西秦岭北缘漳县新生代伸展断陷盆地确定及其地质意义

西秦岭北缘断裂带新生代以来挤压逆冲变形起始于何时?挤压逆冲变形之前是否经历过伸展拉张过程?北缘断裂带北侧的新生代红层盆地到底是类前陆压陷挠曲盆地还是拉张断陷盆地?上述问题对西秦岭新生代盆-山构造格局重建和印度-欧亚板块碰撞汇聚的远程构造响应的时间与方式等科学问题的认识具有重要的地质约束。本文通过对西秦岭北缘构造带内漳县渐新世—中新世含盐红层盆地沉积序列和沉积旋回特征以及盆地边界断裂之间的几何学-运动学关系分析,认为西秦岭北缘构造带内漳县含盐红层盆地具有拉张伸展动力学背景下形成的断陷盆地的地质特征。西秦岭北缘构造带内渐新世—中新世断陷盆地的确定,指示了印度板块与欧亚板块碰撞汇聚而导致的青藏高原构造挤压缩短作用至少在盆地沉积充填阶段尚未扩展到西秦岭北缘及以北地区。而漳县含盐红层盆地沉积地层褶皱缩短变形以及之后角度不整合在漳县含盐红层盆地之的上新统韩家沟粗砾岩,可能记录了西秦岭北缘由伸展边界向挤压缩短逆冲边界的转换过程。因此,青藏高原东北缘真正成为青藏高原体系组成部分是在上新世的漳县含盐红层盆地封闭-构造反转之后。这一认识对地学界长期以来认为印度板块与欧亚板块碰撞汇聚而导致的高原隆升和构造挤压早在渐新世就已经波及西秦岭北缘的观点提出了挑战。     

柴北缘早新生代旋转变形特征及其构造意义

青藏高原东北部作为高原北东向扩展的前缘地带,新生代以来变形十分强烈,是研究青藏高原隆升变形过程和生长模式的关键地区之一。然而高原东北部何时卷入印度-欧亚大陆碰撞挤压变形系统以及高原扩展的运动学、动力学过程和机制等仍存在很大争议。大陆碰撞及持续挤压过程往往会伴随块体及其内部的旋转变形,而古地磁磁偏角可以定量恢复块体绕垂直轴发生的旋转变形,在研究块体旋转变形方面具有其独特优势。高原东北部,尤其是柴达木盆地,缺乏早新生代的细致旋转变形研究,制约了我们对高原东北部地区早新生代的旋转变形特征及其对印度-欧亚大陆碰撞远程响应的理解。柴北缘地区出露有近乎连续完整的早新生代路乐河组-下干柴沟组地层,为研究青藏高原东北部早新生代旋转变形提供了理想场所。本文对柴北缘逆冲带北中部的驼南和高泉两剖面早新生代路乐河组和下干柴沟组地层开展精细古地磁旋转变形研究:包括在驼南剖面布设4个时间节点、24个采点260个古地磁岩心样品,高泉剖面布设2个时间节点、14个采点150个古地磁岩心样品。通过系统岩石磁学和热退磁实验分析,揭示两剖面早新生代样品的载磁矿物主要是赤铁矿,并含有少量磁铁矿;所获得31个有效采点的高温特征剩磁方向通过褶皱检验和倒转检验,指示可能是岩石沉积时期记录的原生剩磁方向。结合柴北缘中部红柳沟剖面已有古地磁数据,三剖面古地磁结果一致表明柴北缘地区在45~35 Ma期间发生了显著(约20°)逆时针旋转变形。结合东部陇中盆地同时期古地磁旋转变形记录,发现二者具有反向的共轭旋转变形关系。综合青藏高原东部早新生代(52~46 Ma)旋转变形和渐新世以来走滑断裂活动等证据,我们认为:(1)高原东北部的共轭旋转变形是该地区对印度-欧亚碰撞的远程响应,其时间不晚于中始新世(约45 Ma);(2)早新生代自喜马拉雅东构造结至高原东北部,其两侧系统的共轭旋转变形很可能是该时期喜马拉雅东构造结北北东向压入欧亚大陆引起的右旋和左旋剪切作用导致,且剪切应力及相关的地壳缩短和旋转变形等呈现自东构造结地区沿北北东向逐步向高原东北部传递的特征;(3)古新世—始新世时期高原构造变形可能主要通过南北向挤压-地壳增厚模式、渐新世以来主要以沿主要断裂带的侧向挤出模式来调整。     

