Late Mesozoic-Cenozoic Exhumation of the Northern Hexi Corridor: Constrained by Apatite Fission Track Ages of the Longshoushan

The apatite fission track (AFT) ages and thermal modeling of the Longshoushan and deformation along the northern Hexi Corridor on the northern side of the Qinghai-Tibetan Plateau show that the Longshoushan along the northern corridor had experienced important multi-stage exhumations during the Late Mesozoic and Cenozoic. The AFT ages of 7 samples range from 31.9 Ma to 111.8 Ma. Thermal modeling of the AFT ages of the samples shows that the Longshoushan experienced significant exhumation during the Late Cretaceous to the Early Cenozoic (~130–25 Ma). The Late Cretaceous exhumation of the Longshoushan may have resulted from the continuous compression between the Lhasa and Qiangtang blocks and the flat slab subduction of the Neo-Tethys oceanic plate, which affected wide regions across the Qinghai-Tibetan Plateau. During the Early Cenozoic, the Longshoushan still experienced exhumation, but this process was caused by the Indian-Eurasian collision. Since this time, the Longshoushan was in a stable stage for approximately 20 Ma and experienced erosion. Since ~5 Ma, obvious tectonic deformation occurred along the entire northern Hexi Corridor, which has also been reported from the peripheral regions of the Qinghai-Tibetan Plateau, especially in the Qilianshan and northeastern margin of the plateau. The AFT ages and the Late Cenozoic deformation of the northern Hexi Corridor all indicate that the present northern boundary of the Qinghai-Tibetan Plateau is situated along the northern Hexi Corridor.     

Late Cretaceous‐Cenozoic Multi‐Stage Denudation at the Western Ordos Block: Constraints by the Apatite Fission Track Dating on the Langshan

The apatite fission track dating of samples from the Dabashan(i.e., the Langshan in the northeastern Alxa Block) by the laser ablation method and their thermal history modeling of AFT ages are conducted in this study. The obtained results and lines of geological evidence in the study region indicate that the Langshan has experienced complicated tectonic-thermal events during the the Late Cretaceous-Cenozoic. Firstly, it experienced a tectonic-thermal event in the Late Cretaceous(~90–70 Ma). The event had little relation with the oblique subduction of the Izanagi Plate along the eastern Eurasian Plate, but was related to the Neo-Tethys subduction and compression between the Lhasa Block and Qiangtang Block. Secondly, it underwent the dextral slip faulting in the Eocene(~50–45 Ma). The strike slip fault may develop in the same tectonic setting as sinistral slip faults in southern Mongolia and thrusts in West Qinling to the southwest Ordos Block in the same period, which is the remote far-field response to the India-Eurasia collision. Thirdly, the tectonic thermal event existed in the late Cenozoic(since ~10 Ma), thermal modeling shows that several samples began their denudation from upper region of partial annealing zone(PAZ), and the denudation may have a great relationship with the growth of Qinghai-Tibetan Plateau to the northeast. In addition, the AFT ages of Langshan indicate that the main body of the Langshan may be an upper part of fossil PAZ of the Late Cretaceous(~70 Ma). The fossil PAZ were destroyed and deformed by tectonic events repeatedly in the Cenozoic along with the denudation.     

Latest Triassic to Early Jurassic Thrusting and Exhumation in the Southern Ordos Basin,North China: Evidence from LA‐ICP‐MS‐based Apatite Fission Track Thermochronology

