The Geological Characteristic, Age And Tectonic Setting Of Kekesha Intrusive Rocks Of Early Paleozoic In Dulan County Of The East Kunlun Area

Magmatism in the East Kunlun orogenic belt occurred frequently. The Kekesha intrusive rocks of Early Paleozoic in East Kunlun area of Dulan county area is selected as the research object of the study. After detailed wild-field geological survey, key section measuring and indoor study of microscope image, the wild-field distribution, scale, occurrence and assemblage and petrology of the rocks are ascertained, meanwhile, the geological geochemistry characteristics and crystallizing age of the rocks, as well as its forming mechanism and tectonic settings are confined in preliminary, which provides strong evindences for ascertaining the complex tectonic evolutional history of the East Kunlun area in Early Paleozoic. Main cognitions are acquired as follows:1. The Kekesha intrusive rocks of Early Paleozoic in the East Kunlun area are constituted of gabbros, diorites and granitoids rocks, mainly of diorites rocks, both of which generally experienced low-grade deformation and metamorphism. The majority of the rocks intrude in Baishahe Group and Xiaomiao Group which belong to Paleoproterozoic and Mesoproterozoic respectively, and the local rocks emplace in Hongshuichuan Group of Triassic in the contact of fault and unconformity.2. The rocks belong to middle Potassium calc-alkaline series in general, of which the gabbros show the characteristics of low total alkali, high TiO2, CaO and MgO in content and the granites of high total alkali, low TiO2, CaO, MgO in content, classified to weakly peraluminous series, while, the diorites show the feature of metaluminous, and the content of major elements of which is mostly between the content of gabbros and granites. The common characteristics of the three types of rocks are enrichment of LREE and LILE like Rb, Ba and Th, loss of HREE and HFSE like Zr, Hf and Ta relatively, especially Nb, Y, Ti and P. All of these indicate that the rocks may form in relation to subduction of continental margin and is a result of mixing of intrusive mantle magma and the material of lower-crust and occurred distinct fractional crystallization in later evolution of the magma.3. LA-ICP-MS zircon U-Pb isotopic age of quartz diorite is (515.2±4.4) Ma (MSWD =2.5), which confines the crystallizing age of the majority rocks to Middle Cambrian epoch and corroborates the tectono-magmatism event of the East Kunlun region during the early Caledonian.4. Combined with the above study fruites and regional geological setting, it is concluded that the rocks of Paleozoic in Kekesha area of the east Kunlun orogenic belt formed in the setting of initial continental margin arc-zone or the primary subduction stage of oceanic basin, and the event may be a material response to expansion of proto-Tethys ocean in the East Kunlun area.