發(fā)布時(shí)間：2018-06-21 01:23

  本文選題：克拉通破壞 + 巖石圈減薄��； 參考：《中國地質(zhì)大學(xué)》2017年博士論文

【摘要】：克拉通是地球自形成以來較先固結(jié)的淺部地質(zhì)單元,占現(xiàn)今全球陸地面積的50%以上。由于其面積大、厚度大、地溫梯度低、缺乏易熔組份、密度低、粘度大等因素的影響,使得克拉通巖石圈不易受到后期地質(zhì)作用的破壞而失穩(wěn)。然而,最近研究表明某些克拉通(如華北克拉通東部、北大西洋克拉通、坦桑尼亞克拉通局部)巖石圈并不像過去所認(rèn)為的那樣穩(wěn)定,而是也會(huì)發(fā)生再活化和破壞。但是對于何種驅(qū)動(dòng)力和何種破壞機(jī)制導(dǎo)致了再活化和破壞,依然存在較大爭議。華北克拉通,作為世界上研究程度最高的克拉通之一,其巖石圈破壞現(xiàn)象為舉世所矚目。其巖石圈破壞期間經(jīng)歷了復(fù)雜的地質(zhì)作用,所涉及的驅(qū)動(dòng)力包括俯沖作用、碰撞作用和地幔上涌或地幔柱作用,相關(guān)的減薄機(jī)制包括伸展減薄、拆沉減薄、對流侵蝕減薄、水弱化、熔體-橄欖巖反應(yīng)等,使得華北克拉通巖石圈減薄與破壞的主要驅(qū)動(dòng)力和機(jī)制存在諸多爭議。但相比之下,北大西洋、坦桑尼亞克拉通破壞期間所經(jīng)歷的地質(zhì)作用則較為簡單,主要為地幔上涌或地幔柱作用相關(guān)的熱機(jī)械侵蝕和伸展減薄。本文通過將這三個(gè)克拉通以及全球范圍內(nèi)其它克拉通的地質(zhì)演化歷史、巖石圈改造歷史、巖石圈減薄地球物理特征進(jìn)行對比,定性分析了克拉通邊緣和內(nèi)部減薄的異同點(diǎn),以及大陸單元不同位置處巖石圈減薄的異同點(diǎn)。定性對比分析顯示:(1)邊緣減薄主要與俯沖、碰撞、重復(fù)伸展相關(guān)的交代作用、巖漿作用、拆沉作用、變克拉通化、熔體-橄欖巖反應(yīng)、流體弱化等作用相關(guān)有關(guān),減薄的尺度可達(dá)下地殼深度。(2)而內(nèi)部減薄則與大規(guī)模的伸展作用、大規(guī)模的脫水和水弱化和對流侵蝕作用、大規(guī)模的巖石圈拆沉作用相關(guān)。大尺度的巖石圈減薄還可能受到巖石圈本身穩(wěn)定性的影響。例如巖石圈地幔中層深度(MLD,80-120 km)弱耦合層會(huì)使得巖石圈底部發(fā)生水平方向的遲滯和錯(cuò)位,并產(chǎn)生減薄現(xiàn)象。(3)活動(dòng)大陸邊緣受俯沖相關(guān)的熔體、流體以及深部地幔對流侵蝕作用影響。此外還受(2)中所述的MLD之下巖石圈水平錯(cuò)動(dòng)的影響。(4)被動(dòng)大陸邊緣則受巖石圈由厚到薄轉(zhuǎn)換或地幔柱產(chǎn)生的次生對流侵蝕的破壞。此外還受(2)中所述的MLD之下巖石圈水平錯(cuò)動(dòng)的影響�；谝陨蠈Ρ裙ぷ骱投ㄐ苑治�,筆者選取克拉通內(nèi)部大規(guī)模減薄模型中的幾個(gè)可能機(jī)制(大規(guī)模的脫水和水弱化和對流侵蝕作用、大規(guī)模的巖石圈拆沉作用和大規(guī)模巖石圈水平方向的遲滯和錯(cuò)位)進(jìn)行地球動(dòng)力學(xué)數(shù)值模擬定量分析研究。筆者研究發(fā)現(xiàn):(1)深俯沖的平臥板片大規(guī)模擾動(dòng)富水地幔轉(zhuǎn)換帶(≥0.6 wt%),引起軟流圈和克拉通巖石圈水弱化和次生對流加強(qiáng)可以導(dǎo)致克拉通巖石圈的大規(guī)模減薄。(2)其中富水地幔轉(zhuǎn)換帶中的水主要來自于之前多方向深俯沖板片在地幔轉(zhuǎn)換帶中彎曲、堆積甚至崩塌、穿透到下地幔時(shí)所產(chǎn)生的板片脫水作用和地幔轉(zhuǎn)換帶吸水作用。(3)下地殼尺度的拆沉主要發(fā)生于克拉通邊緣和加厚的大陸高原區(qū)域。對于克拉通內(nèi)部的巖石圈拆沉,MLD深度(80-120km)比下地殼深度(20-40 km)要更容易發(fā)生。(4)對于巖石圈密度較小的克拉通,在大陸漂移過程中會(huì)發(fā)生巖石圈底部沿MLD(80-120km)弱耦合層的解耦,使得巖石圈底部被水平遲滯和錯(cuò)位到大陸漂移尾端的大洋巖石圈之下,并使得大陸漂移前端的巖石圈發(fā)生減薄。在某些克拉通區(qū)域,MLD的性質(zhì)與巖石圈-軟流圈界面性質(zhì)相似,可以作為板塊運(yùn)動(dòng)的底界面。以上數(shù)值模擬研究內(nèi)容和結(jié)果均可以與克拉通對比中所發(fā)現(xiàn)的關(guān)鍵地質(zhì)和地球物理實(shí)例進(jìn)行較好的對比,用地球動(dòng)力學(xué)和地質(zhì)、地球物理資料相結(jié)合的思路支持了筆者觀點(diǎn)在克拉通演化過程中的可適用性。
[Abstract]:Craton is the first consolidation of the earth's shallow geological unit since its formation, accounting for more than 50% of the global land area today. Due to its large area, large thickness, low geothermal gradient, lack of infusible components, low density, large viscosity and other factors, the cratonic lithosphere is not easily damaged by the failure of later geological action. However, recent research has been studied. It shows that some cratonic rocks (such as the eastern North China Craton, the North Atlantic craton, and the local kcraton of Tanzania) are not as stable as they were thought in the past, but also reactivation and destruction. But there is still a big controversy over what driving force and the destruction mechanism has led to reactivation and destruction. As one of the highest degree of cratonic research in the world, its lithospheric destruction has attracted the attention of the world. Its lithosphere has undergone complicated geological processes during the lithosphere destruction, and the driving forces involved include subduction, collision and mantle upwelling or mantle plume, and the thinning mechanism of the lithosphere includes extensional thinning, sedimentation reduction and convection. There are many disputes over the main driving forces and mechanisms of the thinning and destruction of the North China Craton lithosphere, but in contrast, the geological effects of the North Atlantic and Tanzania craton are relatively simple, mainly due to the thermal machinery related to the mantle upwelling or the mantle plume. By comparing the geological evolution history