The contractional structures in the southern Ordos Basin recorded critical evidence for the interaction between Ordos Basin and Qinling Orogenic Collage. In this study, we performed apatite fission track(AFT) thermochronology to unravel the timing of thrusting and exhumation for the Laolongshan-Shengrenqiao Fault(LSF) in the southern Ordos Basin. The AFT ages from opposite sides of the LSF reveal a significant latest Triassic to Early Jurassic time-temperature discontinuity across this structure. Thermal modeling reveals at the latest Triassic to Early Jurassic, a ~50°C difference in temperature between opposite sides of the LSF currently exposed at the surface. This discontinuity is best interpreted by an episode of thrusting and exhumation of the LSF with ~1.7 km of net vertical displacement during the latest Triassic to Early Jurassic. These results, when combined with earlier thermochronological studies, stratigraphic contact relationship and tectono-sedimentary evolution, suggest that the southern Ordos Basin experienced coeval intense tectonic contraction and developed a north-vergent fold-and-thrust belt. Moreover, the southern Ordos Basin experienced a multi-stage differential exhumation during Mesozoic, including the latest Triassic to Early Jurassic and Late Jurassic to earliest Cretaceous thrust-driven exhumation as well as the Late Cretaceous overall exhumation. Specifically, the two thrust-driven exhumation events were related to tectonic stress propagation derived from the latest Triassic to Early Jurassic continued compression from Qinling Orogenic Collage and the Late Jurassic to earliest Cretaceous intracontinental orogeny of Qinling Orogenic Collage, respectively. By contrast, the Late Cretaceous overall exhumation event was related to the collision of an exotic terrain with the eastern margin of continental China at ~100 Ma.     

Cenozoic Exhumation and Thrusting in the Northern Qilian Shan, Northeastern Margin of the Tibetan Plateau: Constraints from Sedimentological and Apatite Fission-Track Data

Abstract: The Qilian Shan lies along the northeastern edge of the Tibetan Plateau. To constrain its deformation history, we conducted integrated research on Mesozoic–Cenozoic stratigraphic sections in the Jiuxi Basin immediately north of the mountain range. Paleocurrent measurements, sandstone compositional data, and facies analysis of Cenozoic stratigraphic sections suggest that the Jiuxi Basin received sediments from the Altyn Tagh Range in the northwest, initially in the Oligocene (~33 Ma), depositing the Huoshaogou Formation in the northern part of the basin. Later, the source area of the Jiuxi Basin changed to the Qilian Shan in the south during Late Oligocene (~27 Ma), which led to the deposition of the Baiyanghe Formation. We suggest that uplift of the northern Qilian Shan induced by thrusting began no later than the Late Oligocene. Fission-track analysis of apatite from the Qilian Shan yields further information about the deformation history of the northern Qilain Shan and the Jiuxi Basin. It shows that a period of rapid cooling, interpreted as exhumation, initiated in the Oligocene. We suggest that this exhumation marked the initial uplift of the Qilian Shan resulting from the India–Asia collision.     

Cenozoic Stratigraphy Deformation History in the Central and Eastern of Qaidam Basin by the Balance Section Restoration and its Implication

The Qaidam Basin, located in the northern margin of the Qinghai–Tibet Plateau, is a large Mesozoic–Cenozoic basin, and bears huge thick Cenozoic strata. The geologic events of the Indian-Eurasian plate–plate collision since ~55 Ma have been well recorded. Based on the latest progress in high-resolution stratigraphy, a technique of balanced section was applied to six pieces of northeast–southwest geologic seismic profiles in the central and eastern of the Qaidam Basin to reconstruct the crustal shortening deformation history during the Cenozoic collision. The results show that the Qaidam Basin began to shorten deformation nearly synchronous to the early collision, manifesting as a weak compression, the deformation increased significantly during the Middle and Late Eocene, and then weakened slightly and began to accelerate rapidly since the Late Miocene, especially since the Quaternary, reflecting this powerful compressional deformation and rapid uplift of the northern Tibetan Plateau around the Qaidam Basin.     

The Exhumation History of North Qaidam Thrust Belt Constrained by Apatite Fission Track Thermochronology: Implication for the Evolution of the Tibetan Plateau

