Precambrian–Palaeozoic geology of Smith Sound, Canada and Greenland: key constraint to palaeogeographic reconstructions of northern Laurentia and the North Atlantic region

Nares Strait separating Greenland and northernmost Canada is floored by continental crust. Most palaeogeographic reconstructions of Laurentia and the North Atlantic region model the seaway as the site of massive sinistral strike–slip and/or compression/transpression, subduction and collision, the supposed manifestations of the hypothetical Wegener Fault. However, these reconstructions fail to take into account the bedrock geology that represents within-plate evolution. Both sides of Smith Sound, the southernmost part of Nares Strait, expose the same early Proterozoic to early Palaeozoic assemblages that are unaffected by seaway-related tectonism or thermal activity. Smith Sound is an intact crustal block or `linchpin' demonstrating that there was no independent Greenland plate. North-west Greenland was not a leading plate margin neither was Nares Strait the site of the plate boundary between Greenland and North America. The Wegener Fault does not exist. The Smith Sound linchpin constitutes a key constraint that must be respected in any palaeogeographic reconstruction of the region.     

祁连山北缘—河西走廊地区大地形变与地震的关系

河西走廊—祁连山北缘地区地处青藏高原北缘,受印度板块与欧亚板块中生代末—新生代早期的碰撞及持续至今的向北推挤作用的远程效应的影响,该地区是现今的地壳活动地区,其中地壳形变是最主要的表现形式。地壳形变监测显示,隆起区垂直位移速率最大可达15mm/a,沉降区最大位移速率为-15mm/a。祁连山和河西走廊的相对隆升变化与该区地震具有密切的关系,河西走廊相对下降、祁连山相对隆升的后期是地震多发时期,河西走廊相对隆升、祁连山相对下降的后期是地震少发时期,这与该区处于挤压体制下的区域构造背景密切相关。GPS水平位移监测显示,河西走廊—祁连山北缘地区全区都一致向东位移,且位移速率非常大,大者大于10mm/a;位移速率具有南部大于北部、东部大于西部的特点,水平位移速率变化与现代活动断裂具有非常密切的关系,并以主要断裂构造为区带的边界;水平位移速率矢量与2002年玉门地震的震源机制解所显示的沿地震破裂面发生的滑动方向非常一致。     

论胶东地区中生代岩石圈减薄的证据及其动力学机制

胶东地区可划分为两个大地构造单元：胶北断块和胶南造山带。前者为华北板块组成部 分，后者为华北和扬子板块的碰撞拼合带。五莲－青岛－海阳－牟平深断裂构成上述两个构造单 元的边界。本文从地质（陆壳隆升、构造岩浆活动与断陷盆地形成）和地球物理（重、磁异常与地震 测深）两个方面论述了胶东地区中生代经历了两个不同构造演化时期：前期（Ｔ３－Ｊ２）陆壳隆升和后 期（Ｊ－Ｋ）陆壳拉伸。我们认为，岩石圈减薄的动力学条件是与库拉－太平洋板块以不同边界类型 向欧亚大陆俯冲以及郯庐断裂以不同方式的强烈活动密切相关。在综合分析基础上建立了胶东地 区岩石圈减薄的动力学模式。     

Formation of diapiric structure in the deformation zone,central Indian Ocean: A model from gravity and seismic reflection data

Analyses of bathymetry, gravity and seismic reflection data of the diffusive plate boundary in the central Indian Ocean reveal a new kind of deformed structure besides the well-reported structures of long-wavelength anticlinal basement rises and high-angle reverse faults. The structure (basement trough) has a length of about 150 km and deepens by up to 1 km from its regional trend (northward dipping). The basement trough includes a rise at its center with a height of about 1.5km. The rise is about 10 km wide with rounded upper surface and bounded by vertical faults. A broad freeair gravity low of about 20 mGal and a local high of 8 mGal in its center are associated with the identified basement trough and rise structure respectively. Seismic results reveal that the horizontal crustal compression prevailing in the diffusive plate boundary might have formed the basement trough possibly in early Pliocene time. Differential loading stresses have been generated from unequal crust/sediment thickness on lower crustal and upper mantle rocks. A thin semi-ductile serpentinite layer existing near the base of the crust that is interpreted to have been formed at mid-ocean ridge and become part of the lithosphere, may have responded to the downward loading stresses generated by the sediments and crustal rocks to inject the serpentinites into the overlying strata to form a classic diapiric structure.     

