羌塘地塊深部電性結(jié)構(gòu)研究及動(dòng)力學(xué)意義
發(fā)布時(shí)間：2018-10-19 19:44
【摘要】：本文主要利用5條大地電磁剖面對(duì)青藏高原中北部羌塘地塊及鄰區(qū)深部電性結(jié)構(gòu)開展詳細(xì)研究探討,并獲得了該區(qū)域殼幔結(jié)構(gòu)及動(dòng)力學(xué)過(guò)程的一些新認(rèn)識(shí)。大地電磁法資料處理時(shí),首先分析了每個(gè)測(cè)點(diǎn)的二維偏離度、電性主軸方向、阻抗相位張量和趨膚深度等參數(shù),再采用NLCG法對(duì)TE和TM兩種模式的視電阻率和相位數(shù)據(jù)進(jìn)行聯(lián)合反演,最終獲得了沿剖面5條測(cè)線的二維電性結(jié)構(gòu)模型�；谶@些電性結(jié)構(gòu)模型,結(jié)合研究區(qū)域已有的地質(zhì)和地球物理資料,我們對(duì)該區(qū)域深部電性結(jié)構(gòu)及動(dòng)力學(xué)過(guò)程取得了如下新認(rèn)識(shí)：(1)羌塘地塊垂向由淺至深大致可分為三個(gè)電性層：第一層為高阻層,電阻率值為幾百至幾千歐姆米；第二層為殼內(nèi)高導(dǎo)層,電阻率值為幾歐姆米,且高導(dǎo)層沿剖面分布不均勻；第三層為相對(duì)高阻層,電阻率值為幾十至幾百歐姆米。本研究還發(fā)現(xiàn)南羌塘地塊存在殼內(nèi)雙層高導(dǎo)層,證實(shí)了青藏高原西部和中部南羌塘地塊存在雙層殼內(nèi)高導(dǎo)層的觀點(diǎn)。(2)橫穿羌塘地塊的三條大地電磁剖面反演結(jié)果顯示：羌塘地塊之下地電結(jié)構(gòu)除具有上下分層的特性外,還有南北兩分的特征。其中南羌塘地塊之下高導(dǎo)層自羌中隆起附近向南傾斜；而北羌塘地塊之下高導(dǎo)層形態(tài)類似于勺子形狀,由金沙江縫合帶之下靠近地表的深度向南傾斜,在北羌塘地塊中部延伸至最大深度的下地殼或上地幔,并開始逐漸向上延伸,在羌中隆起附近到達(dá)近地表深度。南、北羌塘地塊之下的殼內(nèi)高導(dǎo)層均在羌中隆起附近向地表延伸,形成南北對(duì)沖的異常形態(tài)。基于此,認(rèn)為在三疊紀(jì)時(shí)期,松潘-甘孜混雜巖沿金沙江縫合帶向南俯沖,破壞并替代了幾乎整個(gè)羌塘地塊的地殼結(jié)構(gòu)。羌塘地塊殼內(nèi)富水的混雜巖將有利于含水熔融的發(fā)生,進(jìn)而解釋班公湖-怒江縫合帶兩側(cè)明顯的地球物理差異。(3)根據(jù)羌塘地塊殼內(nèi)高導(dǎo)層的分布特征還可推斷：在羌塘地塊中西部,地殼流并非沿金沙江縫合帶向東流動(dòng),而是在羌塘地塊中部自西向東流動(dòng),并在高原東南部逐漸轉(zhuǎn)為沿構(gòu)造薄弱帶流出。而在羌塘地塊中部不斷上涌的幔源巖漿為維持羌塘地塊不變的海拔高度和不斷東流的地殼流之間的平衡提供物質(zhì)支持。(4)兩條跨越班公湖-怒江縫合帶的的大地電磁剖面的反演結(jié)果顯示：殼內(nèi)高導(dǎo)體在班公湖-怒江縫合帶以南30～40km的位置(地表對(duì)應(yīng)改則-色林錯(cuò)逆沖斷裂)規(guī)模最大,并且具有南北對(duì)沖特征和向上地幔延伸的趨勢(shì)。本人認(rèn)為這一相互對(duì)沖的高導(dǎo)異常可能反映了中特提斯洋殼雙向俯沖的殘留痕跡。班公湖-怒江縫合帶之下淺部與深部電性結(jié)構(gòu)明顯的錯(cuò)動(dòng)說(shuō)明了在新生代時(shí)期,班公湖-怒江縫合帶兩側(cè)發(fā)生過(guò)強(qiáng)烈的逆沖推覆構(gòu)造運(yùn)動(dòng),使得班公湖-怒江縫合帶上蛇綠巖發(fā)生構(gòu)造侵位,進(jìn)而導(dǎo)致淺部與深部構(gòu)造錯(cuò)斷,而南羌塘地塊雙層殼內(nèi)高導(dǎo)層中的淺部高導(dǎo)層即為這一系列逆沖推覆構(gòu)造所形成的構(gòu)造滑脫面。(5)由衛(wèi)星重、磁數(shù)據(jù),發(fā)現(xiàn)羌塘地塊中部雙湖地塹具有由地表向下地殼延伸的趨勢(shì)。通過(guò)比較羌塘地塊各種地質(zhì)事件發(fā)生的先后順序,推測(cè)羌塘地塊中部的雙湖地塹是由于高原隆升至最大高度后,增厚的巖石圈地幔發(fā)生重力垮塌,進(jìn)而形成了該南北向斷裂。
[Abstract]:In this paper, five magnetotelluric profiles are used to study the deep electrical structures of the Qiangtang block and the adjacent region in the Qinghai-Tibet Plateau, and some new understandings of the structure and dynamic process of the shell structure are obtained. In the data processing of magnetotelluric method, the two-dimensional deviation, electrical principal axis direction, impedance phase tensor, skin depth and other parameters of each measuring point are analyzed, and the apparent resistivity and phase data of TE and TM modes are jointly inverted by NLCG method. Finally, a two-dimensional electrical structure model is obtained along section 5. Based on these electrical structural models, combined with the existing geological and geophysical data in the research area, we have obtained a new understanding of the deep electrical structure and dynamic process of the region: (1) the vertical direction of the Qiangtang plot can be divided into three electrical layers from shallow to deep: the first layer is the high resistance layer, the resistivity value is hundreds to thousands of ohms; the second layer is a high conductivity layer in the shell; the resistivity value is several ohms; and the high conductivity layer is not evenly distributed along the cross section; the third layer is a relatively high resistance layer, and the resistivity value is tens to hundreds of ohms. The present study also found that there are two layers of high conductivity in the shell of the southern Qiangtang block, and the view that the high conductivity layer in the double shell is present in the western part of the Tibetan Plateau and the southern Qiangtang block in the central part of the Qinghai-Tibet Plateau is proved. (2) The inversion results of three magnetotelluric cross sections across the Qiangtang block