【摘要】：青藏高原的大規(guī)模隆升起源于～50 Myrs印度板塊向歐亞板塊的洋陸俯沖轉(zhuǎn)換為陸陸碰撞,之后持續(xù)擠壓歐亞板塊。在這一過程中,青藏高原南部經(jīng)歷了顯著的地殼縮短增厚,從而形成了很高的地形,但是在青藏高原其他區(qū)域,特別是高原邊緣的隆升機制還存在很多爭議。在印度板塊的擠壓下,現(xiàn)在青藏高原中部上地殼在東西方向處于明顯的拉伸狀態(tài),物質(zhì)呈現(xiàn)向東的移動,并從東部邊緣擠出。青藏高原的東南緣作為物質(zhì)的主要流出通道,具有三個典型特征。其一:青藏高原物質(zhì)在東部邊緣受到了四川盆地的阻礙,在青藏高原-四川盆地邊緣形成了非常陡峭的地形,在100 km以內(nèi)從～4500 m下降到～500 m。其二:青藏高原物質(zhì)流在四川盆地分成兩支,一支流向華北地區(qū),另一支流向華南地區(qū),流向華南地區(qū)的物質(zhì)繞著喜馬拉雅東構造結(jié)順時針旋轉(zhuǎn)。其三:青藏高原東南緣構造活動強烈,斷層廣泛分布,大地震多發(fā)。為了解青藏高原東南緣的地質(zhì)演化,我們針對青藏高原-四川盆地邊緣建立了解析模型和數(shù)值模型來模擬龍門山的隆升過程,并確定四川盆地巖石圈粘滯系數(shù)分布以及應力和應變率的變化。同時我們正在著手建立川滇地區(qū)的三維數(shù)值模型,試圖探討青藏高原及其東南緣的淺地表構造對其運動的影響,并建立這一區(qū)域的地殼地幔耦合模式。下地殼通道流理論可以很好的解釋青藏高原東部邊緣的隆起,但是前人的解析模型對于通道流得模擬都存在與事實明顯不符的地方,因此我們建立了新的模型,通道厚度隨著物質(zhì)的流入而增加。我們的解析模型結(jié)果表明,下地殼粘滯系數(shù)越大時,邊界上的地形梯度越大,通過實際地形的約束,四川盆地下地殼的粘滯系數(shù)為1022Pas,是前人研究結(jié)果的10倍。在解析模型的基礎上,我們考慮更多可能影響演化過程的因素,建立數(shù)值模型。數(shù)值模型采用解析模型關于下地殼粘滯系數(shù)的結(jié)果,進一步確定四川盆地上地殼的粘滯系數(shù)為1024Pas,巖石圈地幔粘滯系數(shù)為1023Pas。隆升過程中,應力和應變率在隆升前緣很大,在其他區(qū)域較小,因為四川盆地下地殼粘滯系數(shù)大,物質(zhì)流動收到阻礙。在隆升過程中,龍門山區(qū)域上地殼中的應力狀態(tài)可能經(jīng)歷了從拉伸到壓縮的轉(zhuǎn)變,這一轉(zhuǎn)變可能與龍門山附近多種斷層類型相關。另外,青藏高原與川滇地區(qū)的各向異性特征不同,快波極化方向的轉(zhuǎn)變可能因為青藏高原和川滇地區(qū)的地殼和地幔的形變耦合方式不同。
[Abstract]:The large-scale uplift of the Qinghai-Xizang Plateau originated from the subduction of the Indian plate from 50 Myrs to the oceanic continent of the Eurasian plate into a continental collision, and then sustained compression of the Eurasian plate. During this process, the southern Qinghai-Xizang Plateau experienced significant crustal shortening and thickening, resulting in a very high topography. However, the uplift mechanism in other regions of the Tibetan Plateau, especially the plateau margin, is still controversial. Under the compression of the Indian plate, the upper crust of the central Qinghai-Xizang Plateau is in an obvious stretching state in the east-west direction, with the material moving eastward and extruding from the eastern margin. The southeastern margin of Qinghai-Xizang Plateau, as the main outflow channel of material, has three typical characteristics. Firstly, the matter of Qinghai-Xizang Plateau is blocked by Sichuan Basin on the eastern margin, and a very steep terrain is formed on the margin of Qinghai-Sichuan Basin, which falls from 4500m to 500m within 100 km. Secondly, the material flow in the Qinghai-Xizang Plateau is divided into two branches in Sichuan Basin, one flowing to North China and the other to South China, and the matter flowing to South China rotates clockwise around the eastern Himalayan tectonic junction. Third, the southeast margin of Qinghai-Xizang Plateau has strong tectonic activity, wide distribution of faults and multiple earthquakes. In order to understand the geological evolution of the southeastern margin of the Qinghai-Xizang Plateau, an analytical model and a numerical model were established to simulate the uplift process of the Longmen Mountains in view of the margin of the Qinghai-Xizang Plateau and Sichuan Basin. The distribution of lithospheric viscosity coefficient and the variation of stress and strain rate are determined. At the same time, we are establishing a three-dimensional numerical model of Sichuan-Yunnan region, trying to study the influence of shallow surface structure on the movement of Qinghai-Xizang Plateau and its southeast margin, and to establish the crustal and mantle coupling model in this region. The theory of channel flow in the lower crust can explain the uplift of the eastern edge of the Qinghai-Xizang Plateau well, but the previous analytical models are obviously inconsistent with the facts, so we have established a new model. The channel thickness increases with the inflow of matter. The results of our analytical model show that the larger the viscosity coefficient of the lower crust is, the greater the gradient of topography is at the boundary. The viscosity coefficient of the lower crust in Sichuan Basin is 1022 Pasas through the restriction of the actual terrain, which is 10 times of the previous results. On the basis of the analytical model, we consider more factors that may affect the evolution process, and establish a numerical model. Based on the results of the analytical model on the viscosity coefficient of the lower crust, it is further determined that the viscosity coefficient of the upper crust and the lithospheric mantle of the Sichuan basin is 1024 Pasas and 1023 Pasas respectively. In the uplift process, the stress and strain rates are very large in the front edge of uplift and smaller in other regions because of the large viscosity coefficient of the lower crust of Sichuan basin and the obstruction of material flow. During the uplift, the stress state in the upper crust of the Longmen Mountain region may undergo a transition from tensile to compression, which may be related to many types of faults near Longmen Mountain. In addition, the anisotropic characteristics of Qinghai-Xizang Plateau and Sichuan-Yunnan region are different. The transformation of fast wave polarization direction may be due to the different deformation coupling modes of crust and mantle in Qinghai-Xizang Plateau and Sichuan-Yunnan region.
【學位授予單位】：中國科學技術大學
【學位級別】：碩士
【學位授予年份】：2017
【分類號】：P542

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