班公湖-怒江洋形成演化新视角:兼论西藏中部古-新特提斯转换

班公湖-怒江洋的形成演化是认识班公湖-怒江成矿带成矿地质背景的关键,近几年中国地质调查局在青藏高原部署了大量1∶50000区域地质调查工作,取得了很多重要发现。对班公湖-怒江结合带两侧关键性海陆沉积地层对比研究,认为南羌塘地块与拉萨地块晚古生代-晚三叠世地层沉积特征及岩石组合基本一致,二者在班公湖-怒江中生代洋盆形成以前是一个整体,为冈瓦纳大陆北缘被动陆缘环境。班公湖-怒江洋在早中侏罗世裂解形成,至中侏罗世趋于稳定且范围最大;向北俯冲消减作用始于中晚侏罗世,晚侏罗世-早白垩世演化为残留海,早白垩世中晚期出现短暂的裂解,致使海水重新灌入;晚白垩世班公湖-怒江洋盆进入闭合后的隆升造山阶段,发生了残留盆地迁移,形成了磨拉石建造。班公湖-怒江洋类似古加勒比海(现今墨西哥湾地区)的形成机制,并与大西洋、太平洋的形成过程关系密切。对于班公湖-怒江洋的闭合和冈底斯弧的形成,本文提出了另一种可能解释,即,新特提斯洋向北俯冲下,岩浆弧逐步南迁,在弧后形成了一系列伸展性质的弧后盆地,两者组成微陆块由北向南逐渐增生形成了现今的拉萨地体,持续向北俯冲也导致了班公湖-怒江洋最终闭合。     

三江昌宁-孟连带原-古特提斯构造演化

昌宁-孟连特提斯洋的构造演化及其原特提斯与古特提斯的转换方式一直是青藏高原及邻区基础地质研究中最热门的科学问题之一.根据新的地质调查资料、研究成果并结合分析数据,系统总结了三江造山系不同构造单元地质特征,讨论了昌宁-孟连特提斯洋早古生代-晚古生代的构造演化历史.通过对不同构造单元时空结构的剖析和对相关岩浆、沉积及变质作用记录的分析,认为昌宁-孟连结合带内共存原特提斯与古特提斯洋壳残余,临沧-勐海一带发育一条早古生代岩浆弧带,前人所划基底岩系"澜沧岩群"应为昌宁-孟连特提斯洋东向俯冲消减形成的早古生代构造增生杂岩,滇西地区榴辉岩带很可能代表了俯冲增生杂岩带发生了深俯冲,由于弧-陆碰撞而迅速折返就位,这一系列新资料及新认识表明昌宁-孟连结合带所代表的特提斯洋在早古生代至晚古生代很可能是一个连续演化的大洋.在此基础上,结合区域地质资料,构建了三江造山系特提斯洋演化的时空格架及演化历史,认为其经历了早古生代原特提斯大洋扩张、早古生代中晚期-晚古生代特提斯俯冲消减与岛弧带形成、晚二叠世末-早三叠世主碰撞汇聚、晚三叠世晚碰撞造山与盆山转换等阶段.      

What drove late Mesozoic extension of the northern China–Mongolia tract?

The northern China–Mongolia tract exhibited a tectonic transition from contractional to extensional deformation in late Mesozoic time. Late Middle to early Late Jurassic crustal shortening is widely thought to have resulted from collision of an amalgamated North China–Mongolia block and the Siberian plate, but widespread late Late Jurassic–Early Cretaceous extension has not been satisfactorily explained by existing models. Some prominent features of the extensional tectonics of the northern China–Mongolia tract are: (1) Late Jurassic voluminous volcanism prior to Early Cretaceous large-magnitude rapid extension; (2) overlapping in time of contractional deformation in the Yinshan–Yanshan belt with development of extension-related basins in the interior of the northern China–Mongolia tract; and (3) widespread occurrence of alkali granitic plutonism, extensional basins and metamorphic core complexes in the Early Cretaceous. A new explanation is advanced in this study for this sequence of events. The collision of amalgamated North China–Mongolia with Siberia led to crustal overthickening of the northern China–Mongolia tract and formation of a high-standing plateau. Subsequent breakoff at depth of the north-dipping Mongol–Okhotsk oceanic slab is suggested as the main trigger for late Mesozoic lithospheric extension of that tract. Slab breakoff resulted in mantle lithospheric stretching of the adjacent northern China–Mongolia tract with subsequent ascent of hot asthenosphere and magmatic underplating at the base of the crust. Collectively, these phenomena triggered gravitational collapse of the previously thickened crust, leading to late Late Jurassic–Early Cretaceous crustal extension, and importantly, coeval contraction along the southern margin of the plateau in the Yinshan–Yanshan belt. The proposed model provides a framework for interpreting the spatial and temporal relationships of distinct processes and reconciling some seemingly contradictory phenomena, such as the synchronous extension of northerly terranes during major contraction in the neighboring Yanshan–Yinshan belt.     

