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

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.