滇老泰毗邻区早古生代中-基性岩浆岩成因及对原特提斯东缘演化的约束

The evolution of east Proto-Tethys ocean and tectonic activities along the northern margin of east Gondwana during early Paleozoic in the Tibet plateau has been paid much attention in the past decades. Numerous data show that an early Paleozoic Andean-type active continental margin developed along the northern margin of the Gondwana supercontinent, facing the Proto-Tethys Ocean. However, less attention has focused on the early Paleozoic magmatism and associated orogenesis in the southeast Asia, which has also undergone strong crustal reworking during Phanerozoic period. Based on the geological fingerprinting in the reported literature, this project will document new field, geochronological, geochemical, Sr-Nd-Pb-Os and zircon in-situ Hf-O isotopic data for the Intermediate-Mafic rocks and related volcanics from SE Asia (mainly from southwest Yunnan, northeast Thailand and northwest Laos). The aim for this project is to (1) evidence the presence and the temporal-spatial pattern of the early Paleozoic Intermediate-Mafic rocks in SE Asia, (2) recognize a series of early Paleozoic arc and back-arc systems in southeast Asia, early Paleozoic tectonic pattern and its accretionary assembly along the margin of Gondwana, and (3) constrain the evolution process of east Proto-Tethys ocean and tectonic activities along the northern margin of east Gondwana during early Paleozoic.

原特提斯洋东缘演化和冈瓦纳大陆北缘的大地构造属性一直是地学界试图揭开的难题。近年研究证明，青藏高原及邻区原特提斯洋在早古生代向冈瓦纳大陆北缘俯冲，形成了安第斯山型活动大陆边缘。目前对冈瓦纳大陆北缘和原特提斯洋演化仍聚焦于青藏高原主体，对显生宙再造强烈的东南亚滇老泰毗邻区所显示的早古生代岩浆及造山信息的”蛛丝马迹”关注尚少。本项目拟在综合分析东南亚早古生代已有资料的基础上，以现有“蛛丝马迹”为前提，以滇老泰毗邻区的中基性岩浆岩为重点，借助于野外地质、岩石(相)学、岩石/矿物化学、同位素年代学和元素-同位素地球化学等主要研究手段，获取精细年代学和系统配套的地球化学数据，寄望多角度确证滇老泰毗邻区早古生代中基性岩浆岩的存在及时空分布，查明成因，构建早古生代滇缅泰与印支陆块间弧-盆面貌及拼贴过程，为完整理解原特提斯东缘俯冲机制和东冈瓦纳大陆北缘早古生代构造属性提供突破性资料。

滇老泰毗邻区早古生代区域大地构造属性及该区原特提斯洋演化一直是地学界试图揭开的难题。本项目通过对滇老泰毗邻区早古生代岩浆岩开展详细野外地质、岩石(相)学、岩石/矿物化学、同位素年代学和元素-同位素地球化学研究，基本识别了其岩石类型、时空分布、地球化学特征和成因，并基本苟略出了滇老泰毗邻区原特提斯洋-弧-盆体系的时空展布。班控-南汀河-铜厂街一带早古生代MORB与SSZ型共存蛇绿岩的研究说明班控-南汀河-铜厂街一线代表了原特提斯洋缝合带的位置。惠民火山岩、泰国清莱辉长岩和老挝琅南塔辉长岩-辉长闪长岩-闪长岩代表了原特提斯洋东向俯冲的大陆边缘弧，而大中河火山岩、大凹子双峰式火山岩则可能指示了大陆边缘弧后盆地的发育。哀牢山梅子箐和坝头村445–420 Ma的富铌玄武岩、富镁安山岩和高镁玄武岩则说明哀牢山构造带此时为陆内裂谷环境。此外，陆内裂谷环境的哀牢山420 Ma的富铌玄武岩与潘家寨OIB型玄武岩伴生，其成因不同于传统的与埃达克岩伴生的岛弧环境埃达克质熔体交代成因的富铌玄武岩，而是来源于板内裂谷背景下OIB型地幔与弧型地幔混合的源区的部分熔融。