共查询到20条相似文献，搜索用时 531 毫秒
1.
2.
3.
The role of hydrothermal fluids in assisting the activity of strike-slip faults is investigated using a range of new geological, geophysical, and geochemical data obtained on the Argentat fault, Massif Central, France. This fault zone, 180-km-long and 6 to 8 km-width, has experienced coeval intense channeling of hydrothermal fluids and brittle deformation during a short time span (300–295 Ma). According to seismic data, the fault core is a 4-km-wide, vertical zone of high fracture density that rooted in the middle crust (~ 13 km) and that involved fluids in its deeper parts (9–13 km depth). If stress analyses in the fault core and strain analyses in the damage zone both support a left-lateral movement along the fault zone, it is inferred that hydrothermal fluids have strongly influenced fault development, and the resulting fault has influenced fluid flow. Fluid pressure made easier fracturing and faulting in zones of competent rocks units and along rheological boundaries. Repeated cycles of increase of fault-fracture permeability then overpressure of hydrothermal fluids at fault extremity favored strong and fast development of the crustal-scale strike-slip fault. The high permeability obtained along the fault zone permitted a decrease of coupling across the weak fault core. Connections between shallower and lower crustal fluids reservoirs precipitate the decrease of fault activity by quartz precipitation and sulfides deposition. The zones of intense hydrothermal alteration at shallows crustal levels and the zones of fluid overpressure at the base of the upper crust both controlled the final geometry of the crustal-scale fault zone. 相似文献
4.
Charles M. Onasch William M. Dunne Jennie E. Cook Allyson O'Kane 《Journal of Structural Geology》2009,31(9):960
Previous studies [O'Kane, A., Onasch, C.M., Farver, J., 2007. The role of fluids in low-temperature, fault-related deformation of quartz arenite. Journal of Structural Geology 29, 819--836; Cook, J., Dunne, W.M., Onasch, C.M., 2006. Development of a dilatant damage zone along a thrust relay in a low-porosity quartz arenite, Journal of Structural Geology 28, 776–792] found that quartz arenite within two fault zones in the Appalachian foreland thrust belt displays very different structural styles and histories despite deforming at similar pressures and temperatures during the Alleghanian orogeny. A comparison of the grain-scale deformation and fluid histories using transmitted and cathodoluminescence microscopy and fluid inclusion microthermometry, shows that fluid composition was a controlling factor for causing these differences. The Cove fault zone deformed in the presence of aqueous fluids, first a CaCl2 brine and then an iron-rich fluid. The precipitation of quartz cement from the brine kept pace with brittle deformation, maintaining overall rock cohesion in the fault zone. The introduction of iron-rich fluids caused a switch from precipitation to dissolution of quartz, along with precipitation of goethite. In a damage zone along a backthrust in the Cave Mountain anticline, early deformation occurred in the presence of an aqueous fluid from which quartz was precipitated. The latest deformation, however, occurred in the presence of a methane-rich fluid, which inhibited the precipitation of quartz cement producing porous breccias and open fractures despite deformation at 6 km depth. Fluid composition not only affected cementation in the fault zones, but also the selection of grain-scale deformation mechanisms. Therefore, it is a controlling factor in determining the behavior and strength of these fault zones. 相似文献
5.
