新疆北阿尔泰造山带早古生代花岗岩类侵入序列及其构造意义

新疆阿尔泰早古生代造山带侵入岩占构造带面积50％以上,近年大量高精度SHRIMP和LA-ICP-MS锆石U-Pb年代学资料反映其构造属性为奥陶纪碰撞前序列和中志留-早泥盆世后碰撞序列.碰撞前序列岩石组合为(石英)闪长岩-英云闪长岩/奥长花岗岩/花岗闪长岩-二长花岗岩序列,类似TTG组合,锆石U-Pb同位素年龄峰值为450～ 465Ma.后碰撞由二长花岗岩-正长花岗岩及少量碱长花岗岩组成,属于广义的GG组合,同位素年龄峰值390～ 415Ma.前者主要分布在中南部,后者主要分布中北部,分布的极性显示俯冲带在南侧.而区域南侧的阿尔曼太蛇绿岩带同位素年龄与北阿尔泰奥陶纪碰撞前序列时代相同,本文推测该蛇绿岩带与北阿尔泰岩浆链带构成洋脊俯冲带模式;其间的南阿尔泰晚古生代增生带、额尔齐斯强变形带、北准噶尔晚古生代洋内弧带都是后来的上叠产物.

Magmatic sequence of Early Palaeozoic granitic intrusions and its tectonic implications in north Altay orogen, Xinjiang

The Early Paleozoic intrusive rocks occupy 50% proportion of whole north Altay orogenic belt in Xinjiang. Based on a large number of high precision SHRIMP and LA-ICP-MS U-Pb zircon geochronology data in recent years, we have identified the Ordovician sequence before the collision and Silurian to Early Devonian sequence after collision in the orogenic belt. The former was composed of tonalite/oligoclase granite and granodiorite-monzonitic granite series, which belongs to the TTG combination, with isotopic age peak between 450Ma and 465Ma. The latter was composed of monzonitic granite-syenogranite and a small amount of alkali feldspar granite, belonging to the generalized GG combination, with isotopic age peak between 390Ma and 415Ma. The former was mainly distributed in the south, the latter mainly distributed in the northern, showing that subduction zone was distributed in the south. According to the same isotopic ages, authors suggest that the both Armantai ophiolite belt on the south side and Altay magma belt on the north constitute ridge subduction system. The south Altay Late Paleozoic accretionary zones, the Erqisi deformation belt, north Junggar Late Paleozoic intra-oceanic arc belt are later on laminated products.