基于岩浆汇聚区和上升通道特征的火山岩分布规律——以松辽盆地长岭断陷下白垩统营城组为例

Volcanic Rock Distribution Based on Characteristics of Pathway and Magma Chamber:An Example from Lower Cretaceous Yingcheng Formation in Changling Fault Depression of Songliao Basin

关于断陷尺度火山岩充填规律的全面认识,需要从深部岩浆汇聚区开始,到输导体系,再到其喷发分散,进行统一分析;但在研究过程中往往还是以单项分析为主,导致火山岩分布规律的认识不够全面。为了深入分析断陷盆地火山岩分布的规律,利用钻井、地震资料和已有的深部结构研究成果,开展松辽盆地长岭断陷下白垩统营城组火山岩岩浆汇聚区和上升通道对火山岩分布特征的控制作用分析。取得如下认识:营城组火山岩在平面上呈现东西分带和南北分块的特征,在中央洼陷带集中分布;水平断距是火山岩是否发育的敏感参数,垂直断距对火山岩厚度影响更显著;断裂仅是火山岩发育的必要条件,非充分条件;火山岩分布还受软流圈上拱和地壳伸展减薄区域的约束;断陷盆地火山岩充填往往与沉降中心对应,当火山岩体积较小时烃源岩可以与火山岩组成好的生储组合,而当火山岩体积过大时会显著减少细粒沉积岩的沉积空间,不利于烃源岩在空间上延伸。

The distribution pattern of volcanic rocks in a scale of fault depression requires a unified analysis,starting from the deep magma chamber,to the transport system,and then to the eruption and distribution.However,the dominating of individual factor analyses in research process generally leads to an insufficient understanding.To fully understand the spatial distribution of the Lower Cretaceous Yingcheng Formation volcanic rocks in Changling faulted depression,the controlling effects of the magma chamber and ascending pathways are analyzed based on drilling data,seismic data and deep structures.The results are as follows:Laterally,the volcanic rocks of the Yingcheng Formation exhibit characteristics of east-west zonation and north-south blockiness,concentrating in the central depression zone.Horizontal fault throw is a sensitive parameter for determining the development of volcanic rocks,while vertical fault throw has a more significant impact on volcanic rock thickness.Faults are only a necessary condition for the development of volcanic rocks,not a sufficient one.The distribution of volcanic rocks is also constrained by up-doming of the asthenosphere and thinning zones in the crust due to extension.Volcanic material filling corresponds to the basin subsidence center in general.When the volume of volcanic rocks is limited,hydrocarbon source rocks can form a good source-reservoir combination with volcanic rocks.However,when the volume of volcanic rocks is large,it significantly reduces the deposition space for fine-grained sedimentary rocks and limits the spatial extension of hydrocarbon source rocks.