渤海海域沙东地区馆陶组火山通道相构型及成因机制

Structures and genetic mechanism of volcanic vent in Guantao Formation of Shadong Area in Bohai Sea

为探讨渤海海域沙东地区火山活动规律,以相对易识别的火山通道相为研究对象,利用沙东A区三维地震资料和少量钻井资料,采用构型解剖的方法,分析了火山通道相形态特征、活动期次及展布规律。结果显示:火山通道由上部锥形体和下部管体2部分组成,上部锥形体可识别出底面、顶面和内部充填3个构型要素;根据地层接触关系,顶面可以分为上超型、发散型和整一型3种;底面主要为削截型;内部充填主要包括块状充填和似层状充填2种。利用沉积作用对岩浆活动的响应特征来分析通道相的活动期次,总结出地层接触关系和上覆地层厚度变化2种期次判别的标准,并识别出3期火山活动。馆陶组火山主要为裂隙式喷发,火山通道沿断裂带呈串珠状展布。受NNE向的郯庐断裂和NWW向的张蓬断裂带双走滑共轭剪切影响,工区馆陶组时期断层活动较为强烈,热地幔柱也比较活跃,形成了该区多期岩浆喷发事件。该研究可为沙东地区火山岩油气勘探提供一定借鉴和指导。

To clarify patterns of volcanic activities in Shadong Area of Bohai Sea, volcanic vents that can be easily identified were studied. By using 3D seismic data and a small quantity of drilling data available in the Shadong-A Area, features, active stages and distribution of volcanic vents have been analyzed through structural dissection. Re- search results show the volcanic vents are composed by two parts ： upper cone and lower tube sections. In the upper cone section, 3 structural elements, namely bottom surface, top surface and internal fillings, can be identified; With consideration to stratigraphic contact relationship, the top surfaces can be classified into three categories： o- verlapping, dispersion and integral ; bottom surfaces are predominantly truncated type ; internal fillings include pre- dominantly mass filling and layered filling. With consideration to impacts of magmatism on sedimentation, active stages of vents can be analyzed. Eventually, stratigraphic contact relationship and changes in thickness of covering formations can be used as two kinds for standards for determination of evolution stages. In this way, volcanic activi- ties in 3 stages have been identified. Volcanic activities in Guantao Formation are dominated by fissure eruption with volcanic vent distributed in string configuration along the fault. Due to the double strike-slip conjugate shear of Tan- lu Fault in NNE and Zhangpeng Fault in NWW, faulting activities in the Guantao Formation of the Study Area were quite active. During the period, hot mantle plumes were also active to generate lava eruption events in different sta- ges in the Study Area. The study may provide valuable references and guidance for oil-gas exploration in volcanic rocks of the Shadong Area.