本文選題：大洋俯沖 + 板片傾角��； 參考：《中國(guó)科學(xué)院研究生院(廣州地球化學(xué)研究所)》2016年博士論文

【摘要】：本文選擇大洋俯沖和大陸碰撞的動(dòng)力學(xué)演化過(guò)程作為主題,利用系統(tǒng)的數(shù)值模擬實(shí)驗(yàn)深入分析了各主要?jiǎng)恿W(xué)參數(shù)如何影響大洋板片傾角及大陸俯沖模式。通過(guò)研究將影響大洋俯沖動(dòng)力學(xué)過(guò)程的參數(shù)分為與俯沖大洋板片浮力相關(guān)、與板間耦合作用相關(guān)、與洋-陸匯聚速率相關(guān)和與俯沖帶流變性質(zhì)相關(guān)等四類。而板片正浮力作用(例如年輕大洋或增厚洋殼的俯沖)、俯沖板塊和上覆板塊之間的強(qiáng)耦合作用(例如低的初始俯沖角度或厚的上覆大陸巖石圈)、較高的上覆大陸向洋的絕對(duì)逆沖速率和大洋絕對(duì)俯沖速率之比以及有利于板片彎折的俯沖帶流變性質(zhì)等都是造成大洋低角度俯沖的有利因素。模擬結(jié)果表明,并不存與平板俯沖發(fā)育呈充分必要關(guān)系的特定參數(shù)條件。平板俯沖的發(fā)生與否不能歸功于某一個(gè)或是某一類參數(shù)的單獨(dú)作用,而往往與多類因素多個(gè)參數(shù)的共同作用相關(guān)。大洋平板俯沖的發(fā)生必須要滿足一些“異�！钡膭�(dòng)力學(xué)條件,而這很可能就是平板俯沖難以產(chǎn)生的主要原因。結(jié)合模型實(shí)驗(yàn)結(jié)果和現(xiàn)今平俯沖區(qū)域的統(tǒng)計(jì)資料,我們認(rèn)為由年輕的或含增厚洋殼的大洋俯沖所導(dǎo)致的俯沖板片正浮力作用是導(dǎo)致大洋平板俯沖的主導(dǎo)因素,其它因素也會(huì)在大洋俯沖過(guò)程中進(jìn)一步促進(jìn)平板俯沖發(fā)生。通過(guò)力學(xué)分析方法,俯沖板片的幾何形態(tài)在力學(xué)本質(zhì)上受控于板片重力矩和吸力矩的合力矩大小和方向,通過(guò)調(diào)節(jié)板片重力矩或吸力矩的大小最終影響大洋俯沖型式�；谀Ｐ椭懈_大陸板片的演化特征,將大陸俯沖分為大陸穩(wěn)定俯沖和大陸非穩(wěn)定俯沖。大陸穩(wěn)定俯沖表現(xiàn)為俯沖至軟流圈深度的大陸板片仍能保持較高流變強(qiáng)度而以特定角度持續(xù)俯沖至地幔深部;根據(jù)大陸板片傾角,又可進(jìn)一步分為大陸陡俯沖和大陸平俯沖兩個(gè)亞類。而在大陸非穩(wěn)定俯沖中,大陸板片不能保持其幾何和力學(xué)完整性,碰撞區(qū)域的重力不穩(wěn)定受控于俯沖大陸板片斷離或增厚巖石圈拆沉。根據(jù)俯沖大陸板片的形變特征,大陸非穩(wěn)定俯沖表現(xiàn)為“多階段斷離”、“持續(xù)性流入”和“大規(guī)模拆沉”三種類型。模型實(shí)驗(yàn)表明,中-高速大陸匯聚和低-中溫巖石圈熱結(jié)構(gòu)有利于大陸穩(wěn)定俯沖的產(chǎn)生,而具體發(fā)育何種類型(大陸陡俯沖或平俯沖)則主要由大陸地殼的流變性質(zhì)控制。大陸非穩(wěn)定俯沖的三種不同類型(“多階段斷離”、“持續(xù)性流入”和“大規(guī)模拆沉”)分別與低匯聚速率、中-高速匯聚下的巖石圈高溫?zé)峤Y(jié)構(gòu)和低匯聚速率下的中等-高流變強(qiáng)度地殼有關(guān)。對(duì)于具中等-高流變強(qiáng)度地殼的大陸巖石圈發(fā)生非穩(wěn)定俯沖時(shí),無(wú)論分幾個(gè)演化階段以及前期演化階段的類型如何,一般都會(huì)以碰撞區(qū)域增厚巖石圈地幔的大規(guī)模拆沉終止。大陸平俯沖型式的發(fā)育必須滿足兩個(gè)條件:高地殼流變強(qiáng)度和高速俯沖,兩者缺一不可。高地殼流變強(qiáng)度一方面增加隨大陸巖石圈地幔進(jìn)入俯沖通道乃至軟流圈的地殼體積,減小大陸板片的平均密度;另一方面提高大陸板片的整體流變強(qiáng)度,兩方面的共同作用有利于大陸平俯沖的產(chǎn)生。大陸高速俯沖減少大陸板片在軟流圈淺部的滯留時(shí)間,減弱大陸板片在軟流圈內(nèi)的熱傳導(dǎo)增溫效應(yīng),從而使板片保持相對(duì)高的流變強(qiáng)度而有利于大陸平俯沖產(chǎn)生。針對(duì)印度-亞洲碰撞的模型實(shí)驗(yàn)結(jié)果表明,要造成上覆亞洲大陸的強(qiáng)烈縮短變形以及現(xiàn)今青藏高原造山帶的巖石圈結(jié)構(gòu),上覆亞洲大陸相對(duì)較低的地殼流變強(qiáng)度和相對(duì)高溫的巖石圈熱狀態(tài)是其必要條件�；谀Ｐ蛯�(shí)驗(yàn)結(jié)果,識(shí)別出了兩種不同的大陸平俯沖型式:第一種型式是俯沖大陸巖石圈直接墊置于上覆大陸巖石圈地幔之下,第二種型式是俯沖大陸巖石圈直接墊置于上覆大陸地殼之下。前者需要俯沖側(cè)和上覆側(cè)大陸都具較高的流變強(qiáng)度,后者要求上覆大陸具備比俯沖大陸低的流變強(qiáng)度。但不論是何種類型,都需要俯沖大陸具較高流變強(qiáng)度和較高俯沖速率。藏南動(dòng)力學(xué)演化的數(shù)值模擬研究表明,該地區(qū)大陸動(dòng)力學(xué)演化過(guò)程與第二種大陸平俯沖型式類似。印度大陸的持續(xù)向北俯沖促使亞洲大陸巖石圈地幔逐漸與上部地殼發(fā)生拆離并進(jìn)入軟流圈內(nèi),最終導(dǎo)致在藏南地區(qū)印度大陸直接墊置于亞洲大陸地殼之下。此過(guò)程伴隨青藏高原造山帶區(qū)域的中下地殼軟弱層的廣泛發(fā)育、碰撞區(qū)域內(nèi)異常厚地殼的形成以及由深埋印度地殼物質(zhì)重熔溢出而導(dǎo)致的高喜馬拉雅地體內(nèi)強(qiáng)烈?guī)r漿作用,這些在第二類模型演化過(guò)程中都能得到體現(xiàn)。另外,綜合多方面模型實(shí)驗(yàn)結(jié)果,我們推測(cè)喜馬拉雅造山帶東西向巖石圈結(jié)構(gòu)差異可能由多種因素造成,包括印度大陸力學(xué)性質(zhì)差異性、亞洲大陸溫度場(chǎng)差異性、印度與亞洲初始碰撞時(shí)的聚速率差異性以及青藏北緣巖石圈結(jié)構(gòu)差異性等。
[Abstract]:In this paper, the dynamic evolution process of ocean subduction and continental collision is chosen as the theme, and the numerical simulation experiments of the system are used to analyze how the main dynamic parameters affect the dip angle of Ocean plate and the continental subduction mode. It is related to the interplate coupling, related to the oceanic and continental convergence rate and the relationship with the rheological properties of the subduction zone, which are related to four types. The plate positive buoyancy (such as the subduction of the young ocean or thickened oceanic crust), the strong coupling between the subducted and overlying plates (such as low initial subduction angle or thick overlying continental lithosphere), higher overlying The absolute thrust rate of the continent and the ratio of the absolute subduction rate of the ocean and the rheological properties of the subduction zone, which benefit the bending of the plate, are all favorable factors for the low angle subduction of the ocean. It is often related to the interaction of a number of parameters in one or a certain class of parameters. The occurrence of an ocean plate subduction must satisfy some "abnormal" dynamic conditions, which is probably the main reason for the difficulty of the flat subduction. We believe that the positive buoyancy of the subduction plate caused by the young or thickened oceanic subduction is the leading factor in the subduction of the ocean plate, and the other factors will further promote the subduction of the plate in the process of ocean subduction. The geometric form of the subduction plate is in the mechanical nature by the mechanical analysis. The size and direction of the resultant force moment controlled by the plate heavy moment and the suction moment will affect the ocean subduction pattern by adjusting the plate gravitational torque or the suction moment. Based on the evolution characteristics of the subduction continental plate in the model, the continental subduction is divided into continental stable subduction and continental unstable subduction. The continental stable subduction is manifested by subduction to soft subduction. The continental plates with the depth of the flow still maintain high rheological strength and continue to subduction to the deep mantle in a particular angle. According to the dip angle of the continental plate, they can be further divided into two subsubduction subduction subduction and continental subduction. In the non stable subduction of the continent, the continental plate can not hold its geometric and mechanical integrity, the gravity of the collision region. The instability of the continental plate is controlled by the deformation characteristics of the subducted continental plate. The unstable subduction of the continent is characterized by three types of "multi stage disconnection", "continuous inflow" and "large scale disintegration". The model experiments show that the thermal structure of middle and high speed large land convergence and low middle temperature lithosphere is beneficial to the model. The formation of the continental stable subduction, and what type of specific development (Continental steep subduction or flat subduction) is controlled mainly by the rheological properties of the continental crust. Three different types of continental unstable subduction ("multi stage disconnection", "continuous inflow" and "mass delamination") and low convergence rate respectively, and the lithosphere under middle and high speed convergence. During the unstable subduction of the continental lithosphere with moderate to high rheological strength, the high temperature thermal structure and the low convergence rate are related to the crust of the continental lithosphere with medium high rheological strength. The development of