Martine D. Buatier Brice Lacroix Pierre Labaume Virginie Moutarlier Delphine Charpentier Jean Pierre Sizun Anna Travé 《Swiss Journal of Geoscience》2012,105(2):313-324
Thrusting fault zone in foreland basins are characterized by highly foliated zones generally enriched in phyllosilicates which can play a major role on the mechanical behaviour of the fault. In this context, investigations of synkinematic clay minerals permit to determine the origin of the fluid from which they precipitated as well as the mechanisms of deformation. Our study is focused on clay mineral assemblages (illite and chlorite) in a major thrust fault located in the Monte Perdido massif (southern Pyrenees), a shallow thrust that affects upper cretaceous-paleocene platform carbonates and lower Eocene marls and turbidites. It implied 3?km of displacement of the Monte Perdido thrust unit with respect to the underlying Gavarnie unit. In this area the cleavage development by pressure-solution is linked to the Monte Perdido and Gavarnie thrust activity. The core zone of the fault, about 6?m thick, consists of an interval of intensely deformed clay-bearing rocks bounded by major shear surfaces. The deformed sediment is markedly darker than the protolith. Calcite-quartz shear veins along the shear planes are abundant. Detailed SEM and TEM observations of highly deformed fault zone samples indicate that clay mineral enrichment in the core zone of the fault is not only related to passive increase by pressure-solution mechanism but that dissolution?Crecrystallization of phyllosilicates occurs during deformation. A mineral segregation is observed in the highly deformed zone. Newly formed 2M 1 muscovite is present along the cleavage whereas IIb chlorite crystals fill SV2 shear veins suggesting syntectonic growth of phyllosilicates in the presence of fluids in low-grade metamorphic conditions. These mineralogical reactions act as weakening processes and would favour Monte Perdido fault creeping. 相似文献
6.
Wei-min Donald Chen Hidemi Tanaka Hui-jen Huang Chung-bin Lu Chy-yu Lee Chien-ying Wang 《Tectonophysics》2007,443(3-4):243
In order to understand the fault zone architecture and mechanisms that caused the Chi-Chi earthquake, the Chelungpu drilling project was conducted during April 2000 through a collaborative project between Japan and Taiwan. In this study, chemical and mineralogical variations within the overall Chelungpu fault zone, including variations between less damaged host rocks, damaged zones, and fault cores caused by the Chi-Chi earthquake were examined. Slopes of TiO2 immobile isocons were consistently > 1 for analyses comparing host rocks with rocks from damaged zones or with gouges from fault cores, indicating that volume loss occurred in damaged zones and the fault cores. These results strongly imply that pervasive fluid infiltration occurred within the fault zone. Volume loss within the damaged zone and fault core is interpreted to result from a two-stage process involving: (i) coseismic mechanical wearing and/or dissolution in the fault core, and (ii) fluid infiltration within the fault zone during postseismic and interseismic periods along cracks caused by seismic failure. Semi-quantitative XRD analysis indicates that the kaolinite content consistently increases from the less damaged host rocks to the damaged zone and gouges in each fault core. Mineralogic changes indicate that pervasive acidic fluid infiltration occurred within the fault zones and reacted with the feldspars or muscovite to form kaolinite. Enrichment of kaolinite and illite found in the fault zones of southern drilling site could play some role on the slipping behavior of the southern part of the Chelungpu fault. Greater volume loss in the fault core may have resulted from moderate permeability, combined with the very fine grain nature of pulverized material in the fault core, which enhanced chemical reactions including transformation of feldspars and muscovite to clay minerals. The study results indicate that pervasive fluid infiltration occurred and changed the mineralogical and chemical architecture of fault zones caused by the cyclic earthquakes. 相似文献
7.
断层导波研究加利福尼亚兰德斯和海克特曼恩地震断层带的四维特征(英文) 总被引：1，自引：0，他引：1
Yong—gangLI 《地学前缘》2003,10(4):479-505
美国加利福尼亚州兰德斯和海克特曼恩地区于1992年和1999年先后发生7.4级和7.1级地震,分别在地面产生80km和40km长的断裂带。震后在断裂带布置的密集地震站台记录到明显的断层导波(fault-zone guided waves)。这些导波由断层带内的余震和人工震源激发产生,走时在S波之后,但具有比体波更强的振幅和更长的波列,并具有频散特征。通过对2～7 Hz断层导波的定量分析和三维有限差分数字模拟,获得了震深区断裂带的高分辨内部构造图像以及岩石的物理特性。数字模拟结果表明这些断裂带上存在被严重破碎了的核心层,形成低速、低Q值地震波导。核心破碎带宽约100～200 m,其内地震波波速降为周围岩石的40％～50％,Q值约为10～50。根据岩石断裂力学观点,这一低速、低Q值带可被解释为地震过程中处于断层动态断裂前端的非弹性区(或称之为破碎区,相干过程区)。在兰德斯和海克特曼恩断裂带测得的破碎区宽度与断裂带长度之比约为0.005,基本上符合岩石断裂力学预期的结果。观察到的断层导波还显示兰德斯和海克特曼恩地震中多条断层发生滑移和破碎。兰德斯地震时多条阶梯形断层相继断裂;而在海克特曼恩地震中,断裂带南北两端均出现分枝断裂,深处的分枝断裂较地表出现的破裂状况更为复杂。由三维有限元模拟的动态断裂过程表明,? 相似文献
8.