青藏高原东北缘何时卷入现今青藏高原构造系统?——来自西秦岭北缘漳县盆地新生代沉积记录的约束

新生代以来印度-欧亚板块持续碰撞汇聚形成号称世界第三极的青藏高原。青藏高原的扩展生长和构造变形系统形成的动力学过程是地球科学研究的重大科学问题。青藏高原东北缘新生代以来构造演化过程及其与印度-欧亚板块碰撞汇聚的动力学耦合关系研究对于揭示青藏高原扩展生长过程具有重要地质意义。尽管前人已经开展了大量研究探索,提出各种构造-隆升模型,但青藏高原东北缘何时卷入印度-欧亚碰撞汇聚的青藏高原构造系统尚未达成共识。作为青藏高原东北缘组成部分的西秦岭北缘构造带漳县地区不仅新生代地层记录齐全,而且断裂构造发育,构造变形现象丰富,是研究青藏高原东北缘新生代构造演化及印度-欧亚碰撞汇聚远程构造响应的良好区域。通过对西秦岭北缘构造带漳县地区新生代沉积盆地地层构造格架、沉积地层序列和沉积旋回等详细野外观测研究,结合区域断裂带几何学-运动学及变形历史分析,取得如下认识:(1)西秦岭北缘漳县地区新生代沉积地层主要由为不整合分隔的两套构造性质完全不同的构造地层单元组成,即渐新世—中新世伸展断陷盆地沉积和上新世再生前陆磨拉石盆地沉积;(2)渐新世—中新世时期的地壳伸展拉张构造环境与印度-欧亚碰撞汇聚的挤压环境相悖,指示了西秦岭北缘在渐新世—中新世尚未卷入现今的印度-欧亚碰撞汇聚构造系统;(3)上新世磨拉石盆地的发育标志着西秦岭北缘构造带从伸展到挤压的构造体制转换,可能指示了印度-欧亚碰撞汇聚的挤压构造作用这时才波及西秦岭北缘;(4)上新世粗砾岩、西秦岭造山带地层和中生代沉积地层共同经历了抬升剥蚀作用,形成了西秦岭北缘广泛发育的夷平面。第四纪以来夷平面的抬升和解体、现代河流侵蚀系统和多级河流阶地的出现,指示了青藏高原东北缘整体的不均匀大规模抬升而进入现今青藏高原构造系统。     

青藏高原的现今地壳活动性

古近纪以来,印度板块与欧亚大陆的碰撞和持续的俯冲作用,造成了青藏高原强烈的陆内变形,引起了古造山带的复活;同时也使高原前陆盆地和内部的一些中小型盆地内数百米至数千米厚的新生代地层发生褶皱和冲断,遍布全区的逆冲推覆构造、走滑断裂和活动褶皱,在区域性的北东-南西向的构造应力作用下,导致高原地壳缩短加厚和整体向东滑移。高原的抬升是整体地、间歇性地、不均速地隆升。它经历了古近纪缓慢抬升一新近纪末至更新世快速抬升一全新世地壳振荡运动频繁的三个阶段。自7Ma至今,青藏高原累计抬高了3000～3500m,喜马拉雅山从古地中海崛起以来,至少上升了5000m。现代地热、地震发生,至今没有停止活动。     

