Geochemistry and petrogenesis of the Paleoproterozoic ortho-gneisses and granitoids of the Banded Gneissic Complex, central Rajasthan, NW India: Implications for crustal reworking processes.

Granitoids and orthogneisses (~ 1.7 Ga) from the northern part of the Banded Gneissic Complex (BGC-II domain), Aravalli Craton (NW India) are geochemically analyzed to understand the geodynamic condition and crustal evolution processes. The samples are metaluminous to peraluminous (molar A/CNK: 0.74–2.12), and characterized by Eu-anomaly ranging from 0.17 to 1.06, Fe2O3T/(Fe2O3T + MgO) from 0.8 to 0.9 and high magmatic zircon saturation temperature (> 830 °C) which are the features suggestive of A-type granite affinity. Tectonic discrimination diagrams classify the samples as post-collisional extensional A2-type granites. Geochemical characteristics along with trace element ratios [(Y/Nb)N = 0.15 to 4.33 (avg. 0.76), (Th/Nb)N = 4.63 to 255.47 (avg. 63.13), (Th/Ta)N = 1.37 to 9.84 (avg. 8.86), (Ce/Pb)N = 0.05 to 3.05 (avg. 1.43)] indicate that the rocks were derived from a plagioclase-rich and garnet-free crustal source under low-pressure conditions. Further, it is also proposed that tonalite-trondhjemite-granodiorite (TTG) rocks which occur dominantly in southern Rajasthan (BGC-I) are precursors and their partial melting led to the generation of the studied A-type granite samples. The studied samples also bear close geochemical similarity with A-type granites of similar age (~1.7 Ga) near the Sakhun-Ladera region of northern BGC-II. The studied A-type granites are believed to be coeval to similar aged A-type granites of the Khetri and Alwar sub-basins of the North Delhi Fold Belt (NDFB). They are comparable in age and magmatic history to recorded A-type magmatism in North America and parts of the Chinese craton. The large geographical extents of synchronous A-type granites are proposed to be related to the Columbia Supercontinent assembly (ca. 1.7 Ga; post-collisional granites). Thus, based on the studied extensional granites, we surmise that BGC-II was part of the Columbia Supercontinent. [ABSTRACT FROM AUTHOR]