阿尔金中北部中-晚奥陶世古地理演化研究

The paleogeographic evolution of micro-continental blocks is a key problem and new field in the reconstruction of the global supercontinent and the restoration of paleogeography. The assembly of the Central Altun Block (or micro-continental block) with Tarim Block and North China Block is the key to the tectonic conversion of the complex ocean-continent frameworks in the early Paleozoic of Proto-Tethys Ocean in East Asia. From middle to late Ordovician, the stratigraphic distribution, distribution of sedimentary sequence and facies belt, and the nature of the proto-type basin in central-northern parts of Altun have been uncertainty. The affinities of the early Paleozoic continental blocks with these micro-continental blocks have been unclear. There are still gaps in the plate tectonism, boundary attributes and sedimentary filling mechanism. This proposal will be based on the study of small (micro) continental sedimentary sequences and depositional systems. The relationship between sedimentary sequence developments and tectonic events, the relation between sedimentary sequences and sea level eustasy in the middle and late Ordovician of the central and northern Altun will be analyzed; the sedimentary sequence profiles with the isochronicity and continuous genesis will be established; the paleogeography of the Middle and late Ordovician in the area will be reconstructed; the tectonic properties and time constrains of the Central Altun Block- North Altun Ocean- Tarim Block will be reveal in tectonic-sedimentary sequences. It provides important supports for the ocean-continent transition processes, mechanisms and effects of major continents / microcontinent block during the early Paleozoic in the Proto-Tethys of East Asia. It is of great significance to the final formation of the Pangea supercontinent. And it will also provide the new scientific evidences for the formation mechanisms of oil and gas reservoir and solid mineral resources in the southern parts of the Tarim Basin and the central and northern Altun, respectively.

微陆块古地理变迁是全球超大陆重建、古地理恢复中的难点及新领域。中阿尔金陆块与塔里木、华北陆块的拼合是早古生代东亚原特提斯复杂洋-陆格局体制转换关键。阿尔金中北部中-晚奥陶世地层分布、沉积序列与相带展布、原型盆地性质不确定，早古生代各陆块的亲缘性不清，对板块构造作用及边界属性与沉积充填机制的研究尚处于空白阶段。本项目将以小(微)陆块沉积序列和沉积体系研究为切入点，分析阿尔金中北部中-晚奥陶世沉积层序发育与构造事件的对应性、沉积序列与海平面升降的关系，建立具有等时性、成因连续的沉积层序剖面，重建阿尔金中北部中-晚奥陶世古地理，揭示中阿尔金陆块-北阿尔金洋-塔里木陆块的构造作用性质及时限；为东亚原特提斯早古生代主要陆块／微陆块的洋-陆变迁过程、机制、效应提供重要支撑，对全球Pangea 超大陆的重构具有重要意义，也将为塔里木盆地及阿尔金中北部油气和固体矿产成矿机理提供新的科学依据。

本项目以阿尔金中北部中上奥陶统沉积层序与沉积环境、新元古代裂陷为主要研究对象，以解析关键构造期构造-地层发育和演化历史为主线，重建研究区中晚奥陶世和新元古代构造古地理，并探讨了关键期盆山关系和油气资源效应。研究获得的主要进展和成果：（1）建立了阿尔金中北部奥陶系沉积层序格架，开展塔里木盆地与阿尔金中北部奥陶纪沉积环境对比，明确了陆块间不同沉积体系对比关系和差异。（2）阿尔金中北部中晚奥陶世与塔里木盆地中西部均发育开阔台地相碳酸盐岩建造，并形成了礁滩相沉积组合，反映了它们具有相似的古地理环境。据沉积地层发育、蛇绿混杂岩、俯冲至碰撞花岗岩的组成、形成时代及位置，指示了原特提斯洋分支红柳沟-拉配泉洋向北俯冲闭合的极性。推断后期阿尔金陆块相对于塔里木陆块受车儿臣和阿尔金山前断裂带控制，经历了大型左旋剪切构造运动，运动距离在150km以上，明确了加里东中期塔里木盆地南缘盆山关系，对盆地山前带深层油气勘探具有重要意义。（3）阿尔金中北部和塔里木盆地中央隆起带基底的对比研究发现，中央隆起带基底与中阿尔金基底岩相、时代、成因均不同，而与北阿尔金北缘米兰群有亲缘性，进一步界定了陆块间差异，厘定了盆地东南缘盆山早期关系。（4）明确了基底之上不同世代新元古界裂陷几何特征和演化序次：中阿尔金陆块初始裂陷早于北阿尔金和塔里木陆块；刻画了北阿尔金和塔里木盆地新元古代裂陷群分布特征和三阶段演变形成机制，并初步分析了超深层油气资源条件和勘探方向。