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Research Paper | Geology | India | Volume 11 Issue 12, December 2022
Petrology and Geochemistry of Ultramafic-Mafic Suite of Rocks from the Singhbhum Craton, Eastern India: Implications on Petrogenesis and Geodynamic Setting
Pawan Kumar Yadav [6] | Manorama Das [4]
Abstract: This work intends to present a detailed field characteristic, petrographic, mineral chemistry, and whole-rock geochemical data of the ultramafic-mafic suite of rocks for the first time in Purnapani and Asanbani areas, Singhbhum Craton, India. It is a contribution to constrain the alteration processes, crustal contamination, tectono-magmatic evolution, geodynamic setting, and mantle composition of the ultramafic-mafic suite for the first time in the study area. A petrographic study shows that ultramafic rock is represented by the peridotite whereas the mafic rocks are identified as gabbro and anorthositic gabbro. The peridotite shows low SiO2 (39.29-45.04 wt.%), Al2O3 (3.15-4.49 wt.%), and TiO2 (0.25-0.47 wt.%) contents and high contents of MgO (27.41-35.25 wt.%), CaO (2.44-7.07 wt.%), LOI (4.05-8.32 wt.%), Ni (130-1700 ppm), Cr (425-8240 ppm), and V (123-260 ppm). It shows low variation in (La/Yb)N = 1.20-3.90; (La/Sm)N = 0.97-2.96; (Gd/Yb)N = 0.75-1.29, (Sm/Nd)N = 0.79-2.24 ratios, ?REE (11.73-23.66 ppm), and positive Eu anomalies (Eu/Eu* = 1.96-8.69). Besides, gabbro and anorthositic gabbro exhibit relatively higher SiO2 (50.28-53.84 wt.% in gabbro; 50.85-57.44 wt.% in anorthositic gabbro), Al2O3 (10.39-15.74 wt.%; 14.03-22.63 wt.%), and CaO (6.66-8.85 wt.%; 6.34-8.61 wt.%) contents and lower MgO (4.85-7.66 wt.%; 1.02-3.56 wt.%), and LOI (1.37-1.97 wt.%; 0.87-2.34 wt.%). Their rare earth and trace element patterns exhibit mild to moderate fractionation with coherent patterns (La/Yb = 4.43-9.65 in gabbro; 5.22-20.20 in anorthositic gabbro), Eu anomalies (Eu/Eu* = 0.64-1.22 in gabbro; 0.67-0.85 in anorthositic gabbro), and negative Nb anomalies. The analyzed data of the ultramafic-mafic suite were plotted in different discriminating diagrams for understanding the geodynamic setting. On the basis of the discriminating plots and the chemical characteristics, it can be stated that the derivation of ultramafic-mafic suites of rocks was generated through fractional crystallization of magma in a magma chamber at a transitional depth of the spinel-garnet regime with subsequent crustal contamination in a continental arc environment. The genesis of these ultramafic-mafic suites of rocks has quite coincided with the widespread crustal growth event in the Singhbhum Craton.
Keywords: Ultramafic-mafic suites, Geochemistry, Petrogenesis, Tectono-magmatic evolution, Singhbhum Craton
Edition: Volume 11 Issue 12, December 2022,
Pages: 93 - 121