FLUID INCLUSIONS IN CHARNOCKITES FROM KODAIKANAL MASSIF (SOUTH-INDIA)- P-T RECORD AND IMPLICATIONS FOR CRUSTAL UPLIFT HISTORY

Citation
A. Mohan et al., FLUID INCLUSIONS IN CHARNOCKITES FROM KODAIKANAL MASSIF (SOUTH-INDIA)- P-T RECORD AND IMPLICATIONS FOR CRUSTAL UPLIFT HISTORY, Mineralogy and petrology, 57(3-4), 1996, pp. 167-184
Citations number
56
Categorie Soggetti
Mineralogy,"Geochemitry & Geophysics
Journal title
ISSN journal
09300708
Volume
57
Issue
3-4
Year of publication
1996
Pages
167 - 184
Database
ISI
SICI code
0930-0708(1996)57:3-4<167:FIICFK>2.0.ZU;2-B
Abstract
The Kodaikanal massif is part of a Precambrian terrane characterized b y granulite facies rocks. It is dominated by the widespread occurrence of charnockites. The observed textural relationships in these rocks a re consistent with the following main reactions: i. Biotite + Quartz = Orthopyroxene + Alkali feldspar +/- Garnet + Vapour ii. Garnet + Quar tz = Orthopyroxene + Plagioclase iii. Pyrope = Mg Tschermaks + Enstati te (in Opx) Garnet consuming reactions and the preservation of biotite -quartz-orthopyroxene-plagioclase symplectites are indicative of a dec ompression event. Progress of such reactions with decreasing pressure together with fluid inclusion data has implications for the constructi on of P-T vectors. Quartz from the charnockites contains the following fluid inclusions: (1) monophase high density CO2-rich (0.968/-1.014 g /cm(3)) as the dominant fluid phase; (2) aqueous biphase CO2-H2O (0.88 8-0.915 g/cm(3)) and (3) late minor aqueous H2O inclusions with no vis ible CO2. CO2-isochores for the high density fluid inclusions yield a pressure limit of ca. 6.5 kbars, at granulite facies temperatures of c a. 800 degrees C, which is in accordance with the estimation from mine ralogical thermobarometry. The P-T path delineated from combined miner alogical and density data on carbonic inclusions is characteristically T-convex suggesting an isothermal decompression path and rapid uplift followed by cooling of a tectonically thickened crust.