Neoproterozoic–Cambrian synsedimentary magmatism in the Central Iberian Zone (Spain): geology,petrology and geodynamic significance

Petrographic, geochemical and field studies in low grade metamorphic areas (Ciudad Rodrigo-Hurdes-Sierra de Gata domain, CRHSG, central-western Spain) show that Neoproterozoic-Lowermost Cambrian series in the Central Iberian Zone (CIZ) record two kinds of provenance sources including: (1) detrital material derived from recycled orogens and (2) a Cadomian coeval juvenile contribution that governs their isotopic signature. Evidence of magmatism contemporaneous with Neoproterozoic-Cambrian sedimentation is provided by the presence of coherent, massive volcanic rocks (metabasalts, metaandesites, and metarhyolites), volcaniclastic shales, sandstones, conglomerates and breccias. The appearance of volcanogenic lithic fragments and crystals mixed in different proportions with siliciclastic constituents and also present within calcareous components in the sedimentary succession, reinforces this evidence. Although most of the selected volcanic and volcaniclastic samples appear to show tholeiitic affinity, some of them display calc-alkaline affinity. Different trace element ratios, such as Sm/Nd, Nb/Yb and Ta/Yb, suggest a magmatic evolution in the same tectonic setting. The geochemical results reported here support the existence of an active geodynamic setting as a direct contributor to the synsedimentary and magmatic content of the Neoproterozoic–Lowermost Cambrian successions in the CIZ. In particular, the relatively high Nd _(T) values and the high range of f ^Sm/Nd ratios are consistent with an active margin during the Neoproterozoic–Early Cambrian. The existence of tectonic activity is also confirmed by the presence of synsedimentary deformation and volcanic rocks. All of these traits favour a geodynamic model in which the Iberian Cadomian segment represented in the CIZ would have been part of an active northern margin of Gondwana, with an associated magmatic arc and related basins during Neoproterozoic–Lower Cambrian times. A proposed link between the Ossa Morena and the Central Iberian Zones might account for late Cadomian pull-apart basins developed on both sides of the magmatic arc, sharing the same scenario and involving similar magmatic activity during the Neoproterozoic–Cambrian transition.

汶川地震区北西向断裂带遥感分析

利用北京一号小卫星遥感影像判读汶川地震区的断裂构造,发现了一系列100km左右等间距排列的北西向断裂,结果已部分地得到实地考察验证。龙门山断裂与北西向断裂的交汇部位发生强烈地震的几率较高。这些新发现将对汶川Ms8.0级地震发生机理、龙门山断裂带活动性分段、断裂同震位移自南西向北东、由右旋走滑逆断层向右旋走滑断层转变等重大问题提供了新的合理解释。     

Structural controls on fractured coal reservoirs in the southern Appalachian Black Warrior foreland basin

Coal is a nearly impermeable rock type for which the production of fluids requires the presence of open fractures. Basin-wide controls on the fractured coal reservoirs of the Black Warrior foreland basin are demonstrated by the variability of maximum production rates from coalbed methane wells. Reservoir behavior depends on distance from the thrust front. Far from the thrust front, normal faults are barriers to fluid migration and compartmentalize the reservoirs. Close to the thrust front, rates are enhanced along some normal faults, and a new trend is developed. The two trends have the geometry of conjugate strike-slip faults with the same σ₁ direction as the Appalachian fold-thrust belt and are inferred to be the result of late pure-shear deformation of the foreland. Face cleat causes significant permeability anisotropy in some shallow coal seams but does not produce a map-scale production trend.     

