Structural and statistical characterization of joints and multi-scale faults in an alternating sandstone and shale turbidite sequence at the Santa Susana Field Laboratory: Implications for their effects on groundwater flow and contaminant transport     

《Journal of Structural Geology》2016

This paper describes the properties of faults and fractures in the Upper Cretaceous Chatsworth Formation exposed at Santa Susana Field Laboratory and its surroundings (Simi Hills, California), where groundwater flow and contamination have been studied for over three decades.The complex depositional architecture of this turbidite consisting of alternating sandstones and shales, interacting with formative stress conditions are responsible for multi-scale fault hierarchies and permeable fractures in which nearly all groundwater flow occurs.Intensity and distribution of background fractures and their relation to bedding thickness are established for sandstones, the dominant lithology. The architecture of faults with increasing displacement is described, and relationships among fault dimensional parameters captured.Data from ∼400 boreholes and piezometers reveal the effect of faults and fractures on groundwater flow. Large hydraulic head differences, observed across fault zones with shale-rich cores, indicate these structures as cross-flow barriers. Moreover, hydraulic head profiles under ambient conditions, and pumping tests suggest strong hydraulic connectivity in all directions to depth of hundreds of meters.This outcrop-based structural characterization relates the horizontal hydraulic conductivity to the observed well-connected fracture network, and explains the strong vertical connectivity across low-hydraulic conductivity shales as faults and sheared fractures provide flow pathways.  相似文献   

Structural control of geothermal reservoirs in extensional tectonic settings: An example from the Upper Rhine Graben     

《Journal of Structural Geology》2016

In extensional tectonic settings major structural elements such as graben boundary faults are typically oriented subparallel to the maximum horizontal stress component S_Hmax. They are often structurally accompanied by transfer zones that trend subparallel to the extension direction. In the Upper Rhine Graben, such transfer faults are typically characterized by strike-slip or oblique-slip kinematics. A major re-orientation of the regional stress field by up to 90° of the Upper Rhine Graben in the Early Miocene led to the present-day normal and strike-slip faulting regimes in the North and South of the Upper Rhine Graben, respectively, and a transition zone in-between. Consequently, conditions for fault frictional failure changed significantly. Moreover, it has been observed during tracer and stimulation experiments that such transfer faults may be of major importance for the hydraulic field of geothermal reservoirs under the present stress condition, especially, when located between production and injection well.In this context we have investigated slip and dilation tendencies (T_S and T_D) of major structural elements at reservoir scale for two representative geothermal sites, Bruchsal (Germany) and Riehen (Switzerland), located close to the Eastern Main Boundary Fault of the Upper Rhine Graben. We have evaluated the quality and uncertainty range of both tendencies with respect to potential variation in S_Hmax orientation. Despite significant differences in orientation of the structures and the stress regimes, the resulting variation of T_S and T_D reveal major similarities concerning the reactivation potential of both, the graben-parallel structures and the transfer faults. The conditions of criticality for tensile failure and non-criticality for shear failure suggest that transfer faults are most likely naturally permeable structures with low stimulation potential. This is in agreement with the absence of both immediate tracer recovery and seismicity in the studied geothermal sites.  相似文献   

Frictional properties of simulated anhydrite-dolomite fault gouge and implications for seismogenic potential     

《Journal of Structural Geology》2016

The frictional properties of anhydrite-dolomite fault gouges, and the effects of CO₂ upon them, are of key importance in assessing the risks associated with CO₂ storage in reservoir formations capped by anhydrite-dolomite sequences, and in understanding seismicity occurring in such formations (such as the Italian Apennines). Therefore, we performed velocity-stepping direct-shear experiments on simulated dolomite, anhydrite and 50:50 anhydrite/dolomite gouges, at representative in-situ conditions (120 °C and σ_n^e = 25 MPa). They were conducted under vacuum, or else using water or CO₂-saturated water as pore fluid (P_f = 15 MPa). Friction coefficients varied between 0.55 and 0.7. All dry samples exhibited velocity-weakening behavior, whereas all wet samples exhibited velocity-strengthening behavior, without or with CO₂. This is consistent with trends previously reported for such gouges. A compilation of literature data shows that the transition from velocity-strengthening to velocity-weakening occurs in these materials between 80 and 120 °C when dry, and between 100 and 150 °C when wet. This implies little seismogenic potential for wet dolomite, anhydrite and mixed gouges under CO₂ storage conditions at 2–4 km depth. Seismic slip in the Italian Apennines at depths of ∼6 km and beyond may be explained by the velocity-weakening behavior expected in anhydrite and especially dolomite at temperatures above 150 °C.  相似文献   

