Cenozoic post-collisional brittle tectonic history and stress reorientation in the High Zagros Belt (Iran, Fars Province)

The Zagros fold-and-thrust belt of SW-Iran is among the youngest continental collision zones on Earth. Collision is thought to have occurred in the late Oligocene–early Miocene, followed by continental shortening. The High Zagros Belt (HZB) presents a Neogene imbricate structure that has affected the thick sedimentary cover of the former Arabian continental passive margin. The HZB of interior Fars marks the innermost part of SE-Zagros, trending NW–SE, that is characterised by higher elevation, lack of seismicity, and no evident active crustal shortening with respect to the outer (SW) parts. This study examines the brittle structures that developed during the mountain building process to decipher the history of polyphase deformation and variations in compressive tectonic fields since the onset of collision. Analytic inversion techniques enabled us to determine and separate different brittle tectonic regimes in terms of stress tensors. Various strike–slip, compressional, and tensional stress regimes are thus identified with different stress fields. Brittle tectonic analyses were carried out to reconstruct possible geometrical relationships between different structures and to establish relative chronologies of corresponding stress fields, considering the folding process. Results indicate that in the studied area, the main fold and thrust structure developed in a general compressional stress regime with an average N032° direction of σ₁ stress axis during the Miocene. Strike–slip structures were generated under three successive strike–slip stress regimes with different σ₁ directions in the early Miocene (N053°), late Miocene–early Pliocene (N026°), and post-Pliocene (N002°), evolving from pre-fold to post-fold faulting. Tensional structures also developed as a function of the evolving stress regimes. Our reconstruction of stress fields suggests an anticlockwise reorientation of the horizontal σ₁ axis since the onset of collision and a significant change in vertical stress from σ₃ to σ₂ since the late stage of folding and thrusting. A late right-lateral reactivation was also observed on some pre-existing belt-parallel brittle structures, especially along the reverse fault systems, consistent with the recent N–S plate convergence. However, this feature was not reflected by large structures in the HZB of interior Fars. The results should not be extrapolated to the entire Zagros belt, where the deformation front has propagated from inner to outer zones during the younger events.     

Late-Quaternary Slip Rate and Seismic Activity of the Xianshuihe Fault Zone in Southwest China

The Xianshuihe fault zone is a seismo-genetic fault zone of left-lateral slip in Southwest China. Since 1725, a total of 59 Ms ≥ 5.0 earthquakes have occurred along this fault zone, including 18 Ms 6.0–6.9 and eight Ms ≥ 7.0 earthquakes. The seismic risk of the Xianshuihe fault zone is a large and realistic threat to the western Sichuan economic corridor. Based on previous studies, we carried out field geological survey and remote sensing interpretation in the fault zone. In addition, geophysical surveys, trenching and age-dating were conducted in the key parts to better understand the geometry, spatial distribution and activity of the fault zone. We infer to divide the fault zone into two parts: the northwest part and the southeast part, with total eight segments. Their Late Quaternary slip rates vary in a range of 11.5 mm/a –(3±1) mm/a. The seismic activities of the Xianshuihe fault zone are frequent and strong, periodical, and reoccurred. Combining the spatial and temporal distribution of the historical earthquakes, the seismic hazard of the Xianshuihe fault zone has been predicted by using the relationship between magnitude and frequency of earthquakes caused by different fault segments. The prediction results show that the segment between Daofu and Qianning has a possibility of Ms ≥ 7.0 earthquakes, while the segment between Shimian and Luding is likely to have earthquakes of about Ms 7.0. It is suggested to establish a GPS or In SAR-based real-time monitoring network of surface displacement to cover the Xianshuihe fault zone, and an early warning system of earthquakes and post seismic geohazards to cover the major residential areas.     

徐家围子断陷营城组火山岩分布特征及火山喷发机制的新认识

基于深层钻井和连片处理三维地震资料,结合同位素测年,本文对松辽盆地北部徐家围子断陷白垩系营城组火山岩的分布特征及其喷发机制进行了研究。本区火山岩分布广、厚度大、沿深大断裂串珠状分布;纵向上分为下部营一段和上部营三段两套;营一段分布于断陷中部及其以南地区,岩性以酸性为主;营三段分布于断陷中部及其以北地区,酸性和中、基性火山岩均有发育。本区断裂类型及其组合复杂,正、逆、走滑和花状断裂都有发育;两组断裂交汇部位是火山喷发的主要通道。深大断裂与火山岩时空展布关系显示,营一段火山岩主要受徐中断裂控制,由北向南依次喷发,岩性以酸性为主;营三段火山岩主要沿着徐东花状断裂带由南向北依次喷发,表现为基性与酸性交替的双峰式。营城组火山岩喷发类型有三种:裂隙式、中心式与复合式。徐家围子断陷营城组火山岩储集性能优良且毗邻烃源岩,与断裂、源岩及盖层有利匹配,可构成有利的生储盖组合,具有良好的天然气勘探前景。     

