Geochemistry of the Neoarchean Dodguni carbonates of Chitradurga greenstone belt, Dharwar Craton, India: Implications on depositional environment

The carbonates of the Dodguni area of the Chitradurga greenstone belt, Dharwar Craton, India were studied to understand the Archean diagenetic and palaeo-depositional conditions using carbon and oxygen isotopes along with whole-rock geochemistry. These carbonates show significant variation in delta C-13 and delta O-18 (-1.73 parts per thousand Vienna Peedee Belemnite [VPDB] to -0.45 parts per thousand VPDB and delta O-18 vary from -13.51 parts per thousand VPDB to -8.46 parts per thousand VPDB, respectively). The rare earth element (REE) + Y (rare earth elements and yttrium) of the studied carbonate rocks exhibit flat and uniform patterns (Pr-SN/Yb-SN = 0.4-1), slight positive La, Eu and Gd anomalies (Ce-SN/Ce-SN* = 0.8-0.9; Eu-SN/Eu-SN* = 0.7-1.4 and Gd-SN/Gd-SN* = 2-2.3, respectively) with slight positive Ce anomalies (Pr-SN/Pr-SN* = 0.84-0.86) and superchondritic Y/Ho ratios (Y/Ho = 29-45; chondritic Y/Ho = 28). Their negative delta C-13 (-1.75 parts per thousand to -0.45 parts per thousand) values are attributed to the influence of higher bio-productivity during their deposition and oxidation of organic carbon. The geochemical and isotopic systematics suggest that the Dodguni limestones are not affected by the diagenetic and metamorphic processes and record the REE geochemistry of the ancient seawater in which they were precipitated. The comprehensive geochemical including the isotopic studies of the Archean carbonate rocks of the Dharwar Craton, indicate their deposition in shallow marine conditions, precipitation in high temperatures with significant hydrothermal input under the influence of high bio-productivity, thereby providing valuable constraints on the palaeoceanography and geochemical evolution of the Archean sea.