十万大山构造带变形—岩浆演化过程：对华南大陆印支运动的限定

发布时间：2018-04-02 19:33

  本文选题：印支运动　切入点：华南　出处：《中国地质大学(北京)》2017年硕士论文

【摘要】：华南板块位于全球板块动力学活动最频繁的特提斯和太平洋两大构造域之间。华南板块印支期构造岩浆演化过程及其与周缘板块俯冲和陆块碰撞等动力学过程的内在联系,一直以来是国内外地球科学领域研究的热点,也是争议的焦点。本文选取华南大陆西南部的十万大山构造带为研究区,在详细的野外填图基础上,结合构造变形、岩石学、地球化学及同位素年代学分析手段,重建了该构造带的二叠纪-三叠纪构造-岩浆演化史,为了解古太平洋板块的俯冲作用如何控制华南大陆印支期陆内变形-岩浆演化提供了地质依据。野外地质填图及古构造应力场反演结果证实,晚二叠世-中三叠世,NW-SE挤压应力场导致十万大山构造带广泛缩短变形,形成了一系列自SE向NW逆冲的断层和相关褶皱构造,和~N-S走向左行和~E-W右行走滑断裂。总体上,构造变形由SE向NW强度逐渐变弱,表现为明显的由SE向NW扩展、薄皮逆冲式的变形展布规律,其可能记录了古太平洋板块俯冲作用导致的安第斯型陆内造山运动。这期地壳挤压缩短过程并不是连续的,其间穿插了一次短暂的岩浆-热事件,即:大容山-十万大山花岗岩侵位、抬升和高级变质岩的退变质作用。大容山-十万大山花岗岩呈NE-SW向带状展布,与十万大山构造带走向平行。LA-ICP-MS锆石U-Pb测年显示,大容山花岗岩体侵位于~250-240 Ma。岩石地球化学分析表明,该花岗岩体属高钾钙碱性S-型花岗岩类,为古-中元古代壳源物质重熔的产物,与区域内的高温麻粒岩包体和紫苏花岗岩的形成同期。它们的动力学成因可能为:古太平洋板块俯冲过程中,因俯冲板片断离(slab breakoff)作用影响,高温岩石圈地幔和软流圈物质沿通道上涌,诱发上覆地壳发生超高温-高温熔融作用,并在不同层次形成高温麻粒岩、紫苏花岗岩和S型花岗岩。本研究还新识别一条宽约300 m的韧性剪切带,命名为钦州-防城韧性剪切带,其走向NE-SW,倾角80°,拉伸线理近水平,以右行走滑运动学为主,剪切变形温度~400℃,时代为~250 Ma,其形成可能与早三叠世华南板块与印支地块陆-陆碰撞作用有关。
[Abstract]:The South China Plate is located between the Tethys and the Pacific tectonic regions, where the global plate dynamics is most frequent.The evolution of the Indosinian tectonic magma in the South China plate and its internal relationship with the dynamic processes such as the subduction of the peripheral plate and the collision of the continental blocks have been the hot spots in the field of geoscience both at home and abroad and are also the focus of controversy.In this paper, the Shiwandashan tectonic belt in southwestern South China is selected as the study area. On the basis of detailed field mapping, combined with structural deformation, petrology, geochemistry and isotopic geochronology,The history of Permian-Triassic tectonic-magmatic evolution of the tectonic belt has been reconstructed, which provides a geological basis for understanding how subduction of the paleo-Pacific plate controls intra-continental deformation-magmatic evolution in the Indosinian South China continent.Field geological mapping and inversion of paleotectonic stress field confirmed that the late Permian-Middle Triassic NW-SE compressive stress field resulted in extensive shortening and deformation of Shiwandashan tectonic belt, resulting in a series of faults and related fold structures from SE to NW thrust.The N-S strike left and the E-W right strike slip fault.On the whole, the strength of tectonic deformation gradually weakens from SE to NW, which is characterized by the spreading of SE to NW and the distribution of thin crust thrusts, which may record the Andes intracontinental orogeny caused by subduction of the paleo-Pacific plate.The process of crustal compression and shortening in this period is not continuous, during which a brief magma-thermal event, I. e., the emplacement, uplift and retrograde metamorphism of high metamorphic rocks, occurred in Darongshan-Shiwandashan granite.The Dalongshan-Shiwandashan granite distributes in a NE-SW zonal direction, parallel to the strike of Shiwandashan tectonic belt. LA-ICP-MS zircon U-Pb dating shows that the dalongshan granite transgression is located at 250-240 Ma.The petrogeochemical analysis shows that the granitic body belongs to the high-potassium calc-alkaline S- type granitoids and is the product of the remelting of Paleo-Mesoproterozoic crustal materials, which coincides with the formation of the high-temperature granulite inclusions and perilla granites in the region.Their dynamic origin may be that during the subduction process of the paleo-Pacific plate, the high-temperature lithospheric mantle and the asthenosphere material welled up along the channel due to the influence of the subduction plate fragments from the slabs to break off, which induced the super-high-temperature and high-temperature melting of the overlying crust.High temperature granulites, perilla granites and S-type granites were formed at different levels.A ductile shear zone with a width of about 300 m was also newly identified in this study, named Qinzhou Fangcheng ductile shear zone, with a trend of NE-SW, an angle of 80 掳, a near horizontal tensile lineage, mainly a right-strike-slip kinematics, and a shear deformation temperature of 400 鈩，

本文编号：1701801