哀牢山构造带深变质岩系年代学及构造属性研究

The Ailao Shan high-grade metamorphic belt is well known as the south-eastern exposure of the Yangtze pre-Neoproterozoic crystalline basement. However, this conception has been challenged by recent several new findings of young (post-Neoproterozoic) components that never reported before. This proposal is going to carry on more detailed works on the Ailao Shan high-grade metamorphic belt, to make further constraints on this debate. The main tools include detailed and systematic field works to define the lithological characters, LA-MC-ICP-MS/SHRIMP geochronology and zircon Hf isotopic compositions to define the formation and metamorphism ages of the protolith of various metamorphic rocks and hence potential sources. The goal of this proposal is to develop improved understanding of the tectonic affinity and geodynamic environment of the Ailao Shan high-grade metamorphic belt. This proposal may also shed light on the evolutionary history of the south-western margin of the Yangtze craton, as well as the geodynamic significance of this belt in extrusion process related to the India/Eurasia collision.

哀牢山深变质带是滇西地区著名的带状变质带，长期被认为是扬子陆块古老结晶基底组成部分。近来有研究发现哀牢山深变质岩系不全是古老的基底岩石，哀牢山深变质带属于扬子陆块古老结晶基底的传统认识受到挑战。本申请拟在详细野外地质调查和岩石学研究基础上，利用LA-MC-ICP-MS/SHRIMP技术对哀牢山深变质岩系开展精细的年代学及Lu-Hf同位素研究工作，深入剖析不同类型变质岩的原岩形成与变质时代，构建哀牢山深变质带原岩年代学格架及变质时序。结合区域地质资料，分析它们的物质源区特征，综合限定哀牢山深变质带的构造属性及其形成地球动力学背景，进而为探讨扬子西南缘演化历史和哀牢山构造带在印度-欧亚大陆碰撞区域构造响应方面提供约束。

哀牢山深变质带是滇西地区著名的带状变质带，长期被认为是扬子陆块古老结晶基底组成部分。近来有研究发现哀牢山深变质岩系不全是古老的基底岩石，哀牢山深变质带属于扬子陆块古老结晶基底的传统认识受到挑战。本项目在详细野外地质调查和岩石学研究基础上，利用LA-MC-ICP-MS技术对哀牢山深变质岩系开展精细的年代学研究工作，深入剖析不同类型变质岩的原岩形成与变质时代，构建哀牢山深变质带原岩年代学格架及变质时序,综合限定哀牢山深变质带的构造属性及其形成地球动力学背景。研究结果表明哀牢山变质岩系是一个原岩复杂的变质杂岩带，它的原始物质至少包含新元古代（728Ma，727Ma）岩浆岩，晚寒武世（495Ma）沉积地层，晚三叠世岩浆岩（220Ma，231Ma）和侏罗纪（170Ma，）沉积地层地层，而不是以往认为的古元古代结晶基底。现今所见的哀牢山岩群“古老”岩石面貌主要是由地质历史上的浅变质或未变质的地层和岩浆岩在新生代27.8-23.7Ma发生变质变形作用改造的结果。哀牢山变质带的源区物质特征和主要岩浆事件与扬子陆块西缘十分相似，具有亲扬子的构造属性。晚渐新世（27.8-23.7Ma）地壳深熔与左行走滑韧性剪切的共同作用导致了哀牢山深构造带的深变质岩系的形成。