Primary vs. secondary curved fold axes: Deciphering the origin of the Aït Attab syncline (Moroccan High Atlas) using paleomagnetic data     

《Journal of Structural Geology》2015

The Aït Attab syncline, located in the Central High Atlas, displays a curved geometry in plan view, and is considered as one of the most spectacular fold shapes in the Central High Atlasic belt. We conducted a paleomagnetic study in Jurassic-Cretaceous red beds to investigate the origin of this geometry. The Natural Remanent Magnetization (NRM) is dominated by a secondary magnetization carried by haematite with unvarying normal polarity that has been dated at about 100 Ma. The regional fold test performed in both limbs of the syncline is positive and the paleomagnetic vectors (after tectonic correction) are parallel throughout the curvature, indicating a negative oroclinal bending test. These results are inconsistent with previous works that consider the bent geometry of this syncline to result from subsequent distortion of originally NE–SW trending structures by rotation about a vertical axis. We interpret the NRM data to demonstrate that the changing trend of the Aït Attab syncline is a primary feature, resulting from the influence of pre-existing, NE–SW and E-W-striking extensional faults that developed during a strike-slip regime. Paleomagnetic results also reveal that the tilting observed in the sampled red beds is post Albian, probably linked to the Cenozoic inversion of the High Atlasic belt.  相似文献   

粤东梅州地区1：5万区调主要成果与进展     

卓伟华  张忠进  吴小辉  彭峰  唐富贵 《华南地质与矿产》2011,27(4):319-326

在粤东梅州地区完成的1：5万区域地质调查,对区内地层进行了多重划分和对比研究,理清了地层层序;将“兴梅混合岩田”解体为变质表壳岩和变质深成岩;采用双重填图法,查明了火山岩相、火山机构分布特征,划分了火山活动旋回;对侵入岩进行重新划分和研究,首次将永和北．三枫侵入体解体为超基性、中性和中酸性侵入岩;对构造形迹进行调查研究...  相似文献   

新疆乌东矿区八道湾向斜两翼瓦斯地质规律研究     

马利军 《中国煤炭地质》2011,(7):33-35,68

以煤矿钻孔煤样瓦斯数据及井下实测瓦斯含量为依据,分析了乌东矿区构造对瓦斯赋存的控制作用,认为区内以七道湾背斜、八道湾向斜和F2逆冲断层为主要构造形迹,并控制了煤层的赋存状态和瓦斯分布规律;八道湾向斜南翼地层倾角陡近乎直立,地层局部倒转,有利于瓦斯逸散,而北翼煤层倾角缓,且受到矿区南部碗窑沟逆冲断层（F2）挤压作用,断面形成瓦斯的＂隔挡＂面,阻断了瓦斯的逸散通道,造成向斜北翼瓦斯含量高于南翼;瓦斯含量与煤层埋深呈正相关关系。随着各矿向下延深开采,瓦斯涌出量将会逐渐加大。因此,掌握矿区的瓦斯地质规律,对其安全生产具有指导意义。  相似文献   

Fan-shaped staurolite in the Bolton syncline, eastern Connecticut: evidence for porphyroblast rotation during growth     

M. D. BUSA  N. H. GRAY 《Journal of Metamorphic Geology》2005,23(9):881-895

Fan‐shaped polycrystalline staurolite porphyroblasts, 3–4 cm in length and 0.5 cm in width, occur together with centimetre‐sized euhedral prismatic staurolite porphyroblasts in pelitic schists of the Littleton Formation on the western overturned limb of the Bolton syncline in eastern Connecticut. The fans consist of intergrown planar splays of [001] elongated prisms, which are crudely radial from a single apex. The apical angles of the radial groupings range up to 70°. The orientations of the individual staurolite prisms are related by a rigid rotation about an axis perpendicular to the fan plane. The zone axes [001] always lie in the plane of the fan. Although the angle between the [100] zone axes of the individual prisms is uniform in each fan, it ranges from +30° to ?30° in different fans. Internally, the fans display: (i) remnants of a passively captured S_i foliation defined by disc‐shaped quartz blebs (type 1 inclusions) and layers of very fine carbonaceous material and tabular ilmenite platelets; (ii) bent staurolite blades and undulose extinction along low‐angle (010) subgrain boundaries near the apex of the fans; (iii) wedge‐shaped dilatational zones containing equigranular inclusion‐free quartz, mica and staurolite, and (iv) growth‐related quartz inclusion trails roughly perpendicular to a crystal face (type 2 inclusions). The S_i inclusion trails are typically perpendicular to the fan surface, radiate parallel to the blades, and show little to no curvature except at the very edge of the fans where they abruptly curve through nearly 90° into parallelism with an external S_e foliation. Careful examination of the three‐dimensional geometry of fans based on U‐stage measurements, serial sections and two‐circle optical goniometric measurements permits a detailed reconstruction of their sequential development. The origin of a fan involves limited intracrystalline deformation and brittle crack dilation, spalling, rotation, and growth of small marginal fragments and of new staurolite along wedge‐shaped zones along the S_i inclusion surfaces. Fans preferentially develop in porphyroblasts in which S_i is subparallel to the 010 cleavage. These internal features reflect the rotation and deformation of a brittle porphyroblast relative to syn‐growth shear stresses.  相似文献   