Plateau archives of lithosphere dynamics,cryosphere and paleoclimate: The formation of Cretaceous desert basins in east Asia

Southeastern Eurasia is a global window to the Cretaceous paleoclimate and lithosphere coupling. China contains one of the most complete and complex sedimentary records of Mesozoic desert basins on planet Earth. In this study, we perform the spatio-temporal tracking of 96 Cretaceous palaeoclimate indicators during 79 Myr which reveal that the plateau paleoclimate archives from East Asia resulted from an Early to Mid-Cretaceous ocean–atmosphere coupling and a shift to a preponderant role of Late Cretaceous lithosphere dynamics and tectonic forcing on high-altitude depositional systems linked to the subduction margins of the Tethys and Paleo-Pacific realms beneath the Eurasian plate. The crustal response to tectonic processes linked with the spatio-temporal evolution of the Tethyan and Paleo-Pacific margins defined the configuration of major sedimentary basins on this region. The significant increase and decrease in the number of active sedimentary basins that occur during the Cretaceous, from 16 in the Early Cretaceous, to 28 in the Mid-Cretaceous, and a decreasing to 20 sedimentary basins in the Late Cretaceous, is a direct response of lithospheric dynamics associated with the two main subduction zones (Tethys and Pacific domains). A shift in subduction style from an Early Cretaceous Paleo-Pacific Plate slab roll back to a Late Cretaceous flat-slab mode might have triggered regional plateau uplift, blocked intraplate volcanism, thus enhancing the denudation and sediment availability, and created wind corridors that led to the construction and accumulation of extensive Late Cretaceous aeolian sandy deserts (ergs) that covered Mid-Cretaceous plateau salars. At the same time, plateau uplift associated with crustal thickening following terrane assembly in the Tethyan margin triggered altitudinal cryospheric processes in sandy desert systems. Evidence of an active Cretaceous cryosphere in China include Valanginian-Hauterivian glacial debris flows, Early Aptian geochemical signature of melt waters from extensive ice sheets, and Cenomanian–Turonian ice-rafted debris (IRD). These cryospheric indicators suggest an already uplifted plateau in southeastern Eurasia during the Cretaceous, and the marked correlation between cold plateau paleoclimate archives and marine records suggests a strong ocean-atmosphere coupling during Early and Mid-Cretaceous cold snaps. We thus conclude that lithospheric tectonics during Cretaceous played a fundamental role in triggering high-altitude basin desertification and spatio-temporal plateau paleohydrology variability in the Cretaceous of south-eastern Eurasia.     

Geochemistry of Cadmium in Mesozoic Phosphorites of the East European Platform

Cadmium is the most toxic admixture in mineral fertilizers. The Cd concentration in Mesozoic phosphorites, which are widespread in the East European Platform, has not been investigated. The present study was stimulated by the scanty and contradictory nature of the published data on this issue. We determined Cd concentration in 21 phosphorite samples from major deposits and checked the reliability of obtained results by external replicate analyses. It has been established that the Cd concentration in phosphorites varies from 5 ppm in the Late Jurassic–Early Cretaceous basin to 2 ppm in the Late Cretaceous basin. Cadmium does not enter the structure of phosphate and sulfide minerals. The Cd concentration is independent of the phosphorus abundance. However, all studied samples show a positive correlation of Cd with organic matter mainly contained in phosphates, supporting the biophilic nature of Cd. Mesozoic phosphorites of the East European Platform accumulated in epicontinental basins. They are significantly depleted in Cd relative to Mesozoic–Cenozoic phosphorites in pericontinental basins of the southern margin of the Tethys Ocean. The Cd concentration is more stable in Mesozoic phosphorites than in Mesozoic–Cenozoic deposits.     

