西藏拉轨岗日构造带孔木韧性剪切带特征

在拉轨岗日构造带佩枯错新发现了一条韧性剪切带,至少存在3期变形.韧性剪切作用可能与应变能转化的热能有关,应变能常沿断裂集中,形成方解石脉;然后,经由北往南的逆冲推覆,形成(叠瓦状)逆冲推覆构造;最后,由于山体重力势能的作用,伸展跨塌.该剪切带成为藏南拆离系的组成部分.     

西藏拉轨岗日构造带孔木韧性剪切带特征

在拉轨岗日构造带佩枯错新发现了一条韧性剪切带，至少存在3期变形。韧性剪切作用可能与应变能转化的热能有关，应变能常沿断裂集中，形成方解石脉；然后，经由北往南的逆冲推覆，形成(叠瓦状)逆冲推覆构造；最后，由于山体重力势能的作用，伸展跨塌。该剪切带成为藏南拆离系的组成部分。     

论吕梁山区近周营—罗家岔一带五台晚期韧性剪切带特征

吕梁山区晚期构造变形主要表现为在收缩构造体制下形成一系列线状同斜倒转褶皱及逆冲推覆型韧性断层及韧性剪切带,并伴随有壳源型花岗岩浆活动。韧性剪切带主要发育在近周营—罗家岔一带的吕梁群两侧边界上,为区内规模大、影响广的区域性构造。由北至南,主剪切带走向由近南北向过渡为向东西向延伸,剪切带内构造岩石类型主要有变余糜棱岩、构造片岩。剪切带内矿物拉伸线理及各类旋转应变标志指示上盘相对下盘逆冲推覆;从剪切带所涉及的地质体及与周围构造的相互关系确定,主体形成于新太古代五台运动末期的造山过程。     

一种走滑剪切一逆冲推覆相互转换的变形体系——以桂东南那卜地区NE向和NW向两组韧性剪切带为例

桂东南那卜地区潭超单元及其围岩中，主期变形变质作用形成的韧性剪切带可分为2类：NE向右行走滑性质的韧性剪切带；NW向逆冲推覆性质的韧性剪切带。通过对以上2类韧性剪切带的构造样式、显微组构以有运动学特征等的综合分析表明，它们形成的构造应力是NE－SW向的，在这一应力的作用下，使早期NE向和NW向构造重新活动，从而构成了一种NE向走滑－NW向逆冲的相互转换程式，即NE向右行走滑性质韧性剪切带和NW向逆冲推覆性质韧性剪切带相互转换的韧性变形体系。     

对吕梁山区大蛇头一带吕梁晚期推覆型韧性剪切带特征的分析

吕梁山区吕梁晚期构造变形表现为区域性褶皱构造和北东向逆冲推覆型韧性剪切带。其中大坡-大蛇头一带吕梁晚期推覆型韧性剪切带具代表意义,通过对韧性剪切带构造形迹研究,对认识吕梁造山运动具有重要意义。     

雷山县开觉韧性剪切带特征及其构造意义

通过对开觉韧性剪切带的研究，认为开觉断层两盘岩石的变质变形差异主要是由于韧性剪切作用所造成的：北西盘岩石仅发生了区域变质；南东盘岩石则发生了区域变质和韧性剪切热变质。韧性剪切应变和热变质作用是重力滑动－逆冲推覆构造体系发展演化过程中的一个表现，韧性剪切应变的一些组构，具有明显的构造运动学意义。     

襄樊——广济断裂西段三里岗——三阳构造混杂岩带构造变形与演化

襄樊——广济断裂西段的三里岗——三阳地区出露有构造混杂岩,以含蛇绿岩残块为特征,经历了复杂的构造变形和演化过程。不同区段的构造解析与对比表明,中生代以来该构造混杂岩带主要遭受了4期变形构造的叠加改造:1)高温塑性变形(D₁),表现为蛇绿岩残块内部具网状强应变带和透镜状弱应变域相互交织的构造变形样式,强应变带形成以镁铁质糜棱岩为特征的高温韧性剪切带,显示深层次构造变形特征;2)逆冲推覆变形(D₂),构造混杂岩带发育叠瓦状逆冲推覆构造和双冲构造,南界韧性剪切带是构造混杂岩带整体运移的主推覆面,发育长英质糜棱岩,形成于中等构造层次,岩石中发育镁铁质糜棱岩糜棱面理的褶皱构造,显示陆内逆冲推覆对先期高温塑性变形构造的叠加改造;3)韧脆性右行平移剪切(D₃),形成构造混杂岩带内部浅层次构造变形,构造混杂岩带南侧的花山群钙质片岩揉皱变形,形成枢纽近直立的不对称褶皱,指示右行平移剪切变形;4)伸展正断层(D₄),主要发育于构造混杂岩带北侧,呈NW——SE向展布,控制晚白垩世断陷盆地的形成与沉积充填。     

