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1.
Calcite veins are invariably associated with en-echelon kimberlite dyke–fracture arrays. A detailed microstructural study of veining indicates four vein types. Type I stretched or ataxial veins are defined by high aspect ratio calcite fibers that are crystallographically continuous with calcite of the kimberlite matrix wall rock, by elongated phenocrystic phlogopite with sharp crystal terminations centered on contacts between adjacent calcite fibers and by phenocrystic phlogopite that grows or extends across these veins. Type I vein mineralogy indicates syn-dilational crystallization of vein minerals in local tensional areas within the kimberlite. Vein Types II (stretched to syntaxial elongate-blocky) and III (antitaxial) indicate late crystallization vein mineral growth during subsequent or repeated dilation. Calcite fibers in Type I to Type III veins are orthogonal to the contacts of their host dykes regardless of the orientation of vein margins. Type IV calcite veins, with blocky or mosaic/polycrystalline textures, are attributed to minor post-intrusion extension, which was potentially accompanied by repeated kimberlite intrusion within a given dyke array. Syn-crystallization/syn-intrusion Type I veins and an ubiquitous dyke-parallel fracture cleavage, in a zone up to 4 m on either side of dyke contacts, suggest that en-echelon kimberlite dyke–fracture arrays occupied the approximate center of zones of active dilation within the brittle carapace of the upper crust. Type II and III veins indicate that extension or dilation continued, independently of an occupying kimberlite fluid phase, after initial intrusion. Arrested mobile hydrofracturing, under low differential stress within the upper brittle or seismic carapace of the continental crust, followed by repeated dilation of the dyke–fracture system, is proposed as a mechanism for producing the features observed in this study. The conditions constrained in this study indicate passive dyke intrusion into dilating fracture arrays during crustal extension. 相似文献
2.
《Journal of Structural Geology》2001,23(6-7):873-885
The development of fibrous morphology and capability of fibres for tracking the opening trajectory were investigated using numerical simulations of a natural antitaxial fibrous vein. Starting from a non-unique best case, variation of fracture opening velocity, grain size, wall roughness, growth anisotropy and crystal growth velocity shows that these parameters differ in importance for crystal morphology and tracking capability. Fibrous veins can be simulated using crack–seal opening of the fracture. Grain boundaries track the opening trajectory if the wall roughness is high, opening increments are small and crystals touch the wall before the next crack increment starts. 相似文献
3.
Microstructural observations on natural syntectonic fibrous veins: implications for the growth process 总被引：3，自引：0，他引：3
Syntectonic antitaxial and ataxial fibrous veins were investigated using SEM, microprobe, cathodoluminescence (CL) and optical microscopy. In antitaxial calcite veins, fibres and surrounding selvage grew simultaneously, with similar growth rates of crystallographically differently oriented grains. New material precipitated at the vein margin in antitaxial and bi-mineralic ataxial microstructures. Bridges of country rock material formed during vein growth in an initial en-echelon vein system. In our antitaxial and bi-mineralic ataxial samples, the spacing of solid inclusions does not reflect individual crack-seal openings. 相似文献
4.
构造驱动大巴山前陆烃类流体排泄:含烃包裹体纤维状方解石脉证据 总被引：3，自引：0，他引：3
含烃包裹体纤维状方解石脉被认为是超高压下油气流体形成和排泄的标志。大巴山前陆构造带一些断裂和下古生界黑色泥岩和泥灰岩烃源岩微裂隙中分布有含烃包裹体纤维状方解石脉,成分分析表明其为低镁方解石。纤维状方解石脉δ13CVPDB和δ18OVPDB比围岩碳酸盐岩的明显变轻,前者δ13CVPDB和δ18OVPDB变化范围分别为-1.9%～-4.8‰和-8.4%～-12.8‰,后者分别为-1.7%～+3.1‰和-8.7%～-4.5‰,且δ13C与δ18O具有明显的线性关系,反映出纤维状方解石脉具有成岩有机流体与浅部流体混合的流体特征。纤维状方解石脉含有共生的固体沥青包裹体、含甲烷液相包裹体和气液二相盐水包裹体等多相态包裹体,其中沥青包裹体为油气运移的残余沥青。气液二相盐水包裹体均一温度主要位于140℃和196℃之间（峰值为179℃）,盐度较高（平均为9.7wt% NaCl）。分别应用盐水包裹体和甲烷包裹体等溶线P-T相图确定出含烃包裹体纤维状方解石脉形成的流体压力为150~200 MPa,属于异常超高压流体。地质和地球化学特征分析认为,大巴山含烃包裹体纤维状方解石脉不具有泥岩因压实成岩作用而形成的超高压流体特征。结合沉积和构造演化历史分析认为,印支碰撞造山运动和燕山前陆构造作用导致大巴山褶皱隆起并伴随天然气藏破坏和改造,挤压环境下的超高压构造应力驱动天然气流体排泄,大巴山前陆构造带含烃包裹体纤维状方解石脉就是超高压构造应力驱动天然气排泄的产物。 相似文献
5.