青藏高原南部拉萨地体的变质作用与动力学

拉萨地体位于欧亚板块的最南缘,它在新生代与印度大陆的碰撞形成了青藏高原和喜马拉雅造山带。因此,拉萨地体是揭示青藏高原形成与演化历史的关键之一。拉萨地体中的中、高级变质岩以前被认为是拉萨地体的前寒武纪变质基底。但新近的研究表明,拉萨地体经历了多期和不同类型的变质作用,包括在洋壳俯冲构造体制下发生的新元古代和晚古生代高压变质作用,在陆-陆碰撞环境下发生的早古生代和早中生代中压型变质作用,在洋中脊俯冲过程中发生的晚白垩纪高温/中压变质作用,以及在大陆俯冲带上盘加厚大陆地壳深部发生的两期新生代中压型变质作用。这些变质作用和伴生的岩浆作用表明,拉萨地体经历了从新元古代至新生代的复杂演化过程。(1)北拉萨地体的结晶基底包括新元古代的洋壳岩石,它们很可能是在Rodinia超大陆裂解过程中形成的莫桑比克洋的残余。(2)随着莫桑比克洋的俯冲和东、西冈瓦纳大陆的汇聚,拉萨地体洋壳基底经历了晚新元古代的(～650Ma)的高压变质作用和早古代的(～485Ma)中压型变质作用。这很可能表明北拉萨地体起源于东非造山带的北端。(3)在古特提斯洋向冈瓦纳大陆北缘的俯冲过程中,拉萨地体和羌塘地体经历了中古生代的(～360Ma)岩浆作用。(4)古特提斯洋盆的闭合和南、北拉萨地体的碰撞,导致了晚二叠纪(～260Ma)高压变质带和三叠纪(～220Ma)中压变质带的形成。(5)在新特提斯洋中脊向北的俯冲过程中,拉萨地体经历了晚白垩纪(～90Ma)安第斯型造山作用,形成了高温/中压型变质带和高温的紫苏花岗岩。(6)在早新生代(55～45Ma),印度与欧亚板块的碰撞,导致拉萨地体地壳加厚,形成了中压角闪岩相变质作用和同碰撞岩浆作用。(7)在晚始新世(40～30Ma),随着大陆的继续汇聚,南拉萨地体经历了另一期角闪岩相至麻粒岩相变质作用和深熔作用。拉萨地体的构造演化过程是研究汇聚板块边缘变质作用与动力学的最佳实例。     

Tectonic evolution of the southern margin of Laurasia in the Black Sea region

The Black Sea region comprises Gondwana-derived continental blocks and oceanic subduction complexes accreted to Laurasia. The core of Laurasia is made up of an Archaean–Palaeoproterozoic shield, whereas the Gondwana-derived blocks are characterized by a Neoproterozoic basement. In the early Palaeozoic, a Pontide terrane collided and amalgamated to the core of Laurasia, as part of the Avalonia–Laurasia collision. From the Silurian to Carboniferous, the southern margin of Laurasia was a passive margin. In the late Carboniferous, a magmatic arc, represented by part of the Pontides and the Caucasus, collided with this passive margin with the Carboniferous eclogites marking the zone of collision. This Variscan orogeny was followed by uplift and erosion during the Permian and subsequently by Early Triassic rifting. Northward subduction under Laurussia during the Late Triassic resulted in the accretion of an oceanic plateau, whose remnants are preserved in the Pontides and include Upper Triassic eclogites. The Cimmeride orogeny ended in the Early Jurassic, and in the Middle Jurassic the subduction jumped south of the accreted complexes, and a magmatic arc was established along the southern margin of Laurasia. There is little evidence for subduction during the latest Jurassic–Early Cretaceous in the eastern part of the Black Sea region, which was an area of carbonate sedimentation. In contrast, in the Balkans there was continental collision during this period. Subduction erosion in the Early Cretaceous removed a large crustal slice south of the Jurassic magmatic arc. Subduction in the second half of the Early Cretaceous is evidenced by eclogites and blueschists in the Central Pontides and by a now buried magmatic arc. A continuous extensional arc was established only in the Late Cretaceous, coeval with the opening of the Black Sea as a back-arc basin.     

