Characteristics And Significance Of Fluid Inclusions Of The Permian Volcanic-intrusive Complex In The Baiyin Wula Area,Erlianhaote,Inner Mongolia

Baiyinwula is located in the Erlianhot-Dongwuqi tectonic belt on the southeastern margin of the Central Asian orogenic belt.The Late Paleozoic volcanic-intrusive rocks were developed in the area.Through detailed field geological surveys,a complete volcanic-intrusive complex with four lithologies was identified:it was blue-gray rhyolite,brick-red rhyolite porphyry,fine-grained alkaline granite and coarse-grained alkaline granites from early to late,and the magma properties have evolved from calc-alkaline to alkaline.In order to further define the genesis of the volcanic-intrusive complex,this paper focuses on the measurement of fluid inclusions and gas and liquid chromatography of population inclusions,and analyzes the genesis and source characteristics of rocks based on petrography and mineralogy.By collecting geochemical data from the study area,the genesis and tectonic setting of the set of rock masses are discussed.The study shows that the fluid inclusions of the Baiyin Wula complex have a uniform temperature of about 350°C,and it has low salinity,most of which are concentrated in 0²wt%NaCl.The density of the fluid is between 0.3⁰.95gcm³ and the oxygen fugacity is high.The magma emplacement is shallow to the surface?less than 1km?.The results of the population inclusion test of K-feldspar and quartz indicate that the gas phase composition of the group inclusions is mainly N₂ and CO₂,which is similar to the volatile fractions in the fluid inclusions found in the study of eastern mantle rocks,indicating the volatile of fluid inclusions may come from mantle.The mantle source may be involved in the formation of alkaline granite.At least some of the early mantle source fluids?gas?are involved in the parent magma of the alkaline granite.The liquid phase component shows that the fluid contains a certain amount of Ca²⁺,K⁺,Na⁺,Cl^-,SO₄^2-,indicating that the process of magma emplacement may have undergone crustal fluid replacement and the fluid has been modified.The formation of the rock mass in the Baiyinwula area is due to the process of magma embed from the deep magma chamber to the shallower part,and it breaks through the limitations of the surrounding rock and located along the fissure at the shallow surface.When the surface is ejected,the fluid is boiled with the changes in temperature and pressure,and form gas-liquid two-phase fluid inclusion,pure gas phase fluid inclusion and daughter-phase multiphase fluid inclusion,and the magma gradually forms a blue-gray flow with time.In the second stage,the magma with the same characteristics is emplaced to the same part,and the pressure has been released.The gas-liquid two-phase inclusions are formed due to the faster cooling rate;the third stage alkaline magma emplaces to the same depth and the crystallization is fast and form the fine-grained alkaline granite.When the fourth stage alkaline magma emplaces to the same depth,the temperature of the magma mineral is relatively slow due to the existence of the previous magma or cooled rock mass,and the later magma mineral crystallizes well and forms the coarse-grained granite,which eventually forms Baiyinwula volcanic-intrusive complex.