上部地壳岩石流动与显微构造演化--天然与实验岩石变形证据

岩石流动性和变形显微构造的发育直接受温度、压力、应变速率和流体相等制约 ,致使在不同地壳层次岩石的流动性表现出很大的差异。对上部地壳环境条件下天然和实验变形岩石的显微构造分析揭示出一系列具有不同特点以及由不同的成核、扩展和联合方式形成的破裂与微破裂型式的存在。讨论了在上部地壳环境中 ,温度与围压的变化对岩石破裂的影响 ,并阐述了高压破裂与低压破裂及其力学、流变学和显微构造特点 ,提出高压破裂对应于天然变形环境下出现的剪切 (挤压 )破裂 ,而碎裂岩带是典型的天然低压破裂 ,其低压环境的出现可以是浅部低围压或深部高流体压力所致。流体相的存在不仅可以引起石英 ,也可以引起方解石类碳酸盐岩矿物的水解弱化 ,并进而导致岩石流动机制的转变。岩石变形及流体等因素所致的岩石粒度变化 ,则从另一个方面影响着上部地壳岩石流动性的变化。从变形环境考虑 ,随着深度的加大 ,温度和压力升高 ,导致岩石由脆性向韧性转变 ;转变域内岩石的变形是一个复杂过程 ,是多种不同脆性和晶质塑性机制的综合。     

Transcrystalline shear fracturing and pseudotachylite generation in a meta-anorthosite (Harris, Scotland)

The meta-anorthosite is locally deformed by brittle shear fracturing, which progressively increases from isolated fractures with little cataclasite to many generations of closely spaced fractures, the intervening rock being highly deformed, in both a plastic and brittle way. In most cases an E-W compression on gently dipping to steep reverse shear planes occurs, which we relate to a Caledonian thrust zone.In places, the highly deformed rock is cut by pseudotachylite veins, which locally form networks. The pseudotachylite is generally intrusive, but does not appear to be related to movement on major slip surfaces. Very locally it may have formed in situ. Pseudotachylite only occurs in highly deformed rock, is only very occasionally deformed itself and, thus, generally represents at each locality the last stage of a complex deformation history, as if its presence welded the rock and prevented further deformation. These striking differences from the country-rock gneisses (in which pseudotachylite occurs on well developed fractures in very slightly deformed rock) are considered to be due to the low anisotropy of the meta-anorthosite, to its lower shear strength and to the easy propagation and branching of the shear fractures in plagioclase. The source of the heat necessary to generate the pseudotachylite melt is not clear—it may come from crack propagation as well as frictional sliding.     

Low-Temperature Plasticity of Naturally Deformed Calcite Rocks

Optical, cathodoluminescence and transmission electron microscope (TEM) analyses were conducted on four groups of calcite fault rocks, a cataclastic limestone, cataclastic coarse-grained marbles from two fault zones, and a fractured mylonite. These fault rocks show similar microstructural characteristics and give clues to similar processes of rock deformation. They are characterized by the structural contrast between macroscopic cataclastic (brittle) and microscopic mylonitic (ductile) microstructures. Intragranular deformation microstructures (i.e. deformation twins, kink bands and microfractures) are well preserved in the deformed grains in clasts or in primary rocks. The matrix materials are of extremely fine grains with diffusive features. Dislocation microstructures for co-existing brittle deformation and crystalline plasticity were revealed using TEM. Tangled dislocations are often preserved at the cores of highly deformed clasts, while dislocation walls form in the transitions to the fine-grained     

Interaction of chemical and physical processes during deformation at fluid-present conditions: a case study from an anorthosite–leucogabbro deformed at amphibolite facies conditions