Determining the spatio-temporal distribution of the deformation tied to the India-Eurasian convergence and the impact of pre-existing weaknesses on the Cenozoic crustal deformation is significant for understanding how the convergence between India and Eurasia contributed to the development of the Tibetan Plateau. The exhumation history of the northeastern Tibetan Plateau was addressed in this research using a new apatite fission track (AFT) study in the North Qaidam thrust belt (NQTB). Three granite samples collected from the Qaidam Shan pluton in the north tied to the Qaidam Shan thrust, with AFT ages clustering in the Eocene to Miocene. The other thirteen samples obtained from the Luliang Shan and Yuka plutons in the south related to the Luliang Shan thrust and they have showed predominantly the Cretaceous AFT ages. Related thermal history modeling based on grain ages and track lengths indicates rapid cooling events during the Eocene-early Oligocene and since late Miocene within the Qaidam Shan, in contrast to those in the Cretaceous and since the Oligocene-Miocene in the Luliang Shan and Yuka region. The results, combined with published the Cretaceous thermochronological ages in the Qaidam Shan region, suggest that the NQTB had undergo rapid exhumation during the accretions along the southern Asian Andean-type margin prior to the India-Eurasian collision. The Cenozoic deformation initially took place in the North Qaidam thrust belt by the Eocene, which is consistent with the recent claim that the deformation of the northeastern Tibetan Plateau initiated in the Eocene as a response to continental collision between India and Eurasia. The immediate deformation responding to the collision is tentatively attributed to the pre-existing weaknesses of the lithosphere, and therefore the deformation of the northeastern Tibetan Plateau should be regarded as a boundary-condition-dependent process.     

东昆仑中生代隆升剥露历史

位于中央造山带西段的东昆仑造山带因多期次造山和复杂演化历史而备受关注,约束其中生代隆升剥露历史,对于理解青藏高原大规模隆升在东昆仑地区的扩展及影响颇具意义。东昆仑造山带内中生代侏罗系-白垩系地层缺失严重,体现中生代以来强烈的隆升剥露过程,也是该区热演化的研究难点。本文通过对东昆仑造山带样品的磷灰石、锆石裂变径迹分析和热演化史研究,并结合东昆仑及周缘地区现有低温热年代学研究,识别出东昆仑造山带所经历的五次隆升冷却事件,即201~193Ma（早侏罗世）、172~152Ma（中-晚侏罗世）、120~98Ma（早白垩世末-早白垩世初）、98~20Ma（晚白垩世-中新世）及20~0Ma（中新世至今）。所获5个年龄组响应东昆仑地区所经历的构造热事件,其中201~193Ma年龄组响应南部羌塘地块与昆仑地块的碰撞事件;172~152Ma年龄组为中-晚侏罗世古特提斯洋闭合后,造山后伸展的构造事件的记录;120~98Ma热事件吻合拉萨地块和羌塘地块碰撞事件;98~20Ma年龄组为东昆仑地区长期缓慢剥蚀去顶过程的印证;20~0Ma的快速隆升剥露事件则为东昆仑周缘断裂系活化相伴,多期隆升剥蚀事件均得到地层不整合及沉积记录等研究成果的证实。区内剥蚀起始时间从由南到北逐渐变老,体现东昆仑地区隆升剥蚀的不均一性。     

Cooling history and tectonic exhumation stages of the south-central Tibetan Plateau (China): Constrained by 40Ar/39Ar and apatite fission track thermochronology

Between the Qiangtang Block and Yalung-Zangpo Suture Zone in the south-central Tibetan Plateau, the following geological units and suture zones have been identified from south to north: the Gangdese Granitic Belt, the Lhasa Block, the Nyainqentanghla Shear Zone, the Dangxiong–Sangxiong Tectono-granitic Belt and the Bangong–Nujiang Suture Zone. To better constrain the tectonic evolution and cooling histories of these units, ⁴⁰Ar/³⁹Ar muscovite, biotite and K-feldspar, as well as apatite fission track dating and thermochronological analysis have been carried out. The analytical results indicate that the south-central Tibetan Plateau, with the exception of the Nyainqentanghla Shear Zone, provides a record of three cooling stages at 165–150, 130–110 and ∼45–35 Ma. Fission-track data modelling also indicates that the stages of cooling were different in the different tectonic belts or blocks. Very different cooling phases occurred in the south-central Tibetan Plateau, compared with southern Tibet, as well as along the Yalung–Zangpo Suture Zone. There is no thermochronological evidence to indicate that the south-central part of Tibetan Plateau was influenced by the underthrusting of Indian Plate.The three-stage cooling history and the stages of tectonic exhumation were controlled completely by the closure of the Bangong–Nujiang Suture Zone along its eastern segment during Middle–Late Jurassic (165–150 Ma) and its western segment in the Early–Late Cretaceous (130–110 Ma), as well as by the collision between the Indian and Asian plates in the Paleogene (45–35 Ma).     

