Carbonatite melts derived from the mantle are enriched in CO2- and H2O-bearing fluids. This melt can metasomatize the peridotitic lithosphere and liberate a considerable amount of CO2. Experimental studies have also shown that a CO2–H2O-rich fluid can form Fe- and Mg-rich carbonate by reacting with olivine. The Sung Valley carbonatite of NE India is related to the Kerguelen plume and is characterized by rare occurrences of olivine. Our study shows that this olivine is resorbed forsterite of xenocrystic nature. This olivine bears inclusions of Fe-rich magnesite. Accessory apatite in the host carbonatite contains CO2–H2O fluid inclusions. Carbon and oxygen isotopic analyses indicate that the carbonatites are primary igneous carbonatites and are devoid of any alteration or fractionation. We envisage that the forsterite is a part of the lithospheric mantle that was reprecipitated in a carbonatite reservoir through dissolution–precipitation. Carbonation of this forsterite, during interaction between the lithospheric mantle and carbonatite melt, formed Fe-rich magnesite. CO2–H2O-rich fluid derived from the carbonatite magma and detected within accessory apatite caused this carbonation. Our study suggests that a significant amount of CO2 degassed from the mantle by carbonatitic magma can become entrapped in the lithosphere by forming Fe- and Mg-rich carbonates.

中文翻译：

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镁橄榄石再沉淀和岩石圈地幔与碳酸盐熔体相互作用过程中的二氧化碳截留：来自印度东北部梅加拉亚邦松谷超镁铁-碱性-碳酸岩复合体的案例研究

源自地幔的碳酸岩熔体富含二氧化碳2- 和 H2O 轴承流体。这种熔体可以交代橄榄岩岩石圈并释放出大量的二氧化碳2. 实验研究还表明，CO2-H2富氧流体与橄榄石反应可形成富铁和富镁碳酸盐。印度东北部的 Sung Valley 碳酸盐岩与 Kerguelen 羽流有关，其特点是罕见的橄榄石。我们的研究表明，这种橄榄石是异晶性质的再吸收镁橄榄石。这种橄榄石含有富铁菱镁矿的包裹体。主体碳酸岩中的辅助磷灰石含有 CO2-H2O 流体包裹体。碳和氧同位素分析表明，碳酸盐岩是原生火成碳酸盐岩，没有任何蚀变或分馏。我们设想镁橄榄石是岩石圈地幔的一部分，通过溶解-沉淀在碳酸岩储层中再沉淀。这种镁橄榄石的碳化，在岩石圈地幔和碳酸岩熔体相互作用的过程中，形成了富铁菱镁矿。一氧化碳2-H2源自碳酸岩岩浆并在辅助磷灰石中检测到的富氧流体导致了这种碳化。我们的研究表明，大量的 CO2碳酸盐岩岩浆从地幔中脱气后，可通过形成富含铁和镁的碳酸盐而被困在岩石圈中。