葛店矿双庙扩大区三维地震勘探     

张彦湘 《中国煤炭地质》2008,20(2):53-56

葛店煤矿双庙扩大区位于豫、皖两省交界处。勘探区为一轴向北北东向的不对称向斜构造,地层倾角26°～30°,测区深部有岩浆岩侵入体,严重影响煤层赋存形态;地表条件复杂,村庄密集、河流较多,测区东侧塌陷区水塘大面积分布．三维地震勘探野外施工难度大。本区地震勘探观测系统设计为12线18炮制,为避免偏移归位及叠加次数降低等问题,在向斜轴部两侧、村子周边及河岸处适当加密炮点,并在塌陷区利用钢钎插置检波器以保证CDP点完整性。数据处理采取了叠前反褶积、叠前时间偏移等技术,数据处理效果显著。遵循多波组对比、多个数据体综合解释的原则,以纵向、横向和任意时间剖面相结合,充分利用三维可视化技术进行地震资料解释。本次勘探成果查明了主采煤层三2^2、二2煤层的构造形态及埋藏深度;解释落差5m以上断层34条,其中修改原有断层5条;另外新发现小于5m的异常断点22个。经巷道验证煤层底板标高误差0．43％～1．96％,巷道已揭露断层7条,与解释成果基本一致。  相似文献   

贾汪煤田为何未能向北东继续延伸     

刘明雷  冯建强 《中国煤田地质》2003,15(2):5-7

贾汪煤田的基本构造形态为贾汪向斜。通过对贾汪向斜北东延长段原地系统和外来系统的分析研究，认为在贾汪石炭——二叠纪煤田北界伏山前断裂的北东盘上，受构造应力的影响，奥陶系沿着其与寒武系界面间的软弱层被推覆，在原地代之以大面积分布的是青白口——震旦系及部分寒武系而非石炭——二叠系，从而造成了贾汪煤田没有向北东继续延伸。  相似文献   

Halocinèse précoce associée au rifting jurassique dans l'Atlas central de Tunisie (région de Majoura–El Hfay)     

Dorra Tanfous Amri  Mourad Bédir  Mohamed Soussi  Hajer Azaiez  Lahoussine Zitouni  M. Hédi Inoubli  Kamel Ben Boubaker 《Comptes Rendus Geoscience》2005,337(7):703-711

Seismic and sequence stratigraphy analyses, petroleum-well control and surface data studies of the Majoura–El Hfay region in the Central Atlas of Tunisia had led to identify and calibrate Jurassic seismic horizons. Seismic stratigraphic sections, seismic tectonics analyses, isochron and isopach mapping of Jurassic sequences show a differentiated structuring of platform and depocentre blocks limited by deep-seated NE–SW, north–south east–west and NW–SE faults intruded by Upper Triassic salt. The early salt migration seems to have started by the platform fracturing during the Lower Liassic rifting event. These movements are fossilized by thickness variations of Jurassic horizons, aggrading and retrograding onlap and toplap structures between subsiding rim-syncline gutters and high platform flanks intruded by salt pillows and domes. The salt migration is also attested by Middle and Upper Jurassic space depocentre migrations. Around the Majoura–El Hfay study blocks bounded by master faults, Triassic salt have pierced the Cretaceous and Tertiary sedimentary cover in a salt diapir extrusion and salt wall structures. To cite this article: D. Tanfous Amri et al., C. R. Geoscience 337 (2005).  相似文献   

地质图切剖面中褶皱构造的计算机辅助编绘   总被引：7，自引：2，他引：7  

方世明  赵温霞等 《地质与勘探》2002,38(3):52-54

计算机对褶皱的处理能力的强弱，是决定地质图切剖面计算机辅助编绘系统实用价值大小的一个重要指标。以兰姆赛分类方案为基础，通过褶皱形态的几何特征分析，提出一种针对简单背，向斜构造的计算机辅助设计算法，并编写出相应的褶皱剖面形态的模拟程序，利用各种不同形态的褶皱实例进行试验。证明该种算法正确可靠，将其嵌入作先前开发的地质图切剖面编绘程序中，可大大提高地质图切剖面编绘的自动化水平。  相似文献   

圆梁山隧道毛坝向斜段典型岩溶现象及发育分布特征   总被引：11，自引：0，他引：11  

屈科  许模  徐则民  王科  蒋良文 《地质灾害与环境保护》2001,12(1):43-47

圆梁山隧道毛坝向斜段核部及两翼的可溶地层中发衣分布有大量的典型岩溶现象，本文详尽讨论了岩溶洼地，槽谷，巨型组合槽谷和地下溶洞等大型岩溶形态的基本特征，形成机制，受控因素，并进一步认识到其发育分布主要受控于岩性和构造因素。  相似文献   

山西交城水峪贯区域构造及地貌形成因素分析     

何晓东 《吉林地质》2013,(4):23-26

交城水峪贯区域地质构造复杂,三大岩类齐全,岩浆岩类发育,岩层露头特征明显,并伴有煤、铁等矿产分布。区内主要发育NNW、NNE、SN向构造体系,从构造、地貌、地层及岩浆岩等因素分析,本区域经历了多次地质构造运动,对其影响最大的为燕山运动。在早燕山期构造运动中近EW向的主应力作用下形成了本区域古洞道向斜、鲁沿向斜、山前大断裂等构造及狐偃山六大岩浆岩体,后期受应力转变造成本区域X型剪节理发育及构造扭曲等现象。形成了本区域现代地质构造及地貌轮廓。  相似文献