Overprinted strike-slip deformation in the southern Valley and Ridge in Pennsylvania

Two major faults, over 32 km long and 6.4 km apart, truncate or overprint most previous folds and faults as they trend more northerly than the previous N25°E to N40°E fold trends. The faults were imposed as the last event in a region undergoing sequential counter-clockwise generation of tectonic structures. The western Big Cove anticline has an early NW verging thrust fault that emplaces resistant rocks on its NW limb. A 16 km overprint by the Cove Fault is manifested as 30 small northeast striking right-lateral strike-slip faults. This suggests major left-lateral strike-slip separation on the Cove Fault, but steep, dip-slip separation also occurs. From south to north the Cove Fault passes from SE dipping beds within the Big Cove anticline, to the vertical beds of the NW limb. Then it crosses four extended, separated, Tuscarora blocks along the ridge, brings Cambro-Ordovician carbonates against Devonian beds, and initiates the zone of overprinted right-lateral faults. Finally, it deflects the Lat 40°N fault zone as it crosses to the next major anticline to the northwest. To the east, the major Path Valley Fault rotates and overprints the earlier Carrick Valley thrust. The Path Valley Fault and Cove Fault may be Mesozoic in age, based upon fault fabrics and overprinting on the east–west Lat 40°N faults.     

Origin of fault domains and fault-domain boundaries (transfer zones and accommodation zones) in extensional provinces: Result of random nucleation and self-organized fault growth

In many extensional provinces, large normal faults dip in the same direction forming fault domains. Features variously named transfer faults, transfer zones, and accommodation zones (hereafter non-genetically referred to as fault-domain boundaries) separate adjacent fault domains. Experimental modeling of distributed extension provides insights on the origin, geometry, and evolution of these fault domains and fault-domain boundaries. In our scaled models, a homogeneous layer of wet clay or dry sand overlies a latex sheet that is stretched orthogonally or obliquely between two rigid sheets. Fault domains and fault-domain boundaries develop in all models in both map view and cross-section. The number, size, and arrangement of fault domains as well as the number and orientation of fault-domain boundaries are variable, even for models with identical boundary conditions. The fault-domain boundaries in our models differ profoundly from those in many published conceptual models of transfer/accommodation zones. In our models, fault-domain boundaries are broad zones of deformation (not discrete strike-slip or oblique-slip faults), their orientations are not systematically related to the extension direction, and they can form spontaneously without any prescribed pre-existing zones of weakness. We propose that fault domains develop because early-formed faults perturb the stress field, causing new nearby faults to dip in the same direction (self-organized growth). As extension continues, faults from adjacent fault domains propagate toward each another. Because opposite-dipping faults interfere with one another in the zone of overlap, the faults stop propagating. In this case, the geometry of the domain boundaries depends on the spatial arrangement of the earliest formed faults, a result of the random distribution of the largest flaws at which the faults nucleate.     

从重力异常探讨威宁地区深部地质构造

从1：20万布格重力异常分离出来的剩余重力异常和水平梯度重力异常为主要研究对象,结合威宁地区的地质、物化探、遥感资料,揭示该区深部存在8条断裂,火山机构1个,基性-超基性侵入岩体1个。     

准噶尔盆地玛湖凹陷三叠系源上砂砾岩扇—断—压三控大面积成藏模式

准噶尔盆地玛湖富烃凹陷下三叠统百口泉组新近发现了我国首个源上大面积连续型砂砾岩油藏群,是对全球"连续型"油气藏研究的新补充,但其成藏机理和模式并不很清楚。为加强对其的理论认识,并为下步勘探提供参考,基于油气生、储、盖、圈、运、保等基础石油地质条件,并结合油气藏特征,进行了成藏条件与成藏模式的综合研究。结果表明,优质充足的下二叠统风城组碱湖油气来源、规模有效的扇三角洲前缘砂砾岩储层、多重组合的扇三角洲平原致密砾岩、泥岩和断裂封盖保存、沟通良好的高角度断裂输导体系、平缓连续的构造背景奠定了大面积连续成藏的地质基础。在此背景下,高成熟的风城组所生成油气,在切穿烃源灶和储层的高角度压扭性断裂沟通下,优先充注物性相对好的扇三角洲前缘水下河道砂岩和砂质细砾岩,并且在地层异常高压促进下,控制着油气富集程度,使得油气成藏表现为大型缓坡浅水扇三角洲沉积控制下的源上扇-断-压三控大面积"连续型"。百口泉组油气藏具有的油质轻且含气、微裂缝广泛发育,以及异常高压等,决定了砾岩储层虽总体低孔低渗,但依旧能够高产。在油源断裂沟通的斜坡区上倾方向,叠合地层异常高压以及扇三角洲前缘水下河道砂砾岩的区域是下步有利勘探方向。     

