Collision tectonics in the Canadian Shield?

Major late Aphebian faults cutting the margin of the western Superior craton and exhibiting large dextral offsets are considered to be a direct result of collision between suturing Superior and Churchill plates. Following initial collision in northern Quebec (Cape Smith belt) and in Ontario (west of James Bay), the Winisk River fault developed and suturing continued along the Fox River belt of the circum-Superior suture. Development of the Kenyon structure, another major shear zone, and subsequent faults, permitted further plate convergence to accommodate the stepped form of the edge of the Churchill plate. In this way the Superior craton was progressively sliced as suturing proceeded from east to southwest. The fault directions were controlled by pre-existing transform faults linking segments of a consuming trench system at the edge of the Churchill plate. Final stages of convergence and collision resulted in thickening of the Churchill plate and major sinistral motion along the Thompson-Owl River shear zone.     

Mesozoic ophiolites,sutures, and arge-scale tectonic movements in Afghanistan

The tectonic history of Afghanistan appears to be the result of successive accretion of fragments of Gondwana to the active margin of Laurasia since the end of the Paleozoic. The margin, in Afghanistan, lies along the present Herat and Panjshir faults, south of Hindu Kush, swings around the central Pamirs and can presumably be traced along the present western Altyn Tagh and Kunlun faults in Tibet. North of this boundary, Paleozoic rocks have been deformed in the Upper Paleozoic, whereas south of it, there is no trace of the Hercynian orogeny. The first collision of Gondwanian fragments with Laurasia probably occurred in the early Mesozoic along the Hindu Kush and Kunlun. To the south, ophiolites along the Panjao and Pangong-Nu Chiang sutures (respectively in central Afghanistan and central Tibet) testify for another suturing event in the Upper Jurassic or Lower Cretaceous. The Indus-Tsangpo suture between India and Tibet corresponds, in eastern Afghanistan, to two ophiolite subbelts, near Kabul and Khost. Both ophiolite complexes have been emplaced between Maestrichtian and Lower Eocene by choking of two northward-dipping subduction zones. After complete contact between the Indian and Asian continents was achieved, presumably in the end of Eocene, the penetration of India into Asia caused large-scale intra-continental shortening. A large part of the shortening was accommodated by strike-slip faulting along Mesozoic and more ancient sutures. Central Afghanistan, in particular, was extruded to the west along the Herat suture by the protrusion of the Pamir wedge. It subsequently collided with the Lut block.     

A regional structural model of the Labrador Trough,northern Quebec,from gravity studies,and its relevance to continent collision in the Precambrian

The Labrador Trough is a linear fold-belt marking the junction of the Superior and Churchill structural provinces in northern Quebec. Gravity profiles across the trough are characterized by gently decreasing anomalies over the Superior Province reaching a minimum beneath the trough and thence increasing abruptly over the Churchill Province to a level some 15 mgal higher than the Superior. Superimposed on this higher level are several broad maxima parallel to the trough, one of which corresponds to an extensive outcrop of migmatites.The gravity profiles may be interpreted in terms of a relatively elevated Conrad discontinuity beneath the Churchill Province isostatically compensated by a thickened lower crust. Such a model is consistent with basement reactivation following collision of the Superior and Churchill continental plates. Collision results in crustal thickening by ductile flow in the upper mantle and consequent partial melting in the lower crust leads to differentiation of the crust into a refractory lower part and potash-rich upper part separated by a zone of migmatites.The geological history of the Labrador Trough, and its present-day structure as deduced from gravity studies, is consistent with a sequence of events involving the gradual closure of a small ocean dividing the Superior and proto-Churchill crustal plates in Aphebian times. The closure was effected by subduction beneath the Churchill culminating in collision during the Hudsonian Orogeny and the formation of the present structural configuration after deep erosion.     

