Late Paleoproterozoic magmatism in Delhi Fold Belt, NW India and its implication: evidence from EPMA chemical ages of zircons

Abstract

Zircons from six granitoid plutons, occurring in the northern part of the Delhi Fold Belt, NW India, have been chemically dated using an electron microprobe. Most of the zircons occurring in the granites are chronologically unzoned and gave ages around 1.78–1.71 Ga, but younger ages of 1.1–0.9 Ga have also been obtained from the rim of some grains. Monazite and zircons from the metasediments of Delhi Supergroup adjacent to the granitoids were also analyzed. The older age of 1.9–1.7 Ga obtained for monazites could possibly indicate their provenance age. Detrital zircon grains (mostly rounded) in the Delhi metasediments, which gave older ages of >1.9 Ga could possibly have been derived from the Archaean basement rocks exposed in this Aravalli Delhi Fold Belt. The geochemical signatures of these granitoids are consistent with an extensional tectonic regime. It is quite likely that contrary to the prevailing assumption of the granitoids being ‘intrusive’, our geochronologic data suggests them to be the basement for sedimentation. The new geochronologic information on these granitoids in the northern part of the Delhi Fold Belt and their comparison with other correlative events establishes a widespread thermal event during late Paleoproterozoic.