LAUSR

The depositional ages of two Proterozoic supracrustal belts, the older Aravalli Supergroup and the younger Delhi Supergroup, overlying the Aravalli Banded Gneissic Complex in NW India are still unresolved. This study presents new combined detrital zircon U–Pb and Lu–Hf isotope data of two quartzite successions from the Alwar complex of North Delhi Supergroup to constrain the depositional ages and Precambrian crustal evolution. The new results show about 90% of detrital zircon population at ca. 1850 Ma, with minor age peaks at ca. 2900, 2700, 2500 and 2200 Ma and older Eo- to Paleoarchean zircon grains at 3655 ± 20 and 3222 ± 27 Ma. The age peaks of 1850 and 2500 Ma correspond to the known magmatic events, while the detritus for others were derived from a so-far unknown crustal source(s) in the region. The data also suggest two metamorphic overprints at 1470–1420 Ma and ca. 1650 Ma, which are consistent with known events of metamorphism in the region. The zircon U–Pb ages, Hf isotopes and field relations indicate that the sedimentary protoliths of the studied quartzite were deposited at ca. 1750 Ma in a collisional setting after the emplacement of subduction-related ca. 1850 Ma granitoids, but prior to the intrusion of 1730–1700 Ma rift-related A-type granites. The regional correlations suggest that the quartzite successions are not part of the Alwar Group as currently considered, but that they apparently belong to the older Aravalli Supergroup. Largely subchondritic εHf values for most of the zircon population signify predominance of crustal reworking during Neoarchean and Paleoproterozoic. The Hf model ages of the Eoarchean zircon indicate the existence of an ancient crust at ca. 4000 Ma in the Aravalli orogen and/or its hinterland.