滇西高黎贡东南缘混杂岩带与班公湖－怒江缝合带的南向延伸

The identification of the Goligong Meso-Tethyan suture zone is very important to show the southern extension of the Bangonghu-Nujiang suture zone. Although the early Cretaceous granite belt in Gaoligong orogeny related with subduction and collision give an important evidence for the Meso-Tethyan suture zone, it have still been debated because of the lack of the key evidences, such as Mesozoic ophiolitic mélange belt , which are similar to that in the north belt of the Bangonghu-Nujiang suture zone. The characteristics of the chaotic matrix of pelagic sediments，tectonic blocks with different ages, lithological features and provenance for the mélange belt in southern Gaoligong orogen will be identified by the data of the field surveying, mapping, petrology,isotopic chronology, geography and paleobiology. The tectonic setting and evolution of this mélange belt and its relationship with the subduction of the Meso-Tethyan ocean and collision of the Tengchong and Baoshan blocks will be shown based on these new data together with the tectonic setting of the Jurassic to early Cretaceous magmatism in the Gaoligong orogen. The identification of this mélange belt can give the vital information to confirm the Gaoligong orogen is a suture zone and the southern extension of the Bangonghu-Nujiang suture zone.

高黎贡中特提斯缝合带的厘定对确定班公湖－怒江缝合带的南向延伸至关重要，但构造带内至今未识别出与班公湖－怒江缝合带北带相对应的中生代蛇绿混杂岩带等关键性标志，致使其缝合带的性质至今仍难以定论。为此，本项目将以高黎贡东南缘中生代混杂岩带为对象，通过地质剖面测制及构造地质学、岩石学、同位素年代学、沉积地层学和古生物学等方法，结合区域地质资料，查明混杂岩带混杂基质和岩块的岩石组合、空间分布、接触关系、沉积相和形成时代，恢复超基性岩块、硅质岩块、辉长岩/辉绿岩脉/墙和复理石沉积建造关系，确定混杂岩带的性质及其形成的大地构造背景；结合构造带内侏罗纪－早白垩世岩浆活动特点，并与班公湖－怒江缝合带北带相对应的蛇绿混杂岩带进行对比分析，揭示高黎贡构造带东南缘中生代混杂岩带的形成与怒江洋俯冲及腾冲地块与保山地块碰撞的关系，为确定高黎贡构造带古缝合带性质及其与班公湖－怒江缝合带的关系提供关键性信息。

高黎贡东南缘混杂岩带分布于龙陵－瑞丽一带，宽3-5km，长约130km，由浊积岩基质和蛇纹石化橄榄岩、玄武岩、辉长岩/辉绿岩、硅质岩、碳酸盐岩等岩块组成，其间为断层接触。.浊积岩是龙陵－瑞丽构造混杂岩带的主体，由粉砂质、钙质页岩、泥岩、硅质泥岩和含放射虫硅质岩与细砂级和粉砂级杂砂岩互层组成具有明显韵律的岩石组合，结合岩层内鲍马序列发育，局部可见包卷层理和锰结核，显示其形成于稳定的浊积扇外扇亚相的深海环境。杂砂岩碎屑锆石最小206Pb/235U年龄为212Ma，以及其中没有收到区内广泛发育的早白垩世岩浆岩锆石信息，揭示其形成于晚三叠世-侏罗纪。.蛇纹石化橄榄岩呈块状呈规模不等的透镜体断续分布，单个块体出露面积0.05～2km2，在块体边部片理化强烈，在接触带附近，片理化、糜棱岩化强烈，强片理化带或糜棱岩化带构成其与围岩的边界。蛇纹石化橄榄岩原岩由纯橄岩和方辉橄榄岩组成，局部发育辉石岩脉/墙。其中，方辉橄榄岩主要由橄榄石、斜方辉石及少量单斜辉石和、铬尖晶石组成。纯橄岩由橄榄石和少量铬尖晶石。铬尖晶石的Cr#、Mg#分别为56-94和20-72，橄榄石Fo、Fa分别为90-95和8-11.在尖晶石Cr#-Mg#和橄榄石Mg#-尖晶石Cr#图解上，所有样品都落在SSZ型橄榄岩区，并经历了20%以上的融熔。展示其SSZ型橄榄岩特征。辉石岩锆石LA-ICP-MS U-Pb年龄为188Ma，代表辉石岩的形成时代。.玄武岩块和辉长岩块呈透镜状或薄层状分布于浊积岩中，主要由单斜辉石和斜长石组成，都具有富钛、高Mg#值。稀土配分模式和微量元素蛛网图曲线与OIB玄武岩完全一致，在Nb/Y-Zr/Ti和Zr/（P2O5*10000）图解上，所有样品都落在碱性玄武岩区，说明其属于富钛碱性OIB型玄武岩类。.总体来看，高黎贡东南缘混杂岩带为俯冲增生杂岩带，是晚三叠世-侏罗纪班怒洋南缘怒江洋壳向腾冲地块下俯冲的产物。