古特提斯-新特提斯复杂演变过程中多期变质事件的性质及其对洋（陆）-陆碰撞造山的制约

The metamorphic complex belts (including the eastern, central and western belts) in the Sanjiang area, southeastern Tibetan Plateau record a long-term complex evolutionary history from Paleo-Tethys ocean-continent collisional orogeny until Neo-Tethys continent-continent collisional orogeny. Therefore, these metamorphic complex belts in the Sanjiang area provide a well natural laboratory for investigating the plate boundaries, and the complex processes of break-off and amalgamation of micro-continents. On the integrated studies of metamorphism and tectonic deformation, together with petrology, genetic mineralogy, geochemistry and geochronology, this applying project will put emphases on multiple metamorphic events and complex tectonic evolutionary histories in the Sanjiang and adjacent areas. The aims are to reveal the spatial extension of lawsonite-bearing eclogite and blueschist, (low-temperature) high-pressure meta-sedimentary rocks, and high-pressure mafic and pelitic granulites, constrain the P-T conditions for different metamorphic stages in each metamorphic event, precisely draw up the P-T-t paths and chronological frameworks of multiple metamorphic events, and clarity the genetic relationship between multiple metamorphic-deformation events and Paleo- and Neo-Tethys evolutions. Compared to the Longmu Co-Shuanghu suture zone, and Song Ma suture zone and Dai Nui Con Voi (DNCV) complex belt in the North Vietnam, the final aims in this project are to design a tectonic evolutionary model of Paleo-Tethys ocean-continent collisional orogeny and Neo-Tethys continent-continent collisional orogeny in the Sanjiang and adjacent areas. The anticipative results of metamorphism, tectonic deformation and geochronology in this project will provide new insight into the geodynamic process of break-off and amalgamation of micro-continents from Paleo-Tethys until Neo-Tethys orogeny in the Sanjiang and adjacent areas.

西南三江地区发育多条与古特提斯洋闭合相关的洋-陆俯冲-碰撞造山带，以及与新特提斯印度板块与欧亚板块俯冲-碰撞相关的陆-陆碰撞造山带。它们记录了丰富多彩的自古特提斯至新特提斯复杂的多期变质-变形历史，是研究洋-陆和陆-陆俯冲-碰撞边界、多陆块裂解-聚合、古特提斯至新特提斯形成演化的立典靶区。本项目以变质作用和构造变形研究为主线，结合岩石学、成因矿物学、相平衡模拟、同位素地球化学和多种矿物同位素年代学的综合研究，揭示含硬柱石榴辉岩和含硬柱石蓝片岩、巨量（低温）高压变沉积岩、高压基性麻粒岩和高压泥质麻粒岩的空间展布及延伸规律，查明原岩性质及其形成的构造背景，理清洋-陆和陆-陆俯冲碰撞的重大构造边界，系统阐明多期变质-构造变形事件序列，限定多期变质事件不同演化阶段的P-T条件，精确构建多期变质演化P-T-t轨迹及年代格架。阐明多期变质-变形事件性质与洋-陆和陆-陆俯冲-碰撞造山、特提斯演化之间的成因链接。重点查明古特提斯洋壳冷俯冲-高压变质-快速折返过程的岩相学、地球化学和同位素年代学的确凿证据，重点研究古特提斯洋壳俯冲的的性质和启动时间、古特提斯洋的最终闭合时间。在与龙木错-双湖缝合带、越南北部马江-大象山杂岩带进行综合对比研究的基础上，建立西南三江及邻区古特提斯洋-陆碰撞造山至新特提斯陆-陆碰撞造山的构造演化模式。该项研究不仅对揭示古特提斯至新特提斯多陆块裂解-聚合的动力学过程、引领国际特提斯变质作用研究具有重要的科学意义，而且为深入探讨古特提斯至新特提斯复杂的构造演变历史提供可靠的变质演化、构造变形和同位素年代学的制约。

昌宁-孟连—龙木措-双湖（CM-LS）、越北马江—点苍山-哀牢山（MJ-DA）缝合带记录了自古特提斯到始新世-中新世复杂的构造演化历史，是研究特提斯洋-陆到陆-陆俯冲碰撞及复合造山的立典靶区。本项目以两条缝合带新发现的高压-超高压变质岩为重点研究对象，通过多学科的综合研究，取得以下亮点成果：首次在CM缝合带发现典型洋壳型和陆壳型榴辉岩，洋壳型榴辉岩-蓝片岩的原岩时代为451-250Ma；在MJ缝合带率先识别出洋壳型榴辉岩，而并非前人认为的陆壳榴辉岩，结合蛇绿岩资料，明确MJ-DA洋壳形成时代为425-280Ma，表明CM-LS和MJ-DA缝合带是在晚志留世就已打开并持续扩张演化至中二叠世-早三叠世两个独立的古老大洋。在CM缝合带洋壳型和陆壳型榴辉岩-蓝片岩中发现大量硬柱石包体，发卡式顺时针变质P-T-t轨迹揭示洋壳和陆壳沿着5-8 ℃/km的极端低地温梯度线，连续冷俯冲到45 km至95 km深度，并发生硬柱石蓝片岩相和榴辉岩相变质，峰期变质时代为~246-227Ma，CM-LS缝合带是迄今为止世界上发现规模最大的冷俯冲造山带。MJ榴辉岩以不含硬柱石为特征，近等温减压顺时针P-T-t轨迹揭示大洋壳沿8-10 ℃/km地温梯度线发生暖俯冲至~75km地幔深处，并经历了榴辉岩相变质，峰期变质时代为239-233Ma。古特提斯陆壳型榴辉岩和巨量变沉积岩高压变质事件（246-227Ma）的厘定，揭示CM-LS和MJ-DA缝合带是青藏高原及东南缘古特提斯大洋俯冲-闭合到陆-陆俯冲-碰撞的重要转换带；发现中-新三叠世（245-220Ma）和始-中新世（50-15Ma）两期高压麻粒岩相变质事件及其伴随的强烈深熔事件，揭示CM-LS和MJ-DA缝合带是典型的复合型造山带；厘定CM-LS、MJ-DA古特提斯巨型造山带空间延伸规模分别可达2000、1000余公里，率先构建从洋-陆到陆-陆冷、暖俯冲-碰撞造山演化的新模式。上述亮点成果对深入探讨特提斯构造域俯冲带热结构与成因机制、探索地球深部物质循环过程、揭示俯冲带关键金属富集成矿规律均具有重要科学意义。