Early Cretaceous subduction initiation beneath southern Tibet caused the northward flight of India

Collision between the Indian and Eurasian plates formed the ～2500 km long Yarlung Zangbo Suture Zone and produced the Himalaya mountains and Tibetan plateau.Here we offer a new explanation for tectonic events leading to this collision:that the northward flight of India was caused by an Early Cretaceous episode of subduction initiation on the southern margin of Tibet.Compiled data for ophiolites along the Yarlung Zangbo Suture Zone show restricted ages between 120 Ma and 130 Ma,and their supra-subduction zone affinities are best explained by seafloor spreading in what became the forearc of a north-dipping subduction zone on the southern margin of Tibet.The subsequent evolution of this new subduction zone is revealed by integrating data for arcrelated igneous rocks of the Lhasa terrane and Xigaze forearc basin deposits.Strong slab pull from this new subduction zone triggered the rifting of India from East Gondwana in Early Cretaceous time and pulled it northward to collide with Tibet in Early Paleogene time.     

羌塘-三江古生代-中生代沉积盆地演化

羌塘-三江构造-地层大区的古生代-中生代沉积盆地和构造演化受特提斯洋的控制.通过综合分析前人对羌塘-三江地区大量岩石地层、生物地层、同位素年代学及构造学等研究资料,对羌塘-三江构造-地层大区各分区古生代-中生代的沉积盆地类型进行了划分,并分析了各个沉积盆地的形成和演化过程,探讨了该区的大地构造演化:早古生代该区主体属于大洋环境;晚古生代随着特提斯洋向南东、北东方向的俯冲,该区开始发育一系列活动陆缘沉积盆地,产生金沙江弧后洋、澜沧江弧后洋和甘孜-理塘弧后洋,形成多岛洋弧盆系;中生代,随着特提斯洋向北东的俯冲消减,弧后洋逐渐闭合,羌塘-三江地区发生大规模弧-弧、弧-陆碰撞增生,逐渐转化成陆.随着白垩纪特提斯洋的闭合,印度板块与中国西部碰撞、造山,羌塘-三江地区发育陆内盆地.      

Tectonic evolution of the Intra-Pontide suture zone in the Armutlu Peninsula, NW Turkey

The Armutlu Peninsula and adjacent areas in NW Turkey play a critical role in tectonic reconstructions of the southern margin of Eurasia in NW Turkey. This region includes an inferred Intra-Pontide oceanic basin that rifted from Eurasia in Early Mesozoic time and closed by Late Cretaceous time. The Armutlu Peninsula is divisible into two metamorphic units. The first, the Armutlu Metamorphics, comprises a ?Precambrian high-grade metamorphic basement, unconformably overlain by a ?Palaeozoic low-grade, mixed siliciclastic/carbonate/volcanogenic succession, including bimodal volcanics of inferred extensional origin, with a possibly inherited subduction signature. The second unit, the low-grade znik Metamorphics, is interpreted as a Triassic rift infilled with terrigenous, calcareous and volcanogenic lithologies, including basalts of within-plate type. The Triassic rift was unconformably overlain by a subsiding Jurassic–Late Cretaceous (Cenomanian) passive margin including siliciclastic/carbonate turbidites, radiolarian cherts and manganese deposits. The margin later collapsed to form a flexural foredeep associated with the emplacement of ophiolitic rocks in Turonian time. Geochemical evidence from meta-basalt blocks within ophiolite-derived melange suggests a supra-subduction zone origin for the ophiolite. The above major tectonic units of the Armutlu Peninsula were sealed by a Maastrichtian unconformity. Comparative evidence comes from the separate Almacık Flake further east.Considering alternatives, it is concluded that a Mesozoic Intra-Pontide oceanic basin separated Eurasia from a Sakarya microcontinent, with a wider Northern Neotethys to the south. Lateral displacement of exotic terranes along the south-Eurasian continental margin probably also played a role, e.g. during Late Cretaceous suturing, in addition to overthrusting.     

班公湖-怒江结合带西段多岛弧盆系时空结构初步分析

笔者依据班公湖地区1：25万喀纳幅、日土县幅、羌多幅地质填图和专题研究工作取得的阶段性成果,将班公湖带的多岛弧盆系时空结构厘定为3条蛇绿混杂岩亚带。该3条亚带为盆地所隔,从北而南依次为班公湖带北亚带、班摩掌侏罗纪弧间盆地、班公湖带中亚带、日土-巴尔穷侏罗纪—早白垩世复合弧后盆地和班公湖带南亚带等。初步认为班公湖-怒江特提斯洋经历了晚三叠—早侏罗世往北俯冲、中晚侏罗世早期向北、往南双向俯冲、早白垩世往南俯冲等3次俯冲消亡阶段;同时,讨论了在班公湖带研究中存在的问题及其在反演班公湖-怒江结合带西段构造演化和在找矿方面的意义,以及进一步研究方向。     

