本文選題：板塊俯沖 + 地幔對流�。� 參考：《武漢大學(xué)》2016年博士論文

【摘要】：為了深入研究板塊俯沖對重大地震事件、火山活動等區(qū)域性地質(zhì)現(xiàn)象的深遠(yuǎn)影響,板塊俯沖的動力學(xué)過程模擬已經(jīng)發(fā)展成為地球科學(xué)的一個重要研究方向。本文運(yùn)用二維數(shù)值模擬技術(shù)研究板塊俯沖動力學(xué)與地幔對流的耦合作用,模擬不同俯沖模型的板塊俯沖動力學(xué)過程,分析板塊俯沖動力學(xué)演化的影響因素,探討關(guān)鍵參數(shù)對于與板塊俯沖相關(guān)的弧后變形及中深源地震等地質(zhì)現(xiàn)象的影響,提煉西太平洋俯沖板塊的俯沖動力學(xué)特征,解釋西太平洋主要俯沖板塊的俯沖形態(tài)及有關(guān)的地質(zhì)現(xiàn)象。論文的主要工作和成果概括如下：利用有限差分方法,計(jì)算了全地幔對流模式和雙層地幔對流模式下日本海溝俯沖板塊熱結(jié)構(gòu)、浮力及P波速度異常分布,基于亞穩(wěn)態(tài)橄欖石相變模型推測亞穩(wěn)態(tài)橄欖石的存在范圍。結(jié)果表明,雙層地幔對流模式下模擬的P波速度異常分布與層析成像結(jié)果更為相符,也與深源地震的分布有較好的相關(guān)性。俯沖板塊所受負(fù)浮力在400 km深度附近達(dá)到最大值,亞穩(wěn)態(tài)橄欖石的存在使負(fù)浮力逐漸減小,甚至在板塊內(nèi)部產(chǎn)生正浮力,不利于俯沖板塊穿透660 km間斷面。運(yùn)用Underworld 1.7數(shù)值模擬軟件,探討了全動力學(xué)俯沖模型和運(yùn)動學(xué)-動力學(xué)俯沖模型的板塊熱結(jié)構(gòu)與黏度演化、板塊俯沖過程中的應(yīng)力分布與地幔對流特征等。研究結(jié)果表明,在上下地幔密度差異的作用下,全動力學(xué)模型的板塊俯沖表現(xiàn)為非穩(wěn)定的俯沖過程,與新生代板塊運(yùn)動觀測結(jié)果較為相符。上覆板塊的應(yīng)力狀態(tài)在弧前和弧后區(qū)域表現(xiàn)出不同的變化特征,主要與上覆板塊與俯沖板塊的相互作用及上覆板塊底部地幔流動有關(guān)。在板塊的俯沖作用下,地幔中呈現(xiàn)出較為復(fù)雜的地幔對流模式,其變化對于板塊俯沖形態(tài)及淺部的應(yīng)力狀態(tài)都有較大的影響。基于全動力學(xué)俯沖模型,討論了不同參數(shù)對板塊俯沖動力學(xué)的影響。模擬結(jié)果表明,當(dāng)上下地幔密度差異或黏度差異較大時,在海溝后撤的作用下,板塊能夠形成平臥于660 km間斷面之上的俯沖形態(tài),但板塊在黏度差異作用下俯沖過程趨于穩(wěn)定。板塊在俯沖至上下地幔交界面之前的俯沖傾角與板塊強(qiáng)度及上覆板塊的年齡有關(guān)。當(dāng)板塊俯沖至下地幔后,板塊的俯沖傾角主要取決于海溝后撤的速度。俯沖板塊的板塊年齡對俯沖動力學(xué)的影響相對較小。上覆板塊弧前區(qū)域均為擠壓應(yīng)力狀態(tài),而弧后區(qū)域的應(yīng)力呈現(xiàn)出持續(xù)的拉伸應(yīng)力作用或出現(xiàn)由拉伸應(yīng)力向擠壓應(yīng)力的轉(zhuǎn)變,與上覆板塊年齡、海溝的運(yùn)動模式及上覆板塊底部的地幔流向有關(guān)。分析總結(jié)了板塊俯沖的動力學(xué)特征,結(jié)合西太平洋俯沖板塊的具體情況,針對西太平洋上較為典型的俯沖板塊,對其俯沖形態(tài)、弧后變形及中深源地震成因給出了一定的解釋。結(jié)果表明,700℃等溫線深度與板塊俯沖速率(或匯聚速率)呈現(xiàn)出一種對數(shù)增加的變化關(guān)系,俯沖板塊上的深源地震可能是由于板塊內(nèi)部溫度過低而發(fā)生橄欖石的亞穩(wěn)態(tài)相變引起的。板塊在抗彎作用下的應(yīng)力狀態(tài)與俯沖板塊上所觀測到的大多數(shù)雙地震帶分布范圍及其震源機(jī)制有較好的一致性,因而能夠較為合理的解釋發(fā)生在俯沖板塊上的中源地震,特別是雙地震帶的形成機(jī)制。西太平洋俯沖板塊上不同的俯沖形態(tài)與海溝的后撤和推進(jìn)作用有關(guān)。該區(qū)域弧后變形的間歇性變化是海溝運(yùn)動、上覆板塊年齡及大范圍的地質(zhì)構(gòu)造活動共同作用的結(jié)果。
[Abstract]:In order to further study the profound influence of plate subduction on major seismic events, volcanic activity and other regional geological phenomena, the simulation of the dynamic process of plate subduction has become an important research direction of earth science. In this paper, the coupling effect of plate subduction and mantle convection is studied by two dimensional numerical simulation. The dynamic evolution process of plate subduction in different subduction models is used to analyze the influence factors of plate subduction dynamics, and to discuss the influence of key parameters on the geological phenomena such as post arc deformation and middle deep source earthquake related to plate subduction, to extract the subduction dynamics of the subduction plate of the Western Pacific, and to explain the subduction of the main subduction plates in the Western Pacific. The main work and results of this paper are summarized as follows: using the finite difference method, the thermal structure, buoyancy and P wave velocity of the subduction plate of the subduction plate of the Japanese trench under the full mantle convection model and the double mantle convection model are calculated. Based on the metastable olivan phase transformation model, the existence of the metastable olivine is speculated. The results show that the anomalous distribution of the P wave velocity simulated under the double layer mantle convection model is more consistent with the results of the tomography, and has a good correlation with the distribution of deep source earthquakes. The negative buoyancy under the subduction plate reaches the maximum near the depth of 400 km, the metastable olivine is deposited