Kumar Ankit Britta Nestler Michael Selzer Mathias Reichardt 《Contributions to Mineralogy and Petrology》2013,166(6):1709-1723
In order to address the growth of crystals in veins, a multiphase-field model is used to capture the dynamics of crystals precipitating from a super-saturated solution. To gain a detailed understanding of the polycrystal growth phenomena in veins, we investigate the influence of various boundary conditions on crystal growth. In particular, we analyze the formation of vein microstructures resulting from the free growth of crystals as well as crack-sealing processes. We define the crystal symmetry by considering the anisotropy in surface energy to simulate crystals with flat facets and sharp corners. The resulting growth competition of crystals with different orientations is studied to deduce a consistent orientation selection rule in the free-growth regime. Using crack-sealing simulations, we correlate the grain boundary tracking behavior depending on the relative rate of crack opening, opening trajectory, initial grain size, and wall roughness. Further, we illustrate how these parameters induce the microstructural transition between blocky (crystals growing anisotropically) to fibrous morphology (isotropic) and formation of grain boundaries. The phase-field simulations of crystals in the free-growth regime (in 2D and 3D) indicate that the growth or consumption of a crystal is dependent on the orientation difference with neighboring crystals. The crack-sealing simulation results (in 2D and 3D) reveal that crystals grow isotropically and grain boundaries track the opening trajectory if the wall roughness is high, opening increments are small, and crystals touch the wall before the next crack increment starts. Further, we find that within the complete crack-seal regime, anisotropy in surface energy results in the formation of curved/oscillating grain boundaries (instead of straight) when the crack-opening velocity is increased and wall roughness is not sufficiently high. Additionally, the overall capability of phase-field method to simulate large-scale polycrystal growth in veins (in 3D) is demonstrated enumerating the main advantages of adopting the novel approach. 相似文献
6.
Atsushi Okamoto Taketo Kikuchi Noriyoshi Tsuchiya 《Contributions to Mineralogy and Petrology》2008,156(3):323-336
Pelitic schists of the Sanbagawa metamorphic belt contain several types of polymineralic veins that formed during the late
stages of exhumation. The vein mineral assemblages are quartz + albite + K-feldspar + chlorite ± calcite (Type I, II) and
quartz + albite + calcite (Type III). Type I and II veins contain quartz and albite with stretched-crystal and elongate-blocky
textures, respectively. The mineral species within Type I veins vary with compositional bands within the host rocks. Type
III veins are characterized by euhedral to subhedral quartz grains with concentric zoning and a homogeneous distribution along
the vein length. The vein textures vary depending on the crack aperture during multiple crack-seal events: <0.08 mm for Type
I, and 0.5–10 mm for Type III. Type II veins show intermediate features between Type I and III veins in terms of mineral distribution
(weak dependence on the host rock composition) and apparent crack aperture (less than 1–15 mm). These observations suggest
a transition in the dominant transport mechanism of vein components with increasing crack aperture, from diffusion from host
rocks to fluid advection along cracks. 相似文献
7.
Veins are common features in rocks and extremely useful structures to determine stress, strain, pressure, temperature, fluid composition and fluid origin during their formation. Here we provide an overview of the origin and terminology of veins. Contrary to the classical tripartite division of veins into syntaxial (inward growth), antitaxial (outward growth) and stretching veins (no consistent growth direction), we emphasise a continuum between syntaxial and stretching veins that form from the crack-seal process, as opposed to antitaxial veins that grow without the presence of an open fracture during growth. Through an overview of geochemical methods that can be applied to veins we also address the potential, but so far little-investigated link between microstructure and geochemistry. There are basically four mechanisms with increasing transport rates and concomitant decreasing fluid–rock interaction: (1) diffusion of dissolved matter through stagnant pore fluid; (2) flow of fluid with dissolved matter through pores; (3) flow of fluid with dissolved matter through fractures and (4) movement of fractures together with the contained fluid and dissolved matter (mobile hydrofractures). A vein system is rarely the product of a single transport and mineral precipitation mechanism, as these vary strongly both in space and time within a single system. 相似文献
8.
