桂北摩天岭花岗岩体中片麻状构造的成因

摩天岭花岗岩体为一大型韧性剪切带,岩体中广泛发育的片麻理实际上是糜棱面理,其总体走向为NNE向,倾向NWW-SWW,倾角30～70°,拉伸线理向SWW或NWW倾伏,根据S-C面理构造、长石和石英不对称眼球等剪切指向标志体判断,韧性剪切带运动学为正滑剪切。     

南天山中段桑树园子韧性剪切带的形成时限及其构造意义

南天山中段桑树园子韧性剪切带是一条近东西走向的剪切带,带内面理、线理、不对称构造广泛发育,通过运动学分析判断该剪切带为左旋走滑性质。剪切带内糜棱岩中的白云母40Ar/39Ar测年获得坪年龄(393±6)Ma和等时线年龄(389±3)Ma;带内雁行式裂隙中的黑云母40Ar/39Ar测年获得坪年龄(366.5±2)Ma和等时线年龄(365±3)Ma。结合区域大地构造背景,笔者认为,桑树园子韧性剪切带是由塔里木板块和哈萨克斯坦—伊犁板块斜碰撞产生的同碰撞走滑构造带,在斜碰撞过程中起到平行板块边界方向的应变分解作用。     

鲁西青邑韧性剪切带运动学涡度及剪切作用类型

青邑韧性剪切带是晚太古代末期发育在鲁西前寒武纪基底花岗岩中一条规模较大的韧性剪切带。剪切带NW走向,面理直立,线理水平,剪切标志反映右行剪切。石英光轴法求得运动学涡度在0．96～0．99之间变化,极摩尔圆法求得糜棱岩化岩石运动学涡度为0．91,初糜棱岩运动学涡度为0．87,糜棱岩运动学涡度为0．81,超糜棱岩运动学涡度为0．60。运动学涡度表明,剪切带剪切作用类型为一般剪切,变形初期以单剪为主,随应变的增大,运动学涡度值逐渐减小,变形的纯剪分量不断增加,最后以纯剪为主。剪切作用类型及三维参照变形分析表明,青邑韧性剪切带属加长一变宽类型的一般剪切带并且在Y轴方向上有所增长。韧性剪切在太古代末期克拉通化过程中具有加厚陆壳的作用。     

太行山南段自立庄韧性剪切带变形特征

太行山南段临城自立庄地区古元古界甘陶河群中低级变质岩中发育一条左行逆冲型韧性剪切带。自立庄韧性剪切带出露长约10 km,宽约1 km,走向NNE,往西缓倾,在EW方向上由若干条强变形带与其间的弱变形域或岩块组成,平面上呈现平行式的组合特征。该韧性剪切带内发育糜棱岩、拉伸线理和皱纹线理、不对称褶皱、石香肠构造和构造透镜体、S-C面理和旋转碎斑等宏观和微观构造。S-C面理、旋转碎斑、不对称褶皱等宏微观变形特征一致表明自立庄韧性剪切带上盘由西往东逆冲的运动学性质。在对韧性剪切带宏观、微观构造特征研究基础上,结合区域资料,认为自立庄韧性剪切带的形成与华北克拉通古元古代末期西部陆块与东部陆块的EW向碰撞拼合有关,是18.5 Ga吕梁运动的产物。自立庄韧性剪切带的厘定为太行山南段古元古代构造演化提供了基础资料。     

内蒙古查干通格地区中浅构造相韧性剪切变形特征及构造运动学意义

内蒙古查干通格地区中浅构造相韧性剪切变形地质体中构造形迹保存较好的有柳树沟岩组绢云石英片岩、石英岩,祖宗毛道基性岩墙和哈拉霍疙特组三段灰岩.变形岩石片理、矿物拉伸线理均非常发育,在不同构造部位和不同岩性中,矿物的变形特征存在明显差异,出现不同的构造样式.白云鄂博群哈拉霍疙特组三段灰岩中发育大量同斜倒转褶皱,且矿物拉伸线理与褶皱枢纽平行;绢云石英片岩中发育大量杆状构造、鞘褶皱.矿物拉伸线理、杆状构造均属a型线理,其延伸平行剪切运动方向.横向上中间变形强,向两侧逐渐变弱.宏观及微观的“S-C”组构、“云母鱼”等指示的运动方式为北东东向的斜下落剪切运动,变质程度为低绿片岩相.     