西昆仑山东段库牙克断裂与康西瓦断裂、阿尔金断裂关系的地球化学证据

新疆昆仑山中部库牙克地区,处于不同大地构造单元的结合部位,一些重要构造线均交会于此,确定它们之间的关系,关键在于库牙克断裂。1：20万区域化探最新成果显示,库牙克地区绝大多数元素两分性特征突出、南北差异明显,北部整体富集MgO、K2O、Na2O、Al2O3、CaO、Cr、Ni、Co、V、Ti、Au、La、Be,而贫Hg、As、Sb、B、Li,南部正好相反。两者之间的分界线从东向西依次对应于阿尔金断裂西段、库牙克断裂、阿什库勒断裂和康西瓦断裂东端。因此,从地球化学角度对库牙克断裂的延伸进行了推断,提出库牙克断裂东连阿尔金、西经阿什库勒与康西瓦断裂相接的新认识。     

西昆仑山前东段新生代褶皱冲断带及其锥形楔机制

西昆仑山前东段的和田-柯克亚构造带与塔里木盆地内的麻扎塔格构造带相距为200 km,两者近似平行,遥相对应,麻扎塔格构造带是和田-柯克亚构造带的前沿,山前挤压变形量沿古近系阿尔塔什组膏泥岩向北传递约200 km到麻扎塔格,形成往北东逆冲的断层传播褶皱,在盆地腹部表现为一条显著的北西向地形隆起。因此,整个西昆仑山前东段新生代褶皱冲断带宽约为270 km,长约为220 km,由和田-柯克亚构造带、麦盖提斜坡和麻扎塔格构造带组成。中部近200 km的麦盖提斜坡内没有明显构造变形,且整个褶皱冲断带的锥形楔角度远小于活动造山带的临界锥形角,说明古近系底部阿尔塔什组膏泥岩以及新生代沉积体的形态是这个褶皱冲断带锥形楔形成的主控原因,膏泥岩控制了锥形楔的顶面坡度α基底构造形态及上覆沉积楔形体则控制了锥形楔的底部滑脱层倾角β。     

倾角导向体控制的气烟囱识别技术及其在海拉尔盆地贝尔凹陷中的应用

在调研了国内外气烟囱研究成果与思路的基础上,通过全新的地震解决方案——OpendTect平台提供的基于属性多层感知器(MLP)的人工神经网络(ANN)的方法预测气烟囱的发生概率体,并利用倾角导向体对算法进行改进,提出倾角控制下的地震气烟囱识别技术,很好地补充并发展了模式识别技术在地震勘探领域的应用。通常该技术一方面可以解释运移通道和浅层气成藏的原因;另一方面,形成的气烟囱地震数据体还可以预测源岩的发育情况;此外,对于判别断层封闭性也非常适用。最后应用这一技术对海拉尔盆地贝尔凹陷一含油区块的运移通道和成藏规律进行研究,分析该研究区的断裂发育特征和运移通道类型,总结了油源、通道、储层和盖层的空间配置关系,并建立相应的成藏模式。     

走滑活动断裂带断错冲沟变形角特征及其构造意义初探

阐述了通过走滑活动断裂断错冲沟形成变形角研究冲沟形成年代,进而探讨断裂活动特征的方法。并以天桥沟－黄羊川断裂东段为例,对变形角大小和冲沟形成年代及冲沟水平断错距之间的关系进行了探讨,结果表明它们之间关系密切。最后论述了变形角用于走滑活动断裂研究的可能性及意义。     

惠民凹陷中央隆起带沙四上亚段滩坝与风暴岩组合沉积

惠民凹陷沙四上亚段沉积时期,盆地边缘发育三角洲和扇三角洲沉积,受波浪和沿岸流的影响,在中央隆起带滨浅湖区形成了与岸线走向平行或斜交的滩坝砂体和风暴沉积。滩坝沉积成熟度较高,泥质含量少,岩性以中细砂岩和粉砂岩为主,也有少量砾石,砂岩中常见含双壳类化石、生物碎屑和炭屑。滩坝沉积可分为砂坝、砂滩和滩坝间微相,平面上该区滩坝砂体可分为近岸砂滩、近岸砂坝、坝间砂滩、远岸砂坝、远岸砂滩、水下隆起处砂坝和水下隆起处砂滩。此外,受风暴浪的影响,在浪基面和风暴浪基面之间的地带形成风暴沉积,主要由块状层理段、递变层理段、丘状交错层理段、平行层理段和块状泥岩段构成。该组合沉积体系的形成主要受古地形、物源性质、湖平面变化等方面的影响。