Deformation characteristics of granitic rocks in Erguna ductile shear zone,NE China

The Erguna ductile shear zone is situated in the Erguna Massif,which has been exposed along the eastern bank of the Erguna River in northeastern China.The authors present comprehensive study results on the macro-and micro-structures,finite strain and kinematic vorticity,quartz electron backscatter diffraction(EBSD)fabrics,and geochronology of granitic rocks in the Erguna ductile shear zone.The deformed granitic rocks have experienced significant SE-trending dextral strike-slip shearing.Finite strain and kinematic vorticity in all deformed granitic rocks indicate that the deformation is characterized by simple sheardominated general shearing with S-L tectonites.Mineral deformation behaviors and quartz C-axis textures demonstrate that the deformed granitic rocks developed under greenschist to amphibolite facies conditions at deformation temperatures ranging from 450 to 550℃.New LA-ICP-MS zircon U-Pb ages indicate that these granitic rocks were formed in Early Triassic(~248.6 Ma)and Early Cretaceous(~136.7 Ma).All the evidence indicates that this deformation may have occurred in Early Cretaceous and was related to the compression resulting from the final closure of the Mongol-Okhotsk Ocean.

A Large Ductile Sinistral Strike-Slip Shear Zone and Its Movement Timing in the South Qilian Mountains, Western China

There is a large ductile shear zone, 2 km wide and more than 350 km long, inthe South Qilian Mountains, western China. It is composed of volcanic, granitic and calcareousmylonites. The microstructures of the ductile shear zone show nearly E-W extending subverticalfoliation, horizontal and oblique stretching lineations, shearing sense from sinistral to obliquesinistral strike-slip from east to west, 'A' type folds and abundant granitic veins. Measuredlattice preferred orientations (LPOs) of the mylonitic and recrystallized quartz of the graniticmylonite in the west segment suggest a strong LPO characterized by the dominant slip systems (1010) formed at high temperature (>650 deg C). K-feldspar of the mylonite shows an ^(39)Ar/^(40)Arhigh-temperature plateau age of 243.3 +- 1.3 Ma, and biotite, 250.5 +- 0.5 Ma, which represent theformation age of the ductile shear zone. The ^(39)Ar/^(40)Ar plateau ages of 169.7 +- 0.3 Ma and160.6 +- 0.1 Ma and the ^(39)Ar/^(40)Ar isochron ages of 166.99 +- 2.37 Ma and 160.6 +- 0.1 Ma ofbiotites in the mylonite represent the subsequent deformation age. These ages indicate that thisductile shear zone is similar to the Altun and South Kunlun sinistral ductile shear zones in itsages of movement, formation, reactivation and duration.

Analysis of the Ore-Controlling Structure of Ductile Shear Zone Type Gold Deposit in Southern Beishan Area, Gansu, Northwest China

The ductile shear zone-type gold deposit is a kind that both the ore-forming mechanism and ore-controlling factors are closely related to the ductile shear zone and its evolution. Ductile shear zone develops in Beishan area, Gansu of Northwest China, and develops especially well in the south belt. The controls of the ductile shear zone on gold deposits are as follows. （1） The regional distribution of gold deposits （and gold spots） is controlled by the ductile shear zone. （2） The ductile-brittle shear zone is formed in the evolution process of ductile shear zone and both are only ore-bearing structures and control the shape, attitude, scale, and distribution of mineralization zones and ore-bodies. （3） Compresso-shear ductile deformation results in that the main kind of gold mineralization is altered mylonite type and the main alteralization is metasomatic. （4） Ore-bearing fracture systems are mainly P-type ones, some D-type and R-type ones, but only individual R＇-type and T-type ones. （5） Dynamic differen- tiation and dynamic metamorphic hydrothermal solution resulting from ductile deformation is one of the sources of ore-forming fluid of gold mineralization, and this is identical with that ore-forming materials are mainly from metamorphic rocks, and ore-forming fluid is mainly composed of metamorphic water, and with the fluid inclusion and geo-chemical characteristics of the deposit. （6） There is a negative correlation between the gold abundance and susceptibility anlsotropy （P） of the altered mylonlte samples from the deposit, which shows that the gold mineralization is slightly later than the structural deformation. All above further expound the ore-forming model of the ductile shear zone type of gold deposits.