and the negative buoyancy is gradually reduced, even within the plate. The positive buoyancy can not help the subduction plate penetrate the 660 km cross section. Using the Underworld 1.7 numerical simulation software, the plate thermal structure and viscosity evolution of the fully dynamic subduction model and the kinematic dive model, the stress distribution and the mantle flow characteristics during the plate subduction are discussed. The results show that the upper and lower mantle density is close to the lower mantle. Under the action of the degree difference, the plate subduction of the fully dynamic model is an unstable subduction process, which is more consistent with the results of the Cenozoic plate motion observation. The stress state of the overlying plate shows different changes in the pre arc and back arc regions, mainly with the interaction between the overlying plate and the subducted plate and the bottom mantle of the overlying plate. Flow is related. Under the subduction of the plate, the mantle convection model is more complex in the mantle. The change has great influence on the plate subduction form and the shallow stress state. Based on the full dynamic subduction model, the influence of the different parameters on the plate subduction dynamics is discussed. The simulation results show that the upper and lower mantle density is shown. When the difference or viscosity varies greatly, the plate can form a subduction form above the 660 km cross section under the action of the trench, but the subduction process tends to stabilize under the effect of the viscosity difference. The subduction angle of the plate before subduction to the upper mantle interface is related to the strength of the plate and the age of the overlying plate. The subduction and dip angle of the plate mainly depends on the retreating velocity of the trench. The plate age of the subduction plate has a relatively small influence on the subduction dynamics. The pre arc region of the overlying plate is the state of extrusion stress, while the stress in the back arc region presents a continuous tensile stress or the transition from tensile stress to extrusion stress. The variation is related to the age of the overlying plate, the movement pattern of the trench and the mantle flow in the bottom of the overlying plate. The dynamic characteristics of the plate subduction are analyzed and summarized. The subduction plate, which is a typical subduction plate on the Western Pacific, has been given to the subduction form, the post arc deformation and the middle deep source earthquake. The results show that the depth of the isotherm at 700 C is associated with a logarithmic increase in the plate subduction rate (or convergence rate). The deep source earthquake on the subduction plate may be caused by the metastable phase transition of olivine due to the low temperature in the plate. The stress state of the plate and the subduction plate under the bending of the plate The distribution of most of the double seismic belts and its source mechanism have good consistency, so it is able to reasonably explain the middle source earthquakes occurring on the subduction plate, especially the formation mechanism of the double seismic belts. The different subduction forms on the subduction plate of the Western Pacific are related to the withdrawal and propulsion of the trenches. The intermittent change of post arc deformation is the result of the trench movement, the age of overlying plate and the large-scale tectonic movement.

【學(xué)位授予單位】：武漢大學(xué)
【學(xué)位級別】：博士
【學(xué)位授予年份】：2016
【分類號】：P542

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