松辽盆地北部徐家围子断陷营城组火山岩受控机制分析

Controlling mechanism on volcanic rocks of the Yingcheng Formation of the Xujiaweizi rift depression in the northern Songliao Basin

营城组火山岩是松辽盆地北部徐家围子断陷天然气最有利的储集体,其中营一段火山岩以中酸性为主,分布于断陷的中、南部;营三段火山岩以酸性为主,分布于断陷的中、北部。最新三维地震勘探研究成果表明,两者具有不同的发育特征:营一段火山岩喷发和分布明显受徐中断裂控制,表现为从断陷中部向南端扩展的特征;营三段火山岩喷发和分布则受徐东断裂构造带控制,表现为从断陷中部向北端扩展的特征。对火山岩厚度与断裂的叠合关系及区域构造特征分析表明,营城组火山岩的发育特征与西太平洋板块对东亚陆缘俯冲造成松辽盆地岩石圈拉伸减薄的地质规律相吻合,火山活动从断陷中部往南北两端扩展受构造应力场特征及断陷演化规律控制。

Yingcheng Formation volcanic rocks in the Xujiaweizi rift depression of the northern Songliao Basin are most favorable reservoirs for natural gases,of which the first section is composed of an intermediate-acidic volcanic rock mainly distributed in the central and southern rift depression,while the third section belongs to an acidic volcanic rock chiefly deposited in the central and northern rift depression.The latest research results of three-dimensional seismic exploration indicated that the two have different developmental characteristics,the volcanic eruption and distribution for the first section of the Yingcheng Formation were significantly controlled by the Xuzhong fault,volcanos erupted from north to south（i.e.from the central depression to the southern depression）,while the volcanic eruption and distribution for the third section were subjected to the Xudong fault zone,volcanos then erupted from south to north（i.e.from the central depression to the northern depression）.Analyses on the composite correlation between the thickness of volcanic rocks and faults as well as regional tectonics characteristics showed that the developmental characteristics of volcanic rocks in the Yingcheng Formation are consistent with the geological law that the extensional thinning of the Songliao Basin lithosphere caused by the Pacific Plate subduction downward to the East Asian continental margin,the characteristics that volcanic rocks of the Yingcheng Formation erupted from the central rift depression to both the north and the south are consistent with the characteristics of the tectonic stress field and evolution rule of the rift depression.