The Palaeo-Tethyan suture: A line of demarcation between two fundamentally different architectural styles in the structure of Asia

Abstract The Palaeo-Tethyan suture separates regions characterized by two fundamentally different tectonic styles in the structure of the Tethysides. North of the suture in Iran, Turkmenistan, Afghanistan, Tadjikistan, Kirgizstan, Uzbekistan, Kazakhstan and large parts of the Russian Federation and China, orogenic development is characterized by very large subduction-accretion complexes developed since the late Proterozoic. Magmatic arc axes migrated radially outwards from the 'Old Vertex of Eurasia' and consolidated the accretionary prisms into a 'basement complex' dominated by a pelitic composition. In such orogens, called the 'Turkic-type' after the dominant ethnic population of Central Asia, ophiolites are unreliable indicators of sutures, because they are present throughout the 'basement' as in-faulted shreds and rarely as nappes. By contrast, south of the Palaeo-Tethyan suture, orogeny was commonly characterized by a Sumatra- or Andean-type continental margin arc (e.g. the Transhimalaya arc) that in places became an island arc by back-arc basin rifting (e.g. the Black Sea behind the Rhodope-Pontide fragment) and later collided with an Atlantic- (as in the Himalaya) or California-type (as in the Alps) continental margin to create Alpine- or Himalayan-type orogenic belts. Turkic-type orogenic belts result from the exaggeration of the Himalayan-type as a result of the subduction of very large oceanic areas that contain great amounts of sediment. They contribute to the enlargement and also possibly the growth of the continental crust which has a composition more silicic than basalt. The Palaeo-Tethyan suture is thus a line across which the rate of continental enlargement by subduction-accretion changed dramatically.     

Terrane analysis and accretion in North-East Asia

Abstract A terrane map of North-East Asia at 1:5 000 000 scale has been compiled. The map shows terranes of different types and ages accreted to the North-Asian craton in the Mesozoic–Cenozoic, sub-and superterranes, together with post-amalgamation and post-accretion assemblages. The great Kolyma-Omolon superterrane adjoins the north-east craton margin. It is composed of large angular terranes of continental affinity: craton fragments and fragments of the passive continental margin of Siberia, and island arc, oceanic and turbidite terranes that are unconformably overlain by shallow marine Middle-Upper Jurassic deposits. The superterrane resulted from a long subduction of the Paleo-Pacific oceanic crust beneath the Alazeya arc. Its south-west boundary is defined by the Late Jurassic Uyandina-Yasachnaya marginal volcanic arc which was brought about by subduction of the oceanic crust that separated the superterrane from Siberia. According to paleomagnetic evidence the width of the basin is estimated to be 1500–2000 km. Accretion of the superterrane to Siberia is dated to the late Late Jurassic-Neocomian. The north-east superterrane boundary is defined by the Lyakhov-South Anyui suture which extends across southern Chukotka up to Alaska. Collision of the superterrane with the Chukotka shelf terrane is dated to the middle of the Cretaceous. The Okhotsk-Chukotka belt, composed of Albian-Late Cretaceous undeformed continental volcan-ites, defines the Cretaceous margin of North Asia. Terranes eastward of the belt are mainly of oceanic affinity: island arc upon oceanic crust, accretion wedge and turbidite terranes, as well as cratonic terranes and fragments of magmatic arcs on the continental crust and metamorphic terranes of unclear origin and age. The time of their accretion is constrained by post-accretionary volcanic belts that extend parallel to the Okhotsk-Chukotka belt but are displaced to the east: the Maastrichtian-Miocene Kamchatka-Koryak belt and the Eocene-Quaternary Central Kamchatka belt which mark active margins of the continent of corresponding ages.     