桐柏地区高压变质地体在地壳中的抬升机制

桐柏杂岩位于秦岭与大别造山带之间,南北两侧为NWW-SEE向延伸的含榴辉岩高压变质地体,其构造就位过程及其与高压变质地体的构造关系为地质学家们所关注.本文研究表明,所谓的桐柏杂岩实际上是一个早白垩世花岗质片麻岩杂岩体,其内包裹一定数量的三叠纪中高级变质岩石.桐柏杂岩南北两条边界韧性剪切带具有相反的运动学指向,分别为大型右行和左行韧性剪切带,其形成时代为131Ma.这两条韧性剪切带中的剪切面理分别朝SSW和NNE向倾斜,韧性剪切带及杂岩体内部发育的拉伸线理均稳定地朝SEE方向缓倾伏.而在杂岩体的东端发育低角度近南北向韧性剪切变形带,其糜棱面理朝SEE方向低角度缓倾斜,矿物拉伸线理也朝SEE方向低角度缓倾伏,运动学标志指示东侧地质体朝295°～310°的方向逆冲.因此,桐柏杂岩实际上被一个顺造山带的韧性剪切带所围限,这个韧性剪切带及杂岩体内部韧性变形运动学指示了一个早白垩世由东向西的低角度抬升过程,而这一过程直接导致了含榴辉岩高压变质地体沿着造山带的方向从地壳深部抬升到近地表.这一研究结果对理解和认识桐柏-大别-苏鲁地区高压一超高压变质地体的晚期抬升过程具有重要意义.     

里德尔剪切：滑劈理的一种形成机制

微断裂中的倾斜标志层的拖曳褶皱（１）是滑劈理区别于其它类型劈理的标志。随里德尔剪切（Ｒ）发育的劈理，它与面理化岩石的各向异性面斜交并且与剪切带的各种角度（与α有关）相交。褶皱（２）在应变椭球体的ＸＺ面上发育，褶轴平行于高角度与Ｒ剪切相交的瞬态λ＿１。在递进剪切变形过程中，褶皱和劈理间的夹角发生了变化。在递进扭张带（α＜１）中，出现了最大的反向（反时针）Ｒ剪切旋转和祸皱间初始夹角的最大程度打开，达１７０°。从几何学上讲，这在简单剪切和压扭带中是不可能的，但是过长的Ｒ剪切的向前旋转受到了剪切带稳定的或逐渐变小的厚度的限制。细褶皱（３）增大了断裂的倾斜标志层的拖曳褶皱并在较高的应变下其轴面平行于劈理。在较高级褶皱（４）中，由于最初增量变形椭球体ＹＺ面上纯剪切和沿层间界线弯滑运动诱导的剪切作用影响，使得Ｒ剪切重新定位于轴平面位置。在它们垂直于谓轴的滑动中，褶皱翼部的拉伸和微劈石的非共轴变形使得以前的拖曳和细褶皱变形而呈一种特殊的型式。保存在劈理面上的条痕和／或微弱线理与剪切方向一致。劈理—褶皱截面、垂直劈理且平行于条痕线理的平面中的不对称构造都指示了剪切方向。     

桂北四堡韧性剪切带的发现及其构造意义

通过野外观察、室内显微构造分析和磁组构测量方法,在桂北四堡地区浅变质地层中厘定出一条NE30°走向,南东倾,倾角约40°的大型左旋斜冲韧性剪切带——四堡韧性剪切带;该韧性剪切带内发育糜棱岩系列、糜棱面理、拉伸线理、A型褶皱、S-C组构、亚颗粒、显微分层及石英条带等宏观和微观构造特征;磁各向异性度测量结果显示四堡韧性剪切带由一宽约4 km的强应变带及边缘弱带组成,全带宽达10 km,长度超30 km;在对韧性剪切带运动学、构造年代学研究的基础上,结合区域地质资料,认为四堡韧性剪切带是华南加里东晚期华夏地块由南东向北西作低角度斜冲到扬子地块的产物。这一发现揭示了扬子地块与华夏地块碰撞拼合的方式,为深化华南构造演化提供了新资料。     

