NDLI: Origin and evolution of gneiss-charnockite rocks of dharmapuri district, tamil nadu, india

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Origin and evolution of gneiss-charnockite rocks of dharmapuri district, tamil nadu, india

Content Provider	NASA Technical Reports Server (NTRS)
Author	Rao, D. Rameshwar Narayana, B. L.
Copyright Year	1988
Description	A low- to high-grade transition area in Dharmapuri district was investigated petrologically and geochemically. The investigation confirmed the presence of a continuous section through a former lower crust, with felsic charnockites predominating the lower part and felsic gneisses the upper part. The structure of original gneisses is preserved in charnockites and the latter show petrographic evidence for prograde metamorphism. The prograde metamorphism is of isochemical nature as revealed by the similarity of compositions of tonalitic gneisses and tonalitic charnockites. However, the depletion of LIL elements particularly Rb, caused variation in K/Rb ratios from low values (345) in the gneisses in upper part to higher values (1775) in the charnockites in the lower crust. This variation in K/Rb ratio in a north to south traverse is related to the progressive break-down of hydrous minerals under decreasing H2O and increasing CO2 fluid conditions. Metasomatism and partial melting has also taken place to a limited extent along shear planes and weak zones. During cooling the H2O circulation affected substantial auto-regression in the transition zone resulting in the formation of second generation biotite.
File Size	106476
Page Count	2
File Format	PDF
Alternate Webpage(s)	http://archive.org/details/NASA_NTRS_Archive_19890012872
Archival Resource Key	ark:/13960/t2w42nk01
Language	English
Publisher Date	1988-01-01
Access Restriction	Open
Subject Keyword	Geophysics Water Fractionation Petrography Cooling Melting Mineralogy Crystallization Carbon Dioxide Gneiss Granite India Analogies Depletion Biotite Earth Crust Metamorphism Geology Ntrs Nasa Technical Reports Server (ntrs) Nasa Technical Reports Server Aerodynamics Aircraft Aerospace Engineering Aerospace Aeronautic Space Science
Content Type	Text
Resource Type	Article

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