桂林地区碳酸盐岩层滑断裂构造地球化学系统的特征和动力分异机制

Basted on the theory and method of the tectonic geochemistry,the geometry, occurrence and zoning structures of a relatively pure and complete tectonic geochemical system of the layer-slid fault in the carbonate rocks in Guilin area will be explained clearly through these means such as the investigation of tectonic background, measurement of small structure, microstructural petrology and fabric study and analysis of main and trace elements and so on.The functional characteristics of the tectonic geochemical system of the layer-slid fault will be identified, which contains dissloution subsystem, transport and sediment subsystem. .The tectonic geochemical nature of the characteristic elements will be summarized, the regularities of migration and enrichment of the different elements will be understood and the activity sequence of the different elements will be set up.Base on these combined methods such as microscopic structure-composition analysis, compatible elements，rare-earth elements analysis, geochemistry of fluid inclusions, isotope geology of carbon and oxygen, phase analysis of carbon, electron microprobe in tectonite, the simulated experiments of tectonic geochemistry and so on, the mechanisms of dynamic differentiation of tectonic geochemistry in the layer-slid fault in the carbonate rocks will be figured out,the actions and types of the tectonic geochemistry in the forming process of the layer-slid fault in the carbonate rocks will be revealed , and the impact of the lithological characters, tectonic stress and the nature of fluid on the differentiation of tectonic geochemistry will be confirmed. On the base of above all, the forming and evolutional model of the tectonic geochemical system in the layer-slid fault in the carbonate rocks on the regional geological tectonic background will be established.

运用构造地球化学理论和方法，选择桂林地区相对纯化和完整的碳酸盐岩层滑断裂构造地球化学系统，通过宏观构造地质背景调查、小构造测量、显微构造岩石学研究、主元素和微量元素地球化学分析等手段，阐明层滑断裂构造地球化学系统的几何形态、产状特征和分带结构；厘定层滑断裂构造地球化学系统的功能特性-溶出区、输运通道和沉淀区；总结特征元素的构造地球化学性质，认识不同元素的迁移富集规律，建立元素的活动性序列。通过显微构造分析、碳酸盐岩相容元素、稀土元素、包裹体地球化学、碳氧同位素地质学、碳的物相分析、电子探针技术和构造地球化学模拟实验等综合手段，阐明层滑断裂构造地球化学系统的动力分异机制，揭示碳酸盐岩层滑断裂形成过程中的构造地球化学作用及类型；确定原岩岩性、构造应力和流体性质等因素对构造地球化学分异作用的影响；在上述研究的基础上，建立基于区域地质构造背景下的碳酸盐岩层滑断裂构造地球化学系统形成和演化模型。

灌阳层滑断裂具有良好的结构分带。下部为灰岩-同构造重结晶方解石带-劈理带或揉皱带-同构造重结晶方解石带-灰岩；上部为灰岩-碎裂岩-层间裂隙充填方解石脉-碎裂岩-灰岩。层滑断裂韧性变形的标志有S-C面理、压溶纹、压溶缝合线、压力影、方解石残斑拖尾、肠状方解石、亚颗粒、波状消光、动态重结晶、双晶纹和扭折等。S-C面理、残斑拖尾示逆向剪切。X射线粉晶和电子探针分析显示，劈理域矿物成分为方解石、石英、伊利石、蒙脱石、磷灰石、石墨、磁铁矿、金红石等，新生方铅矿、闪锌矿的发现具有重要意义。动力重结晶方解石a0=4.98504-4.98940，c0=17.04070-17.05580，裂隙充填的方解石a0=4.98870 -4.99170，c0=17.05370-17.06540。晶胞参数的减小可以解释压剪性构造环境对方解石晶格的净化作用。综合考虑富集系数、元素组合和矿物组合，可确定碳酸盐岩层滑断裂常量元素的稳定性系列由大至小为：C、P、Si、K、Al、Ti、Fe、Mn、Mg、Ca、Na、H2O。微量元素最稳定的有Cr、V、Cu、Mo、Li、Rb、Cs、Ba、Nb、Ta、Th、Hf、Zr等；较活动的有W、Sn、Co、Ni等。最活动的有Pb、Zn、Cd、As、Ag等。Cu、Mo在下部压剪性带中残留富集；Pb、Zn、Cd、As、Ag等在上部张剪性带中再沉淀。这可能可以解释某些碳酸盐建造中铜、铁、铅、锌层控矿床的形成机制。碳酸盐岩的相容元素Sr、Pb、Zn、Cd等可作为构造地球化学环境的特征指示元素。层滑断裂是一个断裂构造系统。劈理带作为活动组分的源区，同构造重结晶方解石带兼作为源区和输运通道，裂隙充填方解石脉作为沉淀区，构成一个完整的构造地球化学系统。碳酸盐岩层滑断裂形成包括动力分异作用、压溶扩散作用、水解弱化作用、氧化还原作用。构造地球化学实验结果证实：构造动力是活泼金属Pb、Zn活化迁移的驱动力，Pb、Zn元素由围岩趋向于构造界面迁移。