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In the Proterozoic complex of the Schirmacher region of East Antarctica, a retrograde pressure–temperature (P–T) history has been inferred through quantitative geothermobarometry and fluid inclusion studies of the mafic granulites. Microthermometric investigations of the fluid phases trapped in quartz and garnet identified three types of inclusions, namely, earliest pure CO2 inclusions (0·987–1·057 g cm−3), CO2–H2O inclusions and aqueous inclusions.The temperature and pressure of metamorphism have been estimated through different calibrations of geothermometers and geobarometers. The mineral reactions and compositional zoning in the minerals record P–T conditions from nearly 837 ± 26°C, 7·1±0·2 kbar to 652 ± 33°C, 5·9 ± 0·3 kbar. A good correlation between the fluid and mineral data is observed. The isochores typical of highdensity CO2 fluids fall well within the P–T box estimated by mineral thermobarometry. The abundance of primary CO2 inclusions in early metamorphic minerals (notably quartz and primary garnet) and the general correspondence between fluid and mineral P–T data indicate a ‘fluid-present’ carbonic regime for the high-grade metamorpism; however, from the present data largescale CO2 advection could not be envisaged. The subsequent stages involved a decrease in CO2 density, a progressive influx of hydrous fluids and the generation of retrograde amphibolite facies metamorphism in the area.The estimated P–T conditions of the region suggest that the rocks were metamorphosed at a depth of 19–24 km, with a geothermal gradient of c. 3°5C km−1. The estimated P–T conditions of the rocks imply a clockwise P–T–t path with a gradual decrease in temperature of around 250°C and a decrease in pressure of around 1700 bar. They have a dP/dT gradient of ≈7 ± l bar °C−1, arguing for an isobaric cooling history of the terrane under normal thickened crust after the underplating of mantle-derived material.

In the Lahaul-Spiti region of Himachal Pradesh two meta-granite bodies (Jispa granite and Ratilaman granite) emplaced in the low grade Haimanta Formation which is tectonically overlying the Central Crystallines. Field, petrographical and geochemical features of these meta-granites are compared with the orthogneisses of the Central Crystallines. Geochemical signatures of these meta-granites and orthogneisses suggest that they are products of peraluminous melt generated by partial melting of older crustal rock, with high A/CNK values and higher normative corundum. Decrease in Fe203, MgO, CaO, Ti02, Sr and Zr and enhancement in K20, Si02 and Rb as well as Rb/Sr ratios from melanocratic (margin) to leucocratic (core) portion of these bodies indicate that they are consistent with fractional crystallization processes. Decrease of total REE, moderate LREE/HREE ratios and more pronounced negative Eu anomalies are also in accord with fractional crystallization.The heat source for these lower Paleozoic granite magmas may be due to the lithospheric extension which resulted in mantle melting beneath the crust which led to anomalous heat flow, and triggered crustal melting. Felsic magmas thus produced have intruded into shallow crustal levels. INTRODUCTIONIn the Himalayan region the 500 Ma granitic emplacement is probably the most widespread phenomenon around the Cambro-Ordovician boundary and this event can be followed in some 5000 km distance across Antarctica upto central Australia (Le-Fort et al., 1986). These early Pa leozoic meta-granites are concentrated in the crystalline thrust sheets of Lesser Himalaya, in the Higher Himalayan Crystallines and also in the metamorphosed basal portions of the Tethyan sedimentary sequence. Meta-granite bodies belong to this period have also been reported from the northern Himalaya or Lhagoi-Kangri plutonic belts (Le-Fort et al., 1986).These early Paleozoic meta-granite bodies have common petrographical and geochemical charac teristics and they are peraluminous with high ini tial Sr isotopic ratio (Le-Fort et al., 1986). These early Paleozoic meta-granites in the NW-Himalaya have been deformed and metamorphosed during the Himalayan Orogeny.In this paper two such meta-granite bodies of lower Paleozoic age, namely, the Jispa and Ratilaman occurring in the low grade Haimanta Formation of Lahaul-Spiti region are taken up for their petrogenesis.The geochemistry of these meta-granites is compared with the orthogneisses occurring within the Rohtang gneissic complex (Higher Himalayan Crystallines) for source char acteristics and genetic relationships. GEOLOGICAL SETTINGThe Higher Himalayan Crystalline rocks of the Lahaul-Spiti region is classified into two main tectonic units, namely the lower Central Crystallines or the Rohtang gneissic complex and the upper Haimanta Formation (Fig. 1). These two units are separated by a thrust, designated as Tethyan thrust (Choudhury et al., 1992; Rawat and Thakur, 1988). In the southeast Zanskar and Lahaul region (part of the investigated area), (Fig. 1)...