Nine marble horizons from the granulite facies terrane of southern India were examined in detail for stable carbon and oxygen isotopes in calcite and carbon isotopes in graphite. The marbles in Trivandrum Block show coupled lowering of d 13 C and d 18 O values in calcite and heterogeneous single crystal d 13 C values (x1 to x10ù) for graphite indicating varying carbon isotope fractionation between calcite and graphite, despite the granulite facies regional metamorphic conditions. The stable isotope patterns suggest alteration of d 13 C and d 18 O values in marbles by in®ltration of low d 13 C±d 18 O-bearing¯uids, the extent of alteration being a direct function of the¯uid-rock ratio. The carbon isotope zonation preserved in graphite suggests that the graphite crystals precipitated/recrystallized in the presence of an externally derived CO 2 -rich¯uid, and that the in®ltration had occurred under high temperature and low f O 2 conditions during metamorphism. The onset of graphite precipitation resulted in a depletion of the carbon isotope values of the remaining¯uid+calcite carbon reservoir, following a Rayleigh-type distillation process within¯uid-rich pockets/pathways in marbles resulting in the observed zonation. The results suggest that calcite±graphite thermometry cannot be applied in marbles that are affected by external carbonic¯uid in®ltration. However, marble horizons in the Madurai Block, where the effect of¯uid in®ltration is not detected, record clear imprints of ultrahigh temperature metamorphism (800±1000 uC), with fractionations reaching <2ù. Zonation studies on graphite show a nominal rimward lowering d 13 C on the order of 1 to 2ù. The zonation carries the imprint of¯uid de®cient/absent UHT metamorphism. Commonly, calculated core temperatures are >1000 uC and would be consistent with UHT metamorphism.

The appropriateness of Zr as an 'immobile element' during garnet-hornblende (Grt-Hbl) vein formation potentially caused by the Cl-rich fluid or melt infiltration under upper amphibolite facies condition is examined. The sample used is a Grt-Hbl vein from Brattnipene, Sør Rondane Mountains, East Antarctica that discordantly cuts the gneissose structure of the mafic gneiss.Modal analysis of the wall rock minerals combined with the quantitative determination of their Zr contents reveals that most of the whole-rock Zr resides in zircon whereas~5% is hosted in garnet and hornblende. The Zr concentration of garnet and hornblende is constant irrespective of the distance from the vein. Zircon shows no resorption or overgrowth microstructures. Moreover, the grain size, chemical zoning (CL, Th/U ratio and REE pattern) and rim ages of zircon are also similar irrespective of the distance from the vein. LA-ICPMS UPb dating of zircon rims does not give younger ages than the granulite facies metamorphism reported by previous studies. All of these detailed observations on zircon support that zircon is little dissolved or overgrown, and that Zr is not added nor lost during the Grt-Hbl vein formation. Therefore, Zr can be described as an appropriate 'immobile element' during the Grt-Hbl vein formation. Detailed microstructural observation of zircon is thus useful in evaluating the appropriateness of Zr as an immobile element.

Ultrahigh-temperature (UHT) metamorphism in the Madurai Block of the southern Indian granulite terrain has been verified using the calcite-graphite isotope exchange thermometer. Carbon isotope thermometry has been applied to marbles from a locality near the reported occurrence of sapphirine granulites that have yielded temperature estimates of around 1000 degrees C. The delta(13)C and delta(18)O values of calcite are homogenous, implying equilibration of the isotopes during metamorphism. However, the delta(13)C values of single graphite crystals show variations in the order of 1 per thousand within a hand specimen. Detailed isotopic zonation studies indicate that graphite preserves either the time-integrated crystal growth history or reequilibrium fractionation during its cooling history. The graphite cores preserve higher delta(13)C values than the rims. The fractionation between calcite and graphite cores gives the highest metamorphic temperature of about 1060 degrees C, which matches the petrologically inferred temperature estimates in the high-magnesian pelites. The fractionation between graphite rims and calcite suggests a temperature of around 750 degrees C, which is interpreted to reflect retrograde cooling. This event is also observed in the sapphirine granulites. Calcite-graphite thermometry thus provides a useful tool to define UHT metamorphism in granulite terrains.