Evolution of the ductile shear zone of the Paishanlou gold deposits,western Liaoning,China

The combination of field surveys with analysis of microstructure of tectonite and Electron Backscatter Diffraction (EBSD) on quartz fabric indicated that three periods of ductile shear events developed in the Paishanlou gold deposits and the E-W and NE-striking ductile shear zones were formed during each event. The E-W-striking ductile shear zone, accompanied by compressional and dextral shear slip, was shear-cut by the NE-striking shear zones, accompanied by compressional-sinistral shear slip and sinistral-normal shear slip, successively. An E-W-striking ductile shear zone developed at a deeper tectonic level and at middle- to high-temperatures, accompanied by abundant microstructures, including microlayering between a polycrystal quartz belt and mica, and quartz deformation was depended on cylinder (10-10) 〈a〉 or 〈c〉 glide. The development of an E-W-striking shear zone can be seen as a tectonic pattern in the region of the Paishanlou gold deposits of the collision between the Mongolian tectonic belt and the North Archean Craton from Suolun to the Linxi suture zone during the Indosinian. The NE-striking ductile shear zone developed approximately 160 Ma during the early Yianshanian at middle to shallow tectonic levels and at middle- to low-temperatures, accompanied by typical microstructures, including polycrystal quartz aggregation and quartz subgrain rotation recrystallization, etc., and quartz deformation was depended on prismatic (1011) 〈a〉 glide. The last ductile shear event around the NE-striking shear zone developed at low temperatures and shallow tectonic levels, yielding to a pre-existing NE-striking shear zone, accompanied by abundant microstructures, including low-temperature quartz grain boundary migration and bulging recrystallization. The last ductile shear movement may be related to lithosphere thinning and the destruction of the North China Craton from approximately 130-120 Ma, and this shear event resulted directly in the mineralization in the Paishanlou region.     

阿尔金断裂东端的旋转构造及其动力学意义

在阿尔金主断裂与祁连山北缘断裂的交汇部位，发育一个反时针旋转构造——照壁山旋转构造，它是新构造运动期阿尔金断裂左行走滑运动的结果。结合前人资料，对照壁山旋转构造变形及其发育过程进行了初步分析，认为阿尔金断裂与祁连山北缘断裂的构造转换是通过旋转构造变形来实现的。沿阿尔金断裂一系列旋转构造的存在和青藏高原东北缘旋转构造的发育表明，伴随青藏高原北部物质绕喜马拉雅东构造结的顺时针旋转运动，使旋转构造成为高原北部边缘带转换、吸收构造变形的重要表现形式。     

Shear zones within the Bloody Bluff fault zone: Analysis and tectonic implications

The Bloody Bluff fault zone, which divides the New England Avalon zone and Nashoba zone, contains at least two shear zones that are within Avalonian rocks. The Rice Road shear zone (sinistral, strike-slip) affects the Westboro Formation and is intruded by the 630 Ma Dedham Granite. The Rice Road shear zone, and equivalent pre-granite mylonites appearing in drill cores, parallel the terrane boundary, and may have controlled the later mylonitization. The Nobscot shear zone (dextral, strike-slip) is a prograde shear zone cutting a granite assumed to be related to the surrounding 630 Ma plutons. Similar shear zones have been seen cutting Late Proterozoic plutons in the New England Avalon zone, and represent a series of en echelon strike-slip shears. The Burlington mylonite zone (shear sense equivocal) is part of the terrane boundary. This is a retrograde shear zone that forms the southeastern border of the Wolfpen lens, a lenticular body of sheared and altered metamorphic and intrusive rock that has been assumed to be part of the New England Avalon zone. Microstructural characteristics indicate that the Burlington mylonite zone was active after the Nobscot shear zone. In particular, quartz in the Nobscot shear zone was dynamically recrystallized by a combination of grain boundary migration and rotation recrystallization processes, thought to occur during shearing at upper-greenschist conditions. In contrast, quartz in the Burlington mylonite zone was recrystallized predominantly by rotation recrystallization, indicating lower-greenschist, retrograde, deformation. The two shear zones are too close for these differences to be a result of a simple thermal field gradient.While mineral assemblages in most of the study area indicate no metamorphic grade higher than upper-greenschist temperatures, the Wolfpen lens contains amphibolites with assemblages formed at temperatures above the oligoclase isograd, indicating mid-amphibolite facies metamorphism. As metamorphic contrast is one of the key features differentiating the Nashoba zone from the New England Avalon zone, the Wolfpen lens cannot be assumed to be part of Avalon. It may be a small block of rocks of intermediate grade between the two terranes.     

