北极生长的多年海冰晶体结构分析   总被引：2，自引：4，他引：2  

李志军  康建成 《冰川冻土》2001,23(4):383-388

对中国首次北极科学考察钻取的一根从表面到底面长2.2m的海冰冰芯样，依据冰芯样采取时造成的长度，不等间距地自上而下垂直切片，剖析了冰芯样的晶体结构，获得以纯热力学生长为主的多年海冰正交偏光镜下晶体结构剖面，由晶体结构剖面确定出该海冰为三年冰，此外，还发现北极海冰越夏过程中生成一种动力碎屑凝聚冰，除给出偏光镜下晶体结构和冰芯层理分析外，还描述了动力碎屑凝聚冰的结构特点。  相似文献   

Fabric development during shear deformation in the Main Central Thrust Zone, NW-Himalaya, India   总被引：2，自引：0，他引：2  

A.R. Bhattacharya  K. Weber 《Tectonophysics》2004,387(1-4):23-46

Quartz microfabrics and associated microstructures have been studied on a crustal shear zone—the Main Central Thrust (MCT) of the Himalaya. Sampling has been done along six traverses across the MCT zone in the Kumaun and Garhwal sectors of the Indian Himalaya. The MCT is a moderately north-dipping shear zone formed as a result of the southward emplacement of a part of the deeply rooted crust (that now constitutes the Central Crystalline Zone of the Higher Himalaya) over the less metamorphosed sedimentary belt of the Lesser Himalaya. On the basis of quartz c- and a-axis fabric patterns, supported by the relevant microstructures within the MCT zone, two major kinematic domains have been distinguished. A noncoaxial deformation domain is indicated by the intensely deformed rocks in the vicinity of the MCT plane. This domain includes ductilely deformed and fine-grained mylonitic rocks which contain a strong stretching lineation and are composed of low-grade mineral assemblages (muscovite, chlorite and quartz). These rocks are characterized by highly asymmetric structures/microstructures and quartz c- and a-axis fabrics that indicate a top-to-the-south sense that is compatible with south-directed thrusting for the MCT zone. An apparently coaxial deformation domain, on the other hand, is indicated by the rocks occurring in a rather narrow belt fringing, and structurally above, the noncoaxial deformation domain. The rocks are highly feldspathic and coarse-grained gneisses and do not possess any common lineation trend and the effects of simple shear deformation are weak. The quartz c-axis fabrics are symmetrical with respect to foliation and lineation. Moreover, these rocks contain conjugate and mutually interfering shear bands, feldspar/quartz porphyroclasts with long axes parallel to the macrosopic foliation and the related structures/microstructures, suggesting deformation under an approximate coaxial strain path.On moving towards the MCT, the quartz c- and a-axis fabrics become progressively stronger. The c-axis fabric gradually changes from random to orthorhombic and then to monoclinic. In addition, the coaxial strain path gradually changes to the noncoaxial strain path. All this progressive evolution of quartz fabrics suggests more activation of the basal, rhomb and a slip systems at all structural levels across the MCT.  相似文献   

Evaluating magnetic lineations (AMS) in deformed rocks   总被引：3，自引：0，他引：3  

Josep M. Pars  Ben A. van der Pluijm 《Tectonophysics》2002,350(4):283-298

Magnetic lineation in rocks is given by a cluster of the principal axes of maximum susceptibility (K_max) of the Anisotropy of Magnetic Susceptibility (AMS) tensor. In deformed rocks, magnetic lineations are generally considered to be the result of either bedding and cleavage intersection or they parallel the tectonic extension direction in high strain zones. Our AMS determinations, based on a variety of samples that were taken from mudstones, slates and schists from the Pyrenees and Appalachians, show that strain is not the only factor controlling the development of magnetic lineation. We find that the development and extent to which the magnetic lineation parallels the tectonic extension direction depends on both the original AMS tensor, which in turn depends on the lithology, and the deformation intensity. Rocks having a weak pre-deformational fabric will develop magnetic lineations that more readily will track the tectonic extension.  相似文献   

实验变形煤的光性组构分析   总被引：4，自引：1，他引：4       下载免费PDF全文

周建勋  邵震杰  王桂梁 《地质科学》1994,29(3):276-290

三种R_max^o分别为0.67%,3.41%和4.90%的煤样,在t=350-700℃、P_c=400-600MPa、ε=10%-30%、ε=3.63×10^-4-2.59×10^-5s^-1条件下的变形实验表明:(1)煤光性组构的成因是芳环层片在构造应力作用下重新定向所致,重新定向的主要机制是煤化过程中芳环层片的择优成核生长,同时存在物理转动定向机制的作用;(2)芳环层片的重新定向主要发生在煤级相对较低阶段,VRI的Z轴主要反映这一阶段的构造应力方向;(3)YRI的形态特征并非仅与有限应变有关,它不能直接作为有限应变分析的标志。  相似文献   