Paul D. Bons Michael Montenari Ronald J. Bakker Marlina A. Elburg 《International Journal of Earth Sciences》2009,98(2):327-343
Scanning electron microscopy revealed micron-sized globular and coccoid objects, associated with filaments and mucus-like
patches in antitaxial fibrous calcite veins from Oppaminda Creek, Northern Flinders Ranges, South Australia. Chemically the
objects only differ from their calcite (CaCO3) matrix by a higher sulphur content. The ∼585 Ma veins formed at about 3–6 km below the surface. Fluid inclusions indicate
a temperature of formation of about 60–80°C, and not exceeding 100°C. A non-biogenic origin of the objects is discussed, but
considered unlikely. Instead, morphology, chemistry and size distribution all indicate that the objects are fossilised microbes
that lived in the veins at the time and depth of vein formation. 相似文献
9.
Flexural slip folds are distinctive of mixed continuous-discontinuous deformation in the upper crust, as folding is accommodated by continuous bending of layers and localized, discontinuous slip along layer interfaces. The mechanism of localized, layer-parallel slip and the stress and fluid pressure conditions at which flexural slip occurs are therefore distinctive of shear localization during distributed deformation. In the Prince Albert Formation mudstone sequence of the Karoo Basin, the foreland basin to the Cape Fold Belt, folds are well developed and associated with incrementally developed bedding-parallel quartz veins with slickenfibers oriented perpendicular to fold hinge lines, locally cross-cutting axial planar cleavage, and showing hanging wall motion toward the fold hinge. Bedding-parallel slickenfiber-coated veins dip at angles from 18° to 83°, implying that late increments of bedding-parallel shear occurred along unfavorably oriented planes. The local presence of tensile veins, in mutually cross-cutting relationship with bedding-parallel, slickenfiber-coated veins, indicate local fluid pressures in excess of the least compressive stress.Slickenfiber vein microstructures include a range of quartz morphologies, dominantly blocky to elongate-blocky, but in places euhedral to subhedral; the veins are commonly laminated, with layers of quartz separated by bedding-parallel slip surfaces characterized by a quartz-phyllosilicate cataclasite. Crack-seal bands imply incremental slickenfiber growth, in increments from tens of micrometers to a few millimeters, in some places, whereas other vein layers lack evidence for incremental growth and likely formed in single slip events. Single slip events, however, also involved quartz growth into open space, and are inferred to have formed by stick-slip faulting. Overall, therefore, flexural slip in this location involved bedding-parallel faulting, along progressively misoriented weak planes, with a range of slip increments. 相似文献
10.
根据岩石中裂隙脉的研究方法和理论,对煤中方解石脉的形成机理进行了系统探讨,发现煤中方解石脉以对生式和背生式为主,组合式裂隙脉比较少见。同时,发现了流体压力致裂裂隙的存在,且为多期张裂-闭合作用的结果。 相似文献
11.
ABSTRACT
Large septarian concretions from the Kimmeridge Clay, up to 1.2 m in diameter, have centres comprising anhedral calcite microspar passing into margins of radiating fibrous calcite microspar, with a pyrite-rich zone at the transition. Septarian veins formed and were lined with brown calcite synchronously with fibrous matrix growth, with white calcite precipitated in septarian cavities after concretion growth ceased. Septarian veins, filled only with white calcite, formed later, at the same time as the outermost calcite microspar crystals were enlarged.
The concretions were buried in the Late Jurassic to about 130 m, and in the Late Cretaceous to about 550 m, with uplift between. Oxygen isotopes show that the concretion grew throughout the first burial, with septarian veins forming from about 30 m depth onwards. Later septarian veins formed between about 200 and 500 m during the second burial.