We have examined microstructures, mineralogical composition, geochemical alteration, and texture of four selected fault rock samples from the Deep Geodynamical Laboratory (DGLab) Gulf of Corinth project using optical microscopy, cathodoluminescence microscopy (CL), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and synchrotron X-ray diffraction measurements. The fault core is composed of red and gray clayey gouge material and surrounded by a damage zone of brecciated limestones. Pressure solution features, calcite veins and calcite clasts in the breccia and gouge material attest the presence of paleo-fluids and fluid-driven mass transfer during deformation. Differences in CL-colors between the matrix and calcite vein cement and inside the vein cement suggest repeated infiltration of fluids with different composition from various sources (formation water and meteoric water). Twin lamellae densities estimated in calcite veins are used as paleo-piezometer. The deduced differential stress is ∼140 ± 70 MPa for the older vein generation and appears to be higher than stress for the youngest veins (45 ± 23 MPa). In spite of the relatively small clay content in both samples, newly formed clay minerals have been observed in gray as well as red clayey gouge material. Differences between gray and red clay gouge material are found in fault rock composition, porosity and clay fabric. The proportion of chlorite in the red gouge is significantly less than that in the gray gouge whereas the initial porosity is significantly higher than in the gray gouge material. The detection of a well-oriented clay fabric in red clay gouge samples is unique in comparison to other major fault zones. 相似文献
9.
Abdullah Mete Ozguner 《Resource Geology》2006,56(1):65-74
Abstract. Replacement-type subsurface sulphur ores of Keciborlu are situated in fault controlled and metasomatically altered fragmental ophiolite media between alkaline Pliocene volcanics of Isparta and Afyon regions, SW Turkey. Subsurface volcanic sulphur-mineralising fluids and gases were brought up along the sulphur-hosting oblique slip fault zone into the oxidising meteoric water-saturated media and the sulphur-ore bodies were developed at more porous, cross-fault locations.
Chemically the sulphotaric alteration of the parent rock and sulphur ore formation is characterised by outward volcanic gas and sulphuric acid leaching and oxidation to sulphur from the crushed porous centres. Consequently, concentric pyritiferous, opaline and argillaceous zones developed adjacent to the sulphur ores. The inner alteration zones progressed and widened toward the outer zones through time and the central sulphur ore developed during a single, continuous phase of mineralisation in the water saturation zone such that the alteration zones do not cross each other. 相似文献
Chemically the sulphotaric alteration of the parent rock and sulphur ore formation is characterised by outward volcanic gas and sulphuric acid leaching and oxidation to sulphur from the crushed porous centres. Consequently, concentric pyritiferous, opaline and argillaceous zones developed adjacent to the sulphur ores. The inner alteration zones progressed and widened toward the outer zones through time and the central sulphur ore developed during a single, continuous phase of mineralisation in the water saturation zone such that the alteration zones do not cross each other. 相似文献
10.
11.
