【作者】 孟艳宁；

【导师】 王国灿；

【作者基本信息】 中国地质大学 ， 构造地质学， 2009， 硕士

【摘要】 青藏高原作为一个年轻的造山带,现今依然继续活动,作为地球的第三极影响着人类的生存的环境,所以青藏高原的隆升过程及机制的研究一直都是科学界的焦点问题。中外学者从不同角度对青藏高原进行研究,取得了一系列有价值的成果,并且建立了青藏高原隆升模式的格架。演化模式分递进式隆升和阶段性隆升,通过不同的研究方法,阶段性模式的研究者对高原达到最大高度的时间有不一致的认识,14Ma、8Ma、3.4Ma、第四纪晚期都有其证据。持续递进式的隆升模式根据高原广泛分布的夷平面的时代,认为高原经历了三次强烈的隆升。青藏高原西部是构造隆升强烈的地区,它的隆升过程和机制的研究是青藏高原研究的重要组成部分。而青藏高原西部主要造山带地区差异隆升的研究就是重要的科研课题。本文正是在这样一种思路下,选取了青藏高原西部的两个典型造山带地区的新生代沉积盆地,利用碎屑裂变径迹的研究方法,从盆山耦合的角度,揭示沉积源区造山带地区的构造热事件的时间、隆升过程及冷却剥蚀的速率,并最终从低温热年代学的角度建立青藏高原西部新生代的隆升过程。碎屑裂变径迹年代学的研究矿物磷灰石和锆石,能够记录源区构造隆升热事件引起的大量物质通过其封闭温度(110℃、220℃)的时间。这样系统剖面上样品的大量磷灰石和锆石的统计峰值就记录了源区造山带地区的构造活动热事件的时间,并且通过Lag time的研究分析能推算源区的冷却剥蚀速度和构造隆升的强度。西昆仑山前盆地位于青藏高原的西北部,其西南面为西昆仑造山带,东北面为塔里木板块的西南缘。前人研究资料及沉积剖面分析都表明,西昆仑山前盆地新生代的沉积物源来自于盆地的南部。在盆地中实测了完整的新生代沉积齐姆根剖面和叶城柯克亚剖面,16件碎屑裂变径迹样品的研究表明,存在多个对应于不同区域构造事件或快速抬升冷却的裂变径迹年龄峰值。109～165Ma期间,青藏高原班公湖-怒江缝合带的发育演化和俯冲消减,远源的来自青藏高原南部的样品和近源的西昆仑造山带样品,都记录了这此构造热事件;41.9～67.6 Ma的年龄峰值正好对应于区域上的欧亚板块与印度板块的碰撞拼接时间,反映在青藏高原整体汇聚造山的背景下,两昆仑地区普遍强烈的构造活动发育和快速剥蚀冷却;19.7～21.2 Ma的年龄峰值表现最为显著,与整个青藏高原此阶段普遍出现的强的挤压缩短时间相协调,应该记录的是印度板块与欧亚板块的持续挤压而引起的西昆仑地区的强烈南北向缩短,并导致岩石的快速抬升冷却;2.6～5Ma期间,通过对西域砾岩以及阿图什组中系列样品的最年轻组分的变化的分析,认为西昆仑地区存在在高原整体大幅度快速隆升的背景下局部地区的构造隆升活动的响应。札达盆地的形成和发育受控于青藏高原“两体三带”的构造格局的发展演化,即札达盆地位于喜马拉雅造山带的北坡,喀喇昆仑造山带的东南端(阿伊拉日居山),雅鲁藏布江缝合带西北端的结合地带,也是沿冈底斯地体和喜马拉雅地体结合部发育的新生代沉积盆地。札达盆地的西南面的控盆构造为藏南拆离系,东北面为阿伊拉日居山断裂(喀喇昆仑断裂的东南端)。本文对札达盆地做了详细的物源分析,论证了札达盆地的新生代沉积物源来自与盆地的北面,碎屑裂变径迹年龄记录的是源区阿伊拉日居山地区由喀喇昆仑断裂活动引起的差异隆升和构造热事件。物源分析的证据有以下几个方面:盆地沉积厚度由北到南增大,沉积中心在盆地的南端,说明古水系是由北流向南,沉积物源来自北部的阿伊拉日居地区;野外实测剖面的砾岩层(第1、3、5、7、9、34层)中砾石扁平面的产状,作出的玫瑰花图,扁平状砾石的长轴总体倾向南南东,反映古流向为北北西向南南东,与现代盆地内象泉河的流向相反;沉积地层的砂岩层中,发育大量的板状斜层理,前积纹层倾向南南西,板状斜层理的前积纹层的倾向代表水流方向,由此可以判断,盆地内古流向为北北西向南南东;盆地内新生代砾石层进行成分分析,砾石成份主要为花岗岩和砂岩,同时有少量的石英岩和变质岩,并且层位向上花岗岩成份明显增多,砾石成分与盆地北部地区出露地层的岩性一致,与盆地南部大量出露中生代的蛇绿混杂岩、砂岩、浅变质岩及元古代变质岩不匹配,也说明沉积的物源主要来自于盆地北部的阿伊拉日居山脉地区。进一步对札达盆地中新生代碎屑裂变径迹研究得出一下结论:12.6～15.3Ma与19.88～22.2Ma时期为快速冷却事件的静态峰,反映源区的构造带断层发育活动的时间;碎屑锆石的裂变径迹年龄峰值28.6～33.2Ma,对应的磷灰石的峰值年龄27.1～33Ma,反映阿伊拉日居山、喀喇昆仑地区的另一次构造热事件;3.6～1.4Ma上新世末期到第四纪之间发生了一次快速的隆升剥露事件;锆石、磷灰石FT热历史拟合分析,源区32.6～9.5Ma之间的龄却速率是15.4℃/Ma;33.2～14.8Ma样品通过锆石、磷灰石之间的封闭温度时是快速的,剥蚀速度达1.19mm/a～0.94mma;札达盆地FT热年代结构与喀喇昆仑东南端阿伊拉日居山地区的热事件年龄结构吻合,从热年代学角度很好地揭示了盆山耦合过程,札达盆地是受喀喇昆仑断裂东南端断层活动影响,发育的一个新生代沉积盆地。综合分析两个剖面的碎屑裂变径迹年代学研究成果,藏高原西部隆升过程划分为:109～165Ma,前新生代俯冲碰撞的阶段;41～67Ma,古近纪同碰撞过程的构造隆升阶段;19.7～22.2Ma,中新世早期高原西部的快速差异隆升阶段;5～1.4Ma,上新世以来青藏高原西部剧烈隆升及快速剥蚀阶段。藏高原西部隆升过程的空间性规律为:渐新世之前,在陆陆碰撞拼接过程中,青藏高原西部其隆升过程和强度是由南向北递进的;渐新世之后,青藏高原西部几个造山带同时强烈隆升剥蚀,差异性不大,在时间框架上具有准同时性。更多还原

【Abstract】 As one of the youngest orogenic belts,Tibet plateau is still keeping on activities now;and also as the earth’s third pole,it effects the survival environment of human,thus,the uplift of Tibet plateau is the focus problem of geoscience at all times,chinese and foreign researchers study Tibet plateau from different sides,have obtained a series of valuable results,and established model and framework of the uplift of Tibet plateau.Evolvement mode includes progressive and phased uplift,those who support later also have different view about when Tibet plateau reached the highest level,14Ma,8Ma,3.4Ma and quaternary are the main points,according to wide planate surfaces,the supporter of progressive uplift believe that Tibet plateau experienced three strong uplift.The west of Tibet plateau is one of strong structure uplift regions,whose uplift process and