We present microstructural and chemical analyses of chemically zoned and recrystallized plagioclase grains in variably strained samples of a naturally deformed anorthosite–leucogabbro, southern West Greenland. The recorded microstructures formed in the presence of fluids at mid-crustal conditions (620–640 °C, 7.4–8.6 kbar). Recrystallized plagioclase grains (average grain size 342 μm) with a random crystallographic orientation are volumetrically dominant in high-strain areas. They are characterized by asymmetric chemical zoning (An₈₀ cores and An₆₄ rims) that are directly associated with areas exhibiting high amphibole content and phase mixing. Analyses of zoning indicate anisotropic behaviour of bytownite plagioclase with a preferred replacement in the $ \left\langle {0 10} \right\rangle $ direction and along the (001) plane. In areas of high finite strain, recrystallization of plagioclase dominantly occurred by bulging recrystallization and is intimately linked to the chemical zoning. The lack of CPO as well as the developed asymmetric zoning can be explained by the activity of grain boundary sliding accommodated by dissolution and precipitation creep (DPC). In low-strain domains, grain size is on average larger and the rim distribution is not related to the inferred stress axes indicating chemically induced grain replacement instead of stress-related DPC. We suggest that during deformation, in high-strain areas, pre-existing phase mixture and stress induced DPC-caused grain rotations that allowed a deformation-enhanced heterogeneous fluid influx. This resulted in local plagioclase replacement through interface-coupled dissolution and precipitation and chemically induced grain boundary migration, accompanied by bulging recrystallization, along with neocrystallization of other phases. This study illustrates a strong interaction and feedback between physical and chemical processes where the amount of stress and fluids dictates the dominant active process. The interaction is a cause of deformation and external fluid infiltration with a result of strain localization and chemical re-equilibration at amphibolite facies conditions.     

How does shear zone nucleate? An example from the Suretta nappe (Swiss Eastern Alps)

In order to address the question of the processes involved during shear zone nucleation, we present a petro-structural analysis of millimetre-scale shear zones within the Roffna rhyolite (Suretta nappe, Eastern central Alps). Field and microscopic evidences show that ductile deformation is localized along discrete fractures that represent the initial stage of shear zone nucleation. During incipient brittle deformation, a syn-kinematic metamorphic assemblage of white mica + biotite + epidote + quartz precipitated at ca. 8.5 ± 1 kbar and 480 ± 50 °C that represent the metamorphic peak conditions of the nappe stacking in the continental accretionary wedge during Tertiary Alpine subduction. The brittle to ductile transition is characterized by the formation of two types of small quartz grains. The Qtz-IIa type is produced by sub-grain rotation. The Qtz-IIb type has a distinct CPO such that the orientation of c-axis is perpendicular to the shear fracture and basal and rhombhoedric slip systems are activated. These Qtz-IIb grains can either be formed by recrystallization of Qtz-IIa or by precipitation from a fluid phase. The shear zone widening stage is characterized by a switch to diffusion creep and grain boundary sliding deformation mechanisms. During the progressive evolution from brittle nucleation to ductile widening of the shear zone, fluid–rock interactions play a critical role, through chemical mass-transfer, metasomatic reactions and switch in deformation mechanisms.     

实验变形岩石低温破裂作用的微观机制

通过对湿度和压力分别达300℃和3GPa干条件下实验变形的一系列花岗岩样品的系统光学和扫描电镜显微构造分析,识别出了几种具有不同特点及不同变形机制的显微破裂型式:a.微破碎带;b.微透镜带;c.短程破裂;d.扭折带破裂;e.粒内破裂;f.颗粒边界破裂。评价了它们与高压型和低压型破裂的显微构造对应性,认为a和f是低压破裂的特征性构造型式;b、c和d在高压破裂中最为典型;而e则可以出现在两种破裂型式中。本文阐述了破裂作用的微观机制,包括破裂的成核、扩展、生长和连接。破裂作用、由破裂诱发的脆性破裂和碎裂流动在目前实验变形条件下占主导地位,而在相对较高温条件下晶质塑性也起着一定的作用。破裂作用的成核可以始于颗粒边界,而引起摩擦颗粒边界滑移,也可以始于相邻颗粒或晶内包体颗粒的一些端点,或始于晶内双晶和解理面。破裂的生长和扩展一般是由于一些破裂的侧向延伸、相近破裂系统的联合和不同破裂系统的转变。低压样品的最终破裂一般归咎于一些贯穿性微断层的出现及主断层附近微破裂群的产生,微破碎角砾岩是其主要构造岩类型,类似于天然张性断层带构造;而沿主高压破裂附近却从未见到这种微破裂群的出现,主要表现为主破裂面及一些均匀分布的短程破裂构造, 典型构造岩为构造透镜体, 类似于天然压性与压扭性断层构造。两种破裂在成核、扩展与位移发育诸方面表现出的差别有助理解它们在声发射方面的差异。     

