C-, O- isotope and whole-rock geochemistry of proterozoic Jahazpur carbonates, NW Indian Craton

The Jahazpur Group (NW Indian craton) meta-pelite-carbonate-quartzite sequence of presumed Palaeoproterozoic age unconformably overlies the volcano-sedimentary rocks of Hindoli Group and a tonalitic gneiss-leucogranite complex (Jahazpur Granite) basement. Leucogranite, the younger component of the Jahazpur Granite Complex, has been considered to be coeval with the ca. 2.5 Ga Berach Granite. The lowermost unit of the Jahazpur Group, the basal conglomerate, which unconformably overlies the Hindoli Group, is conformably overlain by a phyllite-dolomite-phyllite sequence. This sedimentary package is developed in two belts, designated as the Eastern and Western Jahazpur Belts. Preliminary C- and O-isotopic results, and relevant whole-rock geochemical data on representative dolomitic limestone samples are presented and discussed in this paper. The Lower Dolomite unit shows significantly negative to near zero delta(13)C values (-4.8 to +0.9parts per thousand(V-PDB)), while the Upper Dolomite (developed in the western belt only) shows near zero values. Various geochemical parameters (Mn/Sr and Ca/Mg ratios) and non-correlative delta(13)C and delta(18)O values indicate well-preserved isotopic characteristics. The isotopic signatures of Jahazpur Dolomites are significantly different from the highly positive delta(13)C values reported from the Palaeoproterozoic Aravalli Supergroup rocks occurring around Udaipur (Jhamarkotra Formation). The Jahazpur carbonates show some similarity in the C-isotopic characteristics with the Delwara Formation carbonates which underlie the Jhamarkotra Formation. However, the observed negative delta(13)C values in the Delwara Formation carbonates have possibly resulted from effects of metamorphic decarbonation.