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关于太古宙早期地壳演化构造机制的争论已经持续了数十年,其焦点主要集中于水平构造还是垂向构造两大经典构造模式的探讨.对于早期地壳构造演化方面的研究,将会有助于我们更好地理解早前寒武纪的地球动力学机制.本文对华北克拉通东北部鞍山地区花岗-绿岩带内齐大山韧性剪切带的构造变形特征进行了详细的解析,揭示了该区新太古代垂向构造作用样式.研究结果表明,齐大山韧性剪切带内花岗质岩石长英质矿物塑性拉长特征明显,条带状构造发育,面理向NWW方向陡倾,不对称组构特征和矿物拉伸线理产状指示向NWW的陡倾正滑移剪切作用.变形岩石中的长英质矿物均发育中低温显微变形特征,石英C轴电子背散射衍射（EBSD）组构分析揭示石英以菱面＜a＞和底面＜a＞滑移系为主,岩石经历了中低温非共轴变形.根据矿物的变形行为以及石英的结晶优选方位推测变形温度约为400~500℃,岩石变形特征以位错蠕变为主.有限应变分析结果表明,靠近铁矿带方向,构造岩类型由L=S构造岩过渡为LS构造岩,岩石应变强度呈明显增强趋势.运动学涡度测量结果显示齐大山韧性剪切带内大多数岩石样品的Wk值大于0.75,岩石形成于以简单剪切作用为主的一般剪切作用.对比花岗-绿岩带西侧的白家坟韧性剪切带,显示二者均具有相向的陡倾正滑移运动学特征,表明新太古代时期鞍山地区地壳构造演化模式以垂向构造作用为主. 相似文献
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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
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大别山北缘的晓天—磨子潭韧性剪切带主体发育在北大别片麻岩之上,具有近水平左行剪切的运动学特征;剪切带自中心向外围依次发育超糜棱岩、糜棱岩、初糜棱岩、变形片麻岩(片岩)、围岩,发生变形的主要造岩矿物包括石英、长石、角闪石、云母等。岩石有限应变测量和矿物颗粒形态学优选方位统计显示,随着糜棱岩化程度的加强,主要造岩矿物平均粒径均呈递减变化;矿物长短轴所反映的应变均呈加强的趋势,矿物长轴与X的锐夹角皆逐渐变小;以90°为一个区间统计的矿物长轴定向显示,变形矿物的长轴在钝角区间(顺剪切方向)有优选,以15°为一个区间统计的矿物长轴定向显示,矿物定向存在一定对称性,即在锐夹角区的优选区间和钝夹角区的优选区间互为补角区间。此外,云母矿物的应变在不同样品中均显示最大,其次为石英、角闪石、长石;随着构造岩类型的不同,应变的变化趋势最明显的也是云母,其次为石英,角闪石和长石变化不明显;矿物长轴与X轴夹角的统计表明,云母、角闪石长轴与X轴锐夹角比石英、长石均偏小。矿物的变形还表明,指示剪切带剪切方式最明显的是云母类矿物,尤其是云母鱼构造,是判定运动方向的可靠标志,其次是角闪石,较之斜长石更易形成不对称残斑构造;综合矿物在剪切带中的含量和分布,结构特点,以及对剪切带应变反映的"灵敏性"等方面的因素,石英矿物最能表现剪切带的整体应变状态,是较为理想的应变标志矿物。上述结果表明不同矿物随变形环境的渐变,在粒径、应变、形态学优选等方面具有较统一的变化,即不同变形矿物在反映剪切带的剪切作用方式、应力—应变等特征时是较为一致的;同时不同矿物在上述变化中又表现出区别于其他矿物的各自特点,这反映了矿物自身的晶体结构、结晶形态、力学性质、变形习性等特性。所以,对于研究韧性剪切带而言,针对不同研究内容,要综合不同矿物的变形情况来选取合适的变形矿物及其变形组构来研究,才能得到更准确的结果和更合理的解释。 相似文献
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结合灰度分界阈值分割法和粒子图像测速技术,对单轴压缩条件下花岗岩变形破坏过程中不同矿物成分(黑云母、长石和石英)的变化特征进行了研究。由室内单轴压缩试验获得花岗岩变形破坏过程的试验视频图像;由灰度分界阈值分割法获得视频图像中岩石表面不同矿物成分的位置;使用粒子图像测速技术得到岩石表面不同时刻的位移;采用应变计算公式的差分格式得到不同位置不同方向的应变大小;在此基础上,研究了不同变形阶段岩石中不同方向应变的变化特征及其与矿物成分分布的关系。结果表明:裂缝出现前,花岗岩表面各矿物成分变形方向主要沿水平方向;裂缝发展过程中,长石变形方向主要是竖直方向,石英变形方向主要是水平方向;三种矿物成分中,最大主应变从大到小的顺序为黑云母、长石、石英。 相似文献
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岩石显微构造分析现代技术——EBSD技术及应用 总被引：10，自引：0，他引：10
EBSD技术的发展,为岩石显微构造分析开辟了一个全新的领域。它与现代扫描电子显微镜和能谱分析等设备配合,可以同时对块状样品进行晶体结构与成分分析,从而使显微构造、微区成分与结晶学数据分析有机结合起来。
