The Wanhe ophiolitic mélange is redefined along the Wanhe-Mengku-Dananmei line.It is located on the eastern side of the Tongchangjie ophiolitic mélange of Paleotethys in southwestern Yunnan Province.The rocks are composed of phengite-bearing quartz schist,green-schist and amphibolite schist,tonalite and plagioclasite,laminated amphibolite and gabbros,and retrograded eclogitem,respectively equivalent to pelagic sediments,sea-floor basalt,leucocrate,mafic cumulate rock and HP-UHP pyrolite in the ophiolite suite.The LAICP-MS U-Pb zircon age of 470.8 ± 5.3 Ma indicates that the Wanhe ophiolitic mélange was formed in Early Paleozoic.Based on cumulate plagioclasite in Mannahe section at northern Mengku Town in Shuangjiang County,the authors described the characteristics of major elements,REE and trace elements from igneous rocks in the Wanhe ophiolitic mélange.All igneous rocks could be divided into two types:① leucorate,with the data SiO2 =57.00% ~69.68%,Na2O=1.36% ~6.38%,K2O=0.26% ~2.45%,and average Na2O/K2O=10.12,thus belonging to typical sodium granite with rich LREE and "L" distribution patterns.② basic rocks,with the data SiO2 =48.72 % ~ 53.72 %,TiO2 =0.75 % ~ 1.96 %,K2O =0.45 % ~ 1.29 %,and depleted-slightly enriched LREE distribution patterns,similar to features of MORB or E-MORB;in the diagrams of Th-Hf-Nb and Nb-Zr-Y,the samples fall into MORB-CBA/arc-volcanic basalt.On the whole,the samples from Mangnahe section at northern Mengku Town in Shuangjiang County correspond to MORB or E-MORB and,what is more,there exist some arc-volcanic characteristics,which are similar to features of FAB (forearc basalt),or MORB-like basalt.H-Mg and Nb-rich basalt indicates that Proto-Tethys Ocean experienced its peak of development in late Early Ordovician,followed subsequently by ocean crust's subduction in Changning-Menglian tectonic belt.Afterwards,Paleotethys Ocean accomplished inheritance evolution from Proto-Tethys Ocean through the rapid spreading of Mid Ocean Ridge along Tongchangjie to Niujingshan area.%在铜厂街蛇绿混杂岩带东侧的湾河-勐库-大南美一线新近厘定了一条早古生代的蛇绿混杂岩——湾河蛇绿混杂岩.现存岩石有多硅白云母石英片岩、绿片岩-斜长角闪片岩、英云闪长岩-斜长岩、纹层状斜长角闪岩-变质堆晶辉长岩、退变质榴辉岩等.代表了蛇绿岩套的远洋沉积、洋底玄武岩、浅色岩系、镁铁质堆晶杂岩、高压-超高压变质岩.在双江县勐库乡北忙那河剖面上的堆晶斜长岩中获得了470.8±5.3 Ma的锆石LA-ICP-MS U-Pb年龄值,表明湾河蛇绿混杂岩形成于早古生代.本文以忙那河剖面上的资料为例,详细介绍了湾河蛇绿混杂岩中岩浆岩的主量元素、稀土元素及微量元素地球化学特征.研究表明,其可划分为2类:①浅色岩系,其SiO2=57.00%~69.68%,Na2O=1.36% ~6.38%,K2O=0.26% ~2.45%,平均Na2O/K2O=10.12,为典型的钠质花岗岩,具有LREE强烈富集的“L”型稀土元素配分曲线,主要为斜长岩-英云闪长岩.②基性岩类,其SiO2-48.72%~53.72%,TiO2=0.75% ~1.96%,K2O=0.45%~1.29%,具有LREE亏损-弱富集的稀土元素配分曲线,与洋脊-准洋脊型玄武岩相当.在Hf-Th-Nb、Nb-Zr-Y图解中,样品落在洋脊玄武岩区(MORB)-岛弧钙碱性玄武岩区(CBA)/火山弧玄武岩区.从总体上看,忙那河剖面上的样品具有洋脊-准洋脊玄武岩的特点,同时又具有一些弧火山岩的特征,类似所谓的弧前玄武岩,或类洋中脊玄武岩,暗示了昌宁-孟连构造带上的原特提斯大洋盆地在早奥陶世晚期达到了鼎盛,开始出现了洋壳的俯冲消减作用.随后,沿铜厂街-牛井山一线的古特提斯洋盆迅速扩张,完成了从原特提斯洋向古特提斯洋的继承性演化.
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