松辽盆地长岭断陷早白垩世火山岩地球化学研究

长岭断陷早白垩世火山岩富硅、富碱,岩石以非碱性系列为主,包括钙碱性和高钾钙碱性系列,碱性系列火山岩为钾玄岩系列。酸性岩与中、基性岩的微量元素特征差别明显,岩石总体微量元素特征与造山带火山岩相似,富集LREE、Rb、K和大离子亲石元素,TiO2含量低,贫Sr。火山岩的形成与造山带岩石圈拆沉作用引起地壳拉张减薄的大地构造背景有关。研究区基性火山岩为地幔岩部分熔融作用的产物,岩浆演化过程中存在单斜辉石和橄榄石等矿物的分离结晶作用,中性岩为原生玄武质岩浆分异演化的产物,营城组酸性火山岩的形成与构造活动存在直接关系,为构造剪切挤压应力致使上地壳重熔的结果。

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.