show that the electric structure under the Qiangtang block has the characteristics of two points of north and south besides the characteristics of upper and lower layers. wherein the high conductivity layer below the southern Qiangtang block is inclined to the south from the middle of the uplift; and the high conductivity layer below the northern Qiangtang block is similar to the spoon shape, the depth of the high conductivity layer below the north Qiangtang block is inclined to the south, and the middle part of the north Qiangtang block extends to the lower earth crust or the upper crust of the maximum depth, and begins to extend gradually upward, reaching a near surface depth in the vicinity of the ridge in the ridge. In the south and the northern Qiangtang block, the high conductivity layer in the shell extends to the earth surface in the vicinity of the uplift, thus forming the abnormal form of the north-south hedge. On the basis of this, it is believed that during the Triassic, Songpan-Ganzi hybrid rocks subducted to the south along the same suture zone, destroyed and replaced the crustal structure of almost the whole Qiangtang block. The water-rich mixed rock in the shell of the Qiangtang block will be beneficial to the occurrence of water-containing melting, and further explain the obvious geophysical difference between the two sides of the Bangong Lake-Nujiang suture zone. (3) According to the distribution characteristics of the high conductivity layer in the shell of the Qiangtang block, it can be concluded that in the west and west of the Qiangtang block, the earth's crust flow does not flow eastward along the north-west suture zone, but flows eastward from west to east in the middle part of the Qiangtang block, and gradually turns out along the structural weakness zone in the southeast part of the plateau. In the middle of the Qiangtang block, the flood-source magma poured into the middle of the northern Qiangtang block provides material support for maintaining the constant altitude of the Qiangtang block and the constant flow of the earth's crust. (4) The inversion results of the magnetotelluric cross section of the two suture zones across the Bangong Lake-Nujiang River show that the height of the high conductor in the shell is the largest in the 30 ~ 40km south of the Bangong Lake-Nujiang suture zone (corresponding to the change of the surface corresponding to the reverse impact of the color forest). and has a trend of north-south hedge characteristics and up-and-down extension. I believe that this one-sided high anomaly may reflect the vestiges of a two-way dive in the Tethys oceanic crust. The obvious misinterpretation of shallow part and deep electrical structure under Bangong Lake-Nujiang suture zone shows that there has been a strong reverse thrust-over tectonic movement on both sides of Bangong Lake-Nujiang suture zone during the Cenozoic era, so that the ophiolite in Bangong Lake-Nujiang suture belt has tectonic invasion position. in addition, that shallow part and the deep structure are staggered, and the shallow part high-permeability layer in the high-permeability layer in the double-layer shell of the south Qiangtang block is the structure slip surface formed by the series of reverse punching and pushing-over structure. (5) From the satellite weight and magnetic data, it is found that the double-lake graben in the middle of the Qiangtang block has a tendency to extend downward from the earth's surface. By comparing the sequence of various geological events in the Qiangtang block, it is estimated that the two-lake graben in the middle part of the Qiangtang block is due to the high plateau uplift to the maximum height, and the thickened lithospheric surface is collapsed and the north-south fault is formed.