沂沭断裂带古应力值的探讨

本文侧重于利用变形矿物显微构造估算断裂带古应力值的一些理论分析和方法介绍。并以变形石英晶内自由位错密度ρ和方解石变形双晶百分比分别估算了沂沭断裂带西支北段的沂水-汤头断裂及鄌郚-葛沟断裂燕山晚期(K_1后)构造活动的应力值,其结果分别为1000—1500巴和700—1100巴量级。断裂带显微构造可能表明在地质时期的构造应力场作用中,稳态位错蠕变既可发生于韧性变形,又可发生于脆—韧性变形过程中。考虑到断层带“水”的因素,估算中采用McCormick关系式较Weathers关系式可能更接近实际     

花岗闪长岩中剪切带构造岩的变形显微构造

本文讨论了美国加州内华达山花岗闪长岩体中剪切带构造岩的变形显微构造。利用化学浸蚀法揭示的动态重结晶石英颗粒粒度分布表明,石英粒度与岩性关系不大,但随着构造岩的剪切应变增大,粒度显著减小。因此,在较大的应变条件下,使用动态重结晶石英颗粒度古应力计时应当谨慎     

DEFORMATION MECHANISM OF GRANITIC ROCKS IN BRITTLE-PLASTIC TRANSITION ZONE

Field studies and seismic data show that semi-brittle flow of fault rocks probably is the dominant deformation mechanism at the base of the seismogenic zone at the so-called frictional-plastic transition. As the bottom of seismogenic fault, the dynamic characteristics of the frictional-plastic transition zone and plastic zone are very important for the seismogenic fault during seismic cycles. Granite is the major composition of the crust in the brittle-plastic transition zone. Compared to calcite, quartz, plagioclase, pyroxene and olivine, the rheologic data of K-feldspar is scarce. Previous deformation studies of granite performed on a quartz-plagioclase aggregate revealed that the deformation strength of granite was similar with quartz. In the brittle-plastic transition zone, the deformation characteristics of granite are very complex, temperature of brittle-plastic transition of quartz is much lower than that of feldspar under both natural deformation condition and lab deformation condition. In the mylonite deformed under the middle crust deformation condition, quartz grains are elongated or fine-grained via dislocation creep, dynamic recrystallization and superplastic flow, plagioclase grains are fine-grained by bugling recrystallization, K-feldspar are fine-grained by micro-fractures. Recently, both field and experimental studies presented that the strength of K-feldspar is much higher than that of quartz and plagioclase. The same deformation mechanism of K-feldspar and plagioclase occurred under different temperature and pressure conditions, these conditions of K-feldspar are higher than plagioclase. The strength of granite is similar to feldspar while it contains a high content of K-feldspar. High shear strain experiment studies reveal that granite is deformed by local ductile shear zones in the brittle-plastic transition zone. In the ductile shear zone, K-feldspar is brittle fractured, plagioclase are bugling and sub-grain rotation re-crystallized, and quartz grains are plastic elongated. These local shear zones are altered to local slip-zones with strain increasing. Abundances of K-feldspar, plagioclase and mica are higher in the slip-zones than that in other portions of the samples (K-feldspar is the highest), and abundance of quartz is decreased. Amorphous material is easily formed by shear strain acting on brittle fine-grained K-feldspar and re-crystallized mica and plagioclase. Ductile shear zone is the major deformation mechanism of fault zones in the brittle-plastic transition zone. There is a model of a fault failed by bearing constant shear strain in the transition zone:local shear zones are formed along the fractured K-feldspar grains; plagioclase and quartz are fine-grained by recrystallization, K-feldspar is crushed into fine grains, these small grains and mica grains partially change to amorphous material, local slip-zones are generated by these small grains and the amorphous materials; then, the fault should be failed via two ways, 1)the local slip-zones contact to a throughout slip-zone in the center of the fault zone, the fault is failed along this slip-zone, and 2)the local slip-zones lead to bigger mineral grains that are in contact with each other, stress is concentrated between these big grains, the fault is failed by these big grains that are fractured. Thus, the real deformation character of the granite can't be revealed by studies performing on a quartz-plagioclase aggregate. This paper reports the different deformation characters between K-feldspar, plagioclase and quartz under the same pressure and temperature condition based on previous studies. Then, we discuss a mode of instability of a fault zone in the brittle-plastic transition zone. It is still unclear that how many contents of weak mineral phase(or strong mineral phase)will control the strength of a three-mineral-phase granite. Rheological character of K-feldspar is very important for study of the deformation characteristic of the granitic rocks.     

