Fracturing and calcite cementation controlling fluid flow in the shallow-water carbonates of the Jandaíra Formation,Brazil     

《Marine and Petroleum Geology》2017

The shallow-marine carbonate rocks of the Jandaíra Formation have been subject to significant permeability variations through time due to various events of fracturing and calcite cementation. As a consequence, the Jandaíra Formation accommodated fluid flow only during specific moments in time. We reconstructed these episodes of fluid flow based on isotope characterizations and microscope characteristics of calcite veins and host rock cements. The Jandaíra Formation, which belongs to the post-rift sequence of the Potiguar Basin in northeast Brazil, was deposited from the Turonian onward until a marine regression exposed it in the Campanian. Due to the subaerial exposure, meteoric waters flushed out marine connate waters, leading to an event of early diagenesis and full cementation of the Jandaíra Formation. Fluid flow through the resulting impermeable carbonate formation appears to be closely related to fracturing. Fracturing in the Late Cretaceous induced a drastic increase in permeability, giving rise to extensive fluid circulation. Host rock dissolution associated to the circulating fluids led to calcite vein cementation within the fracture network, causing it to regain an impermeable and sealing character. In the research area, fluid flow occurred during early burial of the Jandaíra Formation at estimated depths of 400–900 m. This study documents the first application of fluid inclusion isotope analysis on vein precipitates, which allowed full isotopic characterization of the paleo-fluids responsible for calcite vein cementation. The fluid inclusion isotope data indicate that upwelling of groundwater from the underlying Açu sandstones provided the fluids to the fracture network. In Miocene times, renewed tectonic compression of a lower intensity created a secondary fracture network in the Jandaíra Formation. The density of this fracture network, however, was too low to induce a new episode of fluid circulation. As a result, this tectonic event is associated with the development of barren extensional fractures.  相似文献   

Fluid behaviors from the seismogenic region of Longmenshan fault zone,eastern Tibetan PlateauSCIEI北大核心CSCD     

李春锐  李海兵  司家亮  王焕  吴琼  张进江 《岩石学报》2022,(11):3559-3577

震间期、同震期和震后期流体对断裂带物质的强度和运动性质起到重要作用。前人已识别出断裂带浅部区域流体对断层的弱化以及矿物沉淀导致的断层愈合,然而对于断裂带深部流体的研究鲜有报道。为深入了解孕震区流体行为以及地震成核过程中流体对断层的影响,本文以龙门山断裂带的映秀-北川断裂南段虹口乡八角庙村附近碎裂岩滑动带中石英和方解石脉为研究对象,通过对断裂带脉体的显微构造、碳氧同位素和主量元素含量等分析,开展地震相关脉体的特征结构、流体来源和矿物沉淀环境的研究。结果表明,碎裂岩主滑移带由颜色结构不同的三层断层泥和细小的方解石条带组成,在主滑动带边部和上盘碎裂岩中则分别发育了指示震间期、同震期和震后期三个阶段断层活动的脉体:(1)沿阶步生长的纤维状方解石脉和拉伸型柱状颗粒方解石脉;(2)断层泥楔入脉;(3)近等粒状方解石脉以及具有横向竞争生长结构的非等粒状方解石脉和石英脉。它们分别代表了震间期封闭的还原环境下的微滑动、同震外源高压流体注入以及震后开放的氧化环境至还原环境下的矿物沉淀。碳氧同位素结果表明主滑动带和碎裂岩方解石脉δ^(18)O V-PDB值为-20.5‰~-20.3‰,低于围岩碳酸钙胶结物,表明方解石脉具有大气水来源特征。方解石沉淀温度结合地温梯度表明方解石脉的形成深度大于4km,与碎裂岩形成深度及龙门山断裂带震源深度一致。该地区方解石脉和石英脉的研究深化了关于龙门山断裂带孕震区流体行为的理解,并且对进一步认识震间期、同震期和震后期断层的强度变化机制具有重要意义。  相似文献   

Characterisation of deformation and flow mechanics around porphyroclasts in a calcite marble ultramylonite by means of EBSD analysis   总被引：1，自引：0，他引：1  

Michel Bestmann  David J. Prior  Bernhard Grasemann 《Tectonophysics》2006,413(3-4):185-200