韩国和顺煤田淳昌剪切带的构造特征

沿着和顺煤田东部边界分布的淳昌剪切带持有N—S至NE—SW走向的不连续性韧性剪切带,局部地段尚可表现出一些连续性韧性剪切带的特征。在前寒武纪花岗质片麻岩区内发育着宽数米至700m不等的糜棱岩带,具有低侧伏角的拉伸线理和高角度糜棱岩叶理构造。基底岩中糜棱岩带剪切位移量推算为3km以上。由于二轴性应变作用,使剪切带中发生强烈的非均质性多相变形,并伴随叶理构造,它具有渐发性弯曲及各种非对称微细构造。其错动方向属右型运动,从应变分析获知,剪切带有限应变为简单剪切加上较弱的纯剪切和伴随体积减少的渐进应变过程累积形成。推测韧性剪切作用是在绿片岩相变质条件下于三叠纪末至侏罗纪中期发生的。     

北祁连山俯冲杂岩带的韧性剪切作用

北祁连山加里东褶皱带中的蓝片岩(包括蓝闪片岩和榴辉岩)产于原岩为中寒武统的典型蛇绿俯冲杂岩带之中,是北祁连古板块缝合线的标志之一。蓝片岩带中强烈的韧性剪切变形作用代表了本区古板块持续俯冲到碰撞过程中地壳深部层次的变形行为。构造分析表明,该蛇绿混杂岩带经历了早、晚两期韧性剪切变形的改造。其中早期韧性剪切变形(DF_1)与区域D_2变形幕有关,蓝闪片岩相矿物(蓝闪石、石榴子石、绿帘石和多硅白云母)是伴随变形叶理生长的同构造产物。晚期韧性剪切变形与区域D_3变形幕有关,伴随有绿泥石、冻蓝闪石等的出现和石英、方解石的动态重结晶作用。运动学指示标志,如拉伸线理、与拉伸线理平行的各种褶皱枢纽、同构造变斑晶的旋转、S-C组构及石英光轴组构等,都清楚地显示DF_1运动方向为南东-南南东,伴有左行旋转,晚期DF_2为由NE向SW的逆冲剪切,伴有右行旋转。方解石和石英光轴组构表明晚期逆冲剪切的古挤压应力方向为北北东-南南西。     

胶南地区的伸展作用——以胶南—诸城一带为例

胶南地区的胶南—诸城一带存在两期不同方向的伸展构造。早期以形成近ＥＮ向的拉伸线理为特征，并在不同构造层次上显示出不同的变形。出露于研究区中部桃林尚庄隆起的含榴辉岩片麻岩中，主要以ＬＳ的组构为特征，显示出早期伸展作用下地壳岩石的垂直轴缩短、ＥＷ向拉伸的共轴应变；而在把下地壳含榴辉岩片麻岩与以变沉积岩为主的中上地壳岩石分开的韧性滑脱带上，此期伸展作用则表现为从东向西剪切的非共轴简单剪切变形，具有近水平的拉伸线理及近水平的ＥＷ向剪切褶皱和鞘褶皱枢纽。晚期伸展作用表现为近ＳＮ的伸展垮塌作用，形成向北和向南倾斜的两条韧性正剪切带，且遭受低角闪岩高绿片岩相条件下的透入性均匀简单剪切变形，剪切方向分别向北和向南。     

The Eastern Ghats Mobile Belt,India: A Collage of Juxtaposed Terranes (?)

Examination of Landsat TM images, reconnaissance field traverses and the published geological maps from the Eastern Ghats Mobile Belt (EGMB), India, reveal a network of major ductile shear zones both within and at the margins. These shear zones are characterized by mylonitic foliation, grain size reduction, metamorphic retrogression, stretching lineations and distinct signatures of alkaline, anorthositic and granitic magmatism. These shear zones divide the EGMB into distinct terranes, which are heterogeneously deformed with extensive tracts of foliated mylonitic gneisses and ultramylonites. The main gneissic foliation in all the terranes is refolded in near non-coaxial manner generally about the axis subparallel to the elongation of the terrane.Structural history in each terrane is distinct in the orientation of stretching lineations, attitude of gneissosity and early fold axial planes, lithological assemblages and available geochronological data. It is possible to recognise nine large terranes within the EGMB and the characteristics of each terrane have been described. The terrane distribution in the EGMB could well fit a thrust tectonic, allochthonous model of amalgamation and accretion. Different terranes could be different thrust nappes or allochthonous tectonic sheets representing tectono-stratigraphic terranes.     