鲜水河断裂西北段的断层泥特征及其地震地质意义

对鲜水河断裂的断层泥样品进行原样的结构、构造和碎砾的显微构造、刻蚀形貌结构的观测统计,断层泥的粒度分析和分形研究,认为,断裂处于强烈的定向应力场作用之下,其运动方式是以粘滑运动为主,且晚更新世和全新世时期断裂仍有活动。从断层泥的粒度分布和分形分析可将断层分为：甘孜－格篓、格篓－恰叫、恰叫－乾宁３段,这与前人的地形变分析的分段结果相一致     

Texture and petrology of modern river, beach and shelf sands in a volcanic back-arc setting, northeastern Japan

Abstract The focus in the present study is on characterizing spatial patterns of textural and petrological variabilities, and on evaluating mechanisms influencing the textural and petrological components of modern river, beach and shelf sands in a volcanically active back‐arc tectonic setting. Abashiri Bay and the surrounding area in eastern Hokkaido, Japan, has volcanic source land within a back‐arc region associated with subduction of the Pacific Plate beneath the Okhotsk (North American) Plate. A total of 41 river, beach and shelf sands were obtained for grain‐size and modal composition analyses. Multivariate analytical techniques of hierarchical cluster and principal component analyses were performed on the textural and petrological data for investigating relations among quantitative variables. On the basis of grain‐size data, four sedimentary zones were identified: zone I, palimpsest zone; zone II, relict zone; zone III, modern (proteric) zone; zone IV, coastal sedimentary zone. All sands are feldspatholithic and quartz‐deficient. The framework (quartz, feldspar and rock fragment) modal compositions were also classified into four clusters, A–D. The characteristic components of each cluster are as follows: cluster A, felsic volcanic rock fragments; cluster B, andesitic–basaltic volcanic rock fragments; cluster C, mixed or plagioclase; cluster D, sedimentary rock fragments. Almost all sands in western and central Abashiri Bay belong to cluster A, where the original compositions are influenced by Kutcharo pyroclastic flow deposits. Andesitic–basaltic lava and Neogene volcaniclastic and sedimentary rocks have a major influence on the compositions of shelf sands in eastern Abashiri Bay. The modal compositions are basically controlled by the source lithology. Compositional maturity (percentage of quartz to feldspar and rock fragments; Q/FR%) slightly increased, in order, from river (1.2), zone IV (coastal, 1.7), zone II (relict, 2.2), zone I (palimpsest, 3.6), to zone III (modern proteric, 7.0). Greater maturity in the recycled sediments is indicative of weathering under the sea or abrasion by transportation induced by sea‐level fluctuations, waves, or sea currents. Several controlling factors – (i) source lithological; (ii) mineralogical; (iii) climatic; and (iv) geomorphological controls – might still cause low maturity through all sedimentary zones other than the continental margin sands previously reported.     

