The Nagercoil Granulite Block, southern India: petrology, fluid inclusions and exhumation history

U–Pb electron probe geochronology of the Nagercoil granulites, Southern India: Implications for Gondwana amalgamation

“…Detailed petrologic, pressure-temperature and fluid inclusion studies of the charnockites and associated rocks from the Nagercoil granulites, including those from many of the locations included in the present study, were recently reported by us in a separate study (Santosh et al, 2003a). The results indicate that the rocks in Nagercoil granulites have been subjected to granulite facies metamorphism at high temperature and medium pressure conditions, in the presence of CO 2 as the ambient fluid species.…”

“…5, which has a distinct maximum at 565 Ma. The younger rims are unlikely to be caused by marginal Pb diffusion because the theoretical blocking temperature of Pb in monazite (O900 8C, Cherniak and Watson, 2001) is close to the maximum temperature thought to have been experienced by these rocks (Santosh et al, 2003a). Instead, these rims are interpreted to represent recrystallised monazite, or new monazite that grew isostructurally mantling pre-existing monazite on the retrogression path, possibly in concert with CO 2 or H 2 O fluid circulation (Mahadevan, 2003).…”

“…Detailed field studies in the Nagercoil region, along the contact zone of the massive charnockites with metapelites of the adjacent KKB (Tagawa, 2004), indicate that interlayered charnockite-metasedimentary sequences are limited to the contact region, and towards the centre of the charnockite massif, recognisable supracrustal rocks are rare or absent. At the southwest border of the unit, the charnockites contain enclaves of garnet-biotite gneiss (leptynite), garnetsillimanite-cordierite-spinel metapelite (khondalite) and minor calc-silicate rocks that have been interpreted as xenoliths (Santosh et al, 2003a).…”

“…The region incorporates a collage of polymetamorphic terrains with long-lived tectonic histories from Early Archaean to earliest Palaeozoic dissected by major shear zones that were active in the Neoproterozoic and early Palaeozoic, some of these are locales of important mineralisation (Drury et al, 1984;Harris et al, 1994;Santosh et al, 2003a;Santosh and Collins, 2003). The Peninsular Shield of southern India comprises an Archaean cratonic nuclei (the Dharwar craton) bound to the south by a Proterozoic mobile belt of predominantly high-grade rocks and punctured by several magmatic plutons.…”

“…The Trivandrum Block comprises metasedimentary gneisses of the Kerala Khondalite Belt (KKB, Chacko et al, 1992) and the charnockitic granulites of the Nagercoil region in the south. The Nagercoil granulites are lithologically different from the rocks of the remainder of the Trivandrum Block and were isolated as a third tectonic block (the Nagercoil Granulite Block) by Santosh et al (2003a). Here, we include it within the Trivandrum Block as the tectonic boundary between the two units is still unclear.…”