ilmenite-series typology. Despite this, the data obtained could also be explained within a model in which some sulphur is of deep-seated igneous origin, having a distinctive isotopic composition, and some additional sulphur would be derived from the country rock via assimilation processes that resulted in the Central Western Carpathians granitoid rocks.

Keywords: Western Carpathians, Hercynian orogeny, sulphur isotopes, granitic rocks, country rocks, granite typology

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