EBSD技术可以精确、快速定量标定包括各种晶系晶体颗粒的晶格方位和描述晶体颗粒的边界、形态等特征,对于具有低角度边界的晶体颗粒提供精确数据,为阐述岩石变形机制提供重要约束,并为高级晶族和不透明矿物结晶学组构与变形机制研究提供了有效的手段。EBSD尤其使获取微米级甚至纳米级尺度上颗粒（亚颗粒）或相之间的定向差别（达到20 nm的空间分辨率和0.3度角度分辨率）成为可能。EBSD技术在矿物相鉴定、亚微域内的应变分析、矿物出溶作用等方面的应用,进一步证明了这一新技术在显微构造分析及相关领域的应用前景。其广泛应用必将带来岩石显微构造研究的新突破,也将成为未来岩石变形机制与岩石圈流变学研究取得飞速发展不可或缺的技术手段。 相似文献
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变形石墨对构造- 热过程的定量约束及流变弱化意义 总被引：1，自引：0，他引：1
岩石变形过程的精细厘定是构造地质学研究中的难点和重点。石墨是碳的同素异形体，摩擦实验研究表明，增加少量石墨化碳质物能够显著降低岩石的摩擦系数和力学强度，具有固体润滑剂的流变学意义。本研究针对红河- 哀牢山剪切带新生代变形，开展了详细的野外观测和构造解析，针对不同变形- 变质程度的天然含石墨岩石样品，利用光学显微镜、场发射扫描电子显微镜、电子背散射衍射(EBSD)、拉曼光谱方法，开展了详细的显微及亚显微变质与变形构造、矿物晶格优选定向、石墨拉曼地质温度计应用等深入分析。发现深变质岩中，石墨晶体常常与黑云母共生且定向拉伸或生长，呈现出晶质片状、条带状、膝折等变形构造特征；在强烈塑性变形的岩石中，石墨表现出塑性到超塑性流动构造特征；细粒化石墨富集形成微型滑移带/面，承载流变弱化的“干”润滑作用；在低级变质- 弱变形岩石中，石墨有序度低，呈弥散状分布。EBSD组构显示石墨发育柱面、菱面到低温底面晶格滑移系，对应的石墨拉曼地质温度范围为600~500℃、530~460℃、450~400℃。变形石墨的位错滑移系具有与石英位错滑移系类似的演化特征，具有成为变形温度计的潜力。 相似文献
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石英c轴组构影响因素探讨:以郯庐断裂带糜棱岩为例 总被引：1，自引：1，他引：0
石英是自然界中最主要的造岩矿物之一,也是地壳流变过程的主要变形矿物,其c轴组构特征与变形温度、剪切指向具有密切的关系,因而常被用来获取剪切指向、估计变形温度、计算运动学涡度等。但由于受到变形分解、先存构造、流体等因素的影响,同一岩石中常会得到多个不同的石英c轴组构结果。如果天然变形岩石同时受到多种因素的影响,其石英c轴组构会表现为何种特征?与岩石变形温度、剪切旋向是否仍具有很好的对应性?基于以上问题,本次工作以大别山东缘郯庐断裂带内经历了多期变形、富含流体活动的超糜棱岩为研究对象,在同一岩石薄片中选择不同区域,利用EBSD开展石英c轴组构分析。分析结果表明,选择的超糜棱岩的石英c轴组构点极密分布形态指示岩石变形发生于非共轴变形条件下;剪切指向方面,6个分析区域中区域1表现为左旋剪切指向特征,与薄片中优势剪切指向一致,而除区域4外的其他4个区域显示出与优势剪切指向相反的右旋剪切指向特征;变形温度方面,区域4以柱面滑移为主,显示了高温变形特征,而其余5个区域均以底面滑移为主,指示了低温变形环境。根据本次石英c轴组构特征分析结果,可以得出一些认识:岩石中石英表现为完全的GBM动态重结晶,所指示的温度明显高于大量沿糜棱面理分布的绿泥石所指示的绿片岩相环境,显示流体活动促进了岩石变形;而石英c轴组构指示的变形温度为绿片岩相环境,与绿泥石存在的现象一致,表明糜棱岩化过程中流体活动对石英c轴组构的影响并不明显。在发生过多期变形事件的岩石中,岩石中早期高温变形信息有可能保留下来并记录在石英c轴组构特征中,因而通过石英c轴组构分析有可能获得早期事件的信息;虽然石英c轴组构影响因素众多,但首先开展详细的显微镜下观察,然后有选择地对剪切指向清晰区域开展石英c轴组构分析,仍然能够得到与岩石中优势剪切指向一致的石英c轴组构结果。 相似文献
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阿尔金北缘大平沟韧-脆性变形带特征 总被引：3，自引：2，他引：1
大平沟韧-脆性变形带出露于紧邻阿尔金北缘断裂北侧的新太古界达格拉格布拉克群钾长片麻岩中,与阿尔金走滑断裂索尔库里段相距约50km。总体呈东西向展布,高角度向南倾斜,倾角65～85°。次级变形带呈北西西向-东西向波状起伏延伸。单个次级变形带规模一般长数百米,宽数十米。变形带内岩石的线理、面理构造发育,石英、钾长石矿物粒内变形效应明显,同构造变形的新生矿物绢云母比较发育。变形性质为韧-脆性压扭性构造变形,发育糜棱岩系列岩石,特别是含钾长石残斑的绢云母石英质糜棱岩最为常见。变形岩石组构显示石英以底面和近于底面滑移的方式发生变形,反映出是中-低温条件(250～350℃);有限应变测量显示岩石变形强度中等,应变椭球轴比为2.9～4.8;变形运动学特点为右行逆冲,变形主压应力方向为北北西向,最大差应力为59～61MPa。结合区域构造演化,作者认为该韧-脆性变形带是发生于早古生代板块碰撞的大地构造背景条件下,并反映了板块碰撞过程中基底岩块的变形特点。 相似文献
