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嫩江洋闭合机制是大兴安岭地区一个争议较大的科学问题。音德尔杂岩为大兴安岭与松辽盆地盆山结合带上新发现的一套俯冲增生杂岩,岩石强烈韧性变形,其构造变形样式及时间较好的记录了嫩江洋闭合过程。该套杂岩基质由绢云片岩、绿泥石片岩及阳起石片岩等组成,岩块主要包括闪长岩、辉长岩、玄武安山岩及花岗岩。宏观变形样式观察和微观组构分析表明,音德尔杂岩发育两期构造变形:早期变形以倾向NW的片理、片麻理及糜棱面理为标志,并发育有NNW向倾伏的构造线理,线理倾伏角一般较大,指示NW-SE方向强烈挤压背景下形成的一期逆冲线理;晚期变形以NE向倾伏的低角度矿物拉伸线理为标志,石英及长石等矿物通过晶内位错滑移与膨凸式重结晶等塑性流变方式显著定向拉长,构造形迹指示一期NE-SW走向的左行走滑剪切作用,晚期线理普遍改造或置换早期线理。两期构造变形事件分别对应兴安增生地体与松嫩地块碰撞造山早期的强烈挤压阶段和造山晚期伸展走滑调整阶段。构造岩与围岩接触关系年代学研究限定音德尔杂岩构造变形发生于早石炭世末期(323Ma)之前。早石炭世早期嫩江洋开启双向俯冲模式,在兴安增生地体东缘和松嫩地块西缘形成大量增生楔。早石炭世末期嫩江洋闭合,兴安增生地体与松嫩地块碰撞拼贴并发生强烈挤压造山,两侧增生楔在NW-SE方向汇聚应力驱使下呈花状仰冲隆起,伴随斜向走滑形成早期高角度叶理与线理。造山晚期,兴安增生地体与松嫩地块之间发生显著的左行走滑剪切作用,形成了NE-SW走向的低角度矿物拉伸线理。嫩江洋闭合相关构造的解析表明其具有双向俯冲的特征。 相似文献
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桐柏地区高压变质地体在地壳中的抬升机制 总被引：9，自引：7，他引：2
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. 相似文献
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矿物拉伸线理和面理是研究岩石韧性变形运动学的基本要素。然而自然界许多应变带内拉伸线理和面理产状分布往往并不单一。如何正确认识这类变形组构,并利用这些组构开展构造变形分析至今仍备受争议。本文基于Eshelby理论,通过数值模拟,研究了岩石经历两期不同韧性变形后面理和拉伸线理的产状特征。模拟结果显示岩石经历两期构造变形时,岩石中的较软矿物仅能保留下最后一期构造变形运动学信息。这一认识得到了北大别穹隆内变形组构的支持。北大别穹隆内产状复杂的拉伸线理只记录了造山后伸展期变形。本次数值模拟结果对野外构造观察和分析以及确定构造变形时间具有指导意义。 相似文献
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桐柏山太白顶、殷店和天河口一带,发育有大量的L构造岩,拉伸线理极其发育,面理较弱,线理产状向南东东倾伏,倾伏角为1°～20°。桐柏山L构造岩具有以下主要特征：在三维空间上,L构造岩强烈发育杆状构造,这种“杆”状构造是由大量沿X轴方向定向排列连在一起的椭球体矿物构成的,其变形机制主要为石英的颗粒边界迁移和长石的位错蠕变,形成的平均压力为0.59GPa,平均温度为550 ℃～600 ℃,形成于中-高温-中压环境,变质相为高绿片岩相到低角闪岩相,形成深度大致在15～20 km,属于中地壳的产物。L构造岩在桐柏山的发现可能反映了桐柏山造山带中桐柏杂岩岩块相对两侧榴辉岩岩片具有近东西向挤出构造的特征。 相似文献
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位于中亚造山带与塔里木克拉通结合部位的新疆库鲁克塔格是研究中亚造山带及塔里木克拉通关系的一个关键地区。野外观测、显微构造分析以及Ar–Ar测年结果揭示:(1)库鲁克塔格地区震旦纪—早古生代岩系地层变形样式为底部强烈褶皱,面理密集向北缓倾,顶部褶皱较宽缓、劈理稀疏向北陡倾,构成具有向南构造指向的铲式构造样式;(2)库鲁克塔格地区基底与盖层之间存在一条E–W走向、厚度约2 km的韧性滑脱带,带内普遍发育糜棱岩及A型剪切褶皱等,糜棱岩面理向N或S缓倾、拉伸线理向NW或SE倾伏,不对称旋转构造及糜棱岩中石英晶格优选方位图(EBSD测试)指示韧性滑脱带上盘滑脱方向为自NW向SE;(3)韧性滑脱带中糜棱岩内白云母的Ar–Ar测年结果表明滑脱时代早于383 Ma。滑脱–褶皱构造是塔里木地块与中天山岩浆弧带碰撞后发生陆内俯冲的产物,说明塔里木盆地东北缘库鲁克塔格存在早古生代造山事件。 相似文献
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位于苏鲁超高压变质地体南部的中国大陆科学钻探工程（CCSD）主孔岩石经历了超高压变形及多期折返变形。第一期折返变形为伸展折返变形,榴辉岩发生角闪岩相退变质作用,没有新生面理或线理的发育,基本保留了超高压阶段的S-L组构,并有显示熔融体特征的强退变榴辉岩发育。第二期折返变形为SEE-NWW向挤压折返变形,超高压变形期形成的不同岩石类型在本期变形中表现出不同的叠加变形现象,榴辉岩类岩石早期形成的S倾面理主体部分转为SEE倾,但拉伸线理产状与超高压变形期的近SN走向基本一致,反映早期面理沿NNE轴向的重褶作用,局部又被向SEE缓倾的韧性剪切带切割;而片麻岩类岩石在超高压变形期形成的S-L组构的主体部分已被新生成的总体向SEE缓倾的S-L组构置换,反映早期面理不仅重褶,而且大部分再度发生韧性剪切变形,具SEE向NWW的逆冲剪切指向,矿物普遍重新定向。第三期折返变形发育具NWW向SEE正滑剪切指向的韧性剪切带,并伴随大量“Z”型褶皱构造的发育。第四期折返变形以NWW向SEE正滑的张性或张扭性脆性断裂活动为主。探讨了苏鲁超高压变质地体折返变形的力学机制及CCSD主孔岩石面理变化的形成机制。 相似文献
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黑龙江虎林盆地位于兴凯地块北部,盆地内部中央隆起区出露一套呈NE走向展布的虎林杂岩,岩石强烈韧性变形,对其变形样式及其动力学背景的探讨,为进一步研究兴凯地块乃至中国东北东部中生代构造属性和古太平洋构造体制下构造演化过程提供一个独特的视角。虎林杂岩主体由云母片岩和侵位其中的花岗质岩脉组成,塑性变形特征明显,发育倾向NW向片麻理,走向NE-SW的低角度矿物拉伸线理。岩石矿物组合、微观构造特征和石英EBSD组构分析显示岩石表现中低温变形样式,变形温度为350～450℃,石英变形机制以位错滑移和膨凸重结晶为主。结合宏观变形样式可知,虎林杂岩早期变形以NW倾向片麻理为标志,指示NW-SE向伸展作用,晚期变形以NE倾伏低角度矿物拉伸线理为标志,指示NE-SW向左行走滑事件。侵位的变形闪长玢岩的锆石年代学研究限定晚期左行走滑事件晚于闪长玢岩就位时间1070±17Ma。早白垩世期间,伊泽奈崎板块(古太平洋)NW向斜向俯冲和板片后撤,导致东北东部乃至整个中国东部NW-SE向伸展,造成大陆岩石圈减薄、岩浆活动和虎林伸展断陷盆地的形成。在早白垩世末(104Ma之后),伊泽奈崎板块高速向欧亚大陆俯冲由NNW转向N,由低角度俯冲替代高角度俯冲,使得中国东部再次遭受区域性挤压,导致虎林杂岩发育大规模NE向压扭性左行走滑变形和持续性隆升。 相似文献
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西秦岭北缘武山—鸳鸯镇构造带磁组构特征 总被引：2，自引：0，他引：2