Formation of Paleoproterozoic eclogitic mantle, Slave Province (Canada): Insights from in-situ Hf and U–Pb isotopic analyses of mantle zircons

In-situ Hf isotope analyses and U–Pb dates were obtained by laser ablation-MC-ICP-MS for a zircon-bearing mantle eclogite xenolith from the diamondiferous Jericho kimberlite located within the Archean Slave Province (Nunavut), Canada. The U–Pb zircon results yield a wide range of ages (2.0 to 0.8 Ga) indicating a complex geological history. Of importance, one zircon yields a U–Pb upper intercept date of 1989 ± 67 Ma, providing a new minimum age constraint for zircon crystallization and eclogite formation. In contrast, Hf isotope systematics for the same zircons display an intriguing uniformity, and corresponding Hf depleted mantle model ages range between 2.1 ± 0.1 and 2.3 ± 0.1 Ga; the youngest Hf model age is within error to the oldest U–Pb date.

The Jericho eclogites have previously been interpreted as representing remnants of metamorphosed oceanic crust, and their formation related to Paleoproterozoic subduction regimes along the western margin of the Archean Slave craton during the Wopmay orogeny. Hf isotope compositions and U–Pb results for the Jericho zircons reported here are in good agreement with a Paleoproterozoic subduction model, suggesting that generation of oceanic crust and eclogite formation occurred between 2.0 and 2.1 Ga. The slightly older Hf depleted mantle model ages (2.1 to 2.3 Ga) may be reconciled with this model by invoking mixing between ‘crustal’-derived Hf from sediments and more radiogenic Hf associated with the oceanic crust during the 2 Ga subduction event. This results in intermediate Hf isotope compositions for the Jericho zircons that yield ‘fictitiously’ older Hf model ages.     

SmNd study of Archean alkalic rocks from the Superior Province of the Canadian Shield

The Abitibi Volcanic Belt in eastern Superior Province of the Canadian Shield is the largest continuous greenstone belt in the world and is a key example of late Archean crust. This belt has, in general, suffered a low intensity of metamorphism and deformation, and, as a result, the stratigraphy and geology are well established. Tholeiitic and calc-alkaline series of igneous rocks are present in this belt in about equal proportions. However, the undersaturated potassic and leucitic volcanics of the Timiskaming Group are a unique feature of this belt.SmNd systematics were determined for twelve Timiskaming volcanic rocks. These rocks show nepheline, diopside and/or olivine plus leucite in the norm and a highly fractionated REE pattern. Sm and Nd concentrations range from 25 to 160 and 45 to 300 times the chondritic abundance, respectively. The Sm and Nd isotopic data yield an isochron age of 2702±105Ma for these volcanic rocks with an initial ε_Nd of +1.9±1.6. This age establishes the Timiskaming alkalic rock to be one of the oldest of their kind. From stratigraphic relations, 2705 Ma is an upper limit for the age and the ε_Nd values of +1.8 to +2.2 at this age for the twelve rocks are also upper limits. Further, this small but positive ε_Nd value for the isochron, when compared to other mantle-derived Archean rocks in the Superior Province, indicates that the Archean mantle was heterogeneous beneath the Canadian Shield and that the Timiskaming alkalic lavas were derived from a depleted mantle.     

渤海湾盆地区燕山期构造特征与原型盆地

结合近几年来渤海湾盆地区深层地震勘探与解释的成果，重点论述了渤海湾盆地区燕山期构造特征与盆地原型，提出燕山期构造变形样式总体在纵向上可分为三个构造层，分别称为上部、中部和下部；横向上总体可分为三个构造带，西部为向西逆冲的薄皮逆冲带，中部为冲断—走滑带，东部为厚皮褶皱—冲断带，主体由两期挤压方向皆为NW—SE向的褶皱—逆冲变形形成；并将其演化分为三个阶段：燕山早期、燕山中期和燕山晚期。但是，渤海湾盆地区燕山期的构造变形特征和原型盆地有所变化，其空间上的差异是基底构造格局及其空间差异叠合的结果。综合其它研究结果还表明，渤海湾盆地区燕山期构造是在西太平洋大陆边缘弧的挤压构造背景下，陆内壳下拆沉和壳内挤出逃逸构造的综合动力作用下形成的。     

