中国大陆岩石圈壳幔韧性剪切带系统

众多地震测深剖面的地质构造解析显示,大陆岩石圈存在既有显著差异又有密切联系的两套断裂系统,即以地壳表层脆性剪切带为主的浅层断裂系统和以切割莫霍界面的壳幔韧性剪切带为主的深部断裂系统。根据地震测深速度结构特征,结合深部构造岩石地球化学的综合研究,将切割莫霍界面或壳幔过渡带的壳幔韧性剪切带划分为三类(俯冲带、缝合带和剪切带)五型(大陆岩石圈边缘海沟俯冲带、大陆岩石圈碰撞缝合带、挤压型壳幔韧性剪切带、伸展型壳幔韧性剪切带和走滑型壳幔韧性剪切带)。建立起中国大陆岩石圈构造变形由地壳表层向深部扩展以及由壳幔过渡带向地壳中上部扩展的岩石圈双向扩展模式。壳幔韧性剪切带既是无机成因天然气等深部流体的通道,又是地震活动区的发震构造之一,因此研究大陆岩石圈壳幔韧性剪切带具有重要学术价值和实际意义。

高土石坝心墙水力破坏机制研究进展

心墙是高土石坝防渗体系的关键部位,在高库水压力的作用下,心墙可能产生水力破坏从而造成过量渗漏乃至溃坝的严重后果。预防心墙水力破坏的关键在于揭示心墙中初始渗漏通道的产生机理和条件。水力劈裂曾被广泛认为是心墙中初始渗漏通道的产生原因,简要回顾了土石坝黏土心墙水力劈裂研究的进展,讨论了水力劈裂理论在解释土石坝黏土心墙水力破坏机制方面的不足。近年来,在心墙压实黏土的剪切渗流特性研究方面取得了新进展,发现严重超固结的压实黏土在剪切后会形成高渗透性剪切带的试验事实。在此基础上提出了高土石坝黏土心墙水力破坏的剪切渗透弱面机制。触发剪切渗漏弱面的应力条件较传统水力劈裂判别的应力条件更容易满足,并且预测的渗漏位置更符合工程实际,因此在实际工程设计中应更重视高渗透性剪切带的评价和处置。

华北地台南缘金矿床的成因和成矿模式

本文阐述了华北地台南缘金矿床形成的构造环境和地质地球化学条件，认为该区金矿具有形成多期性、成因多重性和物质多源性的特征，它们构成了一个完整的成矿系列，据此建立了成矿模式。

Casting effect on compressive brittleness of bulk metallic glass

An interesting phenomenon of cooling-rate induced brittleness in Zr52.5Cu17.9Ni14.6Al10Ti5 bulk metallic glass （BMG） was reported. It was found that the as-cast BMG specimens exhibited a brittle-ductile transition when the larger specimens were machined into smaller specimens through removing the cast-softening surface layer by layer. After compression tests, the as-machined small specimens, owing to the absence of the cast-softening surface, displayed highly dense and intersecting shear bands, and extensive plastic deformation. This is in contrast to the catastrophic failure and low deformability in the as-cast large specimens. More free volume was detected in the smaller as-fractured specimens, by differential scanning calorimetry, which may be attributed to the occurrence of strain softening and increased plasticity. Compared with the relatively smooth fracture surface in the smaller specimens, the larger specimens showed more diverse features on the fracture surface due to their graded structures.

山西右玉金矿床地质成因认识及找矿方向

山西右玉金矿主要产于韧(脆)性剪切带强变形域,由新太古界集宁岩群片麻岩和新太古-古元古代变质石榴花岗岩等构成的含矿岩系。矿床严格受剪切带构造控制,剪切构造既是有利的导矿构造,也是良好的容矿构造。受五台、吕梁期以及后期多期次、多级区域构造活动影响,金的成矿作用也伴随剪切构造带经历了从韧性、脆-韧性到脆性的构造演化叠加过程。成矿流体主要来自变质热液,金的成矿作用主要分为四个阶段,黄铁矿为金的主要伴随金属矿物,对金矿化具有重要的指示意义。研究认为矿床成因是与脆-韧性剪切带构造密切相关的变质-热液型金矿床。本次研究提出找矿方向,为矿区及外围进一步开展金矿地质找矿工作提供参考。

Failure characteristics of three-body model composed of rock and coal with different strength and stiffness