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根据我国东部煤田一些实例和高温高压变形实验模拟结果表明,含煤地层中石英C-轴组构普遍具有稀疏小圆环带型式,其环带轴具有显著的应力指向意义。稀疏小圆环带型式组构的形成与石英底面滑移系的运动有关,是点极密型式的过渡状态,与石英颗粒的塑性应变量较小有关。造成含煤地层中石英颗粒塑性应变量较小的原因,除构造变形强度较小外,还与岩石中普遍存在软弱矿物有关。软弱矿物的存在吸收了大部分塑性应变 相似文献
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The behaviour of quartz during metamorphism is studied based on two case studies from the Barrovian terrains of Sulitjelma in arctic Scandinavia and Loch Tay in the Central Highlands Dalradian of Scotland. Both terrains preserve evidence for metamorphism in pelites involving nucleation and growth of garnet at different times in the deformation history. Data are presented on the size, shape and crystallographic orientation of quartz preserved as inclusions in garnet and as grains in the surrounding matrix. While quartz-grains remain small and dispersed between mica grains, deformation appears to be dominated by grain-boundary sliding accommodated by dissolution–precipitation. At amphibolite facies, textural coarsening occurs by dissolution of small quartz grains and growth of larger quartz grains, coupled with segregation of quartz from mica. As a result, quartz deforms by dislocation creep, developing crystallographic preferred orientations (CPO) consistent with both coaxial and non-coaxial strain. Quartz CPOs with <0001> axes lying parallel to foliation and stretching direction are commonly developed, and best explained by mechanical rotation of inequant (detrital?) quartz grains. There is no evidence for selective entrapment of quartz inclusions in garnet on the basis of quartz crystallographic orientation. 相似文献
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John Starkey 《Tectonophysics》1979,58(1-2)
The regional development of distinct patterns of preferred orientation of quartz c-axes in the Saxony Granulites has been well documented in the literature. A suite of specimens representative of these fabrics has been examined both by optical universal stage, to determine quartz c-axis orientation, and by X-ray diffraction, to obtain orientation data from r, z, m and a. The data are combined to