Regional features of seismotectonic deformations in East Asia based on earthquake focal mechanisms and their use for geodynamic zoning

Seismotectonic deformations of crustal volumes related to geographical coordinates were calculated from data on earthquake focal mechanisms. The crust of the western part of Asia, including the Tien Shan, Tarim massif, Tibet, Pamir-Karakorum, and Kun Lun, undergoes predominantly longitudinal shortening and latitudinal extension. In the eastern part, longitudinal extension and latitudinal shortening are observed. The notional boundary separating these parts is determined over a fairly wide range between longitudes 95° and 103° E and is apparently related to the northward compression from the Indian plate in the south and the westward compression from the Okhotsk and Philippine plates in the east. At the same time, this boundary may indicate the maximum zone of influence of the Indian plate. The boundaries of the Amurian plate are inferred from changes in seismotectonic deformations in the eastern part of Asia. Differences in the seismotectonic deformation of the Earth’s crust are found within the northern part of the Okhotsk plate and the surrounding area.     

东秦岭的泥盆系及构造演化

本文简述了有关秦岭构造演化的不同解释;从沉积、古地理、古构造等方面讨论了北带泥盆系与与中、南带泥盆系的明显差异及它们的分界位置;论述了秦岭属印支带及其东延的主要证据;提出了秦岭构造演化模式。     

辽宁板块构造特征及大地构造单元划分

利用板块构造理论,依据近年来1：5万区域地质调查及相关科研成果,对辽宁地壳发展演化进行了分析研究,提出辽宁地壳发展可暂划分为早前寒武纪大陆增生构造体制和中元古宙以来的板块构造体制.中太古代-古元古代发现了绿岩地体和古元古宙裂谷,因此将早前寒武纪视作原始板块,中元古代-古生代视作古板块,中生代以来视作现代板块.在此基础上对辽宁大地构造单元进行了划分.辽宁Ⅰ级构造单元为塔里木-华北板块.Ⅱ级构造单元为天山-赤峰陆缘活动带和华北陆块.Ⅲ级构造单元5个,分别为建平-西丰华力西陆缘造山带、冀辽地块、铁岭-清原微地块、辽吉地块及下辽河-辽东湾新生代裂谷.Ⅳ级构造单元16个.为清楚地了解辽宁地壳发展演化特点,对5个Ⅲ级构造单元地质特征进行简要阐述.     

Crustal architecture of central Victoria: results from the 2006 deep crustal reflection seismic survey

A ～400 km long deep crustal reflection seismic survey was acquired in central Victoria, Australia, in 2006. It has provided information on crustal architecture across the western Lachlan Orogen and has greatly added to the understanding of the tectonic evolution. The east-dipping Moyston Fault is confirmed as the suture between the Delamerian and western Lachlan Orogens, and is shown to extend down to the Moho. The Avoca Fault, the boundary between the Stawell and Bendigo Zones, is a west-dipping listric reverse fault that intersects the Moyston Fault at a depth of about 22 km, forming a V-shaped geometry. Both the Stawell and Bendigo Zones can be divided broadly into a lower crustal region of interlayered and imbricated metavolcanic and metasedimentary rocks and an upper crustal region of tightly folded metasedimentary rocks. The Stawell Zone was probably part of a Cambrian accretionary system along the eastern Gondwanaland margin, and mafic rocks may have been partly consumed by Cambrian subduction. Much of the Early Cambrian oceanic crust beneath the Bendigo Zone was not subducted, and is preserved as a crustal-scale imbricate thrust stack. The seismic data have shown that a thin-skinned structural model appears to be valid for much of the Melbourne Zone, whereas the Stawell and Bendigo Zones have a thick-skinned structural style. Internal faults in the Stawell and Bendigo Zones are mostly west-dipping listric faults, which extend from the surface to near the base of the crust. The Heathcote Fault Zone, the boundary between the Bendigo and Melbourne Zones, extends to at least 20 km, and possibly to the Moho. A striking feature in the seismic data is the markedly different seismic character of the mid to lower crust of the Melbourne Zone. The deep seismic reflection data for the Melbourne Zone have revealed a multilayered crustal structure that supports the Selwyn Block model.     