吉林省辉南地区含金韧性剪切带的构造地质特征

吉林省辉南地区韧性剪切带岩石变形特征复杂多样。通过对剪切带内岩石的有限应变测量和变形环境的分析,认为本区韧性剪切带发育在地壳浅层次的低温低压环境,为逆冲推覆韧性变形,其变形变质作用相当于低绿片岩相,具有独特的构造组合和岩石变形特征,差异应力值为４５－５４ＭＰａ,剪切位移量约为１２．５ｋｍ,形成时间为中元古宙。     

西藏冈底斯带扎雪-门巴韧性变形带形成时代及构造背景

扎雪-门巴韧性变形带位于冈底斯构造带中部,是一条由北而南的逆冲推覆兼具右行走滑的斜冲韧性剪切带。带内所形成的构造岩主要为构造片麻岩和糜棱岩类,对花岗质糜棱岩中的黑云母进行40Ar/39Ar年龄测试,获得105.2±1.7Ma,认为该韧性剪切带形成于早白垩世。岩石组合和显微构造特征表明该韧性剪切带形成于中绿片岩相到高绿片岩相环境,可能与班公湖-怒江弧后洋盆的闭合碰撞有关。     

小北湖韧性剪切带特征

小北湖韧性剪切带分布于敦密断裂北侧泥盆纪地层中,为逆冲推覆韧性剪切带,发育各种糜棱岩、叶理和线理构造及显微构造,其变形机制为简单剪切变形,属低温韧－－脆型剪切带。     

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.     

Deformation condition determination and strain analysis: Application of microstructural and microthermometry study of the Zamanabad Shear Zone (East of Iran)

Microstructural analysis and microthermometry are useful methods for determining the deformation evolution. To address this issue, rheological behavior of quartz, feldspar and calcite in veins and host rocks during deformation, are presented in the mylonite zone of the dextral reverse Zamanabad Shear Zone (ZSZ), in northern part of Sistan Suture Zone (SSZ), in east of Iran. Microstructure evidences revealed two evolution stages of high and low temperature deformation. Quartz microstructures in the ZSZ show abundant evidences for early high-temperature plastic deformation (e.g. Bulging recrystallization (BLG)) which are as microstructures with SW directed ductile shearing in the central parts of the ZSZ. This shear zone shows progressively decreasing strain away from the central of shear zone toward the wall. High-temperature microstructures are overprinted partly or completely during shearing by the later low-temperature deformation (e.g. Pressure solution, fractures, veinlets). Microstructural observations of veins (quartz and calcite) confirms the results of microstructures in the host rock, as quartz veins occurred from peak metamorphic conditions (<400°C) and then in lower P–T conditions have been formed calcite veins (~250°C). According to microthermometric studies, two primary fluid groups are observed in quartz veins: (1) fluids trapped during peak deformation conditions, with higher-salinity, They were initially trapped at ~300–400°C, (2) smaller fluids by trapping of low-salinity inclusions at ~240–180°C that related to subsequent phases of shear zone exhumation in lower deep. Microthermometry results and microstructural analysis indicate deformation under lower greenschist facies conditions for the ZSZ, and then exhumation of the early of high-temperature rocks within regime of ductile-brittle transition to brittle.     

海南岛西部戈枕含金剪切带及其金矿成矿系列

古生代以来，海南西部戈沈含金剪切带至少经历了三次类型不同的构造变形，并发生了三次相关的金矿化。该剪切带的构造变形，在加里东旋回发生于抱板群矿源层下构造层次，表现为韧性剪切，其晚期形成含金长英质脉；在海西－印支旋回发生于中构造层次，表现为韧－脆性变形，形成糜棱岩型和石英脉型金矿床。     

新疆萨尔托海石英菱镁岩中发育的韧性剪切带及其对金矿的控制

萨尔托海金矿产在达拉布特蛇绿混杂岩带中。本文首次在该金矿区厘定出韧性剪切带,糜棱岩或者糜棱岩化石英菱镁岩中构成糜棱面理的矿物(铬云母、石英)形成于韧性剪切变形过程中,而切割糜棱面理的方解石-石英-黄铜矿-白云母脉代表脆性变形阶段的流体活动。根据矿物组合相互切割关系,识别出三期构造变形:早期NE向韧性变形(形成铬云母-石英组合)之后,发生了应力方向显著不同的破裂,形成NNW向分布的方解石-石英-黄铜矿-白云母脉;再晚期,应力方向又恢复到NE向,发育了浅层次的脆性构造破坏,形成了白云母-石英细脉。韧性剪切变形向脆性变形转换期间形成了石英-碳酸盐脉,其中往往含硫化物和自然金,此阶段是萨尔托海金矿的主要成矿时期。韧性剪切带控制着萨尔托海地区的金矿分布,成矿作用主要受沿剪切带迁移流体的控制,穿切糜棱面理的方解石-石英-黄铜矿-白云母脉是主要的找矿标志。韧性剪切带对金矿的显著控制表明,韧脆性转换期间形成的含硫化物石英碳酸盐脉以及相伴生的热液蚀变使金富集成矿,矿体一般赋存在断裂构造复杂的膨胀部位。萨尔托海金矿的成因与蛇绿岩的形成和演化没有关系。对韧性剪切带的系统研究是在该地区取得找矿勘探突破的关键。     