Carbon isotopes show that the compact inner matrix grew in the sulphate reduction zone, the end of which is marked by the pyrite-enriched zone. Dissolving shells, and possibly minor methanogenic carbonate, slowly diluted sulphate reduction-zone carbonate during deeper burial. During early concretion growth, Mg and Sr were depleted in the pore water. During later stages of the first burial, Mg, Sr, Mn and Fe all increased, especially after concretion growth ceased. During the second burial, Fe, Mn and Mg decreased as calcite precipitated, implying relatively closed systems for these elements.
Synchronous formation of septarian fractures and fibrous calcite matrix shows that the Kimmeridge Clay became overpressured during the later stages of both burials. 相似文献
Large septarian concretions from the Kimmeridge Clay, up to 1.2 m in diameter, have centres comprising anhedral calcite microspar passing into margins of radiating fibrous calcite microspar, with a pyrite-rich zone at the transition. Septarian veins formed and were lined with brown calcite synchronously with fibrous matrix growth, with white calcite precipitated in septarian cavities after concretion growth ceased. Septarian veins, filled only with white calcite, formed later, at the same time as the outermost calcite microspar crystals were enlarged.
The concretions were buried in the Late Jurassic to about 130 m, and in the Late Cretaceous to about 550 m, with uplift between. Oxygen isotopes show that the concretion grew throughout the first burial, with septarian veins forming from about 30 m depth onwards. Later septarian veins formed between about 200 and 500 m during the second burial.
Carbon isotopes show that the compact inner matrix grew in the sulphate reduction zone, the end of which is marked by the pyrite-enriched zone. Dissolving shells, and possibly minor methanogenic carbonate, slowly diluted sulphate reduction-zone carbonate during deeper burial. During early concretion growth, Mg and Sr were depleted in the pore water. During later stages of the first burial, Mg, Sr, Mn and Fe all increased, especially after concretion growth ceased. During the second burial, Fe, Mn and Mg decreased as calcite precipitated, implying relatively closed systems for these elements.
Synchronous formation of septarian fractures and fibrous calcite matrix shows that the Kimmeridge Clay became overpressured during the later stages of both burials. 相似文献
12.
The interplay between fracture propagation and fluid composition and circulation has been examined by deciphering vein sequences in Silurian and Devonian limestones and shales at Kosov quarry in the Barrandian Basin. Three successive vein generations were recognised that can be attributed to different stages of a basinal cycle. Almost all generations of fracture cements host abundant liquid hydrocarbon inclusions that indicate repeated episodes of petroleum migration through the strata during burial, tectonic compression and uplift.The earliest veins that propagated prior to folding were displacive fibrous “beef” calcite veins occurring parallel to the bedding of some shale beds. Hydrocarbon inclusions within calcite possess homogenisation temperatures between 58 and 68 °C and show that the “beef” calcites originated in the deeper burial environment, during early petroleum migration from overpressured shales.E–W-striking extension veins that postdate “beef” calcite formed in response to Variscan orogenic deformations. Based on apatite fission track analysis (AFTA) data and other geological evidence, the veins probably formed 380–315 Ma ago, roughly coinciding with peak burial heating of the strata, folding and the intrusion of Variscan synorogenic granites. The veins that crosscut diagenetic cements and low-amplitude stylolites in host limestones are oriented semi-vertically to the bedding plane and are filled with cloudy, twinned calcite, idiomorphic smoky quartz and residues of hardened bitumen. Calcite and quartz cements contain abundant blue and blue–green-fluorescing primary inclusions of liquid hydrocarbons that homogenise between 50 and 110 °C. Geochemical characteristics of the fluids as revealed by gas chromatography–mass spectrometry, particularly the presence of olefins and parent aromatic hydrocarbons (phenonthrene), suggest that the oil entrapped in the inclusions experienced intense but geologically fast heating that resulted in thermal pyrolysis of its hydrocarbons. This implies that the organic fluids in the fractures may have been partly influenced by heating associated with igneous intrusions that are hidden below the surface.Subvertical N–S-striking veins represent the most recent fracturing event(s). Some of these veins are only a few millimeters thick and sparsely mineralised with thin leaf-like quartz crystals that contain tiny blue and yellow–orange-fluorescing hydrocarbon inclusions. Most of the N–S veins, however, occur as thick calcite veins that generally crystallised at 70 °C or less from H2O–NaCl solutions of variable salinity with admixture of petroleum. The origin of these fluids is interpreted in terms of deeply circulating meteoric waters that partially mixed with deep basinal fluids. Wider structural considerations combined with fission-track analysis of adjacent host sediments suggest that N–S veins formed during post-Mesozoic uplift of the area, probably in response to major Tertiary Alpine deformations transmitted far into the Bohemian Massif. 相似文献
13.