Grain scale deformation in ultra-high-pressure metamorphic rocks—an indicator of rapid phase transformation

Conspicuous grain scale deformation is observed in some ultra-high-pressure (UHP) metamorphic rocks of the Dora Maira Massif, Western Alps, although no significant strain is discernible on the mesoscopic scale. In a jadeite–kyanite–quartz rock, some of the jadeite crystals reveal (100) deformation twins, indicating local differential stress levels above 0.3 GPa. Many kyanite crystals show marked kink or deformation bands, with a slip system (100)[001]. In contrast, the adjacent coarse-grained quartz matrix (grain size ca. 0.2 mm), which has formed from coesite during exhumation from >100 km depth, reveals a foam structure. The quartz grain boundary configuration is controlled by interfacial free energy, the grains are optically strain-free, and there is no crystallographic preferred orientation. Preservation of this foam microstructure, which indicates grain growth during low-stress annealing, precludes that deformation of the jadeite and kyanite crystals is a result of a late-stage low-temperature overprint. The orientation distribution of jadeite and kyanite with and without twins or deformation bands, respectively, has been investigated with a combination of universal stage and EBSD techniques. On the scale of a thin section, there is no preferred orientation of twinned jadeite and bent kyanite crystals and undeformed crystals, respectively. Thus, the orientation of the inferred local shortening direction is random. This precludes deformation driven by a homogeneous far field tectonic stress, but suggests an internally controlled stress field which is highly inhomogeneous on the scale of a few grain diameters. Laboratory experiments show that the coesite to quartz transformation proceeds within hours after decompression from 3.0 to 2.7 GPa at 800 °C. The microstructures of incompletely transformed samples indicate that the quartz growing at the expense of coesite undergoes crystal plastic deformation and recrystallizes with a very fine grain size during transformation. In this case, the deformation of quartz is attributed to the volumetric strain ΔV=+10% inherent in the coesite–quartz transformation, which causes a highly inhomogeneous stress field inside the sample related to the progress of the transformation. We propose that a similar process has taken place in the polyphase natural rock during exhumation, with the transient stresses causing mechanical twinning of jadeite and bending or kinking of kyanite. When the transformation had gone to completion, grain growth obliterated the microstructures of the quartz matrix, while the deformed jadeite and kyanite crystals preserved the record of inhomogeneous deformation at high temperatures. The peak differential stresses locally exceeded 0.3 GPa, which indicates very high strain rates and a correspondingly rapid transformation of coesite to quartz, comparable to the laboratory results.     

Features and origin time of Mesozoic strike-slip structures in the Yilan-Yitong Fault Zone

The NE-striking Yilan-Yitong Fault Zone(YYFZ) with a length of ca. 900 km is an important major fault zone in northeastern China. Its origin has been a controversial issue for a long time. Detailed field investigation and comprehensive analyses show that strike-slip faults or ductile shear belts exist as the origination structures on the both shoulders of the Cretaceous-Paleogene grabens. These strike-slip structures are dominated by brittle transcurrent faults, and appear as ductile shear belts only in the Weiyuanpu-Yehe and Shulan parts in the south and middle of the fault zone, respectively. The shear belts strike NE-SW and show steep mylonitic foliation and gentle mineral elongation lineation. Outcrop structures, microstructures and quartz c-axis fabrics demonstrate a sinistral shear sense with minor reverse component for the ductile shear belts. The microstructures suggest deformation temperatures of 400–450°C for the Weiyuanpu-Yehe shear belts and 350–400°C for the Shulan shear belt. A series of zircon U-Pb dating results for deformed and undeformed plutons or dikes in the shear belts constrain the strike-slip motion to the time between 160 and 126 Ma. It is further inferred from ages of main geological events in this region that the fault zone originated in the earliest Early Cretaceous. It is suggested therefore that the southern and middle parts of the Tan-Lu Fault Zone, which originated in Middle Triassic, propagated into northeastern China along the sinistral YYFZ under the earliest Early Cretaceous regional compression that is referred to as the Yanshan B event. The earliest Early Cretaceous initiation of the YYFZ results from both the high-speed oblique subduction of the Izanagi Plate and the final closure of the Mongol-Okhotsk Ocean, but the Izanagi Plate subduction played a major dynamic role in the fault zone origin.     

