The Influence of Late Triassic volcanism on the development of Chang 7 high grade hydrocarbon source rock in Ordos Basin
The Influence of Late Triassic volcanism on the development of Chang 7 high grade hydrocarbon source rock in Ordos Basin
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发表时间：
2009
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通讯作者：
Z. Hui
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作者：
Z. Hui
通过大量岩心、露头和岩石剖面的野外观察，发现鄂尔多斯盆地延长组长7段优质烃源岩中广泛发育薄层状和层状凝灰岩，薄层凝灰岩成分以中酸性为主，SiO2含量在49.37%~ 72.45%之间，根据岩相学观察结果，凝灰岩可分为结晶凝灰岩、玻璃质凝灰岩和结晶-玻璃质凝灰岩，层积凝灰岩有时在成分和粒度上都表现出有序结构，这是火山喷发、大气降水和随后的沉积作用同时发生的特征。根据岩石类型、主量和微量元素组成，锆石U-Pb测年结果及凝灰岩的空间分布特征，长7优质烃源岩中的凝灰岩可能是秦岭造山带同期火山喷发的产物，扬子陆块与华北陆块的碰撞以及由此引起的秦岭造山带区域构造运动是导致长7优质烃源岩中凝灰岩形成的主要原因长7期最大湖泛事件的主要动力学要素，为优质烃源岩的发育提供了基本的地质条件，同时湖底频繁的火山喷发和热液活动，也为烃源岩的大规模发育提供了有利条件。
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 Yanchang 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.