Competitive macroscopic deformation processes

Macroscopic deformation mechanisms such as folding, fracturing–faulting and formation of rock fabrics compete with one another in a fashion similar to the competition among crystalline deformation mechanisms such as cataclasis, grain boundary sliding, dislocation creep and diffusive mass transfer. Many authors seek to develop a unique structural chronology for a given field area based on what are considered exclusive overprinting relationships between structures. In contrast the approach taken here suggests that relative changes in external or internal variables within a rock mass can cause significantly different `dominant' types of macroscopic deformation to be developed in hand specimen and/or outcrop at the same time. Rather than representing distinct structural `facies', observed dominant macroscopic features are waypoints in continuum processes.     

Impact of solid second phases on deformation mechanisms of naturally deformed salt rocks (Kuh-e-Namak,Dashti, Iran) and rheological stratification of the Hormuz Salt Formation

Viscosity contrasts displayed in flow structures of a mountain namakier (Kuh-e-Namak - Dashti), between ‘weak’ second phase bearing rock salt and ‘strong’ pure rock salt types are studied for deformation mechanisms using detailed quantitative microstructural study. While the solid inclusions rich (“dirty”) rock salts contain disaggregated siltstone and dolomite interlayers, “clean” salts reveal microscopic hematite and remnants of abundant fluid inclusions in non-recrystallized cores of porphyroclasts. Although the flow in both, the recrystallized “dirty” and “clean” salt types is accommodated by combined mechanisms of pressure-solution creep (PS), grain boundary sliding (GBS), transgranular microcracking and dislocation creep accommodated grain boundary migration (GBM), their viscosity contrasts observed in the field outcrops are explained by: 1) enhanced ductility of “dirty” salts due to increased diffusion rates along the solid inclusion-halite contacts than along halite–halite contacts, and 2) slow rates of intergranular diffusion due to dissolved iron and inhibited dislocation creep due to hematite inclusions for “clean” salt types Rheological contrasts inferred by microstructural analysis between both salt rock classes apply in general for the “dirty” salt forming Lower Hormuz and the “clean” salt forming the Upper Hormuz of the Hormuz Formation and imply strain rate gradients or decoupling along horizons of mobilized salt types of different composition and microstructure.     

Rheologic evolution of low-grade metasedimentary rocks and granite across a large strike-slip fault zone: A case study of the Kellyland fault zone,Maine, USA

We examine a large strike-slip fault zone that juxtaposes low-grade clastic metasedimentary rocks with coarse-grained granite near the brittle-ductile transition. The load-bearing matrixes in granite-derived ultramylonites and pelite and wacke metasedimentary intervals are texturally similar, and all deformed by diffusion-assisted granular flow. Granite underwent rapid strengthening as the pluton cooled followed by rapid weakening driven by brittle grain-size reduction and mixing that catalyzed ultramylonite formation. The textural and mineralogical similarity of pelitic intervals across the zone indicates they experienced little textural and reaction weakening. Wacke intervals record progressive textural and reaction weakening in an open system. Quartz recrystallized grain sizes in granite-derived ultramylonites record ∼2-times more differential stress than those in metasedimentary rocks in the interior of the zone. The relative weakness of metasedimentary rocks is correlated with fluid influx that likely enhanced diffusion and grain-boundary sliding in pelitic and wacke intervals and catalyzed textural and reaction weakening in wacke intervals. The lack of evidence for fluid and ionic communication with granitic rocks indicates that fluid movement was restricted to foliation-parallel pathways within single rock units. This localized fluid influx is the best explanation for the strength contrasts between texturally similar fault rocks deformed by similar mechanisms.     

