Chemical reactions between carbonates and pyrolite mantle and the origin of ultra-deep diamonds

尽管在地幔条件下进行了许多研究，但对主要的下地幔硅酸盐--布里奇曼石(地球上最丰富的矿物)和CaSiO_3钙钛矿中的碳溶解和/或碳-硅替代作用知之甚少(如果有的话)。我们和其他小组对碳酸盐在高压和高温下的行为进行了调查(在第一个资助期的框架内)，发现形成了许多含有CO4-单元的化合物。这些工作指出，在约70 GPa和2000K以上的碳酸盐的晶体化学发生了剧烈的变化。对硅酸盐和含碳体系的新观察有力地表明，碳可能包含在镁、铁、铝或钙硅酸盐钙钛矿中，甚至可能在下地幔最下部形成硅酸盐-碳酸盐相(S)，也可能在地球形成早期的其他地区，当温度较高时。因此，该项目的主要目标之一是在地球下地幔条件下，对(Mg，Fe)(Si，Al)O_3(桥锰矿)和CaSiO_3钙钛矿中可能的碳掺入和/或同时含有CO4和SiO_6基团的复杂化合物的形成进行实验研究。如果碳真的能溶解在硅酸盐钙钛矿中，这将对我们理解深层碳循环、可能的深层碳库以及能够在地球深处循环大量碳的过程产生重大影响。

Despite the number of studies performed at conditions of the Earth's mantle, very little (if something at all) is known about the carbon solubility and/or carbon-silicon substitution in major lower mantle silicates - bridgmanite (the most abundant mineral in the Earth) and CaSiO3 perovskite. Our and other groups investigations (in framework of the first funding period) of carbonate's behaviour at high pressures and temperatures reveal the formation of numerous compounds containing CO4-units. These works pointed out drastic changes in the crystal chemistry of carbonates above approximately 70 GPa and 2000 K. The novel observations on silica and carbon-bearing systems strongly suggest carbon may possibly be incorporated in Mg-, Fe-, Al-bearing or Ca-silicate perovskites, or even form silicate-carbonate phase(s) in the lowermost part of the lower mantle, and maybe in other regions of the Earth in its earlier stages of formation, when temperatures were higher. One of the major aims of this project is therefore the experimental investigation of possible carbon incorporation in (Mg,Fe)(Si,Al)O3 (bridgmanite) and CaSiO3 perovskite and/or the formation of complex compounds, containing both CO4 and SiO6 groups, at conditions of Earth's lower mantle. If carbon can really dissolve into silicate perovskites, it would have a major impact on our understanding of the deep carbon cycle, possible deep carbon reservoirs, and processes which may be capable of recycling a big amount of carbon deep inside the Earth.