∼2.1 Ga intraoceanic magmatism in the Central India Tectonic Zone: Constraints from the petrogenesis of ferropicrites in the Mahakoshal supracrustal belt

Autor: A. Keshav Krishna, V.V. Sesha Sai, D.V. Subba Rao, Michael Bizimis, Tarun C. Khanna, Manavalan Satyanarayanan
Rok vydání: 2017
Předmět:
Zdroj: Precambrian Research. 302:1-17
ISSN: 0301-9268
DOI: 10.1016/j.precamres.2017.09.012
Popis: Picrites with anomalous high-Fe (ferropicrites), have erupted from the Archean to recent, however, their incidences are extremely limited. Particularly, post-Archean occurrences are scarce. Experimental studies indicate that ferropicrites are derived from partial melting of the upper mantle at moderate pressures (≤4 GPa). The origin of the anomalous Fe-enrichment in their source, however, remains elusive, and in part attributed to the presence of silica-deficient pyroxenite. In this contribution we present a detailed account of ferropicrites in the Chitrangi Formation of the Paleoproterozoic Mahakoshal supracrustal belt in the Central India Tectonic Zone. The Lu-Hf isotope systematics of these rocks imply an age between ∼2.3 Ga and ∼1.8 Ga. Compared to the Lu-Hf isotopic system, the Sm-Nd isotopic system appears to be disturbed. Nevertheless, the combined Hf and Nd depleted mantle model ages of these lavas are consistent at ∼2.1 Ga, which we propose as the maximum age. Geochemically, the rocks have moderate to high concentrations of Fe 2 O 3 (T) (13–19 wt%) and MgO (6–18 wt%), with moderate to low SiO 2 (49–42 wt%) and Al 2 O 3 (14–9 wt%) contents, and low Al 2 O 3 /TiO 2 ( N ∼10. The primitive mantle normalized positive Nb anomalies in combination with key trace element ratios, and their Hf, Nd isotope systematics preclude contamination by Archean upper continental crust. Further, their juvenile Hf, Nd isotope systematics are inconsistent with long lived recycled crustal or sedimentary components in the mantle source of the Mahakoshal ferropicrites. In contrast, the enrichments in the incompatible lithophile elements suggest that the source of the Mahakoshal ferropicrites was refertilized by melts, possibly from an upwelling mantle plume shortly prior to eruption. The preserved pillow structures imply that magmatism took place in an ocean basin. Therefore, we argue for the existence of a proto-ocean prior to the amalgamation of the northern cratonic block consisting of Aravalli and Bundelkhand proto-continents, and the southern cratonic block consisting of Singhbhum, Bastar and Dharwar proto-continents, which were still adrift at ∼2.1 Ga.
Databáze: OpenAIRE
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