东昆仑南缘韧性剪切带变形特征及其形成时代的限定

中生代巴彦喀拉-松潘甘孜地体向东昆仑地体斜向俯冲,在东昆仑南缘形成一条巨型的韧性剪切带。剪切带中发育的旋转碎斑、书斜构造、解理阶步、云母鱼、S-C组构、不对称褶皱、雁列脉等宏微观构造,显示剪切带兼具右行和左行的特征,且右行早于左行剪切,但总体以左行剪切为主。对西大滩糜棱岩化花岗岩和小南川未变形花岗岩进行了LA-ICP-MS锆石UPb测年,西大滩岩体侵位于199.3±2.2Ma,小南川岩体形成于196.4±1.3Ma。西大滩与小南川岩体中的锆石为典型的岩浆锆石,其年龄代表了岩体侵位的时代。鉴于2个岩体的变形程度完全不同,东昆仑南缘在199~196Ma之间发生了左行韧性剪切。     

Palaeozoic late collisional strike-slip deformations in Tianshan and Altay, Eastern Xinjiang, NW China

ABSTRACT In Central Asia, thrusts and shear zones resulting from Palaeozoic accretional events were reworked by E–W-trending ductile strike-slip faults during late Palaeozoic–early Mesozoic time. In the Tianshan range, microstructures and quartz C-axis fabrics show a main dextral shearing associated with sinistral localized shear zones. The relationship between these conjugate structures indicates a NNW–SSE-trending bulk shortening. In the Chinese Altay mountains, the existence of δ-type microstructures in an important sinistral mylonitic zone infers high rates of deformation. This shear zone is bordered by a late dextral ductile fault synchronous with a granite emplacement. Field evidence and datings from the literature provide chronological constraints. In the late Carboniferous, the sinistral mylonitic deformation took place in the Erqishi–Irtysh shear zone in the northeastern part of Xinjiang and in Kazakhstan. During the Early Permian, a regional dextral event occurred in the Tianshan range and under the whole of northern Xinjiang.     

Deformation conditions, kinematics, and displacement history of shallow crustal ductile shearing in the Norumbega fault system in the Northern Appalachians, eastern Maine

The Norumbega fault system in the Northern Appalachians in eastern Maine experienced complex post-Acadian ductile and brittle deformation from middle through late Paleozoic times. Well-preserved epizonal ductile shear zones in Fredericton belt metasedimentary rocks and granitic batholiths that intrude them provide valuable information on the nature, geometry, and evolution of orogen-parallel strike-slip Norumbega faulting. Metasedimentary rocks were ductilely sheared into phyllonite schistose mylonite, whereas granite into mylonite within the ductile shear zones. Ductile shearing took place at conditions of the lower greenschist facies with peak temperatures on the order of 300–350° based on comparison of plastic quartz and brittle feldspar microstructures, confirming a shallow crustal environment during faulting.Ductile shear strain was partitioned into two major shear zones in easternmost Maine—the Waite and Kellyland zones—but these zones converge toward the southwest. Megascopic, mesoscopic, and microscopic kinematic indicators confirm that fault motion in both zones was dominantly dextral strike-slip. Detailed mapping, especially in the plutonic rocks, reveals a complex ductile deformation history in the area where the Waite and Kellyland zones converge. Shear strain is broadly distributed in the rocks between Kellyland and Waite zones, and increases toward their junction. Multiple dextral high-strain zones oblique to both zones resemble megascopic synthetic c′ shear bands. Together with the Kellyland and Waite master shear zones, these define a megascopic S–C′ structure system produced in a regional-scale dextral strike-slip shear duplex that developed in the transition zone between the deeper (south-central Maine) and shallower (eastern Maine) segments of the Norumbega fault system.Granite plutons caught within the strike-slip shear duplex were intensely sheared and progressively smeared into long and narrow slivers identified by this study. The western lobe of the Deblois pluton and the Lucerne pluton have been recognized as the sources, respectively of the Third Lake Ridge and Morrison Ridge granite slivers. Restoration of both granite slivers to their presumed original positions yields approximately 25 km of dextral strike-slip displacement along only the Kellyland and synthetic ductile shear zones.     

