Petrology and Geochemistry of Appinites from Omalur Igneous Complex, Salem District, Tamil Nadu

Petrological and geochemical characters of two appinite intrusives associated with syenite and their related rocks occurring within the Omalur Igneous Complex of the Southern Granulite Terrain at Manathal and Seelakarattu Hamlets are presented here. Field observations imply their generation as small volume melts which were later emplaced into their host rock through pre-existing discontinuities. They are composed of phenocrystal hornblende, clinopyroxene and biotite enclosed within a matrix made up of second-generation mafic phases, alkali-feldspar, sodic-feldspar and minor plagioclase. Based on modal mineralogy, the Manathal appinite (Jl) is classified as monzonitic - appinite and the Seelakarattu appinite (Dl), as gabbroic - diorite appinite. Mantle compatible trace elements reflect a mantle influence, while the incompatible elements: LILE, HFSE and REE, suggest a subduction environment. Trace elements in the discussed appinites suggest involvement of crustal and mantle components in their genesis. Trace element ratios imply different degrees of partial melting from metasomatized protoliths/sources. The observed geochemistry of these appinites implies that they are not co-magmatic. These appinites are suggested to have been derived from evolved, hydrous parental melts unrelated to the parental melts of their host rocks. They are also, not products of late stage or residual hydrous melts of their host rocks. The appinites described in this study are suggested to be related to a pre-plate collisional (Dl) to post - collisional subduction (Jl) tectonic setting.Their presence within the Southern Granulite Terrain suggests their use as possible tectonic markers and are assumed to be the last set of hybrid mafic intrusives emplaced within their host rocks.