西昆仑及邻区岩石圈结构构造演化——塔里木南—西昆仑多学科地学断面简要报道

通过深地震反射剖面,宽频天然深地震探测,广角折射、反射剖面,结合地表地质观察、岩石矿物和地球化学研究,以及弹性模拟计算等,对当前国际上流行的所谓高原北缘向南呈A型俯冲,南缘向北俯冲构成的青藏高原地壳加厚、隆升的“双俯冲”(two-sidedsubduction)模式提出质疑,认为高原北缘至少在西昆仑与塔里木(欧亚板块)之间不存在长距离的俯冲,在新生代以来的强劲挤压中,塔里木起到了一定的阻挡作用,在这里呈现南北向挤压应力场,因而青藏高原西北缘陆-陆碰撞造山、盆山的形成受到“南北双向挤压模式”所控制,也是造成青藏高原西北缘新生代期地壳加厚、隆升的重要动力因素     

西昆仑及邻区岩石圈结构构造演——塔里木南——西昆仑多学科地学断面简要报道

通过深地震反射剖面，宽频天然深地震探测，广角折射、反射剖面，结合地表地质观察、岩石矿物和地球化学研究，以及弹性模拟计算等，对当前国际上流行的所谓高原北缘向南呈A型俯冲，南缘向北俯冲构成的青藏高原地壳加厚、隆升的“双俯冲”（two-sided subduction）模式提出质疑，认为高原北缘至少在西昆仑与塔里木（欧亚板块）之间不存在长距离的俯冲，在新生代以来的强劲挤压下，塔里木起到了一定的阻挡作用，在这里呈现南北向挤压应力场，因而青藏高原西北缘陆-陆碰撞造山、盆山的形成受到“南北双向挤压模式”所控制，也是造成青藏高原西北缘新生代后期地壳加厚、隆升的重要动力因素。     

新生代大陆板内伸展盆-山耦合与大陆碰撞效应——以渤海湾盆地济阳坳陷、周缘隆起及边界断裂构造演化为例

新生代印欧大陆碰撞引发了中国西部前缘大规模多阶段地壳挤压缩短、构造变形与隆升及岩浆事件,在中国东部,新生代山脉的抬升、盆地的伸展、沉降,以及郯庐断裂带新生代的活动与青藏高原的隆升具有准同时性,伸展盆地-伸展山脉之间存在耦合关系。这种对应关系呈"幕式"变化,主要表现在印欧大陆碰撞岩石圈增厚、构造变形和抬升的高峰时期,对应盆地岩石圈伸展、减薄、快速构造沉降以及郯庐断裂带活动等阶段,当构造转入相对稳定(松弛)时期,表现为高原剥蚀夷平、岩浆活动频繁以及盆地构造沉降速率减缓等阶段。从全球板块构造的角度来看,中国西部、东部新生代挤压、伸展和走滑活动属同一动力学体系条件下的耦合关系,驱动力可能是两大板块碰撞、深部地幔脉动上涌以及新生代太平洋板块与欧亚板块俯冲和速率变化的共同作用。     

平衡剖面技术恢复云南兰坪—金顶地区白垩纪地层缩短历史及其意义

兰坪盆地为中新生代陆内盆地, 地处欧亚板块与印度板块的拼合带, 其中兰坪金顶地区白垩系发育, 很好地记录了该区的区域构造运动特征。通过野外实测和室内资料整理, 在兰坪金顶地区选择一条北西—南东向地质剖面, 用平衡剖面技术恢复研究区白垩系因欧亚板块与印度板块碰撞而引起的北西—南东向地层缩短量, 揭示盆地的性质及变形历史, 检验其地质构造解释的正确合理性, 并进行数字化分析。研究结果表明, 白垩系景星组下段至南新组沉积期间地层总缩短量为2.938 km, 在南新组构造活动最为强烈。      

