南天山造山带南缘渭干河碎屑锆石U-Pb年代学研究及地质意义

Research of Detrital Zircon U-Pb Age of Weigan River in Southern Slope of South Tianshan Orogenic Belt and Its Geological Significance

渭干河流经南天山造山带南缘,为了解南天山洋演化历史,对该河流河砂样品中碎屑锆石进行U-Pb定年测试,结果表明,碎屑锆石年龄主要集中在460~400 Ma和310~260 Ma,少量分布在660~610 Ma和830~760 Ma,无中生代和新生代年龄记录。据本文数据并结合南天山北缘河流样品中已发表的锆石U-Pb年龄数据对比研究表明:南天山洋古生代期间俯冲消减作用具长期性和多阶段性。830~610 Ma(新元古代中期)超大陆裂解,南天山洋打开;460~400 Ma(晚奥陶世至中泥盆世)南天山洋南北双向俯冲产生了大量的大陆弧岩浆作用,380~320 Ma(晚泥盆世至中石炭世)南天山洋为单一的北向俯冲,310~260 Ma(晚石炭至早二叠世)南天山洋最终闭合并伴随发生后碰撞岩浆构造活动。

Intend to understand the evolutionary history of the South tianshan ocean,in this paper,through U-Pb isotope of detrital zircons from Weigan river in the southern slope of South Tianshan orogenic belt shows two prominent age populations at 460~400 Ma and 310~260 Ma,and subordinate Precambrian ages 660~610 Ma and 830~760 Ma,but no Mesozoic and Cenozoic grains were detected.These results,combined with age data from modern rivers in northern slope of South Tianshan orogenic belt,comparisons shows:at the middle Neoproterozoic(830~610Ma),super continent breakup,and the south tianshan ocean opened;the 460~400 Ma(Late Ordovician to Middle Devonian)age population substantiate the existence of Early Palaeozoic continental arc magmatism due to double-sided subduction of the South Tianshan Ocean;while the 380~320 Ma(Late Devonian to Middle Carboniferous)events were related the northward subduction of the South tianshan ocean;the 310~260 Ma(Late Carboniferous to Early Permian)magmatic event is thought to the closure of the South and concomitant post-collision magmatic tectonic activity.