华北克拉通东北边界带岩石圈电性结构及其深部流体分布定量研究

发布时间：2018-06-23 20:33

本文选题：华北克拉通 + 中亚造山带　；参考：《中国地震局地质研究所》2015年博士论文

【摘要】：华北克拉通东北边界带由北部的中亚造山带与南部的华北克拉通构成,该区域属于古亚洲洋与太平洋域的叠合部位。显生宙以来,中亚造山带与华北克拉通经历了多阶段的构造演化,尤为显著的是,在晚中生代到新生代时期内,华北克拉通经历了广泛而强烈的岩石圈构造活化,其东部岩石圈发生了大规模的减薄。为了更好地理解华北克拉通与中亚造山带的构造演化过程,在国家自然科学基金的支持下,本文利用大地电磁测深法沿一条起于中亚造山带,分别穿过了西拉木伦河断裂带、南北重力梯度带、燕山褶皱带、郯庐断裂带,止于辽东半岛的长约1200km的NW-SE走向剖面开展了深部结构探测研究。作者通过数据采集、处理与分析和反演,获得了沿剖面的地下深部二维电阻率结构；结合研究区的地质以及其它地球物理观测资料,对获得的电性结构特征进行了分析与地质解释；基于电阻率模型,利用实验室岩石电导率研究结果,估算了岩石圈地幔流体含量；综合电性结构特征、估算的流体含量与其它地球物理和岩石学的研究,探讨了华北克拉通破坏的机制及动力学过程。本论文主要研究内容和取得成果概述如下：1.MT数据采集、处理与分析沿剖面共采集到48个测点的宽频带大地电磁测深数据,为了达到岩石圈尺度的探测深度,在其中11个测点进行了长周期大地电磁观测。采用带远参考道的Robust技术对宽频带数据与长周期数据的时间序列进行了处理,获得了高质量的大地电磁张量阻抗数据,并对于既有长周期观测数据又有宽频带观测数据的测点,进行了数据的拼接。采用GB张量分解、相位张量及感应矢量分析技术对数据的维性及电性主轴方位进行了详细的分析,结果表明沿剖面的数据具有较好的二维性,能够利用二维反演方法来近似解释,同时结合区域地质构造走向确定了沿剖面的电性主轴方位。将沿剖面所有测点数据旋转到电性主轴方位,并确定了大地电磁数据的TE与TM两种极化模式,对旋转后不同极化模式的数据作了定性分析,了解了沿剖面视电阻率与相位的变化情况。2.MT数据二维反演二维反演前,采用一维Rhoplus反演拟合对数据质量进行了评估,剔除了受干扰影响较严重的数据。采用非线性共轭梯度算法对编辑后的数据进行了二维各向同性反演。在反演过程中,通过选用不同反演极化模式数据、不同的旋转角度、不同的正则化因子及不同数据误差门槛值,进行了大量的二维反演。经过对大量反演模型的比较与模型验证,最终选择了正则化因子为3,TE模式数据的视电阻率与相位的误差门槛分别为20%、5%,TM模式数据的视电阻率与相位的误差门槛分别为10%、5%,Tipper的误差门槛为0.05,经过迭代200次,总的数据拟合均方差为2.57的反演模型为最可靠的地下电阻率模型。另外,利用非线性共轭梯度二维各向异性MT反演代码对数据进行了二维各向异性反演,二维各向异性电阻率模型基本与各向同性反演模型一致,但是,在郯庐断裂存在平行于剖面方向的电性各向异性。3.电阻率模型解释结合地质学和其它地球物理观测数据,对二维各向同性反演的电阻率模型进行全面分析解释与构造涵义讨论。二维电阻率模型显示在索伦山缝合带的中下地壳存在一个北西倾向的低阻层,可能代表着北部西伯利亚板块与南部华北克拉通最终缝合的位置,该低阻层可能是由富硫的石墨薄层形成。剖面西北段中亚造山带与东南段华北克拉通的上地幔电阻率呈现明显的差异性,中亚造山带的电阻率值相对较高(300-1000Ω.m),而华北克拉通的电阻率值相对较低(10-100Ω.m),电阻率整体上的减小可能与华北克拉通上地幔具有较高的温度和富含流体有关。沿剖面上地幔存在三个局部低阻体,分别位于西拉木伦河断裂、南北重力梯度带和郯庐断裂带附近,它们可能由水与部分熔融形成的,与软流圈的物质上涌有关。4.上地幔流体含量的估算基于获得的二维电阻率模型,利用实验室岩石电导率研究成果、改进的阿尔奇公式和上地幔的温度结构,对中亚造山带与华北克拉通两个典型测点上地幔40-100km深度范围的含水量与部分熔融份数进行了估算。对于中亚造山带测点,55-65km深度以上观测的电阻率需要由含水与部分熔融来解释,而这个深度以下,仅仅含水就可以解释观测的电阻率值,且55-65km的含水量高达800-1000 ppm,说明在这个深度中亚造山带岩石圈发生了水化,但随着深度增加,含水量明显减小。而对于华北克拉通的测点,在40-100km深度观测到电阻率需要由含水与约1%的部分熔融来解释,并且在100km深度的水含量达500 ppm,明显的高于稳定克拉通的含水量。比较沿剖面的上地幔的水与部分熔融份数,无论是含水量还是部分熔融份数,华北克拉通都要高于中亚造山带的值,暗示华北克拉通遭到了强烈的水化并导致了部分熔融的发生。5.华北克拉通破坏的动力学过程与机制综合电性结构特征、估算的上地幔流体含量和其它的地球物理、地球化学数据分析表明,本文研究区的华北克拉通的岩石圈发生减薄并呈现空间不均一性,并且不同地点减薄机制可能不同,燕山造山带以拆沉作用为主,而郯庐断裂带附近可能以热侵蚀作用为主；华北克拉通岩石圈的高含水量与部分熔融份数可能与西太平洋板块的俯冲有关,俯冲板块的脱水作用释放了大量水上涌至华北克拉通,使岩石圈地幔发生强烈的水化,同时水的增加导致了岩石发生部分熔融,进一步使岩石圈的强度减低,最终导致岩石圈发生拆沉或侵蚀而遭到破坏。从这个角度来说,华北克拉通破坏的主要动力学因素可能是西太平洋板块的俯冲。
[Abstract]:The northeastern border zone of the North China Craton consists of the northern Central Asian orogenic belt and the North China Craton in the south. The region belongs to the overlapping part of the ancient Asian Ocean and the Pacific region. Since the phanus, the Central Asian orogenic belt and the North China Craton experienced multiple stages of tectonic evolution, especially in the late Mesozoic to the Cenozoic era, North China. In order to better understand the tectonic evolution process of the North China Craton and the Central Asian orogenic belt, in order to better understand the tectonic evolution process of the North China Craton and the Central Asian orogenic belt, the paper uses the magnetotelluric sounding method along a central Asian orogenic belt to cross the west, respectively. The Mulun River fault zone, the North-South gravity gradient belt, the Yanshan fold belt, the Tan Lu fault zone, and the long approximately 1200km NW-SE strike section of the Liaodong peninsula have been investigated for deep structural exploration. And other geophysical data, the characteristics of the electrical structure obtained are analyzed and geological interpretation. Based on the