断裂带是一个宽度、长度和高度均与断距呈正比关系的三维地质体,具有典型的二分结构：即断层核和破碎带。断层核由多种类型的断层岩和后期胶结物组成,具有分选差,粘土含量高,颗粒粒径小等特征,表现为具有比围岩更低的孔渗性。破碎带同围岩相比发育大量的裂缝,裂缝的密度随着离断层核距离的增大而逐渐减小,孔渗性较高。断层岩类型取决于断移地层的岩性、成岩程度和断裂变形时期。对于同生断层而言,泥岩和不纯净的砂岩主要发生泥岩涂抹作用;纯净砂岩发生解聚作用,形成颗粒重排的变形带。中成岩阶段发生断裂变形,泥岩发生泥岩涂抹作用,不纯净的砂岩发生碎裂作用和层状硅酸盐涂抹作用,形成碎裂岩和层状硅酸盐 框架断层岩;纯净砂岩主要发生碎裂作用,形成碎裂岩。晚成岩阶段发生断裂变形,碎裂作用成为主要的变形机制,泥岩破碎形成大量断层泥,不纯净的砂岩和纯净的砂岩均形成碎裂岩,其中纯净砂岩形成的碎裂岩由于石英的压溶胶结变得更致密。因此不同成岩阶段、不同岩性形成的断层岩类型不同,泥岩涂抹的排替压力高于层状硅酸盐 框架断层岩和碎裂岩,即使都是碎裂岩,其渗透率相差7个数量级。从断裂带结构看油气运移和保存,断层垂向封闭主要靠剪切型泥岩涂抹的连续性,侧向封闭能力取决于断层岩物性,物性很高的碎裂岩自身封闭能力很差,依靠两盘岩性对接封闭油气,最小断距决定油水界面位置。物性很低的断层岩一般能封住一定高度的油气柱,其是断裂带中泥质含量的函数。断层在储盖层段变形机制差异,决定了断裂输导与封闭油气的耦合,即破碎带双向输导充注,盖层段剪切型泥岩涂抹顶部封闭,断层核遮挡成藏。 相似文献
12.
Gatan Milesi Roger Soliva Patrick Moni Philippe Münch Mathieu Bellanger Olivier Bruguier Michael Bonno Audrey Taillefer Sylvain Mayolle 《地学学报》2019,31(6):569-576
(U‐Th)/He ages on apatite obtained in the vicinity of the Têt fault hydrothermal system show a large variability. In the inner damage zone adjacent to the fault core, where fluid flows are concentrated, AHe ages display a large scatter (3–41 Ma) and apatite ageing. Samples from the outer damage zone show young ages with less dispersion (0.9–21.1 Ma) and apatite rejuvenation. Outside the damage zone, ages are consistent with the regional exhumation history between 20 and 12 Ma. The important age dispersion found in the damage zone is interpreted as the result of 4He mobility during fluid infiltration. Our results show that thermochronological data close to a fault should be interpreted with caution, but may offer a new tool for geothermal exploration. 相似文献
13.
Field studies of fracture systems associated with 58 normal fault zones crosscutting sedimentary rocks were performed in the Northwest German Basin. Fracture orientations, densities, apertures and lengths, as well as fault zone structural indices, were analysed separately for fault damage zones and host rocks. The results show a pronounced difference between carbonate and clastic rocks: mainly in carbonate rocks we found presence of clear damage zones, characterized by higher fracture densities than in the host rocks. While the maximum aperture is similar for both units, the percentage of fractures with large apertures is much higher in the damage zones than in the host rocks.Based on laboratory measurements of Young's moduli and field measurements of fracture densities, we calculate effective stiffnesses Ee, that is the Young's moduli of the in situ rock masses, within the normal fault zones. Compared with carbonate rocks, Ee computed for clastic-rock damage zones decreases significantly less due to lower fracture densities. We conclude that normal fault zones in carbonate rocks have more profound effects on enhancing permeability in fluid reservoirs than those in clastic rocks. The results are of great importance for modelling the hydromechanical behaviour of normal fault zones in subsurface fluid reservoirs. 相似文献
14.