新疆及周边古地磁研究与构造演化

新疆古地磁研究始于1979年,20年来通过对塔里木、准噶尔、昆仑山等地区的古地磁研究,获得了古生代—新生代塔里木板块、准噶尔板块和青藏板块古地磁极移曲线和古纬度资料。震旦纪以前塔里木板块尚未形成,晚震旦世在赤道附近各地块才联合成塔里木板块的主体部分。后经历了两次快速北移,一次快速南移。准噶尔板块早古生代为一个独立的微板块,在晚古生代与哈萨克斯坦板块联合成一体,组成了哈萨克斯坦-准噶尔板块;塔里木板块震旦纪时还属冈瓦纳大陆的一个组成部分,早古生代逐渐脱离了冈瓦纳大陆,快速向北漂移,晚古生代早期与准噶尔板块首次在东部碰撞,成为劳亚大陆南缘的一个增生体。将介于劳亚大陆和冈瓦纳大陆之间的古陆体,称之谓华夏古陆群。晚古生代末—中生代早期,华夏古陆群先后增生到劳亚大陆南缘;早古生代早期古特提斯洋尚未形成,诸地块处于冈瓦纳大陆范围内,位于南半球的赤道附近。在中-晚志留世,这些地(板)块才快速向北漂移,由于洋扩张,形成了古特提斯洋,构成了三大陆块群夹两个大洋的古地理格局;二叠纪是特提斯构造演化关键时期,晚侏罗-早白垩世昆仑地块与柴达木地块和塔里木地块发生碰撞,联合成一体。早侏罗世早期柴达木地块等与塔里木地块发生碰撞联合,造成了古特提斯洋消亡。早侏罗世中期,开     

Tectonic Evolution and Key Geological Issues of the Proto‐South China Sea

There are numerous controversies surrounding the tectonic properties and evolution of the Proto-South China Sea(PSCS).By combining data from previously published works with our geological and paleontological observations of the South China Sea(SCS),we propose that the PSCS should be analyzed within two separate contexts:its paleogeographic location and the history of its oceanic crust.With respect to its paleogeographic location,the tectonic properties of the PSCS vary widely from the Triassic to the mid-Late Cretaceous.In the Triassic,the Paleo-Tethys and the Paleo-Pacific Oceans were the major causes of tectonic changes in the SCS,while the PCSC may have been a remnant sea residing upon Tethys or Paleo-Pacific oceanic crust.In the Jurassic,the Meso-Tethys and the Paleo-Pacific oceans joined,creating a PSCS back-arc basin consisting of Meso-Tethys and/or Paleo-Pacific oceanic crust.From the Early Cretaceous to the midLate Cretaceous,the Paleo-Pacific Ocean was the main tectonic body affecting the SCS;the PSCS may have been a marginal sea or a back-arc basin with Paleo-Pacific oceanic crust.With respect to its oceanic crust,due to the subduction and retreat of the Paleo-Pacific plate in Southeast Asia at the end of the Late Cretaceous,the SCS probably produced new oceanic crust,which allowed the PSCS to formally emerge.At this time,the PSCS was most likely a combination of a new marginal sea and a remnant sea;its oceanic crust,which eventually subducted and became extinct,consisted of both new oceanic crust and remnant oceanic crust from the Paleo-Pacific Ocean.In the present day,the remnant PSCS oceanic crust is located in the southwestern Nansha Trough.     

Denudation and cooling of the Lake Teletskoye Region in the Altai Mountains (South Siberia) as revealed by apatite fission-track thermochronology

Lake Teletskoye occupies a narrow graben located in the northwestern sector of the Altai fold belt in South Siberia. The lake basin is thought to have formed during the Pleistocene as a distant result of the Cenozoic collision of India and Eurasia that caused a tectonic reactivation of the Palaeozoic Gorny–Altai (GA) and West Sayan (WS) blocks.The present work reports of a pilot fission-track study performed on 13 apatite separates collected from rocks that were sampled along two profiles in close proximity of the lake. The age–length data and AFT thermochronological modelling reveal two important phases of cooling in the Altai Mountains, a first one during the Late Jurassic–Early Cretaceous and a second one that started in the Miocene–Pliocene and that persists until today. The first event is interpreted to result from uplift-induced denudation probably related to the closure of the Mongol–Okhotsk Ocean; the second event can be linked to the young Cenozoic movements that lie at the origin of the formation of the Lake Teletskoye basin.     

