DISCUSSION ON THE CHARACTERISTICS AND TECTONIC SETTING OF THE MESOZOIC VOLCANIC SEQUENCES IN LUJIANG-ZONGYANG AREA
安徽庐枞中生代火山岩系的特征及其形成的构造背景

An intensive volcanic activity took place in Lujiang-Zongyang volcanic basin during J3 K1. The volcanic rocks consist of trachytic basalt, basaltic latite, latite and trachyte. The characteristics of this volcanic sequence are: low TiO2 and silica saturation, high alkalis, high K2O/Na2O value and Fe2O3/FeO value, high and variable Al2O3, enrichment in Rb, Sr, Ba, Zr, U, Th and LREE. Sr, Ph and O isotopes indicate that the primary magmas of this volcanic sequence were derived from the upper mantle. Therefore, it is deemed to the shoshonite series.According to the analyses of geodynamic situation for generate potassic to ultrapotassic magmas, it is considered that they are products of extensional igneous activity. They are also characterized by generating at the transitional stage between extrusion to extensioll.Although the alkaline rocks occurred in Early Cretaceous Period, the Yangzi valley was not typical continental rift at that time. After the late stage of Early Cretaceous, as the subdue non zone moved backward and the rate of subduction slowed down, further extension evolved the volcanic arcs and the intracontinental rift ernergecl and developed in East China.