含流体相条件下白云岩的低温流动变形--破裂与溶解-结晶的耦合过程

应用光学显微分析、阴极发光显微分析和TEM亚微分析．对于取自阿尔卑斯逆冲断层系底部的变形白云岩开展了详细的显微构造与岩石流动机制分析．光学显微构造和阴极发光分析表明岩石具有典型的类碎裂结构．微角砾常常是白云石颗粒的集合体组成,常常呈浑圆的形态和不规则的边界。基质颗粒中以新生结晶颗粒集合体为主．部分具有溶蚀特点的残余微角砾．而且它们经常具有新生结晶边。对于碎裂岩中变形残斑的透射电镜分析揭示出岩石的脆性特点．主要表现为各种不规则和缠结位错亚微构造特点的出现．而变形基质颗粒却很少具有或仅有微弱发育的位错亚结构。阴极发光显微结构分析进一步证实基质颗粒与微角砾之间在微量元素成分及形成时代上的差异。提出破裂(碎裂)及随后发生的溶解-迁移-结晶过程是断层带岩石细粒化与岩石应变的重要机制．认为破裂与溶解-结晶的耦合以及由此所致的岩石弱化为阿尔卑斯逆冲断层带巨大位移的形成做出了重要的贡献。     

上部地壳岩石变形与方解石质岩石的低温流动

系统总结了上部地壳环境中方解石质岩石的浅成流动机制与低温糜棱岩成因研究的几个重要方面：（１）地壳岩石脆－韧性转变域与岩石变形机制;（２）变形作用过程中流体相的物理与化学意义;（３）方解石质岩石的流动机制、变形特点与蠕变规律。同时讨论了对于地壳浅部层次方解石质石流主变学研究中存在的主要问题以及解决这些问题的基本思路与科学意义。     

Microstructural and metamorphic evolution of a high‐pressure granitic orthogneiss during continental subduction (Orlica–Śnieżnik dome,Bohemian Massif)

A microstructural and metamorphic study of a naturally deformed medium‐ to high‐pressure granitic orthogneiss (Orlica–?nie?nik dome, Bohemian Massif) provides evidence of behaviour of the felsic crust during progressive burial along a subduction‐type apparent thermal gradient (～10 °C km^?1). The granitic orthogneisses develops three distinct microstructural types, as follows: type I – augen orthogneiss, type II – banded orthogneiss and type III – mylonitic orthogneiss, each representing an evolutionary stage of a progressively deformed granite. Type I orthogneiss is composed of partially recrystallized K‐feldspar porphyroclasts surrounded by wide fronts of myrmekite, fully recrystallized quartz aggregates and interconnected monomineralic layers of recrystallized plagioclase. Compositional layering in the type II orthogneiss is defined by plagioclase‐ and K‐feldspar‐rich layers, both of which show an increasing proportion of interstitial minerals, as well as the deformation of recrystallized myrmekite fronts. Type III orthogneiss shows relicts of quartz and K‐feldspar ribbons preserved in a fine‐grained polymineralic matrix. All three types have the same assemblage (quartz + plagioclase + K‐feldspar + muscovite + biotite + garnet + sphene ± ilmenite), but show systematic variations in the composition of muscovite and garnet from types I to III. This is consistent with the equilibration of the three types at different positions along a prograde P?T path ranging from <15 kbar and <700 °C (type I orthogneiss) to 19–20 kbar and >700 °C (types II and III orthogneisses). The deformation types thus do not represent evolutionary stages of a highly partitioned deformation at constant P?T conditions, but reflect progressive formation during the burial of the continental crust. The microstructures of the type I and type II orthogneisses result from the dislocation creep of quartz and K‐feldspar whereas a grain boundary sliding‐dominated diffusion creep regime is the characteristic of the type III orthogneiss. Strain weakening related to the transition from type I to type II microstructures was enhanced by the recrystallization of wide myrmekite fronts, and plagioclase and quartz, and further weakening and strain localization in type III orthogneiss occurred via grain boundary sliding‐enhanced diffusion creep. The potential role of incipient melting in strain localization is discussed.     