Apatite fission track thermochronology of the Precambrian Aksu blueschist, NW China: Implications for thermo–tectonic evolution of the north Tarim basement

The Precambrian Aksu blueschist is located in the northwestern margin of the Tarim Block, NW China. In recent decades, many studies were carried out with focus on the metamorphic age. However, a complete understanding of the evolution of the Tarim Block requires the cooling history of the Precambrian metamorphic rocks and the time–temperature paths as determined by low-temperature thermochronometry. Therefore, apatite fission track (AFT) technique was applied on the Precambrian Aksu blueschist to reveal the thermo–tectonic evolution of the north Tarim basement. All of the six blueschist samples analysed in this study yielded AFT ages spanning 107.5–62.5 Ma, much younger than the blueschist facies metamorphic age of Neoproterozoic, and confined track lengths are between 10.46 and 12.12 µm. Based on regional stratigraphic sequences, the AFT thermal history modeling as well as previous chronological results, the thermo–tectonic evolution of the Aksu blueschist can be roughly reconstructed with four stages: (1) the Precambrain Aksu blueschist exhumed to the surface soon after its formation. Erosion during the Early Sinian is indicated by the lack of sedimentation until the Late Sinian; (2) the Late Sinian strata are continuous, while the Middle–Upper Silurian and the Lower–Middle Carboniferous strata are absent. The total thickness of the Late Sinian and Paleozoic strata probably reached 10,000 m and resulted in the total annealing and thermal resetting of AFT ages; (3) the AFT ages in the Cretaceous are related with the widespread uplift in Tian Shan and its adjacent regions that restarted the AFT clock during the Late Mesozoic. These reflect a distant effect of the collision of the Lhasa terrane with Eurasia in the Late Jurassic–Early Cretaceous; and (4) sediments of Cenozoic are documented in the Aksu area. The Aksu blueschist was heated to partial annealing zone with the overlying Cenozoic sediments. During Miocene time, the Aksu blueschist was re-exhumed which was probably a distant response to the ongoing India–Eurasia convergence.     

雪峰山构造带古构造应力场

华南地区构造复杂, 中生代动力体制经历了从特提斯构造域向滨太平洋构造域的转换。雪峰山位于华南内部, 其隆升机制也存在广泛争议, 对雪峰山及其邻区古应力场研究, 为华南大陆构造演化动力机制提供了依据。古应力反演显示, 中生代以来, 研究区受到NE向、近SN向、NW向、NNE向四期的构造挤压。NE向与近SN向是华南块体印支期顺时针旋转以及古特提斯洋闭合的结果, NW向挤压是古太平洋板块俯冲作用导致, 而NNE向挤压则与印、藏碰撞的远程效应有关。     

对雅鲁藏布江结合带形成演化的再探讨

通过1∶5万区域地质调查和收集相关资料的综合研究,本文对雅鲁藏布江结合带的形成演化作了进一步的探讨。雅鲁藏布江特提斯洋具有弧后扩张洋盆的性质,在早三叠世至中三叠世中期洋盆初步形成,中三叠世晚期至晚三叠世洋盆全面形成,从早侏罗世至晚白垩世洋盆逐步萎缩,到古新世至始新世关闭。南带的蛇绿岩主要为洋中脊扩张型(MORB型),形成于中三叠世晚期至晚三叠世。北带的蛇绿岩主要为与洋内俯冲相关的俯冲带上盘型(SSZ型),形成于早中侏罗世。带内侏罗纪至白垩纪其他岩浆岩主要为前弧玄武岩类(FAB型)。显示雅鲁藏布江特提斯洋从早侏罗世开始发生了洋内俯冲,并同步向北向冈底斯带之下主动俯冲消减和向南向喜马拉雅地块之下被动俯冲消减,持续发展到晚白垩世,在古新世至始新世俯冲碰撞消亡转化为结合带。     