青藏高原中东部早期构造隆升对古近纪盆地充填和演化的影响

青藏高原中东部分布着一系列中小型古近纪断陷盆地和走滑-拉分盆地。印度-欧亚板块碰撞已引起盆地构造、沉积和岩浆活动等地质事件的响应。古近纪断陷盆地和走滑-拉分盆地中广泛分布的巨厚粗碎屑岩充填、新特提斯海湾消亡、大规模地壳挤压褶皱冲断和高钾岩浆活动、周缘前陆盆地形成、干旱-温暖极热事件以及古近纪盆地的封闭和裂解等。详细的野外地质调查、盆地构造-沉积学、生物地层学和岩浆岩同位素年代学研究结果表明,北部玉树-囊谦地区断陷盆地发生了大规模挤压掀斜和冲断,在盆缘形成高陡地层和挤压向斜,盆地内地层发生明显的褶皱变形。盆地内部充填了巨厚层状底砾岩、紫红色陆源碎屑岩夹火山碎屑岩、碳酸盐岩和石膏层,并被晚期岩浆岩所切割。南部巴塘-丽江地区形成走滑-拉分盆地。区域地层对比、细碎屑岩内孢粉和古植物、火山碎屑岩和侵入岩的U- Pb和40Ar/39Ar年代学结果表明,盆地内充填沉积物形成于始新世(56~32 Ma)。古近纪紫红色细粒沉积物、碳酸盐岩和石膏层的出现表明盆地封闭期处于干旱-炎热的古气候环境。38~32 Ma是自印度-欧亚板块陆-陆碰撞以来,青藏高原中东部从转换挤压到转换伸展的过渡阶段,出现了大规模高钾火山喷发和随后的岩浆侵入,并导致青藏高原中东部古近纪盆地的封闭和裂解。北部盆地的封闭时间(约37 Ma)早于南部盆地的裂解(约32~28 Ma)。青藏高原中东部古近纪盆地的封闭和裂解主要是自约38 Ma以来,印度-欧亚板块碰撞引起的陆壳挤压、变形和缩短,及由高原早期构造隆升诱导的逆冲挤压和走滑拉分引起的。     

地幔内异常热熔变与青藏高原的隆升

本文利用中法合作研究获得的定日—格尔木天然地震记录资料所揭示的青藏岩石圈存在的各向异性变化，讨论了雅鲁藏布江缝合带南北地幔物质运动方向的差异。结合区域重力场、地热和大量地质资料，提出了解释青藏高原形成和隆升的新模式。青藏高原是在印度板块和欧亚板块强烈碰撞挤压下，地壳缩短变形增厚，碰撞挤压达于极限，地幔内物质产生热熔变，导致了受热幔壳的急剧膨胀，托浮起上覆地壳整体，形成了巨大高耸而且地形平坦的高原。喜马拉雅造山带则是印度板块北缘俯冲受阻，逆冲叠覆堆积变形的结果。     

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 deform...     

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.     

柴达木盆地及邻区侏罗纪原型盆地恢复及油气勘探前景

侏罗系是柴达木盆地最重要的源储层系之一。通过野外地质、剖面实测、地震解释、显微构造分析等大量系列资料的综合应用与分析,认为研究区自中生代以来,经历了印支期右行逆冲-走滑构造运动、早—中侏罗世伸展运动、早白垩世北西-南东向挤压及新生代南北向挤压运动,它们与早侏罗世至中侏罗世早期(小煤沟组至大煤沟组)在NE向伸展应力场作用下形成的断陷盆地、中侏罗世晚期至晚侏罗世(彩石岭组—洪水沟组)热力沉降坳陷盆地、早白垩世南北向挤压坳陷盆地密切相关。侏罗纪原型盆地发育三类沉积边界,即盆缘不整合边界(缓坡型和陡坡型边界)、盆内正断层边界、后期逆断层改造边界。不同的现存盆地边界类型对原型盆地恢复的作用不同。侏罗纪盆地以东昆仑构造带为界具有"北陆南洋"的古地理格局,柴达木地区的侏罗纪盆地主要发育在沿岸造山带和岛弧带的山前坳陷以及薄弱的柴北缘加里东俯冲碰撞带之上,形成相对分隔的独立盆地群。柴达木早、中、晚侏罗世原型盆地的分布因受到古特提斯洋向北偏东方向的俯冲作用和阿尔金断裂左旋走滑作用的影响,其沉积中心和沉积范围呈现出从早到晚向东北方向逐渐迁移的规律。早侏罗世盆地的沉积沉降中心主要位于柴北缘西部的冷湖—马海一带,中侏罗世盆地的沉积沉降中心主要位于柴北缘中段的大柴旦—怀头他拉一带,而晚侏罗世盆地的沉积沉降中心主要位于德令哈—乌兰一带。     

