辽西建平县义县组火山岩形成构造环境的地球化学鉴别

对辽西建平县平庄-马厂盆地的火山岩进行了岩石学、地球化学、同位素年代学研究.结果表明，火山岩属白垩纪.义县组火山作用可分为2个亚旋回.火山岩主要为流纹岩类、粗面岩类和粗安岩类.义县旋回火山岩属高钾钙碱性岩石系列.火山岩具有高SiO2，Al2O3，K2O，Na2O和低MgO，TiO2的特征.火山岩富集大离子亲石元素(LILE)K，Rb，Sr，Zr，Ba，Pb，Li等，高场强元素(HFSE)Nb，Ti，P及相容元素Co，Ni，Cr，V亏损.火山岩为轻稀土富集型，总体显示弱负铕异常、无铈异常.对火山岩形成的构造环境的地球化学判别，表明义县组火山岩成岩物质主要来源于下地壳的部分熔融，岩浆在上升过程中受到了一定程度的上地壳物质的混染.火山岩形成于板内岩石圈不均匀伸展作用环境，具有大陆板内造山带火山岩的基本特征.

Geochemical Discrimination of Tectonic Environments of Volcanic Rocks of Yixian Formation in Jianping of Western Liaoning

Petrology， geochemistry， isotope geochronology of the volcanic rocks distributed in Pingzhuang Machang basin of Jianping of western Liaoning were studied. The results showed that the volcanic rock is the Cretaceous. The volcanism of Yixian formation may be divided into two sub cycles. The volcanic rocks mainly consist of rhyolites， trachyte and trachyandesites. The volcanic rocks belong to the high K calc alkaline magmatic series. The volcanic rocks are characterized by components of high SiO2， Al2O3， K2O and Na2O， and comparatively low MgO and TiO2. The volcanic rocks are obviously enriched in large ion lithophile elements (K， Rb， Sr， Zr， Ba， Pb and Li)， and depleted in high field strength element (Nb， Ti， P)as well as compatible elements (Co， Ni， Cr and V). The volcanic rocks is rich in LREE. There is a slight negative Eu anomaly and no Ce anomaly. A detailed geochemical discrimination of the selected elements allowed us to identify that the volcanic rocks of Yixian formation mainly derived from the partial melting of lower crust materials， but also has been contaminated by upper crustal materials during its ascent process in some degree. The volcanic rocks of Yixian volcanic cycle were generated in response to lithosphere inhomogeneous extension in the continental intraplate orogenic belt. They have the basic characteristics of continental intra plate volcanic rocks.