Computer Science
Scientific paper
Jan 1991
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1991gecoa..55..303d&link_type=abstract
Geochimica et Cosmochimica Acta, vol. 55, Issue 1, pp.303-308
Computer Science
2
Scientific paper
Stratiform barite beds, interlayered with (fuchsite) quartzites and mafic metavolcanics and containing minor disseminations of sulfides, occur in the Archaeagn (>3.3 Ga) Sargur Group of rocks at Ghattihosahalli, in the state of Karnataka, south India and near Jagat, within quartzites and metamorphosed flood basalts underlying the middle Proterozoic (~2.0 Ga) Aravalli Supergroup in the state of Rajasthan, northwest India (Fig. 1). The Sargur barites have 34 S in the range of 4.02 to 7.45 ( ). Disseminations of detrital pyrite, occurring in layers in the barite have 34 S between -3.62 and-5.87 . These barites are also characterized by low 87 Sr / 86 Sr ratios (~0.7018 ± 7). The basal Aravalli barites, in contrast, have exceptionally high 87 Sr / 86 Sr ratios (0.72284 to 0.72382) and 34 S between 17.11 and 21.24 ( ). 34 S in disseminated chalcopyrite within banded barite-amphibolite samples from the same occurrence varies between 6.21 and 8.52 ( ). The isotopic data of the Sargur barites most probably reflect Archaean coeval seawater composition. The mantle-like values indicate buffering of the seawater by mantle-derived basaltic crust. In contrast, the Aravalli barites bear the signature of a Proterozoic sea whose sulfur isotope composition is closer to that of present-day oceans. The unusually high 87 Sr / 86 Sr ratios point, however, to a local, highly radiogenic source, which had affected the Sr isotopic composition of coeval, `normal' seawater.
Bauman A.
Deb M.
Hoefs Joachim
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