兴蒙造山带的基底属性与构造演化过程

为了解兴蒙造山带基底属性和多个构造体系演化与叠加历史,系统总结了近年来在基础地质研究中取得的新成果,并利用这些成果讨论了兴蒙造山带的基底属性与演化历史.兴蒙造山带是指我国东北地区古生代构造作用影响的地区,这些地区也遭受了中生代构造作用的叠加与改造.兴蒙造山带主要由微陆块和其间的造山带组成.虽然传统上认为属于前寒武纪结晶基底的地质体主要已解体为古生代和早中生代,但随着新太古代和古元古代地质体的相继发现,以及新生代玄武岩中幔源古元古代橄榄岩包体的发现,可以判定兴蒙造山带内微陆块应具有古老的前寒武纪基底,并且壳幔是耦合的.微陆块内部地壳增生以垂向增生为主,且主要发生在新元古代和中元古代,以及次要的新太古代和古生代.相反,陆块间造山带或岛弧地体的陆壳则以侧向增生为主,且主要发生在新元古代和古生代.额尔古纳地块与兴安地块的拼合发生在早古生代早期;兴安地块与松嫩地块的拼合发生在早石炭世晚期;松嫩地块与佳木斯地块的拼合发生在早古生代晚期,中生代早期又经历了裂解与再闭合的构造演化过程;华北克拉通北缘增生杂岩带与北方微陆块群的最终拼合发生在晚二叠世-中三叠世,古亚洲洋的最终闭合发生在中三叠世,且为剪刀式闭合.晚古生代晚期蒙古-鄂霍茨克大洋板块南向俯冲作用的发生以及早中生代(三叠纪-早侏罗世)的持续南向俯冲,控制了大兴安岭-冀北-辽西地区的岩浆活动,蒙古-鄂霍茨克大洋的闭合发生在中侏罗世,晚侏罗世-早白垩世主要表现为闭合后的伸展环境.古太平洋板块中生代的俯冲起始时间为早侏罗世,晚侏罗世-早白垩世早期东北亚陆缘主要表现为走滑的构造属性和陆缘地体从低纬度到高纬度的构造就位过程,早白垩世晚期-古近纪岩浆作用的向东收缩揭示了古太平洋板块的持续俯冲和俯冲板片的后撤过程,古近纪晚期日本海的打开标志着东北亚陆缘从活动陆缘已经转变为沟-弧-盆体系,并且标志着东亚大地幔楔的形成.     

Seismotectonics and tectonic history of the andaman sea

The Andaman Sea is considered as an actively spreading back-arc basin. Seismicity and newly determined focal-mechanism solutions in the Andaman Sea area support this view. The tectonic history of the region is inferred from magnetic lineations in the northeastern Indian Ocean and the northward motion of Greater India. The mid-oceanic ridge which migrated northward along the east side of the Ninetyeast Ridge collided with the western end of the “old Sunda Trench” in the Middle or Late Miocene (10–20 m.y. B.P.). This ridge—trench collision released much of the compressional stress in the back-arc area and the continued northward movement of India that collided with Eurasia exerted a drag on the back-arc region, causing the opening of the Andaman Sea. In appearance, the subducted ridge jumped to the back-arc area. Thus, the Andaman Sea is not an ordinary subduction-related back-arc basin, but probably a basin formed by oblique extensional rifting associated with both ridge subduction and deformation of the back-arc area caused by a nearby continental collision.     

Age of Detrital Zircons from Sandstones of the Mesozoic Flysch Formation in the South Anyui Suture Zone (Western Chukotka)

The South Anyui fold zone (western Chukotka) is considered a suture zone related to closure of the South Anyui oceanic basin and collision of Eurasia with the Chukotka–Arctic Alaska microcontinent in the Early Cretaceous. The existence of a compensatory sedimentation basin (foredeep) during folding in the terminal Jurassic–initial Cretaceous remains debatable. This work presents first data on age estimates of detrital zircons from Upper Mesozoic terrigenous sequences of the South Anyui suture zone obtained by the fission-track method. The distal flysch of presumably Late Jurassic age and the proximal flysch of probably Late Triassic age were sampled in the Uyamkanda River basin. The fission-track dating showed that sandstones from the flysch sections contain detrital zircons of two different-age populations. Young zircon populations from sandstones of distal turbidites in the upper course of the Uyamkanda River (two samples) are 149 ± 10.2 and 155.4 ± 9.0 Ma old (Late Jurassic), whereas those from coarse-grained proximal turbidites sampled in the lower course of the Uyamkanda River (one sample) is 131.1 ± 7.5 Ma old (Early Cretaceous). The data obtained indicate that the Late Mesozoic folding in the South Anyui suture zone was accompanied by the formation of a marginal sedimentary basin. Sediments accumulated in this basin compose tectonic nappes that constitute a fold–thrust structure with the northern vergence.