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首页> 外文期刊>Contributions to Mineralogy and Petrology >Magmatic graphite in dolomite carbonatite at Pogranichnoe, North Transbaikalia, Russia
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Magmatic graphite in dolomite carbonatite at Pogranichnoe, North Transbaikalia, Russia

机译：俄罗斯北Transbaikalia的Pogranichnoe的白云岩碳酸盐岩中的岩浆石墨

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摘要

A recently discovered dolomite carbonatite at Pogranichnoe, North Transbaikalia, Russia, dated at 624 ± 3 Ma, contains xenoliths of calcite-bearing dolomite carbonatite with graphite spherulites. Apatite and aegirine are the other rock-forming minerals. Chemically the carbonatites are ferrocarbonatite and ferruginous calciocarbonatite. The graphite forms <1 mm up to 1.5 mm diameter spherulites, with Raman spectra similar to published spectra of microcrystalline, amorphous carbon and disordered graphite, with G and D bands at 1,580?1,600 cm?1 and at around 1,350 cm?1. Alteration has formed Fe-bearing calcite to Ca-bearing siderite compositions not previously reported in nature around the graphite along cracks and fractures. Mineral and stable isotope geothermometers and melt inclusion measurements for the carbonatite all give temperatures of 700°–900°. It is concluded that the graphite precipitated from the ferrocarbonatite magma. There are three candidates to control the precipitation of graphite (a) a redox reaction with FeII in the magma, (b) potential presence of organics in the magma (c) seeding of, or dissolution in, the magma of graphite/diamond from the mantle, and further work is required to identify the most important mechanism(s). Graphite in carbonatite is rare, with no substantial published accounts since the 1960s but graphite at other localities seems also to have precipitated from carbonatite magma. The precipitation of reduced carbon from carbonatite provides further evidence that diamond formation in carbonate melts at high mantle pressures is feasible.
机译：最近在俄罗斯北Transbaikalia的Pogranichnoe上发现的白云石碳酸盐岩，年龄为624±3 Ma，其中含有方解石和石墨球石的异岩。磷灰石和a草碱是其他成岩矿物。化学上，碳酸盐为铁碳酸盐和铁质钙碳酸盐。石墨形成直径小于1毫米至1.5毫米的球晶，其拉曼光谱类似于已发表的微晶，无定形碳和无序石墨的光谱，其G和D谱带分别在1,580？1,600 cm？1 和约1,350 cm ？1 。蚀变已形成石墨中沿裂缝和断裂未曾报道过的含铁方解石至含钙菱铁矿成分。矿物和稳定的同位素地热仪以及对碳酸盐岩的熔融包裹体测量都给出了700°–900°的温度。结论是石墨从铁碳酸盐岩浆中析出。有三种控制石墨沉淀的方法：（a）岩浆中与FeII 的氧化还原反应，（b）岩浆中有机物的潜在存在（c）石墨岩浆的晶种或溶解/地幔中的/金刚石，还需要进一步的工作来确定最重要的机制。碳酸盐岩中的石墨很少见，自1960年代以来没有大量发表的记载，但是其他地方的石墨似乎也从碳酸盐岩岩浆中沉淀出来。从碳酸盐岩中还原碳的沉淀提供了进一步的证据，表明在高地幔压力下在碳酸盐熔岩中形成金刚石是可行的。

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