构造与磁组特征揭示出武山-鸳鸯镇构造带为一条复合性断裂带,变形样式表现为花状构造形态。野外及显微构造特征表明,先期韧性变形为右行剪切,发育于中、深构造层次;66个构造岩样品的磁化率椭球形态分析表明,其以平面和压扁应变为主,总体较高的磁化率各向异性度表现了构造带的强变形特征;磁化率椭球主轴方位显示NW和NEE走向两组磁面理的存在,暗示高应变剪切带在平面上可能以共轭或网格状形态出露,锐夹角分线近EW向;高角度磁面理及较为发育的低倾伏角磁线理暗示了沿构造带近EW向的走滑剪切,部分高倾伏角磁线理可能与构造带的挤压和(或)转换挤压相关,而相对集中的磁面理与相对分散的磁线理也表明了构造带的平面及压扁应变体制。强烈的右行转换挤压奠定了西秦岭北缘现今的反"S"型区域构造,表明碰撞造山过程中,西秦岭诸中、小块体一定程度的向西挤逸。中、新生代沿构造带继承性的发育以西秦岭北缘(渭河)断裂为中心的一系列正花状左行走滑构造,构成青藏高原东北边缘物质逃逸及应力释放与调整的重要边界。 相似文献
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胶南地区的伸展作用——以胶南—诸城一带为例 总被引：11，自引：0，他引：11
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ＥＮ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、ＥＷ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ＥＷ向剪切褶皱和鞘褶皱枢纽。晚期伸展作用表现为近ＳＮ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。 相似文献
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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. 相似文献
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The Ghouri area in southwest Iran exposes a cross section through the Zagros orogenic belt. The area provides an opportunity to investigate quantitative finite strain (Rs), kinematic vorticity number (Wk), proportions of pure shear and simple shear components, sense of shear indicators, steeply plunging lineations, and other moderate to steeply plunging stretching lineations in a transpressional zone. Based on a classical strain analysis of deformed microfossils with oblate strain ellipsoid shape, the Zagros orogenic belt is classified as a pure-shear dominated zone of transpression, but asymmetry of shear-sense indicators suggests that a significant component of simple shear was involved along the deformation zone boundaries. The long axes of the microfossils and stretched pebbles of a deformed conglomerate were used to indicate the stretching direction in this zone. The stretching lineations have a steep to moderate plunge but a constant strain magnitude. Characteristics of dextral inclined transpressional kinematics in the Zagros continental collision zone were quantified and indicate an estimated k-value < 1, an angle between the maximum horizontal axis of the instantaneous strain ellipsoid and the zone boundary (θ = 32°), asymmetrical dextral shear-sense indicators, and an angle of relative plate motion (α = 25°). 相似文献
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Mubarak shear belt provides an opportunity to investigate quantitative finite strain (Rs), proportions of pure shear and simple shear components, sense of shear indicators, subhorizontal to steeply plunging mineral lineations, in a dextral transpressional zone. The structural style of the Mubarak shear belt is consistent with dextral transpression within the Central Eastern Desert where dextral and reverse shear have developed simultaneously with the regional foliation. The high strain zone of the Mubarak shear belt is characterized by steeply dipping foliation with sub-horizontal stretching lineation (simple shear) surrounded by thrust imbrications with slightly plunging stretching lineations. Strain estimates from the Mubarak shear belt are used to determine how pure and simple shear components of deformation are partitioned. The axial ratios in XZ sections range from 1.16 to 2.33 with the maximum stretch, S X , ranges from 1.06 to 1.48. The minimum stretch, S Z , ranges from 0.65 to 0.92 indicating a moderate variation in vertical shortening. Volcaniclastic metasediments and metagabbros were subjected to prograde low-grade regional metamorphism in the range of greenschist to lower amphibolite facies (450–650°C at 2–4 kbar). Medium