大别-苏鲁超高压榴辉岩石榴石“#32467;构水”#30340;赋存状态

项目名称： 大别-苏鲁超高压榴辉岩石榴石“#32467;构水”#30340;赋存状态

项目编号： No.40872136

项目类型： 面上项目

立项/批准年度： 2009

项目学科： 轻工业、手工业

项目作者： 刘祥文

作者单位： 中国地质大学（武汉）

项目金额： 42万元

中文摘要： 超高压榴辉岩石榴石"结构水"的存在得到了广泛证实，但是其赋存状态、变化规律以及对流变学机制的影响等许多问题都还没有得到详细而系统的研究。本课题拟以大别碧溪岭、双河及中国大陆科学钻探岩心的超高压榴辉岩石榴石为代表，采用红外光谱、电子探针、同步辐射白光形貌术、透射电镜以及高温高压实验等综合研究方法，对石榴石"结构水"的赋存状态进行系统研究。一方面，利用同步辐射及透射电镜等研究结构水与位错之间的相关性，检验位错管道赋存模式的合理性；另一方面，进行高温脱水实验以及高温高压含水实验，研究石榴石中晶格替代型、位错吸附型及间隙型"结构水"的含量差异、分布特征、进入及逸出特征等。最终对石榴石结构水的赋存状态有一个全面正确的认识。本研究若获成功将为进一步深入探讨"结构水"对超高压榴辉岩石榴石流变强度的弱化机制、大陆深俯冲与折返动力学、壳幔流体循环与物质交换以及成岩成矿过程等提供重要的约束资料。

中文关键词： 双河；榴辉岩；石榴石；水；晶体缺陷

英文摘要： Although several studies detected the presence of structural water in garnets from ultrahigh-pressure eclogites, there is little work on water existing state, transformation law and their effect on rheologic mechanism of garnets. In this project, garnets in ultrahigh-pressure eclogites from Shuanghe in eastern Dabieshan were studied by Fourier transform infrared spectroscopy, electron probe microanalysis and transmission electron microscopy. First, the results show that the water content of garnets varied as a function of it's chemical component, which showed a positive correlation with Grs+Adr mol.%, and a negative correlation with Prp and Alm+Sps mol.%, respectively. Especially when water content ranked more than 500 ppm, this relationship showed more obviously. Based on the shape and position of the former three groups of OH absorption band and the relationship between water content and chemical component, we thus conclude that the OH in garnets is present in the form of [SiO4]4-=[(OH)4]4-, which is called hydrogrossular substitution; While, if the water content ranks less than 500 ppm, the relationship between water content and chemical component is complicated, which indicates that there are other formats of OH except for hydrogrossular substitution in the low water content garnets, such as [(OH)3O] or [SiO3(OH)] in the tetrahedron site which caused by cation couple substitution in octahedron or dodcahedron site. The influence on heterogeneity of water content which is made by chemical component in garnets is also expressed on a large area scale. Second, the results also show that the water content of garnet hasn't obvious relation to its dislocation density, while it has a positive correlation with dislocation submicrostructure density. That is, as the water content increases, the quantity of dislocation array, dislocation wall, dislocation network and subgrain boundaries also increase. Its dislocation submicrostructure is induced by dislocation's slipping and climbing, and is the characteristic of dislocation recovery in high temperature plastic deformation, which is the evidence of garnets plastic deformation were controlled by dislocation creep and recovery process. Water in the garnets will promote the dislocation recovery process. So, we have the conclusion that the major mechanism of garnets plastic deformation is water induced recovery-accommodated dislocation creep.

英文关键词： Shuanghe; Eclogite; Garnet; Water; Crystal Defect