Palaeopermeability structure within fault-damage zones: A snap-shot from microfracture analyses in a strike-slip system     

《Journal of Structural Geology》2016

Understanding fault zone permeability and its spatial distribution allows the assessment of fluid-migration leading to precipitation of hydrothermal minerals. This work is aimed at unraveling the conditions and distribution of fluid transport properties in fault zones based on hydrothermally filled microfractures, which reflect the ‘‘frozen-in’’ instantaneous advective hydrothermal activity and record palaeopermeability conditions of the fault-fracture system. We studied the Jorgillo Fault, an exposed 20 km long, left-lateral strike-slip fault, which juxtaposes Jurassic gabbro against metadiorite belonging to the Atacama Fault System in northern Chile. Tracings of microfracture networks of 19 oriented thin sections from a 400 m long transect across the main fault trace was carried out to estimate the hydraulic properties of the low-strain fault damagezone, adjacent to the high-strain fault core, by assuming penny-shaped microfractures of constant radius and aperture within an anisotropic fracture system. Palaeopermeability values of 9.1*10⁻¹¹ to 3.2*10⁻¹³ m² in the gabbro and of 5.0*10⁻¹⁰ to 1.2*10⁻¹³ m² in the metadiorite were determined, both decreasing perpendicularly away from the fault core. Fracture porosity values range from 40.00% to 0.28%. The Jorgillo Fault has acted as a left-lateral dilational fault-bend, generating large-scale dilation sites north of the JF during co-seismic activity.  相似文献   

Main Frontal thrust deformation and topographic growth of the Mohand Range,northwest Himalaya     

《Journal of Structural Geology》2016

The Main Frontal thrust (MFT) uplifts the Himalayan topographic front. Deciphering MFT deformation kinematics is crucial for understanding how the orogen accommodates continuing continental collision and assessing associated hazards. Here, we (a) detail newly discovered fault-zone exposures along the MFT at the Mohand Range front in northwestern India and (b) apply contemporary fault zone theory to show that the MFT is an emergent fault with a well-developed fault zone overlain by uplifted Quaternary gravels over a horizontal length of ∼700 m. Northward from the front, the fault zone grades from a central, gouge-dominated core to a hanging-wall, rock-dominated damage zone. We observed incohesive, non-foliated breccia, fault gouge, and brittle deformation microstructures within the fractured country rocks (Middle Siwaliks) and outcrop scale, non-plunging folds in the proximal hanging wall. We interpret these observations to suggest that (1) elastico-frictional (brittle) deformation processes operated in the fault zone at near surface (∼1–5 km depth) conditions and (2) the folds formed first at the propagating MFT fault tip, then were subsequently dismembered by the fault itself. Thus, we interpret the Mohand Range as a fault-propagation fold driven by an emergent MFT in contrast to the consensus view that it is a fault-bend fold. A fault-propagation fold model is more consistent with these new observations, the modern range-scale topography, and existing erosion estimates. To further evaluate our proposed structural model, we used a Boundary Element Method-based dislocation model to simulate topographic growth from excess slip at a propagating fault tip. Results show that the frontal topography could have evolved by slip along a (a) near-surface fault plane consistent with the present-day MFT location, or (b) blind MFT at ∼3 km depth farther north near the drainage divide. Comparing modelled vs. measured high resolution (∼16 cm) topographic profiles for each case provides permissible end-member scenarios of an either dynamically-evolving, high erosion, northward-migrating frontal scarp or a static, low, and symmetric, MHT-related fold, respectively. Our integrated approach is expected to deliver an improved understanding of coupled fault-generated deformation and topographic growth that may be applied more broadly across the entire Himalayan front.  相似文献   

Numerical modelling of fault reactivation in carbonate rocks under fluid depletion conditions – 2D generic models with a small isolated fault     

《Journal of Structural Geology》2016

This generic 2D elastic-plastic modelling investigated the reactivation of a small isolated and critically-stressed fault in carbonate rocks at a reservoir depth level for fluid depletion and normal-faulting stress conditions. The model properties and boundary conditions are based on field and laboratory experimental data from a carbonate reservoir. The results show that a pore pressure perturbation of −25 MPa by depletion can lead to the reactivation of the fault and parts of the surrounding damage zones, producing normal-faulting downthrows and strain localization. The mechanism triggering fault reactivation in a carbonate field is the increase of shear stresses with pore-pressure reduction, due to the decrease of the absolute horizontal stress, which leads to an expanded Mohr's circle and mechanical failure, consistent with the predictions of previous poroelastic models. Two scenarios for fault and damage-zone permeability development are explored: (1) large permeability enhancement of a sealing fault upon reactivation, and (2) fault and damage zone permeability development governed by effective mean stress. In the first scenario, the fault becomes highly permeable to across- and along-fault fluid transport, removing local pore pressure highs/lows arising from the presence of the initially sealing fault. In the second scenario, reactivation induces small permeability enhancement in the fault and parts of damage zones, followed by small post-reactivation permeability reduction. Such permeability changes do not appear to change the original flow capacity of the fault or modify the fluid flow velocity fields dramatically.  相似文献   