东昆仑地区昆仑河韧性剪切带的识别、时代厘定及构造意义

位于东昆仑造山带的青海昆仑河地区发育一条走向近东西向的大型韧性剪切带,卷入韧性剪切变形的岩石主要为中-新元古界万宝沟群变质中基性火山岩、碎屑岩和大理岩,奥陶系纳赤台群变质碎屑岩、玄武岩和大理岩,以及古生代（志留纪）中酸性侵入岩,剪切带内的岩石多已发生糜棱岩化。剪切带中发育的σ型旋转碎斑、S-C组构、糜棱面理、石英脉的不对称褶皱等构造标志,总体指示以右行走滑剪切为主,晚期有左行走滑剪切作用叠加。LA-ICP-MS锆石U-Pb定年结果显示,剪切带中变形的花岗闪长岩及未变形的白云母花岗岩的结晶年龄分别为432.3±1.2Ma和423.3±1.5Ma,从而限定昆仑河韧性剪切带的形成时代介于中-晚志留世432~423Ma之间。结合区域构造演化特点,认为昆仑河韧性剪切带反映了东昆仑原特提斯洋关闭后,昆北与昆南地块于中-晚志留世碰撞造山运动的构造响应,晚期的左行走滑则可能受控于昆南断裂带燕山早期的左行走滑作用。     

越城岭花岗岩体西侧滑脱型韧性剪切带的发现及其形成的构造体制

越城岭花岗岩体西侧片麻状花岗岩带主体是一条由韧性剪切作用形成的复合糜棱岩带,包括早期高绿片岩相条件下形成的糜棱片麻岩和晚期低绿片岩相条件下形成的糜棱岩。高绿片岩相韧性剪切带和低绿片岩相韧性剪切带具有基本一致的运动学性质,为滑脱型韧性剪切带,总体为在向NWW缓倾的糜棱面理上向SW方向滑动,并在平面上表现为左旋效应。根据构造对比研究,认为越城岭西侧滑脱型韧性剪切带形成于后造山阶段的伸展构造体制。     

Geometrical analysis of mesoscopic shear zones in the crystalline rocks of MCT zone of Garhwal Higher Himalaya

The crystalline rocks of the MCT Zone of Garhwal Higher Himalaya exhibit well-preserved mesoscopic shear zones. Majority of these shear zones are of ductile and brittle ductile type with both sinistral and dextral sense of movement. Detailed analysis of mesoscopic shear zones reveals that sinistral shear zones exhibit a strike variation from NNE to ENE and dextral shear zones exhibit variation from NNW to WNW directions thus forming a conjugate pair. The bisectors of statistically preferred orientations of the two sets of the shears indicate that they generated due to NNE–SSW horizontal compression. These dextral and sinistral shear zones exhibit strike–slip geometry developed during progressive ductile shearing.     

Interactions between serpentinite devolatilization, metasomatism and strike-slip strain localization during deep-crustal shearing in the Eastern Alps

The Greiner shear zone in the Tauern Window, Eastern Alps, changes from a zone of distributed (dominantly sinistral) shear in supracrustal rocks to a series of narrow, gully forming dextral splays where it enters basement gneisses. Within these splays, granodiorite is transformed into quartz‐poor biotite and/or chlorite schists, reflecting hydration, removal of Si, Ca and Na, and concentration of Fe, Mg and Al. Stable isotope analyses show a prominent increase in δD and a decrease in δ¹⁸O from granodiorite into the shear zones. These changes indicate significant channelized flow of an externally derived, low‐δ¹⁸O, high‐δD fluid through the shear zones. The shear zone schists are chemically similar to blackwall zones developed around serpentinite bodies elsewhere in the Greiner zone and the stable isotope data support alteration via serpentinite‐derived fluid. Monazite in schist from one shear zone yields spot dates of 29–20 Ma, indicating that the fluid influx and switch from sinistral to dextral shear occurred at or shortly after the thermal peak of the Alpine orogeny (c. 30 Ma). We suggest that Alpine metamorphism of serpentinites released large amounts of high‐δD, low‐δ¹⁸O, Si‐undersaturated, Fe + Mg‐saturated fluids that became channelized along prior zones of weakness in the granodiorite. Infiltration of this fluid facilitated growth of chlorite and biotite, which in turn localized later dextral strain in the narrow splays via cleavage‐parallel slip. This dextral strain event can be linked to other structures that accommodated tectonic escape of major crustal blocks during dextral transpression in the Eastern Alps. This study shows that serpentinite devolatilization can play an important role in modifying both the chemistry and rheology of surrounding rocks during orogenesis.     

