Paleoproterozoic calc-alkaline lamprophyres from the Sidhi Gneissic complex, India: Implications for plate tectonic evolution of the Central Indian Tectonic Zone

Abstract

Calc-alkaline lamprophyres are widely regarded as important probes for unravelling continental-scale geodynamic processes. We present petrographic, mineral chemical, bulk-rock geochemical, and Sr-Nd isotope data on eleven unmetamorphosed lamprophyre dykes intruding the ca. 2.5 Ga Sidhi Gneissic Complex in the Central Indian Tectonic Zone (CITZ) – an intercontinental suture which separates the Northern Indian (Aravalli-Bundelkhand Craton) and the Southern Indian (Dharwar-Bastar-Singhbhum Craton) blocks. The Sidhi dykes have porphyritic-panidiomorphic texture typical of lamprophyres, with phlogopite/biotite as the dominant phenocryst phase, in a orthoclase dominated groundmass. Based on mineralogy and geochemistry, the Sidhi dykes can be classified as calc-alkaline lamprophyres in general and minettes in particular. All these dykes are characterised by negative Ti, Ta and Nb anomalies typical of subduction-related global calc-alkaline lamprophyres. The trace element ratios of the Sidhi lamprophyres suggest derivation from variable degrees of partial melting of a similar magma source which experienced crustal input. Bulk-rock Rb-Sr isochron of the Sidhi lamprophyres yielded an age of ca. 2278 ± 230 Ma which is consistent with the Paleoproterozoic emplacement ages reported for other rocks from this region of CITZ. Negative ɛNdT (−3.68) values of the Sidhi lamprophyres suggest their derivation from an isotopically enriched mantle source whilst their TDM Nd model ages (~2.6 Ga) imply source enrichment that took place during the Neoarchaean. Petrogenetic modelling indicate that the Sidhi lamprophyres are generated from low degree partial melting of a mantle source metasomatised by sediment-derived melt having < 4% crustal material as an input in the E-DMM. Our study support models proposing a northward subduction of the Southern Indian Block beneath the Northern Indian Block along the CITZ.