Four different types of three-body model composed of rock and coal with different strength and stiffness were established in order to study the failure characteristics of compound model such as roof-coal-floor. Through stress analysis of the element with variable strength and stiffness extracted from the strong-weak interface, the tri-axial compressive strength of the weak body and strong body near the interface as well as the areas away from the contact surface was found. Then, on the basis of three-dimensional fast Lagrangian method of continua and strain softening constitutive model composed of Coulomb-Mohr shear failure with tensile cut-off, stress and strain relationship of the four three-body combined models were analyzed under different confining pressures by numerical simulation. Finally, the different features of local shear zones and plastic failure areas of the four different models and their development trend with increasing confining pressure were discussed. The results show that additional stresses are derived due to the lateral deformation constraints near the strong-weak interface area, which results in the strength increasing in weak body and strength decreasing in strong body. The weakly consolidated soft rock and coal cementation exhibit significant strain softening behavior and bear compound tension-shear failure under uni-axial compression. With the increase of confining pressure, the tensile failure disappears from the model, and the failure type of composed model changes to local shear failure with different number of shearing bands and plastic failure zones. This work shows important guiding significance for the mechanism study of seismic, rock burst, and coal bump.

Evaluation of dynamic performance and ballistic behavior of Ti-5Al-5Mo-5V-3Cr-1Zr alloy

Terminal ballistic tests using 7.62 mm armor-piercing incendiary （API） projectiles were performed to evaluate the resistance to penetration of Ti-5Al-5Mo-5V-3Cr-IZr （Ti-55531） alloy. The dynamic properties were determined by a split Hopkinson pressure bar （SHPB） test system. Ti-55531 plates were subjected to two kinds of heat treatments, leading to the formation of high-strength and high-toughness plates. The results of SHPB test exhibit that the maximum impact absorbed energy of the high-strength plate at a strain rate of 2200 s^-1 is 270 MJ/m^3; however, the maximum value for the high-toughness plate at a strain rate of 4900 s^-1 is 710 MJ/m^3. The ballistic limit velocities for the high-strength and high-toughness plates with dimensions of 300 mm×300 mm×8 mm are 330 and 390 m/s, respectively. Excellent dynamic properties of Ti-55531 alloy correspond to good resistance to penetration. The microstructure evolution related to various impact velocities are observed to investigate the failure mechanism.

Effect of minor Nb addition on mechanical properties of in-situ Cu-based bulk metallic glass composite

In-situ formed （Cu0.6Zr0.3Ti0.1）95Nb5 bulk metallic glass （BMG） composite with Nb-rich dendrite randomly dispersed in hard glassy matrix was prepared by casting into a water-cooled copper mold. The dendrite has much smaller hardness and elastic modulus than glassy matrix, and the stress concentration at interface provides a channel for the initiating and branching of shear bands upon loading, thus leading to a high compressive fracture strain of 6.08% and fracture strength about 2200 MPa. Comparing with other Cu-based BMG composite, the fracture strength of present （Cu0.6Zr0.3Ti0.1）95Nb5 composite is not significantly reduced, indicating that the addition of Nb in the current work is an effective and effortless way to fabricate new practical BMG composites with enhanced strength and good plasticity.

The Origin of the 2008 Wenchuan Earthquake Determined by the Analysis on the Active Longmenshan Nappe in Terms of Rockmass Mechanics

On 12 May 2008, the magnitude 8.0 Wenchuan Earthquake occurred along the Longmen Shan nappe, Sichuan, China. This devastating earthquake led to a heavy death toll of greater than 80,000. The seismic origin of this earthquake is currently hotly debated. We suppose that it is a special type of intraplate earthquake called an active-nappe-type earthquake. Using a holistic methodology, incorporating rockmass structure cybernetics and Byerlee's law, we present a comprehensive study on the geological origin of macroseisms in the Longmen Shan area and the seismic origin of the 2008 Wenchuan earthquake. Previous studies of neotectonic activity indicate that the Longmen Shan nappe moves at a rate of 1~3 mm/yr, due to horizontal compressive stress from the Tibetan Plateau. The difference between movement rates in the Bayankala block, Longmen Shan nappe and Sichuan Basin cause slow shear stress and strain accumulation in the Longmen Shan nappe. It is exhibited a relatively simple linear relations for the shear strength and the buried depth of the structural planes, and the detachment layer of the nappe has a higher shearing-sliding strength compared to the overlying fault planes and the underlying ductile shear belts, thus making it more prone to stick-slip deformation. Therefore, the detachment layer was the main section responsible for the Wenchuan earthquake. The initial rupture burst in the detachment layer under the Yingxiu-Beichuan fault, the rupture area nearly 1.4454 × 104 km2,encompassed the cross point of the Yingxiu and the Anxian-Guanxian faults with the detachment layer, then caused the Yingxiu-Beichuan and Anxian-Guanxian faults took an active part in this earthquake, so this earthquake might consist of three chain-like earthquake stages, totally increasing the duration of this earthquake an unusually large amount, to 120 s. The focal depth spanned range of 10-20km,consistent with the observed result of this focal depth by several agencies.

