西准噶尔巴尔鲁克山北坡晚石炭世–早二叠世火山岩及其对准噶尔洋闭合时限的制约

The West Junggar is an important part of the southern Central Asian Orogenic Belt and its formation was related to the subduction and closure of the Junggar Ocean, a branch of the southern Paleo-Asian Ocean. However, there has been a hot debate on the closure time of the Junggar Ocean. A study of tectonic setting of the widespread Late Carboniferous–Early Permian volcanic rocks in the central West Junggar is the key to solving the issue. Whether these volcanic rocks were formed by ridge subduction or in a post-collisional environment is an issue that has not yet been resolved. In this project, on the base of field investigations, an integrated study of petrography, zircon U–Pb dating, whole-rock major and trace elements, Sr–Nd isotopes, and in-situ zircon Hf–O isotopes would be performed to constrain the occurrences, rock types, ages, petrogenesis and source features of the Late Carboniferous–Early Permian volcanic rocks from the northern Barleik Mountains. Combined with other available data, we discuss the tectonic settings of these volcanic rocks, which could provide important insights into the closure time of the Junggar Ocean.

西准噶尔是中亚造山带西南部的重要组成部分，其形成与古亚洲洋西南部的重要分支即准噶尔洋的闭合过程密切相关，但准噶尔洋的闭合时限仍在讨论中。西准噶尔中部广泛出露的晚石炭世–早二叠世火山岩构造环境的研究是解决上述问题的关键，它们究竟是与洋脊俯冲作用有关抑或形成在后碰撞环境中，亟待深入研究。项目选择巴尔鲁克山北坡该时期火山岩作为研究对象，拟在详细的野外观测基础上，开展岩相学、锆石U–Pb年代学、全岩主微量元素地球化学和Sr–Nd同位素以及锆石原位Hf–O同位素的系统研究，限定火山岩的野外产状、岩石组合、精确形成时代、成因和岩浆源区性质。结合区域已有地质资料，探讨这些火山岩的构造背景，为限定准噶尔洋的闭合时限提供重要约束。

西准噶尔作为中亚造山带西南部的重要组成，其形成与准噶尔洋的俯冲-闭合有关。然而，前人对于准噶尔洋的演化过程，特别是闭合时限仍有不同认识。根据前期研究基础，本项目选取西准噶尔巴尔鲁克山北坡石炭纪-二叠纪火山岩为重要研究对象，开展野外地质解析、岩石组合、精确形成时代和构造环境研究；同时研究巴尔鲁克北坡晚泥盆世侵入岩和增生杂岩，以期重建准噶尔洋构造演化历史。.项目执行三年来，获得的重要结果和关键数据包括：（1）巴尔鲁克山北坡火山岩包括早石炭世（339-323 Ma）和早二叠世（296-286 Ma）两期，利用岩石组合和地球化学属性，将准噶尔洋晚期演化划分为早石炭世洋内俯冲阶段和早二叠世后碰撞演化阶段；结合新识别出的晚石炭世区域性角度不整合，认为准噶尔洋盆可能闭合于晚石炭世末期。（2）锆石Hf-O同位素分析显示，早石炭世火山岩具有亏损Hf同位素（εHf(t)值为+11.2~+12.9）和类似地幔的锆石O同位素（δ18O值为+4.12‰~+6.09‰）特征，显示与洋内俯冲作用有关的地壳侧向生长；早二叠世火山岩则同样亏损Hf同位素（εHf(t)值为+8.4~+14.1）但低于地幔值的δ18O（+3.20‰~+4.95‰），代表后碰撞阶段新生地壳再造。（3）西准噶尔巴尔鲁克山北坡存在晚泥盆世侵入岩（368 Ma），其高正εNd(t)值（+6.6~+7.0）特点暗示哈萨克斯坦山弯内弧带北段延伸至西准噶尔地区，但该段岛弧基底应明显区别于内弧带南段大陆弧的基底；（4）西准噶尔南部在埃迪卡拉纪-奥陶纪期间存在洋内俯冲作用，而在晚志留世-早泥盆世期间发生海山增生作用。.相关成果已分别发表在Lithos、Journal of Earth Science、Journal of Geodynamics和Geological Journal上，为后续研究奠定了可靠的基础。