11:45 AM - 12:15 PM
[SMP35-10] UHT metamorphism and tectonic models of Eastern Gondwana: problems and possibilities
Apart from the dry orthopyroxene bearing UHT granulites, hydrous-sapphirine granulties (gedrite-staurolite-cordierite bearing) are also reported from some of these terrains. Whether these rare, but important rocks have undergone UHT metamorphism is an area of debate. The timing of metamorphism is very much similar to that of other UHT occurrences though the sense of P-T path and assemblages are completely different. The relation between these sapphirine granulites and the orthopyroxene bearing sapphirne granultes are never discussed. Recent studies suggest the N-S trending UHT belt in Madurai Block as a terrane boundary, which will contradict all the existing concepts and models proposed from eastern Gondwana.
In this presentation, a comprehensive review is made on the UHT rock occurrences, their textural characteristics and variations, mineral chemical characteristics, thermodynamic constraints on P-T evolution and ages. Several models were proposed for the evolution of these terrenes though many of them contradict each other. The models include basaltic underplating, slab breakoff, ridge subduction, double subduction and self-heating through radiogenic sources. The presentation intends to evaluate these models along with its problems and other possibilities, and also looks forward to a possibly acceptable model for the pressure-temperature-time evolution of ultra-hot collisional orogeny during the assembly of Gondwana.