Genesis of the Hongzhen metamorphic core complex and its tectonic implications

The Hongzhen metamorphic core complex is situated in the Yangtze plate to the east of the Dabie oro- genic belt. Its ductile detachment zone in the foot wall overprints on the metamorphic complex of the Proterozoic Dongling Group. The present profile of the ductile shear zone with consistent SW-dipping mineral elongation lineation shows antiform and reversed S-shape from northeast to southwest respectively. Exposure structures, microstructures and quartz C-axis fabric all indicate top-to-SW movement for the ductile shear zone. Recrystallisation types of quartz and feldspar in the mylonites demonstrate that the shear zone was developed under the amphibolite facies condition and at mid-crust levels. The metamorphic core complex formed in the Early Cretaceous with a muscovite plateau age of 124.8±1.2 Ma. Regional NE-SW extension along a SW-dipping, gentle detachment zone was responsible for formation of the core complex. Intrusion of the Hongzhen granite with a biotite plateau age of 124.8±1.2 Ma rendered the ductile shear zone curved, uplifted and final localization of the core complex. The Hongzhen metamorphic core complex suggests that the Early Cretaceous magma- tism in this region took place under the condition of regional extension and the eastern Yangtze plate also experienced lithospheric thinning.     

基于团簇的岩石动态CT图像可视化与结构变形分析

岩石的变形机制是研究岩石圈变形和局部构造活动的重要基础,岩石的微观结构是研究其变形机制的关键。微观层析成像（微观CT）技术可以无损地获取样品内部高精度三维数字化图像,为观测岩石内部结构提供了技术保证。新近发展起来的动态CT技术,使得观测岩石变形过程成为可能。本文利用一组莱塔石灰岩受差应力变形的三维动态CT图像数据,通过图像切割、图像分割等处理步骤,以团簇为基本表征单位,表征不同形状、大小孔隙的动态变化过程,分析对比全部孔隙、大团簇、小团簇和裂隙型小团簇的动态图像。结果表明:随着岩石的压缩变形,其大孔隙在不断地缩小;在变形的初始阶段,靠近施压活塞的样品上部出现了密集的新生小孔隙;当岩石所受差应力到达73 MPa时,其下半部出现了明显的剪切带,具体表现为大量的新生裂隙生成并且新生裂隙集中带与轴向成约45°交角。此前的研究观测到该样品中下部若干压缩带形成的过程;本文通过基于团簇的可视化技术,观测到了高孔隙度岩石变形过程中压缩带和剪切带共同形成的过程。同时,新生的沿剪切带分布的微小裂隙并没有显示与剪切带相同的方向,而是具有各方向均匀分布的特征。该特征可能与岩石内部复杂的局部孔隙结构有关,是值得进一步探讨的问题。      

沂沭断裂带中段基底韧性剪切带

在沂沭断裂带中段的泰山群结晶基底中,存在着一系列北东、北北东走向的左行韧性剪切带。对其中发育糜棱岩的韧性剪切带的结构构造、应变测量、变形岩石的显微构造、显微组构以及长石粒度和含量的变化规律进行了观测分析。讨论了韧性剪切带的变形条件和机制。及其递进发展的趋势。指出基底韧性剪切带是沂沭断裂带元古宙时期断裂活动时在地壳较深层次上形成的构造表象。在此基础上,讨论了地壳不同层次上的断裂变形及断裂岩石的综合分类问题     

滇西地区壳幔解耦与腾冲火山区岩浆活动的深部构造研究

根据青藏东部边缘的深部地球物理资料,分析了滇西地区壳幔耦合和腾冲火山区岩浆活动的深部构造特征,确认了地幔各向异性与上地幔速度结构(包括P波速度和S波速度)的内在联系,指出产生这一结果的原因与以腾冲火山区为中心的地幔热物质上涌有关:上地幔顶部平均温度升高导致介质强度降低,在印支块体的侧向挤压或印缅块体的向东俯冲作用下发生韧性变形,造成滇西地区地幔各向异性的快波方向与青藏东部地壳块体的旋转方向不一致.此外,鉴于中下地壳低速层的横向非均匀性,估计韧性流动并非贯通青藏高原的东部边缘,而是被不同的构造块体和边界断裂限定在局部地区.总体而言,滇西地区下地壳的地震波速度和电阻率偏低,具备发生韧性变形的构造条件.作为地壳和上地幔之间的解耦层,它使得青藏东部地壳块体旋转产生的构造应力未能传输至上地幔.腾冲火山区的地壳结构与不同时期的岩浆活动有关,火山区东侧的高速结构代表了上新世时期火山通道内冷凝固结的岩浆侵入体或难以挥发的高密度残留物质,火山区西侧的低速结构反映了更新世以来持续至今的岩浆活动,壳内岩浆源主要分布在10～20km的深度范围内,横向尺度约为15～20km,有可能通过地壳深部的断裂与上地幔岩浆源区相连,估计腾冲火山区下方的岩浆活动将持续进行.     