The emplacement of calcite-filled veins perpendicular to the Dead Sea Fault Zone in northern Israel reflects strain partitioning during transpression. We present structural, geochemical, and U–Th geochronological data that constrain the mechanism, conditions and timing of vein formation. Vein walls are strongly brecciated and commonly cemented with coarsely crystalline calcite, whereas calcite-filled veins are composed of wall-parallel bands of calcite crystals. Elongated blocky and fibrous calcite crystals grew perpendicular to the vein walls and are characterised by a truncate sealing-hiatus morphology, indicating episodes of partial or complete sealing of the fractures during calcite precipitation. Stable isotope and rare-earth element and yttrium (REY) analyses indicate that calcite-filled veins precipitated by karst processes, involving meteoric water and limited fluid-rock interactions. U–Th dating results show a prolonged history of vein growth. While some veins initiated prior to 500 ka, the majority of the veins were active between 358 and 17 ka. Age constraints on vein activity correspond to an ∼E–W regional shortening phase in this sector of the Dead Sea Fault Zone, associated with an increased component of convergence during the late-Pleistocene. 相似文献
14.
Sealing of fluid pathways in overpressure cells: a case study from the Buntsandstein in the Lower Saxony Basin (NW Germany) 总被引：1，自引：0，他引：1
Sofie Nollet Christoph Hilgers Janos Urai 《International Journal of Earth Sciences》2005,94(5-6):1039-1055
We studied veins in the Triassic Buntsandstein of the Lower Saxony Basin (NW Germany) with the aim of quantifying the evolution
of in-situ stress, fluids and material transport. Different generations of veins are observed. The first generation formed
in weakly consolidated rocks without a significant increase in fracture permeability and was filled syntectonically with fibrous
calcite and blocky to elongate-blocky quartz. The stable isotopic signature (δ18O and δ13C) indicates that the calcite veins precipitated from connate water at temperatures of 55–122°C. The second vein generation
was syntectonically filled with blocky anhydrite, which grew in open fractures. Fluid inclusions indicate that the anhydrite
veins precipitated at a minimum temperature of 150°C from hypersaline brines. Based on δ34S measurements, the source of the sulphate was found in the underlying Zechstein evaporites. The macro- and microstructures
indicate that all veins were formed during subsidence and that the anhydrite veins were formed under conditions of overpressure,
generated by inflation rather than non-equilibrium compaction. The large amount of fluids which are formed by the dehydrating
gypsum in the underlying Zechstein and are released into the Buntsandstein during progressive burial form a likely source
of overpressures and the anhydrite forming fluids. 相似文献
15.
LIU Guanglin LIU Xianyang MA Xiaofeng MA Shuang WANG Xiaofeng LI Shuo SHI Zhiqiang WANG Yanxin 《《地质学报》英文版》2023,97(5):1490-1502
To explore the genesis of the laminated calcite veins developed in the black shale of Chang 73 submember of the Ordos Basin, the petrology, microstructure and geochemistry of calcite veins are studied using thin sections, fluid inclusions, trace elements and isotopic geochemistry. The source, the time of formation, the mechanism of formation, and the dynamic background of the veins are discussed. The veins are mostly made up of calcite, mixed with lenticular or spindle-shape solid wall rock inclusions. Three structures are identified in the calcite minerals: fibrous, rhombic cleavage, and wedge-like structure. Trace elements and isotopes of carbon and oxygen confirm that the calcite veins were formed from a high density hydrothermal fluid. It is assumed that calcite veins formed prior to wall rock consolidation during the formation of the Qinling Orogenic Belt in the Middle and Late Triassic. The results show that the sedimentary sources of Chang 73 submember were influenced by hydrothermal materials besides terrigenous detritus. The fibrous calcite is different from the fibrous calcite reported in the morphology and mechanism of formation. In this way, the research complements and improves the morphology and the mechanism of formation of fibrous calcite. 相似文献
16.
