The Geological Characteristic, Age And Tectonic Significance Of Kekesha-Kekekete Mafic-ultramafic Rocks In Dulan County Of The East Kunlun Region

The east Kunlun region is a compound continental orogenic belt, and contains quite a few significant tectonic boundaries. During the 1:50000 regional geological survey at Kekesha-Kekekete and its western area, Dawate, in the west of Qingshuiquan area in the east Kunlun region, the author discovered a suite of unreported mafic-ultramafic rock belt, which is suspected to the part of Qingshuiquan ophiolite, and the study on which can shed light on the resolution to intensively disputed tectonic framework of the east Kunlun region in the Early Palaeozoic, furthermore, on which study the regional tectonic evolution process of the area in the Early Palaeozoic can be discussed deeply.Guided by the Plate Tectonic theory and continental dynamics and dominated by systematic studies on wild-field geological characteristic, petrology, petrologic geochemistry and isotopic geochronology of the rock assemblage, the following cognitions are acquired in the essay after the wild-field geological mapping and detailed indoor experiments and analysis to the collected samples of the study area.1. The suite of mafic-ultramafic rocks exposed in Kekesha area of Dulan county in the east Kunlun region is mainly composed of serpentinized peridotite, lherzolite, gabbro, pyroxenite and metamorphic basalt, and so on.2. The mafic rocks in the rock assemblage is classified to the transitional type between oceanic tholeiite series and island arc calc-alkaline series, and show geochemical characteristics of enriched in LILE, like Rb and Ba, and apparent fractionation between LREE and HREE, similarly to the transitional type of T-MORB basalt, meanwhile, the ultramafic rocks of which are characterized by the content of low alkaline and high mafic, and the elements enrichment of Rb, Ba, Nb, Ta and Cr, and the same of the conspicuous fractionation between LREE and HREE, all of which indicate that the rocks are contaminated fiercely by the material of the continental Crust and derived from a resource area with more enriched oceanic lithospheric mantle material.3. It is suggested that the suite of rocks is a typical decomposed rock block derived from an ophiolite complex, and is more likely formed in the environment of an back-arc basin or spreading ridge of a small oceanic basin, and should be categorized to SSZ-type(Supra-Subduction Zone) or the East Mediterranean type according to ophiolite classification.4. The LA-ICP-MS zircon U-Pb isotopic age of the gabbro from the mafic-ultramafit complex is about (509.4±6.8)Ma (MSED=1.4), which shows that the rocks may crystallize in the Middle Cambrian epoch of the Early Palaeozoic.5. The mafic-ultramafic complex and the Qingshuiquan ophiolite have the consistent crystallizing age and similar geochemical characters, which suggests that the former evolved from the cracking of the latter, and the latter distributes along SWW direction to the west in the space.6. There is a spreading oceanic basin in Qingshuiquan-Kekesha area of the east Kunlun region in the Middle Cambrian epoch of the early period of the Early Palaeozoic, which is more likely resulted from the spread of the east margin of the Proto-Tethys ocean after the split of the Rodinia supercontinent in the east kunlun region.