This paper studies the flow heterogeneity around porphyroclasts associated with greenschist facies deformation of a calcite marble shear zone. Microstructural data from electron backscatter diffraction analyses (EBSD) are used to constrain the flow mechanics of this dominantly non-coaxial type of deformation. The microstructure of the undisturbed ultramylonite (grain-size range 5–100 μm, mean 40 μm) is interpreted to represent steady-state (time-independent) flow conditions with flow planes parallel to the shear zone boundary. Single calcite porphyroclasts (grain-size 1–3 mm) caused flow perturbation in the fine-grained marble ultramylonite. It is the shape, in particular, of these rigid porphyroclasts that controls their rotational behaviour during deformation and, therefore, the development of specific flow fabrics. The flow planes around elongated-rhomboidal, stable porphyroclasts change the orientation to become roughly parallel to the porphyroclast margin, whereas the geometry of flow planes around nearly equant, rotating porphyroclasts describes a δ-type flow pattern. We infer that to some extent decoupling at the clast–matrix interface has occurred to guarantee a stable orientation of elongated porphyroclasts, but was not sufficient to reduce the rotation rate of equant clasts to zero. According to the flow deflection, the general crystallographic preferred orientation (CPO) with its single c-axis maximum perpendicular to the flow plane is rotated about an axis which is (sub)parallel to the kinematic rotation axis of the shear zone. Ultramylonite microstructures, CPOs and misorientation data are best explained by the dual operation of grain-size-insensitive (dislocation creep with recovery and recrystallization) and grain-size-sensitive (diffusion creep) mechanisms. The limited grain-size reduction around porphyroclasts suggests that the grain-size-insensitive mechanisms controlled rheology.  相似文献   

Speleogenetic history of the Hungarian hydrothermal karst   总被引：2，自引：0，他引：2  

Y. V. Dublyansky 《Environmental Geology》1995,25(1):24-35

The hydrothermal karst of Hungary displays at least two principal stages of development in two differing environments. Caves of an early stage were formed within a deep zone of low thermal gradient. These caves (vugs) are small (tens of centimeters) and lined with scalenohedral crystals of calcite that are often in association with barite. Calcite yields fluid inclusion temperatures of 55–95°C and is depleted in¹⁸O (–11.2 to –17.6 per mil PDB). The caves were formed by ascending thermal waters charged with CO₂. Solubility of CaCO₃ in such a system gradually increases with the ascent of the fluid (solutional zone) but drops sharply at a depth of –250 m to –500 m below the water surface (depositional zone). Caves formed in the solutional zone may be shifted into the depositional zone due to tectonic uplift, and calcite lines their walls. Large caves (tens to thousands of cubic meters) of a late stage were formed within a shallow zone of high thermal gradient immediately below and above the thermal water table. The calcite of the phreatic crusts has a rhombohedral habit, displays lower fluid inclusion temperatures (35–55°C and less), and a depletion in¹⁸O of –9.5 to –14.6 per mil PDB. Several powerful cave-forming processes may operate there including convection, mixing/cooling corrosion, and condensation corrosion. Due to differences in the rate of tectonic uplift, rate of hydrothermal system decay, and hydrogeologic pattern, these caves were either filled with water for a long period of time (phreatic calcite crusts are formed) or partly dewatered early in their history (waterline and subaerial speleothems are formed). The zones of thermal cave formation recognized in Hungary may have a universal character. Very similar features are found in other hydrothermal karst areas of the world (Kirghizia, Algeria, South Dakota).  相似文献   

Broad distribution of crystal-field environments for Nd<Superscript>3+</Superscript> in calcite     

S. H.?Withers  R. E.?PealeEmail author  A. F.?Schulte  G.?Braunstein  K. M.?Beck  W. P.?Hess  R. J.?Reeder 《Physics and Chemistry of Minerals》2003,30(7):440-448

Calcite crystals were grown from solution with single-crystal dimensions up to 3 mm and doped up to 0.1 at% with Nd³⁺ ions. Phase purity was verified by powder X-ray diffraction. The concentration of Nd³⁺ was measured by energy-dispersive spectrometry and Rutherford backscattering spectrometry. Micro X-ray fluorescence mapping of the calcite grains indicates uniform Nd distribution in as-grown crystal grains. X-ray absorption fine structure suggests that Nd³⁺ is substituted for Ca²⁺ with local lattice distortion. Temperature-dependent near-infrared spectroscopy of Nd³⁺ impurities in calcite reveals large inhomogeneous linewidths and smooth line profiles that are characteristic of glassy hosts, though the samples are well crystallized.  相似文献   

Magnetic anisotropy of calcite at room-temperature     

Volkmar Schmidt  Detlef Günther  Ann M. Hirt 《Tectonophysics》2006,418(1-2):63

The intrinsic room temperature magnetic properties of pure calcite were determined from a series of natural crystals, and they were found to be highly dependent on the chemical composition. In general, dia-, para-, and ferromagnetic components contribute to the magnetic susceptibility and the anisotropy of magnetic susceptibility (AMS). With a combination of magnetic measurements and chemical analysis these three contributions were determined and related to their mineralogical sources. The intrinsic diamagnetic susceptibility of pure calcite is − 4.46 ± 0.16 × 10^− 9 m³/kg (− 12.09 ± 0.5 × 10^− 6 SI) and the susceptibility difference is 4.06 ± 0.03 × 10^− 10 m³/kg (1.10 ± 0.01 × 10^− 6 SI). These diamagnetic properties are easily dominated by other components. The paramagnetic contribution is due to paramagnetic ions in the crystal lattice that substitute for calcium; these are mainly iron and manganese. The measured paramagnetic susceptibility agrees with the values calculated from the known concentration of paramagnetic ions in the crystals according to the Curie law of paramagnetic susceptibility. Substituted iron leads to an increase in the AMS. The paramagnetic susceptibility difference was found to correlate linearly with the iron content for concentrations between 500 and 10,000 ppm. An empirical relation was determined: (k₁ − k₃)^para (kg/m³) = Fe-content (ppm) × (1 ± 0.1) × 10^− 12 (kg/m³/ppm). The maximum susceptibility difference (Δk = k₁ − k₃) was found to be unaffected by iron contents below 100 ppm. Ferromagnetic contributions due to inclusions of ferromagnetic minerals can dominate the susceptibility. They were detected by acquisition of isothermal remanent magnetization (IRM) and their contribution to the AMS was separated by high-field measurements.  相似文献   