yield inverse pole figures of schistosity and lineation.The finite strain of the Saxony Granulites is thought to be essentially a flattening and there is no evidence that the deformation path is other than one of continuous flattening. Elongation in the plane of the schistosity is local and not extreme. Because of this apparently simple deformation picture, and because preliminary transmission electron microscopy reveals the presence of dislocation structures similar to those found in deformed metals, an attempt is made to interpret the quartz orientation in terms of dislocation slip mechanisms. There is some evidence that the activation of different mechanisms is perhaps primarily controlled by temperature. At least some of the patterns of preferred orientation of quartz were probably produced by deformation in the field of stability of α-quartz. 相似文献
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Quartz Crystallographic Preferred Orientation (CPO) patterns are most commonly a result of deformation by dislocation creep. We investigated whether Dissolution–Precipitation Creep (DPC), a process that occurs at lower differential stresses and temperatures, may result in CPO in quartz. The Purgatory Conglomerate is part of the SE Narragansett basin where strain intensity increases from west to east and is associated with top-to-the-west transport and folding during the Alleghanian orogeny. Within the Purgatory Conglomerate, DPC led to quartz dissolution along cobble surfaces perpendicular to the shortening direction, and quartz precipitation in overgrowths at the ends of the cobbles (strain shadows), parallel to the maximum extension direction. Quartz c-axis orientations as revealed by Electron Backscatter Diffraction (EBSD) methods were random in all analyzed domains within the cobbles and strain shadows irrespective of the intensity of strain or metamorphic grade of the sample. Quartz dissolution probably occurred exclusively along the cobbles' margins, leaving the remaining grains unaffected by DPC. The fact that quartz precipitated in random orientations may indicate that the strain shadows were regions of little or no differential stress. 相似文献
15.