resistivity model, the results of the laboratory rock conductivity research results are used to estimate the fluid content of the lithosphere mantle, the comprehensive electrical structure characteristics, the estimated fluid content and other geophysical and petrology studies. The mechanism and dynamic process of the failure of the North China Craton. The main contents and achievements of this paper are summarized as follows: 1.MT data acquisition, processing and analyzing the wide-band magnetotelluric data of 48 measuring points collected along the profile. In order to reach the depth of the lithosphere scale, 11 of them have carried out long period geoelectricity. Magnetic observation. The Robust technology with far reference channel is used to process the time series of broadband data and long period data, and high quality magnetotelluric impedance data are obtained, and the data are spliced for both long period observation data and wideband observation data. GB tensor decomposition, phase tensor, and phase tensor are used. The technology of induction vector analysis is a detailed analysis of the dimension of the data and the orientation of the electric spindle. The results show that the data along the section has a good two-dimensional character. It can be approximated by the two-dimensional inversion method, and the direction of the electric spindle along the section is determined with the direction of the regional geological structure. The two polarization modes of TE and TM of magnetotelluric data are determined, and the data of different polarization modes after rotation are qualitatively analyzed. The data quality is evaluated by one dimension Rhoplus inversion fitting before the two-dimensional inversion of.2.MT data along the profile apparent resistivity and phase. The nonlinear conjugate gradient algorithm is used to retrieve the edited data by using the nonlinear conjugate gradient algorithm. In the inversion process, a large number of two dimensional inverse is carried out by selecting different inversion polarization mode data, different rotation angles, different regularization factors and different threshold values of different data errors. After the comparison and model verification of a large number of inversion models, the regularization factor is selected as 3. The error threshold of apparent resistivity and phase of TE model data is 20%, 5%, and the error threshold of apparent resistivity and phase is 10%, 5%, and Tipper error threshold is 0.05 respectively, and the total data is fitted through iterative 200 times. The inversion model with a variance of 2.57 is the most reliable underground resistivity model. In addition, the two-dimensional anisotropic inversion of the nonlinear conjugate gradient MT inversion code is used for two-dimensional anisotropic inversion, and the two-dimensional anisotropic resistivity model is basically consistent with the isotropic inversion model, but the Tan Lu fault is parallel to the section direction in the Tan Lu fault. The interpretation of electrical anisotropy.3. resistivity model, combined with geology and other geophysical data, discusses the comprehensive analysis and interpretation of the resistivity model of two-dimensional isotropic inversion. The two-dimensional resistivity model shows that there is a low resistivity layer in the middle and lower crust in the middle and lower crust of the susushan suture zone, which may be representative. The final suture of the northern Siberia plate and the southern North