Paul Wilson Rob L. Gawthorpe David Hodgetts Franklin Rarity Ian R. Sharp 《Journal of Structural Geology》2009,31(8):759-775
The geometry and architecture of a well exposed syn-rift normal fault array in the Suez rift is examined. At pre-rift level, the Nukhul fault consists of a single zone of intense deformation up to 10 m wide, with a significant monocline in the hanging wall and much more limited folding in the footwall. At syn-rift level, the fault zone is characterised by a single discrete fault zone less than 2 m wide, with damage zone faults up to approximately 200 m into the hanging wall, and with no significant monocline developed. The evolution of the fault from a buried structure with associated fault-propagation folding, to a surface-breaking structure with associated surface faulting, has led to enhanced bedding-parallel slip at lower levels that is absent at higher levels. Strain is enhanced at breached relay ramps and bends inherited from pre-existing structures that were reactivated during rifting. Damage zone faults observed within the pre-rift show ramp-flat geometries associated with contrast in competency of the layers cut and commonly contain zones of scaly shale or clay smear. Damage zone faults within the syn-rift are commonly very straight, and may be discrete fault planes with no visible fault rock at the scale of observation, or contain relatively thin and simple zones of scaly shale or gouge. The geometric and architectural evolution of the fault array is interpreted to be the result of (i) the evolution from distributed trishear deformation during upward propagation of buried fault tips to surface faulting after faults breach the surface; (ii) differences in deformation response between lithified pre-rift units that display high competence contrasts during deformation, and unlithified syn-rift units that display low competence contrasts during deformation, and; (iii) the history of segmentation, growth and linkage of the faults that make up the fault array. This has important implications for fluid flow in fault zones. 相似文献
15.
Fault affecting silicoclastic sediments are commonly enriched in clay minerals. Clays are sensitive to fluid–rock interactions and deformation mechanisms; in this paper, they are used as proxy for fault activity and behavior. The present study focuses on clay mineral assemblages from the Point Vert normal fault zone located in the Annot sandstones, a Priabonian-Rupelian turbidite succession of the Alpine foredeep in SE France. In this area, the Annot sandstones were buried around 6–8 km below the front of Alpine nappes soon after their deposition and exhumed during the middle-late Miocene. The fault affects arkosic sandstone beds alternating with pelitic layers, and displays throw of about thirty meters. The fault core zone comprises intensely foliated sandstones bounding a corridor of gouge about 20 cm thick. The foliated sandstones display clay concentration along S–C structures characterized by dissolution of K-feldspar and their replacement by mica, associated with quartz pressure solution, intense microfracturation and quartz vein precipitation. The gouge is formed by a clayey matrix containing fragments of foliated sandstones and pelites. However, a detailed petrographical investigation suggests complex polyphase deformation processes. Optical and SEM observations show that the clay minerals fraction of all studied rocks (pelites and sandstones from the damage and core zones of the fault) is dominated by white micas and chlorite. These minerals have two different origins: detrital and newly-formed. Detrital micas are identified by their larger shape and their chemical composition with a lower Fe–Mg content than the newly-formed white micas. In the foliated sandstones, newly-formed white micas are concentrated along S–C structures or replace K-feldspar. Both types of newly formed micas display the same chemical composition confirmed microstructural observations suggesting that they formed in the same conditions. They have the following structural formulas: Na0.05 K0.86 (Al 1.77 Fe0.08 Mg0.15) (Si3.22 Al0.78) O10 (OH)2. They are enriched in Fe and Mg compared to the detrital micas. Newly-formed chlorites are associated with micas along the shear planes. According to microprobe analyses, they present the following structural formula: (Al1,48 Fe2,50 Mg1,84) (Si2,82 Al1,18) O10 (OH)8. All these data suggest that these clay minerals are synkinematic and registered the fault activity. In the gouge samples, illite and chlorite are the major clay minerals; smectite is locally present in some samples.In the foliated sandstones, Kubler Index (KI) ((001) XRD peak width at half height) data and thermodynamic calculations from synkinematic chlorite chemistry suggest that the main fault deformation occurred under temperatures around 220 °C (diagenesis to anchizone boundary). KI measured on pelites and sandstones from the hanging and footwall, display similar values coherent with the maximal burial temperature of the Annot sandstones in this area. The gouge samples have a higher KI index, which could be explained by a reactivation of the fault at lower temperatures during the exhumation of the Annot sandstones formation. 相似文献
16.
