U–Pb and Lu–Hf Systematics of Zircons from Sargur Metasediments, Dharwar Craton, Southern India:New Insights on the Provenance and Crustal Evolution

Abstract

A study of U-Pb and Lu-Hf-Yb isotope data in zircons from metamorphosed psammopelite and quartzite from the type area of Archaean Sargur Group, Dharwar Craton, India is carried out. Two age populations are observed: an older population with concordant U-Pb ages between 2.7 and 2.8 Ga, and a younger population with ages in the 2.4-2.6 Ga age range. The Hf values of 0 to +2.0 for the older zircon population suggest that they were derived from juvenile crust formed at 2.7-2.8 Ga. Sub-chondritic Hf values for the younger population indicate metamorphism and/or crustal reworking at ~2.5 Ga. Metasedimentary enclaves in the Sargur type area are therefore part of the gneiss-supracrustal complex of different antiquities and may not have an independent stratigraphic status.

U–Pb and Hf isotope study of detrital zircon and Cr-spinel in the Banavara quartzite and implications for the evolution of the Dharwar Craton, south India

“…Our limited new geochronological results emphasize the need for further intensive U-Pb geochronology and Lu-Hf systematic studies of zircons in the Sargur Group supracrustal rocks in order to resolve the complex stratigraphic relationships of this group relative to the low-grade supracrustal rocks in the Dharwar greenstone belts. The current data endorse the interpretation by Maibam et al (2017) that the Sargur Group is a complex of rocks of more than one age, some pre-dating the Dharwar Supergroup and others of the same age as the Dharwar Supergroup.…”

“…We suggest from our data that the supracrustal rocks of the WDC were probably derived from the gneissic rocks of the Dharwar Craton. The combined geochronological data and current detrital zircon ages reinforce our earlier interpretation that not all Sargur supracrustal rocks were derived from >3.0 Ga crust (Maibam et al 2017), which contrasts with the commonly accepted 3.4 to 3.0 Ga age range for the Sargur Group (e.g. Naqvi & Rogers, 1987;Jayananda et al 2008Jayananda et al , 2015.…”

“…The new dataset reinforces the interpretation that the Sargur Group supracrustal enclaves are a combination of older (>3.0 Ga) and younger (<3.0 Ga) components (Maibam et al 2017). Not all enclaves in the gneiss terrain are older than those in the greenstone belt.…”

“…Hf isotope compositions of the 3.1 to 2.9 Ga zircons are chondritic to superchondritic (ϵHf ranging between þ0.8 and þ6.4) and juvenile in nature, which differs from younger zircons (<2.9 Ga) with subchondritic Hf isotopes. Our results and younger ages from the Sargur Group rocks (Hokada et al 2013;Maibam et al 2017) indicate that the Sargur Group supracrustal rocks were not derived from >3 Ga crust.…”

“…During the past decade, numerous U-Pb dating studies have been conducted on granitoid rocks of the Dharwar Craton using modern microbeam techniques (ion probe and laser ablation multi-collector/ quadrupole inductively coupled plasma mass spectrometry (LA-MC/Q-ICP-MS)). Although isotopic age datasets have outlined the geochronological framework of the formation and evolution of the Archaean gneissic continental crust of the Dharwar Craton (Maibam et al 2011(Maibam et al , 2016(Maibam et al , 2017Lancaster et al 2015;Guitreau et al 2017), the provenance study of metasediments of the Archaean supracrustal units is lacking.…”