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°C. The &dgr;13C and &dgr;18O values of calcite are homogenous, implying equilibration of the isotopes during metamorphism. However, the &dgr;13C values of single graphite crystals show variations in the order of 1‰ 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 &dgr;13C values than the rims. The fractionation between calcite and graphite cores gives the highest metamorphic temperature of about 1060°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°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.

中文翻译：

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印度南部马杜赖麻粒岩中的超高温变质作用：来自碳同位素温度测定法的证据

使用方解石-石墨同位素交换温度计验证了印度南部麻粒岩地块马杜赖地块的超高温（UHT）变质作用。碳同位素测温法已被应用于据报道的蓝宝石麻粒岩产地附近的大理石，其温度估计值约为 1000°C。方解石的 &dgr;13C 和 &dgr;18O 值是同质的，这意味着在变质过程中同位素平衡。然而，单个石墨晶体的 &dgr;13C 值在手标本中显示出 1‰ 数量级的变化。详细的同位素分带研究表明，石墨在其冷却过程中保留了时间积分的晶体生长历史或再平衡分馏。石墨芯保持比轮辋更高的 &dgr;13C 值。方解石和石墨核之间的分馏给出了约 1060°C 的最高变质温度，这与高镁质泥质岩中岩石学推断的温度估计值相匹配。石墨边缘和方解石之间的分馏表明温度约为 750°C，这被解释为反映了逆行冷却。这一事件也在蓝宝石麻粒岩中观察到。因此，方解石-石墨温度测量法为定义麻粒岩地形中的 UHT 变质作用提供了有用的工具。这被解释为反映逆行冷却。这一事件也在蓝宝石麻粒岩中观察到。因此，方解石-石墨温度测量法为定义麻粒岩地形中的 UHT 变质作用提供了有用的工具。这被解释为反映逆行冷却。这一事件也在蓝宝石麻粒岩中观察到。因此，方解石-石墨温度测量法为定义麻粒岩地形中的 UHT 变质作用提供了有用的工具。