China Craton may be formed by a thin layer of sulfur rich graphite. The resistivity of the Central Asian orogenic belt in the northwestern section of the section and the North China Craton in the southeast section is distinctly different. The resistance rate of the Central Asian orogenic belt is relatively high (300-1000 Omega.M), while the North China carat is relatively high. The resistivity of the tong is relatively low (10-100 Omega.M). The reduction of the resistivity as a whole may be related to the higher temperature and fluid rich in the upper mantle of the North China Craton. There are three local low resistance bodies along the section of the mantle, which are located in the Mulun River fault, the north and South gravity gradient zones and the Tanlu fault zone, which may be from water and part. The estimation of the fluid content of the upper mantle on the.4. upper mantle with the material upwelling of the asthenosphere is based on the obtained two-dimensional resistivity model, using the results of the laboratory rock conductivity study, the improved Archie formula and the temperature structure of the upper mantle, on the 40-100km depth range of the upper mantle of the Central Asian orogenic belt and the North China Craton two typical measurements. For the Central Asian orogenic belt, the resistivity of the 55-65km depth above is explained by water and partial melting. Below this depth, water content only can explain the observed resistivity value, and the water content of 55-65km is up to 800-1000 ppm, indicating that the depth of the Central Asian orogeny at this depth. The lithosphere is hydrated, but with the depth increasing, the water content is obviously reduced. And for the North China Craton survey point, the resistivity of the 40-100km depth is explained by the partial melting of water and about 1%, and the water content of the 100km depth is up to 500 ppm, obviously higher than the water content in the stable craton. The number of water and partial melting portion of the mantle, whether water content or partial melting portion, is higher than the value of the Central Asian orogenic belt, suggesting that the North China Craton has been strongly hydrated and resulted in the dynamic process of the damage of the.5. North China Craton with partial melting and the characteristics of the mechanical integrated electrical structure, and the estimated upper mantle flow. The analysis of the body content and other geophysical data shows that the lithosphere of the North China Craton in this study area has been thinner and spatial heterogeneity, and the mechanism of thinning in different locations may be different. The Yanshan orogenic belt is mainly dismantling, and the main part of the Tanlu fault zone may be thermal erosion, and North China carat. The high water content and partial melting portion of the lithosphere may be related to the subduction of the Western Pacific plate. The dehydration of the subducted plate releases a large amount of water to the North China Craton, which makes the lithosphere mantle strongly hydrated, and the increase of water leads to the partial melting of the rock, which further reduces the strength of the lithosphere and ultimately leads to the strength of the lithosphere. The main dynamic factor of the destruction of the North China Craton may be the subduction of the Western Pacific plate from this point of view.
【学位授予单位】：中国地震局地质研究所
【学位级别】：博士
【学位授予年份】：2015
【分类号】：P631.325

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