龙门山冲断隆升及其走向差异的裂变径迹证据

大量的低温年代学研究用来讨论龙门山晚新生代的隆升,但很少涉及其走向差异和中生代隆升。本文分别沿龙门山北、中、南段3条剖面进行了锆石和磷灰石裂变径迹测试,结合已有的热年代学数据,以期揭示整个中-新生代期间龙门山隆升历史及其时空变化。中生代以来,龙门山主要有印支期(约200 Ma)、早白垩世末(约100 Ma)、早新生代(65～30 Ma)以及晚中新世(15～9 Ma)等或快或慢的冷却事件,总体上经历了中生代至早新生代的缓慢冷却和晚新生代快速冷却2个阶段,快速剥露开始于15～9 Ma,剥蚀速率由早期的0.1 mm/a增加到0.15～0.3 mm/a左右,局部可达0.9 mm/a左右。走向上,龙门山北段相对偏小的锆石裂变径迹年龄和相对偏大的磷灰石裂变径迹年龄反映其在中生代较中、南段隆升更快,而裂变径迹年龄总体上从北段向中、南段减小,表明中、南段在新生代发生了更快的隆升。倾向上,多种热年代学数据显示新生代期间在北川断裂和彭灌断裂两侧存在明显的差异剥露,这种差异在中、南段表现比北段更为突出。龙门山晚新生代快速隆升和剥露是青藏高原区域隆升背景上叠加的冲断活动所致,而非下地壳流动驱动。     

新生代渭河盆地沉积-构造迁移与渭北隆起及东秦岭耦合关系探讨

渭河盆地、渭北隆起及东秦岭造山带地处青藏块体东北缘、华北克拉通和扬子克拉通的交界处,形成了特有的盆山体系,分布有油气、氦气及地热等多种能源矿产资源。新生代是渭河盆地沉积-构造演化及渭北隆起和东秦岭隆升的重要时期,缺乏该时期盆山体系耦合关系的研究,制约了对区域矿产资源分布规律的认识。盆山耦合体现在时间、空间、物质、构造作用及地表形态等多方面。以大量钻孔资料为依托,运用“回剥法”分析了渭河盆地新生代的沉降幅度及沉降速率,并根据主沉降期新近纪以来不同阶段沉积地层厚度展布特征恢复了盆地沉积演化历史。研究表明渭河盆地新生代以来沉降中心具有自西南方向西安凹陷向北东方向固市凹陷迁移的特征。古近纪始新世以来,渭河盆地发生快速构造沉降,中新世早-中期以西安凹陷为主要沉积、沉降中心,晚中新世以来以西安、固市两个凹陷为主要沉积、沉降中心,晚上新世-早更新世沉降中心转移到东北部固市凹陷,晚更新世以来,西安凹陷和固市凹陷均发生快速沉降。裂变径迹的分析测试结果表明渭北隆起约45～32 Ma整体快速抬升,同步于东秦岭太白山和华山约57～40 Ma的快速隆升阶段,与渭河盆地古近纪始新世约40 Ma的基底快速沉降具有耦合关系。晚中新世约7.3 Ma以来,渭河盆地的持续快速沉降,与渭北隆起上新世约5 Ma及东秦岭太白山约10～9.6 Ma、华山约8～5 Ma以来的快速耦合关系明显。太平洋板块的俯冲、欧亚板块与印度板块始新世约55～45 Ma碰撞及青藏高原约10～8 Ma隆升外扩的远程效应对研究区影响较大。     

