Archean crustal evolution of the Aravalli Banded Gneissic Complex, NW India: Constraints from zircon U-Pb ages, Lu-Hf isotope systematics, and whole-rock geochemistry of granitoids

Abstract

The Aravalli Banded Gneissic Complex forms a block of Archean gneisses and granitoids in the southern domain of the Aravalli orogen in NW India. Results of U-Pb-Hf isotope analyses on zircon grains combined with whole-rock geochemical data reveal that the gneissic complex is made up of TTGs, which intruded during the Paleoarchean (3310 Ma) and Neoarchean (2563–2548 Ma), and granite-granodiorite-quartz diorite emplaced between 2545 and 2485 Ma. Zircon xenocrysts additionally point to Meso- and Neoarchean magmatic episodes at 3100–3000, 2880–2800, 2690 and 2660–2630 Ma. Ages from zircon rims in conjunction with previously published Sm-Nd isotope data suggest metamorphic events at ca. 2450 and 520 Ma. Medium-HREE characteristics and near chondritic εHf3.31 Ga of −0.4 suggest formation of the Paleoarchean TTGs by partial melting of a deep-seated mafic crust, derived from CHUR-like mantle immediately prior to the TTG formation. In contrast, the high-HREE characteristics and subchondritic εHf2.56-2.55 Ga from −3 to −8 of the Neoarchean TTGs suggest partial melting at relatively shallow depth of a younger oceanic crust, which was derived from a depleted mantle source at <3.1–3.4 Ga. The Neoarchean granitoids (2540–2485 Ma) with εHft from −8 to +2 in magmatic and xenocrystic zircon were likely originated by internal reworking of a heterogeneous felsic crust, consisting of Paleo-, Meso- and Neoarchean rocks. The Neoarchean quartz diorite (ca. 2545 Ma) represents a hybrid rock, which resulted from mixing of enriched mantle-derived mafic melts (εHf2.55Ga = −3.4) with felsic melts formed by anatexis of Paleoarchean crust (εHf2.55Ga = −11.7). Comparison of our new data from the Aravalli Banded Gneissic Complex with those of the adjacent Bundelkhand Craton indicate that both cratonic nuclei underwent different evolutionary histories during the Archean.