Episodic Arc Volcanism Related to the Precambrian Supercontinent Cycle: Insights from Geochemical and Nd Isotopic Compositions of Felsic Tuffs from Proterozoic Sedimentary Basins of India

The Indian Peninsula hosts large (area of several thousand km²) intracratonic Proterozoic (2.5-0.5 Ga) sedimentary basins. In the absence of fossiliferous strata, the timing of the sedimentation in these basins is defined by the dating of intercalated rhyolitic tuff horizons. The periodic occurrence of these volcanic tuff horizons has been interpreted as the far field effect of the collisional events resulting due to the formation of the Proterozoic supercontinents (e.g. Columbia and Rodinia). We report major, trace element concentrations and Nd isotopic compositions of tuffs collected from the different Indian Proterozoic basins to understand their petrogenesis. We have also compiled existing geochemical and Nd isotopic data for some of these tuff samples. Data are reported for representative samples of 1.63, 1.5, 1.45 and 1.0 Ga old tuffs from the Vindhyan basin, Singhora proto basin, Khariar basin and Chhattisgarh basin, respectively. The Vindhyan basin occurs in the Bundelkhand craton while the Singhora, Khariar and Chattisgarh basins occur in the Bastar craton. Major and trace element concentrations were determined using an Inductively Coupled Plasma Mass Spectrometer (ICP-MS, Thermo Scientific, X Series 2) and the Nd isotope measurements were performed using a Thermal Ionization Mass Spectrometer (TIMS, Triton Plus), both at CEaS, IISc. The tuffs show LREE enrichment and negative Eu anomaly in a chondrite-normalized plot. Significant enrichments of LILEs (e.g. Rb, Th, U) and notable depletions of Nb and Ta in primitive mantle normalized plots suggest derivation from subduction-related processes, which is consistent with earlier studies [1]. In plots of Ce/Pb vs Ce and Nb/Ta vs Zr/Sm the compositions of these tuffs overlap with that of global arcs. The initial Nd isotope composition (ɛNd(t)) of these tuffs ranges from 0.2 to -9.0. The initial Nd composition of the tuffs from the Vindhyan, Singhora and Chattisgarh basins with formation age ranging from 1.63 Ga to 1.0 Ga (600 million years interval) falls on the same Nd isotope evolution curve indicating a single source which has been melting periodically. The Khariar basin tuffs do not plot on the same trend suggesting their derivation from a different mantle-source. [1] Chakrabarti et al, (2007) Precambrian Research