Cyclical one-way continental rupture-drift in the Tethyan evolution: Subduction-driven plate tectonics

Numerous continents have rifted and drifted away from Gondwana to repeatedly open ocean basins over the past-500 millionyears.These Gondwana-derived continents drifted towards and collided with components of the Eurasian continent to successively close the preexisting oceans between the two.Plate tectonics satisfactorily describes the continental drift from Gondwana to Eurasia but does not define the geodynamic mechanism of continuously rifting to collisions of continents in the Tethy an Realm.After reappraisal of geological records of the rift,collision and subduction initiation from the surface and various geophysical observations from depth,we propose that Eurasia-directed subducting oceanic slabs would have driven Tethyan system in the Phanerozoic.The Eurasia-directed subduction would have dragged the passive Gondwana margin to rift and drift northwards,giving birth to new oceans since the Paleozoic.The closure of preexisting oceans between the Gondwana-derived continents and Eurasia led to continental collisions,which would have induced the initiation of oceanic subduction in the Tethyan Realm.Multiple episodic switches between collision-subduction-rift repeatedly led to the separation of continental fragments from Gondwana and dragged them to drift towards Eurasia.The final disappearance of Neo-Tethy s would have induced collision of the Gondwana-derived continents with the Eurasian continent,giving rise to the Cenozoic Alpine-Zagros-Himalayan collisional system.Therefore,the Eurasia-directed oceanic subduction would have acted as a 'one-way train' that successively transferred the ruptured Gondwana continental fragments in the south,into the terminal in the north.In this regard,the engine of this "Tethyan one-way train" is the negative buoyancy of subducting oceanic slabs.     

History and modes of Mesozoic accretion in Southeastern Russia

Abstract The history of Mesozoic accretion and growth of the Asia eastern margin, occupied by Southeastern Russia, includes five main events; two main tectonic regimes were responsible for the growth of the continent. In the Triassic-Jurassic, Early Cretaceous and Late Cretaceous-Paleogene, the subduction of the oceanic lithosphere resulted in the formation of wide accretionary wedges of the Mongol-Okhotsk, Khingan-Okhotsk and Eastern Sikhote-Alin active continental margins, respectively. These stages of the comparatively slow growth of the continent were broken by stages of rapid growth and drastic changes in the shape of the continent, since at these stages large terranes of various tectonic nature collided with active continental margins. At the end of the Early-Middle Jurassic, the Bureya terranes collided with the Mongol-Okhotsk active margin, and at the beginning of the Late Cretaceous there was collision of the Central and Southern Sikhote-Alin terranes with the Khingan-Okhotsk active margin.
Collision-related structural styles in all cases are indicative of oblique collision and great strike-slip motions along the main sutures. The peculiarities of the terrane's geological structure show that prior to collision with the Mongol-Okhotsk and Khingan-Okhotsk active margins, they had already accreted to Asia and then migrated along its margins along the strike-slip faults. The Bureya terranes were squeezed out of the compression zone between Siberia and North China. This compression zone originated after the Paleozoic oceans which divided these cratons had closed. The Khanka terranes and Mesozoic accretionary wedge terranes of the Sikhote-Alin shifted along the strike-slip faults subparallel to the Asia Pacific margin. Strike-slip motions resulted in duplication of the primary tectonic zonation.     

