Petrochronological evolution of Mg-Al granulites and associated metapelites from the contact zone of the Archean Bastar Craton and Proterozoic Eastern Ghats Province, and its implications

Abstract

• Mg-Al granulites and khondalites in the Bastar Craton-Eastern Ghats Belt interface. • Ultrahigh-temperature peak metamorphic conditions along a clockwise P-T path. • Mg-Al granulites record decompression-cooling from 8.5kbar, 925°C to 5.5kbar, 770°C. • Texturally controlled in-situ monazite dating reveal two distinct age populations. • Tonian age amalgamation of the Bastar craton with the EGP and subsequent reworking. Mg-Al granulites and associated metapelites occurring in a shear zone at the contact of the Archean Bastar Craton and the Proterozoic Eastern Ghats Province (EGP) have been studied here. Reaction textures, geothermobarometry and P-T pseudosection studies reveal that the rocks record ultrahigh peak temperatures (>900°C) at pressures of 8-8.5 kbar and were exhumed along a retrograde decompression-cooling trajectory reaching ∼770°C and 5-6 kbar following an overall clockwise P-T path. Texturally constrained in-situ monazite chemical dates establish the age of peak metamorphism at 920 ± 11 Ma. Another prominent age cluster is at ∼500 Ma, which is ascribed, on the basis of petrographic characteristics, to tectonothermal reworking in the presence of reactive fluid. UHT metamorphism at ∼920 Ma along a clockwise path and extensive amphibolite facies reworking accompanying fluid infiltration at ∼500 Ma for the studied rocks contrast with the known petrological history of the EGP. We tentatively correlate these features in the contact shear zone to Tonian age amalgamation of the Bastar Craton with the EGP and subsequent tectonothermal reworking, aided by fluid infiltration, during the Kuunga orogeny.