Experimental Studies of the Mechanism of Diamond Crystallization From COH Supercritical Fluid in SiO2-Rich Media

十年前，超高压变质岩中微金刚石的发现引发了对大陆碰撞沉积物认识的革命。已知两个概念来解释这种金刚石的起源：（1）从超临界COH流体中结晶;（2）从含流体的碱性碳酸盐熔体中结晶。传统上，复制天然金刚石形成的实验尝试是基于在高度还原的环境中在金属-碳系统中的合成。直到最近，在高P和T条件下天然金刚石的实验建模才扩展到H2O存在下的碱-碳酸盐-碳体系。我们已经建立实验，H2O是一种活性催化剂，促进金刚石结晶石墨在高压和高温下，孵化时间是依赖于溶液中的金属离子。 特别是，我们发现，镁促进成核和硅不。这项工作将扩展我们在金刚石合成方面的工作，重点是在COH-SiO2系统中在不同参数下的金刚石成核，如压力，温度，时间和氧逸度，以限制金刚石在石英长石质片麻岩和石英岩中生长的机制。超临界COH流体合成金刚石的实验研究是金刚石稳定性研究领域中一个新的但发展迅速的研究领域，对于理解大陆俯冲岩石中金刚石的结晶机制具有重要意义，并可能为金刚石的工业合成带来有趣的应用。

DobrzhinetskayaEAR-0229666The recognition of microdiamonds within ultra-high pressure metamorphic rocks a decade ago initiated a revolution in the understanding of continental collision terranes. Two concepts are known to explain the origin of such diamonds: (1) crystallization from a supercritical COH fluid; (2) crystallization from fluid-bearing alkaline-carbonate melt. Traditionally, experimental attempts to replicate natural diamond formation have been based on synthesis in metal-carbon systems in a highly reduced environment. Only recently has experimental modeling of natural diamonds at high P and T conditions been extended to the alkaline-carbonate-carbon system in the presence of H2O. We have established experimentally that H2O is an active catalyst promoting diamond crystallization from graphite at high pressure and high temperature and that incubation time is dependent on metal ions in solution. In particular, we find that Mg facilitates nucleation and Si does not. This work will extend our work in diamond synthesis with a focus on diamond nucleation in the COH-SiO2 system at varying parameters such as pressure, temperature, time and oxygen fugacity to constrain the mechanism of diamond growth in quartzofeldspathic gneisses and quartzites from ultra-high pressure metamorphic terranes. Experimental investigations related to diamond synthesis from supercritical COH fluid in the diamond stability field is a new but fast-growing research field of great importance for understanding of the mechanism of diamond crystallization within subducted rocks of continental affinity and may bring interesting application for industrial diamond synthesis.