青藏高原冈底斯带及邻区重磁三维反演及岩浆岩特征研究

岩浆岩在青藏高原的大陆动力学研究中有着重要的作用,它既是构造演化的记录,又是重要构造-岩浆-成矿带的指示.本文主要基于冈底斯带及邻区的地面重力和航磁数据,首先进行地质-地球物理先验信息约束下的重磁2.5维交互式反演,再将2.5维反演结果作为参考模型加入到三维反演计算中,得到地下三维密度和磁化率结构.结合岩浆岩密度、磁化率统计资料和岩浆岩地球化学成果,推断研究区基性岩、Ⅰ型花岗岩和S型花岗岩的三维分布图,得到如下结论：S型花岗岩主要分布在冈底斯东带和冈底斯弧背断隆带以北;北冈底斯的西部无明显的岩浆活动,而在其南侧和北侧,发现大量的隐伏基性岩和零散分布的Ⅰ型花岗岩;中生代Ⅰ型花岗岩在南冈底斯和冈底斯弧背断隆带广泛分布,且到新生代才出现大量的S型花岗岩.上述结果为中生代班公湖-怒江洋壳和新特提斯洋壳的双向剪刀式俯冲模式的观点提供了重要佐证,并认为班公湖-怒江洋壳在北冈底斯西部约84°E-88°E的范围内先后存在向北和向南俯冲的可能,北向羌塘地体下俯冲,南向冈底斯地体下俯冲.

     

Evolution of a section of the Africa-Europe plate boundary: Paleomagnetic and volcanological evidence from Sicily

New paleomagnetic data relative to Upper Cretaceous, Neogene and Quaternary volcanic rocks from eastern Sicily definitively indicate that Sicily is a part of the African plate, which collided with the European continental plate in Middle Miocene times. These data and the tectonic evolution of Sicily as inferred from the nature, age and distribution of volcanic products, are broadly consistent with the motions of Africa relative to Europe since the Upper Trias. During the Mesozoic, eastern Sicily was affected by extensional tectonics with associated alkali basaltic volcanism, and oceanic crust was produced in the meantime between the diverging African and European plates. Near the end of Mesozoic times the two plates started to converge with consequent consumption of oceanic crust. Different times of oceanic plate consumption along the Sicily-Calabria section of the plate boundary are suggested by the occurence of andesitic volcanism of different ages. The tectonic significance of late Tertiary to present basaltic activity in eastern Sicily is also discussed.     

中国及其邻区地球三维结构初始模型的建立

对人工地震测深及天然地震面波体波三维层折反演数据进行统一处理，建立了中国及其邻区地球三维结构初始模型．此模型图像表明，中国及其邻区地球各圈层横向变化明显．岩石圈及软流圈内速度分布主要反映这一区域自古生代以来板块及地块拼合模式．各主要板块或地块（塔里木、扬子、中朝、青藏、哈萨克斯坦、印度、印度支那）岩石圈增厚或有很深的地慢根，板块或地块间的造山带岩石圈减薄，软流圈速度降低。下地幔底部及核幔边界D″层出现高速异常，表明古太平洋及古特提斯洋俯冲板块因重力坍塌已进入地球深层，形成亚洲超级下降地幔柱。这一下降地幔柱引起地球表层物质向中亚、东亚地区集中，印度半岛、青藏高原、新疆、蒙古至贝加尔一带，成为全球岩石圈最大的汇聚场所．     

Definition of pre-2000 m.y. apparent polar movements

In this paper palaeomagnetic poles known to be older than 2000 m.y. in age are assessed in the context of a continental reconstruction derived from younger Precambrian palaeomagnetic results. It is found that the combined data from North America and Africa define a single apparent polar wander path during the intervals 2700-2500 m.y. and 2160-2000 m.y. using the same continental reconstruction as that derived from younger poles. A rapid polar shift is identified at ca. 2150 m.y. and a closed loop is present in the curve between 2160 and 2000 m.y. Palaeomagnetic results from the Rhodesia/Kaapvaal, Kasai, West Africa and North America (Slave and Superior) cratons define segments of this loop which are statistically identical within errors of the pole positions and their assigned ages.These results in common with younger Proterozoic data (2000-800 m.y.) confirm that the crust behaved as an integral unit during these times, although undergoing internal deformation along mobile zones which has not yet proved detectable by the palaeomagnetic method. The 2700-2000 m.y. interval includes the Archaean-Proterozoic transition during which major structural anisotropy began to be imprinted on the sialic crust. Tectonic straight belts and deformed anorthosites lie within a single great-circle belt on the continental reconstruction incorporating Gondwanaland and North America. This same belt later developed into an arc of major tectonic and magmatic activity (<2250 m.y.) including massive anorthosites, rapakivi granites, acidic volcanism and mobile belts.     

