川东北地区通南巴背斜中三叠世以来构造变形时间厘定及其地质意义

摘要

通南巴背斜位于四川盆地东北部,中三叠世以来经历多期构造挤压与叠加作用,其形成与演化主要受到米仓山构造带由北西向南东冲断挤压作用的控制以及大巴山构造带由北东向南西构造叠加的影响,因此,厘定通南巴背斜的构造活动时间可以有效约束米仓山中三叠世以来陆内变形时间,亦对区域构造变形时序以及米仓山基底冲断变形特征有指示意义.本文以两条地质剖面为基础,刻画出背斜南翼中-上侏罗统旋转生长地层特征,表明地层发生褶皱的启动时间为中侏罗世晚期-晚侏罗世早期,并且通过长剖面解释,认为米仓山基底发育楔入冲断构造,楔端点位移沿前震旦系滑脱层向盆地扩展传递导致了通南巴背斜NE向构造的形成.磷灰石裂变径迹热模拟显示,通南巴背斜分别于晚白垩世早期(95～90 Ma)和新生代中晚期(～24 Ma)开始快速隆升剥蚀,隆升速率分别为0.06～0.085 mm/a和0.133 mm/a左右.通过汇总区域低温热年代学样品点,分区建立构造变形时空序列,得出川东北地区在中-晚侏罗世、白垩纪以及始新世-中新世分别发生一次米仓山由北向南的构造扩展以及大巴山由北东向南西的构造叠加作用.%Tongnanba anticline lies in the northeastern Sichuan Basin and experienced multi-stages tectonic compression and superimposition since the Middle Triassic.Its formation and evolution process are chiefly controlled by the squeezing and thrusting from the Micangshan structure belt from NW to SE and subjected to the tectonic superimposition from the Dabashan structure belt from NE to SW.Therefore,to confine the timing of Tongnanba anticline multi-stages deformation is of great effectiveness to constrain the timing of Micangshan intra-continental deformation since the Middle Triassic,and also provides significant indications to the regional tectonic time-space sequence and Micangshan basement-involved thrusting characteristics.In this paper,the anticline's south limb rotating growth strata within the Middle-Upper Jurassic,based on interpretation of two geological section,is featured,indicating that the folding of the strata started around the late Middle Jurassic-Early Late Jurassic and together with the interpretation of long seismic profile,we believe that basement-involved wedge-thrusting structure style is developed in Micangshan structure belt and the basin-ward movement of the displacement of the wedge tip along the Pre-sinian detachment layer results in the formation of the NE structure of Tongnanba anticline.Apatite fission track thermal simulation indicates that Tongnanba anticline started experiencing rapid uplifting and denudation in the early Late Cretaceous (95-90 Ma) and the Middle-Late Cenozoic (about 24 Ma) with uplift speed 0.06-0.085 mm/a and around 0.133 mm/a respectively.Through the summary of regional historical low temperature thermochronology data,geographical partition based tectonic time-space sequence is established,suggesting that northeastern Sichuan Basin experienced N-S basin-ward tectonic spreading from Micangshan structure belt and NE-SW tectonic super imposition from Dabashan structure belt during the Middle-Late Jurassic,Cretaceous and Eocene-Miocene respectively.