龙门山冲断带（中段）异地系统晚三叠世地层标定与原型盆地恢复

Based on the new data from the cores of scientific exploratory wells(including the Wenchuan Fault scientific drilling (WFSD), the well Longshen 1 and the well Chuanke 1) in Longmen Shan thrust belt(middle segment) and front area, the object of this study is to carry on recovery of the tectonic prototype of indosinian orogenic wedge and foreland basin system. The fundamental techniques used in this project includes tectonic-sequence stratigraphy, splicing of tectonic slices, sedimentary microfacies analysis, paleostructural recovery technique(eg. paleogegraphic method,balanced section technique, flattening technique) and basin modeling. Based on splicing the Late Triassic stratigraphic sequence and sedimentary facies in allochthonous system ,we will recognise the late Triassic stratigraphic sequence, sedimentary facies, conglomerate layer,seismites,unconformity in the allochthonous system, and correlate tectonic events between the allochthonous system and autochthonous system. The sedimentary record and material composition change in residual foreland basin are used to recognise the tectonic evolutionary process of indosinian orogenic wedge(provenance area) , and the provenance analysis, marginal facies, stability coefficient of heavy minerals, the maturity index of light minerals are also used to recognise the boundary of the indosinian orogenic wedge and foreland basin and its migration. The results of this study will provide quantitative methods to study the migration rate of boundary between basin and orogenic belt, and establish the coupling relationship between the migration rate of boundary and the advance rate of orogenic wedge. The results of this study will also provide scientific evidence for recovering continental accretion on the western margin of the Yangtze platform in Indosinian and the uplift mechanism of Longmen Shan.

本项目以龙门山冲断带（中段）及前缘地区科学探井的钻孔岩芯（包括汶川地震科钻（WFSD）、龙深1井和川科1井）为切入点，以印支期造山楔-前陆盆地系统的构造原型恢复为研究目标，以构造-层序地层技术、构造岩片的地层拼接技术、沉积微相分析技术、古构造恢复技术（古地理学方法、平衡剖面技术、层拉平技术）和盆地模拟为基本技术，在对异地系统晚三叠世地层序列与沉积相进行拼接的基础上，开展异地与原地系统的晚三叠世地层、沉积相、砾岩层、震积岩、不整合面的标定和构造事件对比，利用残留前陆盆地的沉积记录和物质成分变化反演印支期造山楔（物源区）的构造演化过程，并利用物源分析、边缘相、重矿物稳定系数、轻矿物成熟度系数等标定印支期造山楔-前陆盆地的边界及其迁移规律，定量化反演印支期盆山边界的迁移速率及其与造山楔推进速率之间的耦合关系。本项研究成果可为印支期扬子地台西缘大陆增生作用的恢复和龙门山隆升机制的甄别提供科学依据。

本项目利用构造-层序地层技术、构造岩片的地层拼接技术、沉积微相分析技术、古构造恢复技术和盆地模拟为基本技术，对龙门山及前陆盆地开展了晚三叠世地层标定、原型盆地恢复、盆山耦合关系等方面的研究。主要获得以下6方面认识：（1）震积岩发育频率显示须家河组二段有5个地震活跃期平静期交替出现；（2）物源分析表明晚三叠世卡尼期前陆盆地的西侧边界为茂汶断裂，瑞替期前陆盆地的西侧边界为北川-映秀断裂；（3）古地形分析表明晚三叠世、晚侏罗世-早白垩世和晚白垩世-中新世为冲断带构造负载阶段，前陆盆地发育楔状地层，早、中侏罗世、中白垩世夹关期和晚新生代为冲断带剥蚀卸载阶段，前陆盆地发育板状地层；（4）晚三叠世早期前陆缓坡带鲕粒滩-硅质海绵礁迁移规律分析，表明龙门山造山楔在前陆盆地发育早期推进速率约为18 mm/a；（5）盆地模拟显示浅层滑脱层控制局部褶皱断层构造，而深部基底滑脱层是控制龙门山褶皱冲断带整体构造样式主要因素；（6）提出了晚三叠世以来3种龙门山隆升作用与前陆盆地充填作用的耦合机制类型。