Geochemistry and Petrogenesis of Archean Mafic Volcanic Rocks of Iron Ore Group, Jamda-Koira Basin, Singhbhum Craton

Subbaraman, Rahul (2022) Geochemistry and Petrogenesis of Archean Mafic Volcanic Rocks of Iron Ore Group, Jamda-Koira Basin, Singhbhum Craton. Masters thesis, Department of Earth Sciences.

Text (MS dissertation of Rahul Subbaraman (17MS043)) 17MS043_Thesis_file.pdf - Submitted Version Restricted to Repository staff only Download (9MB)

Abstract

The mechanism of generation of the Archean crust and its subsequent evolution is a matter of huge debate. Archean Eon has witnessed several cycles of volcanism and sedimentation. Cratons worldwide preserve in their volcano-sedimentary sequences compositionally diverse volcanic rocks, which give insight into Archean mantle characteristics and crustal evolution. Singhbhum Craton, being one of the oldest cratons globally, preserves the protracted history of crustal evolution from Hadean to Paleoproterozoic. The Iron Ore Group, particularly the Jamda-Koira basin, is one supracrustal succession that preserves Archean basalts which provides insight into the Archean mantle and help us unravel the role of mafic magmatism in Archean crust formation. Little is known about the age of the basin, petrogenesis of the rocks, and the tectonic setting of the volcano-sedimentary assemblage. Mafic volcanic rocks, interlayered with BIF and Fe-Mn-rich phyllite/shale, were sampled from the core region of the Noamundi-Koira synclinorium. I present whole-rock geochemical and Nd-isotope data and integrate it with petrographic and field observations to address these issues. The IOG basalts are chemically basaltic andesites to andesites and display a calc-alkaline affinity. Their flat HREE pattern, low positive εNdi, and low TiO2/Yb and (Lu/Hf)PM indicate their derivation from a depleted spinel lherzolitic mantle source at shallow depth. The rocks are enriched in LILE and LREE, with pronounced negative Nb-Ta-Ti anomalies indicating crustal contamination of source magma. Integrating geological evidences and earlier sedimentological studies, it is inferred that the Jamda-Koira basin is deposited in an intracontinental to continental margin setting over the stable Singhbhum Craton.

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