Geochemical Characteristics and Genesis of Volcanic Rocks of Yixian Formation in Jianping, Western Liaoning

摘要

The volcanic rocksdistributed in Pingzhuang-Machang basin of Jianping countryshould belongs to Yixian Formation, thevolcanism may be divided into two subcycles. The volcanic rocks mainly consists of rhyolites, trachyte and trachyandesites. The geochemical characteristicsindicate that the volcanic rocks belong to thehigh-K calc-alkalinemagmatic serious. The volcanic rocks are obviously enriched in large ion lithophile element elements (K, Rb, Sr, Zr, Ba, Pb, Li), and depleted inhigh field-strength element (HFSE) (Nb,Ti,P,Th,U,HREE) as well as compatible elements (Co, Ni, Cr, V). The volcanic rocks is rich in LREE. There is a slight negative Euanomaly, no Ce anomaly. A detailed geochemical discrimination of selected elements allowed us to identify that the volcanic rocks of Yixian Formation mainly derived from the partial melting of lower crust materials, but has been contaminated by upper crustal materials during its ascent process in some degree. The volcanic rocks of Yixian volcanic cycle weregenerated in response to lithosphere inhomogeneous extension in thecontinental intraplateorogenic belt. They have the basic characteristics of continental intra-plate volcanic rocks.