新疆西天山伊犁地区石炭纪火山—沉积序列及盆地性质

新疆西天山伊犁地区作为中天山微板块的一部分,呈"倒三角形"被缝合带或断裂带所围限。其上广泛出露的石炭纪火山—沉积岩系,是研究西天山石炭纪盆地性质和天山古生代造山作用演化过程最为直接的载体。本文通过对石炭纪火山—沉积剖面的岩石组合、地层序列、构造环境及盆地演化过程研究表明:伊犁地区石炭纪火山—沉积岩与下伏地层(前寒武纪结晶基底或前石炭纪褶皱基底)之间呈广泛的区域性角度不整合接触;火山—沉积岩系由下到上可以划分为2个序列,分别对应于盆地伸展—裂陷演化的两个旋回:序列Ⅰ:大哈拉军山组底部扇三角洲相、向上出现2次爆发相—喷溢相的火山喷发旋回,阿克沙克组底部扇三角洲相,向上过渡为滨浅海相—开阔台地相;序列Ⅱ:伊什基里克组由下到上由3次爆发相—喷溢相的火山喷发旋回构成,东图津河组为浅海陆棚相。西天山伊犁地区石炭纪火山—沉积序列反映了后碰撞伸展环境下的裂谷盆地充填演化过程。

东北地区深层侏罗系火山—沉积序列与储盖组合及勘探意义——以海拉尔盆地侏罗系为例

为揭示东北地区侏罗系火山—沉积序列与储盖组合等地质特征,进一步评价深层油气勘探潜力,本文基于勘探现状,利用露头调查、钻测井对比、岩芯观察、结合地震解释等方法,分析了东北地区侏罗纪盆地构造背景,认为早—中侏罗世和晚侏罗世具有不同的构造环境和盆地性质。早—中侏罗世为受控于蒙古-额霍茨克造山作用的挤压型断陷-坳陷盆地,受到了后期构造的强烈改造。晚侏罗世为陆内伸展环境下与火山活动相关的火山断陷盆地。东北地区晚侏罗世火山活动频繁,形成广泛分布的火山—沉积序列。海拉尔盆地晚侏罗世塔木兰沟组发育典型火山—沉积序列,以火山岩与沉积岩的互层为特征,表现为砂泥岩—中酸性火山岩—砂泥岩—中基性火山岩序列。岩石组合在不同凹陷单元差异性较大,中部凹陷带以火山岩和砂泥岩为主,外围凹陷以火山岩和砂砾岩为主。火山—沉积序列的岩性复杂,储层岩石类型多样,主要有"火山岩、火山碎屑岩、砂砾岩"3类岩性储层,储层物性普遍较低,总体属于中低孔极低渗储层-致密储层。依据火山—沉积序列的不同岩石组合及油气显示情况,可识别出砂泥岩或砂灰泥岩储盖组合、火山岩内幕储盖组合、火山岩-沉积岩复合岩类储盖组合、基岩风化壳储盖组合等四大类九小类油气储盖组合。最有利储盖组合是与烃源岩毗邻的砂泥岩储盖组合,其次是火山爆发相-喷发相的火山碎屑角砾岩、凝灰岩与火山岩的储盖组合。火山—沉积序列发育中等较好的暗色泥岩烃源岩,有一定的生烃潜力,油气成藏条件较好。围绕中部凹陷带的红旗凹陷、乌尔逊北凹陷烃源岩分布区的最有利储盖组合,是侏罗系深层火山—沉积序列的主要勘探领域。通过该研究,可以为其他地区火山—沉积序列的油气勘探提供一定的启示和借鉴意义。

南秦岭竹山地区洋岛型玄武岩的发现及构造意义

南秦岭竹山地区官渡一带发育碱性玄武岩—火山碎屑岩—枕状玄武岩—碳酸盐岩沉积组合。火山—沉积地层序列、岩石学研究表明,该套玄武岩组合具洋岛海山火山岩—碳酸盐岩双层式结构特征,形成于大洋板内洋岛或海山环境。稀土微量元素地球化学资料显示,这些岩石具有轻稀土富集,重稀土亏损特征,无明显Eu异常,且高场强元素Nb、Ta、Hf、Ti等元素明显富集(如Nb/La=1.2～2.3),类似于典型洋岛玄武岩,可能形成于板内环境。提出该套岩石组合是竹山地区混杂岩带的一部分,与陕西平利地区混杂岩、勉略带混杂岩共同构成南秦岭增生混杂岩带。

Architecture of volcanic sequence and its structural control of Yingcheng Formation in Songliao Basin

Yingcheng Formation is a set of volcanic strata composed of lava rocks,volcanic clastic rocks and sedimentary rocks,filled in some fault depressions in Songliao Basin,early Cretaceous.The study about litho-facies succession of Yingcheng Formation in the outcropped area of the southeast margin and in Xujiaweizi fault depression and its distribution based on analysis of seismic data,shows that the sequence of volcanic strata is quite different from the clastic sedimentary sequence.To study the architecture of volcanic sequence and its structural control of Yingcheng Formation in Songliao Basin,in this work,dividing of the volcanic sequence and dating of the sequence boundaries were finished firstly,then displacement and displacement rate of faults were calculated.The results show that,sample ages of top of the first member,the seconde member,and the third member are 127 Ma,115 Ma,110.7 Ma,respectively and sample age of the bottom of the third member is 114.7 Ma.The maximum displacement and displacement rate of the fault 1 are 3 km and 300 m/Ma,respectively,and those of the fault 2 are 3 km and 1000 m/Ma.Studies suggest that,the cooling unit of lava rock or pyroclastic rock is a basic genetic stratigraphic unit in volcanic sequence stratigraphy.Cooling units can construct a parasequence reflecting a volcanic eruption stage.A sequence was superimposed by some parasequences,responding to a volcanic active cycle.There are three types of volcanic sequences in Yingcheng Formation: type of explosion,type of effusion and type of mixed explosion-effusion.The surface of the volcanic sequence,an unconformity surface widely spread and traced in seismic profiles,is a base for analysis of volcanic sequence.The development of volcanic sequence was controlled by faulting,and the curves of fault displacement(rate)can reflect this control.The preservation of volcanic sequence was controlled by the type of volcanic structure and the regional subsidence,also different from that of the sedimentary.The type of volcanic structure of Xujiaweizi was a volcanic depression during the forming of Yingcheng Formation,and the breakdowns of volcanoes and structural subsidence were key factors in the volcanic sequences preservation.