of the three cratonic cratonic and other cratonic cratats worldwide, the history of the lithosphere transformation and the lithosphere thinning of the geophysical characteristics, this paper qualitatively analyzed the similarities and differences between the cratonic edge and the internal thinning, as well as the similarities and differences between the lithosphere thinning at different locations in the continental unit. The qualitative contrast analysis shows: (1) the thinning of the edges is mainly related to subduction, collisions, repeated extension related metasomatism, magmatism, delamination, carat Tonghua, melts peridotite reaction, fluid weakening and so on, and the thinning scale can reach the lower crust depth. (2) the internal thinning is extended with large-scale extension and large-scale removal. The weakening of water and water and convective erosion are related to the large-scale lithosphere delamination. Large scale lithosphere thinning may also be affected by the stability of the lithosphere itself. For example, the weak coupling layer of the middle layer of the lithosphere mantle (MLD, 80-120 km) will cause the sluggish and dislocation of the square direction of water in the bottom of the lithosphere and the thinning phenomenon. (3) The active continental margin is affected by subduction related melts, fluids and convective erosion in the deep mantle. In addition, the influence of the lithospheric horizontal dislocation below MLD is also affected. (4) the passive continental margin is damaged by the secondary opposite flow erosion caused by the lithosphere from thick to thin or from the mantle plume. In addition, under the (2) of the (2) MLD Based on the above comparison work and qualitative analysis, the author selects several possible mechanisms in the mass thinning model within the craton (large scale dehydration and water weakening and convective erosion, large-scale lithospheric dehydration and large scale hysteresis and dislocation in the horizontal direction of the rock circle). The study found that: (1) the deep subducted flat plate with large scale disturbed water rich mantle transition zone (> 0.6 wt%) caused the weakening of the water and the secondary convection in the asthenosphere and cratonic lithosphere. (2) the water in the water rich mantle transition zone is mainly derived from the water. The previous multi directional deep subduction plates bend in the mantle transition zone, accumulate even collapse, and penetrate into the lower mantle. (3) the reduction of the lower crustal scale mainly occurs at the cratonic edge and the thickened continental plateau region. The lithosphere disintegration within the craton, MLD depth (80) -120km) is more likely to occur than the lower crust depth (20-40 km). (4) for the craton with smaller lithosphere density, the bottom of the lithosphere will be decoupled from the weak coupling layer of the MLD (80-120km) in the course of the continental drift, causing the bottom of the lithosphere to be stagnant and misplaced to the oceanic lithosphere at the end of the continental drift, and before the drift of the continent. In some cratonic regions, the properties of MLD are similar to the lithosphere and asthenosphere interface, which can be used as the bottom interface of the plate movement. The above numerical simulation research and results can be compared with the key geological and geophysical examples found in the craton comparison, using geodynamics. The combination of geological and geophysical data supports the applicability of the author's viewpoint in the evolution of craton.
【學(xué)位授予單位】：中國地質(zhì)大學(xué)
【學(xué)位級別】：博士
【學(xué)位授予年份】：2017
【分類號(hào)】：P541;P31
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本文編號(hào)：2046540