龙木错--双湖、昌宁-孟连缝合带属于同一构造缝合带吗？

A mosaic of terranes or blocks and associated Late Paleozoic to Early Mesozoic sutures form an extensive curved belt, the notheastern Tibet belt, which is approximately 2500 km long and 500 km wide along the northeastern margin of the Tibetan Plateau. Numerous high quality geochronological and geochemical data greatly improved our understanding of the northeastern Tibet belt; mean while a lot of new problems appear. A key problem concerns whether or not the Longmu Co-Shuanghu suture in the northcentral Tibet connects with the Changning-Menglian suture in the Sanjiang belt. A rational answer of this question will provide some positive constraints on tectonic evolution of the northeastern Tibet belt, which will further help to reconstruct the continent break-up and assemblage process of the southern Eurasia. The Longmu Co-Shuanghu and Changning-Menglian sutures seem to joint in a region of Mangkang-Yanjin, western portion of the middle segment of the northeastern Tibet belt, where numerous mafic to ultramafic fragments and Permo-Triassic arc-like volcanics have been identified. These mafic to ultramafic fragments form a belt, which separates two geologic units both consisting of Low Carboniferous low grade metamorphosed strata. Geological mapping results have demonstrated that the Low Carboniferous strata along two sides of this belt are quite different in sediments, in structural style, and in metamorphism. Thus, the mafic-ultramafic belt likely represents a major tectonic boundary. At the present time, however, no detailed information is available about this mafic-ultramafic belt and associated geologic units, including timings of the mafic to ultramafic rocks, the structural style and polarity, the metamorphic facies and spatial pattern, and, collectively, the tectonic facies of the Carboniferous rocks. Providing this proposal is accepted, we try to (1) determine the timings of the mafic rocks by zircon SHRIMP U/Pb technique, new bulk geochemistry is used to constrain their tectonic affinity; (2)reveal the tectonic facies of the Low Carboniferous strata by detail structural observations and measurement, petrological observation and microprobe analysis combined with detrital zircon LA-ICP-MS U/Pb and Lu/Hf studies; (3) determine the deformation and metamorphic timings by muscovite 40Ar/39Ar method; and/then, (4) synthesize all available data to discuss the tectonic relationship between the Longmu Co-Shuanghu suture and the Changning-Menglian suture. This study likely results in a completely new tectonic reconstruction for the Paleotethyan evolution of the northeastern Tibet belt.

可可西里-玉树-西南三江组成了一条超过2500公里，向北东凸出的弧形构造带-藏东北构造带。大量高质量年代学、地球化学数据的发表加深了对该构造带的认识，同时也提出了一系列新问题。其中一个关键问题是：位于构造带北西段的龙木错-双湖缝合带与位于南段的昌宁-孟连缝合带有何动力学关联？对该问题的回答可以为构建更为合理的藏东北古特提斯阶段构造演化模型提供制约，进而帮助人们理解欧亚大陆南缘的陆块聚散过程。该弧形构造带中段西部的芒康-盐井地区位于两个缝合带的潜在连接部位，发育大量超镁铁岩块以及二叠-早三叠纪弧火山岩，可能代表一个重要的大地构造分界。本申请拟用大地构造相理论，从变质岩岩石学、构造地质学、岩石地球化学、同位素年代学角度对该区展开综合研究，确定研究区岩石组合与时代、变形-变质特点与时代；分析大地构造相及空间组合样式。运用大地构造相对比方法，探讨龙木错-双湖构造带与昌宁-孟连缝合带之间的动力学关系

青藏高原及其东南缘（三江造山带）的一个主要大地构造问题为位于高原腹地的龙木错-双湖缝合带与位于三江造山带南段的昌宁-孟连缝合带是否可以相连，从而组成一个完整的大型构造界限—古特提斯主洋盆消失的位置。本项目主要目标是确定古特提斯缝合带在三江造山带中段的具体位置，进而建立龙木错-双湖缝合带与昌宁-孟连缝合带之间的动力学关联。基本研究思路及手段为大地构造相分析。根据项目设计，我们完成了三江造山带中段（维西-六库地区）六条近东西向剖面详细野外调查，合计路线长度约190千米；收集了大量构造要素数据；采集各类样品700余件；完成全岩地球化学分析120件（包括44件Sm/Nd同位素）、锆石测年37件（包括9件砂岩碎屑锆石）、5件云母40Ar/39Ar测年。结合前人资料，基本查明了三江造山带中段古特提斯阶段大地构造相及空间分布，完成了项目设定的目标。我们的新数据显示，古特提斯主缝合带位于福贡—碧江一线，与怒江小角度斜交。缝合带东侧为崇山-碧罗雪山变质杂岩带，主要由早、中三叠世火成岩经变质、变形而成；属江达-维西-云县古特提斯阶段弧岩浆带的一部分。缝合带西侧为石炭-二叠纪浅变质被动陆缘石英砂岩、泥质砂岩、泥岩、灰岩组成，上部夹具OIB属性玄武岩，其碎屑锆石年龄组成可与拉萨地块同时期地质体对比。除了确定主缝合带位置外，本项目其他重要进展还包括：（1）发现古特提斯阶段弧岩浆岩发育的纵向不均匀性及位于中段的magmatic flare-up；（2）被肢解的第三纪海相弧后前陆盆地。这些新数据及发现对加深青藏高原及东南缘构造演化认识具有重大意义。

内容获取失败，请点击重试