郯庐断裂(安徽段)两侧肥东群与霍邱群特征性岩石对比研究   总被引：1，自引：0，他引：1  

聂峰  张忠宝  石永红  王娟  唐盼  任光雪 《岩石学报》2016,32(4):1087-1100

郯庐断裂带(安徽段)内部物质组成十分复杂,现有研究认为郯庐内部以扬子板块为主体,对于是否存在西侧华北板块物质混入尚不清楚。为此本文选取了3个特征性样品展开了细致的岩相学研究、温压估算以及锆石U-Pb定年分析,分别为:霍邱群样品WS069-1(磁铁石榴角闪岩)以及样品WS070-1(石榴黑云母片岩);肥东群样品TF003-1(石榴黑云母片岩)。研究发现,霍邱群磁铁石榴角闪岩与肥东群磁铁石榴角闪岩的矿物组合及矿物主量元素特征基本一致。针对霍邱群石榴黑云母片岩与肥东群石榴黑云母片岩的峰期变质条件评价也相互匹配。本文在霍邱群仅发现了~3.2Ga、3.0Ga、2.80Ga、2.74Ga等四组反映源区结晶时代的碎屑锆石年龄,但结合前人对霍邱群和五河群的研究可以认为霍邱群的峰期变质年龄应为2.44Ga,这与肥东群磁铁石榴角闪岩和石榴黑云母片岩的峰期变质年龄2.47~2.41Ga吻合。因此肥东群和霍邱群相同特征性岩石磁铁石榴角闪岩从岩相学、变质P-T条件及变质时代等方面皆具可比性,从而推测肥东群磁铁石榴角闪岩和石榴黑云母片岩构造透镜体应为因郯庐断裂左旋走滑作用而卷入肥东群中的霍邱群岩片。  相似文献   

胶西北新城金矿床热液蚀变作用   总被引：5，自引：3，他引：2  

张潮  黄涛  刘向东  刘育  赵海  王旭东 《岩石学报》2016,32(8):2433-2450

新城金矿床是胶西北金矿集区中典型的破碎带蚀变岩型金矿床,其矿体受控于NE-NNE向焦家断裂及其次级断裂系统,主要赋存于断裂下盘(黄铁)绢英岩与红化花岗岩体中。焦家断裂下盘分带性明显,自主断裂面向外依此发育主断裂面和断层泥、挤压片理带、构造透镜体带、密集节理带和稀疏节理带。其中,主断裂面和断层泥发育粘土化蚀变;挤压片理带发育面状黄铁绢英岩化蚀变,其内赋存黄铁绢英岩型矿体;构造透镜体带发育脉型(黄铁)绢英岩化、面状绢英岩化和硅化蚀变,其次级断裂内赋存石英硫化物脉型矿体;节理带(包括密集节理带和稀疏节理带)主要发育成红化和细脉型(黄铁)绢英岩化,沿节理面赋存细脉型矿体。碳酸盐化蚀变叠加于上述热液蚀变之上。焦家断裂带表现为以水平为主的蚀变-矿化特征,(黄铁)绢英岩化蚀变与金成矿关系最为密切。论文在厘定断裂构造分带与蚀变-矿化分带空间关系的基础上,通过对各类蚀变岩与新鲜新城花岗岩体元素地球化学分析,剖析了热液蚀变作用过程及其机制。选取TiO_2作为不活动组分,质量平衡计算表明,成矿前新城花岗岩体发生红化作用时,带入组分有Fe_2O_3、K_2O、Al_2O_3以及少量Au、Ag、Cu、Pb、Zn、Sb和Bi等,而被带出组分有SiO_2、CaO和Na_2O等;成矿期红化花岗岩体蚀变为(黄铁)绢英岩过程中,明显带入组分有SiO_2、Fe_2O_3、FeO、Al_2O_3、Mg O、K_2O、Au、Ag、As、Cu、Pb、Zn、Sb和Bi等,而被带出组分为Na_2O。稀土元素地球化学特征与REE球粒陨石标准化配分模式曲线表明,红化和(黄铁)绢英岩化热液蚀变作用影响REE迁移。REE分别在红化和(黄铁)绢英岩化蚀变中带入和带出;Eu在红化过程中呈显著带入,表现为显著Eu正异常(δ_(Eu)=1.34),而在(黄铁)绢英岩化蚀变中活化带出,表现出Eu负异常(0.89~0.95)。成矿期发生(黄铁)绢英岩化蚀变时,Eu从氧化态Eu~(3+)转变为Eu~(2+),进入流体被带走,造成Eu负异常。金主要以Au(HS)~-_2形式在变质流体中运移。成矿流体沿片理面运移时,在挤压片理带发生黄铁绢英岩化蚀变,硫化作用使得流体还原硫活度降低,导致Au(HS)~-_2络合物失稳沉淀并赋存于黄铁矿和石英等矿物裂隙或晶格中,形成黄铁绢英岩型矿化;在构造透镜体带,成矿流体沿次级断裂面和碎裂岩裂隙发生蚀变形成脉型(黄铁)绢英岩,成矿元素在次级断裂面/裂隙内沉淀并形成石英硫化物脉型矿化;在节理带,成矿流体压力瞬时降低导致流体发生不混溶现象,使得Au(HS)~-_2络合物失稳沉淀并充填节理中形成细脉型矿化。  相似文献   

