The Kodaikanal region of the Madurai Block in southern India exposes a segment of high-grade metamorphic rocks dominated by an aluminous garnet-cordierite-spinel-sillimanite-quartz migmatite suite, designated herein as the Kodaikanal Metapelite Belt (KMB). These rocks were subjected to extreme crustal metamorphism during the Late Neoproterozoic despite the lack of diagnostic ultrahigh-temperature assemblages. The rocks preserve microstructural evidence demonstrating initial-heating, dehydration melting to generate the peak metamorphic assemblage and later retrogression of the residual assemblages with remaining melt. The peak metamorphic assemblage is interpreted to be garnet + sillimanite + K-feldspar + spinel + Fe-Ti oxide + quartz + melt, which indicates pressure-temperature (P-T) conditions around 950-1000 °C and 7-8 kbar based on calculated phase diagrams. A clockwise P-T path is proposed by integrating microstructural information with pseudosections. We show that evidence for extreme crustal metamorphism at ultrahigh-temperature conditions can be extracted even in the cases where the rocks lack diagnostic ultrahigh-temperature mineral assemblages. Our approach confirms the widespread regional occurrence of UHT metamorphism in the Madurai Block during Gondwana assembly and point out the need for similar studies on adjacent continental fragments.
Bibliographical noteFunding Information:
One of the field sessions for this study was supported by a project led by M. Yoshida. We are grateful to the journal reviewers Dave E. Kelsey, Ian S. Buick and Toshiaki Tsunogae for their critical, detailed and very constructive review which greatly aided in improving an earlier version. We are also thankful to an anonymous reviewer who provided informal but very useful review which improved the quality of this work. We are thankful for the critical comments and corrections from Ingo Braun on an early draft. We thank Profs. T. Itaya and Y. Osanai for facilities and encouragement. We acknowledge support through Grant-in-aid for JSPS Fellows (Krishnan Sajeev, No: P05066) and the Grant-in-Aid for Scientific Research from the Ministry of Education, Culture, Sports, Science and Technology, Japan (M. Santosh, No. 17403013). This work is a contribution to Open Research Center, Okayama University of Science.
- Kodaikanal Metapelite Belt
- Southern India
- UHT metamorphism
ASJC Scopus subject areas
- Geochemistry and Petrology