pressure (6–8 kbar at 530°C) was estimated from the high strain zone within the dextral strike-slip shear zones. Retrograde metamorphism occurred at a temperature range of 250–280°C. There is a trend towards decreasing the ratio of 100Mg/(Mg + Fetot + Mn) away from the high strain zone of the Mubarak shear belt. Integrated strain and temperature estimates indicate that the simple shear (non-coaxial) components of deformation played a significant role in formation and exhumation of the Mubarak shear belt during the accumulation of finite strain and consequently during progressive transpression and thrusting. 相似文献
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Field, microstructural, and anisotropy of magnetic susceptibility (AMS) or magnetic fabric studies were applied to identify the sequence and character of the Pan-African structures in the basement of Eastern Cameroon at both sides of the regional scale Bétaré-Oya Shear Zone (BOSZ). The NE-SW trending BOSZ separates older gneisses and migmatites towards SE (domain I) from the younger rocks of the Lom meta-volcano-sedimentary basin towards NW (domain II). In domain I, early, ductile compressional deformation occurred in two events, D1 and D2, under relatively high T conditions. During subsequent cooling, strain partitioned between the competent basement gneisses with only mild compression and the bordering shear zone (BOSZ) with intense simple shear-wrenching (D3). Strain in the less competent rocks of domain II is dominated by simple shear, strike-slip wrenching (D3), with an earlier stage of compressional deformation preserved only in some low strain pods.Magnetic fabrics (AMS) document a progressive change from oblate ellipsoids towards prolate ellipsoids in domain I, when proceeding from the south towards the BOSZ. Foliations are mostly steep but define a girdle with a pole plunging gently towards WSW. The magnetic lineations also plunge mostly towards WSW at shallow angles. These fabrics indicate a compression approximately normal to the BOSZ, which is also the SE margin of the Lom Basin. In the Lom metasediments (domain II), AMS ellipsoids are typically oblate. Foliations trend NE-SW with mostly steep dips. Magnetic lineations plunge gently NE or SW. This fabric with foliations mostly steep and subparallel with the major BOSZ, combined with generally subhorizontal lineations implies the BOSZ as a Pan-African strike–slip shear zone with a subordinate component of compression.At a larger scale, the area is part of a continent-scale shear zone, separating external Pan-African domains of compression along the northern margin of the Congo craton from internal domains dominated by high-angle strike–slip and transpressional deformation. Together with published data, the present study thus demonstrates that transpression is a regional phenomenon in the Pan-African orogen of central and eastern Cameroon. 相似文献
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《Journal of South American Earth Sciences》2007,23(2-3):176-192
