安徽歙县绍村—雄村地区构造变形与金矿成矿关系

发布时间：2018-04-20 16:48

本文选题：绍村-雄村 + 韧性剪切带　；参考：《中国地质大学(北京)》2017年硕士论文

【摘要】：皖南地处华夏板块与扬子板块结合处,属江南造山带东段,同时也是钦杭成矿带东段,区域上各类矿点数百个,且成矿类型多样,其中受韧性剪切带控制占主导地位。皖南地区除自然地理条件差以外,其地质构造复杂,研究程度较低,尤其是基础构造研究薄弱。因此更深一步了解韧性剪切带特征及其演化史与金矿成矿的时空对应关系成为急需解决的问题。本文通过对皖南歙县绍村-雄村地区详细地野外地质调查,发现研究区普遍经历了韧性剪切变形作用,变形程度强弱交替,野外露头新鲜面可见有明显的糜棱面理,石英、长石定向拉长以及剪切作用下形成的旋转碎斑等多种变形特征组合。野外观测到的多种膝折等小型褶皱现象,以及石英脉的侵入,发育有硅化现象,指示同期或后期发生较强的构造运动。通过对镜下定向薄片的显微观察得出:石英颗粒定向排列,具有σ型残斑,S-C组构,指示方向为右行挤压剪切,部分为膨凸重结晶及核幔构造,可观察到由静态恢复重结晶作用形成的规则边界的新晶体。根据石英重结晶类型及绢云母塑性变形认为该韧性剪切带为中高温条件下变形,叠加后期低温变形。通过EBSD实验结果得知剖面全程滑移系以菱面a滑移为主,变形条件均为中温-中低温,变化幅度不大,部分还经历晚期的低温条件下的变形作用。使用极摩尔圆法估算定向样品的运动学涡度,其数值极大多数低于0.71,因此绍村-雄村剖面主要为纯剪切作用。结合韧性剪切带地化剖面中元素分布以及构造变形强弱关系得出∶在构造变形程度强的位置,金元素富集现象不明显,在变形程度较弱地方,金矿物富集。分析原因为,构造变形程度强的地方压力大,致使含矿热液沿构造断裂带流向压力小的区域。因此,说明韧性剪切带更多的是为金元素提供空间及含矿热液运移的通道,而不是主要的控矿因素。绍村-雄村韧性剪切带的形成时间为加里东期,与华南地区加里东期隆升构造有关,基底岩石在地下深处因隆升作用发生韧性变形,经历了中温到低温作用,之后发生脆性变形;在燕山期由逆冲推覆构造被推覆至地表。
[Abstract]:The south of Anhui is located at the junction of the Huaxia plate and the Yangtze plate, which belongs to the eastern section of the Jiangnan orogenic belt and is also the eastern section of the Qinghang metallogenic belt. There are hundreds of all kinds of occurrences in the area, and the metallogenic types are various, among which the ductile shear zone dominates. Except for the poor physical and geographical conditions, the geological structure is complex and the research degree is relatively low, especially the basic structure research is weak in the south of Anhui province. Therefore, a deeper understanding of the characteristics of the ductile shear zone and the relationship between the evolution history and the temporal and spatial correspondence between gold mineralization and the ductile shear zone becomes an urgent problem to be solved. Based on a detailed field geological survey of Shaomun-Xiongcun area in Shexian County, southern Anhui Province, it is found that the study area generally experienced ductile shear deformation, the degree of deformation was alternately strong and weak, and the fresh surface of outcrop in the field could be seen to have obvious surface texture and quartz. There are many kinds of deformation characteristic combinations, such as directional stretching of feldspar and rotating debris formed by shear. A variety of small fold phenomena, such as knee fold, and the intrusion of quartz veins, have been observed in the field, which indicate the occurrence of strong tectonic movement in the same period or later period. Through the microscopic observation of the directional thin slices under the microscope, it is found that the quartz particles are arranged in a directional direction, with 蟽 -shaped macular S-C fabric, indicating a right compression shear direction, and some of them are expanded convex recrystallization and core-mantle structure. A new crystal with regular boundary formed by static recovery recrystallization can be observed. According to the type of quartz recrystallization and the plastic deformation of sericite, the ductile shear zone is deformed at medium and high temperature and deformed at low temperature in the late superimposed period. The results of EBSD experiment show that the whole slip system of the profile is mainly rhombohedral a slip, and the deformation conditions are medium temperature to medium low temperature, with little change, and some of them also undergo late deformation at low temperature. The kinematic vorticity of the directional samples is estimated by using the polar molar circle method. The maximum value of the vorticity is less than 0.71, so the Shaomun-Xiongcun section is mainly pure shearing. In combination with the distribution of elements in the geochemistry section of the ductile shear zone and the relationship between the tectonic deformation and the intensity of the tectonic deformation, it is concluded that the enrichment of gold elements is not obvious in the position of strong tectonic deformation, but the gold is enriched in the area of weak deformation. The reason is that the local pressure with strong tectonic deformation is high, which leads to the flow of ore-bearing hydrothermal fluid along the structural fault zone to the area with low pressure. Therefore, the ductile shear zone provides more space for gold elements and channels for hydrothermal migration of ore-bearing elements than the main ore-controlling factors. The forming time of the Shaocun-Xiongcun ductile shear zone is Caledonian, which is related to the Caledonian uplift structure in South China. Then brittle deformation occurred, and the thrust nappe structure was pushed to the surface during the Yanshanian period.
【学位授予单位】：中国地质大学(北京)
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：P618.51

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