铧厂沟金矿床区域韧性剪切带特征

首次对铧厂沟金矿床区域韧性剪切带进行了较为系统的研究。根据野外地质调查和室内显微构造分析 ,区内发育一条较大区域韧性剪切带 ,无论沿走向还是顺倾向均呈舒缓波状 ,强变形带和弱变形域呈镶嵌形式。区域韧性剪切带经历了右行—左行—右行多期 (次 )活动 ,剪切方位也多次变化 ;早期形成温度约 5 0 0℃ ,以右行剪切为主 ,古应力值大于 0 .0 75GPa。控矿韧脆性剪切带是区域韧性剪切带演化的产物 ,最终形成脆性断裂。区域韧性剪切作用控制矿床、矿带的分布 ,并使部分金从矿源层分溢出来 ,产生第一阶段金的富集。次级韧脆性剪切带 (控矿剪切带 )控制富矿体的分布。因此 ,铧厂沟金矿床可称为韧性剪切带型金矿床。另外 ,中 -下泥盆统三河口群第一岩段第一岩层 (D1 -2 SH1a)部分原岩有明显海底热水同沉积特征 ;在矿床之西万家山—张家山应注意寻找硅化石英粗糜棱岩型金矿石。     

Transpression,extrusion, partitioning,and lateral escape in the middle crust: Significance of structures,fabrics, and kinematics in the Bronson Hill zone,southern New England,U.S.A.

Fabrics in the mid-crustal Bronson Hill zone of the southern New England Appalachian orogen record a range of apparent finite strains and conflicting kinematics, but structural relationships indicate coeval development. At the smallest scale of this study, shortening was accommodated in granitic orthogneiss, while transcurrent deformation was partitioned into relatively thin zones of metastratified rocks along the margins. The Monson orthogneiss can be broadly characterized by subvertical to steeply dipping S > L tectonites, subvertical to subhorizontal stretching lineations, closed to isoclinal folds, and dextral/reverse kinematics. The east-bounding Conant Brook shear zone and Greenwich syncline are characterized by steeply dipping mylonitic foliations, a range of lineations, and dextral/reverse kinematic indicators. The west-bounding Mt. Dumplin high strain zone is comprised of steeply dipping mylonites, subhorizontal lineations, and sinistral/normal kinematics. These structures reflect coeval partitioned dextral transpression, vertical extrusion, and north-directed lateral escape of the orthogneiss that was facilitated by bounding conjugate shear zones. Comparison of structural subdomains with transpressional modeling indicates vertical pseudo-monoclinic to inclined triclinic coaxial to simple shear influenced transpression. Compatibility between laterally adjacent subdomains was maintained by meso-/microscale partitioning. Absolute and relative timing constraints show that transpression was sustained from 330 Ma to 300 Ma.     

长乐-南澳断裂带晚中生代岩浆活动 与变质-变形关系

长乐-南澳断裂带是东南沿海地区陆内强烈变质-变形带。带内沉积岩、火山岩和早白垩世的钙碱性角闪石黑云花岗岩和花岗闪长岩都已发生可达角闪岩相的变质和石英-长石相韧性剪切变形。鉴于高温矿物和强烈韧性变形多出现在深成岩附近;远离深成岩,变质和变形就逐渐减弱,故本文认为,至少有一部分变质变形的热源是由岩浆提供的。韧剪组构和糜棱质花岗岩是在岩浆侵位的晚期或长乐-南澳断裂带左旋走滑时,在中地壳部位同时形成的,长乐断裂带中花岗岩的组构记录了一期同走滑变形的岩浆作用,“软变形”作用。据此,长乐-南澳带内花岗岩的形成是受走滑剪切应力和岩浆热双重制约的,是在走滑过程中实现的。其动力来源可能与晚中生代的太平洋板块沿日本中央构造线—台湾纵谷带朝东亚陆缘的斜向俯冲有关。     