Transportation of REE in the Ductile Shear Zone in Hetai Gold Deposit, Guangdong Province

The REE transportation in two sorts of mylonites of ductile shear zone, in Hetai gold deposit, Guangdong province was studied. The results show that there is REE compositional variation regularly in the ductile shear zone. When mica-quartz schist and migmatite are changing into mylonites or ultramylonites, i.e., along with intensifying deformation, the contents of each rare earth element and the total contents of the LREE, HREE and REE increase or decrease regularly, but the REE patterns of the rock are accordant. The isocon diagram of the tectonic rocks before and after deformation shows that the REE compositional variation of the mylonites or ultramylonites are very small, but there is a few REE moving in or out in the rock deformation. The reason of the REE compositional variation is that there are volume change and fluid flow in the rock deformation, and it leads to the LREE relative enrichment and HREE relative loss.

Multi-Layered Low-Angle Ductile Detachment System in Dabie-Sulu UHPM and HPM Belts, China

The present-day observed crustal-scale tectonic style of ultrahigh-pressure metamorphic (UH-PM) and high-pressure metamorphic (HPM ) belts in the Dabie-Sulu region was dominantly formedby extensional processes, postdating the Triassic collision between the Sino-Korean and Yangtze cratons. The extensional structures overprinting the previous structures related to contraction that produced the thickened continental crust of the UHPM and HPM belts, in particular display the typical features of a Cordilleran-type metamorphic core complex, in which at least four regionalscale, low-angle ductile shear zones that constitute a detachment system, are recognized in the Dabie region. In the Sulu region, the extensionaI structures show in the form of small-scale domes or a regional-scale SE-dipping pseudo-monocline. The geometry and the kinematics of tbe detachment zones are briefly described and their significance for the exhumation of UHPM and HPM rocks is discussed. It is iniliated that the subhorizontal crustal-scale extensional flow in the middle-lower crust, under amphibolite- to greenschist-facies conditions, was an important tectonothermal process at 200- 170 Ma and the exhumation or the UHPM and HPM rocks was achieved at least in part along multi-layered detachment zones. The regional detachment system has been the main factor enabling UHPM and HPM rocks to be brought from middle-lower crustal levels to middle-upper crustal levels.

Sequence of Ductile Shear Zones in UHP Metamorphic Province with in Dabie Massif,China

Structural studies in the Dabie massif show that distribution of strain is extremely heterogeneous and illustrates the pattern of deformation partitioning in the ultra high pressure (UHP) metamorphic province on all scales. Based on the field structural analysis along with microstructural observation, at least five widespread episodes of ductile shear zone systems are identified by using geometric, kinematic and rheological indicators and they constitute a shear zone sequence in the UHP metamorphic province within the Dabie massif (DM), China. Each shear zone system, for example, the UHP eclogite facies shear zone system in the sequence, exhibits its own features including geometric styles, mineral assemblages, metamorphic pt conditions and deformation regimes during the formation of such shear zone system. Detailed macro and micro scopical features of different episodes of the shear zones are given with respect to mechanism of strain localization and deformation partitioning. The tectonic significance during the creation and exhumation of the UHP metamorphic rocks is evaluated briefly, as well. It is argued that the ductile shear zones in the UHP metamorphic province play an important role in the Dabie mountain building geodynamic process.

Timing of the Early Paleozoic Yangtze and Cathysian Convergence： Constraint from U-Pb Geochronology of Hydrothermal Zircons from Mafic Mylonite within the Shoucheng-Piaoli Ductile Shear Zone, Northern Guangxi

Objective The northern Guangxi region is in the southwestern part of the Southern China continent,which is located at the junction of the southwest section of the Early Paleozoic Yangtze block and Cathaysian block.A series of NNE-trending ductile shear zones are developed in this region,and these ductile shear zones are mostly previously suggested boundary faults of the Early Paleozoic Yangtze block and Cathaysian block,such as the Shoucheng–Piaoli ductile shear zone in Northern Guangxi （Meng Yuanku et al., 2016; Zhang Xuefeng et al., 2015）.