Interaction of cataclasis and pressure solution in a low-temperature carbonate shear zone

The mineralogical and elemental variations across the main shear zone of the Saltville thrust at Sharp Gap in Knoxville, Tennessee, U.S.A., were studied in a suite of deformed and undefromed carbonate rock samples using X-ray diffraction and electron microprobe methods. An examination of the samples for deformation effects at mesoscopic scale and under the optical microscope reveals familiar cataclastic deformation features including foliated cataclasites and microbreccias occurring in a well-defined, 1–2 m wide zone of intense deformation, plus evidence of hydrofracturing and extensive syndeformational pressure solution. There exists a clear correlation between the observed cataclastic deformation and mineral and elemental distribution which we interpret to result from a deformation-induced dolomite to calcite transformation in the shear zone. The transformation has resulted in removal of Mg from the shear zone, selective deposition of calcite as an intergranular cement in cataclasite/microbreccia units and a relative increase in the concentration of detrital quartz and feldspars.The compositional difference between the shear zone and wall rocks is explained in connection with cataclastic deformation features in terms of a model in which a dual pressure-solution/cataclastic flow mechanism leads to a gradual cementation-hardening of segments of the shear zone. Instabilities could occur via permeability reduction and increased pore pressure within these segments. Hydrofracturing of the hardened segments along with high strain rate reordering of the shear zone materials reset the ruptured zone back to the dual deformation mechanism regime. As a long-term effect, the compositional transformation of the shear zone is expected to prolong periods of creep and cause smaller coseismic stress drops since under the imposed conditions calcite is more ductile and soluble than dolomite.     

Ductile deformation and its geological implications for retrograded eclogites from the Hongqiyingzi Complex in Chicheng,northern Hebei,China

The rheology of rocks at depth remains a key point in earth sciences. Deformation of high-temperature–highpressure rocks from the subduction zone has not been fully studied; in particular, the deformation behavior of eclogites remains poorly understood. This research is focused on the microstructure and fabric of retrograded eclogites from the Hongqiyingzi Complex in Chicheng, north Hebei, China, based on photomicrography, scanning electron microscopy(SEM) and electron backscattered diffraction(EBSD) analysis. The analytical results show that plastic deformation occurred in the garnets during exhumation, but they do not show an obvious lattice preferred orientation(LPO). This can be interpreted as being caused by the simultaneous activation of multiple slip systems in the garnets during deformation by dislocation creep. The plagioclases have a special fabric; the(001) LPO presents a maximum in Z direction which can be correlated with a new [100](001) slip system. The misorientation angle distribution(MAD) of the plagioclases in the deformed retrograded garnet augens shows a special bimodal distribution with peaks in both a low-angle range(40?) and a high-angle range(140?). In the retrograded garnet augens(i.e. "white eye socket" garnets) the maximum peak moves from a high-angle range to a low-angle range when we analyze only those plagioclases surrounding the residual garnet porphyroclast. Deformation behavior is controlled by the crystallographic orientation of the host grain and the grain boundary sliding process. Hornblendes in different layers and the retrograded garnet augens show almost the same strong LPO patterns, which are correlated with the [001](010) slip system; and MAD diagrams show a peak in a low-angle range(40?). Integrating recent studies on metamorphism and geochronology, we argue that ductile deformation occurred during the exhumation periods together with retrograded metamorphism.     

