Geochemistry,petrogenesis and tectonic significance of the Newer Dolerites from the Singhbhum Orissa craton,eastern Indian shield |
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| Abstract: | The Singhbhum Orissa craton, eastern India contains rocks as old as 3.6 Ga. The Newer Dolerites occur in two distinct orientations (NE/SW and NW/SE) in the Singhbhum Granitoid Complex (SBGC). These dikes are mostly tholeiites and quartz-normative dolerites associated with subordinate norites. We recognize three geochemical groups of the Newer Dolerites that were emplaced in the SBGC. Group I dikes contain lower SiO2 ( < 53.29%) and higher Mg #, Ni and Cr than group II dikes. Group III dikes have higher SiO2 than groups I and II. A few investigated samples show boninitic geochemical features. They have high-MgO (>8%), high-SiO2 (>52%) and low-TiO2 ( ≤ 0.5%) bulk-rock compositions. The main feature of the Newer Dolerite spidergrams is enrichment in the large-ion lithophile elements (LILE, e.g. Rb, K and Ba) relative to high field-strength elements (HFSE), resulting in high LILE/HFSE ratios. These geochemical characteristics suggest that the Newer Dolerites are subduction related. High La/Ta ratios (21–66) support a non-plume source. Therefore, we conclude that the Newer Dolerites show geochemical signatures similar to those of back-arc basalts. |
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| Keywords: | Newer Dolerites Precambrian crustal evolution X-ray fluorescence fractional crystallization |
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