台湾海峡地区横向构造及其对东南沿海地震的作用

台湾海峡两岸存在一系列断续分布、横贯台湾海峡的NW向断裂,研究表明为一系列具有走滑运动的横向构造,根据地壳运动、区域变形和断裂特征分为巴士断裂带、台中-晋江断裂带和宁德-三貂角断裂带。中部的台中-晋江断裂带是一条控制地壳运动南北差异的重要分界断裂,断裂带以北的东南沿海北部和台湾北部地壳整体向东运动,与琉球俯冲带右行走滑运动方向基本相同,形成一致的变形取向;断裂带以南处于华南地块与菲律宾海板块相向运动挤压变形环境,地壳变形比北部强烈。东南沿海地震强度增强趋势、地震南强北弱与该应变场和横向走滑有关:(1)由于该断裂以南比以北地区应力应变场变化大,多场耦合复杂,耦合程度降低,造成蠕动变形不均产生应力闭锁,孕育地震发生。(2)福建东部比台湾海峡地壳均一性差、地球物理场变化明显,组成更为复杂的多元、多场耦合,耦合场稳定性差,容易受横向构造活动干扰,产生弹性变形而孕育地震强度增强。     

Age of granitoids in the Pripechora fault zone of the basement of Pechora Basin: First U–Pb (SIMS) data

Upper Precambrian basement of the Pechora Basin that is located between the Urals and Timan and is a part of the Pechora plate lies beneath 1–7 km of Ordovician-Cenozoic sediment cover. On the base of geophysical data and drilling the basement of the Pechora plate is subdivided into the Timan crustal block and the Bolshezemel crustal block which differ by composition and the character of magmatism. The boundary between the crustal blocks is a system of deep faults called the Pripechora and Ilych-Chikshino faults that strike in a northwestern direction, extending from the Urals to the Pechora Sea. Granitoids of Charkayu complex which were penetrated by several deep boreholes in Pripechora fault zone are interpreted as suprasubduction (island arc and collision) magmas associated with the Timan orogeny. First U–Pb dating (SIMS, using SHRIMP-II and SHRIMP-RG) of zircons from granitoids indicate that granitoid magmatism which accompanied the final stages of the Timanide orogeny occurred in the Late Vendian about 555–544 Ma. The age of zircons from granites of the 1-Charkayu borehole is 544 ± 6 Ma, from granites of 1-East Charkayu borehole is 545 ± 5 Ma, and from granodiorites of 1-South Charkayu borehole is 555 ± 2 Ma.     

中国大陆现今构造应变率场及其动力学成因研究

通过分析中国大陆地壳运动GPS速度场得到现今构造应变率场。结果显示在印度板块北向推挤作用下 ,青藏高原内部及其邻域形变场并不局限于少数大型走滑断裂 ,而是在大范围内广泛分布 ,各地区构造运动驱动机制也可能各有不同。藏南地区主应变率场呈均衡的约 2× 10 -8a-1南北向挤压和东西向拉张 ,显示印度板块下插造成的地壳增厚和岩石圈拆离可能形成上地壳与上地幔间形变解耦 ,地壳内部在南北向挤压及重力场作用下产生东向塑性流驱使上地壳产生东西向拉张。西藏中部羌塘地区主应变率场显示均衡的约 2× 10 -8a-1北北东向挤压和北西西向拉张 ,反映本地区一系列走向北东和北西的共轭剪切断裂的活动 ,可能源于南北向挤压和软流层内东向塑性流的驱动。柴达木盆地及周边地区主应变率场呈约 2× 10 -8a-1北东向压缩和约 (0 1)× 10 -8a-1北西向拉张 ,表明地壳增厚造成的地壳温度上升可能还不足以造成上下地壳的充分解耦 ,南北向的消减还未能有效地转换成东西向的拉张 ,形变以褶皱和逆冲断裂运动为主。当今青藏高原形变场的形成应是构造运动从南到北阶段性发展过程中地壳与上地幔介质性质差异造成驱动机制不同的结果。     

