【作者】 宋键；

【导师】 邓志辉； 唐方头；

【作者基本信息】 中国地震局地质研究所 ， 构造地质学， 2010， 博士

【摘要】 喜马拉雅东构造结(简称东构造结)周围地区是青藏高原构造应力作用和构造变形最强的地区,也是地球上变化剧烈、构造类型复杂、保存完整的地区。该地区汇集了喜马拉雅、拉萨、羌塘、川滇地块和印度板块及主边界断裂、主中央断裂、雅鲁藏布江断裂、嘉黎断裂、怒江断裂、墨脱断裂、阿帕龙断裂等,可以说东构造周围地区是检验青藏高原晚新生代构造变形机制不同理论和学说的关键地区之一。由于本区是主要由海拔4000m以上高山和雅鲁藏布江、怒江、澜沧江和金沙江等构成的高山峡谷地貌,工作环境恶劣,而且地质构造复杂等多种原因,在短时间内很难利用单一手段确定其构造变形的运动场和对不同构造部位、不同性质、不同活动方式的断裂现今运动进行定量研究。因此,本文主要采用了多种方法综合分析来研究东构造结周边地区的构造变形和主要断裂的运动特征:通过野外地质调查获取研究区构造地块和边界断裂的几何特征和活动性质;通过高精度GPS观测技术的应用,在关键构造部位加密观测,获取研究区现今地壳变形速度场和主要断裂运动方式;通过地球物理探测资料的综合研究,分析地壳介质的物理参数和深部地质结构;通过大型数值模拟分析,探讨主要断裂的运动特征和区域构造变形的动力学机理。一、研究方法本文主要通过三种方法来研究本区的地壳变形速度场和主要断裂的运动方式:1.传统地质学研究野外实地调查是地质研究中不可缺少的方法,可以直接反映主要断裂带在历史时期的活动特征。通过对前人野外调查及GPS资料的分析,我们选择性地对雅鲁藏布江断裂、嘉黎断裂及怒江断裂的关键构造部位及前人研究工作存在分歧的地区进行了实地地质调查。在调查过程中,重点对各主要断裂晚第四纪以来运动的地质剖面进行了研究,获取了更多本区主要断裂晚第四纪以来运动特征的地质学证据。2.GPS观测与分析为了深入研究东构造结及其周边地区现今构造变形特征,作者系统分析了研究区内“中国地壳运动观测网络工程”GPS站点多年观测数据,并在原有GPS站点缺少的地区,与唐方头老师等一起新建了12个GPS观测点,现已进行了两期观测,获得了最新观测数据。本文采用跨断层GPS速度剖面和断层位错模型对不同构造部位主要断裂的运动特征进行研究。前者是将断层带两侧的GPS测点的速度矢量分解成垂直剖面的速度分量和平行剖面的速度分量,其中垂直剖面的速度分量反映断裂带的倾滑运动特征,平行剖面的速度分量则反映断裂带的走滑运动特征,断裂带两侧之间的差异运动代表其运动特征;后者是采用OKADA断层位错模型来对断层的运动速率及特征进行反演。3.有限元数值模拟有限元方法可以很好地对地质过程进行恢复再现和活动预测,基于三维有限元分析方法,以主要断裂为边界,通过已有的地质和地球物理资料对青藏高原不同区域岩石圈介质参数进行反演,建立东构造结地区的构造变形模型,以“中国地壳运动观测网络工程”和“中国大陆构造环境监测网络工程”最新GPS观测资料及国家自然科学基金资助的“喜马拉雅东构造结周边地区主要断裂现今运动的GPS观测研究”项目所布设的GPS观测点的最新观测数据作为边界约束位移和运动速率检验参考对象,对本区主要断裂的运动学特征进行模拟研究。二、研究内容及结果1.主要断裂的晚第四纪运动特征通过野外实地调查,发现雅鲁藏布江断裂自朗县以东段活动明显,多处出现断裂错断了晚第四纪地层。嘉黎断裂以东构造结为界分为了三段;西北段(那曲—通麦)右旋走滑运动明显,右旋走滑速率3.2～3.7mm/a;东构造结地区(通麦段)为右旋走滑运动,相对嘉黎断裂西北段来说弱些;嘉黎断裂的东南段(通麦—察隅)嘉黎断裂的运动性质发生了改变,在嘎龙寺附近的冰碛垄被嘉黎断裂左旋位错,走滑速率为3.8mm/a左右。怒江断裂在郭庆至田妥段,断层主要表现为挤压性质,显示晚第四纪以来活动不明显;东南段晚第四纪以来活动明显,多处可见断层错断了晚第四纪以来的地层。金沙江断裂西北段,地貌显示断裂影响了一系列冲沟水系的流向,造成冲沟水系左旋扭动,左旋运动明显;中段,没有发现错断晚第四纪堆积物和地貌面的地质剖面,显示晚第四纪以来活动不明显;南段显示金沙江断裂晚第四纪以来影响了冲沟水系的发育,造成冲沟水系的右旋扭动,多处出现晚第四纪地层被错断现象。2.GPS观测与分析通过跨过断层带的GPS剖面及位错模型研究,揭示了各断裂的活动性质和运动速率。雅鲁藏布江断裂右旋走滑特征明显,拉萨段右旋走滑速率2.4～3.9mm/a,挤压速率1.3～4.7mm/a左右,林芝段右旋挤压运动,其走滑速率为6.2～6.8mm/a,挤压速率为0.6～6.0mm/a左右。嘉黎断裂西北那曲附近地区表现为右旋挤压运动,走滑速率为4～5.8mm/a,挤压速率为4.6mm/a±;通麦附近表现为弱右旋挤压运动,走滑速率为1.3～2.0 mm/a,挤压速率为2.5mm/a±;东南察隅附近地区表现为左旋挤压运动,其走滑速率为3.7～4.0mm/a,挤压速率为6.2mm/a±。怒江断裂带在西北那曲附近地区,主要表现为挤压运动,挤压速率为1.2～2.0mm/a;中段主要表现为右旋走滑运动,走滑速率2.1mm/a;南段同样主要表现为右旋走滑运动,走滑速率3.2mm/a。走滑速率自北向南逐渐增大。金沙江断裂在青藏公路附近地区表现为左旋挤压运动,走滑速率3.0～4.0mm/a±,挤压速率3.5mm/a±;昌都、江达、白玉附近地区主要表现为右旋挤压运动,走滑速率3.4～4.3mm/a±,挤压速率1.8～2.9mm/a±;在巴塘、得荣附近地区主要表现为右旋挤压运动,走滑速率3.0～3.1mm/a±,挤压速率0.4～2.0mm/a±。3.有限元数值模拟结果通过数值模拟研究取得以下几点认识:1)东构造结北侧和东侧地块总体上围绕构造结发生顺时针旋转。右旋走滑的东南边界断裂不是嘉黎断裂,可能是阿帕龙断裂。2)嘉黎断裂不是整体右旋走滑断层,其西北段和东构造结顶端的通麦段为右旋挤压性质,东构造结以东的东南段运动性质发生了转变,由右旋走滑运动转变为左旋走滑运动;如果嘉黎断裂东南支与实皆断裂不相通,阿帕龙断裂与实皆断裂相连时,模拟结果与GPS观测值有更好的拟合效果,这一结果间接地证明嘉黎断裂与实皆断裂目前可能是不相连的,至少不是简单连通的;而阿帕龙断裂和实皆断裂可能是相连的。3)东构造结目前依然起着一定的作用,它与阿萨姆角共同影响着现今区域构造变形,许多断裂活动转换和重要构造事件都发生在它们之间或很近的区域。雅鲁藏布江断裂、怒江断裂、嘉黎断裂运动速率的变化、活动性质的转变和嘉黎断裂在阿萨姆角附近延伸终止,阿帕龙断裂活动强烈,并发生了1950年察隅8.6级地震,这些都可能与东构造结和阿萨姆角的共同作用有关。三、主要结论通过综合分析研究,主要取得如下几点初步认识:1.雅鲁藏布江断裂晚第四纪以来右旋走滑运动明显,自西向东活动性增强。拉萨段右旋走滑速率2.4～3.9mm/a,林芝段右旋走滑速率6.2～6.8mm/a。2.嘉黎断裂不是整体右旋走滑断层,其在不同的构造部位运动性质和速率具有分段差异特征,大致以东构造结为界分为三段,东构造结以西为嘉黎断裂西北段,东构造结顶端通麦段为嘉黎断裂中段,东构造结东南部分为嘉黎断裂的东南段,其西北段为右旋挤压运动,走滑速率3.2～5.8mm/a,中段弱右旋挤压运动,走滑速率1.3～2.0mm/a;东南段为左旋挤压运动,走滑速率3.7～4.0mm/a。3.怒江断裂在不同的构造部位其晚第四纪以来活动性是不同的。西北段以挤压运动为主;中段,地质结果表明晚第四纪以来活动不明显,GPS结果显示右旋走滑速率2mm/a;南段晚第四纪以来活动相对明显,在多处出现的断层剖面可见断层错断了晚第四纪以来的地层,右旋走滑速率2.3～3.2 mm/a。4.金沙江断裂在不同的构造部位其晚第四纪以来运动性质不同。西北段,断裂影响了一系列冲沟水系的流向,造成冲沟水系左旋扭动,左旋运动明显,左旋走滑速率3.0～4.0mm/a±;中段,地质结果显示晚第四纪以来活动不明显,GPS结果显示为右旋走滑,走滑速率3.4～4.3mm/a;南段断裂晚第四纪以来影响了冲沟水系的发育,造成冲沟水系的右旋扭动,右旋运动明显,速率3 mm/a。5.东构造结北侧和东侧地块总体上围绕构造结发生顺时针旋转,右旋走滑的东南边界断裂不是嘉黎断裂,而可能是阿帕龙断裂;6.数值模拟结果表明,嘉黎断裂与实皆断裂目前可能是不相连的,至少不是简单连通的;阿帕龙断裂和实皆断裂可能是相连的;7.东构造结目前依然起着一定的作用,它与阿萨姆角共同影响着现今区域构造变形,许多断裂活动转换和重要构造事件都发生在它们之间或很近的区域。更多还原