How do lineations reflect the strain history of transpressive shear zones? The example of the active Alpine Fault zone,New Zealand

Lineations within mylonites exhumed in the hanging wall of New Zealand's active Alpine Fault zone have a complicated relationship to contemporary plate kinematics. The shear zone is triclinic and macroscopic object lineations are not usually parallel to the simple shear direction, despite high total simple shear strains (γ ≥ 150). This is mostly because the lineations are inherited from pre-mylonitic fabrics, and have not been rotated into parallelism with the mylonitic stretching direction (which pitches c. 44° in the fault plane). Furthermore, some lineations have been variably rotated depending on whether they are present in shear bands or microlithons, which accommodated bulk strains with different vorticities. Total strains required to obtain parallelism between the finite maximum principal stretching direction calculated from transpression models and these mylonitic lineations, are pure shear stretch, S₁ ∼ 3.5; simple shear 11.7 < γ < 150. The observations and numerical models also show that linear features are not rotated much during simple shear because they initially lie within the shear plane, and that inherited fabric components may not be destroyed until very high simple shear strains have been attained.     

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.     

Non-cylindrical, flexural slip folding in the Ardwell flags—a statistical approach

Non-cylindrical, flexural slip folding is described from the well-known coastal section between Ardwell Bay and Kennedy's Pass, near Girvan, southwest Scotland. Bedding plane slip is recognised by the ubiquitous slickenside striations on bedding surfaces, and these linear elements define the ac kinematic plane of fold formation. This intersects the axial surfaces of folds (ab) in the common direction a which is the movement direction during fold propagation. Statistical treatment of the orientation of structural and kinematic elements yields important conclusions concerning fold formation: the Ardwell folds are markedly non-cylindrical and this is a primary feature amplified during the Ardwell Fold Phase.     

韧性剪切带的剪切作用类型和韧性减薄量

韧性剪切带组构的演化和剪切作用类型受到许多研究者的关注。运用极莫尔圆法、有限应变法、刚性颗粒法、石英光轴组构结合有限应变测量法、拖尾形态法、剪切带内变形脉体(岩墙)法、碎斑法等方法可以估算剪切带变形过程中的运动学涡度,进而判别剪切带中单剪切组分与纯剪切组分的相对含量。自然界的剪切带一般介于单剪与纯剪之间,运动学涡度Wk介于0~1之间,表明韧性剪切带在变形过程中发生了垂直于剪切带边界(Z轴)方向的韧性减薄。剪切带变形过程中的韧性减薄量可依据有限应变测量与运动学涡度估算求得,也可依据剪切带内的石香肠(布丁)构造求解,还可依据构建极莫尔圆求解。以华北克拉通北缘的楼子店变质核杂岩及其韧性剪切带,以及希腊西奈山的Chelmos剪切带为例,介绍估算韧性剪切带韧性减薄的方法,这种韧性减薄是对大规模岩石圈减薄的有益补充和完善。研究结果表明,定量估算与变质核杂岩相关的韧性剪切带的剪切作用类型是分析变质核杂岩形成机制的有效途径和方法。     

韧性剪切带的剪切作用类型和韧性减薄量

韧性剪切带组构的演化和剪切作用类型受到许多研究者的关注。运用极莫尔圆法、有限应变法、刚性颗粒法、石英光轴组构结合有限应变测量法、拖尾形态法、剪切带内变形脉体（岩墙）法、碎斑法等方法可以估算剪切带变形过程中的运动学涡度,进而判别剪切带中单剪切组分与纯剪切组分的相对含量。自然界的剪切带一般介于单剪与纯剪之间,运动学涡度Wk介于0~1之间,表明韧性剪切带在变形过程中发生了垂直于剪切带边界（Z轴）方向的韧性减薄。剪切带变形过程中的韧性减薄量可依据有限应变测量与运动学涡度估算求得,也可依据剪切带内的石香肠（布丁）构造求解,还可依据构建极莫尔圆求解。以华北克拉通北缘的楼子店变质核杂岩及其韧性剪切带,以及希腊西奈山的Chelmos剪切带为例,介绍估算韧性剪切带韧性减薄的方法,这种韧性减薄是对大规模岩石圈减薄的有益补充和完善。研究结果表明,定量估算与变质核杂岩相关的韧性剪切带的剪切作用类型是分析变质核杂岩形成机制的有效途径和方法。     

一个韧性转换挤压带的变形分解作用：以阿尔金断裂带东段为例

变形构造研究显示阿尔金划分成具有近水平拉伸线理的韧性左行走滑变形域和具有陡角度倾伏拉伸线理的收缩变形域。在ＳＳ与ＰＳ之间的过渡区域还发现中等角度倾伏的拉伸线理。