mechanism play a important role in the research of Tibet plateau,differential uplifting is the main uplift characteristics about the west of Tibet plateau.Based on above ideal,using the method of detrital fission-track,from the angel of coupling basin and mountain,this paper reveals the time of the structure thermal events,uplift process and the rate of cooling denudation about the deposition sources,and set up the uplift framework of the west of Tibet plateau from the angel of low temperature thermal chronology.Zircon and apatite which are the minerals detrital fission track researched on can memorize the time when rocks pass through the closed temperature(110℃、220℃) caused by tectonic uplifting event in source terrains.So statistical peak ages of abundant systematic samples collected from sedimental sections have recorded the time of tectonic-thermal event in the source terrians,further more we can conclude provenance’s cooling rate and tectonic uplifting extent.West Kunlun forland basin located in the northwest of Tibet,souththwest of the basin is westkunlun orogenic belt and northeast of the basin is the southwest margin of the Tarim plate. Numbers of previous’s studies and analyse through sedimentary profiles indicate that sendimentary source area of West Kunlun forland basin is from south.We have measured the integrated Cenozoic sections Qimugen profile and Yecheng Kekeya profile,and studies of 16 fission track samples concluded as below:during the period 109～165Ma,Bagong Co-Nujiang suture zone developed and experienced subduction,While samples in West Kunlun which is derived from the south of Tibet recorded the tectonic thermal event;During the period 41.9～67.6 Ma,Eurasian plate and India plate collided and spliced,and under the setting of orogenic convergence overall the Tibet,tectonic movement developed and exhumation accelerated.During the period 41.9～67.6 Ma,Indian plate and Tibet plate colliding continuously and subducting severly in the south,while rigid block Tarim plate as a barrier in the north,the lithosphere delaminantion leading West Kunlun terrain shorterning north-south,so this peak age is dominantly in all the detrital fission track samples.During the period 2.6～5 Ma,analysing the xiyu conglomerate and the change of youngest peak age in Atushi formation,WestKun region existed lacal tectonic uplifting response to the rapid and large scale ascending in the whole Tibet.The development and evolution of Zanda basin controlled by“two terrain and three orogenic belt”in Tibet,that is to say Zanda basin lies in the convergence area of north of the Himalaya orogenic belt、southeast of Karakurum orogenic belt and northwest of Yarlung Zangbo Suture Zone,and it is also a Cenozoic basin located between the Gandese terrane and Himalaya terrane.South Tibet detachmemtal is the controlling structure in the southwest of Zanda basin and Ayilariju fault(south east of the Karakurum fault)is the controlling structure in the northeast.In this article I have analysed the source area detailedly and demonstrated that the Cenozoic detrital matters comes from north of the basin.Detrital fission track ages reflect the differential uplifting and tectonic-thermal events’time in Ayiliriju region caused by the activity of Karakorum fault.The evidences of