【Abstract】 The area around the Eastern Himalayan Syntaxis(EHS) characterized by most intensive tectonic deformation, complicated tectonic types, and well-preserved geological traces. This area contains the Himalalyan, Lhasa, Qiangtang, and Sichuan-Yunnan block , involves the Indian Plate and the main boundary fault, the main central fault, the Yaluzangbu fault, Jiali fault, the Nu jiang fault, Motuo fault and Apalong fault. It can be thought that the area around the EHS is one of the key areas testing the different theories and doctrines about late Cenozoic deformation mechanisms of the Tibetan Plateau. As this area lies in mountains above 4000m with valley-mountain landscapes of Yaluzangbu jiang, Nu jiang, and Lancang jiang, bad working conditions and various reasons such as complicated geological structure, make it difficult to use a single way to determine the movement field of tectonic deformation and to conduct quantitative research of the faults with different natures and different ways of current movement on different structural parts in a short time. Therefore, this thesis uses a various of methods to make a comprehensive analysis of the tectonic deformation and the movement characteristics of main faults in the area around the EHS. They include collecting data of geometric and active features of tectonic blocks and boundary faults by field investigation, crustal deformation and the movement type of the main faults by high- accuracy of GPS observation technology with more observation sites in key tectonic parts, physical parameters and deep geological structure of crust by the comprehensive analysis of geophysical exploration data, discussing the movement features of main faults and the kinetic mechanism of tectonic deformation by large-scale numerical simulation analysis.Ⅰ、Research methodsThis work, uses three methods to study the crustal deformation velocity field and motion styles of the main faults movement:(ⅰ) Traditional geologyField survey is an indispensable way of geological research. It can directly observe the active features of main faults in the historical period. By analysis of previous field investigations and GPS data, several places are selected for field geological investigation, which are the Yaluzangbu fault, Jiali fault and Nu jiang fault and the area with different views in previous studies. During the investigation, the study was focused on the cross section of the main faults which are active since the late Quaternary, to obtain more geological evidence about the movement features of major faults in this area since the late Quaternary. (ⅱ) GPS observation and analysisIn order to study the present tectonic deformation features of the EHS and the surrounding areas deeply, this