GPS观测研究现今青藏高原地壳形变机制——来自阿尔金断裂三维运动场及高原地壳减薄的证据

发布时间：2018-01-11 22:23

本文关键词：GPS观测研究现今青藏高原地壳形变机制——来自阿尔金断裂三维运动场及高原地壳减薄的证据　出处：《国际地震动态》2017年09期 　论文类型：期刊论文

【摘要】：自50~55 Ma以来,印度次大陆向北与欧亚大陆碰撞后形成喜马拉雅—青藏高原造山带,碰撞导致地壳增厚致使高原大幅隆升,改变了亚洲大陆岩石圈的构造格局,也对东亚地区的气候和环境产生了巨大影响。阿尔金断裂作为青藏高原北缘的主控边界断裂,其运动学性质在20世纪70年代备受关注,不同量级的滑动速率引出了块体运动与东向逃逸和连续变形与地壳增厚两种端元模型。约10~15 Ma以来,在青藏高原南部与北部出现地堑与裂谷,为高原东西向拉张运动提供了证据,表明青藏高原开始经历地壳减薄过程。青藏高原形成以来形变场经历怎样变化,长时间尺度的地质学构造过程与现今GPS观测是否能够统一?10~15 Ma以来青藏高原地壳减薄过程造成高原高程怎样的变化?青藏高原北缘,尤其是跨阿尔金断裂具有怎样的现今三维地壳变形场,地壳应变是如何在北阿尔金断裂、祁漫塔格断裂和阿尔金断裂之间分配的?青藏高原北缘与塔里木盆地具有怎样的力学性质,对跨阿尔金断裂构造形变场造成怎样的影响?最后,GPS观测得到的现今地表形变场能够对青藏高原形变模式的争论作出何种解答?上述科学问题的解答,对于研究青藏高原隆升与变形过程具有十分重要的意义。本研究分为两部分。第一部分是青藏高原北缘三维震间运动场的观测与研究。在青藏高原北缘跨阿尔金断裂中段自建9个GPS连续台站并开展观测,根据区域研究特点设计无人值守的观测台站,具有低成本投入、高质量观测的特点。上述连续GPS台站的建立填补了青藏高原北缘,尤其是在阿尔金无人区地壳形变观测研究的空白,积累了宝贵的连续GPS数据;截止2015年7月,共有4年的连续GPS观测。数据分析结果证明,设计建站方法行之有效,GPS台站稳定、观测数据质量稳定、数据连续性稳定。结合使用中国大陆构造环境监测网络在研究区及邻域GPS连续台站数据作位置时间序列与速度场解算,获得青藏高原北缘地区跨阿尔金断裂中段现今三维形变场。使用三维线弹性后向滑移(backslip)块体运动模型,反演塔里木块体、北阿尔金块体、柴达木块体和祁漫塔格块体的三维块体运动。结果表明,北阿尔金山相对于塔里木盆地有(1.32±0.2)mm/a的抬升速率,相对于柴达木盆地具有(0.73±0.3)mm/a的抬升速率,可解释为北阿尔金块体存在显著的造山过程;阿尔金断裂有(8.21±0.60)mm/a的左旋走滑速率、(0.66±0.60)mm/a的缩短速率;祁漫塔格断裂有(0.53±0.60)mm/a的左旋走滑速率、(1.53±0.60)mm/a的缩短速率;北阿尔金断裂有(0.87±0.60)mm/a的左旋速率、(0.69±0.60)mm/a的缩短速率。同时,阿尔金断裂中、西两段滑动速率基本一致,约为8.0~10.0mm/a。定量研究结果支持连续形变与地壳增厚模型,表明相对塔里木块体,青藏高原北缘地区正在抬升、增厚,以北阿尔金山地区最为明显,抬升速率约达1.3mm/a。跨青藏高原北缘的阿尔金断裂、北阿尔金断裂和祁漫塔格断裂近200km的宽泛变形带内,南北向地壳缩短并不明显,缩短量仅约为2.9mm,且近一半缩短量发生在祁漫塔格山南侧。GPS观测阿尔金断裂车尔臣河段(~86°E)剖面表明,断裂两侧存在非对称变形特征。本文采用非对称变形模型反演GPS速度剖面数据,获得断裂两侧塔里木盆地和青藏高原北部的地壳介质剪切模量差异。结果显示,塔里木盆地地壳介质剪切模量约为青藏高原北部剪切模量1.53倍,相应S波波速比值为1.24,与Yang等人得到的地壳和上地幔三维VSV模型结果一致。地震学研究结果认为,青藏高原北部与东部地区在中地壳存在低速层,局部区域可能发生部分熔融;Hacker等进一步确认羌塘地块中地壳到深部地壳存在熔融现象。本文的研究运用了与地震学完全不同的资料,通过大地测量方法推导青藏高原北部与塔里木盆地的地壳介质力学性质差异,得到与地震学研究得到的S波波速比及其构造物理学解释相当一致的结果。成果为青藏高原力学演化模型提供新的约束。本论文第二部分内容是使用覆盖青藏高原及周边的GPS速度场,计算青藏高原内部应变率场。GPS观测速度场不仅显示了南东东-北西西向的地壳拉张过程,也揭示了青藏高原内部更加重要的地壳减薄过程。结果显示,青藏高原北部和南部的垂向应变率(减薄应变率)分别为(8.9±0.8)nanostrain/a和(7.4±1.2)nanostrain/a,青藏高原西南部的垂向应变率为(12.0±3.2)nanostrain/a,表明青藏高原内部大尺度范围应变率测量结果的一致性。并且青藏高原内部的拉张应变率观测也相当一致,青藏高原北部,沿着N114±1°E主应变方向的拉张应变率为(21.9±0.4)nanostrain/a;高原南部沿着N93±1°E主应变方向的拉张应变率为(16.9±0.2)nanostrain/a;高原西南部沿着N74±3°E主应变方向的拉张应变率为(22.2±1.8)nanostrain/a。如果地壳减薄开始于10~15 Ma,并且现今观测得到应变率适用于整个时间跨度,那么地壳累积减薄5.5~8.5km。应用Airy地壳均衡理论,青藏高原的平均高程将下降~1km。青藏高原北部、南部和西南部相似的垂向应变速率也表明,在3个区域的地壳拉张、正断裂运动和地壳减薄过程由相同的物理机制所支配。综合上述两部分研究成果,发现青藏高原现今垂向运动在高原内部和边缘地区存在很大差别。高原内部地区正在经历地壳减薄,而高原边缘地区正在经历不同程度的增厚与隆升。青藏高原北缘地区的垂向应变率约5~20nanostrain/a,如果考虑重力均衡作用,对应的垂向隆升速率在0.04~0.14mm/a左右。但是,对于局部地区如北阿尔金块体,其底部受到塔里木盆地南缘下插挠曲板块的支持,在没有重力均衡情况下,垂向隆升速率可能达到1mm/a。喜马拉雅地区呈现不同水平的垂向形变,垂向应变强烈(约10~80nanostrain/a),山脉底部受到印度下插板片的支持,无法通过重力均衡假定由垂向应变率估计隆升速率。但由GPS与水准数据约束的俯冲板片模型推测山脉隆升速率达到约7mm/a。而对于祁连山地区,GPS应变率推测得到垂向应变率约20~40nanostrain/a,应用地壳均衡理论,平均隆升速率为0.15~0.3mm/a;而由于逆冲推覆构造与褶皱变形带的存在,中下地壳有可能仍存在弹性变形,不能实现完全重力均衡,实际隆升速率有可能高于这一估计。本文研究给出青藏高原不同地区三维形变场与形变速率的定量估计,是对连续形变与地壳增厚形变模型的重要修正。结果并不支持块体运动与东向逃逸模型,并认为高原南北双向俯冲模型中的塔里木块体南向俯冲几乎不存在。
