Geochemical characteristics of Permian adakitic granodiorite in Bayinwula of Sonid Left Banner, Inner Mongolia
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    Abstract:

    Permian adakitic granodiorite and quartz-diorite in Bayinwula of Sonid Left Banner are distributed on the northern side of the Erlian-Hegen Mountain ophiolite zone. The 1∶200000 regional geological survey has assigned it to Late Variscan intrusive mass(γδ4(3) ). Studies show that the rocks have characteristics of high aluminum (Al2O3=13.69%~16.48%), higher sodium(Na2O=3.53%~4.58%), lower potassium((K2O=2.12%~4.10%)and higher strontium(Sr=425.1×10-6~645.2×10-6), SiO2=62.13%~72.87%,Y<18×10-6(7.23×10-6~14.29×10-6),δEu=0.71~0.83. The fractionation of light-weight thulium is sharp and the partition curve of thulium forms a right-oblique model. Europium anomaly is not conspicuous, suggesting typical adakitic rock. The spidergram of traced elements relative to the original mantle obviously shows a Sr peak and a Nb valley, and the original earth mantle standard curve is in accordance with that of adakites but obviously different from things of island arc andesite, dacite and rhyolite and continental arc andesite, dacite and rhyolite. The zircon U-Pb age of granodiorite is 256.1±0.9 Ma, implying a product of Early Permian magmatic movement. Mg# is quite high(>50), indicating that the northward subduction of the Late Paleozoic oceanic crust experienced partial melting and formed adakitic melt at 75~85 km (the transitional point of amphibolites facies and eclogite facies) , which then intruded the earth's crust and eventually formed adakites.

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张玉清,2009,内蒙古苏尼特左旗巴音乌拉二叠纪埃达克质花岗闪长岩类地球化学特征及其地质意义[J].岩石矿物学杂志,28(4):329~338. ZHANG Yu-qing,2009,Geochemical characteristics of Permian adakitic granodiorite in Bayinwula of Sonid Left Banner, Inner Mongolia[J]. Acta Petrologica et Mineralogica,28(4):329~338.

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