Agust Gudmundsson 《Comptes Rendus Geoscience》2004,336(1):85-92
Elastic crack models predict a linear relationship between displacement (u) and rupture (trace) length (L) during slip in a fault zone. Attempts to find universal-scaling laws for L/u, however, have generally failed. Here I propose that these attempts have failed because they do not take into account the changes in the mechanical properties, in particular Young's modulus (stiffness), of the fault zone as it evolves. I propose that Young's modulus affects fault displacement both spatially and temporally: spatially when the trace of a fault at a given time dissects host rocks of different stiffnesses, and temporally when the stiffness of the fault zone itself changes. During the evolution of an active fault zone, the effective Young's modulus of its damage zone and fault core normally decreases, and so does the L/u ratio of the fault. By contrast, during inactive periods sealing and healing of the damage zone and core may increase the stiffness, hence the L/u ratio in subsequent slips. This model predicts that not only will the scaling of L/u within a given fault population vary in space and time, but also that of individual faults. To cite this article: A. Gudmundsson, C. R. Geoscience 336 (2004). 相似文献
17.
胶东中生代金成矿系统 总被引：74，自引：50，他引：24
胶东是我国最重要的金矿集区,其内已发现金矿床150余处,探明金资源储量4000余吨。虽然其金矿床数量众多、资源储量巨大、分布地域广泛、产出空间各异、矿化类型多样,但它们的成矿地球动力学背景、赋矿围岩环境与产出条件及其成矿作用特征总体一致:(1)胶东是一个主要由前寒武纪基底岩石和超高压变质岩块组成、中生代构造-岩浆作用发育的内生热液金矿集区,约130~110Ma的金成矿事件比区域变质作用晚约2000Myr;(2)区域金成矿系统形成于早白垩世的陆缘伸展构造背景,大规模金成矿事件发生在区域NW向伸展转换为NE向伸展后的NEE向挤压变形作用过程中,对应于中国东部岩石圈大规模减薄、华北克拉通破坏和大陆裂谷作用的高峰;(3)金矿床群聚于NNE向玲珑、鹊山和昆嵛山变质核杂岩周边,主要沿前寒武纪变质岩与中生代花岗岩体接触带形成的区域NE-NNE向拆离断层带分布;(4)控矿断裂带经历了早期的韧-脆性变形和晚期的脆性变形构造叠加,在三维空间上呈舒缓波状延展,控制了金矿体的侧伏和分段富集;(5)矿化样式以