[Abstract]:Since the 50~55 Ma since the collision between India and Eurasia Continental North after the formation of the Himalaya Tibet Plateau orogenic belt, resulting in a collision caused crustal thickening plateau uplift, changed the tectonic pattern of the Asian continental lithosphere, also have great influence on the regional climate and environment. The Altun fault as the main boundary faults of Northern Tibetan Plateau the kinematic properties, has attracted much attention in 1970s, the slip rate of different levels leads to the block movement and eastward escape and continuous deformation and crustal thickening in two kinds of endmember model. About 10~15 Ma to appear in the rift graben and Northern and southern Tibetan Plateau, plateau that provides evidence to the tension movement. Show that the Tibetan Plateau began to experience crustal thinning process of Tibetan Plateau. Since the formation of deformation field experience change, geology tectonic processes long time scale and the GP S 10~15 Ma whether the observations can be unified? Since the Qinghai Tibet Plateau crust thinning process caused by changes in elevation how? The northern margin of the Tibetan Plateau, especially across the Arkin fault with how the present 3-D crustal deformation field, the crustal strain is how the North Arkin fault, diffuse distribution between the lattice tower Qi and Arkin faults? The northern margin of the Tibetan Plateau how has the mechanical properties and the Tarim Basin, due to the influence of Arkin on how to cross fault deformation? Finally, GPS observed the surface deformation field to Qinghai Tibet Plateau deformation mode of argument to what answer? The scientific questions, has very important significance for the study of the uplift of the Tibetan Plateau and the deformation process this paper is divided into two parts. The first part is the observation and Study on the northern margin of the Tibetan Plateau three-dimensional interseismic motion field. In the northern margin of the Tibetan Plateau, the Elgin cross The central segment of the fault self 9 GPS continuous observation stations were carried out, according to the regional characteristics of the design of observation station unattended, with low cost, high quality of observation. The establishment of continuous GPS stations to fill the gaps in the northern margin of the Tibetan Plateau, especially the study and observation on crustal deformation the uninhabited areas, the accumulation of continuous GPS data precious; by the end of July 2015, a total of 4 years of continuous GPS observation data. The analysis results prove that the effective design of station method, GPS station observation data is stable, stable quality, continuity of data stability. Combined with the use of China continental environmental monitoring network in the study area and neighborhood GPS continuous stations data position time series and velocity field is obtained in the northern margin of the middle part of Tibetan Plateau across the Altyn fault of three dimension deformation. Using three-dimensional linear elastic backward sliding block motion model (backslip), The inversion of the Tarim block, North Altyn Tagh block, 3D block movement in the Qaidam block and Qimantag block. The results show that the North Altyn mountain relative