Characteristics of Compositional Migration in Mylonites from the Ductile Shear Zones of the Southern Tancheng-Lujiang Fault Belt, Eastern Anhui Province

On the basis of field geology, three typical ductile shear zones in the southern part of the Tancheng-Lujiang fault belt have been chosen for a detailed study. Altogether ten samples of the tectonites have been collected for this study. The paper is focused on a comprehensive study of the tectonites in the medium-lower horizons of the ductile shear zones. The mineral compositions of the rocks are analyzed with EPMA and some typical whole-rock samples analyzed by chemical and ICP methods. Based on the comprehensive study of the characteristics of the deformation, the mineral assemblages and the changes of chemical composition of the bulk rocks, this paper presents a discussion on the relationship between the volume loss, the fluid flow and compositional changes during mylonitization of the ductile shear zones in this region. Our study shows that there are a large amount of fluids flowing through the shear zones during the process of mylonization, accompanied by the loss of rock volume and migration of elements and components. Modelling calculation results under different saturation conditions of fluids show that the maximum volume loss of the tectonites is about 60% relative to their protolith, while the fluid/rock ratio ranges from 10 to 103 in different ductile shear zones.

The aggregation characteristics and formation mechanism of nanoparticles in ductile shear zone

1 Introduction Nanoparticles are widely found in the ductile shear zone and it is considered to have a close relation with faulting.The sizes of these nanoparticles are generallyless than 100 nm.They have a variety of morphologies like globular structure rod-like and tubular,by the order aggregating of these nanoparticles various aggregations

Study on the Physical and Chemical Conditionsof Ore Formation of Hetai Ductile Shear Zone-Hosted Gold Deposit and Discovery of Melt Inclusions

The Hetai ductile shear zone-hosted gold deposit occurs in the deep-seated fault mylonite zone of the Sinian-Silurian metamorphic rock series. In this study there have been discovered melt inclusions, fluid-melt inclusions and organic inclusions in ore-bearing quartz veins of the ore deposit and mylonite for the first time. The homogenization temperatures of the various types of inclusions are 160℃, 180-350℃, 530℃ and 870℃ for organic inclusions, liquid inclusions, two-phase immiscible liquid inclusions and melt inclusions, respectively. Ore fluid is categorized as the neutral to basic K\++-Ca\+\{2+\}-Mg\+\{2+\}-Na\++-SO\+\{2-\}\-4-HCO\+-\-3-Cl\+- system. The contents of trace gases follow a descending order of H\-2O>CO\-2>CH\-4> (or <) H\-2>CO>C\-2H\-2>C\-2H\-6>O\-2>N\-2. The concentrations of K\++, Ca\+\{2+\}, SO\+\{2-\}\-4, HCO\+-\-3, Cl\+-, H\-2O and C\-2H\-2 in fluid inclusions are related to the contents of gold and the Au/Ag ratios in ores from different levels of the gold deposit.This is significant for deep ore prospecting in the region. Daughter minerals in melt inclusions were analyzed using SEM. Quartz, orthoclase, wollastonite and other silicate minerals were identified. They were formed in different mineral assemblages. This analysis further proves the existence of melt inclusions in ore veins. Sedimentary metamorphic rocks could form silicate melts during metamorphic anatexis and dynamic metamorphism, which possess melt-solution characteristics. Ore formation is related to the multi-stage forming process of silicate melt and fluid.

Petrological Study on the Ductile Shear Zones in the Core of the Eastern Qinling Orogenic Belt in Western Henan

A series of ductile shear zones of the overthrust and strike-slip-types and related ductile shear metamorphicrocks, including tectonic melange and mylonites. were formed in the core of the Qinling orogenic belt in thecourse of the Caledonian-Indosinian ductilc and brittle-ductile reworking. The study on their petrography. va-riations in composition and conditions of formation is conducive to revealing the metamorphism-deformationhistory of the core of the Qinling orogenic belt and further to understanding the dynamic mechanism of its evo-lution.

Introduction of Simulating the Motion of Rigid Ellipsoidal Objects in Ductile Shear Zone Based on the Jeffery's Theory

Rigid ellipsoidal objects(gravels and porphyroclasts)in ductile zone is an important factor to indicate the kinematics and dynamics.Jeffery’s theory(Jeffery G,1922),a quantitative research method,for the rotation ofthe rigid objects(no deformation)in the Newtonian fluid of the simple deformation field has been widely applied by geologists to the study of fabrics in rocks.The theory

Strain and kinematic vorticity analysis of the Louzidian low-angle ductile shear detachment zone in Chifeng,Inner Mongolia,China