Mitsuhiro Toriumi Jun Teruya Megumi Masui Hidesato Kuwahara 《Contributions to Mineralogy and Petrology》1986,94(1):54-62
A number of microstructural features indicate a difference in the dominant deformation mechanism between the higher temperature Ryoke and the lower temperature Sambagawa and Shimanto metamorphic belts of Japan. The microstructures of metacherts containing deformed radiolaria are divided into two types: in both the Sambagawa and Shimanto belts the quartz grains are tabular while in the Ryoke belt they are equiaxed. TEM studies of these metacherts revealed that the tabular grains contain abundant subboundaries consisting of large numbers of network dislocations and bowe-out dislocations, while the equiaxed grains contain no subboundaries and have low densities of dislocations which are not bowed-out. There is a corresponding difference in the textures (lattice preferred orientation of quartz): the Ryoke metacherts display randomly distributed c-axes of quartz, while the Sambagawa and Shimanto metacherts show conspicuous crossed girdle patterns with some asymmetry. There is a third difference between these regions: in the metacherts of the Ryoke metamorphic belt, the strain magnitudes determined from deformed radiolaria increase with increasing volume fraction of mica in the same metamorphic P and T conditions, while in the Sambagawa and the Shimanto metamorphic cherts the strain magnitudes decrease with increasing the mica fraction.These microstructures, textures, and rheological behaviours of quartz-mica rocks suggest a change of deformation mechanism between the lower temperature Sambagawa and Shimanto, and the higher temperature Ryoke metamorphic belts. Since random fabrics of c-axes of quartz are inconsistent with lattice rotation due to dislocation glide, the Ryoke metacherts may have deformed by pressure-solution. 相似文献
16.
We show that naturally-deformed hematite from the Quadrilátero Ferrífero Province, Minas Gerais, Brazil, develops CPOs by dislocation creep, strongly influenced by basal plane parallel glide, even when this is not the favored slip system. Characterization of microstructure and texture, particularly intragranular misorientations, of naturally deformed hematite aggregates by EBSD allowed us to determine the importance of different slip systems, and confirm dislocation creep as the dominant deformation mechanism. Viscoplastic self-consistent (VPSC) models were constructed to constrain the slip systems required to operate for the observed CPO to develop, and its rheological implications. Changes in the CRSS ratio of hematite prism and basal slip systems and deformation regime lead to the development of distinct patterns of hematite crystallographic orientations. The basal slip-dominated simple shear model is the only one that can develop quasi-single-crystal CPO of the kind observed in highly deformed rocks from Quadrilátero Ferrífero. Comparison between naturally deformed hematite aggregates and VPSC models shows that CPO development of hematite is strongly influenced by a highly viscoplastic anisotropy through dislocation creep on hematite basal plane. Nonetheless, our results demonstrate that even the unfavorable slip systems should be regarded when the bulk rheology of mineral aggregates is evaluated. 相似文献
17.
Bruno Boulogne Patrick Cordier Jean-Claude Doukhan 《Physics and Chemistry of Minerals》1988,16(3):250-261
Berlinite, AlPO4, is a structural analog of quartz and a number of physical properties are very similar in both materials. It is thus interesting to compare their mechanical properties and investigate the possible role of water. Constant strain rate tests on wet synthetic crystals have been performed at room temperature and at 600 MPa confining pressure. They indicate that \((000){1 \mathord{\left/ {\vphantom {1 3}} \right. \kern-0em} 3}\langle 11\bar 20\rangle \) is the easy glide system. Detailled investigation of the crystal structure shows that the corresponding a dislocations can glide in such a way that only the weaker Al—O bonds are broken. This explains why this glide system is much more easily activated in berlinite than in quartz. Deformation experiments at higher temperature and at atmospheric pressure clearly show a thermally activated regime. However the actually available crystals are so rich in water that above 300° C the dislocation structure resulting from deformation is completely hidden by water precipitation and coarsening of the as-grown fluid inclusions. Like for wet quartz this later phenomenon generates numerous bubbles and sessile dislocation loops. 相似文献
18.
