滇西双江县勐库地区湾河蛇绿混杂岩的形成时代、岩石地球化学特征及地质意义

发布时间：2018-08-16 18:18

【摘要】：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SiO_2=57.00%~69.68%,Na_2O=1.36%~6.38%,K_2O=0.26%~2.45%,平均Na_2O/K_2O=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SiO_2=48.72%~53.72%,TiO_2=0.75%~1.96%,K_2O=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。
[Abstract]:An early Paleozoic ophiolite-Wan River ophiolite melange has been newly determined in the east of Tongchang Street ophiolite melange belt. The existing rocks include polysilicon Muscovite quartz schist, greenschist-plagioclase schist, dolomite diorite-plagioclase, lamellar amphibolite-metamorphic heap gabbro, retrograde metamorphic eclogite, etc. It represents the ocean-going deposits of ophiolite suite, ocean floor basalt, light-colored rock series, magnesitic heaps, high-pressure and ultra-high pressure metamorphic rocks. A zircon LA-ICP-MS U-Pb age of 470.8 卤5.3Ma was obtained from the DUI cline feldspar in Mengku County, Shuangjiang County, indicating that the Wanhe ophiolite melange was formed in the early Paleozoic. Taking the data from the Shonahe section as an example, the geochemical characteristics of the major elements, rare earth elements and trace elements in the magmatic rocks in the ophiophoric melange of the Wanhe River are introduced in detail in this paper. The study shows that it can be divided into two types: 1 light-colored series, and its SiO2J 57.00 layer is 69.68%, and Na2O2O1.360.36T / 1.380.380.380.38K _ 2O0.26. the average Na _ 2O / K _ 2O _ 2 is 10.12. It is a typical natritic granite with a "L" type REE distribution curve strongly enriched by LREE, which is mainly composed of plagioclase and quartz diorite. 2 basic rocks. The SiO2 / SiO2 / 48.72 / 53.72 / TiO2D / TiO2S / 0.75 / 0.75 / 1.96 / 0.96 / 0.45 / 1.29, with a REE partition curve of LREE deficit and weak enrichment, which is comparable to the oceanic ridge-quasi oceanic basalt. In the Hf-Th-Nb-Zr-Y diagram, the samples are located in the (CBA) / volcanic arc basalts of the (MORB) island arc calc-alkaline basalts in the oceanic ridge basalt area. On the whole, the samples in the Shonahe section have the characteristics of oceanic ridge-quasi-oceanic ridge basalt, and some arc volcanic rocks, similar to so-called prearc basalt or mid-oceanic ridge basalt. It suggests that the Proto-Tethys oceanic basin in the Changning-Menglian tectonic belt reached its peak in the late early Ordovician and began to subduction of the oceanic crust. Subsequently, the ancient Tethys basin along Tongchang Street-Niujingshan line expanded rapidly, completing the succession evolution from the original Tethys Ocean to the Ancient Tethys Ocean.
【作者单位】：云南省地质调查院;中国地质大学地质过程与矿产资源国家重点实验室;
【基金】：云南区域地质调查片区总结与服务产品开发(DD20160345-02) 云南省科技领军人才培养计划项目(2013HA001) 中国地质调查局地质调查项目(12120114014601) 国家自然科学基金项目(41672222)~~
【分类号】：P588.3

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