西藏唐古拉岩浆岩带西段晚三叠世孜锐拉花岗岩体的成因研究

Tanggula magmatic belt was a large multi-granitic batholith with complex ages, formed by multiple phase intrusive activities, which located nearby the Qinhai-Xizang Tibet central uplift and the tectonic boundary of North-South Qiangtang Basin. The most profound unsolved problems in this area are the granite emplacement ages and its petrogenesis. Previous researchers all believe that it’s one compound magmatic arc with Triassic, Jurassic and Paleogene intrusions, compared with the late-Triassic zircon U-Pb ages in Ziruila granite of small amount early work by applicants. Based on detail field geological investigation, Petrology and Mineralogy studies, use mutli-methods contained LA-ICP-MS zircon U-Pb Geochronology and Hf isotopic trace, Geochemistry and Sr-Nd-Pb isotopes, mineral in situ trace element analysis, to learn its petrogenesis of The late-Triassic granite in Tanggula magmatic belt, and discuss the property of the granitic magma sources, crust-mantle mixing effect and the process of dynamic development. It is worthwhile to undertake a deep regional comparison between the late-Triassic granites in Tanggula, central Qiangtang and Taniantaweng in its petrogenesis, tectonic background, and to analysis its similarities, differences and the genetic relationship between them and relationship between the late-Triassic magmatism in collision evolution of the Longmucuo-Shuanghu suture. The achievement would be having great significance to the Paleo-Tethys evolution process.

唐古拉岩浆岩带位于青藏高原羌塘中央隆起带附近，构成南北羌塘的构造界限。前人研究认为该花岗岩带可能为三叠纪、白垩纪及古近纪的复合岩浆弧，存在多期岩浆活动，而申请者获得的少量前期成果均为晚三叠世（孜锐拉花岗岩体）。本课题的研究对象就是这套晚三叠世花岗岩体，在详细的野外地质考察和岩石学、矿物学等基础上，利用主微量元素地球化学、Sr-Nd-Pb同位素及锆石Hf同位素源区示踪、矿物原位微量元素分析等手段，分析并探讨其岩石成因、构造背景、源区性质、壳幔作用及深部岩浆作用过程；同时开展区域上晚三叠世花岗岩体的东西对比，分析并探讨唐古拉地区晚三叠世花岗岩体与羌塘盆地中部、他念他翁一带花岗岩体在岩石成因、构造背景之间的相似性、差异性及其之间的成因联系，为探讨晚三叠世岩浆活动与龙木错-双湖缝合带碰撞闭合的成因联系提供约束，对研究龙木错-双湖缝合带碰撞闭合及整个青藏高原的特提斯演化过程都具有重要意义。

龙木错-双湖-澜沧江缝合带两侧晚三叠世岩浆活动，尤其是唐古拉岩浆岩带的时代、构造背景及成因机制，迄今尚未得到很好约束。唐古拉岩浆岩带位于龙木错-双湖缝合带与澜沧江岩浆岩带的衔接部位，区内并未出现典型的蛇绿混杂岩记录，特殊的构造部位使得有必要对带内晚三叠世岩浆活动开展系统的岩石学、地球化学及同位素年代学研究。本项目研究内容主要包括两个方面，目前均已取得一定进展。在岩石成因及岩浆源区性质、构造背景研究方面，通过对晚三叠世花岗岩体的岩相学、岩石地球化学、锆石U-Pb年代学及Hf同位素等研究，唐古拉花岗岩带应属壳源碎屑沉积物的部分熔融而形成的高钾钙碱性强过铝质S型花岗岩。岩体的侵位时代应该以晚三叠世为主（222-225Ma），而非前人认为的早白垩世、晚白垩世两期。花岗岩体的岩浆物质来源具有较为均一的Hf同位素组成，其时代主体为早元古代中晚期-中元古代早期，表明研究区曾存在较老的基底物质。在晚三叠世岩浆活动的东西对比研究方面，晚三叠世花岗岩体形成于碰撞后的构造背景，应该与龙木错-双湖-澜沧江古特提斯洋盆的碰撞造山作用过程有关，相关成果与认识已经形成论文稿件。后续仍将开展上述三个地区晚三叠世火山岩的成因对比，研究探讨晚三叠世岩浆活动与龙木错-双湖结合带碰撞闭合及特提斯构造演化的成因联系，深化与提升本项目研究成果的深度和质量。本项目研究成果与认识，指示了该带地质矿产调查的主攻方向应为碰撞造山和造山后阶段的矽卡岩型和热液型矿床，对研究龙木错-双湖结合带碰撞闭合及整个青藏高原的特提斯演化过程都具有重要意义。