Structural pattern and ascent model in the Central Extremadura batholith,Hercynian belt,Spain

The Central Extremadura batholith constitutes an important alignment of plutonic rocks occupying part of the internal zones of the Iberian Hercynian belt. It comprises 13 plutons and numerous minor intrusions, and covers a wide compositional range from quartz-diorites to alkali-feldspar granites. Structural study of the individual plutons reveals that their internal structural patterns may be correlated. Correlation between the different structural patterns in the plutons and interpretation of the superimposed deformation in the metasedimentary host rocks indicate that the plutons were emplaced and deformed in an E-W, dextral, intracontinental shear zone developed during the second deformation phase (302–320 Ma). A qualitative ascent model has been established as follows: (1) development of extensional fractures at 45° to the E-W, dextral, shear zone; (2) intrusion of granitic magmas along these fractures and (3) rotation of the earlier intrusions, in a dextral sense, inducing antithetic shear zones (N-S sinistral) and a transverse shortening, perpendicular to the major axis of the earlier, deformed plutons as well as the forced emplacement of the later plutons.     

Relationship between shear zones and igneous activity: The Closepet Granite of Southern India

The late Archaean Closepet granite of southern India is bounded by N-S trending shear zone. At the southern end of the granite both charnockite and granite veins are spatially associated with ductile shears. These shears continue further north and are confined to the contact zones in the central part of the granite outcrop. The main component of the shear zone are highly deformed granite sheets, augen gneisses and mylonites. Field observations and microstructural fabric of mylonites indicate a dextral sense of shear movement. Field evidence suggests that shear deformation was active throughout the evolution of the Closepet granite     

Fabric studies within the Cascade Lake shear zone, Sierra Nevada, California

The Cascade Lake shear zone occurs on the eastern margin of the Tuolumne Intrusive Suite, Sierra Nevada Batholith, California. Foliation in the zone is NNW trending and subvertical, and lineation is moderately south plunging. Deformation is syn-tectonic with emplacement of the Cathedral Peak granodiorite. A deformation gradient exists toward the NE margin of this pluton, with higher strains and lower temperatures of deformation found near the contact. We compare fabric data collected very densely in this shear zone using several techniques: field fabrics, 3D orientation of K-feldspar megacrysts, and AMS (anisotropy of magnetic susceptibility) analysis. In general, the results from the three different methods are in agreement. Deformation in this shear zone is part of a larger pattern of deformation within the Cathedral Peak granodiorite, as recorded by AMS analysis, and dextral shearing associated within the last stage of plutonism within the Sierra Nevada magmatic arc.     

Initiation Timing of the Jiamusi–Yitong Fault Zone in NE China

The NE–striking Jiamusi–Yitong fault zone(JYFZ) is the most important branch in the northern segment of the Tancheng–Lujiang fault zone. The precise shearing time of its large–scale sinistral strike–slip has yet to determined and must be constrained. Detailed field investigations and comprehensive analyses show that strike–slip faults or ductile shear belts exist as origination structures along the western region of Yitong Graben. The strike of the shear belts trend to the NE–SW with steep mylonitic foliation. The zircon U–Pb dating result for the granite was 264.1±1 Ma in the ductile shear belt of the JYFZ. The microstructural observation(rotated feldspar porphyroclasts, S–C fabrics, and quartz c–axis fabrics, etc.) demonstrated the sinistral shearing of the ductile shear zones. Moreover, the recrystallized quartz types show a transitional stage of the subgrain rotation toward the recrystallization of the grain boundary migration(SR–GBM). Therefore, we suggest that the metamorphic grade of the shear zone in the ductile shear zones should have reached high greenschist facies conditions, and the deformation temperatures should approximately 450–500°C, which is obviously higher than the blocking temperature of muscovite(300–400°C). Hence, the ~(40)Ar/~(39)Ar isochron age of muscovite from ductile shear zones should be a cooling age(162.7±1 Ma). We infer that the sinistral strike–slipping event at the JYFZ occurred in the late Jurassic period, and it was further inferred from the ages of the main geological events in this region that the second sinistral strike–slip age of the Tancheng–Lujiang fault zone occurred during the period of tectonic movements in the Circum–Pacific tectonic domain. This discovery also indicates the age of the Tancheng–Lujiang fault zone that stretches to northeastern China. The initiation of the JYFZ in the late Jurassic is related to the speed and direction of oblique subduction of the west Pacific Plate under the Eurasian continent and is responsible for collision during the Jurassic period.     

