摘要:新疆克孜尔河流经南天山造山带南缘，其河流沉积物中记录了流域内地质体的重要信息。为进一步约束南天山造山带的构造演化历史，探讨该造山带古生代地壳生长与演化，对克孜尔河沉积物中的碎屑锆石进行U-Pb定年。结果表明锆石年龄主要集中分布在460～390 Ma和310～260 Ma，少量分布在前寒武纪，暗示南天山造山带在古生代期间发生了强烈的岩浆活动。物源分析表明克孜尔河沉积物中的碎屑锆石主要源于南天山造山带和塔里木克拉通北部，年龄为460～390 Ma的碎屑锆石很可能记录了南天山洋在晚奥陶—早泥盆世期间向南俯冲到塔里木克拉通之下的弧岩浆作用。南天山洋闭合以及塔里木克拉通与伊犁—中天山地块的最终碰撞可能发生在晚石炭世，随后发生同碰撞和后碰撞岩浆作用，以样品中大量310～260 Ma的碎屑锆石为代表。结合南天山造山带内已有的古生代岩浆岩锆石的Hf同位素数据分析表明，晚奥陶—早泥盆世南天山造山带的大陆地壳演化主要以古老地壳的再造和部分新生地幔物质的加入为主，晚石炭—早二叠世该造山带地壳演化则以前寒武纪古老基底岩石的改造为主，仅有限的新生组分加入到岩浆的形成过程中。
关键词: 碎屑锆石/
U-Pb年代学/
Hf同位素组成/
构造演化/
地壳生长/
南天山造山带
Abstract:The Kezier River in Xinjiang passes through the southern margin of the South Tianshan orogenic belt, and the sediments of this river carry important geologic information. The U-Pb isotopic research of detrital zircons was carried out in the Kezier River in order to further constrain the tectonic evolution history and discuss the Paleozoic crustal evolution of the South Tianshan orogenic belt. Detrital zircons from this river sands yield two dominant age populations at 460~390 Ma and 310~260 Ma with several Precambrian age groups. Such age patterns imply that the significant magmatic events occurred during the Paleozoic in the South Tianshan orogenic belt. The provenance analysis shows that the detrital zircons in Kezier River sediments are mainly from the South Tianshan orogenic belt and the North Tarim Craton, the 460~390 Ma zircon population probably record the arc magmatism of a southward subduction of the South Tianshan Ocean during the Late Ordovician to Early Devonian. The closure of the South Tianshan Ocean and the final collision between the Tarim Craton and the Yili-Center Tianshan block possibly took place in the Late Carboniferous, the 310~260 Ma zircon population in river sands suggests syn- and post-collisional magmatism. Base on the Hf isotopic signatures in the Paleozoic magmatic zircons, we proposed that the continental crust evolution of the South Tianshan orogenic belt in the Late Ordovician to Early Devonian is dominated by reworking of the ancient crust with some juvenile materials addition. The crustal formation is mainly characterized by reworking of the Precambrian basement rocks with limited contribution of juvenile components inputted into magma formation during Late Carboniferous to Early Permian.
Key words:Detrital zircon/
U-Pb geochronology/
Hf isotopic compositions/
Tectonic evolution/
Crustal growth/
South Tianshan orogenic belt
PDF全文下载地址:
http://www.dzkx.org/data/article/export-pdf?id=geology_11698