The Serra do Azeite shear zone (SASZ) is a northeast-trending regional structure in southeastern Brazil. Kinematic analysis carried out in the SASZ suggests a ductile sinistral transtensional regime in amphibolite facies conditions. Constrictional, flattened, and simple-shear strain domains occur in mylonites with stretching lineation plunging to the east–southeast. Kinematic indicators suggest oblique top–down-to-the-east–southeast and sinistral strike-slip components along variably oriented shear planes. Results of the simple geometrical construction applied to the shear-zone pattern, coupled with field data and kinematic analysis, suggest that sinistral transtensional shearing resulted from east–northeast-directed crustal extension and sinistral strike-slip displacement, accompanied by north–northeast/south–southwest contraction and vertical thinning. The K/Ar and Ar/Ar cooling ages match the proposed interval for crustal extension in the central Mantiqueira province (0.6–0.58/0.57 Ga) based on ages of alkaline granitoids and volcanic rocks. These data indicate types-I and -S granite magmatism, as well as metamorphism and dextral transpressional deformation along the Ribeira belt. Therefore, we interpret the transtensional regime as a result of southwest-directed lateral extrusion and uplift crustal slices (overall oblique extrusion) during an orogenic-scale partitioned transpressional regime. Our results suggest this regime was coeval with a phase of regional stretching subparallel to the Ribeira belt, which would explain the coexistence of extensional and compressional structures during overall plate convergence. 相似文献
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太行山南段自立庄韧性剪切带变形特征 总被引：1，自引：0，他引：1
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。 相似文献
19.
Jean-Emmanuel Martelat Christian Nicollet Jean-Marc Lardeaux Gérard Vidal Raymond Rakotondrazafy 《Geodinamica Acta》2013,26(3):94-114
AbstractThis paper describes the tectono-metamorphic evolution of a segment of the Precambrian deep crust, in the southern Madagascar island. This crust corresponds to an Archaean basement reworked by a widespread, late panAfrican event (550–580 Ma) during the formation of the Mozambican belt. The finite geometry and associated metamorphism are depicted by satellite imaging, field mapping and P-T estimations using both conventional thermobarometric methods and TWEEQ software program with internally consistent thermodynamic data and uniform set of solution models. The structural pattern developed during high-grade metamorphism shows the juxtaposition of domains with complex fold geometries separated by a 15 km wide ductile shear zone. Within the folded domains, kilometre scale interference patterns associated with strongly dipping metamorphic stretching lineations can be described as superposed folding (F1 and F2 folds). The tight and upright F2 folds result from East-West horizontal shortening. The shear zone is defined by homogeneous orientations of steep foliations, sub-horizontal stretching lineations, and kilometre scale strain gradient. Within the shear zone, we observe dominant non-coaxial criteria at various scales that are consistent with a sinistral strike-slip system during D2 deformation stage. Nevertheless, we have also found in the shear zone, geometries typical of a horizontal shortening. Such a strain pattern is characteristic of transpression tectonics.The synkinematic metamorphic conditions are estimated on mafic garnetiferous metabasites. Results show that regional transpression tectonics has developed under very high and constant thermal regime (about 800°C). A pressure gap, of about 3 kbar between the domains separated by the shear zone is identified. This implies tectonic coupling of two different structural levels during tranpressive tectonic. 相似文献