花岗质超糜棱岩的微观构造与变形机制     

张磊  张波  张进江 《地质学报》2022,96(10):3639-3657

花岗质岩石的变形方式和过程决定大陆地壳的流变学特性。本文聚焦藏南拆离系超糜棱岩化的花岗质岩石，借助传统显微构造分析方法和扫描电镜、阴极发光、矿相自动分析系统和电子背散射衍射等新技术手段，开展微观组分、结构、组构定量化观测和分析。超糜棱岩主要造岩矿物为钾长石、斜长石、石英、黑云母等，显微构造呈现为单矿物相域与多相矿物混合域交织结构。相平衡模拟与斜长石钙含量等值线变形温度估算结果为390～410℃。单相域的矿物集合体条带主要分为钾长石条带与石英条带，其中钾长石条带内变形颗粒呈现典型的核 幔构造。组构分析表明钾长石颗粒具有强烈的晶格优选定向，残斑与动态重结晶的钾长石颗粒具有相似的晶格优选方位(CPOs)特征。施密特因子法分析揭示钾长石残斑变形过程中主要活动的滑移系为(100)\[010\]、(010)\[001\]和(001)\[100\]，基质钾长石颗粒形成机制主要为位错蠕变驱动的亚颗粒旋转重结晶。在混合相域，矿物颗粒发生强烈细粒化而只含有少量残斑，基质颗粒主要为斜长石，斜长石颗粒间广泛分布微米级黑云母颗粒。斜长石无组构或弱组构，主导变形机制为颗粒边界滑动。在单相域条带与混合相域基质内，石英颗粒均发生强烈细粒化，颗粒表面发育溶蚀结构以及细小的新晶晶核，石英＜c＞轴晶格优选定向及形态学长轴优选定向皆平行于线理X方向，变形机制为溶解 沉淀蠕变。这显示在由单相域向混合相域的演化过程中，流体作用至关重要，流体与单相域钾长石进行交代使其分解为细粒的斜长石与石英，并导致花岗质岩石变形机制由位错蠕变向非位错蠕变转换，并诱发岩石的流变弱化。  相似文献   

Tectonics of the Akamas and Mamonia ophiolites, Western Cyprus: magnetic petrofabrics and paleomagnetism     

G. J. Borradaile  K. Lucas 《Journal of Structural Geology》2003,25(12):2053-2076

The Akamas ophiolite is shown to be a distal, off-axis extension of the main outcrop of Cretaceous ophiolite in the Troodos complex of Cyprus. Mantle-sequence harzburgites of both ophiolites share similarly oriented mantle-flow fabrics and the same Tertiary magnetizations acquired during exhumation. However, compared with the Troodos mantle sequence rocks, the Akamas ferromagnetic mineralogy is more oxidized and remanences with lower blocking temperatures were acquired chemically. Paleopoles calculated from published vectors and our own new data define an apparent polar wander path (APWP) for the Troodos microplate. The APWP shows that between 88 and 50 Ma the Troodos microplate was equatorial and the vertical axis for its 60° anticlockwise rotation was located within the microplate. Subsequently, the microplate drifted northward to 34°N with minor anticlockwise rotation at a reduced rate. That requires microplate-rotation about a vertical axis located to the west of Cyprus in the last 50 Ma. The allochthonous Triassic Mamonia terrane docked with the Cretaceous Troodos terrane in SW Cyprus. Within it, disrupted tectonized ophiolite has been regarded as part of a Triassic ocean floor or as sheared fragments of Cretaceous Troodos ophiolite, incorporated into the Mamonia terrane when it docked with the Troodos terrane. Whatever their provenance, their paleomagnetic signals postdate their penetrative deformation and metamorphism and their paleopoles may still be used to track their post-strain motion. Our calculations of paleopoles from published vectors for the Mamonia terrane smear along an extension of the APWP for the Troodos microplate that is, moreover, concentric with the Troodos microplate. This suggests that the paleopole dispersion of the Triassic Mamonia rocks and their post-magnetization disruption occurred during their accretion onto the anticlockwise-spinning Troodos microplate.  相似文献   

