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大量的研究，但对于主要的下地幔硅酸盐-桥锰矿（地球上最丰富的矿物）和CaSiO3钙钛矿中的碳溶解度和/或碳硅取代知之甚少（如果有的话）。我们和其他研究小组（在第一个资助期的框架内）对碳酸盐在高压和高温下的行为进行了研究，揭示了许多含有二氧化碳单位的化合物的形成。这些工作指出，在大约70 GPa和2000 K以上，碳酸盐的晶体化学发生了剧烈的变化。对二氧化硅和含碳系统的新观察强烈表明，碳可能被合并到含镁、铁、铝或含钙的钙钛矿中，甚至在下地幔的最底部形成硅酸盐-碳酸盐相，甚至可能在地球其他地区形成早期阶段，当温度更高时。因此，该项目的主要目的之一是实验研究在地球下地幔条件下，（Mg,Fe）（Si,Al）O3（桥菱铁矿）和CaSiO3钙钛矿中可能存在的碳掺入和/或含有CO4和SiO6基团的复杂化合物的形成。如果碳真的可以溶解在硅酸盐钙钛矿中，它将对我们对深层碳循环的理解产生重大影响，可能的深层碳储层，以及可能能够在地球深处循环大量碳的过程。

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.