Multiple tectonometamorphic imprints in the lower crust: first evidence of ca. 950Ma (zircon U-Pb SHRIMP) compressional reworking of UHT aluminous granulites from the Eastern Ghats Belt, India

• Published in: Geological journal (Chichester, England) Vol. 46; no. 2-3; pp. 217 - 239
• Main Authors: Das, Kaushik, Bose, Sankar, Karmakar, Subrata, Dunkley, Daniel J, Dasgupta, Somnath
• Format: Journal Article
• Language: English
• Published: 01.03.2011
• Subjects: Indexing in process
• ISSN: 0072-1050; 1099-1034; 1099-1034
• DOI: 10.1002/gj.1246

Integrated structural, petrological and geochronological study on a suite of granulites from the central part of the Eastern Ghats Belt (EGB), India unveils polyphase tectonothermal evolution. We document (a) M1 ultrahigh temperature (UHT) metamorphism (~1000 degree C at 6.5-8.5kbar) on an anticlockwise P-T trajectory simultaneously with early deformations D1-D2 involving partial melting, (b) cooling down to ~ 800 degree C, 6kbar that produced a variety of coronae/symplectites (M1R), (c) an unrelated compressional orogeny (D3) that produced deep crustal shears and mylonitic foliation (S3m) at low angles to D1-D2 structures and was associated with slight loading, and possible partial melt extraction under granulite facies condition (M2 ~7kbar, 850 degree C), and (d) localized retrogression (M3) in the presence of melt accompanying D4 deformation. This is the first record of the prograde P-T path of the superimposed granulite facies metamorphism in the EGB. U-Pb SHRIMP data of zircon preserves an inherited grain domain of ca. 1700Ma (207Pb-206Pb age) that traces back the history of EGB with a lineage of the Mesoproterozoic supercontinent, Columbia. The UHT metamorphosed (peakM1 at ca. 1000Ma) and subsequently cooled crustal segment (M1R) was subjected to strong tectonothermal reworking (M2) along a clockwise P-T path at 953+6Ma (concordia age) that partially exhumed the rocks to mid-crustal levels. A later fluid-induced retrogressive event vis-a-vis melt crystallization occurred at ca. 900Ma (207Pb-206Pb age). The post-peak evolution reveals striking similarities with those recorded in the rocks of the Rayner Complex of east Antarctica, thereby strengthening the notion of Indo-Antarctic correlation as part of Rodinia.