低温热年代对黄陵隆起中新生代古地形的约束

低温热年代技术已经广泛应用于造山带的剥露作用和古地形演化的研究。本文对黄陵隆起进行了裂变径迹和(U-Th)/He热年代学研究,分析计算其隆升剥露速率和厚度,恢复黄陵隆起中新生代古地形。依据岩石样品冷却历史计算出的剥露速率以及剥露厚度结果,综合黄陵隆起现今地形起伏,均衡回弹作用以及古海平面变化情况,获得了黄陵隆起早侏罗世、早白垩世、晚白垩世、晚始新世以及现今5个时期的古地形变化情况。结果表明黄陵隆起地形表现为持续降低的趋势,并存在两期剧烈的隆升剥露阶段。分析认为,白垩纪(140~80 Ma±),黄陵隆起的快速隆升剥露作用与秦岭大别造山带大规模的挤压作用密切相关,晚始新世以来(40~0 Ma)黄陵隆起的快速抬升剥露作用则是对喜山期构造运动的响应。     

滇西石鼓杂岩南部早白垩世以来剥露隆升的锆石和磷灰石裂变径迹证据

石鼓杂岩位于青藏高原东南缘经历了多期变质变形作用叠加。为了揭示杂岩体的低温热演化与浅部剥露历史,采集了石鼓杂岩南段石鼓镇-拉巴支村剖面变质岩中的锆石和磷灰石,开展裂变径迹分析。结果表明,石鼓杂岩从早白垩世(133~145Ma)到渐新世(31Ma)经历了一次缓慢的剥露(1.08℃/Ma),而从渐新世开始,其南部经历了较快速的剥露过程(3.23℃/Ma)。磷灰石热史模拟也反映出第二阶段较为快速的冷却过程。结合区域构造分析认为,拉萨与羌塘板块碰撞的远程效应影响早白垩世以来藏东地区地壳结构的调整,导致石鼓杂岩南部出现了第一阶段的剥露作用;而印度与欧亚板块碰撞与后碰撞过程对于石鼓杂岩的新生代剥露具有重要影响。     

循化-化隆盆地晚白垩世以来盆山耦合过程: 来自物源与磷灰石裂变径迹年代学分析的证据

循化-化隆盆地新生代沉积及盆地基底和周缘山系磷灰石裂变径迹年代学分析揭示了青藏高原东北缘晚白垩世以来经历过3期隆升剥露事件: (1)盆地基底及拉脊山和西秦岭北缘构造带磷灰石裂变径迹年龄分析普遍记录了晚白垩世-始新世中期相对快速的区域性的隆升剥露事件, 西秦岭北缘快速抬升的起始时间为84Ma, 受控于向北的逆冲抬升; 向北到循化-化隆盆地中部的拉目峡抬升的起始时间为69Ma; 更北的拉脊山一带快速抬升期主要为40~50Ma, 从而反映晚白垩世-始新世中期的快速抬升由南向北逐渐扩展.这一期构造隆升事件导致循化-化隆盆地和临夏盆地缺失了北部西宁-民和盆地古近纪所具有的西宁群沉积.隆升剥露结束于31Ma左右, 此时化隆-循化盆地向东与同时期的临夏盆地相连为一个统一的大型西秦岭山前盆地, 两者具有相同的构造、沉积演化史, 因此循化-化隆盆地他拉组底部地层年龄最老不会超过临夏盆地最老地层的古地磁年龄, 即29Ma.(2)渐新世晚期约26Ma拉脊山开始双向逆冲隆升, 并可能延续到中新世早期约21Ma, 隆升作用使循化-化隆盆地成为挟持于拉脊山逆冲带和西秦岭构造带之间的山前挤压型前陆盆地, 循化-化隆盆地开始大规模沉积巨厚的他拉组冲积扇相粗碎屑岩.(3)通过循化-化隆盆地咸水河组和临夏组的沉积相分析、古流方向和砾石成分分析, 揭示出拉脊山构造带在中新世8Ma左右发生的最大规模的双向逆冲隆升事件, 这次事件直接导致循化-化隆盆地由前陆挤压盆地转变为山间盆地, 形成现今青藏高原东北缘的盆山地貌基本格局.      

