The Southern Granulite Terrane in southern India preserves evidence for regional-scale high to ultrahigh temperature metamorphism related to the amalgamation of the supercontinent Gondwana. Here we present accessory mineral (zircon and monazite) geochronological and geochemical datasets linked to the petrological evolution of the rocks as determined by phase equilibria modelling. The results constrain the duration of high to ultrahigh temperature (> 900 °C ) metamorphism in the Madurai Block to be c. 40 Ma with peak conditions achieved c. 60 Ma after the formation of an orogenic plateau related to the collision of the microcontinent Azania with East Africa at c. 610 Ma. A 1D numerical model demonstrates that the attainment of temperatures > 900 °C requires that the crust be moderately enriched in heat producing elements and that the duration of the orogenic event is sufficiently long to allow conductive heating through radioactive decay. Both of these conditions are met by the available data for the Madurai Block. Our results constrain the length of time it takes for the crust to evolve from collision to peak P–T (i.e. the prograde heating phase) then back to the solidus during retrogression. This evolution illustrates that not all metamorphic ages date sutures.
We thank Michael Brown and Brad Hacker for their constructive comments. We are particularly grateful to Rebecca Jamieson whose detailed review led to significant improvements in the manuscript. Kevin Blake at James Cook University is thanked for assistance in the use of the electron microprobe. CC and RT acknowledge support from Curtin University Strategic Research Funding. Funding for analyses and fieldwork was provided through Australian Research Council Discovery and DECRA projectsDP0879330 and DE1201030 and Australia-India Strategic Research Fund project #ST030046. Zircon and monazite U–Pb analyses were carried out using the SHRIMP-II Ion Microprobe at the John de Laeter Centre for Isotope Research, Perth, managed by Allen Kennedy on behalf of a consortium consisting of Curtin University, the Geological Survey of Western Australia, and the University of Western Australia with the support of the Australian Research Council. REE analyses were carried out at the LA-ICP-MS Facility at the Dept. of Applied Geology at Curtin University. ASC acknowledges funding from the Australian Research Council Future Fellowship Scheme # FT120100340. ASC's contribution forms TRaX Record #306. This is contribution 513 from the ARC Centre of Excellence for Core to Crust Fluid Systems (http://www.ccfs.mq.edu.au).
- Phase equilibria modelling
- U–Pb geochronology
- High temperature metamorphism
- Gondwana supercontinent
- southern India