The Louzidian low-angle ductile shear detachment zone at the south of Chifeng is a SE-dipping, low-angle normal fault system. It is composed mainly of ductile shear zone, ductile-brittle shear zone and brittle fault zone. The ductile shear zone consists of, from bottom to top, mylonitic rocks, protomylonites and mylonites. Finite strain measurement of feldspar strain markers from those rocks using the Rf /φ method shows that strain intensities (Es) of the mylonite at core of the ductile shear zone (Es=0.65-0.96) are higher than those of the mylonitic rocks close to the granite intrusions (Es=0.59-0.62) and of the protomylonites at top of the ductile shear zone (Es= 0.47-0.70), and the strain types of the protomylonites and mylonties are elongate strain and plane-flattening strain, respectively. The kinematic vorticity values (Wk) estimated by the Polar Mohr diagram and the Rigid Grain Net range from 0.81 to 0.90 with an average of 0.85 for the protomylonites, and from 0.53 to 0.80 with 0.66 on average for the mylonites; Wk values of the extensional crenulation cleavage, i.e., C′, estimated by C′ method range from 0.63 to 0.37 with an average of 0.50. The angles between the maximum principal stress and shearing direction determined using the Maximum effective moment criterion evolved from 61° to 69° and to 75°, and finally normal to shearing direction. The results of strain and kinematic vorticity measurements suggest that high strain corresponds to low kinematic vorticity. Kinematic vorticity measurements show that the Louzidian low-angle ductile shear detachment zone is a result of a combination of simple-dominated general shearing at the early stage and pure-dominated general shearing at the late stage. All these, together with isotope geochronology and regional tectonic background, suggest that the Louzidian ductile shear detachment zone resulted from a combination of crust extension and magma intrusion. The model of simple shear at the early stage and pure shear at the late stage in the formation of metamorphic core complex has probably general significance.

New Zircon U-Pb Geochronology of the Post-kinematic Granitic Plutons in the Diancang Shan Metamorphic Massif along the Ailao Shan-Red River Shear Zone and Its Geological Implications

The Ailao Shan-Red River fault zone is the boundary between the Yangtze block to the northeast and the Indochina block to the southwest.It is an important tectonic zone due to its role in the southeastward extrusion of the Indochina block during and subsequent to the Indian-Eurasian collision.Diancang Shan（DCS） high-grade metamorphic complex,located at the northwest extension along the Ailao Shan-Red River（ASRR） shear zone,is a representative metamorphic complex of the ASRR tectonic belt.Structural and microstructural analysis of sheared rocks in the high-grade metamorphic rocks reveals that they are coherent with solid-state high-temperature ductile deformation,which is attributed to left-lateral shearing along the ASRR shear zone.New LA-ICP-MS zircon U-Pb geochronological and microstructural studies of the post-kinematic granitic plutons provide a straightforward time constraint on the termination ductile left-lateral shearing and exhumation of the metamorphic massif in the ASRR shear zone.It is suggested that the left-lateral shearing along the ASRR shear zone ended at ca.21 Ma at relative lower-temperature or decreasing temperature conditions.During or after the emplacement of the young dikes at ca.21 Ma,rapid brittle deformation event occurred,which makes the DCS massif start fast uplift/exhumation and cooling to a shallow crustal level.

Strain Localized Deformation Variation of a Small-Scale Ductile Shear Zone

A continental-scale strike-slip shear zone frequently presents a long-lasting deformation and physical expression of strain localization in a middle to lower crustal level.However,the deformation evolution of strain localization at a small-scale remains unclear.This study investigated<10 cm wide shear zones developing in undeformed granodiorites exposed at the boundary of the continental-scale Gaoligong strike-slip shear zone.The small-scale ductile shear zones exhibit a typical transition from protomylonite,mylonite to extremely deformed ultramylonite,and decreasing mineral size from coarse-grained aggregates to extremely fine-grained mixed phases.Shearing sense indicators such as hornblende and feldspar porphyroclasts in the shear zone are the more significantly low-strain zone of mylonite.The microstructure and EBSD results revealed that the small-scale shear zone experienced ductile deformation under medium-high temperature conditions.Quartz aggregates suggested a consistent temperature with an irregular feature,exhibiting a dominated high-temperature prism <a> slip system.Additionally,coarse-grained aggregates in the mylonite of the shear zone were deformed predominantly by dislocation creep,while ultra-plastic flow by viscous grain boundary sliding was an essential deformation process in the extremely fine-grained(~50μm)mixed-phases in the ultramylonite.Microstructural-derived strain rates calculated from quartz paleopiezometry were on the order of 10^(-15) to 10^(-13) s^(-1)from low-strain mylonite to high strained ultramylonite.The localization and strain ratelimited process was fluid-assisted precipitation presenting transitions of compositions as hydrous retrogression of hornblende to mica during increasing deformation and exhumation.Furthermore,the potential occurrence of the small-scale shear zone was initiated at a middle-deep crust seated crustal condition dominated by the temperature-controlled formation and rheological weakening.

