Detrital zircon U-Pb-Hf isotope record of conglomerates in the southern Aravalli orogen, NW India: Implications for stratigraphy, provenance and Archean to Paleoproterozoic crustal evolution

The inconsistent stratigraphic framework of the Proterozoic successions in the Aravalli orogen, NW India hinders the detailed reconstruction of its geodynamic evolution during the Archean to Paleoproterozoic. In this study, we present new results of combined U-Pb-Hf isotope data of detrital zircon grains of two conglomerate samples from the southern Aravalli orogen, presently assigned to the upper unit of the Aravalli Supergroup. The youngest concordant zircon grains in both the conglomerates yield concordia ages of 1735 +/- 13 Ma (n = 2) and 1736 +/- 15 Ma (n = 2), respectively, interpreted as maximum ages of deposition. Older zircon grains mostly reveal Neoarchean to Paleoproterozoic age clusters at 2560-2550, 1870-1860 and 1760-1740 Ma, and minor Paleo-archean ages between 3558 +/- 17 Ma and 3239 +/- 14 Ma, corresponding to known magmatic events in the Aravalli orogen. Most detrital zircon grains show subchondritic epsilon Hft values (+6 to-20), signifying minor reworking of late Hadean/Eoarchean crust during the Paleoarchean, and substantial reworking of Paleo-to Neoarchean crust during the late Neoarchean and Paleoproterozoic, with only minor juvenile input. The maximum depositional ages indicate that the investigated conglomerates were deposited either synchronous or after the emplacement of extension-related A-type granites, which intruded the Aravalli orogen between 1733 +/- 9 Ma and 1703 +/- 5 Ma. Furthermore, the data suggest that the conglomerates do not belong to the upper Aravalli unit as envisaged by previously published stratigraphic concepts. Instead, these were deposited earlier, during opening of a rift-related basin, grading from a terrestrial into a marine environment, contemporaneous with other sedimentary successions exposed in the North Delhi basin, which are presently assigned to the North Delhi Supergroup. The compiled zircon age-Hf isotope data additionally provide evidence for a series of late Hadean to Archean juvenile crust formation events in hinterland of the Aravalli orogen at 4200-3300 Ma for east Indian cratonic blocks and 3550-3100 Ma for northern and southern cratonic nuclei, and 2700-2500 Ma all over India. Substantial crustal reworking took place during the late Neoarchean at 2500 Ma, and the late Paleoproterozoic at 1850 Ma and 1730-1700 Ma.

Automated summary

The inconsistent stratigraphic framework of the Proterozoic successions in the Aravalli orogen hinders the reconstruction of its geodynamic evolution. This study provides new results of detrital zircon grains from conglomerate samples, revealing their maximum depositional ages and indicating the earlier deposition of these conglomerates compared to previous concepts. The zircon age-Hf isotope data also provide evidence for a series of crust formation and reworking events in the Aravalli orogen and all over India.