从地震信息看中国东部和中国中西部沉积盆地构造演化动力学与断块油气藏(下) 中国中西部盆地演化及断块(圈闭)油气藏

中国中西部地区以塔里木盆地及其演化为典型代表。震旦纪以来,经历了地台发育、持续沉降、拉张翘倾、挤压坳陷及断陷推覆等构造发育阶段,与中国东部一样,表现为拉张与挤压交互出现的手风琴式演化史,突出的差别在于晚喜马拉雅期在西部地区形成强烈的挤压逆掩推覆构造,而东部地区只形成坳陷式的沉积盆地。中亚—蒙古大洋、秦—祁—昆大洋、古特提斯洋、中特提斯洋、印度洋以及印度板块等在不同地质时期的板块活动是中国中西部地区盆地演化发展的动力学因素。根据地震剖面解释成果,可确定出四种断块油气藏类型,均反映后期挤压逆冲特征,尤其是燕山期—喜马拉雅期推覆前锋带断块油气藏,还可区分为拆离型、褶皱型、前冲型和反冲型等四种,且每一种还可再区分出若干种。     

Neotectonics of the Kharaulakh sector of the Laptev Shelf

Seismotectonic deformation and crustal stress pattern have been studied comprehensively in major seismogenic structures of the Kharaulakh sector of the Verkhoyansk fold system and adjacent parts of the Chersky seismotectonic zone. The study focuses on neotectonic structures, deep structure, and systems of active faults, as well as tectonic stress fields inferred by tectonophysical analysis of Late Cenozoic faults and folds. The results, along with geological and geophysical data, reveal main strain directions and structural patterns of crustal stress and strain in the Arctic segment of the Eurasia-North America plate boundary. The area is a junction of mid-ocean and continental structures evolving in a mixed setting of extension, compression, and their various combinations. The rotation pole of the two plates is presumably located near Buor-Khaya Bay. In this case, extension is expected to act currently upon the neotectonic structures north of the bay and compression to control those in the south and southeast. This inference is consistent with the identified zoning of stress and strain in the Kharaulakh sector.     

On the tectonic origin of Iberian topography

The present-day topography of the Iberian peninsula can be considered as the result of the Mesozoic–Cenozoic tectonic evolution of the Iberian plate (including rifting and basin formation during the Mesozoic and compression and mountain building processes at the borders and inner part of the plate, during the Tertiary, followed by Neogene rifting on the Mediterranean side) and surface processes acting during the Quaternary. The northern-central part of Iberia (corresponding to the geological units of the Duero Basin, the Iberian Chain, and the Central System) shows a mean elevation close to one thousand meters above sea level in average, some hundreds of meters higher than the southern half of the Iberian plate. This elevated area corresponds to (i) the top of sedimentation in Tertiary terrestrial endorheic sedimentary basins (Paleogene and Neogene) and (ii) planation surfaces developed on Paleozoic and Mesozoic rocks of the mountain chains surrounding the Tertiary sedimentary basins. Both types of surfaces can be found in continuity along the margins of some of the Tertiary basins. The Bouguer anomaly map of the Iberian peninsula indicates negative anomalies related to thickening of the continental crust. Correlations of elevation to crustal thickness and elevation to Bouguer anomalies indicate that the different landscape units within the Iberian plate can be ascribed to different patterns: (1) The negative Bouguer anomaly in the Iberian plate shows a rough correlation with elevation, the most important gravity anomalies being linked to the Iberian Chain. (2) Most part of the so-called Iberian Meseta is linked to intermediate-elevation areas with crustal thickening; this pattern can be applied to the two main intraplate mountain chains (Iberian Chain and Central System) (3) The main mountain chains (Pyrenees and Betics) show a direct correlation between crustal thickness and elevation, with higher elevation/crustal thickness ratio for the Central System vs. the Betics and the Pyrenees. Other features of the Iberian topography, namely the longitudinal profile of the main rivers in the Iberian peninsula and the distribution of present-day endorheic areas, are consistent with the Tertiary tectonic evolution and the change from an endorheic to an exorheic regime during the Late Neogene and the Quaternary. Some of the problems involving the timing and development of the Iberian Meseta can be analysed considering the youngest reference level, constituted by the shallow marine Upper Cretaceous limestones, that indicates strong differences induced by (i) the overall Tertiary and recent compression in the Iberian plate, responsible for differences in elevation of the reference level of more than 6 km between the mountain chains and the endorheic basins and (ii) the effect of Neogene extension in the Mediterranean margin, responsible for lowering several thousands of meters toward the East and uplift of rift shoulders. A part of the recent uplift within the Iberian plate can be attributed of isostatic uplift in zones of crustal thickening.     