破碎带蚀变(砾)岩型、(硫化物-)石英脉型和复合脉带型为主,矿石普遍发育压碎、晶粒状和填隙结构,浸染状、细脉浸染状、网脉状、脉状、团块状和块状构造,反映其形成于韧-脆性→脆性变形环境;(6)矿石中金属矿物以黄铁矿、黄铜矿、方铅矿和闪锌矿为主,非金属矿物以石英、绢云母、钾长石、斜长石和方解石为主;金矿物以银金矿和自然金为主、含少量金银矿,主要以可见金的形式赋存于黄铁矿和石英裂隙中、含少量晶隙金和包体金;热液蚀变主要为黄铁矿化、硅化、钾长石化、绢云母化和碳酸盐化;成矿元素为Au-Ag(-Cu-Pb-Zn);呈现出中-低温蚀变矿化组合特征;(7)成矿流体为壳-幔混合来源,以壳源变质流体为主;成矿物质总体来源于中生代活化再造的前寒武纪变质基底岩石,并混入了少量浅部地壳和地幔组分。这种区域成矿特征的一致性,表明胶东金矿集区早白垩世大规模金成矿作用受控于统一的地质事件,属于后生的中-低温热液脉金成矿系统。这些金矿床具有明显的时空群聚分布特征,主要沿三个变质核杂岩周边的岩相接触带产出,且自西向东,金成矿作用年龄由老变新。据此,可划分为胶北隆起蚀变岩-石英脉型、苏鲁超高压变质带硫化物-石英脉型和胶莱盆地北缘蚀变砾岩型三个金成矿子系统。其矿化样式由浸染-细脉、细脉-网脉型和石英脉型→硫化物-石英脉型→蚀变(角)砾岩型变化,矿石结构、构造以细脉浸染状构造为主→环带结构与梳状构造→角砾状构造为特色,反映其成矿作用分别发生于脆-韧性转换带(约15km)→脆性张剪性断裂带→脆性角砾岩带(约5km)环境;矿化、蚀变规模和强度逐渐减弱,成矿物质中浅部壳源组分逐渐增多,可能与其矿床定位空间越来越远离源区有关;成矿温度和压力依次降低、成矿流体中大气降水和/或盆地卤水贡献逐渐增大,与其成矿深度越来越浅、成矿构造环境越来越偏张性的变化趋势一致。这种成矿特征的区域规律性变化反映至少在拆离断层韧-脆性转换带附近→脆性角砾岩带之间的地壳剖面中、在不同的垂向深度上连续成矿。胶东中生代金成矿系统的上述特征明显区别于典型的"与侵入岩有关的金矿"和"造山型金矿",也不同于全球其它已知的金矿床类型,不能被已有成矿模式所涵盖。为合理解释胶东中生代金成矿系统独特的地质与成矿特征,我们提出新的"胶东型金矿"成矿模式,指出古太平洋Izanagi俯冲板片的回转作用可能是引起区域前寒武纪变质基底岩石中成矿物质大规模活化再造的主要驱动机制,成矿流体主体来源于俯冲板片变质脱水,金可能主要以Au(HS)2-络合物的形式在流体中沿拆离断层系输运,在韧-脆性转换带附近→脆性角砾岩带,由于构造空间急剧增大、成矿流体的温度和压力突然降低,CO2、H2S逸出和硫化作用导致Au(HS)2-等金络合物失稳分解,金大规模沉淀富集成矿。 相似文献
18.
藏南金锑铅锌银多金属成矿带又称北喜马拉雅成矿带,是特提斯喜马拉雅成矿域的重要组成部分.康马地区虽处于EW向和SN向断裂交汇的有利成矿位置,但由于海拔高覆盖厚,本区构造控矿规律不明、缺乏有效的勘探方法和可借鉴的找矿范例,这致使找矿工作长期未获突破.近年来,布主金（锑）矿等一批矿床的发现彻底填补了本区的找矿空白.但由于缺乏对矿区断裂带内部组成及其控矿作用的深入认识,布主金（锑）矿的普查勘探工作受到严重制约.本文在详实地质调查基础上,对矿区NW-近EW向和近SN向断裂带内部结构进行了系统剖析,发现两组断裂带均由中部的断层核和外围的破碎带构成.在NW-近EW断裂带,其断层核控制着强揉皱含黄铁矿方解石石英脉型等矿体,而破碎带控制着平直陡倾含多金属硫化物石英脉型和富毒砂石英脉型矿体.在近SN向断裂带,断层核由劈理化带和角砾岩带组成,几乎不含矿.而破碎带中近顺层节理则控制着发育强褐铁矿化和黏土化的高品位矿体.结合区域构造演化,建立了布主矿区断裂带形成、发展及控矿的三阶段演化模型.并在此指导下,以地质事实为基础,结合1:1万土壤化探综合异常及围岩蚀变、矿化露头等找矿信息,圈定找矿靶区6处.并综合考虑多种因素对靶区进行优选,得到A、B、C级靶区各2个.通过对布主矿区断裂带结构、控矿规律、断裂带演化模型等方面的研究和结合化探综合异常的靶区圈定,以期为布主矿区及康马地区矿床成因研究和找矿勘探工作提供有益借鉴. 相似文献
19.
