Mesoarchean gabbro-anorthosite complex from Singhbhum Craton, India

The Singhbhum Craton in Peninsular India preserves some of the oldest continental crust on the globe with Hadean and Paleoarchean zircon record. Here we investigate a gabbro-anorthosite complex from the eastern margin of the craton exposed at Besoi, Kuliana, Sarat and Jashipura areas. These rocks display moderate SiO2 (47.94–53.77 wt%), TiO2 (0.42–2.17 wt%), Al2O3 (8.97–14.96 wt%) MgO (6.14–10.30 wt%) and CaO (10.73–15.07 wt.) at low to moderate Cr (20–862 ppm), Ni (32–636 ppm) and V (81–666 ppm) and are classified as noritic gabbros and gabbros. Their rare earth and trace element patterns exhibit mild to moderate fractionation with coherent patterns (La/Yb = 1.71–14.59), negative to positive Eu anomalies (Eu/Eu* = 0.62–1.44) negative Nb, Ti and sparingly negative to positive ZrHf anomalies. The UPb analysis of zircon grains from the Jashipura gabbros yield upper intercept ages of 3047 to 3099 Ma and the 3047 Ma age is considered to mark the timing of emplacement. Our geochemical data suggest that these rocks were generated through fractional crystallization of magma in a magma chamber at a transitional depth of the spinel-garnet regime with subsequent crustal contam- ination at an active continental margin supporting a continental arc setting. The gabbro-anorthosite suites in this region are synchronous with the adjacent granites and we propose that the mafic magma provided the heat for crustal melting that generated the granitoids. This magmatic event coincides with the ca. 3.1 Ga widespread crustal growth event in the Singhbhum Craton.

Figure: Clinopyroxenes of the studied samples are showing calc-alkaline to tholeiitic nature evolved in an orogenic setting



C. Manikyamba, Arijit Pahari, M. Santosh, Jyotisankar Ray, C.S. Sindhuja, K.S.V. Subramanyam, Mutum Rajanikanta Singh;  Lithos 366–367 (2020) 105541;