云蒙山变质核杂岩抬升过程中伸展拆离和岩浆底辟联合作用的证据

北京地区云蒙山变质核杂岩在白垩纪阶段抬升的早期,伴随着沿四合堂剪切带由北向南的拆离滑脱和大型花岗闪长岩的垂向侵位,晚期变形发生在花岗闪长岩岩基周边及其邻近围岩中,形成云蒙山剪切带,并伴随大量同构造的花岗岩和伟晶岩岩脉灌入。剪切带中所有的岩脉都随时间发生了不同程度的变形,较老的岩脉形成紧闭的圆柱状褶皱,枢纽与剪切带的线理和面理接近平行。岩脉与剪切带中L-S组构的平行化作用主要是由于这种转动的结果。岩脉的成分和长英指数随它们的变形程度发生变化,说明持续的岩浆分异作用与韧性剪切变形是同时发生的。云蒙山剪切带由岩浆底辟引起的上盘岩石重力所驱动,并不断得到同构造侵位岩脉的补充,起到存储和不断改造侵位岩脉的作用。早期伸展体制下形成的四合堂剪切带局部遭受云蒙山剪切带的改造或复合。该地区的岩石、构造和同构造岩脉的变形几何学和运动学证据表明,太古宙结晶基底的抬升是下部岩浆底辟与上部地壳伸展拆离共同作用的结果。     

Coexisting ultramylonite and pseudotachylyte from the eastern segment of the Mahanadi shear zone, Eastern Ghats Mobile Belt

Pseudotachylytes occur associated with mylonite and ultramylonite in the Mahanadi shear zone (MSZ) in the Eastern Ghats Mobile Belt (EGMB). The MSZ is about 200 km long curvilinear high strain zone trending WNW-ESE in its eastern part that splays out in the west. In Kantilo-Ganian segment of MSZ in northern EGMB, an interbanded sequence of granulite facies lithoassemblage has undergone ductile shearing. Kinematic studies of mylonite and ultramylonite indicate MSZ to be a NE-dipping, extensional type ductile shear zone. Non-coaxial metamorphic growth of garnet and presence of truncated sillimanite-fish in ultramylonite suggest high temperature regime during shearing. Pseudotachylytes in MSZ occur as millimetre thick layers to decimetre thick zones containing fragments of mylonite, ultramylonite and lithic clasts. Pseudotachylyte generation veins are mostly sub-parallel to C-planes and the injection veins cross-cut at high angle to these. The presence of an isotropic glassy matrix, injection features, corroded grains and dendritic microlites can be evidences for the existence of a melt phase. The composition of pseudotachylyte matrix (by EPMA) indicates silica deficiency with higher normative hypersthene, plagioclase and lower quartz compared with average whole rock composition for host. Absence of overprinting of mylonitic fabric on pseudotachylytes indicates their formation by brittle failure without passing through a plastic deformation and thus a two stage development for mylonite-ultramylonite and pseudotachylyte generation is suggested.     

大别造山带南界襄樊—广济断裂带的演化规律与构造意义

自中三叠世扬子与华北板块发生碰撞—深俯冲作用以来,大别造山带南界上的襄樊—广济断裂带主要经历过两次变形事件: 1)早期变形事件发生在中三叠世末—晚三叠世初的造山带折返阶段,表现为造山带南边界上的韧性剪切带。这期北西—南东走向的剪切带向南西陡倾,发育北西—南东向的矿物拉伸线理,主要为右行走滑的运动性质,属于造山带斜向折返的侧边界走滑剪切带。造山带折返过程中将前陆褶断带北缘原先东西向褶皱改造为北西—南东走向。2)晚期变形事件发生在晚侏罗世,表现为脆性逆冲断层,使得前陆褶断带向北东逆冲在造山带南缘之上,同时在前陆上形成了一系列的逆冲断层。该断裂带的晚期逆冲活动与郯庐断裂带左行平移同时发生,代表了滨太平洋构造活动的开始。     