黑龙江多宝山铜矿区韧性剪切变形时代及其对铜矿化改造的约束

黑龙江多宝山斑岩铜矿主要赋存于奥陶纪花岗闪长岩中,少量发育于奥陶纪花岗闪长斑岩及奥陶系多宝山组安山岩中,铜矿化以浸染状、细脉-浸染状为主。成矿过程经历了斑岩期、剪切变形期。矿区发育韧性剪切变形带,多宝山组、花岗闪长岩、花岗闪长斑岩、安山质凝灰角砾岩及矿体均发生了剪切变形作用,沿剪切面发育绢云母新生矿物。绢云母的坪年龄和正反等时线年龄分别为280.1±1.2 Ma和281.4±1.3 Ma、281.3±1.3 Ma,在误差范围内基本一致,限定矿区韧性剪切变形的时间为早二叠世(约280 Ma)。多宝山斑岩铜矿床主要成矿作用形成于斑岩期,成矿时代为早奥陶世(约475 Ma),早二叠世的韧性剪切变形作用对原生斑岩铜矿化进行了改造,使矿石的铜进一步富集,品位相对增高。

韧性剪切带中两种线理的地质意义

韧性剪切带中丰富的变形现象记录剪切变形过程的重要信息,线理是韧性剪切带中常见且重要的观测要素,能够为剪切带的形成及演化提供关键的线索。通过野外工作实测观察,总结2种典型线理(皱纹线理和交面线理)的特征、形成原因及其观测方法,预测韧性剪切带的剪切运动方向。研究表明,为避免由于皱纹线理易与擦痕混淆误判剪切运动方向,应对C面理和垂直于C面理的多个截面进行综合判断。

江西崇仁县下庙前金矿地质特征与找矿方向分析

本文通过野外调研、岩心编录、分析测试、综合研究等方法,系统总结了下庙前金矿区地质特征、矿体特征及矿石特征,认为区内构造以NE向逆冲推覆型韧性剪切带为主,金矿化受韧性剪切带控制,浅部金矿体产于韧性剪切带内碎裂石英脉、硅化破碎带中,深部见糜棱岩型金矿体,成矿类型属韧性剪切带型金矿。并指出韧性剪切带中深部缓倾部位、韧性剪切带与燕山期花岗斑岩耦合部位是最有价值的找矿方向,有必要开展进一步找矿验证。

几种重要热液矿床成矿的岩浆作用贡献探讨

本文运用地球科学相关基础学科的基本理论知识,结合地质工作实践认识和矿床地质特征分析,对几种重要热液矿床成矿的岩浆作用贡献进行分析探讨,提出了新的认识。研究结果认为:(1)地下水是通过补给和排泄交替循环的,因此,通过简单的地下水的循环逐步转化为含矿热液成矿是难以实现的,地下水层控热液矿床成矿流体往往是经历了深部岩浆房驱动的热水循环。(2)地下卤水不是形成内生多金属矿床的矿源体,其本身不具有形成多金属矿床的成矿物质条件,产于板缘地热异常带内的热卤水中的多金属元素,是板块活动引起的强烈的岩浆-火山活动所提供,卤水起到了活化、富集和搬运金属元素的作用。(3)MVT铅锌矿床和卡林型金矿床的矿床特征本身说明它们的成矿与岩浆热液有成因关系。(4)根据变质作用和变质岩的定义,所有的变化是在固态条件下进行的,变质作用和变质岩难以形成变质热液矿床,其成因类型可归为岩浆热液矿床。(5)韧性剪切带是岩浆热力作用和构造应力作用下的塑性变形,成矿是岩浆热液在后期脆性断裂中充填交代而成。对矿床成因的正确认识,可有效的指导找矿勘查工作。岩浆成矿作用是最广泛、最强烈的成矿作用之一。

元谋变质核杂岩南部韧性剪切带特征及石墨矿化

通过元谋变质核杂岩南部地质调查及钻探工作,识别出4条韧性剪切带,宏观特征有糜棱岩及糜棱岩化岩石、拉伸线理、S-C组构、尖棱褶皱等,微观特征有石英动态重结晶、旋转碎斑、不对称压力影、云母鱼及微观尖棱褶皱等。已施工钻孔数据表明韧性剪切带范围为晶质石墨矿体良好容矿部位。