Crustal and upper mantle seismic structure of the Australian Plate, South Island, New Zealand

Seismic reflection and refraction data were collected west of New Zealand's South Island parallel to the Pacific–Australian Plate boundary. The obliquely convergent plate boundary is marked at the surface by the Alpine Fault, which juxtaposes continental crust of each plate. The data are used to study the crustal and uppermost mantle structure and provide a link between other seismic transects which cross the plate boundary. Arrival times of wide-angle reflected and refracted events from 13 recording stations are used to construct a 380-km long crustal velocity model. The model shows that, beneath a 2–4-km thick sedimentary veneer, the crust consists of two layers. The upper layer velocities increase from 5.4–5.9 km/s at the top of the layer to 6.3 km/s at the base of the layer. The base of the layer is mainly about 20 km deep but deepens to 25 km at its southern end. The lower layer velocities range from 6.3 to 7.1 km/s, and are commonly around 6.5 km/s at the top of the layer and 6.7 km/s at the base. Beneath the lower layer, the model has velocities of 8.2–8.5 km/s, typical of mantle material. The Mohorovicic discontinuity (Moho) therefore lies at the base of the second layer. It is at a depth of around 30 km but shallows over the south–central third of the profile to about 26 km, possibly associated with a southwest dipping detachment fault. The high, variable sub-Moho velocities of 8.2 km/s to 8.5 km/s are inferred to result from strong upper mantle anisotropy. Multichannel seismic reflection data cover about 220 km of the southern part of the modelled section. Beneath the well-layered Oligocene to recent sedimentary section, the crustal section is broadly divided into two zones, which correspond to the two layers of the velocity model. The upper layer (down to about 7–9 s two-way travel time) has few reflections. The lower layer (down to about 11 s two-way time) contains many strong, subparallel reflections. The base of this reflective zone is the Moho. Bi-vergent dipping reflective zones within this lower crustal layer are interpreted as interwedging structures common in areas of crustal shortening. These structures and the strong northeast dipping reflections beneath the Moho towards the north end of the (MCS) line are interpreted to be caused by Paleozoic north-dipping subduction and terrane collision at the margin of Gondwana. Deeper mantle reflections with variable dip are observed on the wide-angle gathers. Travel-time modelling of these events by ray-tracing through the established velocity model indicates depths of 50–110 km for these events. They show little coherence in dip and may be caused side-swipe from the adjacent crustal root under the Southern Alps or from the upper mantle density anomalies inferred from teleseismic data under the crustal root.     

西秦岭晚中生代-新生代构造层划分及其构造演化过程

从西秦岭晚中生代-新生代红层沉积的岩石组合、空间分布和构造变形特征分析,西秦岭晚中生代-新生代红层沉积可以分为三个构造层,分别对应于三个构造演化阶段。1)晚侏罗世-早白垩世构造层:该构造层以深紫红色、灰色砾岩、砂岩为主,并含有特征性的黑色页岩和煤层为特征;构造变形以北东东向褶皱和断裂构造变形为特征,反映了早白垩世末期(燕山运动)的构造变形动力学为北西-南东向地壳挤压收缩,可能与扬子板块与华北板块陆内斜向汇聚有关。2)晚白垩世-古近纪构造层:该构造层以砖红色、紫红色砾岩、砂岩、页岩为主,间夹有灰色、灰黄色、灰绿色泥岩和页岩层,具有不连续面状分布的特征,指示了其沉积时地壳的广泛拉伸的构造背景;古近纪末期的构造变形以与现今北西向构造线一致的宽缓褶皱和断裂构造变形为特征,可能指示了新生代初印度板块和亚洲板块碰撞的构造动力作用第一次远程构造响应。3)新近纪构造层:该构造层以近水平的产状、典型的细碎屑沉积为主要特征,特别是红粘层、淡水碳酸盐层的存在以及含有的三趾马化石特征,空间上与主夷平面的密切联系指示了新近纪早期经历一个夷平剥蚀期,这一阶段地壳构造稳定,变形以块断作用为主。西秦岭在经历了上述三个阶段构造演化过程后,开始进入了第四纪以来以块体变形和快速隆升的构造阶段,这与印度板块与亚洲板块的持续汇聚导致的周缘山系的崛起和变形相一致。     