Glass forming ability and mechanical properties of Nb-containing Cu-Zr-Al based bulk metallic glasses

Mechanical properties of （Cu50Zr43Al7）100 Nbx （x=0,1,3,6,9） bulk metallic glasses rods with a diameter of 2.5 mm prepared by suction casting method were studied. The results of uniaxial compression tests at room temperture show that the best mechanical properties of 2.8% and 1.98 GPa for plastic strain and fracture strength, respectively, in the sample with x=3. Microstructure, fracture surface and shear bands of the samples were observed by SEM and XRD methods.

中国蓝石棉成矿地质特征

蓝石棉是碱性角闪石的纤维变种,是一种较为稀见的特种非金属矿产。其生成与古板块陆内俯冲或大推覆构造由此而产生的剪切应变作用密切相关。围岩常是富含钠、镁、铁质岩石。矿体多赋存在以蓝闪石、钠长石、黑硬绿泥石、多硅白云母等组合的低温高压蓝片岩变质带中,其产出形态多为脉状。蓝石棉不仅以其极细的纤维使之具有特殊的过滤性能,并作为蓝片岩重要组成矿物,为研究古板块构造提供重要信息,深为地质学家所重视。

Electrical Structure of the Crust Beneath the Ordos Block

The Ordos block is a stable tectonic unit since the Cenozoic. Whether low-resistivity layers exist in the middle and lower crust of this kind block is an open question. This work attempts to reveal the entire crustal structure of the block based on interpretation of magnetotelluric data collected along the profile across this region. The result shows that a layered structure characterizes the crust of the Ordos block, with a low-resistivity layer at depth of about 20km, presumably associated with fluids there. In contrast, in the areas of active tectonics on the east and west of the block, there are no such layered electric structures in the crust, and the low-resistivity zones may be related to the decollement zones (or ductile shear zones) in the crust. The difference in electric structure of crust between the Ordos Block and neighboring areas is of significance to analyze the movement and deformation of varied blocks in the continent.

Formation and timing of the extensional ductile shear zones in Yiwulü Mountain area,Western Liaoning Province,North China

The NNE-trending ductile shear zones in Yiwulü Mountain area were formed in relation to two successive extensional events.The Yiwulü High Temperature Extensional Ductile Shear Zone and the Waziyu Low Temperature Extensional Ductile Shear Zone were related to ductile deformation at higher temperatures and brittle-ductile deformation at lower temperatures,respectively.Both deformations were accompanied by large scale volcanic eruptions and magmatic intrusions.Based on structural analysis of macroscopic and microscopic deformations,and quartz lattice preferred orientations,we show that the early Yiwulü High Temperature Extensional Ductile Shear Zone was resulted from a NE-SW extension at amphibolite facies in the middle crust,whereas the Waziyu Low Temperature Extensional Ductile Shear Zone was due mainly to a NWW-SEE extension at greenschist facies in the upper crust.The SHRIMP zircon age of a syn-tectonic granitic dike emplaced at the late stage of high temperature extension is 155±2 Ma,indicating that the early extensional event took place in the Middle-Late Jurassic.40Ar-39Ar age of muscovite from tectonic schists in the low temperature extensional ductile shear zone is 131.6±1.0 Ma,suggesting that the late extension occurred in the Early Cretaceous.Subsequent overall uplifting succeeded the late extension.The new discovery of the Middle-Late Jurassic NNE-trending extensional ductile shear zone provides evidence constraining the switch of tectonic regimes and Middle Jurassic thinning of lithosphere in the eastern North China Craton.

