Regional geothermobarometry in the granulite facies terrane of South India

Abstract

In the southern part of the Archaean craton of South India, an approximately 3.4–2.9 b.y. old migmatite–gneiss terrane (Peninsular gneiss complex) has been subjected to granulite facies metamorphism about 2.6 b.y. ago. During this event, the extensive charnockite-khondalite zone of southern India developed. A younger metamorphism (Proterozoic?) led to retrogression of the charnockites and khondalites, mainly under the conditions of the amphibolite facies.The physical conditions of metamorphism have been evaluated by applying methods of geothermobarometry to the widespread charnockitic assemblages with garnet, orthopyroxene, clinopyroxene, plagioclase, and quartz. The interpretation of the P–T estimates includes a critical discussion of potential error sources, e.g. errors of the analytical data and the calibrations of the models, and takes into account the complex metamorphic history of the rocks and the kinetics of the mineral equilibria.P-T estimates were obtained for seven subareas from the rim compositions of the coexisting minerals: Shevaroy Hills 680±55°C—7·4±1 kb; Kollaimalai area 680±40°C—8·6± 1 kb; Nilgiri Hills 680±90°C—6·6±0.8kb (upland massif) and 705±60°C—9·3±0.8 kb (northern margin); Bhavani Sagar area 650±50°C—7·2± 1 kb; Sargur-Mysore area 690±60°C—7·6 kb; Bangalore-Kunigal-Satnur area 760±50°C—6 kb. Except for the last subarea, the P-T model data reflect the conditions of a late annealing stage probably related to the retrogressive metamorphism. Conditions near the peak of granulite facies metamorphism (730–800°C—6·5–9·5 kb) are recorded by the core compositions of the minerals. Although a rather uniform cooling history of the main part of the charnockite-khondalite terrane is suggested from the temperature data, differential uplift of smaller blocks is indicated by the regional variation of the pressure data.

Finding the targets of T cells gone bad

“…which the superconducting cuprates have been studied since their discovery (1), direct information about changes in their atomic and electronic structures in the vicinity of the transition temperature is largely lacking, and the mechanism of superconductivity in these materials is still uncertain (2). Copper K-edge x-ray absorption spectroscopy (XAS) measurements have shown that chemical modification of YBa2Cu3O7 (for example, by doping) results in small differences in the x-ray absorption near-edge structure (XANES) indicative of corresponding dunges in structural properties (3).…”

“…Intracrustal compression and crustal melting at 2600 to 2500 Ma produced zones ofhigh strain, deformed the E. J. Krogstad schist belts, caused regional, transgressive, granulite-grade metamorphism, and produced a suite of crustally derived, highpotassium granites (1)(2)(3)(4)(5)(6)(7)(8).…”

Palaeopressures of South Indian two‐pyroxene garnet granulites from thermochemically calibrated CMAS barometers

“…These 'ideal two-site' models are originally from Wood & Banno (1973) and have been used numerous times by subsequent workers (e.g. Wells, 1979;Raith et al, 1982;Bohlen et al, 1983). Recent modelling of orthopyroxene activities from experimental phase equilibria indicates near-adherence to the ideal two-site model (Davidson & Lindsley, 1985) or small positive departures (activities slightly higher than mole fractions: Sack & Ghiorso, 1989;Bhattacharya et al, 1991), as shown in Fig.…”

A retrogressive sapphirine-cordierite-talc paragenesis in a spinel-orthopyroxenite from southern Karnataka, India

“…However, they note that no granulite facies mineralogies were found either in host amphibolites, attributing this to more hydrous recrystallisation, or in the adjacent quartzo-feldspathic gneisses. In a detailed study of the nearby amphibolite-granulite facies transition zone, PT estimates between 635-864 ~ and 7.3-12.1 kbar were obtained from a variety of basic rocks dominated by granulite facies assemblages (Raith et al, 1983). Whilst the Gundlupet area is closer to the charnockitic region to the southeast (Fig.…”