【作者】 蒋荣宝；

【导师】 陈宣华；

【作者基本信息】 中国地质科学院 ， 构造地质学， 2008， 硕士

【摘要】 青藏高原北部的柴达木盆地是世界屋脊青藏高原内部最大的山间盆地,其构造变形研究与盆地周缘造山带岩浆活动和热演化历史的精确定年和热年代学研究将有利于增强对青藏高原的构造演化过程和印-亚碰撞远程效应的认识。柴北缘地区的岩浆活动主要分为两期:第一期发生在奥陶纪-志留纪(～493～420 Ma);第二期发生在晚二叠世(257.8±4.0 Ma)。柴达木盆地东南缘的岩浆活动时间相对比较集中,均发生在晚二叠世-中三叠世(～250～230 Ma),如果不考虑采样位置的因素,柴北缘的第二期岩浆活动时间也可以归到晚二叠世-中三叠世(P-T)。利用本研究在柴达木盆地东南缘、柴北缘得到的LA-ICP MS锆石U-Pb年龄,并结合前人在东昆仑山、阿尔金山东南缘等地的研究,可以认为在晚二叠世-晚三叠世期间,整个柴达木盆地周缘都经历了广泛的岩浆侵入活动。从晚二叠世-晚三叠世(P-T)花岗岩类侵入岩分布范围来看,柴达木盆地东端基底相对于西部基底的地壳缩短量可能在50%左右。柴达木盆地东部都兰一带,由于一系列北东倾的、向南西推覆的逆冲断层作用和温泉断裂的右行走滑作用,将柴达木盆地的变质基底和前中生界沉积基底翘起,从而使得柴达木盆地与共和盆地分隔开来。逆冲断层系磷灰石裂变径迹(FT)测年结果反映了柴达木盆地基底断层作用的规律性。从FT测年结果可以看出,FT年龄分为2组,也就是2个活动时期:第1期为108 Ma至61 Ma:第2期为26.6 Ma至17.8 Ma。第1期反映的断裂活动具有明显的规律性:从柴达木盆地南缘的东昆仑开始,向柴北缘方向,逆冲推覆的断层作用时间逐渐变年轻,从东昆仑的108.0±9.6 Ma(柴达木南缘断裂)变为63.7±4.4 Ma(柴北缘断裂),之后可能有小的跳动。第2期,在原有的一些逆冲断层上形成了新的活动,或形成了一些新的逆冲断层,总体上具有无序或跳跃式变动的特点。该期活动也对应于青藏高原的气候变化事件。东昆仑山基底的逆冲断层具有3个活动时期:第1期为52.9 Ma;第2期为16.3 Ma至10.0 Ma;第3期为5.1 Ma至0.9Ma。第1期反映了青藏高原的一次隆升作用是印-亚陆陆碰撞的最先反映,但隆升后即被剥蚀、夷平成为其南侧可可西里群与北侧路乐河地层的物源区;第2期为发生住中新世中期(～15 Ma)的隆升活动,它精确反映了青藏高原的初次整体隆升,此次隆升事件导致青藏高原的气候变化和埃达克火山岩的大量喷发;第3期活动与有些学者提出的青藏高原面貌的末次快速隆升发生的时间是吻合的。柴东和东昆仑地区裂变径迹热年代学,反映了柴达木盆地东南缘中新世构造挤压变形作用,是从柴东都兰-乌兰一带开始,并向西扩展的。更多还原

【Abstract】 Qaidam basin is one of largest intramontane basins throughout China which is located to the north of Tibetan Plateau,deformation studies within basin,accurate constraints on magmatic activities and thermal histories of its surrounding mountains,are definitely conductive in better understanding of Tibetan Plateau in terms of its tectonic evolution processes,as well as far-field effects resulting from Indo-Eurasian collisions.Two phases of magmatic activities have recorded in Northern Qaidam Basin by LA-ICP MS zircon U-Pb dating.PhaseⅠoccurred during approximately 493～420 Ma between Ordovician and Silurian.PhaseⅡoccurred during late Permian(257.8±4.0 Ma).Ages of magmatic events in Southeastern Qaidam focused primarily on ages between 250～230 Ma(P-T),regardless of sampling localities,the PhaseⅡhappened in Northern Qaidam can be included in the time interval of Southeastern Qaidam.Based on dating results of this study,in conjunction with previous work in Eastern Kunlun Shan,as well as Southeastern Altyn Shan, we can conclude that entire mountains surrounding the Qaidam basin have undertaken thoroughly magmatic activities during time interval ranging from late Permian to late Triassic time.In eastern Qaidam Basin,the metamorphic and sedimentary Pre-Mesozoic basement had been uplifted due to faulting of the East Qaidam Thrust System and then was separated from the Gonghe Basin due to dextral strike-slip faulting of Wenquan Fault.Apatite fission track analyses and thermochronology from eastern Qaidam Basin show two phases exhumation and thrusting since Mesozoic.PhaseⅠspans from 108 Ma to 61 Ma,showing a reduction of AFT cooling ages from south to north,and could be interpreted as the tilting exhumation of the Qaidam basement and thrusting before and at the beginning of Cenozoic. PhaseⅡoccurs during 26.6～17.8 Ma between Paleogene and Neogene,which is expressed as the out-of-sequence Cenozoic thrusting of East Qaidam Thrust System.According to apatite fission track analyses and thermochronology from Eastern Kunlun shan,three phases exhumation and thrusting events have been indicated since Cenozoic.PhaseⅠoccurred in 52.9 Ma, demonstrating a uplifting event accross Tibetan Plateau subsequent to the Indo-Eurasian collisions, however,it had been eroded shortly after it exhumation and became source areas of sedimentary rocks Kekexili Fm.to the south,Lulehe Fm.to the north.PhaseⅡoccurred between 16.3 Ma and10.0 Ma,the uplifting event mainly centered on the middle Miocene(～15 Ma) accurately witnessed the entire uplifting of Tibetan Plateau for the first time,subsequently,significant climate change and Adakitic rocks eruptions have been recorded.The timing of PhaseⅢ,namely spanning 5.1 Ma to 0.9Ma is consistent with the final uplifting event throughout Tibetan Plateau suggested by some researchers.According to the distribution patterns of granitoids intruded during late Permian to late Triassic times, shortening rate of Eastern Qaidam basement is as much as 50%that of the western Qaidam.Apatitie fission track dating in both Eastern Qaidam and Western Qaidam suggest that tectonically compressional deformation in Miocene initiated from Dulan-wulan in Southeastern Qaidam then propagated westernward.更多还原