阿尔泰山脉南部线性花岗岩锆石SHRIMP U-Pb定年及其地质意义

在阿尔泰山脉南部发育长轴呈NW-SE走向的小型线性花岗岩,它们的围岩分别为遭受强烈左行韧性剪切变形的泥盆纪和石炭纪火山沉积岩系.构造变形特征显示,这些线性花岗岩是与该区左行韧性剪切变形同时侵位的.本文报道了对采自其中的阿勒泰南黑云母花岗岩和沙尔布拉克南二云母花岗岩样品的锆石进行sHRIMP U-Pb定年的研究结果,根据地质、岩石学和构造变形等方面的特征和锆石阴极发光图像特征,笔者把沙尔布拉克南二云母花岗岩的(275.1±1.7)Ma年龄解释为该岩体的侵位时代,据此推测该区左行韧性剪切作用可能开始于275 Ma前后.结合已有资料,还对阿尔泰山脉南部二叠纪的构造演化进行了初步讨论.     

辽东铀成矿带连山关地区韧性剪切带与铀成矿作用

连山关地区位于华北克拉通北缘铀成矿省辽东铀成矿带,已知铀矿床（点）均发育在韧性剪切带附近。为了解韧性剪切带运动学、几何学构造变形机制及与铀矿的关系,本文以连山关岩体周缘韧性剪切带为研究对象,通过野外宏观调查和室内微观研究相结合的研究方法,探讨构造变形期次、韧性剪切带形成机理及其对铀成矿的控制作用。研究表明：连山关岩体周缘发育的韧性剪切带与近南北向挤压构造变形有关,其右行韧性剪切带应变类型为压扁应变,属于一般压缩-平面应变范围,Flinn指数K值在0.19~0.69之间,岩石类型属于S/SL型构造岩。研究区内铀矿体均为隐伏盲矿体,主要赋存于沿着连山关岩体和辽河群接触带右行剪切作用形成的背斜褶皱核部,和北东东向断裂关系密切。综合分析认为,连山关岩体南缘北西向韧性剪切带为一级控矿构造,是区内铀矿热液运移的通道,而剪切带边部的晚期北东东向断裂则是铀矿储存空间;铀源可能来自于太古宙古风化壳,并在大型韧性剪切活动（提供热液运移通道）和基性脉岩侵入（提供热源和还原剂）等综合因素作用下运移、富集成矿。     

浙江治岭头金银矿体的控矿构造

治岭头金银矿基底发育八都群变质系,盖层为晚侏罗世火山岩系,金银矿体赋存于变质岩系中,金银矿体受控于变质基底的韧性共轭剪切带。研究认为,NW方向的韧性剪切带具有右行平移性质,NE方向的韧性剪切带具有左行平移性质,EW方向剪切带未见剪切动向,主要为含变质岩角砾的石英脉。NE和NW两个方向的韧性剪切带具有共轭性质,EW方向剪切带位于共轭剪切带交汇部位,受到相向挤压造成的尖端钝化,SN向的脆性断裂对矿体起到破坏作用。     

The Mid-Late Jurassic Kinematic Model and Mechanical Mechanism of the Ductile Shear Zones in the South Qinling Structural Belt

