摘要
辽西地区是中国中生代火山岩主要分布区之一。义县组分为4个岩性段。义县火山旋回可分为4个亚旋回。第一亚旋回分为4个小旋回。从早期至晚期,义县旋回火山岩逐渐由基性向中基性、中性和酸性演化,火山岩岩石组合为基性岩—中性岩—酸性岩组合,从北票—义县,火山活动显示了由老到新的迁移性。主要氧化物关系表明岩石的SiO2与K2O呈正相关,SiO2与MgO、CaO、FeO+Fe2O3呈负相关。TAS图解反映了火山岩较高碱度的总体特征,硅—碱关系图和AFM图解反映了火山岩属于亚碱性系列中的钙碱性系列岩石,在SiO2—K2O关系图上,绝大部分样品落于高钾钙碱性系列区内,少量落于钾玄岩系列区,因此义县旋回火山岩以高钾钙碱性系列岩石为主,部分为钾玄岩系列,表明岩石富钾。义县旋回火山岩具有大陆板内火山岩的基本特征。
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.
出处
《中国地质》
CAS
CSCD
2004年第4期356-364,共9页
Geology in China
基金
中国地质调查局地质大调查项目(0199202053)资助。