to the Tarim Basin (1.32 + 0.2) mm/a uplift rate, relative to the Qaidam Basin is (0.73 + 0.3) mm/a uplift rate, can be interpreted as the north the block has significant orogenic process of the Altun fault; have (8.21 + 0.60) mm/a sinistral slip rate, (0.66 + 0.60) mm/a shortening rate; Qimantag fracture (0.53 + 0.60) mm/a sinistral slip rate, (1.53 + 0.60) mm/a shortening rate; North Altyn fault there is (0.87 + 0.60) mm/a l rate (0.69 + 0.60) shortening rate of mm/a. At the same time, the Altun fault, west two slip rate is basically the same, about 8.0~10.0mm/a. quantitative research results support the continuous deformation and crustal thickening model shows that the relative Tarim block, North Qinghai Tibet Plateau The edge area is uplift, thickening, north of Arkin mountain area is the most obvious, the Arkin fault uplift rate of about 1.3mm/a. across the northern margin of the Tibetan Plateau, the broad North Arkin fault and Qimantag fracture near the 200km deformation zone, shortening of the crust to North-South shortening is not obvious, only about 2.9mm, and nearly half of shortening occurred in the Qimantag mountains on the south side of the.GPS observation Arkin Che'erchen River fault (~86 ~ E) profile shows that the fracture deformation characteristics of non symmetry exists on both sides. This paper uses the asymmetric deformation profile data model GPS velocity inversion, obtain crust shear modulus difference on both sides of faults in the northern Tarim Basin and the Tibetan Plateau. The results showed that the crust of Tarim basin the shear modulus is about 1.53 times of the Northern Qinghai Tibet Plateau shear modulus, the corresponding S wave ratio value of 1.24, and Yang et al of the crust and upper mantle 3D VSV model results Consistent. Seismological research indicates that, in northern and Eastern Tibetan Plateau in the mid crust low velocity layer exists, the local area may occur in partial melting; Hacker further confirmed the Qiangtang block in the crust into the deep crustal melting phenomenon exists. This article uses completely different from seismological data, through the different mechanical properties of crust derived north the measurement method of the Qinghai Tibet Plateau and the Tarim Basin, and get seismology S wave ratio and its tectonic physics explain fairly consistent results. The results provide new constraints for the Qinghai Tibet Plateau mechanical evolution model. In the second part of this paper is to use the coverage of the Tibetan Plateau and its adjacent GPS velocity field, strain rate field calculation in the Tibet Plateau.GPS observation of velocity field not only shows the WNW crustal stretching process, also reveals the interior of the Qinghai Tibet Plateau more Add an important crust thinning process. The results showed that the northern and southern Tibetan Plateau vertical strain rate (thinning strain rate) respectively (8.9 + 0.8) nanostrain/a and (7.4 + 1.2) nanostrain/a, southwest of Qinghai Tibet Plateau vertical strain rate (12 + 3.2) nanostrain/a, consistency the interior of the Qinghai Tibet Plateau