Mylonitic microfabrics from the rocks of MCT zone in Alakhnanda valley,Garhwal Himalaya

MCT Zone of Alakhnanda valley is a major ductile shear zone in Garhwal Himalaya, which is characterised by different types of mylonite rocks. On the basis of grain size and the percentage of matrix in the rock, zones comprising protomylonite, augen mylonite, mylonite and ultramylonite have been identified. The study of microstructures, grain size and crystallographic preferred orientation of quartz c-axis fabric reveals that the rocks of the MCT zone were deformed by a combination of intracrystalline creep (power law creep) and grain boundary migration (sliding super plasticity).     

Water assisted dynamic recrystallization and weakening in polycrystalline bischofite

Artificially prepared specimens of bischofite (MgCl₂-6H₂O) have been experimentally deformed at temperatures between 20 and 100°C, strain rates between 10⁻⁴ and 10⁻⁸⁸ s⁻¹, and confining pressures between 0.1 and 28 MPa. Development of microstructure with strain was studied by in-situ deformation experiments, and results of these were correlated with observations made on thin sections of deformed samples.In a first series of experiments the effect of grain size, impurity content and water content on the flow behaviour was investigated. Addition of about 0.1 wt.% water to dry samples was found to decrease the flow stress by a factor of 5. This effect was found to be associated with the formation of a thin fluid film on grain boundaries, strongly enhancing dynamic recrystallization due to the movement of high-angle grain boundaries, and possibly also to enhanced intracrystalline plasticity due to excess water present in the lattice. In a second series of experiments the strain-rate sensitivity of the flow stress of selected samples was investigated. Two regimes could be distinguished: one with a stress exponent n = 4.5 in the power law creep equation for values of the differential stress above 2.0 MPa, and one with n = 1.5 for stresses below this value.The main deformation mechanisms were intracrystalline slip, twinning, and grain-boundary sliding. Recrystallization occurred by subgrain rotation and high-angle grain-boundary migration. The rates of grain-boundary migration fell into two different regimes, one regime being distinguished by extremely fast migration rates. The applicability of the experimentally found flow law to the behaviour of bischofite rocks in nature is discussed.     

辉绿岩脆-塑性变形转化的高温高压实验研究

以天然叶腊石为传压介质, 在温度800~100 0℃、围压0.6~1.0 GPa和应变速率10-4~10-5 s-1条件下, 对Maryland辉绿岩的脆性-塑性转化进行了实验研究.实验结果表明, 在10-4~10-5 s-1应变速率和固定围压1.0 GPa条件下, 当温度低于800℃时, 岩石变形为典型脆性破裂; 温度高于1000℃时岩石变形以准稳态蠕变为主; 温度在800~950℃之间, 岩石变形从脆性破裂向准塑性流动转化.温度变化对岩石脆-塑性转化影响敏感度高于压力变化对变形的敏感度.显微构造观察显示, 辉绿岩脆-塑性转化以稀疏弥漫状共轭塑性流动网络为特征.      

Very low temperature,natural deformation of fine grained limestone: a case study from the Lucania region,southern Apennines,Italy