西太平洋边缘构造特征及其演化

西太平洋边缘构造带是地球上规模最大最复杂的板块边界,以台湾和马鲁古海为界,自北往南大致可以分为3段。北段是典型的沟-弧-盆体系,千岛海盆、日本海盆及冲绳海槽均为典型的弧后扩张盆地。中段菲律宾岛弧构造带为双向俯冲带,构造复杂,新生代经历大的位移和重组,使得欧亚大陆边缘的南海、苏禄海和苏拉威西海成因存在很大的争议。南段新几内亚—所罗门构造带是太平洋板块、印度—澳大利亚及欧亚板块共同作用的结果,既有不同阶段的俯冲、碰撞,也有大规模的走滑与弧后的扩张,其间既有新扩张的海盆,又有正在俯冲消亡的海盆。台湾岛处于枢纽部位,欧亚板块在此被撕裂,南部欧亚大陆边缘南海洋壳沿马尼拉海沟俯冲于菲律宾岛弧之下,而北部菲律宾海洋壳沿琉球海沟俯冲欧亚大陆之下。马鲁古海是西太平洋板块边界又一转折点,马鲁古海板块往东下插于哈马黑拉之下,往西下插于桑义赫弧,形成反U形双向俯冲汇聚带,其洋壳板块已基本全部消失,致使哈马黑拉弧与桑义赫弧形成弧-弧碰撞。     

Is northern Honshu a microplate?

Seismic slip vectors along the Japan Trench, the eastern margin of the Japan Sea and the Sagami Trough are compared with global relative plate motions (RM2, Minster and Jordan, 1978) to test a new hypothesis that northern Honshu, Japan, is part of the North American plate. This hypothesis also claims that the eastern margin of the Japan Sea is a nascent convergent plate boundary (Kobayashi, 1983; Nakamura, 1983).Seismic slip vectors along the Japan Trench are more parallel to the direction of the Pacific-North American relative motion than that of the Pacific-Eurasian relative motion. However, the difference in calculated relative motions is too small avoid to the possibility that a systematic bias in seismic slip vectors due to anomalous velocity structure beneath island arcs causes this apparent coincidence. Seismic slip vectors and rates of shortening along the eastern margin of the Japan Sea for the past 400 years are also consistent with the relative motion between the North American and Eurasian plates calculated there. Seismic slip vectors and horizontal crustal strain patterns revealed by geodetic surveys in south Kanto, beneath which the Philippine Sea plate is subducting, indicate two major directions; one is the relative motion between the North American and Philippine Sea plates, and the other that between the Eurasian and Philippine Sea plates.One possible interpretation of this is that the eastern margin of the Japan Sea may be in an embryonic stage of plate convergence and the jump of the North American-Eurasian plate boundary from Sakhalin-central Hokkaido to the eastern margin of the Japan Sea has not yet been accomplished. In this case northern Honshu is a microplate which does not have a driving force itself and its motion is affected by the surrounding major plates, behaving as part of either the Eurasian or North American plate. Another possibility is that the seismic slip vectors and crustal deformations in south Kanto do not correctly represent the relative motion between plates but represent the stresses due to non-rigid behaviors of part of northern Honshu.     