大别造山带折返剥露历史:来自合肥盆地南缘中生界变质岩碎屑的证据

在合肥盆地南缘广泛分布的中生界内,砾石主要由变质岩碎屑组成。碎屑在地层中分布及垂向上的变化,为重塑造山带折返剥露历史提供了证据。防虎山组和三尖铺组底部砾岩碎屑组合为:石英片岩+云母片岩+石墨片岩+千枚岩+石英岩+脉石英+片麻岩(局部),表明在早侏罗世晚期Pliensbachian期(距今195Ma)之前,佛子岭群和卢镇关群已经折返到地表并遭受剥露。早白垩世凤凰台组、毛坦厂组和周公山组中砾岩碎屑组合为:片岩+石英岩+片麻岩+混合岩+榴辉岩+角闪岩+斜长岩+花岗岩+大理岩等,榴辉岩以及其它基性岩的微量元素特征表明它们可能是一个在早白垩世以前(距今135Ma)折返到地表并遭受完全剥露,而现在已经从造山带消失的超高压构造地层单元。大别造山带出露的超高压变质带(大别杂岩)在北缘中生代地层中目前尚未发现有可靠的沉积记录,推测它们的大规模折返和剥露可能在新生代,并持续到现在。据此认为大别造山带大规模的折返剥露分为3个阶段:早侏罗世之前、晚侏罗世—早白垩世早期和新生代。     

Partitioning of the Cretaceous Pan-Yangtze Basin in the central South China Block by exhumation of the Xuefeng Mountains during a transition from extensional to compressional tectonics?

The formation of a series of intermountain basins is likely to indicate a geodynamic transition, especially in the case of such basins within the central South China Block (CSCB). Determining whether or not these numerous intermountain basins represent a division of the Cretaceous Pan-Yangtze Basin by exhumation of Xuefeng Mountains, is key to understanding the late Mesozoic to early Cenozoic tectonics of the South China Block (SCB). Here we present apatite fission track (AFT) data and time–temperature modeling in order to reconstruct the evolution history of the Pan-Yangtze Basin. Fourteen rock samples were taken from a NE–SW-trending mountain–basin system within the CSCB, including, from west to east, the Wuling Mountains (Wuling Shan), the south and north Mayang basins, the Xuefeng Mountains (Xuefeng Shan) and the Hengyang Basin. Cretaceous lacustrine sequences are well preserved in the south and north Mayang and Hengyang basins, and sporadically crop out in the Xuefeng Mountains, whereas Paleogene piedmont proluvial–lacustrine sequences are only found in the south Mayang and Hengyang basins. AFT results indicate that the Wuling and Xuefeng mountains underwent rapid denudation post-84 Ma, whereas the south and north Mayang basins were more slowly uplifted from 67 and 84 Ma, respectively. Following a quiescent period from 32 to 19 Ma, both the mountains and basins have been rapidly denuded since 19 Ma. Both the AFT data and sedimentary facies changes suggest that the Cretaceous deposits that cover the south–north Mayang and Hengyang basins through to the Xuefeng Mountains define the Cretaceous Pan-Yangtze Basin. Integrating our results with tectonic background for the SCB, we propose that rollback subduction of the paleo-Pacific Plate produced the Pan-Yangtze Basin, which was divided into the south–north Mayang and Hengyang basins by the abrupt uplift and exhumation of the Xuefeng Mountains from 84 Ma to present, apart from a period of tectonic inactivity from 32 to 19 Ma. This late Late Cretaceous to Paleogene denudation resulted from movement on the Ziluo strike–slip fault, which formed due to intra-continental compression most likely associated with the Eurasia–Indian plate subduction and collision. Sinistral transpression along the Ailao Shan–Red River Fault at 34–17 Ma probably transformed this compression to the extrusion of the Indochina Block, and produced the quiescent window period from 32 to 19 Ma for the mountain–basin system in the CSCB. Therefore, the initiation of exhumation of the Xuefeng Mountains at 84 Ma indicates a switch in tectonic regime from Cretaceous extension to late Late Cretaceous and Cenozoic compression.     

