Characteristics And Metallogenic Potentiality Of The Volcanic Rocks In Tuokuzidaban Group,Aksu River Area,Western Section Of The East Kunlun Belt

The East Kunlun Orogen?EKO?,located along the northern Tibetan Plateau,is a significant part of the Central Orogenic Belt.Late Devonian-Early Carboniferous volcanic rocks?rhyolite and andesite?in the Aksu River area,western section of the East Kunlun Belt are presented in this thesis.According to the petrological evidences,LA-ICP-MS zircon U-Pb ages and geochemical data,this paper investigates the petrogenesis and tectonic setting of these volcanic rocks.Together with the regional geology,Late Devonian-Early Carboniferous tectonic evolution of the north branch of the Paleo-Tethys ocean has been discussed.?1?The Late Devonian-Early Carboniferous volcanic rocks are composed of andesite and rhyolite,and have experienced at least three rhythms of eruption.U-Pb dating of zircon,from bottom to upper in the stratigraphic section yielded weighted mean ²⁰⁶Pb/²³⁸U age of 364.1±3.4Ma,354.8±1.9Ma,343.8±18Ma,respectively,indicating the eruption in the Late Devonian-Early Carboniferous.?2?The volcanic rocks belongs to calc-alkaline series and are characterized by enrichment in Large Ion Lithophile Elements?e.g.Rb,Ba,U,Sr and K?and Light Rare Earth Elements and depletion in some High Field Strength Elements?e.g.Nb,Ta,P and Ti?.The andesite has high La/Nb?1.66-3.63?,but low La/Ba?0.05-0.23?ratios,suggesting the material source of magma derived from mantle.The rhyolite has low Nb/Ta and Zr/Hf ratios and Cr,Ni and Co contents,and has the correlation between SiO₂ and almost all the major elements,indicating that the material source of the rhyolite was mainly crust-derived and has experienced fractional crystallization process.The samples are obviously deleption in Nb,Ta and Ti,showing the characteristics of arc magmatic rocks,which fall into the arc magmatic rock area in the tectonic discrimination diagram.?3?The Late Devonian-Early Carboniferous volcanic rocks tectonic setting is possible subduction-related.The north branch of the Paleo-Tethys oceanic crust between the Bayan Har and East Kunlun-terrane northward subducted beneath the Southern East Kunlun terrane in the Late Devonian-Early Carboniferous,and the north branch of the Paleo-Tethys ocean between the Bayan Har and Southern East Kunlun terrane opening event should be earlier than this time?³64Ma?.