Damage surrounding the core of faults is represented by deformation on a range of scales from microfracturing of the rock matrix to macroscopic fracture networks. The spatial distribution and geometric characterization of damage at various scales can help to predict fault growth processes, subsequent mechanics, bulk hydraulic and seismological properties of a fault zone. Within the excellently exposed Atacama fault system, northern Chile, micro- and macroscale fracture densities and orientation surrounding strike-slip faults with well-constrained displacements ranging over nearly 5 orders of magnitude (0.12 m–5000 m) have been analyzed. Faults have been studied that cut granodiorite and have been passively exhumed from 6 to 10 km depth. This allows direct comparison of the damage surrounding faults of different displacements. The faults consist of a fault core and associated damage zone. Macrofractures in the damage zone are predominantly shear fractures orientated at high angles to the faults studied. They have a reasonably well-defined exponential decrease with distance from the fault core. Microfractures are a combination of open, healed, partially healed and fluid inclusion planes (FIPs). FIPs are the earliest set of fractures and show an exponential decrease in fracture density with perpendicular distance from the fault core. Later microfractures do not show a clear relationship of microfracture density with perpendicular distance from the fault core. Damage zone widths defined by the density of FIPs scale with fault displacement but appear to reach a maximum at a few km displacement. One fault, where damage was characterized on both sides of the fault core shows no damage asymmetry. All faults appear to have a critical microfracture density at the fault core/damage zone boundary that is independent of displacement. An empirical relationship for microfracture density distribution with displacement is presented. Preferred FIP orientations have a high angle to the fault close to the fault core and become more diffuse with distance. Models that predict off-fault damage such as a migrating process zone during fault formation, wear from geometrical irregularities and dynamic rupture are all consistent with our data. We conclude it is very difficult to distinguish between them on the basis of field data alone, at least within the limits of this study. 相似文献
20.
胶东焦家金矿床热液蚀变作用 总被引：12，自引：7，他引：5
胶东作为中国最重要的金矿集区,区内大型-超大型金矿床集中产出,已探明金矿资源量占全国近1/3。其中,破碎带蚀变岩型金矿床是最重要的金矿床类型,占胶东已探明金矿资源量的90%以上,焦家金矿床是著名的"焦家式"破碎带蚀变岩型金矿的命名地,内发育大规模的绢英岩化蚀变带(宽20~200m)和钾化蚀变带(50~300m),蚀变岩型金矿体主要发育在焦家断裂带下盘的绢英岩化蚀变带中。本文通过详细的野外地质观测,查清了焦家金矿床蚀变类型及矿物组合特征,系统采集了不同蚀变类型的岩石样品,进行了岩石元素地球化学分析,运用质量平衡方法讨论了热液蚀变过程中元素迁移规律,初步探讨了焦家金矿床热液蚀变机理。其中,钾化蚀变是成矿前蚀变,钾化花岗岩常以团块状或角砾状残留于黄铁绢英岩和绢英岩内;黄铁绢英岩化和绢英岩化蚀变受焦家断裂及其下盘的次级断裂控制,其规模大小受断裂的规模控制;其中焦家主断裂下盘的绢英岩化蚀变带规模最大,一般宽10~200m;而次级断裂控制的绢英岩化蚀变带规模相对较小,一般以0.1~1m宽的脉状发育在钾化花岗岩内,指示绢英岩化蚀变晚于钾化蚀变。相对于黑云母花岗岩,不同蚀变带岩石普遍表现出高K2O、低Al2O3、CaO和Na2O,而不同蚀变岩石Si、Fe、Mg等元素各表现出不同特征。钾化带岩石表现为K2O的富集,而绢英岩带和黄铁绢英岩带岩石表现为MgO、Fe2O3增加的趋势。黑云母花岗岩发生钾化蚀变过程中,SiO2、K2O表现为明显的带入,指示在钾长石化过程中,流体为富硅的碱性氧化流体。在钾化花岗岩→黄铁绢英岩过程中,Fe2O3表现为明显的带入,可能是由于黑云母等暗色矿物的分解造成的;此外,亲硫元素(Au、Ag、As、Pb、Zn)均表现为带入,特别是成矿元素Au表现为明显的带入。结合本区金的来源可能部分为玲珑黑云母花岗岩,本研究认为钾化过程中的富硅碱性氧化流体通过交代蚀变反应使金从围岩中释放、成为高价态离子活化进入成矿流体,即分散还原态的金(Au0)被活化为氧化态(Au+、Au3+)以AuH3SiO4形式随热液迁移。在绢英岩化过程中,热液中的SiO2等组分损失,引起热液中的AuH3SiO4稳定性降低,造成AuH3SiO4分解,Fe2+、Fe3+被消耗形成黄铁矿,导致金大量沉淀和聚集沉淀,此时完成了金由活化→迁移→沉淀富集成矿。 相似文献