本文關(guān)鍵詞： 祁連造山帶 地震層析成像 速度結(jié)構(gòu) 下地殼塑性流動 殼內(nèi)地震　出處：《西北大學(xué)》2017年碩士論文　論文類型：學(xué)位論文

【摘要】：祁連造山帶作為青藏高原東北緣的重要組成部分,其詳細的地殼-上地幔頂部三維結(jié)構(gòu)特征對探討青藏高原東北緣新生代變形機制、祁連造山帶與華北板塊深部構(gòu)造關(guān)系、以及該區(qū)內(nèi)殼內(nèi)大地震的誘發(fā)機制都具有非常重要的意義。本論文使用研究區(qū)內(nèi)分布的72個固定臺站在2009年到2015年間記錄到的7485個地震事件,包括75999個P波到時數(shù)據(jù)和72178個S波到時數(shù)據(jù),利用天然地震層析成像方法獲得了祁連造山帶地殼-上地幔頂部詳細的三維P、S波速度結(jié)構(gòu)。結(jié)果表明,祁連造山帶地殼-上地幔頂部三維速度結(jié)構(gòu)具有顯著的縱/橫向不均一性。地殼淺部速度結(jié)構(gòu)特征與地表地質(zhì)特征基本一致,總體表現(xiàn)為高、低速的分布與山脈和盆地的分布相對應(yīng)。祁連構(gòu)造帶下地殼內(nèi)廣泛發(fā)育低速異常帶,局部地區(qū)延伸至上地幔頂部。結(jié)合該區(qū)其他地球物理資料,認為該低速異常區(qū)代表了下地殼中因流體和部分熔融體存在而造成的弱化帶,其很可能與青藏高原的隆升與變形及其向北擴展以及局部地區(qū)上地幔物質(zhì)上涌有關(guān)。祁連造山帶下地殼的弱化可使其在地質(zhì)歷史時間尺度發(fā)生塑性流動,而低速異常帶的分布表明,塑性流動的規(guī)模并不很大。北祁連和走廊過渡帶地殼底部以及上地幔頂部內(nèi)存在明顯的高速異常,該高速異�？赡艽砹讼蚱钸B造山帶下方俯沖的阿拉善地塊的巖石圈,該俯沖作用很可能與新生代印度板塊和歐亞板塊的俯沖碰撞過程有關(guān)。研究區(qū)內(nèi)的殼內(nèi)大地震大多數(shù)都分布于區(qū)域內(nèi)的大型斷裂帶上,震源區(qū)位于高、低速異常過渡帶,震源區(qū)下方存在廣泛的低速異常區(qū)。結(jié)果表明大地震的發(fā)生是斷裂、應(yīng)力以及流體綜合作用的結(jié)果,并且與下地殼以及上地幔頂部的動力學(xué)過程緊密相關(guān)。綜上所述,祁連造山帶甚至是整個青藏高原東北緣新生代的變形,可能并非是某種單一機制作用的結(jié)果,而是大陸巖石圈俯沖、下地殼塑性流動以及上地幔物質(zhì)上涌多種機制于不同時段、不同區(qū)段共同作用的結(jié)果。
[Abstract]:The Qilian orogenic belt is an important part of the northeastern margin of the Qinghai-Xizang Plateau, and its detailed three-dimensional structure of the crust and upper mantle is discussed in the Cenozoic deformation mechanism of the northeastern margin of the Qinghai-Xizang Plateau. The Qilian orogenic belt is related to the deep tectonics of the North China plate. The induced mechanism of large earthquakes in the inner crust of this area is of great significance. In this paper, 7485 earthquake events recorded by 72 fixed stations in the study area were recorded between 2009 and 2015. The piece. Including 75999 P-wave time data and 72178 S-wave arrival data, the detailed 3D P values of the crust and upper mantle of the Qilian orogenic belt are obtained by using natural seismic tomography. The results show that the 3D velocity structure of the crust and the upper mantle of the Qilian orogenic belt has obvious longitudinal / lateral heterogeneity, and the velocity structure of the shallow crust is basically consistent with the geological features of the surface. The distribution of high and low velocity corresponds to the distribution of mountains and basins. In the lower crust of the Qilian tectonic belt, a low velocity anomaly zone is widely developed, and the local area extends to the top of the upper mantle, combining with other geophysical data in the area. It is considered that the low velocity anomaly represents the weakening zone in the lower crust caused by the presence of fluids and partially molten bodies. It may be related to the uplift and deformation of the Qinghai-Xizang Plateau and its northward extension, as well as the upwelling of the upper mantle material in some areas. The weakening of the lower crust of the Qilian orogenic belt can make the ductile flow take place on the time scale of geological history. The distribution of low velocity anomaly shows that the scale of plastic flow is not very large. There are obvious high speed anomalies in the crust bottom and upper mantle top of North Qilian and Corridor transition Zone. The high velocity anomaly may represent the lithosphere of the Alashan block subducting to the Qilian orogenic belt. The subduction is probably related to the subduction and collision process of the Cenozoic Indian plate and Eurasian plate. Most of the large earthquakes in the crust in the study area are located on the large fault zone of the region and the focal area is high. In the transition zone of low velocity anomaly, there is a wide range of low velocity anomaly areas below the focal area. The results show that the occurrence of large earthquakes is the result of the combined action of faults, stresses and fluids. In conclusion, the Qilian orogenic belt and even the Cenozoic deformation of the northeastern margin of the Qinghai-Tibet Plateau may not be the result of a single mechanism. It is the result of the subduction of continental lithosphere, the plastic flow of the lower crust and the upwelling of the upper mantle material.
【學(xué)位授予單位】：西北大學(xué)
【學(xué)位級別】：碩士
【學(xué)位授予年份】：2017
【分類號】：P315.2
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本文編號：1461563