张家口地区张家口组火山岩元素地球化学特征及成因

he Early Creataceous Zhangjiakou Formation exposed in Zhangjiakou area, North China, is mainly composed of rhyolite and trachyte. The high-precise analysis of main and trace elements for these volcanic rocks is firstly reported in this study. The results show that, these felsic volcanic rocks are iron enriched and reduced, and have high contents of potassium, total alkali, and incompatible elements such as rare earth elements (REE), Rb, Th, U, Zr, and Ga etc.; but they also exhibit Nb, Ta depelation relative to the light rare earth elements (LREE), and there are no significant negative anomaly of Eu for those less-fractionated samples. The element geochemistry of Zhangjiakou volcanic rocks in Zhangjiakou area is similar to that of reduced A-type granitoid. It is deduced that these felsic volcanic rocks are originated by partial melting of the tholeiitic lower crust of North China craton under the high temperature, low H2O fugacity, and low O2 fugacity condition. The tectonic setting of these rocks is post-collisional environment.