Carbon isotope compositions of fluid inclusions in charnockites from southern India
Carbon isotope compositions of fluid inclusions in charnockites from southern India
复制标题
印度南部霞多丽岩中流体包裹体的碳同位素组成
作者：
D. H. Jackson;D. Mattey;N. Harris
地壳麻粒岩的形成模式，包括无水岩性的变质作用1,2，吸湿花岗岩熔体的提取3,4和CO25-7的通量作用，限制了下地壳的热地球化学演化及其与地幔源挥发物的相互作用。本文采用阶梯燃烧/热裂解碳萃取技术，对来自印度南部早期炭斑岩采石场的片麻岩-麻粒岩对石英和石榴石流体包裹体中的CO2丰度和碳同位素组成进行了研究，该技术量化了有问题的样品污染，并实现了精确的岩性控制。结果表明，早期炭硝岩中的CO2比伴生片麻岩中的CO2更丰富，同位素质量更重，为其形成过程中富CO2流体的流入提供了证据。推断出的这些流体的碳同位素组成与地幔源一致，并且在Ponmudi，共存的石墨和CO2的同位素组成表明流体/岩石体积比超过0.15。
Models for the formation of crustal granulites, which include the metamorphism of anhydrous lithologies1,2, the extraction of hygroscopic granite melts3,4 and fluxing by CO25–7 constrain the thermal and geochemical evolution of the lower crust and its interaction with mantle-derived volatiles. Here we present abundances and carbon isotope compositions of CO2 in fluid inclusions in quartz and garnet from gneiss–granulite pairs from the incipient char-nockite quarries of southern India, determined by a stepped combustion/thermal decrepitation carbon–extraction technique, which quantifies problematic sample contamination and allows precise lithological control. The results show that the CO2 in incipient charnockite is more abundant and isotopically heavier than the CO2 in associated gneiss, providing evidence for the influx of CO2-rich fluids during their formation. The inferred carbon isotope compositions of these fluids are consistent with a mantle source, and at Ponmudi, the isotopic composition of coexisting graphite and CO2 implies fluid/rock volume ratios in excess of 0.15.