辽南金州隆起区构造变形及流体作用

详细的野外和室内宏观及微观构造分析和有限应变测量结果表明,自中生代以来,本区至少经历了两期变形,即早期的收缩为及后期的伸展反应,收缩应变主要表现为滑脱－－逆冲推覆作用,具有显著的构造层次性,自中、下构造怪次至上支次依次表现为：基底与盖层之间以角闪石及长石碎斑为主的糜棱岩为特征的韧性滑脱剪切罗系之上的逆冲推覆构造;在该构造２剪切主上部盖层中的寒武系,石炭系等逆冲于侏罗系之上的逆冲推覆构造;在该构造变形过程中伴随有强烈的岩浆活动,表明当时的区域热流值较高。伸展应变及同时发生的基底隆升作用,主要表现为基底和盖层中的韧性正剪切带及大量的正断层,基底中大量的NNE向张性白垩纪花岗斑岩脉及区域性的NNE向白垩纪盆地的形成都和本期构造活动相关。辽南地壳基底中大量的沿糜棱面理发育的长英质岩脉表明剪切变形过程中具有局部熔融作用的发生。对长英质岩脉经流体包裹体成分测试表明主要成分为分子水。在野外对长英质脉体的研究表明至少有两期：形成与滑脱作用有关的长英质脉体为含钾长石少、斜长石多、白色;而和伸展应变有关的长英质脉体钾长石含量明显增大,呈红色。两种长英质脉的褶皱变形反映了各自的变形机制。剪切作用过程中发生的动态局部熔融作用,具有自反馈的自组织特征,从而使长英质脉体在糜棱岩中呈现出韵律分布特征。辽南地壳在较短的时间内发生从收缩应变向伸展应变的转化。原因可能为收缩应变导致地壳显著缩短和增厚,并且同期的花岗岩浆的活动表明滑脱作用过程中莫霍面的初始温度较高并且区域热流值亦较高。这种地壳及其热状态的不均衡,导致地壳在较短的时间内发生基底的隆升及相伴随的伸展作用。     

郯庐断裂带肥东段剪切活动锆石U-Pb测年

郯庐断裂带肥东段出露的桃源韧性剪切带内发育有长英质超糜棱岩、长英质伟晶岩脉体等。这两种构造岩与剪切带呈现不同的穿切关系, 分别代表着剪切活动不同时期的产物, 它们可以为郯庐断裂带的剪切年限提供重要的年代学制约。本次研究从长英质超糜棱岩的U-Pb锆石测年得出了133.3±4.1 Ma的变质锆石年龄。结合笔者先前得出的伟晶岩脉129±3.3 Ma年龄判断, 郯庐断裂带在133 Ma左右有一次剪切活动, 该次剪切活动在129 Ma左右仍有着较弱的持续, 指示肥东地区在137~126 Ma的时间段内, 有一次挤压活动叠加。此外, 长英质超糜棱岩样品中捕获的1.9 Ga和2.4 Ga的锆石, 很可能来自华南板块基底。     

藏南冈底斯岩浆带中段曲水韧性剪切带的变形特征及其年代学约束

藏南曲水地区鸡公-色甫韧性剪切带系统的运动学和动力学研究,不仅对造山带构造研究具有重要理论意义,而且对青藏高原中-南部区域地质研究具有推进作用.作为藏南冈底斯岩浆带曲水岩基中的重要断裂构造,曲水韧性剪切带经历了新生代以来的大规模构造变形,其中走滑剪切作用最为显著,整体表现为右行走滑为主.通过对曲水剪切带中的构造片岩、初糜棱岩、糜棱岩以及长英质脉体等野外观测并结合室内镜下薄片以及石英EBSD(electron backscatter diffraction)组构分析,认为曲水剪切带主要经历了一期韧性变形事件.根据石英-长石变形矿物对并结合石英EBSD组构分析得出,构造变形发生的温度大约为500~550 ℃,高绿片岩相到角闪岩相.剪切带内普遍发育有不对称的褶皱、构造透镜体、σ碎斑、S-C组构和石香肠等变形组构,显示出右行走滑的特征.对研究区34组糜棱面理和9组拉伸线理进行极射赤平投影,糜棱面理的优选方位约为355°∠70°,拉伸线理产状约为95°∠8°.此外,在糜棱岩中发育两类长英质脉体,根据野外分布特征、显微组构、锆石成因学以及岩石地球化学特征综合研究认为,两类长英质脉体为同构造剪切脉体,其年代学可以对剪切带的形成时限起到很好的制约.通过对两套长英质脉体分别进行LA-ICP-MS锆石U-Pb定年,得到了38.67±0.88 Ma和35.05±0.29 Ma两组加权平均年龄,表明了曲水剪切带韧性变形发生于35~38 Ma的始新世末期(普利亚本期).这一年龄值处于印度-亚洲大陆晚碰撞期,因此曲水韧性剪切带右行走滑事件可能是印度板块持续向北俯冲,构造应力在欧亚板块边缘释放引起的陆内构造响应.