恩格尔乌苏冲断带特征及大地构造意义

THE CHARACTERISTICS AND TECTONIC IMPLICATIONS OF THE THRUST BELT IN EUGERWUSU, CHINA

研究表明恩格尔乌苏冲断带是华北板块和塔里木板块的缝合线，北东东向断续延长８００ｋｍ以上。该冲断带连同南北陆缘地带构造构成典型的陆－弧－陆碰撞造山带，与碰撞造山作用同时，形成区域性透入性劈理。地层学和同位素地质年代学资料表明，碰撞造山作用发生于海西末期或印支早期。碰撞造山作用的动力学过程主要表现为向南的洋壳俯冲和向北的陆壳仰冲，并伴随右旋剪切滑移运动。恩格尔乌苏混杂岩带为韧性－韧脆性冲断推覆构造，其北侧的前陆褶皱冲断带为脆性－脆韧性冲断推覆及褶皱构造。

The thrust belt of Eugerwusu is a suture line between the North China Plate and the Tarim Plate. Its ENE trend continually extends over 800km in length, expressed as a series of thrust nappe structural systems mainly in a northward inverse direction. The thrust belt together with its northern and southern continental marginal zones is composed of typical collisional orogenic belt of continent arc continent. Studies of stratigraphy and isotopic geochronology show that collisional orogeny had occured during the late Hercynian or early Indosinian. The dynamics of the collisional orogeny is mainly a southward subduction of oceanic crust and northward obduction of continental crust, and followed by right handed movement of shear slip, which resulted in compression torsion orogenic belt. The composites of the tectonic pattern in the Eugerwusu have best representativeness. The foreland main shear zone is characterized by the ductile shear. Using the foreland main shear zone as a boundary,the south of it belongs to a forearc melange zone, the north a foreland fold thrust belt. From south to north the latter can be further divided into the duplex and fold structural zones. This study shows that, the forearc melange zone includes many foreigner crushed lamps of ancient oceanic crust and has a typical structural inclusions matrix texture, which with middle deep le vel replacement and deformation belongs to ductile ductilebrittle thrust nappe systems, wheres the foreland fold thrust belt facies with middle shallow level structural deformation was located in the southern passive continental margin of Tarim plate before collision, mainly composed of volcanic sedimentary associations and carbonatites in the Carboniferous Permian Period, and belongs to brittle brittleductile thrust nappe and fold systems. At the same time of collisional orogeny, regional pentrative cleavages had been formed, in which the S 1, S 2 and S 3 three foliations can be distinguished. During late Triassic Epoch typical molasse facies had been accumulated in the forland basin, in which cleavage was not developed.