江汉盆地白垩系渔洋组砂岩的成岩作用及其热力学分析   总被引：4，自引：2，他引：4  

关平张文涛  吴雪松熊金玉 《岩石学报》2006,22(8):2144-2150

江汉盆地白垩系渔洋组砂岩存在五种类型的成岩作用。其中,与油气运移有关并对储层孔隙演化产生重要影响的是硬石膏的胶结与交代作用和后期方解石再次胶结作用。为了更好的研究成岩作用发生的控制因素以及成岩环境的变化,我们通过细致的热力学推导,绘制出包含方解石、白云石和硬石膏等矿物相在内的五组分相图。通过相图分析可以看出,pH 值在成岩作用过程中有着重要的作用。方解石和白云石的胶结及交代作用代表了偏中性或碱性的成岩环境;而硬石膏的胶结及交代作用则表明成岩环境由中性或碱性向酸性转变,例如酸性的油气前锋流体的注入。另外,成岩环境中阳离子(Ca~(2 )、Mg~(2 ))和阴离子(CO_3~(2-)、SO_4~(2-))的浓度对方解石、白云石和硬石膏的胶结、溶解及交代作用也有重要影响。  相似文献   

Interaction of rock and atmosphere: patinas on Mediterranean monuments   总被引：2，自引：0，他引：2  

M. Garcia-Vallès  M. Vendrell-Saz  J. Molera  F. Blazquez 《Environmental Geology》1998,36(1-2):137-149

 This paper analyzes – chemically, mineralogically, and petrolographically – the patinas developed on several Mediterranean monuments made with different stones (siliceous and carbonatic) in order to establish their origin and their evolution under the present environmental conditions, and to evaluate the environmental parameters controling their development. Most of the patinas show a common sequence of layers, which, from the outer to the inner zone, are: (1) present bioactivity and/or biological remains, (2) gypsum-rich patina, and (3) calcitic brown to orange patina. Each one may exhibit different fabrics (from micritic to stromatolitic) and may be more or less continuous and homogeneous. The main mineral components are calcite and gypsum, but Ca-oxalates and Ca-phosphates have also been found associated to biological structures, as well as quartz and clays. The different fabrics and textures have been interpreted as consequence of changes in the environmental conditions which seem to be related to the biological activity, facilitating the growth of different organisms and leading to the development of a deposit with distinct characteristics (fabric, texture, porosity, etc.). The gypsum-rich patina has been interpreted as a sulphation of the underlying calcitic layer by the action of atmospheric pollutants or as dry or wet deposition from the atmospheric dust. The mineralogy and texture of the patina is independent of the nature of the underlying rock and only in few cases a micritization process has been observed as interaction between patina and rock. Recently, the penetration of endolithic microflora produced drillings and the development of a fissuration system parallel to the surface, and thus the detachment of the crust from the rock and even flackening of the rock itself has been observed. Consequently, under the present climatic conditions in the Mediterranean basin, erosion is a more active process than deposition, and the crusts and patinas show a tendency to disappear from the surface of the monuments. Received: 3 November 1996 · Accepted: 10 September 1997  相似文献   

长江三峡库首区某些断层新活动年龄数据应用的制约   总被引：1，自引：0，他引：1  

周继颐  林文祝 《工程地质学报》1998,6(2):134-138

近一、二十年来, 为了研究三峡大坝库首区周围断层活动对大坝稳定性的影响, 采用TL、ESR、FT、14C和U系等测年法测了大量断层活动年龄数据。这些年龄数据范围很宽, 瞠目结舌, 无可措手。本文从1, 各测年法的适用时间段;2, 样品回零条件;3, 断层活动年龄含义;4, 年龄分散性的影响;5, 测年的干扰因素;6, 地质背景对测年结果的判定等六个方面进行探讨, 以期选取更适合于地质背景的年龄数据, 较准确地评价大坝的安全和稳定性。  相似文献   

南京湖山地区方解石晶内变形的发现及其构造意义   总被引：1，自引：0，他引：1  

杜国云 《江苏地质》1996,20(3):189-192

在印支晚期－燕山早期近南北向挤压褶皱与自南页北的构造推覆体制下，南京湖山地区出现了三个与逆掩推覆有关的构造变形事件。最初的构造变形表现为重结晶方解石颗粒的晶内变形，依据方解石双晶化密度计算了作用于汤－仑推覆体上的古构造差异应力为２５．６４ＭＰａ。  相似文献