the source analysis showed below:thickness of the sendimentary basin become larger from north to south,which can illuminate that the ancient flow is from north to south,and the source area is Ayilariju region in the north;Based on the occurrences of the gravel’s flat surface measured in the field,and do the rose diagram,which also presents that the ancient flow in Zanda basin is fom noth to south opposite to the present flow current;Abundant tabular oblique bedding developled in the sandstone stratum,the occurrences of its foreset bedding 185°∠25°、175°∠35°、205°∠15°、195°∠10°、200°∠30°, the tendency representing the ancient flow direction,from which we can conclude the ancient flow in Zanda basin is fom noth to south.Cenozoic basin analysis of gravel layers,gravel composition is mainly granite and sandstone,while a small number of quartzite and metamorphic rocks and granite in the upper layer increased,gravel composition consistent with exposed stratum in the northern part of the Zanda basin,but can’t match the large number of exposed Mesozoic ophiolite,sandstone,shallow Proterozoic metamorphic rocks and metamorphic rocks in the southern part of the basin.As mentioned all the above,the colusinon is that the main source of sediment basin is Ayilariju mountain northern of Zanda basin. Research on Cenozoic detrital fission-track in Zanda basin concluded that:12.6～15.3Ma and 19.88～22.2Ma is the peak of the static with rapid cooling events,reflecting the activity time of the source region’s structure fault belt;Detrital fission track peak age of zircon 28.6～33.2Ma, corresponding to the peak age of apatite 27.1～33Ma,which show that there was a thermal event in the source area Ayilariju and Karakorum region;3.6～1.4Ma,from late Pliocene to the Quaternary there is a rapid uplift and exhumation events;Fitting analysis of zircon and apatite FT thermal history,concludes that the cooling rate in source region during 32.6～9.5Ma is 15.4℃/ Ma;During 33.2～14.8Ma,the zircon and apatite rapidly passed through closure temperature and exhumation rate is 1.19mm/a～0.94mm/a;FT thermochronology structure in Zanda basin matching perfectly with thermal event ages in Ayilariju southeastern tip of the Karakoram fault region,from the perspective of thermochronology revealing well the process of basin-mountain coupling,Zanda basin is a Cenozoic basin affected by the activity of Karakorum fault.Comprehensively analyse the research results about clastic fission track geochronology with the two sections,the uplift process of the west Tibet plateau can be divided into some periods, which including the subduction and collision phase in pre-Cenozoic(109～165Ma),the tectonic uplifting phase of syn-collision in paleogene(41～67Ma),the rapid differential uplifting phase in west plateau in early Miocene(19.7～22.2Ma) and the violent uplift and rapid exhumation phase of the west plateau since pliocene(5～1.4Ma).The uplift of the west Tibet plateau has two spatiality rules.First,before Oligocene,in the process of the continent-continent collision and splice,the uplift process and intensity of the west Tibet plateau progressived from south to north. Second,after Oligocene,several orogenic belts were violent uplifting and severely denudating in the same time,so the difference was small.更多还原