东北亚中生代火山岩的地球动力学意义

东北亚中生代火山岩可划分为陆内环状火山岩带、纬向火山岩带和陆缘北北东向火山岩带,本文通过对俄罗斯、蒙古、中国东北、日本和朝鲜半岛在内的东北亚中生代火山岩分布图的编制,以及火山岩地球化学对比研究,认为东北亚中生代火山岩是古亚洲洋构造域向太平洋构造域转换时期,深部地幔地球化学过程以及东亚大陆与古太平洋板块相互作用的产物。在晚古生代至早中生代古亚洲构造域的闭合和欧亚大陆形成过程中,古亚洲域冷板块向地幔深部潜入而引发的热地幔柱的上升,是东北亚中生代大地构造演化和岩浆作用的重要控制因素。     

全球地震活动性的定量研究(三)——全球地震带的划分和Ⅰ,Ⅱ,Ⅲ带的地震活动

本文根据板块相互作用的原理,对全球地震带作了新的具体的划分:Ⅰ带为美洲西海岸地震带;Ⅱ带为太平洋西北边缘地震带;Ⅲ带为大洋岛弧地震带;Ⅳ带为亚欧地震带;Ⅴ带为全球海岭地震带。各带地震活动水平从强到弱的顺序是Ⅲ,Ⅱ,Ⅰ,Ⅳ,Ⅴ。求出本世纪各年Ⅰ,Ⅱ,Ⅲ三带的地震活动性指数A(b),并对A(b)指数随时间的变化作了最大熵谱分析和周期图分析。结果显示Ⅱ,Ⅲ两带的周期成分与Ⅰ带有明显不同。Ⅰ带的变化较平稳,富于短周期成分,在1942年和1960年有两个峰期;Ⅱ带从1964年以来处于长趋势下降阶段,至八十年代已降至极小;Ⅲ带的五十年代事件效应显著,其变化趋势能较好地代表全球地震活动的变化总趋势。Ⅱ,Ⅲ两带有较强的长周期变化成分,可能与太平洋板块的面积较大有关。      

Constraining the timing of the India-Asia continental collision by the sedimentary record

Placing precise constraints on the timing of the India-Asia continental collision is essential to understand the successive geological and geomorphological evolution of the orogenic belt as well as the uplift mechanism of the Tibetan Plateau and their effects on climate,environment and life.Based on the extensive study of the sedimentary record on both sides of the Yarlung-Zangbo suture zone in Tibet,we review here the present state of knowledge on the timing of collision onset,discuss its possible diachroneity along strike,and reconstruct the early structural and topographic evolution of the Himalayan collided range.We define continent-continent collision as the moment when the oceanic crust is completely consumed at one point where the two continental margins come into contact.We use two methods to constrain the timing of collision onset:(1) dating the provenance change from Indian to Asian recorded by deep-water turbidites near the suture zone,and(2) dating the age of unconformities on both sides of the suture zone.The first method allowed us to constrain precisely collision onset as middle Palaeocene(59±l Ma).Marine sedimentation persisted in the collisional zone for another 20-25 Ma locally in southern Tibet,and molassic-type deposition in the Indian foreland basin did not begin until another 10-15 Ma later.Available sedimentary evidence failed to firmly document any significant diachroneity of collision onset from the central Himalaya to the western Himalaya and Pakistan so far.Based on the Cenozoic stratigraphic record of the Tibetan Himalaya,four distinct stages can be identified in the early evolution of the Himalayan orogen:(1) middle Palaeocene-early Eocene earliest Eohimalayan stage(from 59 to 52 Ma):collision onset and filling of the deep-water trough along the suture zone while carbonate platform sedimentation persisted on the inner Indian margin;(2) early-middle Eocene early Eohimalayan stage(from 52 to 41 or 35 Ma):filling of intervening seaways and cessation of marine sedimentation;(3) late Eocene-Oligocene late Eohimalayan stage(from 41 to 25 Ma):huge gap in the sedimentary record both in the collision zone and in the Indian foreland;and(4) late Oligocene-early Miocene early Neohimalayan stage(from 26 to 17 Ma):rapid Himalayan growth and onset of molasse-type sedimentation in the Indian foreland basin.     