准噶尔盆地南缘前陆冲断带深层地质结构及对油气藏的控制作用:以霍尔果斯—玛纳斯—吐谷鲁褶皱冲断带为例

准噶尔盆地南缘前陆冲断带位于天山北麓,在晚新生代强烈的挤压作用下,地表发育数排背斜带。由于构造变形复杂、地震反射成像质量较差,对深层地质结构争议较大,另外前新生代盆地原型对晚新生代以来的褶皱冲断带构造格局的影响也尚未探讨。霍尔果斯—玛纳斯—吐谷鲁(简称霍-玛-吐)褶皱冲断带位于准噶尔盆地南缘前陆冲断带地表第二排背斜带,利用最新采集和处理的地震反射资料,并结合地表地质露头建立深层构造模型;利用平衡地质剖面复原和构造物理模拟实验的方法探索早侏罗世盆地原型结构对现今褶皱冲断带构造格局的影响;在此基础上分析霍-玛-吐褶皱冲断带深层天然气富集规律。霍-玛-吐褶皱冲断带垂向上发育古近系—第四系逆冲推覆构造、中上侏罗统—白垩系构造楔和下侏罗统半地堑断陷结构。控制早侏罗世半地堑系统的高角度正断层在晚期挤压构造变形体系中充当逆断坡,并控制上覆构造楔和浅层逆冲推覆构造的发育。早侏罗世半地堑系统具有分段性,并通过侧向断坡进行连接,侧向断坡上覆地层发育南北向走滑调节断层。油气勘探现状表明,霍-玛-吐褶皱冲断带内部南北向走滑调节断层具有高效沟通下侏罗统烃源岩的特点,是控制天然气的富集的重要因素。以上研究表明,中西部陆内前陆冲断带前新生代古构造对于晚新生代挤压冲断构造格局和深层天然气富集规律具有重要意义。     

冀中坳陷北部河西务断层结构及新近纪以来的活动特征分析

河西务断层是渤海湾盆地冀中坳陷北部地区一条重要的控盆断裂,新近纪-第四纪时期渤海湾盆地整体进入热沉降 阶段后,该断层仍然存在构造活动,2018年在河北永清县发生的地震就是由该断层的活动所引发。文章利用地震数据对河 西务断层的结构特征和新近纪以来的活动特征进行分析,结果表明,河西务断层新近纪以来具有右旋走滑的张扭特征,主 断层在剖面上具有负花状结构,平面上具有分段性,北段和南段兼具右旋走滑和拉张的特征,中段则主要表现为右旋走滑 特征。运动学模型表明,这种分段差异性主要由各段主断层走向和块体走滑运动方向的夹角所决定。     

Unravelling the evolution of an Alpine to post-glacially active fault in the Swiss Alps

The Gemmi fault is a prominent NW–SE striking lineament that crosses the Gemmi Pass in the central Swiss Alps. A multidisciplinary investigation of this structure that included geological mapping, joint profiling, cathodoluminescence and scanning electron microscopy, stable isotope measurements, luminescence- and U-TH-dating, 3D ground penetrating radar (GPR) surveying and trenching reveals a history of fault movements from the Miocene to the Holocene. The main fault zone comprises a 0.5–3 m thick calcite cataclasite formed during several cycles of veining and brittle deformation. Displaced Cretaceous rock layers show an apparent dextral slip of 10 m along the fault.A detailed study of a small sediment-filled depression that crosses the fault provides evidence for a post-glacial reactivation of the fault. A trench excavated across the fault exposed a Late-Glacial-age loess layer and late Holocene colluvial-like slope-wash deposits that showed evidence for fault displacement of a few centimeters, indicating a recent strike-slip reactivation of the fault. Focal mechanisms of recent instrumentally recorded earthquakes are consistent with our findings that show that the fault at the Gemmi Pass, together with other parallel faults in this area, may be reactivated in today's stress field. Taking together all the observations of its ancient and recent activity, the Gemmi fault can be viewed as a window through geological space and time.