Diamond formation in Earth's mantle: Role of C-O-H fluid composition and host rock lithology.

本研究的中心目标是确定岩石圈下环境中钻石形成的机制，这是了解地球深部碳循环的重要一步。破译钻石形成、氧化还原态和地幔岩性之间的耦合将有助于提高对钻石包裹体的区域差异及其与地球上升流和下升流机制的关系的理解。最近发现的深度低于300公里的钻石包裹体与辉石岩的强亲和力是特别有趣的。迄今为止，人们对辉石岩在钻石形成中的作用关注甚少。因此，本文将重点研究上地幔最下端和地球过渡带条件下辉石岩形成和钻石同生沉淀的机制。这也涉及到与氧化榴辉岩和衍生的部分熔体反应的C-O-H流体的系统分析。最后，为了理解钻石产率的显著差异，我们将研究等化学减压和冷却C-O-H流体的影响，以及等化学沉淀宏观钻石的能力，而不依赖于寄主岩石的组成。这一过程可以解释为什么黑氏岩中大型钻石的产量很高，否则它们就缺乏使钻石结晶的氧气缓冲能力。

The central goal of this study is to identify the mechanisms of diamond formation in sublithospheric environments, which is an important step towards the understanding of Earth s deep carbon cycle. Deciphering the coupling between diamond formation, redox state, and mantle lithologies will aid to improve the understanding of regional differences in diamond inclusions and their association with upwelling and downwelling regimes in Earth s. The very recently discovered strong affinity of diamond inclusions from depth below 300 km to pyroxenites is of peculiar interest. Up to the present, only little attention has been payed to the role of pyroxenites in the formation of diamonds. Hence, this study will focus on the mechanisms that are responsible for the formation of pyroxenites and the syngenetic precipitation of diamonds under conditions of the lowermost upper mantle and Earth s transition zone. This also involves the systematic analysis of C-O-H fluids reacting with oxidized eclogites and derived partial melts. Finally, to understand the striking difference in diamond yields, we will investigate the effect of isochemical decompression and cooling of C-O-H fluids and the capability to isochemically precipitate macroscopic diamonds independent from the host rock s composition. This process would explain high yields of large diamonds in harzburgitic rocks, that otherwise lack the oxygen buffer capacity to crystallize diamonds.