断层与幔源二氧化碳气藏的形成和分布——以渤海湾盆地济阳坳陷为例     

李理  钟大赉  杨长春  赵利 《岩石学报》2016,32(7):2209-2216

幔源CO_2气的形成和分布与不同级别断层早白垩世以来的活动密切相关。郯庐断裂带是研究区最主要的成气断层,拆离断层和变换断层这些地壳断层是次要的成气断层,二者于早白垩世143Ma、124Ma、新生代~43Ma、~24Ma和~8Ma的走滑或伸展活动,以及与之准同时的新生代碱性玄武岩浆活动,控制了幔源CO_2气的分散和聚集。它们与基底断裂、盖层断裂共同组成运移通道,其中拆离滑脱处的低速带和盖层断裂中的顺层断层是重要的水平运移通道。早白垩世古太平洋板块俯冲脱水脱气,产生的幔源CO_2气沿着郯庐断裂带向上分散聚集;新生代以来受控于太平洋板块俯冲方向和速度的改变以及印欧板块碰撞的远程效应,形成幔源CO_2气。与此同时郯庐断裂带切割深度亦逐渐加大,~43Ma碱性岩浆活动亦开始形成幔源CO_2气并主要位于断裂带,24Ma和8Ma(5Ma)为新近纪碱性岩浆活动脱气两个主要形成时期。郯庐断裂带的活动使地幔脱气形成的CO_2沿断层走向向上运移,并在作为重要横向运移通道的拆离断层拆离滑脱处,与因岩浆脱气形成的CO_2汇合,再通过陡倾斜、缓倾斜基底断层、盖层断层的接力传递在浅部聚集成藏。预测郯庐断裂带附近是无机成因油气重要的聚集分布区带。  相似文献   

铜陵矿集区深部发现126Ma的正长花岗岩:来自3000m科学钻探的证据   总被引：4，自引：3，他引：1       下载免费PDF全文

吴才来  董树文  王陆太  王次松  雷敏  吴迪 《中国地质》2016,(5):1495-1513

铜陵矿集区3000 m科学钻揭示,舒家店地区在1775 m以下存在红色的正长花岗岩,从该深度继续钻进约700 m后仍为这种岩石,而这种岩石在地表或其他钻孔中从未见到过。研究表明,正长花岗岩以富硅、富碱,富含高场强元素如Zr、Nb、Y和轻稀土元素(Eu除外)和较低的Mg O、Ba和Sr的含量为特征,全岩的10000Ga/Al比值为2.6,Zr+Nb+Ce+Y350×10-6,稀土元素配分模型具有明显的Eu负异常,微量元素原始地幔标准化曲线具有明显的Ba、Sr、P、Ti亏损,表现出A型花岗岩的地球化学属性。锆石LA-MC-ICP-MS U-Pb定年结果表明,该A型花岗岩的年龄为126 Ma,与长江中下游地区其他A型花岗岩的时代一致,属于长江中下游地区三期岩浆活动当中的第二期岩浆活动的产物。研究表明,长江中下游地区3次岩浆作用与岩石圈的多次拆沉作用密切相关,而且每一次拆沉作用都会使壳幔附近的深位岩浆房向地壳浅部迁移,而A型花岗岩则是迁移到浅部的深位岩浆房诱发的地壳部分熔融形成的岩浆,沿断裂带侵位而形成,也标志着本区的构造背景在126 Ma时处于拉张的高峰期。  相似文献