Silurian tectonic-paleogeographic environment in Kunlun Mountain area and its metallogenic significance

Abstract：In the research work conducted in the Kunlun Mountain area, the authors measured 39 Silurian (S) and Ordovician-Silurian (O-S) geological sections, whose thicknesses range from 169 m to 8260 m, mostly with fault and angular unconformities between various strata. Littoral (shallow sea)-abyssal- littoral (shallow sea)-abyssal paleogeographic sedimentary environments characterize the study area, as shown by these sections.In West Kunlun, Wenquangou Group（S1W）is dominated by sandstone and slate, assuming a shallow sea（shelf sea）sedimentary environment, in west Yingjisha, and by silicalite, sandstone, siltstone and slate in Mazha area, with the existence of tholeiite, demonstrating a deep sea sedimentary environment (subduction zone ocean trench) in this area, a clinoform sedimentary environment in the west and east of Mazha, and thinning of strata northwestward and southeastward. In East Kunlun, Wenquangou Group（S1W）is composed of epimetamorphic rock, sandstone and mudstone, assuming abyssal-bathyal flyuzitage Peak. In middle and late Silurian（S2-3）, Dabangou Group (S2-3D) was bathyal-littoral (shallow sea) in the west and shallow sea sediments such as carbonate and fragmental rock in the east.In East Kunlun, the Baiganhu Formation（S1b）in south Ruoqiang is characterized by abyssal turbidite aggradation with graptolites as the mark of the deep sea basin environment under the tensile tectonic condition. The Saishiteng Formation （S3）in south Geermu City shows the upward evolution from clinoform through continental rise and shallow sea to abyssal facies, characterized by turbidite and semi-pelagic aggradation in relict sea basin, with the zircon LA-ICP-MS U-Pb ages of monzonitic granite being 421±3 Ma and 423±16 Ma. The Nachitai Group（OSN）strata in southeast Geermu City possess ultramafite-diabase-basalt-deep sea silicalite, derived from ocean crust substance. Ultramafite is a part of ocean crust relic fragments, metamorphic basalt marks midoceanic ridge and ocean island arc, silicalite signifies midoceanic ridge or big ocean basin sediments in geochemical features, metamorphic fragmental rock implies clinoform sediments, and carbonate means littoral sediments. The SHRIMP zircon 206Pb/238age of big midoceanic ridge tholeiite（MORB）in the strata is 419±5Ma, suggesting Upper Silurian（S4）. On the whole, the Kunlun Mountain in Silurian was a relict ocean exhibiting a complex ocean system with more islands and basins formed after Caledonian movement. The results obtained by the authors in the study of tectonic-paleogeographic environment provide important evidence for the study of the formation mechanism of the known ore deposits and the arrangement of further ore prospecting work in this area.