柴达木盆地西部地区晚新生代构造变形及其意义

青藏高原东北缘构造变形研究是认识整个青藏高原隆升过程、机制以及印欧板块碰撞远程效应的重要途径。受控于昆仑山断裂、阿尔金断裂、祁连山断裂的柴达木盆地,新生代地层发育,较完整地记录了高原东北缘的构造变形信息。尤其柴达木盆地西部地区,构造变形强烈,晚新生代地层出露完整,是研究其晚新生代构造变形历史及驱动机制的理想地区。文中应用平衡剖面和古地磁构造旋转方法,结合最新的磁性地层年代,定量恢复该地区的构造变形历史。结果表明,在挤压应力的控制下该地区自22 Ma以来,构造变形主要表现为地层缩短与构造旋转,且其强度呈阶段性增长,具体又可划分为3个阶段：22~9.1 Ma构造活动平静期、9.1~2.65 Ma构造变形相对加强期、2.65 Ma以来构造变形顶峰期。研究表明,造成柴西地区地层持续缩短和顺时针旋转的关键推动力是印欧板块晚新生代的持续向北推挤、昆仑山-祁曼塔格山向柴达木盆地强烈挤压推覆以及阿尔金左旋走滑断裂大规模的复活。     

Thermal History since the Paleozoic in the Eastern Qaidam Basin,Northwest China

The Qaidam Basin is the one of the three major petroliferous basins in northeastern Tibetan Plateau, which has experienced multiphase superimposition and transformation. The study of thermal history not only plays an important role on revealing the tectonic origin of the Qaidam Basin and the forming mechanism and uplift history of the Tibetan Plateau,but also can provide scientific evidence for the assessment of oil and gas resources. This work used balanced cross-section technique and apatite fission track ages with modeling of fission track length distribution to infer that the eastern Qaidam Basin has experienced significant tectonic movement in the Early Jurassic movement(～200 Ma), which caused the carboniferous uplift and denudation, the geological movement in the Late Cretaceous, characterized by early stretching and late northeast-southwest extrusion; the Himalayan movement in multi-stage development in eastern Qaidam Basin, which can be divided into the early Himalayan movement(41.1–33.6 Ma) and the late Himalayan movement(9.6–7.1 Ma, 2.9–1.8 Ma), and large-scale orogeny caused pre-existing faults reactivated in late Himalayan movement. On the basis of burial history reconstruction, the thermal history of eastern Qaidam Basin was restored. The result shows that the thermal history in eastern Qaidam Basin shows slow cooling characteristics; the paleo-geothermal gradient of eastern Qaidam Basin was 38–41.5℃/km, with an average value of 39.0℃/km in the Late Paleozoic, 29–35.2℃/km, with an average value of 33.0℃/km in the Early Paleogene; the geothermal gradient of the Qaidam Basin increased in the Late Paleogene, which was similar to the present geothermal gradient in the Late Neogene. The characteristics of the tectono-thermal evolution since Paleozoic in the eastern Qaidam Basin are mainly controlled by magmatic thermal events in the study area.     

150 Million year history of North China Craton disruption preserved in Mesozoic sediments of the Ordos basin

ABSTRACT

The Ordos Basin, situated in the western part of the North China Craton, preserves the 150-million-year history of North China Craton disruption. Those sedimentary sources from Late Triassic to early Middle Jurassic are controlled by the southern Qinling orogenic belt and northern Yinshan orogenic belt. The Middle and Late Jurassic deposits are received from south, north, east, and west of the Ordos Basin. The Cretaceous deposits are composed of aeolian deposits, probably derived from the plateau to the east. The Ordos Basin records four stages of volcanism in the Mesozoic–Late Triassic (230–220 Ma), Early Jurassic (176 Ma), Middle Jurassic (161 Ma), and Early Cretaceous (132 Ma). Late Triassic and Early Jurassic tuff develop in the southern part of the Ordos Basin, Middle Jurassic in the northeastern part, while Early Cretaceous volcanic rocks have a banding distribution along the eastern part. Mesozoic tectonic evolution can be divided into five stages according to sedimentary and volcanic records: Late Triassic extension in a N–S direction (230–220 Ma), Late Triassic compression in a N–S direction (220–210 Ma), Late Triassic–Early Jurassic–Middle Jurassic extension in a N–S direction (210–168 Ma), Late Jurassic–Early Cretaceous compression in both N–S and E–W directions (168–136 Ma), and Early Cretaceous extension in a NE–SW direction (136–132 Ma).     

