冈底斯造山带新生代以来剥露历史的热年代学约束及沉积响应

发布时间：2018-01-03 09:35

本文关键词：冈底斯造山带新生代以来剥露历史的热年代学约束及沉积响应　出处：《中国地质大学(北京)》2016年博士论文　论文类型：学位论文

【摘要】：低温热年代学数据能记录地壳浅部数公里至十几公里的剥露历史,地球内部作用(构造)和外部作用(剥蚀作用)对地貌景观的塑造发挥着强烈的控制作用。为探索他们之间的相互关系,本研究对冈底斯造山带不同地貌和构造背景的地区进行系统采样,应用锆石、磷灰石裂变径迹法和(U-Th)/He方法,对藏南冈底斯造山带新生代剥露历史进行系统研究。同时结合冈底斯砾岩沉积学工作及前人已发表的热年代学数据,揭示冈底斯造山带中段新生代以来的剥露过程及其对应的动力学机制,并对冈底斯不同区域的剥蚀差异进行探讨,理清冈底斯造山带最南缘晚渐新世至早中新世的剥蚀与沉积作用之间的耦合关系。冈底斯造山带不同地貌或地质背景下热年代学数据差异较大,体现在冈底斯北部受河流下切和断层影响较小地区磷灰石裂变径迹年龄主要大于25Ma;冈底斯造山带南部磷灰石裂变径迹年龄主要小于28Ma;而南部网状河谷区域磷灰石裂变径迹年龄主要集中在21-14Ma,(U-Th)/He为9-11Ma;断层带附近样品磷灰石裂变径迹年龄在8-18Ma。热模拟结果显示冈底斯不同地貌或构造背景地区经历了不同的剥蚀历史,晚始新世至早渐新世冈底斯北部发生快速剥蚀,该期剥蚀与拉萨地壳增厚有关,之后冈底斯造山带北部保持相对稳定且缓慢的剥蚀速率。而冈底斯南部经历了多期剥蚀事件,晚渐新世至早中新世快速剥蚀与冈底斯逆冲断裂或与冈底斯逆冲断裂不相容的伸展抬升有关。断裂带附近20-8Ma的局部快速剥蚀事件受到同期南北正断裂或东西向的走滑断裂带作用,或与冈底斯南部网状河流的发育有关。根据冈底斯砾岩野外及前人的地质资料表明冈底斯砾岩沿冈底斯最南缘1300km具有相似的下粗上细,退积序列沉积特点。热年代学数据和模拟结果揭示18-14Ma冈底斯砾岩发生了快速剥蚀事件,但冈底斯砾岩下段与上段存在明显的不整合接触关系,即由深湖相突变过渡为冲积扇的变化,表明18-14Ma剥蚀事件之前区域已经发生了快速抬升。该期快速剥蚀仅沿冈底斯砾岩和冈底斯南部网状河谷区域发育表明该期快速剥蚀可能与冈底斯南部的网状河流形成有关,与之前发生的区域隆升可能存在着时滞关系或无明显直接关系。20-18Ma冈底斯砾岩迅速埋藏至4-7km,主要受大反冲断裂的影响,不支持盆地由于快速沉降埋藏的观点。
[Abstract]:The low-temperature thermochronological data can record the history of the shallowness of the crust, ranging from several kilometers to more than ten kilometers. The Earth's interior (structure) and external (denudation) play a strong controlling role in shaping the landscape. In this study, systematic sampling of different landforms and tectonic backgrounds of the Gangdis orogenic belt was carried out, and zircon, apatite fission track method and U-ThU / he method were used. A systematic study of the Cenozoic denudation history of the Gangdis orogenic belt in southern Tibet is carried out. At the same time, combined with the sedimentology of the Gangdese conglomerate and the previous published thermochronological data. This paper reveals the denudation process and its corresponding dynamic mechanism since the Cenozoic in the middle segment of the Gangdis orogenic belt, and probes into the denudation differences in different regions of the Gangdis orogenic belt. The coupling relationship between late Oligocene and early Miocene denudation and sedimentation in the southernmost margin of the Gangdis orogenic belt is clarified. The fission track age of apatite is more than 25 Main in the north of Gangdis, which is influenced by river undercutting and fault. The fission track age of apatite in the southern Gangdis orogenic belt is less than 28 Ma. The age of apatite fission track in the southern reticular valley is mainly 9-11 Ma. The fission track age of apatite in the vicinity of the fault zone is 8-18 Ma.The thermal simulation results show that different geomorphological or tectonic backgrounds of Gangdese have undergone different denudation history. From the late Eocene to the early Oligocene, rapid denudation occurred in the northern part of Gangdis, which was related to the thickening of the Lhasa crust. After that, the northern part of the Gangdis orogenic belt maintained a relatively stable and slow denudation rate, while the southern Gangdis experienced several denudation events. The rapid denudation from late Oligocene to early Miocene is related to the Gangdis thrust fault or to the incompatible extensional uplift of the Gangdis thrust fault. The local rapid denudation event of 20-8 Ma near the fault zone was subjected to the synchronic north-south normal fault. Or east-west strike-slip fault zone. According to the field data of Gangdese conglomerate and previous geological data, it is shown that Gangdese conglomerate has similar thickness along the southernmost margin of Gangdis, 1300km. Thermal chronological data and simulation results show that rapid denudation occurred in the Gangdis conglomerate at 18-14 Ma, but there is an obvious unconformity contact relationship between the lower Gangdis conglomerate and the upper member. That is, the transition from deep lacustrine facies to alluvial fan. The rapid denudation occurred only along the Gangdese conglomerate and the grid valley in the south of Gangdese, indicating that the rapid denudation may be associated with the south of Gangdes. The formation of a network of rivers. There may be a time-delay relationship or no obvious direct relationship between the uplift and the previous regional uplift. The Gangdis conglomerate of 20-18 Ma is rapidly buried to 4-7 km, which is mainly affected by the large recoil fault. It does not support the view that the basin is buried due to rapid subsidence.
【学位授予单位】：中国地质大学(北京)
【学位级别】：博士
【学位授予年份】：2016
【分类号】：P542

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