Archean to Proterozoic (3535-900 Ma) crustal evolution of the central Aravalli Banded Gneissic Complex, NW India: New constraints from zircon U-Pb-Hf isotopes and geochemistry

The central Aravalli Banded Gneissic Complex, a Proterozoic high-grade polymetamorphic terrane with Archean components in northwest India, is mainly composed of granulites, granitoids, TTG gneisses and metasedimentary rocks. Combined sets of zircon U-Pb-Hf isotopes and whole-rock geochemical data reveal that the gneissic complex is made up of Neoarchean TTGs, Paleoproterozoic A-type granitoids, and Mesoproterozoic nepheline syenite, which intruded at ca. 2550, 1720-1705 and 1440 Ma, respectively. Zircon xenocrysts additionally point to Paleoarchean-Neoarchean magmatic episodes at ca. 3535 and 2665 Ma. The discovery of a ca. 3535 Ma inherited zircon with superchondritic epsilon Hf-t provides the first direct evidence for the existence of an early Paleoarchean crust in the Aravalli orogen, which was formed by the partial melting of a depleted mantle reservoir. Ages from zircon rims suggest Grenville-age metamorphic overprints at ca. 970 Ma and similar to 900 Ma. High HREE contents and subchondritic epsilon Hf-2.55Ga = -7.3 to 0.7 of the Neoarchean TTG suggest partial melting of a heterogenous mafic crust derived from depleted mantle sources during the Paleo- to Mesoarchean. The Paleoproterozoic A-type granitoids with subchondritic eHft between -6.1 and -12.5 originated mainly from internal reworking of a heterogenous, predominantly Neoarchean felsic crust, between 1720 and 1705 Ma. Near chondritic Hf isotope composition of the ca. 1440 Ma Kishangarh nepheline syenite reflects derivation of the parental magma from enriched mantle sources.

Automated summary

The Central Aravalli Banded Gneissic Complex in northwest India is a Proterozoic terrane with Archean components, consisting of granulites, granitoids, TTG gneisses, and metasedimentary rocks. Zircon U-Pb-Hf isotopes and whole-rock geochemical data reveal a complex history of magmatic intrusions and crustal evolution in the region, with evidence of early Paleoarchean crust formation and later Grenville-age metamorphic events. The composition and origins of different rock types, such as Neoarchean TTGs and Paleoproterozoic A-type granitoids, provide insights into the geological processes that shaped the Aravalli orogen.