东天山雅满苏岛弧晚石炭世高铝玄武岩和埃达克岩对北天山洋演化的启示

The North Tianshan Ocean is one of the latest Paleozic closed Oceanic basins in the southwestern margin of the Central Asian Orogenic Belt. Its closure time has been disputed, thus restricting to overall understand the evolution of the multi-island arc and oceanic plate subduction and accretion in this region. The Late Carboniferous volcanic-sendimentary rocks in the Yamansu arc records the important evolution history of the North Tianshan Ocean, which is still unclear yet. Thus, This proposal will main study the Yamansu high-Al basalt and adakite rocks, combined with the other similar volcanic-sendimentary rocks in the area. It will investigate the zircon U-Pb dating, whole-rock Sr-Nd-Hf-B isotopes, in-situ phenocryst mineral compositions and zircon O-Hf isotopes, with aims to recognize their petrogenesis, geochemical dynamics transformation mechanism and tectonic setting during the generation. Combined with the analysis of the main detrital components, detrital zircon U-Pb ages and Hf isotopes of sandstone that aims to recognize their material source and sedimentary environment, the proposal will reveal the evolution of the North Tianshan Ocean during the late Paleozic. These data, compared with the late Paleozic tectonic-magmatic-sedimentary characteristics in the Tianshan Orogenic Belt, will be used to discuss the closure time of the North Tianshan Ocean, and to reveal the tectonic evolution of the Eastern Tianshan.

北天山洋作为中亚造山带西南缘最晚闭合的洋盆之一，其最终闭合的时限一直存在争议，从而制约了对该地区多岛洋俯冲增生历史的整体理解。东天山雅满苏岛弧晚石炭世火山-沉积岩系记录着北天山洋重要的演化历史，但其研究仍十分薄弱。本项目拟以新发现的雅满苏晚石炭世高铝玄武岩和埃达克岩为主要研究对象，结合区内其他相似的火山-沉积岩剖面，系统开展锆石U-Pb年代学、全岩Sr-Nd-Hf-B同位素、斑晶矿物主微量元素以及锆石O-Hf同位素等原位分析，探讨雅满苏岛弧晚石炭世高铝玄武岩和埃达克岩的成因联系、地球动力学转变机制及其构造指示意义。结合沉积砂岩主要碎屑组分、碎屑锆石U-Pb年龄和Hf同位素等物质来源和沉积环境分析方法，揭示北天山洋晚古生代的演化过程。在此基础上，对比研究天山造山带晚古生代构造-岩浆-沉积的演化特征，为探讨北天山洋最终闭合时限以及东天山的构造演化历史等科学问题提供重要依据。

北天山洋是中亚造山带西南缘最晚闭合的洋盆之一，但北天山洋最终在哪，什么时候或者怎样消亡和闭合的科学问题仍悬而未决。为了更好地理解北天山洋的构造演化历史，尤其是在其闭合前的演化历史，我们详细研究了雅满苏火山岩剖面。SHRIMP锆石U-Pb年龄指示这套前人认为是“二叠纪”的火山岩应该形成于晚石炭世。这套火山岩属于双峰式火山岩，SiO2含量在60%与70%之间存在成分间断。基性火山岩课细分为贫LREE玄武岩和富LREE玄武-安山岩。贫LREE玄武岩的岩浆源区很可能是受到俯冲流体交代的中等亏损的地幔楔，而富LREE玄武-安山岩的源区则可能是受到了俯冲沉积物熔体交代的亏损地幔楔，虽然它们或多或少遭受了地壳混染。酸性火山岩主要为I型流纹岩，其源岩则可能是寒武-中元古代的古老岛弧地壳岩。通过综合分析，我们认为康古尔断裂带应代表这北天山洋的最南端。雅满苏岛弧带应属于中天山大陆弧的弧前部分，且形成与北天山洋向南俯冲有关。.另外，岩浆铜镍硫化物矿床在全球造山带陆续有发现，但是在造山带的演化过程中，哪个阶段更有利于铜镍硫化物成矿至今还不清楚。锆石Th/U比值与大地构造应力状态（大陆地壳伸展和挤压环境）有密切的关系。故我们收集了东天山黄山-镜儿泉铜镍成矿带的古生代基性-超基性和酸性岩的岩浆锆石，以及沉积岩碎屑锆石的Th/U比值数据。通过筛选掉非岩浆作用影响的数据之后，剩下的有效数据显示早二叠世锆石具有很高的Th/U比值（高达2.5）和δEu值（高达1.35）。这些表明区域地壳在早二叠世发生了增厚且处于伸展阶段，暗示与晚石炭世末的俯冲碰撞有关。故我们认为碰撞后伸展环境最有利于这些二叠纪铜镍硫化物矿床在<5 Ma的较短时间里形成。