Abstract

The deformation behavior of fine grained limestones from the Monte Sirino area (Lucania region) of the southern Apennines has been analysed by constraining microstructural observations and crystallographic fabrics with data on the metamorphic conditions of deformation. X-ray and infrared analysis of clay minerals, together with illite ‘crystallinity’ data, suggest that the studied rocks underwent very low grade metamorphism in the deep diagenetic zone. The limestones consist of very fine grained (<10 μm) aggregates of micrite. Elliptically-shaped radiolarians, preserved as moulds with coarser (>20 μm) crystalline fillings, provide common strain markers. Optical microstructures and strain analysis indicate heterogeneous intracrystalline strain in the coarser (>50 μm) calcite. On the other hand, SEM and TEM observations, and crystallographic fabrics determined by X-ray texture goniometry, indicate a deformation involving not only intracrystalline slip, but also an important component of grain boundary sliding in the fine grained matrix. The inferred microscopic deformation mechanisms are compared with constitutive flow laws derived from experimental studies. For the maximum inferred temperature of deformation of 250 °C and geologic strain rates of 10^?13?10^?15 s^?1, deformation mechanism maps for calcite suggest twinning and other glide mechanisms to be active in grains larger than about 5?10 μm. Smaller grains would be mostly deformed by grain size sensitive creep mechanisms, which include both diffusion mass transfer processes and grain boundary sliding. Deformation features observed in the study limestones are compatible with the prediction of such temperature-dependent mechanism maps. © 2001 Éditions scientifiques et médicales Elsevier SAS     

Simulations of hydro-fracking in rock mass at meso-scale using fully coupled DEM/CFD approach

The paper deals with two-dimensional (2D) numerical modelling of hydro-fracking (hydraulic fracturing) in rocks at the meso-scale. A numerical model was developed to characterize the properties of fluid-driven fractures in rocks by combining the discrete element method (DEM) with computational fluid dynamics (CFD). The mechanical behaviour of the rock matrix was simulated with DEM and the behaviour of the fracturing fluid flow in newly developed and pre-existing fractures with CFD. The changes in the void geometry in the rock matrix were taken into account. The initial 2D hydro-fracking simulation tests were carried out for a rock segment under biaxial compression with one injection slot in order to validate the numerical model. The qualitative effect of several parameters on the propagation of a hydraulic fracture was studied: initial porosity of the rock matrix, dynamic viscosity of the fracking fluid, rock strength and pre-existing fracture. The characteristic features of a fractured rock mass due to a high-pressure injection of fluid were realistically modelled by the proposed coupled approach.

     

Very low temperature,natural deformation of fine grained limestone: a case study from the Lucania region,southern Apennines,Italy

The deformation behavior of fine grained limestones from the Monte Sirino area (Lucania region) of the southern Apennines has been analysed by constraining microstructural observations and crystallographic fabrics with data on the metamorphic conditions of deformation. X-ray and infrared analysis of clay minerals, together with illite ‘crystallinity’ data, suggest that the studied rocks underwent very low grade metamorphism in the deep diagenetic zone. The limestones consist of very fine grained (<10 μm) aggregates of micrite. Elliptically-shaped radiolarians, preserved as moulds with coarser (>20 μm) crystalline fillings, provide common strain markers. Optical microstructures and strain analysis indicate heterogeneous intracrystalline strain in the coarser (>50 μm) calcite. On the other hand, SEM and TEM observations, and crystallographic fabrics determined by X-ray texture goniometry, indicate a deformation involving not only intracrystalline slip, but also an important component of grain boundary sliding in the fine grained matrix. The inferred microscopic deformation mechanisms are compared with constitutive flow laws derived from experimental studies. For the maximum inferred temperature of deformation of 250 °C and geologic strain rates of 10^–13–10^–15 s^–1, deformation mechanism maps for calcite suggest twinning and other glide mechanisms to be active in grains larger than about 5–10 μm. Smaller grains would be mostly deformed by grain size sensitive creep mechanisms, which include both diffusion mass transfer processes and grain boundary sliding. Deformation features observed in the study limestones are compatible with the prediction of such temperature-dependent mechanism maps.     