Meso‐Cenozoic Evolution of Earth Surface System under the East Asian Tectonic Superconvergence

The East Asian geological setting has a long duration related to the superconvergence of the Paleo‐Asian, Tethyan and Paleo‐Pacific tectonic domains. The Triassic Indosinian Movement contributed to an unified passive continental margin in East Asia. The later ophiolites and I‐type granites associated with subduction of the Paleo‐Pacific Plate in the Late Triassic, suggest a transition from passive to active continental margins. With the presence of the ongoing westward migration of the Paleo‐Pacific Subduction Zone, the sinistral transpressional stress field could play an important role in the intraplate deformation in East Asia during the Late Triassic to Middle Jurassic, being characterized by the transition from the E‐W‐trending structural system controlled by the Tethys and Paleo‐Asian oceans to the NE‐trending structural system caused by the Paleo‐Pacific Ocean subduction. The continuously westward migration of the subduction zones resulted in the transpressional stress field in East Asia marked by the emergence of the Eastern North China Plateau and the formation of the Andean‐type active continental margin from late Late Jurassic to Early Cretaceous (160‐135 Ma), accompanied by the development of a small amount of adakites. In the Late Cretaceous (135‐90 Ma), due to the eastward retreat of the Paleo‐Pacific Subduction Zone, the regional stress field was replaced from sinistral transpression to transtension. Since a large amount of late‐stage adakites and metamorphic core complexes developed, the Andean‐type active continental margin was destroyed and the Eastern North China Plateau started to collapse. In the Late Cretaceous, the extension in East Asia gradually decreased the eastward retreat of the Paleo‐Pacific subduction zones. Futhermore, a significant topographic inversion had taken place during the Cenozoic that resulted from a rapid uplift of the Tibet Plateau resulting from the India‐Eurasian collision and the formation of the Bohai Bay Basin and other basins in the East Asian continental margin. The inversion caused a remarkable eastward migration of deformation, basin formation and magmatism. Meanwhile, the basins that mainly developed in the Paleogene resulted in a three‐step topography which typically appears to drop eastward in altitude. In the Neogene, the basins underwent a rapid subsidence in some depressions after basin‐controlled faulting, as well as the intracontinental extensional events in East Asia, and are likely to be a contribution to the uplift of the Tibetan Plateau.     

Changes of Late Mesozoic Tectonic Regimes around the Ordos Basin (North China) and their Geodynamic Implications

A synthesis is given in this paper on late Mesozoic deformation pattern in the zones around the Ordos Basin based on lithostratigraphic and structural analyses. A relative chronology of the late Mesozoic tectonic stress evolution was established from the field analyses of fault kinematics and constrained by stratigraphic contact relationships. The results show alternation of tectonic compressional and extensional regimes. The Ordos Basin and its surroundings were in weak N-S to NNE-SSW extension during the Early to Middle Jurassic, which reactivated E-W-trending basement fractures. The tectonic regime changed to a multi-directional compressional one during the Late Jurassic, which resulted in crustal shortening deformation along the marginal zones of the Ordos Basin. Then it changed to an extensional one during the Early Cretaceous, which rifted the western, northwestern and southeastern margins of the Ordos Basin. A NW-SE compression occurred during the Late Cretaceous and caused the termination of sedimentation and uplift of the Ordos Basin. This phased evolution of the late Mesozoic tectonic stress regimes and associated deformation pattern around the Ordos Basin best records the changes in regional geodynamic settings in East Asia, from the Early to Middle Jurassic post-orogenic extension following the Triassic collision between the North and South China Blocks, to the Late Jurassic multi-directional compressions produced by synchronous convergence of the three plates (the Siberian Plate to the north, Paleo-Pacific Plate to the east and Lhasa Block to the west) towards the East Asian continent. Early Cretaceous extension might be the response to collapse and lithospheric thinning of the North China Craton.