The structural characteristics, age of origin, and tectonic attribute of the Erguna Fault, NE China

The Erguna Fault runs along the east bank of the Erguna River in NE China and is a large-scale ductile shear zone comprising granitic mylonites. This paper reports on the geometry, kinematic indicators, and 40Ar/39 Ar biotite ages of the granitic mylonites, to constrain the structural characteristics, forming age, and tectonic attribute of the Erguna ductile shear zone. The zone strikes NE and records a top-to-the-NW sense of shear. A mylonitic foliation and stretching lineation are well developed in the mylonites, which are classified as S-L tectonites. Logarithmic flinn parameters(1.18–2.35) indicate elongate strain which approximates to plane strain. Kinematic vorticity numbers are 0.42–0.92 and 0.48–0.94, based on the polar Mohr diagram and the oblique foliation in quartz ribbons, respectively, suggesting that the ductile shear zone formed under general shear, or a combination of simple and pure shear. According to finite strain and kinematic vorticity analyses, the Erguna Fault is a lengthening-thinning ductile shear zone that formed by extension. The deformation behavior of minerals in the mylonites indicates that the fault was the site of three stages of deformation: an initial stage of middle- to deep-level, high-temperature shear, a post-stress recovery phase of high-temperature static recrystallization, and a final phase of low-temperature uplift and cooling. The 40Ar/39 Ar plateau ages of biotite from the granitic mylonites are 106.16 ± 0.79 and 111.55 ± 0.67 Ma, which constrain the timing of low-temperature uplift and cooling but are younger than the ages of metamorphic core complexes(MCCs) in the Transbaikalia-northeast Mongolia region. Using measured geological sections, microtectonics, estimates of finite strain and kinematic vorticity, and regional correlations and geochronology, we conclude that the Erguna Fault is an Early Cretaceous, NNE-trending, large-scale, sub-horizontal, and extensional ductile shear zone. It shares a similar tectonic background with the MCCs, volcanic fault basins, and large and super-large volcanic-hydrothermal deposits in Transbaikalia-northeast Mongolia and the western Great Khingan Mountains, all of which are the result of overthickened crust that gravitationally collapsed and extended in the Early Cretaceous after plate collision along the present-day Sino-Russia-Mongolia border tract.

Deformation characteristics and genesis of the Waziyu metamorphic core complex in western Liaoning of China

The Waziyu metamorphic core complex is situated at the eastern end of the Yanshan tectonic belt.The NNE-striking detachment ductile shear zone in the core complex lies between the Archean metamorphic basement and Fuxin-Yixian rift basin,dips NW gently,and shows corrugation folds.Exposure structures,microstructures,and quartz C-axis fabrics all indicate top-to-the WNW sense of shear,i.e.,ca.285°,for the shear zone.Estimates of the deformation temperatures(ca.550-250°C) demonstrate its mid-crustal origination and progressive deformation from deep to shallow levels.The northern segment of the shear zone shows relatively weak exhumation with exposures of low-temperature mylonites whereas its middle and southern segments have more intense uplifting with exposures of high-temperature mylonites.Biotite and muscovite 40 Ar/39 Ar ages,U-Pb dating results of zircon from dikes and plutons as well as formation ages of the supra-detachment basin all suggest the formation time of 135-100 Ma for the core complex.The formation was also associated with syntectonic emplacement of the Early Cretaceous Shishan pluton.The western margin of the core complex was truncated by the Sunjiawan-Shaohuyingzi brittle normal fault when it uplifted to shallow crust levels,and finally exhumed to near-surface levels.The core complex was developed by the rolling-hinge model under WNW-ESE extension during the Early Cretaceous peak destruction of the North China Craton.Ductile flow did not appear in the lower plate,therefore not supporting the low-crust gravitational collapse.

Interpretation of the experimental data provided by Gómez-Rivas and Griera(2012) in terms of the MEM-criterion

The systematical experiments carried out by G6mez-Rivas and Griera （2012） demonstrate that the ductile shear zones initiate at 55° to 0-1 just as predicted by the MEM-criterion. However, the data are explained in terms of dilatancy, which requires many prerequisites and implies that the ±55° angle is only valid for the used material. In contrast, the -55°predicted by the MEM-criterion is material independent, which makes it widely applicable to explaining the development of ductile shear zones in nature.

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) 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) 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.

How does the initial free volume distribution affect shear band formation in metallic glass?

Introducing heterogeneities into the structure is an effective way to enhance the plasticity in metallic glasses (MGs). As natural heterogeneity, the original randomly distributed free volume in MGs has been found to be in favor of plasticity. However, the exact correlation between the free volume distribution and mechanical response is still unclear. In this paper, we investigate the shear banding in MGs with different structural disorders, characterized by both the free volume concentration (FVC) and the free volume dispersion (FVD). It is found that, either high FVC or wide FVD leads to low activation stress of shear band; wide FVD promotes the multiplication of shear bands but high FVC restricts it. It reveals that the yield strength in MGs is dependent on the amount of free volume while the plasticity mainly relies on the distribution. An optimum combination of the two aspects probably helps to design a MG of both good plasticity and high strength.