Fracturing,fluid flow and shear zone development: Relationships between chemical and mechanical processes in Proterozoic mafic dykes from southwestern Montana,USA

Fluids can play an important role in the localization of deformation in the deep crust, yet the specific mechanisms active during the complex interactions between metasomatism, metamorphism and deformation remain elusive. Precambrian metagabbronorite dykes in southwest Montana contain fractures filled with Hbl±Grt and discrete cm‐scale shear zones with well‐preserved strain gradients. This system offers an ideal opportunity to constrain the chemical and mechanical processes that facilitated strain localization. An early M₁ assemblage of Grt₁+Cpx₁+Pl₁+Qz developed at conditions of 0.51–0.85 GPa and 500–700°C and is preserved largely as a static replacement of relict igneous phases (Opx, Pgt, Pl) in coronitic textures. An M₂ assemblage characterized by Grt₂+Pl₂±Cpx₂+Hbl+Scp+Qz developed at 0.86–1.00 GPa and 660–730°C coincided with fluid flow and deformation associated with shear zone development. Microstructural observations in marginal protomylonite/mylonite and laminated ultramylonite suggest a shear zone evolution that involved (1) nucleation from pre‐existing fractures that were sites for major fluid infiltration, (2) initial widening coincident with grain‐size reduction by microfracturing, dislocation creep, and synkinematic metamorphic reaction by solution transfer, and (3) a switch in the dominant deformation mechanisms active in the ultramylonite from grain‐size insensitive mechanisms to grain‐size sensitive granular flow accommodated by fluid‐assisted diffusion. Throughout this evolution, the effective bulk compositions of the rock volumes responding to metamorphism changed through a combination of mechanical and metasomatic processes.     

Orogenic Gold Mineralization in the Qolqoleh Deposit, Northwestern Iran

The Qolqoleh gold deposit is located in the northwestern part of the Sanandai‐Sirjan Zone, northwest of Iran. Gold mineralization in the Qolqoleh deposit is almost entirely confined to a series of steeply dipping ductile–brittle shear zones generated during Late Cretaceous–Tertiary continental collision between the Afro‐Arabian and the Iranian microcontinent. The host rocks are Mesozoic volcano‐sedimentary sequences consisting of felsic to mafic metavolcanics, which are metamorphosed to greenschist facies, sericite and chlorite schists. The gold orebodies were found within strong ductile deformation to late brittle deformation. Ore‐controlling structure is NE–SW‐trending oblique thrust with vergence toward south ductile–brittle shear zone. The highly strained host rocks show a combination of mylonitic and cataclastic microstructures, including crystal–plastic deformation and grain size reduction by recrystalization of quartz and mica. The gold orebodies are composed of Au‐bearing highly deformed and altered mylonitic host rocks and cross‐cutting Au‐ and sulfide‐bearing quartz veins. Approximately half of the mineralization is in the form of dissemination in the mylonite and the remainder was clearly emplaced as a result of brittle deformation in quartz–sulfide microfractures, microveins and veins. Only low volumes of gold concentration was introduced during ductile deformation, whereas, during the evident brittle deformation phase, competence contrasts allowed fracturing to focus on the quartz–sericite domain boundaries of the mylonitic foliation, thus permitting the introduction of auriferous fluid to create disseminated and cross‐cutting Au‐quartz veins. According to mineral assemblages and alteration intensity, hydrothermal alteration could be divided into three zones: silicification and sulfidation zone (major ore body); sericite and carbonate alteration zone; and sericite–chlorite alteration zone that may be taken to imply wall‐rock interaction with near neutral fluids (pH 5–6). Silicified and sulfide alteration zone is observed in the inner parts of alteration zones. High gold grades belong to silicified highly deformed mylonitic and ultramylonitic domains and silicified sulfide‐bearing microveins. Based on paragenetic relationships, three main stages of mineralization are recognized in the Qolqoleh gold deposit. Stage I encompasses deposition of large volumes of milky quartz and pyrite. Stage II includes gray and buck quartz, pyrite and minor calcite, sphalerite, subordinate chalcopyrite and gold ores. Stage III consists of comb quartz and calcite, magnetite, sphalerite, chalcopyrite, arsenopyrite, pyrrhotite and gold ores. Studies on regional geology, ore geology and ore‐forming stages have proved that the Qolqoleh deposit was formed in the compression–extension stage during the Late Cretaceous–Tertiary continental collision in a ductile–brittle shear zone, and is characterized by orogenic gold deposits.