work analyzed the long-term observation data of GPS sites for "China Crustal Movement Observation Network Project" in the study area systematically. In addition 12 new GPS observation points in the areas of lack GPS sites were built, to conduct two-period observations. In this thesis, GPS velocity profiles across the fault and the fault dislocation model were used for studying the movement characteristics of the main fault of the different structural sections. The former decomposed the velocity vector of GPS measured points on both sides of fault into the velocity components perpendicular to the profiles, which reflect the dip-slip motion of the fault and the velocity components parallel to profiles, which reflect the strike-slip movement of the fault. The difference between the both sides of the fault representes its motion characteristics. The latter used the OKADA dislocation model to retrieve movement rates and characteristics of the fault.(ⅲ) Finite element numerical simulationThe finite element method can reconstruct the geological process and make activity prediction. Based on the three-dimensional finite element method, regarding main faults as boundaries, using the parameters of lithosphere in different areas of the Tibetan Plateau from geological and geophysical data, the tectonic deformation model for the EHS is established. Using the latest GPS observation data of“China Crustal Movement Observation Network”, and data of“China Continental Tectonic Environment Monitoring Network Project”and project“The main faults’current movement observation around Eastern Himalayan Syntaxis area”as the boundary constraints of displacement and the movement rates. This work has made a numerical modeling for the main faults’movement features.Ⅱ、Research contents and results(ⅰ) Movement characteristics of the main faults in Late QuaternaryThrough field investigation, it was found that the Yaluzangbu fault was active significantly from the eastern section of Long County, and that the fault has cut the late Quaternary strata in many places. The Jiali fault can be divided into three sections, and the EHS is its boundary. The northwest section (Naqu-Tongmai) displayed dextral strike-slip, with a rate of 3.2～3.7mm/a. The EHS region (Tongmai Section) has dextral strike-slip, and its rate is slower than the northwest section of the Jiali fault. The active characteristic of the southeast section of the Jiali fault (Tongmai-Chayu) was changed, as shown that the moraine ridge near the Galong Temple was sinistral dislocated by the Jiali fault with the slip rate of about 3.8mm / a. The Nu Jiang fault mainly showed the squeezing property from Guoqing to Tiantuo, and showed no significant activity since Late Quaternary. There is no found that the geological profiles dislocated the Late Quaternary deposits and landscape, and shows no significant activity since Late Quaternary. The south section was active obviously, and the Late Quaternary strata were dislocated in many places. The geomorphy of the northwest section of the Jinsha Jiang fault indicates that the direction of a series of river gullies was changed by this fault, which resulted in sinistral twisting river gullies and obvious sinistral movement. Along the middle- south section of the Jinsha Jiang fault, the development of river gullies was affected since the late Quaternary, which resulted in dextral twisting river gullies and many places of the Late Quaternary strata dislocated.