large scale strain rate measurement results. And the tensile strain rate observed within the Qinghai Tibet Plateau is also quite consistent, along the Northern Qinghai Tibet Plateau, N114 + 1 ~ E principal strain direction tensile strain rate (21.9 + 0.4) nanostrain/a; plateau south along the N93 + 1 ~ E the direction of strain tensile strain rate (16.9 + 0.2) nanostrain/a; Southwest of the plateau along the N74 + 3 ~ E principal strain direction tensile strain rate (22.2 + 1.8) nanostrain/a. if the crust thinning begins at 10~15 Ma, and the observed strain rate for the entire time span, so the crust The cumulative 5.5~8.5km. Airy crustal thinning using the equilibrium theory, the average elevation of the Qinghai Tibet Plateau will drop ~1km. in the northern Tibetan Plateau, South and southwest is similar to the vertical strain rate also shows that in the 3 regions of the crust, is faulting and crustal thinning process by the same physical mechanism dominated. The two part of the research results, found that the present Tibetan Plateau and vertical movement in the marginal area there is a great difference. The interior of the plateau region is experiencing crustal thinning, and the edge of the plateau region is experiencing a different degree of thickening and uplift of the northern Tibetan Plateau. The vertical strain rate is about 5~20nanostrain/a, if we consider the gravity equilibrium. The corresponding vertical uplift rate is about 0.04~0.14mm/a. However, in some areas such as the northern Altyn Tagh block, the bottom supported deflection plate inserted in the southern Tarim Basin, in the There is no gravity equilibrium, the vertical uplift rate may reach 1mm/a. in Himalaya area show different levels of vertical deformation, strong vertical strain (about 10~80nanostrain/a), the base of the mountains by inserted plate support India, assumed by the vertical strain rate estimation of uplift rate can not be balanced by gravity. But the subducting slab model bound by GPS and leveling data that uplift rate reached about 7mm/a. in the Qilian Mountains area, the GPS strain rate deduced vertical strain rate of about 20~40nanostrain/a, using the equilibrium theory, the average uplift rate is 0.15~0.3mm/a; and the thrust and fold deformation zone of the lower crust may still exist elastic deformation, can achieve complete gravity equilibrium, rising rate may be higher than the estimated actual uplift. This study gives different areas on the Qinghai Tibet Plateau 3D deformation field and strain The quantitative estimation of the rate is an important modification for the continuous deformation and the crustal thickening deformation model. The results do not support the block movement and the eastward escape model. It is considered that the South subduction of the Tarim block in the two way subduction model of plateau is almost nonexistent.

【作者单位】：中国地震局地质研究所;
【分类号】：P228.4;P315.7
【正文快照】： GPS观测研究现今青藏高原地壳形变机制——来自阿尔金断裂三维运动场及高原地壳减薄的证据@葛伟鹏$中国地震局地质研究所!北京100029自50~55 Ma以来,印度次大陆向北与欧亚大陆碰撞后形成喜马拉雅—青藏高原造山带,碰撞导致地壳增厚致使高原大幅隆升,改变了亚洲大陆岩石圈的构

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