晚三叠世火山活动对鄂尔多斯盆地长7优质烃源岩发育的影响  

The Influence of Late Triassic volcanism on the development of Chang 7 high grade hydrocarbon source rock in Ordos Basin

作　　者：张文正[1] 杨华[2,3] 彭平安[4] 杨奕华[1] 张辉[1] 石小虎[1] 

机构地区：[1]中国石油长庆油田分公司勘探开发研究院,陕西西安710018 [2]西北大学地质学系大陆动力学国家重点实验室,陕西西安710069 [3]中国石油长庆油田分公司,陕西西安710018 [4]中国科学院广州地球化学研究所,广东广州510640

出　　处：《地球化学》2009年第6期573-582,共10页Geochimica

基　　金：国家自然科学基金(40773028);国家重点基础研究发展计划项目(2003CB214602);教育部长江学者和"油气盆地"创新团队发展计划项目(IRT0559);中国科学院知识创新工程重要方向项目群项目(KZSX2-YW-Q05-05)

摘　　要：岩芯和露头剖面观察结果表明,鄂尔多斯盆地长7优质烃源层中广泛分布薄层和纹层状凝灰岩,薄层凝灰岩的SiO2含量介于49.37%～72.45%之间,以中、酸性为主。岩石薄片的镜下观察结果表明,常见晶屑凝灰岩、玻屑凝灰岩和双屑凝灰岩,并可见到呈有序结构(成分和粒度)的凝灰岩纹层,同期喷发、大气降落沉积特征明显。根据其岩石类型、主元素和微量元素组成、锆石U-Pb年龄等的对比,以及凝灰岩的平面分布特征判断,盆地内长7优质烃源层中的凝灰岩可能主要来自秦岭地区的同期火山喷发活动。扬子与华北陆块碰撞、秦岭造山的区域构造活动的活跃是引起长7最大湖泛的主要动力因素,为优质烃源岩发育提供了基本的地质条件,同期频繁的火山喷发活动与湖底热液活动等共同促进了优质烃源岩的大规模发育。Based on field observation of a great number of drill cores, outcrops and rock profiles, it was found that thin-layered and laminated tuff was extensively developed in the high grade hydrocarbon source rock of Chang 7 Member of Yanehang Formation in the Ordos Basin. The thin-layer tuff is mainly intermediate to acidic in composition, with SiO2 contents varying between 49.37% and 72.45%. According to results of petrographic observation, the tuff can be divided into crystalline tuff, vitric tuff and crystalline-vitric tuff. Also, laminated tuff sometimes shows ordered structure in terms of both composition and grain size, which is characteristic of simultaneous volcanic eruption, atmospheric precipitation and subsequent sedimentation. Based on rock types, composition of both major and trace elements, zircon U-Pb dating results as well as features of spatial distribution of the tuff, it can be inferred that the tuff occurring in Chang 7 high grade hydrocarbon source rock in the basin may be resulted from the simultaneous volcanic eruption in the Qinling orogen. Collision between the Yangtze and North China blocks and consequent regional structural movements in the Qinling orogen were the major dynamic elements leading to the maximum lake flooding event at the Chang 7 period, which provides the basic geological conditions for the development of the high grade hydrocarbon source rock. Meanwhile, the frequent volcanic eruptions and hydrothermal activities that occurred simultaneously at the lake bottom would together facilitate large scale development of the source rock.

关 键 词：优质烃源岩 凝灰岩 火山活动 晚三叠世 秦岭造山活动 鄂尔多斯盆地 

分 类 号：P594[天文地球—地球化学] P595[天文地球—地质学]