(ⅱ) Results of GPS observation profilesThe research of the GPS profiles across the faults and dislocation model revealed the nature of the faults and the movement rates.The Yaluzangbu fault has a clear dextral strike-slip characteristic. The strike-slip rate of Lhasa section of this fault is 2.4 ~ 3.9 mm/a, and the shortening rate is 1.3 ~ 4.7 mm/a. The Linzhi section has the slip rate of 6.2 ~ 6.8 mm/a and the shortening rate of about 0.6 ~ 6.0 mm/a, exhibiting a dextral-compressive motion.The northwest section of the Jiali fault near Naqu shows dextral compression, the strike-slip rate is 4 ~ 5.8mm/a, and the shortening rate is about 4.6mm /a. The fault near Tongmai has weak dextral compression, the strike-slip rate is 1.3～2.0mm/a, and the shortening rate is about 2.5mm/a. The fault near Chayu shows sinistral compression with a strike-slip rate 3.7～4.0mm/a, and shortening rate is about 6.2mm/a.The northwest section of the Nu Jiang fault zone near Nagqu mainly shows the compressive movement at a rate 1.2 ~ 2.0mm/a. The southeast section is mainly of dextral strike-slip with a rate gradually increasing from the north (the strike-slip rate of 2.1m /a) to south (the strike-slip rate of 3.2mm/a).The Jinsha Jiang fault in the vicinity of the Qinghai-Tibet Highway shows sinistral-compressive movement where the strike-slip rate is 3.0 ~ 4.0mm/a, and the shortening rate is about 3.5mm/a. The faults near Cangdu, Jiang Da and Baiyu mainly show dextral-compressive movement with strike-slip rate 3.4 ~ 4.3mm/a, and the shortening rate 1.8 ~ 2.9mm/a. The faults near Batang and Derong mainly show dextral compressive movement, with a strike slip rate 3.0 ~ 3.1mm/a, and the shortening rate 0.4 ~ 2.0mm/a.(ⅲ) Results of the finite element numerical simulationⅰ)The blocks north and east of the EHS rotated clockwise around the EHS. The southeast boundary of the dextral strike-slip fault is not Jiali fault, instead likely the Apalong fault.ⅱ)The Jiali fault was not an overall dextral strike-slip fault. Its northwest section and the Tongmai section at the top of EHS have the dextral compressive properties, and the kinetic property of the southeast section of the EHS has changed from the dextral strike-slip into a sinistral strike-slip movement. If the southeast branch of the Jiali fault was not connected with the Sagaing fault, the simulation results have a better fitting to the GPS observations when the Apalong fault connects the Sagaing fault, and this result indirectly confirms that the Jiali fault may not be connected to the Sagaing fault current, at least not simply connected. The Apalong fault and Sagaing fault may be linked.