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Authors
Affiliations
1 Department of Geology, Manasa Gangotri, Mysore 6, IN
2 Department of Geology, Franklin and Marshall College, Lancaster (Penn.), U. S. A, US
Source
Journal of Geological Society of India (Online archive from Vol 1 to Vol 78), Vol 26, No 3 (1985), Pagination: 163-176
Abstract
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 An60 and b) secondary plagioclase with An94 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 H2O content of the magma.