The South Qinling structural belt, as a part of the Qinling orogen, is bounded by the Shang-Dan suture to the north. Previous studies show the two regional conjugate ductile shear zones developed in the Mid-Late Jurassic epoch, e.g., Ningshan ductile shear zone characteristic of ENE-striking, sinistral shearing, Ankang ductile shear zone typical of NW-direction, dextral shearing, whose shear deformation age respectively is 169~162 Ma and 178~163 Ma respectively. The lineations collected from the two ductile shear zones suggest the maximum principal stress (σ1) is characterized by the direction of NE trending consistent with their obtuse angle bisector, which is corresponded with maximum effective moment criterion. Thus, our work suggests the blocks delimited by the conjugate ductile shear zones (e.g., ENE-striking and NW-trending) in the interior of the Qinling orogen, dominated by NE-SW compression, pinned by the Hannan-Micangshan massif, laterally extruded in the Mid-Late Jurassic time, which is featured by westward escaping in western Qinling belt and eastward in the eastern Qinling belt. This kinematical model probably marks the dominated activity of the Qinling orogen in the Mid-Late Jurassic time.     

40Ar/39Ar dating of the Jiali and Gaoligong shear zones: Implications for crustal deformation around the Eastern Himalayan Syntaxis

We conducted a comprehensive ⁴⁰Ar/³⁹Ar geochronological study of the Jiali and Gaoligong shear zones to obtain a better understanding of crustal deformation and tectonic evolution around the Eastern Himalayan Syntaxis (EHS). The new age data reveal that the main phase of deformation in the Jiali and Gaoligong shear zones occurred from 22 to 11 Ma and from 18 to 13 Ma, respectively. Structural data collected during this study indicate that the Jiali shear zone underwent a change in shear sense from sinistral to dextral during its movement history. Based on a comparison with the deformation histories of other major shear zones in the region, we argue that the initial sinistral motion recorded by the Jiali shear zone was coincident with that of the Ailao Shan–Red River shear zone, which marked the northern boundary of the southeastward extrusion of the Indochina block during the Early Miocene. From the Middle Miocene (～18 Ma), the Jiali shear zone changed to dextral displacement, becoming linked with the dextral Gaoligong shear zone that developed as a consequence of continued northward indentation of the Indian continent into Asia. Since this time, the Jiali and Gaoligong shear zones have been united, defining the southwestern boundary of the EHS during clockwise rotation of the eastward-extruding Tibetan block, as revealed by recent GPS data. The temporal change in regional deformation pattern from southeastward block extrusion to clockwise rotation of crustal fragments may have played an important role in the development of the eastern Himalayan drainage system around the EHS.     

Strain partitioning in the mid-crust of a transpressional shear zone system: Insights from the Homestake and Slide Lake shear zones,central Colorado

Kinematic analysis and field mapping of the Homestake shear zone (HSZ) and Slide Lake shear zone (SLSZ) in central Colorado may provide insight into the interaction between subvertical and low-angle shear zones in the middle crust. The northeast-striking, steeply dipping HSZ comprises a ∼10-km-wide set of anastomosing ductile shear zones and pseudotachylyte-bearing faults. Approximately 4 km south of the HSZ, north–northeast-striking, shallowly dipping mylonites of the SLSZ form three 1–10-m-thick splays. Oblique stretching lineations and shear sense in both shear zones record components of dip-slip (top-up-to-the-northwest and top-down-to-the-southeast) and dextral strike-slip movement during mylonite development. Quartz and feldspar deformation mechanisms and quartz [c] axis lattice preferred orientation (LPO) patterns suggest deformation temperatures ranging from ∼280–500 °C in the HSZ to ∼280–600 °C in the SLSZ. Quartz [c] axis LPOs suggest plane strain general shear across the shear system. Based on the relative timing of fabric development, compatible kinematics and similar deformation temperatures in the SLSZ and the HSZ, we propose that both shear zones formed during strain localization and partitioning within a transpressional shear zone system that involved subvertical shuffling in the mid-crust at 1.4 Ga.