Metamorphic History of Calc-Silicate Lithologies from the Kambam Valley, Tamil Nadu and its bearing on the Evolution of the Southern Granulite Terrain

Kambam valley forms an integral part of the Southern Granulite Terrain. The valley represents a deep crustal break hosting high temperature alkaline intrusives and also a carbonatite body. Common rock types encounterd are charnockite and granulite grade calc-silicate and metapelite. Calc-silicate lithologies are interbanded with mafic granulites on cm scale. Wolfastonite-scapolite-grandite garnet-clinopyroxene indicate high temperature (900°C). Corroborative high temperatures are recorded from associated rnetapelites. Textural features such as the formation of coronal garnet and garnet-quartz double rinds at the expense of calcite, scapolite, wollastonite, clinopyroxene suggest a late isobaric cooling at shallower depths. The cooling event was associated with domainal variation in fluid species. Fluid inclusion studies confirm a late carbonic fluid flux consistent with the carbonation reactions that followed.

The associated metapelitic lithologies in the area preserve textural evidence for a rapid high temperature decompression event. The Kambam valley granulites, thus witnessed high temperature metamorphism, rapid decompression and late isobaric cooling. The above metamorphic history is consistent with those reported from other parts of the Southern Granulite Terrain (SGT). Thermal perturbation associated with extensional thinning and alkaline magmatism explain the high temperature metamorphism, decompression and subsequent cooling.