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The evolution of deeply subducted carbonates and the formation of microdiamonds

深俯冲碳酸盐岩的演化和微金刚石的形成

基本信息

批准号：
15204050
负责人：
OGASAWARA Yoshihide
金额：
$ 20.05万
依托单位：
Waseda University
依托单位国家：
日本
项目类别：
Grant-in-Aid for Scientific Research (A)
财政年份：
2003
资助国家：
日本
起止时间：
2003 至 2005
项目状态：
已结题

来源：
https://kaken.nii.ac.jp/en/grant/KAKENHI-PROJECT-15204050/
关键词：
UHP metamorphic rock microdiamond deep continental subduction carbonate dolomite intraslab UHP metasomatism 流体 UHP metamorphism diamond C isotope carbonate coesite exsolution dolomite aqueous fluid intraslab UHP metasomatism

项目摘要

This study revealed the evidence for the aqueous fluid recycling in the continental materials during deep subduction to form UHP metamorphic rocks and for the metasomatism under UHP conditions. Intraslab UHP metasomatism model was proposed to explain these processes occurred in natural UHP metamorphic rocks. Multicomponent aqueous fluid released from subducted silicate rocks had been infiltrated into carbonate layers and had led to strong metasomatism. During such a metasomatism process, abundant microdiamond could form in carbonate rocks, particularly dolomite marble. Several components could be solved in recycled aqueous fluids under UHP conditions ; TiO2 was one of the representative one. In the Kokchetav UHP metamorphic rocks, Ti-clinohumite occurs in diamond-free UHP dolomitic marble, and the origin of TiO2 in clinohumite could be a solved component in aqueous fluid indicating high H2O activity. This suggest that diamond could be unstable under very high H2O activity even in carbo … More nate rocks and carbon could dissolve into fluid phase. Diopside in this rock contains over 850ppm of H2O as hydroxyl on the basis of micro-FT-IR study. This also means diamond-free dolomitic marble could form under very high H2O activity conditions. Diopside in this marble does not contain K2O-bearing exsolved phases contrary to diamond-bearing dolomite marble. Not only the bulk K2O composition, the solubility of K2O in aqueous fluid under UHP conditions might control the presence of exsolved lamellae in diopside, and probably, K2O had been completely leached out into fluid phase in this rock.K2O-bearing tourmaline had been discovered in tourmaline-K-feldspar-quartz rock, and could be a new mineral because no such high-K2O compositions were reported in tourmaline. The occurrence of this tourmaline also indicates the high activity of volatile components in such rocks and the possibility of aqueous fluid as a carrier for these volatile components.All these results described above strongly suggest the importance of the role of aqueous fluid during UHP metamorphism and lead to the proposed model of“Intraslab UHP metasomatism". Less

揭示了深俯冲过程中陆相物质中含水流体再循环形成超高压变质岩和超高压条件下的交代作用的证据。提出了超高压变质岩的岩内超高压交代模型来解释这些过程。俯冲硅酸盐岩释放的多组分含水流体渗入碳酸盐岩地层，形成强烈的交代作用。在这种交代过程中，碳酸盐岩尤其是白云岩大理岩中可以形成丰富的微金刚石。几种组分可以在超高压条件下在循环水溶液中溶解；TiO2是其中具有代表性的一种。在Kokchetav UHP变质岩中，ti -斜殖石赋存于不含金刚石的UHP白云质大理岩中，斜殖石中TiO2的来源可能是水溶组分，表明其具有较高的H2O活性。这表明，即使在碳中，钻石在非常高的水活度下也可能不稳定……更多的岩石和碳可能溶解成流体相。微傅里叶变换红外光谱分析表明，该岩石中透辉石的羟基含量超过850ppm。这也意味着无金刚石白云岩大理岩可以在非常高的水活度条件下形成。与含金刚石白云石大理岩相反，该大理岩中的透辉石不含含k2o的溶出相。超高压条件下，K2O在水溶液中的溶解度可能控制透辉石中溶出片层的存在，并且可能K2O已完全浸出到流体相中。在电气石-钾长石-石英岩中发现了含k2o的电气石，由于在电气石中未见此类高k2o成分的报道，可能是一种新矿物。这种电气石的出现也表明了这种岩石中挥发性成分的高活性，以及作为这些挥发性成分载体的含水流体的可能性。上述结果有力地说明了含水流体在超高压变质作用中的重要作用，并导致了“实验室内超高压交代”模型的提出。少