Carboniferous back‑arc extension in the southern Yili‑Central Tianshan Block and its significance to the formation of the Kazakhstan Orocline: insights from the Wusun Mountain volcanic belt
Carboniferous back‑arc extension in the southern Yili‑Central Tianshan Block and its significance to the formation of the Kazakhstan Orocline: insights from the Wusun Mountain volcanic belt
复制标题
伊犁中天山地块南部石炭纪弧后伸展及其对哈萨克斯坦斜山形成的意义——来自乌孙山火山带的启示
DOI：
10.1007/s00531-021-02111-y
复制
发表时间：
2022
影响因子：
2.3
通讯作者：
J De Grave
中科院分区：
文献类型：
--
作者：
Wenbo Su;Keda Cai;Min Sun;Xiangsong Wang;Zihe Bao;Zhiyu He;J De Grave
在中亚，石炭纪是天山带形成和哈萨克斯坦构造拼贴体弯曲的关键时期。为揭示该区石炭纪岩浆事件及其构造意义，对乌孙山脉（伊犁-中天山地块南部）早石炭世大哈拉军山组和晚石炭世伊什基力克组火山岩进行了野外调查、锆石U-Pb定年、全岩地球化学和Sr-Nd同位素研究。大哈拉军山组火山岩由钙碱性玄武岩、安山岩和英安岩组成，获得了~ 350 Ma的新锆石U-Pb年龄。全岩εNd（t）值为+0.5 ~+1.6。而伊什基力克组火山岩主要由碱性和钙碱性双峰岩套组成，喷发时间约为337 ~ 313 Ma，全岩εNd（t）值较高（+ 2.3 ~+ 4.3）。这两幕石炭纪岩浆活动与亏损地幔的部分熔融有关，亏损地幔被板片流体交代。晚石炭世乌孙山岩浆带具有相对于伊犁-中天山地块南缘的海沟后退演化的弧后体系特征。这一机制导致了一个拉张机制，岩浆源逐渐减少。南天山洋和准噶尔洋古俯冲带相对于伊犁-中天山地块的不对称后退是哈萨克斯坦造山带弯曲的重要驱动力。
In Central Asia, the Carboniferous is a crucial period in the formation of the Tianshan Belt and associated bending of the Kazakhstan tectonic collage. In order to reveal Carboniferous magmatic events of the region and their tectonic implications, we conducted field investigations, zircon U–Pb dating, whole-rock geochemical and Sr–Nd isotopic studies on the Early Carboniferous Dahalajunshan Formation and Late Carboniferous Yishijilike Formation volcanic rocks of the Wusun Mountain Range (southern Yili-Central Tianshan Block). Volcanic rocks of the Dahalajunshan Formation consist of calc-alkaline basalt, andesite and dacite, yielding new zircon U–Pb ages of ~ 350 Ma. They have positive whole-rock εNd(t) values (+ 0.5 to + 1.6). In contrast, the Yishijilike Formation volcanic rocks dominantly comprise alkaline and calc-alkaline bimodal suites that erupted at ~ 337 Ma to 313 Ma and have higher whole-rock εNd(t) values (+ 2.3 to + 4.3). These two episodes of Carboniferous magmatism were correlated with partial melting of depleted mantle that metasomatized by slab-derived fluids. The late Carboniferous Wusun Mountain magmatic belt shows characteristics of a back-arc system that evolved due to trench retreat relative to the southern margin of the Yili-Central Tianshan Block. This mechanism induced an extensional regime with gradually depleting magma sources. The asymmetric retreat of the paleo-subduction zones of the South Tianshan Ocean and Junggar Ocean relative to the Yili-Central Tianshan Block was hence a vital driving force for the bending of the Kazakhstan Orocline.