A 3.51 Ga bimodal volcanics‐BIF‐ultramafic succession from Singhbhum Craton: implications for Palaeoarchaean geodynamic processes from the oldest greenstone succession of the Indian subcontinent

Abstract

The Palaeoarchaean greenstone belt of the southern Iron Ore Group (SIOG) (3.51 Ga) in the Singhbhum Craton, eastern India, includes lowstrained and low-greenstone grade bimodal volcanics, Banded Iron Formation (BIF) and chromiferous ultramafics as enclaves within tonalitetrondjhemite-granodiorite (TTG) granitoids, collectively referred to as the Singhbhum Granite (3.4 Ga to 3.1 Ga). The succession comprises, from base to top, a lower unit of massive and pillowed basalt conformably overlain by dacitic lava and pyroclastics which in turn is overlain by a major BIF unit. The ultramafics are juxtaposed with the volcanics-BIF succession along a thrust fault. The lithological association of pillow lava, subaqueous dacitic lava and pyroclastic rocks and BIF collectively, suggests that the entire succession was deposited in a deep-marine depositional setting. The ash-poor dacitic volcanic rock succession with evidences of a transition from suppressed-volatile deep-water lava flow and pyroclastics to more evolved mass-flow deposits with increasing trend of subaqueous flow transformation, records a transition from a deep-water low-height volcanic chain to a shallower subaqueous eruption in an aggradational volcanic chain. Geochemical proxies from the bimodal volcanics and ultramafics showing enrichment of La/Nb, Th/Nb, Th/La, Ba/La, Pb/Ce, depletion in Nb-Ta relative to neighbouring REE, together with tectonic discrimination criteria using Nb, Y, Zr, Ti compositions, suggest an extending oceanic arc-forearc geodynamic setting similar to many of the Phanerozoic supra-subduction zone ophiolites where ophiolite development in the extending upper plate in a relatively short time span is facilitated by slab rollback processes. The positive Eu-anomaly together with high Y/Ho values from the BIFs also suggests their deposition in close proximity to spreading centres that might have developed over a rifted arc. The bimodal volcanic rock-BIF-ultramafic succession of the SIOG with evidence of a convergent margin geodynamic setting is an important example for Palaeoarchaean plate tectonic processes operating on Earth.

Geochemical and Sm–Nd isotopic characteristics of the Late Archaean-Palaeoproterozoic Dhanjori and Chaibasa metasedimentary rocks, Singhbhum craton, E. India: Implications for provenance, and contemporary basin tectonics

“…2). Based on their sedimentological analysis in combination with major, trace and REE geochemistry, these authors have inferred an oceanic suprasubduction zone geodynamic setting during the southern IOG sedimentation (Mukhopadhyay et al, 2012; see also Chaudhuri et al, 2015). Our Nd isotopic data thus corroborate the inference of a fore-arc basin setting on Singhbhum-type Mesoarchaean crust as proposed by earlier researchers.…”

“…Interestingly, a subduction-accretion complex in the Singhbhum during the Palaeo-Mesoarchaean time has been inferred by several authors (Saha et al, 2004;Mukhopadhyay et al, 2012; see also Prabhakar andBhattacharya, 2013, Chaudhuri et al, 2015). Based on their Sm-Nd isotope data, Saha et al (2004) have inferred that the provenance of the late Archaean Birtola sandstone (see Mazumder et al, 2012a for discussion) formed in an island arc setting.…”

“…tonalities. Mukhopadhyay et al (2012) have reported an interesting association of bedded chert, pillow lava, deep water dacitic lava, pyroclastics and BIF from the southern IOG (Fig. 2).…”

Tectonic juxtaposition of crust and continental growth during orogenesis: Example from the Rengali Province, eastern India

“…Mafic granulite is medium-to coarse-grained and composed of clinopyroxene, garnet, quartz, plagioclase, ilmenite and hornblende Ghosh et al, 2010;Mukhopadhyay et al, 2012). Samples used in the present study are shown in the map.…”

“…1a) records a remarkable Archean growth history (Saha, 1994). Its southern margin is composed of high-grade granulites along with mediumgrade metasedimentary and metavolcanic rocks, collectively termed as the Rengali Province (Crowe et al, 2001(Crowe et al, , 2003Dobmeier and Raith, 2003) that separate the PaleoeMesoarchean granitegreenstone terrane of the SC (e.g., Saha, 1994;Mukhopadhyay et al, 2012) from the essentially high-grade PaleoeMesoproterozoic Eastern Ghats Mobile Belt (EGMB) Das et al, 2011;Korhonen et al, 2011;Gupta, 2012;Dasgupta et al, 2013 and references therein). Although the Rengali Province constitutes a part of the EGMB, its rock types, metamorphic style and isotopic signatures are different from the major part of the EGMB, known as the Eastern Ghats Province or EGP (Dobmeier and Raith, 2003).…”