the terrestrial subduction type must meet two conditions: the rheological strength of the highland shell and the high speed subduction, both of which are indispensable. The rheological strength of the highland shell increases with the continental lithosphere mantle entering the subduction channel and the soft flow circle, and reduces the average density of the continental plate, on the other hand, the overall rheological strength of the continental plate is improved. The common effect of the two aspects is beneficial to the emergence of the continental flat subduction. The continental high speed subduction reduces the retention time of the continental plate in the shallow part of the asthenosphere and reduces the heat transfer effect of the continental plates in the asthenosphere, thus making the plates relatively high in rheological strength and is beneficial to the horizontal subduction of the mainland. The India Asian collision The results of the model experiment show that, in order to cause the strong shortening of the overlying Asian continent and the lithosphere structure of the present orogenic belt of the Qinghai Tibet Plateau, the relatively low crust rheology intensity and the relatively high temperature of the lithosphere are the necessary conditions to overlay the Asia continent. Based on the experimental results, two different continental subductions have been identified. Type 1: the first type is subducted continental lithosphere under the overlying continental lithosphere mantle, and the second type is subducted continental lithosphere under the overlying continental crust. The former needs both the subduction side and the overlying continent with high rheological strength, and the latter requires the overlying continent to have a lower rheology than the subduction continent. The dynamic evolution of Zangnan's continental dynamics is similar to that of second types of continental subduction. The continuous northward subduction of the mainland of India has led to the gradual and upper mantle of the lithosphere in the Asian continent. The crustal crust is detached and entered into the asthenosphere, which eventually leads to the direct cushion of the India continent in the Zangnan region under the continental crust of the Asian continent. This process is accompanied by the extensive development of the weak layer of the middle and lower crust in the Tibetan Plateau orogenic zone, the formation of the abnormal thick crust in the collision area and the overflow of the crust material remelting of the deep buried India. The strong magmatism in the high Himalaya area can be reflected in the evolution of the second types of models. In addition, we speculate that the structural differences in the East-West lithosphere in the Himalaya orogenic belt may be caused by a variety of factors, including the differences in the mechanical properties of the mainland of India and the temperature field in the Asian continent. The difference is the convergence rate of initial collision between India and Asia and the difference of lithospheric structure in the northern margin of Qinghai Tibet Plateau.

【學(xué)位授予單位】：中國(guó)科學(xué)院研究生院(廣州地球化學(xué)研究所)
【學(xué)位級(jí)別】：博士
【學(xué)位授予年份】：2016
【分類號(hào)】：P542
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本文編號(hào)：1788123