新疆西准噶尔晚古生代大地构造演化的岩浆活动记录

Magmatic Records on the Late Paleozoic Tectonic Evolution of Western Junggar,Xinjiang

晚石炭世-早二叠世是新疆北部最为重要的金属矿床成矿期。西准噶尔的区域大地构造、蛇绿岩、沉积岩、花岗岩、埃达克岩、富镁闪长岩以及广泛出露的中基性岩墙研究显示,该地区直到早二叠世早期(290Ma)仍有残余洋盆存在,并可能存在相关的俯冲活动。在290Ma之后,伴随着红色磨拉石的产出,西准噶尔地区进入碰撞造山阶段,伴有地壳快速抬升,表明准噶尔洋盆的完全闭合。年代学统计表明,西准噶尔地区岩浆活动高峰期在300～310Ma。在这一时期形成组分复杂的花岗岩类(如:A型花岗岩,紫苏花岗岩,I型花岗岩,埃达克岩,富镁闪长岩),同位素特征显示有巨量的新生物质的加入。洋脊俯冲模式可以较好地解释这一巨大变化,该构造模式还可以解释这一时期的铜、金成矿机制。研究表明,在中亚造山带的聚合历史和大陆地壳的增生过程中,洋脊俯冲起到了非常重要的作用。

Carboniferous to Permian is a critical period for tectonic evolution of the Central Asian Orogenic Belt and formation of major metal ore deposits in the northern Xinjiang. As the western Junggar is a ore resource-rich area, its tectonic settings during that period have attracted wide attention. Previous researches on tectonics, ophiolite, sedimentary and igneous rocks indicate that there was ocean basin system and related subduction during the Late Carboniferous-Early Permian（290Ma） in Western Junggar. Since 290Ma Western Junggar evolved into eollisional regime characterized by the formation of the Early Permian red molasse accompanying rapid crustal uplift, which suggest the termination of Junggar ocean system. The statistics of geochronological data indicate that the peak period of magmatic activities is 300-310Ma in Western Junggar. Voluminous granitoids of various types （A-type granites, charnockite I-type granites, adakite, magnesian diorite） formed in this period, and the isotopic data of these rocks suggest significant addition of juvenile material. We argue that this dramatic change was due to the onset of ridge subduction. This model supplies also a plausible explanation for mechanism of Cu-Au mineralization in the period. Moreover, ridge subduction was likely important for amalgamation and crustal growth in the CAOB.