西秦岭温泉岩体的磁组构特征及其侵位机制意义   总被引：6，自引：3，他引：3       下载免费PDF全文

谢晋强  张国伟  鲁如魁  郭秀峰  程斌  梁文天  陈应涛 《地球物理学报》2010,53(5):1187-1195

结合岩石磁学、磁化率各向异性度与区域构造分析了西秦岭温泉岩体的侵位机制及意义.温泉岩体的样品的平均磁化率k_m值总体很大,岩石磁学表明对于磁化率较低的样品,顺磁性矿物（如黑云母等）对磁化率的贡献较大,而少量铁磁性矿物（如磁铁矿等）可能作为剩磁载体.对于磁化率较高的样品,其主要载磁矿物为磁铁矿;花岗岩样品的校正磁化率各向异性度P_J总体小于1.2,显示了岩体为流动磁组构的特征,磁化率椭球体形态参数T总体大于0,扁率E总体大于1,以压扁椭球体为主;岩体的磁面理同磁线理相比更为发育,样品的磁面理普遍表现出围绕岩体边界分布的特点,且倾角较陡;而在岩体内部磁线理与磁面理分布相对散乱,定向性差,这一特征说明温泉岩体的磁组构主要由侵位时的侧向挤压作用形成的;虽然岩体的磁组构特征总体显示了N-NEE和SW向的挤压作用,但岩体侵位时由商丹缝合带闭合所产生的垂直于缝合带方向的挤压作用已相对较弱.本文认为,温泉岩体侵位时是一种弱挤压环境,或者是一种相对稳定的环境甚至可能是一种相对引张的背景,这与温泉岩体形成于后碰撞环境,秦岭造山带已演化至后碰撞拆沉作用发生的伸展阶段所反映的区域构造背景是一致的.  相似文献   

喀喇昆仑断裂带磁组构特征及其构造意义   总被引：11，自引：1，他引：10  

周勇  杨灿尧 《岩石学报》2000,16(1):134-144

本文讨论了喀喇昆仑断裂带的磁组组构特征。磁化率几何平均值随岩石所含矿物不同而有很大改变,校正磁各向异性度ＰＪ在变形强弱不同的岩石中有较大区别。大多数磁化率椭球体有良好的磁面理和最短轴方位,表现出强烈的压扁型应变型式;最短轴方位被视为最大主应力方向,在工作区呈ＮＥ－Ｓ工有低至中等大小的倾角,由于喀喇昆仑断裂走向ＮＮＷ＝ＳＳＥ,表明其走滑运动为右旋,在不同地区断裂两盘则有不同的垂向差异运动。同位素测年  相似文献   

南西天山晚新生代沉积序列磁组构特征及其构造意义     

陈新伟  陈汉林  林秀斌  程晓敢  聂梅 《地质学报》2020,94(6):1675-1688

喀什凹陷西部位于塔里木盆地、帕米尔构造带和南西天山构造带的交接处,在新生代以来接受了大量来自于南天山和帕米尔的沉积物,并记录了新生代以来南西天山构造抬升的信息。本文选择了位于南西天山山前的铁热克萨孜晚新生代剖面开展磁组构研究。铁热克萨孜剖面晚新生代沉积序列自下而上为一套整体上粒度逐渐变粗的陆相沉积,由河流湖泊相逐渐变为扇三角洲相,并最终变为冲积扇相和洪积扇相。岩石磁学结果的分析表明剖面晚新生代沉积序列中的主要磁性矿物为赤铁矿,仅在帕卡布拉克组下部为以磁铁矿为主。磁组构结果表明该剖面的磁组构为早期的同沉积弱变形磁组构,指示了当时构造应力的方向和变化。在22.1Ma以来南西天山山前晚新生代磁组构所反映的构造应力整体上为N-S向挤压,这与帕米尔和南天山的南北向持续汇聚作用相一致。在安居安组和西域组时期,应力方向由N-S向挤压变为NNE-SSW向挤压,这一变化可能是由塔拉斯-费尔干纳断裂的活动所导致的。塔拉斯-费尔干纳断裂(Talas-Fergana Fault, TFF)的右行走滑活动可能吸收了南西天山晚新生代的部分应变量,使得南西天山山前的构造应变量相对TFF以东的南天山山前地区要更小,使得TFF以东的晚新生代山前冲断带活动相对TFF以西地区更为发育和活跃。  相似文献   

Paraglacial Modification of Glacigenic Sediment     

Alastair M. Curry  & Colin K. Ballantyne 《Geografiska Annaler: Series A, Physical Geography》1999,81(3):409-419

The sedimentological characteristics of in situ and paraglacially reworked till are compared at recently deglaciated sites in Norway. Glacigenic deposits reworked by debris flows are shown to retain many of the characteristics of the parent sediments, and cannot readily be distinguished from in situ till in terms of fabric strength or type, clast imbrication, shape, angularity or texture, matrix granulometry or packing. Paraglacially re-worked sediments appear to differ from in situ tills only in terms of preferred clast orientation (down flow rather than downvalley) and their structural and lithofacies characteristics. These criteria are employed to differentiate paraglacial sediments from unre-worked tills exposed in valley-side sections. The stratigraphic relations between these indicate glacial reworking of earlier paraglacial sediments as well as paraglacial remobilisation of glacigenic deposits, indicating cyclic alternation of glacial and paraglacial sediment transport.  相似文献