Fossil Pigeonites and Exsolution Features in Pyroxenes from Ferrosyenites of South India

Pigeonites are typically absent in slowly cooled plutonic rocks, and ortho-pyroxene is totally unkown in alkaline rocks. Ferrosyenites and ferrornonzosyenites of the Chimakurti (Andhra Pradesh) and Sivamalai (Tamil Nadu) areas in south India contain both ortho- and clino-pyroxenes exhibiting various exsolution and inversion textures. The present study on these textures demonstrates the rare presence of 'inverted pigeonites' suggesting very high initial crystallization temperatures for the host rocks and also offers unambiguous evidence for the sub-alkaline (tholeiitic) nature of the host rocks.