帕米尔地区碰撞构造与塔里木盆地的改造

帕米尔地区碰撞构造的岩石与同位素年龄记录了印度板块对亚洲板块的运动,经历了新特提斯洋俯冲消减(113±1.5Ma～71.1±1.4Ma)、印度板块与亚洲板块发生碰撞(36.95±1.2Ma)、印度板块与亚洲板块碰撞后持续榨挤(6.69～6.80Ma)等3个阶段。处于帕米尔冲断带前缘的塔西南侏罗-白垩纪/老第三纪前陆盆地,经印度板块与亚洲板块碰撞作用改造后,仅留下麦盖提斜坡带和塔中-巴楚前缘隆起带两部分;中新世-第四纪前陆盆地的沉降中心向北迁移至叶城-喀什一线,快速的沉降作用堆积了5000～6000m的粗碎屑沉积物。天山造山带南侧的库车中新生代前陆盆地结构上比较完整,改造程度小于塔西南,保留了依奇克里克-克拉苏侏罗-白垩纪/老第三纪前渊沉降带、秋立塔格-亚肯斜坡带和牙哈-塔北前缘隆起带;在中新世碰撞作用期间,大部分三叠-侏罗纪/早白垩世地层则形成了逆冲断层与断弯-断展褶皱带,秋立塔格-亚肯斜坡带的滑脱断层与滑脱褶皱的递进变形带;之后,又被向南迁移的拜城-阳霞上新世-第四纪凹陷所叠加、覆盖而保存,具备了形成大型天然气田的条件。中新世印度板块与亚洲板块碰撞后榨挤与平移挤出作用阶段,在喀什坳陷内形成英吉莎、明遥路等深层原地变形体背斜,西天山山前的阿图什背斜、克拉苏背斜、塔浪河、阿拉布拉克等深部白垩-下第三系,也可能存在属于碰撞构造期(第Ⅱ期)的原地褶皱变形体构造.这些构造应是塔里木盆地的主要勘探目标。

Collision structures in Pamir region and reformation of Tarim Basin

Rock and isotopic age of the collision structures in Pamir region have recorded the movement of Indian plate toward Asian plate, which has experienced subduction and consumption of Neo-Thetys (113±1.5Ma-71.1±1.4Ma), collision of Indian and Asian plates(36.95±1.2Ma) and continuous squeezing after collision (6.69-6.80Ma). The Jurassic-Cretaceous in the southwestern Tarim Basin/Paleogene foreland basin, located in front of the Pamir thrust zone, have been reformed by the collision of Indian and Asian plates, and only the Maigaiti slope zone and Tazhong-Bachu frontal uplift zone have survived. The subsidence center of the Miocene-Quaternary foreland basin has migrated northward to Yecheng-Kashi where 5000～6000m of coarse clastic sediments have been accumulated as a result of rapid subsidence. Kuqa Meso-Cenozoic foreland basin on the southern side of Tianshan orogenic belt has relatively complete structures with smaller reformation than that in southwestern Tarim, hence the Yiqikelike-Kelasu Jurassic-Cretaceous/Paleogene foredeep subsiding zone, Qiulitage-Yaken slope zone and Yaha-Tabei fontal uplift zone have been preserved. Most of the Triassic-Jurassic/Early Cretaceous strata have been transformed into thrust fault and fault-bended and fault-extended fold belts, as well as the aggrading deformable zone of detachment faults and decollement folds in Qiulitage-Yaken slope zone during the Miocene collision. Later, they have been preserved by the superimposition and overlap of the southward migrating Baicheng-Yangxia Pliocene-Quaternary sag, thus they have been provided with the conditions for the formation of large gas accumulations. During the squeezing and strike-slip displacement stages after the Miocene collision of Indian and Asian plates, deep in-situ deformable bodies or anticlines, such as Yingjisha and Mingluyao etc. have been formed in Kashi depression, and in-situ folded deformable structures of collision stage (stage Ⅱ) might also exist in deep Cretaceous-Lower Tertiary in Atushi anticline, Kelasu anticline, Talanghe and Alabulake in west Tianshan mountain front. These structures should be the main exploration targets in Tarim basin.