U-Pb zircon geochronology of granites and charnockite from southern India: Implications for magmatic pulses associated with plate tectonic cycles within a Precambrian suture zone

Abstract

The Palghat-Cauvery Suture Zone (PCSZ) in southern India marks the trace along which continental blocks were sutured during the Precambrian. We report here U-Pb geochronological data based on laser ablation ICP mass spectrometry for zircons in two granite plutons and an associated charnockite from within the PCSZ. The weighted mean of206Pb/238U ages for a rapakivi granite from the southern part of the PCSZ yields 819±26Ma (error: 2σ; N=13). On the other hand, a metamorphosed A-type granite and a charnockite from the central part of the PCSZ yield a markedly older upper intercept age of 2468±36Ma (error: 2σ) and a lower intercept age of 588±36Ma (error: 2σ). Our results provide important constraints on the Precambrian crustal evolution in the PCSZ and demonstrate: (1) Neoarchaean to early Palaeoproterozoic magmatism, generating A-type granites which we correlate with a major global crustal formation event; (2) mid Neoproterozoic magmatism, and generation of the rapakivi granite, probably associated with the subduction of the Mozambique Ocean floor; and (3) latest Neoproterozoic high-grade metamorphism (generating the charnockite) associated with the collisional amalgamation of the Gondwana supercontinent. Together with the previous geochronological data from the PCSZ and adjacent crustal blocks, our results provide information on magmatic pulses associated with the Archaean cratonization event, as well as the Neoproterozoic Wilson Cycle of the Mozambique Ocean culminating in continent-continent collision.