中国岩石圈应力场与构造运动区域特征

笔者系统分析了1918—2005年间中国大陆及其周缘发生的3130个中、强地震的震源机制解,根据其特征进行了岩石圈应力场构造分区,首次得到区域应力场的压应力轴和张应力轴空间分布的统计数字结果。在此基础上研究了应力场的区域特征、探讨了其动力学来源以及构造运动特征。总体结果表明,中国大陆及其周缘岩石圈应力场和构造运动可以归结为印度洋板块、太平洋板块、菲律宾海板块与欧亚板块之间相对运动,以及大陆板内区域块体之间的相互作用的结果。印度洋板块向欧亚板块的碰撞挤压运动所产生的强烈的挤压应力,控制了喜马拉雅、青藏高原、中国西部乃至延伸到天山及其以北的广大地区。在青藏高原周缘地区和中国西部的大范围内,压应力P轴水平分量方位位于20～40°,形成了近NE方向的挤压应力场。大量逆断层型强震集中发生在青藏高原的南、北和西部周缘地区,以及天山等地区。而多数正断层型地震集中发生在青藏高原中部高海拔的地区,断层位错的水平分量位于近东西方向。表明青藏高原周缘区域发生南北向强烈挤压短缩的同时,中部高海拔地区存在着明显的近东西向的扩张运动。中国东部的华北地区受到太平洋板块向欧亚板块俯冲挤压的同时,又受到从贝加尔湖经过大华北直到琉球海沟的广阔地域里存在着的统一的、方位为170°的引张应力场的控制。华北地区大地震的震源机制解均反映出该区地震的发生大体为NEE向挤压应力和NNW向张应力的共同作用结果。台湾纵谷断层是菲律宾海板块与欧亚板块之间碰撞挤压边界。来自北西向运动的菲律宾海板块构造应力控制了从台湾纵谷、华南块体,直到中国南北地震带南段东部地域的应力场。地震的震源机制结果还表明,将中国大陆分成东、西两部分的中国南北地震带是印度洋板块、菲律宾海板块与太平洋板块在中国大陆内部影响控制范围的分界线。     

The role of subduction erosion in the generation of Andean and other convergent plate boundary arc magmas,the continental crust and mantle

Subduction erosion, which occurs at all convergent plate boundaries associated with magmatic arcs formed on crystalline forearc basement, is an important process for chemical recycling, responsible globally for the transport of ~1.7 Armstrong Units (1 AU = 1 km³/yr) of continental crust back into the mantle. Along the central Andean convergent plate margin, where there is very little terrigenous sediment being supplied to the trench as a result of the arid conditions, the occurrence of mantle-derived olivine basalts with distinctive crustal isotopic characteristics (⁸⁷Sr/⁸⁶Sr ≥ 0.7050; ε_Nd ≤ −2; ε_Hf ≤ +2) correlates spatially and/or temporally with regions and/or episodes of high rates of subduction erosion, and a strong case can be made for the formation of these basalts to be due to incorporation into the subarc mantle wedge of tectonically eroded and subducted forearc continental crust. In other convergent plate boundary magmatic arcs, such as the South Sandwich and Aleutian Islands intra-oceanic arcs and the Central American and Trans-Mexican continental margin volcanic arcs, similar correlations have been demonstrated between regions and/or episodes of relatively rapid subduction erosion and the genesis of mafic arc magmas containing enhanced proportions of tectonically eroded and subducted crustal components that are chemically distinct from pelagic and/or terrigenous trench sediments. It has also been suggested that larger amounts of melts derived from tectonically eroded and subducted continental crust, rising as diapirs of buoyant low density subduction mélanges, react with mantle peridotite to form pyroxenite metasomatites that than melt to form andesites. The process of subduction erosion and mantle source region contamination with crustal components, which is supported by both isotopic and U-Pb zircon age data implying a fast and efficient connectivity between subduction inputs and magmatic outputs, is a powerful alternative to intra-crustal assimilation in the generation of andesites, and it negates the need for large amounts of mafic cumulates to form within and then be delaminated from the lower crust, as required by the basalt-input model of continental crustal growth. However, overall, some significant amount of subducted crust and sediment is neither underplated below the forearc wedge nor incorporated into convergent plate boundary arc magmas, but instead transported deeper into the mantle where it plays a role in the formation of isotopically enriched mantle reservoirs. To ignore or underestimate the significance of the recycling of tectonically eroded and subducted continental crust in the genesis of convergent plate boundary arc magmas, including andesites, and for the evolution of both the continental crust and mantle, is to be on the wrong side of history in the understanding of these topics.