保山地块西缘早古生代增生造山作用

Early Paleozoic Accretionary Orogenesis on Western Margin of Baoshan Block

在保山地块西缘泸水-潞西构造带内,出露一套构造混杂岩.主体为强变形的震旦系-古生界蒲满哨群、公养河群浅变质碎屑岩夹碳酸盐岩及火山岩等复理石浊积岩系等构成,另有硅质岩、杂砂岩、灰岩、砾岩、玄武岩及花岗岩等弱变形的构造块体.岩石时代从震旦纪至古生代,跨度大,高度混杂,并有从东向西变新的逐势,表现为后退式增生.构造样式早期为同斜倒转冲断作用的叠瓦构造,后期表现为近N-S向剪切.玄武安山岩、流纹岩类具弧火山岩特征,而玄武岩类则为板内火山岩,2种火山岩分别对应岛弧与弧后拉张洋盆产物.寒武纪、奥陶纪侵位的花岗岩也分为东西2个带,西晚东早,代表了保山陆块西缘岩浆弧的一部分.这样就记录了洋壳俯冲消亡、增生楔形成过程的沉积、火山-岩浆、变质和构造变形的地质事件群,也记录了保山地块西缘早古生代增生造山形成过程的地质事件,并证明了泸水-潞西构造带在震旦纪-古生代存在一洋盆.

On the western margin of the Baoshan block,a set of tectonic m＆#233;lange can be seen along the western Lushui-Luxi tectonic zone.It is characterized by matrices consisting of strongly deformed and low-grade metamorphic clastic rocks bearing graptolite of Sinian-Paleozoic Pumanshao Group and Gongyanghe Group and volcanic flysch turbidite,and structural lens con-sisting of siliceous,graywacke,part limestone,conglomerate,basalt and granite.The ages of these rocks range from Sinian to Paleozoic and get younger from east to west,which shows the characters of retrogressive accretion.In the early stage,the structural styles are characterized by imbricate structures formed by thrust faults and homoclinal-overturned folds,and nearly N-S-trending shear in the late stage.The characteristics of basalt-andesite and rhylite are of arc volcanic rocks,and the basalt shows characteristics of continental intraplate volcanic rocks.Both of the two types of volcanic rocks maybe account for the tec-tonic setting of island arc and back-arc extension.Cambrian and Ordovician granite can be divided into the western belt and eastern belt,and the ages of the latter are earlier than that of the former.Those granites are part of magmatic arc of the west-ern margin of the Baoshan block.Therefore,this tectonic m＆#233;lange records the geological events such as extinction to the sub-duction of the oceanic crust and magmatic sedimentation-volcanic-magmatic-tectonic events during the formation process of ac-cretionary wedge,and also records the information of the Early Paleozoic accretionary orogenesis on the western margin of the Baoshan block.Meanwhile,it suggests the existence of an ocean basin during Sinian-Paleozoic in the Lushui-Luxi tectonic zone.