天山山前主要推覆构造区的地壳缩短

利用平衡地质剖面方法研究天山山前主要褶皱带的地壳缩短,其中3条平衡剖面分别横跨天山南簏的柯坪逆断裂-褶皱带和库车逆断裂-褶皱带,2条剖面横跨天山北簏的玛纳斯活动逆断裂-褶皱带,其余1条剖面横跨吐鲁番中央隆起逆断裂-褶皱带。柯坪活动逆断裂-褶皱带、库车逆断裂-褶皱带、玛纳斯逆断裂-褶皱带和吐鲁番盆地的地壳缩短量分别为40~45km、27~37km、8·5~10·5km和6~7km。天山山前活动逆断裂-褶皱带在EW向上互不重叠,它们的缩短量大致代表了该经度上新生代的最小地壳缩短量,反映出天山地壳缩短由西向东减小的趋势。假定天山山前活动逆断裂-褶皱带开始形成的时间为距今2·5Ma的西域砾岩沉积期,考虑到博阿断裂、塔拉斯-费尔干纳断裂在SN向上的缩短活动分量,上述4个地段的最小缩短速率分别为15·4~17·3mm/a、12·7~16·5mm/a、3·8~4·5mm/a和2·3~2·7mm/a。活动走滑断裂在天山内部特定位置向左偏转,走向由NW转为NWW,在断裂转折的部位走滑活动量转化为天山SN向的缩短变形     

Seismicity and focal mechanism in Tibetan Plateau and its implications to lithospheric flow

The Tibetan Plateau is characterized by its high seismicity produced by the continental collision still working at Himalaya. As seismology had made great contribution to the global tectonics in 1960s, it may also provide some improtant clues to the evolution and tectonics in continents. The present paper summarizes the seismicities, focal mechanisms and neotectionics in Tibetan Plateau. The authors suggest a new classification of the seismic belts or zones in the Plateau. The belt from Yadong to Anduo is an active seismic belt. The features of neotectonics and focal mechanisms are different on the west of this belt to the east of it. Most of the earthquakes with focal depthh>70 km in the Plateau situate on this belt. Different to Yuma, Arakan, the earthquakes withh>70 km in Yadong-Anduo belt are less and smaller, their focal mechanisms are normal faults. Appearance of earthquakes with h>70 km suggests that the uppermost mantle in this belt is unstable and the material is hard enough to accumulate strong strain energy. The authors stress the significance of the northwest-southeast striking fault zone of Yanshiping-Changdu. Several large earthquakes occurred in this fault zone are characterized by left-lateral strike slips. It is the southest one of the several left-lateral strike slip zones in the eastern Tibetan Plateau, and may represent the latest produced one of the left-lateral strike slip zones. South to the Bangong-Nujiang suture, the fault zone of Bengcuo-Jiali is a belt of discontinuous right-lateral strike slips with very strong seismicities. The pair-faults of Yanshiping-Changdu left-lateral strike slips and Bengcuo-Jiali right-lateral strike slips provide an evidence of the eastward flow of materials in the lithosphere of Qiang Tang terrain between the pair-faults. Altyn Tagh, Kun Lun and Xianshuihe may represent the residuals of the boundaries of ancient flow paths. Since the sutures and also the cooling effects were produced progressively from the north to south, the flow paths will move progressively southward during the geological times. The Chinese version of this paper appeared in the Chinese edition ofActa Seismologica Sinica, supp.14, 534–565, 1992.