Petrogenesis of the Mesoarchean (∼3.05 Ga) mafic volcanics from the western Iron Ore Group volcano-sedimentary succession, Singhbhum craton, eastern India: Constraints from geochemical modelling and Sm-Nd geochronology

Cratonic Mesoarchean volcano-sedimentary successions preserve compositionally diverse volcanic rocks which give insight into Archean mantle characteristics and crustal evolution. The late Archean western Iron Ore Group (W-IOG) succession in the Singhbhum craton represents deposition during this time period. As the W-IOG depositional age has remained poorly constrained, to between Paleo- and Mesoarchean, petogenesis and chronology of the interbedded volcanics would be an important geological constraint. Mafic volcanics, interlayered with BIF and Fe-Mn-rich phyllite/shale, were sampled from Kalta and Ongarbira, and petrogenetic modelling of their mantle source and Sm-Nd geochronology were conducted. The Ongarbira basalts show tholeiitic affinity, are depleted in LILE, LREE, Zr and Th and an absence of Nb-Ta-Ti anomalies that imply a depleted MORB-type mantle source. Tholeiitic basalts yield an isochron age of 3050 +/- 71 Ma (25D) with Nd-i = 0.50885 +/- 0.00010, MSWD = 0.17 (n = 10) and epsilon(Nd(T)) = +3.3 +/- 1.6. Geochemical modelling indicates the most primitive tholeiitic basalt (Mg# = 61) formed by similar to 14% partial melting of depleted mantle whereas the most enriched variant formed by its subsequent assimilation-fractional crystallization (AFC) (similar to 15% with r = 0.2 being the ratio between assimilation rate and fractional crystallization rate). In contrast, the Kalta basaltic andesite have calcalkaline affinity, are enriched in LILE, LREE, Zr and Th with pronounced negative Nb-Ta-Ti anomalies indicating incompatible trace element enrichment in their petrogenesis. The basaltic andesite yield an isochmn age of 3041 +/- 94 Ma (2SD) with Nd-i = 0.50875 +/- 0.00009, MSWD = 0.62 (n = 10) and epsilon(Nd(T)) = +1.1 +/- 1.6. Geochemical modelling indicates that their compositions were generated by 20-40% AFC (r = 0.2) of similar to 14% partial melt of depleted mantle. The source magma to the Ongarbira basalt is interpreted to have formed during lithospheric extension of the Singhbhum craton, by partial melting of depleted mantle followed by minor AFC, whereas the Kalta basaltic andesite represents higher extents of AFC of the Ongarbira-type tholeiitic magma.

Automated summary

Cratonic Mesoarchean volcano-sedimentary successions provide valuable information about the Archean mantle and crustal evolution. This study focuses on the late Archean western Iron Ore Group (W-IOG) succession in the Singhbhum craton and aims to determine its depositional age and petrogenesis. Mafic volcanics from Kalta and Ongarbira were analyzed, and it was found that the Ongarbira basalts have a tholeiitic affinity with a depleted MORB-type mantle source, while the Kalta basaltic andesite has a calc-alkaline affinity and enriched trace elements. Petrogenetic modeling suggests that the Ongarbira basalts formed by partial melting of a depleted mantle followed by minor assimilation-fractional crystallization (AFC), whereas the Kalta basaltic andesite represents a higher degree of AFC of the Ongarbira-type tholeiitic magma. The results provide important geological constraints for the understanding of the W-IOG succession.