Petrochemistry of volcanic rocks of the Yixian volcanic cycle in the Beipiao-Yixian area, western Liaoning

Abstract：Mesozoic volcanic rocks are widely distributed in western Liaoning. The Yixian Formation may be subdivided into four members. The Early Cretaceous Yixian volcanic cycle comprises four subcycles. The first subcycle includes 4 small cycles. From early to late, the magma of the Yixian volcanic cycle evolved gradually from basic through intermediate-basic and intermediate to acidic. The rock association of the Yixian Formation is composed of basanite, trachybasalt, olivine basaltic trachyandesite, trachyandesite, trachydacite and rhyolite. From Beipiao to Yixian volcanic activitiers younged. The diagram of main oxides shows that SiO2 content is positively correlated with K2O and negatively correlated with MgO, CaO and FeO+Fe2O3 .the TAS diagram reflects the volcanic rocks generally have a higher alkalinity. The SiO2-K2O+Na2O and AFM diagrams show that volcanic rocks are of the calc-alkaline series in the subalkaline series. On the SiO2-K2O diagram, most samples fall in the field of the high-K calc-alkaline series and some sample plot in the field of the shoshonite series. Therefore the volcanic rocks of the Yixian volcanic cycle predominantly belong to the high-K calc-alkaline series and partly to the shoshonite series, indicating that they have the basic characteristics of continental intraplate volcanic rocks.