Major, trace and platinum group element (PGE) geochemistry of Archean Iron Ore Group and Proterozoic Malangtoli metavolcanic rocks of Singhbhum Craton, Eastern India: Inferences on mantle melting and sulphur saturation history

摘要

The geological and metallogenic history of the Singhbhum Craton of eastern India is marked by several episodes of volcanism, plutonism, sedimentation and mineralization spanning from Paleoarchean to Mesoproterozoic in a dynamic tectonic milieu. Distinct signatures of this Archean-Proterozoic geodynamic process are preserved in discrete crustal provinces that constitute the Singhbhum Craton. Here we report new major, trace and PGE geochemical data from the similar to 3.4 Ga Iron Ore Group (IOG) volcanic rocks of the jamda-Koira basin, a part of the BIF-bearing volcano-sedimentary sequences of the Noamundi-jamda-Koira iron ore basin in the western part of Singhbhum Granite (SBG), and similar to 2.25 Ga metavolcanic rocks of Malangtoli. The lOG and Malangtoli volcanic rocks are porphyritic basalts and despite belonging to different ages, they exhibit similar mineralogical composition marked by clinopyroxene, plagioclase (present as both phenocryst and groundmass), opaques and volcanic glass (restricted to groundmass). The igneous mineralogy of these rocks has been overprinted by greenschist to lower amphibolite grade of metamorphism. The Malangtoli samples show low and high MgO compositional varieties. Immobile trace element compositions classify the LOG samples as andesite having a calc-alkaline composition, whereas the Malangtoli rocks correspond to basalt and andesite displaying a tholeiitic to calc-alkaline trend. The LOG basalts show low to moderate PGE contents marked by 2623-6835 ppb of Sigma PGE, whereas the Malangtoli basalts display a moderate to high concentration of PGE (Sigma PGE = 43.01-190.43 ppb). The studied samples have relatively enriched Sigma PPGE ranging from 24.1-633 ppb (IOG) and 34-227.3 ppb (Malangtoli) against 22-4.1 ppb and 1.9-8.9 ppb Sigma IPGE contents respectively. PPGE/IPGE ratios for IOG and Malangtoli samples range from 7.7-17.6 and 4.8-59.9. HFSE, REE and PGE compositions suggest a low degree (< 1 to 1%) of partial melting in the garnet Iherzolite domain for the generation of IOG volcanic rocks. The parental magma of the Malangtoli basalts were generated by lower to higher degrees (3-<10%) of mantle melting at depths corresponding to spinel to garnet lherzolite regime. Trace element (Zr/Nb, Th/Ta, Th/Nb, Ni/Cu) and PGE (Pd/lr, Pd/Pt, Cu/Pd, Ni/Pd, Cu/Ir) ratios corroborate a sulphide saturated and PGE depleted character of JOG volcanic rocks that underwent crustal assimilation. In contrast, the high MgO Malangtoli basalts exhibit sulphide undersaturated, PGE undepleted nature devoid of crustal contamination whereas the low MgO Malangtoli basalts are sulphide saturated, PGE depleted and crustally contaminated. The JOG volcanic rocks correspond to intraoceanic arc with polygenetic crustal signatures, and show affinity towards arc-generated calc-alkaline basalts. The low- and high MgO basalts of Malangtoli are affiliated to transitional arc to rift-controlled back arc tectonic setting in a basinal environment that developed proximal to an active convergent margin. (C) 2015 Elsevier B.V. All rights reserved.