Tectonic pseudotachylytes, i.e. quenched friction-induced silicate melts, record coseismic slip along faults and are mainly reported from the brittle crust in association with cataclasites. In this study, we document the occurrence of recrystallization of quartz to ultrafine-grained (grain size 1–2 μm) aggregates along microshear zones (50–150 μm thick) in the host rock adjacent to pseudotachylytes from two different faults within quartzite (Schneeberg Normal Fault Zone, Eastern Alps), and tonalite (Adamello fault, Southern Alps) in the brittle crust. The transition from the host quartz to microshear zone interior includes: (i) formation of high dislocation densities; (ii) fine (0.3–0.5 μm) polygonization to subgrains defined by disordered to well-ordered dislocation walls; (iii) development of a mosaic aggregate of dislocation-free new grains. The crystallographic preferred orientation (CPO) of quartz towards the microshear zone shows a progressive misorientation from the host grain, by subgrain rotation recrystallization, to a nearly random CPO possibly related to grain boundary sliding. These ultrafine aggregates appear to be typically associated with pseudotachylytes in nature. We refer the crystal plastic deformation of quartz accompanied by dramatic grain size refinement to the coseismic stages of fault slip due to high differential stress and temperature transients induced by frictional heating. Microshear zones localized on precursory fractures developed during the stages of earthquake rupture propagation and the very initial stages of fault slip. Thermal models indicate that the process of recrystallization, including recovery processes, occurred in a time lapse of a few tens of seconds. 相似文献
19.
A. T. HAWKINS J. SELVERSTONE A. J. BREARLEY R. J. BEANE R. A. KETCHAM W. D. CARLSON 《Journal of Metamorphic Geology》2007,25(5):565-583
High-pressure schists (2–2.5 GPa) from the Eclogite Zone in the Tauern Window contain honeycomb garnet in which fine webs of garnet surround strain-free quartz ± carbonate grains. High-resolution X-ray computed tomography shows that the garnet webs form a cellular structure that coats all surfaces of the inclusions. Electron backscatter diffraction analysis shows that the garnet cells are crystallographically continuous with more massive garnet regions, and that the quartz ± carbonate inclusions have random orientations; in contrast, matrix quartz exhibits a prominent crystallographic preferred orientation (CPO). High-resolution transmission electron microscopy shows few dislocations in either the garnet or the inclusion quartz. Most honeycomb garnet is chemically homogeneous, but some displays asymmetric core–rim zoning. Taken together, these observations are most consistent with formation of the garnet sheets via precipitation from a wetting fluid along quartz–quartz grain boundaries, or possibly via wholesale precipitation of garnet + quartz ± carbonate from a fluid. In either case, a silicate-rich aqueous fluid must have been present. The likelihood that a fully wetting fluid existed at high pressure has important implications for rheology during subduction of metasedimentary rocks: strain may be accommodated by grain rotation and sliding in an aqueous silicate slurry, rather than via dislocation creep mechanisms at high pressures. The absence of a CPO in early quartz may thus point to involvement of a pervasive grain-boundary fluid rather than requiring low differential stresses during subduction. 相似文献
20.
Fabric transitions can arise in materials such as quartz in which more than one set of symmetrically equivalent glide systems must be considered. The external conditions, such as temperature and stress, affect the relative ability of different mechanisms to operate. Adopting the Taylor-Bishop-Hill analysis allows an approximation to the resulting effects in the choice of critical resolved shear stress (CRSS) values for glide on the different dislocation systems. Different CRSS values may be appropriate to simulating fabric development in different deformational environments.For any specific set of CRSS values, for a particular deformation, a set of reorientation trajectories can be defined for differently oriented crystals with respect to the instantaneous stretching axes. There is a basic number of pattern types, and deformation leads to c-axes populating specific end-orientations.The CRSS values on different glide systems can vary smoothly relative to one another, but abrupt changes result in the deformation fabrics at critical CRSS ratios. Quartz fabrics may thus be used to delineate regions subjected to particular conditions of temperature and strain-rate in deformed metamorphic terrains, provided that allowance can be made for other factors such as trace impurity content of quartz. 相似文献