【學(xué)位授予單位】：中國(guó)地質(zhì)大學(xué)
【學(xué)位級(jí)別】：博士
【學(xué)位授予年份】：2016
【分類號(hào)】：P631.325
本文編號(hào)：2282169
[Abstract]:In this paper, five magnetotelluric profiles are used to study the deep electrical structures of the Qiangtang block and the adjacent region in the Qinghai-Tibet Plateau, and some new understandings of the structure and dynamic process of the shell structure are obtained. In the data processing of magnetotelluric method, the two-dimensional deviation, electrical principal axis direction, impedance phase tensor, skin depth and other parameters of each measuring point are analyzed, and the apparent resistivity and phase data of TE and TM modes are jointly inverted by NLCG method. Finally, a two-dimensional electrical structure model is obtained along section 5. Based on these electrical structural models, combined with the existing geological and geophysical data in the research area, we have obtained a new understanding of the deep electrical structure and dynamic process of the region: (1) the vertical direction of the Qiangtang plot can be divided into three electrical layers from shallow to deep: the first layer is the high resistance layer, the resistivity value is hundreds to thousands of ohms; the second layer is a high conductivity layer in the shell; the resistivity value is several ohms; and the high conductivity layer is not evenly distributed along the cross section; the third layer is a relatively high resistance layer, and the resistivity value is tens to hundreds of ohms. The present study also found that there are two layers of high conductivity in the shell of the southern Qiangtang block, and the view that the high conductivity layer in the double shell is present in the western part of the Tibetan Plateau and the southern Qiangtang block in the central part of the Qinghai-Tibet Plateau is proved. (2) The inversion results of three magnetotelluric cross sections across the Qiangtang block show that the electric structure under the Qiangtang block has the characteristics of two points of north and south besides the characteristics of upper and lower layers. wherein the high conductivity layer below the southern Qiangtang block is inclined to the south from the middle of the uplift; and the high conductivity layer below the northern Qiangtang block is similar to the spoon shape, the depth of the high conductivity layer below the north Qiangtang block is inclined to the south, and the middle part of the north Qiangtang block extends to the lower earth crust or the upper crust of the maximum depth, and begins to extend gradually upward, reaching a near surface depth in the vicinity of the ridge in the ridge. In the south and the northern Qiangtang block, the high conductivity layer in the shell extends to the earth surface in the vicinity of the uplift, thus forming the abnormal form of the north-south hedge. On the basis of this, it is believed that during the Triassic, Songpan-Ganzi hybrid rocks subducted to the south along the same suture zone, destroyed and replaced the crustal structure of almost the whole Qiangtang block. The water-rich mixed rock in the shell of the Qiangtang block will be beneficial to the occurrence of water-containing melting, and further explain the obvious geophysical difference between the two sides of the Bangong Lake-Nujiang suture zone. (3) According to the distribution characteristics of the high conductivity layer in the shell of the Qiangtang block, it can be concluded that in the west and west of the Qiangtang block, the earth's crust flow does not flow eastward along the north-west suture zone, but flows eastward from west to east in the middle part of the Qiangtang block, and gradually turns out along the structural weakness zone in the southeast part of the plateau. In the middle of the Qiangtang block, the flood-source magma poured into the middle of the northern Qiangtang block provides material support for maintaining the constant altitude of the Qiangtang block and the constant flow of the earth's crust. (4) The inversion results of the magnetotelluric cross section of the two suture zones across the Bangong Lake-Nujiang River show that the height of the high conductor in the shell is the largest in the 30 ~ 40km south of the Bangong Lake-Nujiang suture zone (corresponding to the change of the surface corresponding to the reverse impact of the color forest). and has a trend of north-south hedge characteristics and up-and-down extension. I believe that this one-sided high anomaly may reflect the vestiges of a two-way dive in the Tethys oceanic crust. The obvious misinterpretation of shallow part and deep electrical structure under Bangong Lake-Nujiang suture zone shows that there has been a strong reverse thrust-over tectonic movement on both sides of Bangong Lake-Nujiang suture zone during the Cenozoic era, so that the ophiolite in Bangong Lake-Nujiang suture belt has tectonic invasion position. in addition, that shallow part and the deep structure are staggered, and the shallow part high-permeability layer in the high-permeability layer in the double-layer shell of the south Qiangtang block is the structure slip surface formed by the series of reverse punching and pushing-over structure. (5) From the satellite weight and magnetic data, it is found that the double-lake graben in the middle of the Qiangtang block has a tendency to extend downward from the earth's surface. By comparing the sequence of various geological events in the Qiangtang block, it is estimated that the two-lake graben in the middle part of the Qiangtang block is due to the high plateau uplift to the maximum height, and the thickened lithospheric surface is collapsed and the north-south fault is formed.
【學(xué)位授予單位】：中國(guó)地質(zhì)大學(xué)
【學(xué)位級(jí)別】：博士
【學(xué)位授予年份】：2016
【分類號(hào)】：P631.325
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