柴达木盆地东部晚海西-印支期剥蚀量与隆升历史--多种古温标与沉积学证据的制约

Late Hercynian-Indosinian denudation and uplift history in the eastern Qaidam Basin:constraints from multiple thermometric indicators and sedimentary evidences

柴达木盆地东部周缘造山带内保存有较完整的晚古生代-早中生代沉积记录,但盆地内至今仍未发现二叠系-三叠系.为探讨柴东地区二叠纪-三叠纪有无沉积及隆升历史等关键地质问题,本文首先利用古温标法恢复晚海西-印支期剥蚀量,随后,通过物源分析法获得印支期柴东北缘隆升的沉积学证据.结果表明,印支运动前,柴东地区残留石炭系顶界面埋深普遍超过2500m,晚海西-印支期剥蚀量为2100~4300m,剥蚀量从南往北逐渐减小.柴东地区曾沉积了2000~3000m的二叠系-三叠系,随后被整体剥蚀.晚二叠世以来,随着古特提斯洋往北俯冲,盆地周缘开始隆升.早三叠世柴东北缘经历了一次快速隆升,先期的多套沉积地层与结晶基底被迅速剥蚀并为宗务隆南缘的隆务河群砾岩沉积提供物源.中三叠世海水往北和往东退出研究区.晚三叠世,松潘-甘孜地体强烈碰撞挤压使得东昆仑-柴达木地体下地壳显著缩短和增厚,柴东地区被整体抬升,并且形成了南高北低的古地貌格局,在古气候与水系作用下,二叠系-三叠系与部分石炭系被全部剥蚀并搬运至宗务隆、南祁连及松潘-甘孜一带.

It is a puzzle that Permian-Triassic sediments,which are widely distributed in the surrounding mountain belts,are not yet found in the eastern Qaidam Basin.In order to figure out whether there was sedimentation and what s uplift history it was,we firstly applied the thermometric indicators method to recover Late Hercynian-Indosinian denudation.Some pieces of sedimentaryevidence with relation to Indosinian uplift in the northern margin of eastern Qaidam Basin were also acquired by using provenance analysis.The results show that the top interface of residual Carboniferous of the eastern Qaidam Basin had been buried under 2500 mbefore Indosinian,and late Hercynian-Indosinian denudation reached up to 2100~4300 m,which was characterized by a decrease from south to north in the eastern Qaidam Basin.So there is an undeniable fact that the eastern Qaidam Basin once deposited Permian-Triassic with a thickness of 2000~3000 m,followed by a complete denudation.In response to northward subduction of the Paleo-Tethys Ocean,northern and southern margins of the eastern Qaidam Basin began to uplift since late Permian.An early Triassic rapid uplift in the northern margin of eastern Qaidam Basin led to significant denudation of previous sediments and crystalline basement,with adequate supplies of gravel provenance for lower Triassic Longwuhe formation in the southern Zongwulong.Then,seawater totally retreated from north and east of the study area in middle Triassic.Late Triassic continental collision between the Songpan-Garzêterrene and East Kunlun-Qaidam terrene caused significant contraction and thickening of lower crust in the East Kunlun-Qaidam,as well as intense surface uplift in the eastern Qaidam Basin,thus resulting in a northward tilting paleogeomorphology.Under the promotion of paleo-climates and drainages,Permian-Triassic and partial Carboniferous were entirely eroded and transported to the Zongwulong,South Qilian and Songpan-Garzê.