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

这项研究的中心目标是确定岩石圈下环境中金刚石的形成机制，这是理解地球深部碳循环的重要一步。解读金刚石形成、氧化还原状态和地幔岩性之间的耦合关系，将有助于提高对金刚石包裹体区域差异及其与地球上涌和下涌机制之间关系的认识。最近发现的金刚石包裹体从深度低于300公里的辉石的强烈亲和力是特别感兴趣的。辉石岩在金刚石形成过程中的作用，迄今为止还很少受到人们的重视。因此，本研究的重点是在上地幔最下部和地球过渡带条件下，辉石岩的形成机制和金刚石的同生沉淀。这也涉及到与氧化榴辉岩和衍生部分熔体反应的C-O-H流体的系统分析。最后，为了理解金刚石产率的显著差异，我们将研究C-O-H流体的等化学减压和冷却的效果，以及等化学沉淀宏观金刚石的能力，而不依赖于寄主岩石的成分。这个过程可以解释方辉岩中大钻石的高产率，否则缺乏氧气缓冲能力来结晶钻石。

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.