DEFORMATION OF THE BRITTLE-PLASTIC TRANSITION ZONE AT THE POST-SEISMIC RELAXATION PERIOD: A CASE STUDY OF THE RED RIVER FAULT

The transition from microscopic brittle deformation to microscopic plastic deformation is called brittle-plastic transition, which is considered as a key layer for determining the limit of lower continental crust seismicity. The depth and deformation mechanism of the brittle-plastic transition zone is controlled mainly by temperature. Besides, the strain rate and fluid pore pressure also affect the transition during the different deformation stages at the seismic cycle. In this paper, microstructure observation of catalcastic samples collected from the Red River Fault was carried out using optical polarized microscopy and scanning electron microscopy. The morphology, microstructures of deformation characteristics, mineral composition, water-rock reaction, pressure solution, exsolution, crack healing in the samples were systematically observed. The mineral components quantitative analyses were examined using the EDS. Water-rock reaction and pressure solution were systematically observed under SEM. The fabric of the main minerals in the samples was measured using electron backscattered diffraction(EBSD). Based on these analyses, the deformation mode was setup for the brittle-plastic transition zone of the fault during the post-seismic relaxation period. Both brittle deformation and plastic deformation were developed in the cataclastic samples. EBSD data shows that the c axial fabrics of quartz present low-temperature plastic deformation characteristics. The feldspar deformed as cataclastic rock, and the micro-fracture in feldspar was healed by static recrystallized quartz and calcite veins. The calcite vein underwent plastic deformation, which represents the post-seismic relaxation deformation. Based on the analysis of deformation mechanism of cataclastic samples in brittle-plastic transition zone of the Red River Fault, and combined with previous studies, we concluded that the brittle fracture and fracture healing is the main deformation mode at brittle-plastic transition zone in the post-seismic relaxation. High stress and high strain rate at post-seismic relaxation lead to brittle fracture of high-strength minerals such as feldspar in rocks. Plastic deformation occurs in low-strength minerals such as quartz and mica. Under the fluid condition, micro-fractures were healed by quartz and calcite. The minerals such as quartz and calcite in the fracture transformed from static recrystallization to dynamic recrystallization with stress gradually accumulating. With fracture healing and stress accumulation, the fault strength gradually increases which could accumulate energy for the next earthquake.     

Microstructural Investigation of Naturally Deformed Leucogneiss from an Alpine Shear Zone (Southern Calabria – Italy)

In order to reveal any correlation between the preferred orientation of quartz and progressive intensity of strain, a suite of deformed leucogneiss collected within a ductile shear zone outcropping in Calabria (southern Italy) was investigated. Based on the microstructural approach and matrix-clast relationships, the method applied here may be useful for appraising the connection between deformation mechanisms of constituent minerals and bulk textural properties of naturally sheared rocks. Accordingly, quartz c-axis orientation patterns were determined by image-assisted analysis. Results revealed a correlation between finite strain and textural features: As strain increases, the matrix develops at the expense of the clast counterpart, which is instead progressively reduced in both size and amount.     

红河和曲江断裂带断层泥的特征及其地震地质意义

活断层产物的研究近年来受到国内外地震地质学者的关注。笔者对地质、地震证据充分的活断层——红河断裂带和曲江断裂带的断层泥进行多种手段的分析研究。它们的显微构造、粒度分布,组构特征以及石英碎砾的SEM显微形貌等显示了活断层中的长期蠕滑研磨作用、地震过程的快速剪切运动以及活断层特定条件下的退变质作用和其他化学作用等成因特征。综合分析指出,红河断裂带南段可能是蠕滑运动为主的活断层,其北段和曲江断裂带则为粘滑运动为主的活断层     

玉树MS7.1级地震前的形变应变场变化特征

基于1999～2007年和2007～2009年的GPS站点观测数据计算的速度场,分析了青藏亚板块的运动特征.利用块体(旋转与线性应变)弹性运动公式计算可可西里-巴颜喀拉块体和羌唐块体的应变率、可可西里-玉树断裂带的运动速度和应变率,研究了玉树7.1级地震前的形变应变特征.结果表明:可可西里-巴颜喀拉块体处于青藏亚板块运...