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Petrology and Geochemistry of the Oddanchatram Anorthosite and Associated Basic Granulites, Tamil Nadu, South India

1985; Springer Science+Business Media; Volume: 26; Issue: 3 Linguagem: Inglês

10.17491/jgsi/1985/260301

0974-6889

A. S. Janardhan, Robert A. Wiebe,

Geological and Geochemical Analysis

Preliminary studies of the Oddanchatram anorthosite body, the largest of the bodies lying along a 100 km linear; on the northern slopes of Patni hilI ranges, show that it has all the chemical and mineralogical characters of Proterozoic massif anorthosites. Plagioclase compositions reveal two types: a) primary plagioclase of An 60 and b) secondary plagioclase with An 94 occurring as breakdown product of garnet. Estimates based on primary pyroxenes indicate intrusive temperatures between 960°C-1000°C; pressures of 5.3 kb. based on garnet breakdown products suggest a steep geothermal gradient. The chemistry suggests that the parental magma was unusually feldspathic; primary hornblende indicates a higher H 2 O content of the magma.