《Journal of Structural Geology》2001,23(6-7):865-872
A two-dimensional numerical model for the simulation of the formation of microstructures in crack-seal veins is presented here. The grain aggregate in the vein is described by grain boundary nodes that link short, straight boundary segments. Growth of crystals into a crack takes place by many small incremental movements of nodes. The rate of growth depends on the chosen growth morphology of the vein-forming material. Different growth morphologies can be defined. For every user-defined number of steps, the wall rock is moved a user-defined distance and direction, which simulates the opening of a crack, after which sealing can proceed again. The shape of the crack-surface (e.g. smooth or with ridges) can be set by the user and can be made to match fracture surfaces found in real rocks. The model is capable of reproducing realistic crack-seal textures and can be used to systematically investigate the role of different parameters on the microstructures of veins. First applications of the model are presented in Part II of this paper (this volume). 相似文献
17.
《Journal of Structural Geology》1994,16(4):571-584
The Doublespring duplex, located in the Lost River Range of Idaho, is a Sevier age fault-related fold complex in massive limestones of the Upper Mississippian Scott Peak Formation. Folds within the duplex closely resemble fault-bend fold geometrics, with open interlimb angles and low-angle bed cut-offs. Narrow, widely spaced, bedding-parallel shear zones with well-developed pressure solution cleavage alternate with massive, relatively undeformed layers on fold limbs. Shear zones are developed only on the limbs of anticlines, and have similar but unique morphologies in each of three different folds. Incremental strain histories reconstructed from antitaxial fibrous overgrowths and veins within the shear zones constrain the kinematics of folding. Shear zones experienced distributed bedding-parallel simple shear (flexural flow) towards pins near axial surfaces, while adjacent massive layers experienced rotation through an externally fixed extension direction. The absence of footwall synclines and morphological differences in shear zones from adjacent folds suggest that faulting preceded folding. Kinematic histories of folds that have experienced different translational histories are identical, and are not compatible with strain histories predicted from previous kinematic models of fault-bend folding. Shear zone development and fiber growth is instead interpreted to have occurred during low amplitude fixed-hinge buckling in response to initial resistance to translation of the thrust sheet. Fault-bend folding with mobile axial surfaces occurred with translation of the thrust sheets once the initial resistance to translation was overcome and resulted in no penetrative strain. 相似文献
18.
《矿物学报》2013,(Z1)
Based on analysisof karst fracture-vuggy filling mineralogy and geochemical fluorite in hercynian, this paper make further research about formation and significance of fluorite in central uplift of Tarim Basin. It is point out that the development of hercynian fracture-vuggy and filling succession of fracture-cave mineral was under the background of the mingling of low-temperature magma hydrotherm and the brine of upper strata. There are overlap or associate relations between generate of fluorite and buried dissolution or oil-gas migration. It was volume decreased 26.4% after calcite metasomatic by fluorite, this reaction made fluorite engender plentiful intergranular space. It’s created appreciable reservoir space. At same time, hydrotherm carried by fluorite generating could erode adjacent rock though fracture or fissure, forming irregular fracture-cave system, and also accompanied with hydrocarbon migration. The time of hydrocarbon migration and accumulation happened in late hercynian-indosinian is inosculates with the sedimentation time such as fluorite and several hydrothermal mineral. 相似文献
19.
Radiaxial fibrous calcite, a common cavity fill in ancient limestones, is characterized by curved twin lamellae, optic axes that converge away from the substrate and subcrystals which diverge in this same direction. The optic axes radiate about three or four axes located in positions between adjacent crystals and orientated parallel with the crystal elongation. The crystals are commonly turbid with inclusions, which may be concentrated along twin lamellae and subcrystal and inter-crystalline boundaries, or form zones parallel to the substrate. Some inclusion patterns reveal the position of former crystal faces. From a consideration of the occurrences, gross morphological characters, the fabrics of the crystals and the inclusion patterns, radiaxial fibrous calcite is interpreted as a replacement of an early diagenetic acicular cement, composed of interfering bundles of radiating crystals. It is suggested that replacement takes place by a solution-precipitation process and the migration of a fluid film through the acicular host, with replacement occurring most rapidly between bundles of acicular carbonate. The optic axis pattern of the fibrous calcite is considered to be inherited from the c-axis orientations of the host acicular crystals. Fibrous calcite intercrystalline boundaries form as fractures after replacement. Some inclusion patterns record the characters of the replaced acicular cement; others, formed of impurities reorganized during the replacement, reveal the form of the replacement front. 相似文献