Cenozoic uplift of the Tibetan Plateau: Evidence from the tectonic-sedimentary evolution of the western Qaidam Basin

Geologists agree that the collision of the Indian and Asian plates caused uplift of the Tibet Plateau.However,controversy still exists regarding the modes and mechanisms of the Tibetan Plateau uplift.Geology has recorded this uplift well in the Qaidam Basin.This paper analyzes the tectonic and sedimentary evolution of the western Qaidam Basin using sub-surface seismic and drill data. The Cenozoic intensity and history of deformation in the Qaidam Basin have been reconstructed based on the tectonic developments,faults growth index,sedimentary facies variations,and the migration of the depositional depressions.The changes in the sedimentary facies show that lakes in the western Qaidam Basin had gone from inflow to still water deposition to withdrawal.Tectonic movements controlled deposition in various depressions,and the depressions gradually shifted southeastward.In addition,the morphology of the surface structures in the western Qaidam Basin shows that the Cenozoic tectonic movements controlled the evolution of the Basin and divided it into(a) the southern fault terrace zone, (b) a central Yingxiongling orogenic belt,and(c) the northern fold-thrust belt;divided by the XI fault (Youshi fault) and Youbei fault,respectively.The field data indicate that the western Qaidam Basin formed in a Cenozoic compressive tectonic environment caused by the India—Asia plate collision. Further,the Basin experienced two phases of intensive tectonic deformation.The first phase occurred during the Middle Eocene—Early Miocene(Xia Ganchaigou Fm.and Shang Ganchaigou Fm.,43.8—22 Ma),and peaked in the Early Oligocene(Upper Xia Ganchaigou Fm.,31.5 Ma).The second phase occurred between the Middle Miocene and the Present(Shang Youshashan Fm.and Qigequan Fm., 14.9—0 Ma),and was stronger than the first phase.The tectonic—sedimentary evolution and the orientation of surface structures in the western Qaidam Basin resulted from the Tibetan Plateau uplift,and recorded the periodic northward growth of the Plateau.Recognizing this early tectonic—sedimentary evolution supports the previous conclusion that northern Tibet responded to the collision between India and Asia shortly after its initiation.However,the current results reveal that northern Tibet also experienced another phase of uplift during the late Neogene.The effects of these two stages of tectonic activity combined to produce the current Tibetan Plateau.     

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.     

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。     

Exhumation History of the Xining Basin Since the Mesozoic and Its Tectonic Significance

The Xining Basin is located in the northeastern Qinghai–Tibetan Plateau, and its continuous Cenozoic strata record the entire uplift and outgrowth history of the Tibetan Plateau during the Cenozoic. The newly obtained apatite fission track data presented here shows that the Xining Basin and two marginal mountain ranges have experienced multiphase rapid cooling since the Jurassic, as follows. In the Middle–Late Jurassic, the rapid exhumation of the former Xining Basin resulted from collision between the Qiangtang Block and the Tarim Block. During the Early–Late Cretaceous, the former Xining Basin underwent a tectonic event due to marginal compression, causing the angular unconformity between the Upper and Lower Cretaceous. In the Late Cretaceous to the Early Cenozoic, collision between the Qiangtang Block and the Lhasa Block may have resulted in the rapid exhumation of the Xining Basin and the Lajishan to the south. In the Early Cenozoic(ca. 50–30 Ma), collision between the Indian and Eurasia plates affected the region that corresponds to the present northeastern Qinghai–Tibetan Plateau. During this period, the central Qilian Block rotated clockwise by approximately 24° to form a wedge-shaped basin(i.e., the Xining Basin) opening to the west. During ca. 17–8 Ma, the entire northeastern Qinghai–Tibetan Plateau underwent dramatic deformation, and the Lajishan uplifted rapidly owing to the northward compression of the Guide Basin from the south. A marked change in subsidence occurred in the Xining Basin during this period, when the basin was tectonically inverted.     

