A Study on Petrological Geochemistry of the Early Cretaceous Volcanic Rocks from Changling Rift,Songliao Basin,China

Early Cretaceous volcanic rocks from Changling rift in Songliao basin are characterized by petrochemically rich silicon and alkali.These samples could be divided into two series as sub alkaline series and alkaline series.The sub alkaline series include high-K calc-alkali series and calc-alkali series.The alkaline series are shoshonitic series.All samples of volcanic rocks in study area were depleted in TiO2 and Sr,enriched in large ion lithophile elements compared to high field strength elements,enriched in light rare earth element other than heavy rare earth element,and enriched in Rb and K.These geochemical features are similar to those volcanic rocks in orogenic belts.These volcanic rocks in the study area are located in the extensive structure setting within the plate of the continental crust,that it caused by orogenic belt collapse.The mafic volcanic rocks are production of partial melting of the mantle.However,there existed fractional crystallization of clinopyroxene,olivine,Ti-Fe oxide and other minerals during magmatic evolution.The forming of intermediate volcanic rocks is a result of differential evolutions of basaltic magma.The formation of acid rhyolite are related to large-scale strike-slip movement of the fault,which can form bearing stress,such as,made upper crustal to re-melt.