ⅲ)The EHS is still playing a role at present, which together with the Assam horn affects the current regional tectonic deformation, and many of the fault activity conversions and important tectonic events occurred in or close to the region between them. The change of the movement rates and activity of the Yaluzangbu fault, the Nu jiang fault and the Jiali fault ends close to the Assam horn, so does the Jiali fault. The Apal Long fault is active highly, where occurred the Ms8.6 Chayu earthquake in 1950, all of which may have a relationship with interaction between the EHS and the Assam horn.Ⅲ、Main conclusionsThrough comprehensive analysis, this work has obtained some new recognitions:ⅰ) There is apparent dextral slip on the Yaluzangbu fault since late Quaternary. The activity increases from west to east. The dextral slip rate of its Lhasa section is 2.4~ 3.9mm/a. The dextral slip rate of its Linzhi section is 6.2~ 6.9mm/a.ⅱ) The Jiali fault isn’t an overall dextral strike-slip fault. Its movement features and rates are variable in different tectonic parts. Generally, it can be divided into three sections by EHS. The fault in west area of the EHS is the northwestern segment of the Jiali fault, the fault in Yigong-Tong mai area on the top of the EHS is the middle segment, and the fault in the southeast area of the EHS is the southeastern segment. The northwestern segment is right-lateral compressive movement, with a strike slip rate 3.2~ 5.8mm/a. The middle segment has weak dextral compressive movement, with a strike slip rate 1.3~ 2.0mm/a. And the southeast segment is left-lateral compressive movement, with a strike slip rate 3.7~ 4.0mm/a.ⅲ) The Nu Jiang fault has different activities in different tectonic parts since late Quaternary. The main activity of northwestern segment of the Nu jiang fault is compressive movement. The activity of the middle segment of the Nujiang fault is not obvious in geology since late Quaternary, but with a strike slip rate 2mm/a by GPS. The activity of south segment of the Nu jiang fault is obvious. It can be seen that the fault dislocation of the late Quaternary strata is present in many areas, and the strike slip rate 2.3 ~ 3.2mm/a.ⅳ) The Jinsha Jiang fault’s activity was also different in different tectonic parts since late Quaternary. In the northwest segment, the Jinsha Jiang fault affected the flow of a series of gullies, causing gullies to experience left-twist, sinistral movement significantly, and the strike slip rate 3.0 ~ 4.0mm/a. The activity is not obvious in middle segment in geology since late Quaternary, but with a strike slip rate 3.4 ~4.3mm/a by GPS. In south segment, the Jinsha Jiang fault affected the development of water-gully systems, causing gullies to undergo right-twist, dextral movement significantly.ⅴ) The northern and eastern blocks of the EHS rotate clockwise around the EHS overal. The southern boundary dextral strike-slip fault is not the Jiali fault, but the Yaluzangbu fault and Apa long fault.ⅵ) Numerical simulation results show that the Jiali fault and Sagaing fault may not be linked, at least not simply connected. The Apa long fault and the Sagaing fault may be connected.ⅶ) EHS still plays a role at present, and affects the current regional tectonic deformation together with the Assam horn. Some fault conversions and important tectonic events occurred between them or very close to the region.更多还原