柴达木盆地西部新生代构造演化及其对青藏高原北部生长过程的制约

柴达木盆地是青藏高原北部的一个中新生代山间陆相含油气盆地,盆地内新生代地层的构造变形记录了青藏高原北部生长、地壳缩短及其形成过程的重要信息.本文运用高精度卫星影像资料、地球物理资料剖面和磁性地层年代学数据等多种学科资料的综合研究,重点对柴达木盆地西部逆冲-褶皱构造带的形成机制和演化过程进行了详细的解析.研究结果表明:(1)由北向南依次发育分布的红三旱、尖顶山-黑梁子、南翼山和油砂山褶皱构造带均由不对称的直立褶皱或同斜褶皱构成,并且显示出背斜相对紧闭、向斜宽缓的”侏罗山式”褶皱特征,表明其下部滑脱构造带的存在;(2)红三旱、尖顶山-黑梁子逆冲-褶皱构造SW翼缓NE翼陡的不对称褶皱形态显示出是由南向北的逆冲作用形成的;两翼相对较对称的南翼山褶皱形态是由NE-SW向双向逆冲作用形成的;SW翼陡(或地层倒转)NE翼缓的油砂山褶皱带是由NE-SW向双向逆冲挤出作用形成的反映出由北向南的逆冲作用的存在;(3)红三旱、尖顶山-黑梁子和南翼山褶皱构造带的初始生长地层依次为始新统下干柴沟组、上新统狮子沟组和更新统七个泉组,高精度磁性地层限定其沉积时代依次为～39.5Ma、～8.2Ma和～2.5Ma,这不仅代表了这些褶皱的初始形成时代,而且代表了其逆冲断裂的形成时代;油砂山褶皱构造带中七个泉组初始生长地层以及上地表发育的一系列现代水系发生了弯曲,表明该逆冲-褶皱构造带从～2.5Ma形成以来一直持续到现在迄今仍在生长;红山旱地区近SN向的直立褶皱以及柴西地区似穹窿状的叠加褶皱,反映出阿尔金断裂带走滑过程中伴随的近EW向挤压的结果;(4)综合柴西地区逆冲-褶皱带构造地貌、生长地层、地球物理剖面、磁性地层年代学等证据,表明柴西存在的一系列逆冲-褶皱带是由南向北的滑脱构造产生,具有后退式生长演化特征,表明印度/欧亚板块碰撞以来,～40Ma其远程效应已到达柴达木盆地北部,并形成红山旱逆冲-褶皱构造带,随后的持续挤压,高原北部呈现出局部向南后退生长特征,依次形成尖顶山、南翼山和油砂山逆冲-褶皱带,其中～2.5Ma以来强烈的近南北向挤压作用产生的南翼山和油砂山逆冲-褶皱带构成了现今的”英雄岭”;～ 8Ma以来的阿尔金断裂带的强烈走滑活动波及到了柴达木盆地.     

Late Jurassic-Early Cretaceous Northern Qaidam Basin, NW China: Implications for the earliest Cretaceous intracontinental tectonism

Formation of Mesozoic western China, which was dominated by tectonic amalgamation along its southern margin and associated intracontinental tectonisms, holds a key for interpreting the succedent Cenozoic evolution. This paper presents new data including lithology, sedimentary facies, stratigraphic contact, seismic interpretation and paleo-structures within the Upper Jurassic-Lower Cretaceous strata in the northern Qaidam Basin, NW China. These data all account for a contractional tectonic deformation in the earliest Cretaceous. The South Qilian Shan, according to the sedimentary features and provenance analysis, reactivated and exhumated during the deformation, controlling the deposition of the Lower Cretaceous sequences. A simplified model for the Late Jurassic-Early Cretaceous paleogeography and tectonics of the northern Qaidam Basin is accordingly proposed. The results also support a ∼25° clockwise rotation of the Qaidam Basin since the Early Cretaceous and a more accurate Mesozoic evolution process for the basin. This earliest Cretaceous deformation, associated with the reactivation of the South Qilian Shan at the time, are part of the intracontinental tectonisms in central Asia during the Mesozoic, and probably driven by both the closure of the Mongol-Okhostk Ocean to the north and the collision of the Lhasa and the Qiangtang blocks to the south.