Research on temporal and spatial distribution,evolutionary character and mechanism of crustal deformation field before and after the Tangshan earthquake

According to the data of precise relevelling and deformation measurement across faults, the temporal and spatial evolution process of crustal deformation field in the source and peripheral regions of the Tangshan earthquake (1976, M S=7.8), from 22 years before the earthquake to 9 years after, is described with the method of crustal deforma tion pattern dynamics. The crustal unstable zones first occur in the exterior, and then surround the focal region by contracting from the exterior to the interior, when the focal region appears to be unstable but does not lose stability. After the transient stable state, the second unstable process from the exterior to interior appears, which results in the instability of focal region. 'Deformation gap', 'earthquake gap' and 'locked fault zone' occur before instability, and their spatial distributions overlap, but their occurrence times have little differences. The earthquake occurs after the impending pre slide of the faults in the focal region. The studied results of the evolution process of crustal deformation field are identical with each other and with that of numeric simulation of crustal stress field, which supports the evolution model of seismogenic system with a strong body as its core.

Effect of Gd Addition on Hot Deformation Behavior and Microstructure Evolution of 7075 Aluminum Alloy

In order to clarify the effect of rare earth Gd on the microstructure evolution and deformation behavior of 7075 aluminum alloy during hot compression,uniaxial compression tests of Al-Zn-Mg-Cu-0.5%Gd were conducted at strain rates of 0.001,0.01,0.1,and 1 s^(-1)with the temperatures ranging from 350 to 450℃.The microstructural evolution during deformation was characterized using optical microscopy and electron backscatter diffraction(EBSD)techniques.The experimental results indicate that the addition of the rare earth element Gd significantly increases the peak flow stress and thermal activation energy of the alloy.Due to the pinning effect of rare earth phases,dislocation movement is hindered,leading to an increased level of work hardening in the alloy.However,the dynamic recrystallization of the alloy is complicated.At a high Z(Zener-Hollomon parameter)values,recrystallization occurs in the form of DDRX(Discontinuous Dynamic Recrystallization),making it easier to nucleate at grain boundaries.As the Z value decreases gradually,the recrystallization mechanism transitions from discontinuous dynamic recrystallization(DDRX)to continuous dynamic recrystallization(CDRX).At a low Z values with the strain rate of 0.001 s^(-1),the inhibitory effect of rare earths weakens,resulting in a comparable recrystallization ratio between Al-Zn-Mg-Cu-Gd alloy and 7075 aluminum alloy.Moreover,the average grain size of the aluminum alloy with Gd addition is only half that of 7075 aluminum.The addition of Gd provides Orowan and substructure strengthening for the alloy,which greatly improves the work-hardening of the alloy compared with 7075 aluminum alloy and improves the strength of the alloy.

Microstructural evolution and deformation mechanisms of superplastic aluminium alloys:A review

Aluminium alloy is one of the earliest and most widely used superplastic materials.The objective of this work is to review the scientific advances in superplastic Al alloys.Particularly,the emphasis is placed on the microstructural evolution and deformation mechanisms of Al alloys during superplastic deformation.The evolution of grain structure,texture,secondary phase,and cavities during superplastic flow in typical superplastic Al alloys is discussed in detail.The quantitative evaluation of different deformation mechanisms based on the focus ion beam(FIB)-assisted surface study provides new insights into the superplasticity of Al alloys.The main features,such as grain boundary sliding,intragranular dislocation slip,and diffusion creep can be observed intuitively and analyzed quantitatively.This study provides some reference for the research of superplastic deformation mechanism and the development of superplastic Al alloys.

Frost deformation and microstructure evolution of porous rock under uniform and unidirectional freeze-thaw conditions

The frost deterioration and deformation of porous rock are commonly investigated under uniform freeze-thaw(FT)conditions.However,the unidirectional FT condition,which is also prevalent in engineering practice,has received limited attention.Therefore,a comparative study on frost deformation and microstructure evolution of porous rock under both uniform and unidirectional FT conditions was performed.Firstly,frost deformation experiments of rock were conducted under cyclic uniform and unidirectional FT action,respectively.Results illustrate that frost deformation of saturated rock exhibits isotropic characteristics under uniform FT cycles,while it shows anisotropic characteristics under unidirectional FT condition with both the frost heaving strain and residual strain along FT direction much higher than those perpendicular to FT direction.Moreover,the peak value and residual value of cumulative frost strain vary as logarithmic functions with cycle number under both uniform and unidirectional FT conditions.Subsequently,the microstructure evolution of rock suffered cyclic uniform and unidirectional FT action were measured.Under uniform FT cycles,newly generated pores uniformly distribute in rock and pore structure of rock remains isotropic in micro scale,and thus the frost deformation shows isotropic characteristics in macro scale.Under unidirectional FT cycles,micro-cracks or pore belts generate with their orientation nearly perpendicular to the FT direction,and rock structure gradually becomes anisotropic in micro scale,resulting in the anisotropic characteristics of frost deformation in macro scale.

Polyphase Deformation of the Weihai-Rongcheng UHP Unit Rocks,NE Sulu:Insights into the Tectonic Evolution of the Dabie-Sulu UHP and HP Belts,China

Different scales of structural data reveal a complex deformation history of ultrahigh- pressure （UHP） rocks exposed in the Weihai-Rongcbeng area, NE Sulu （northern Jiangsu-eastern Shandong）, eastern China. Excluding pre-UHP deformations, at least five major sequential deformational stages （D1-Ds） are recognized. The first deformation （DO produced a weak foliation and lineation in massive eclogites. The foliated eclogite with a dominant foliation containing a stretching and mineral lineation was developed during the I）2 deformation. Both the D1 and D2 deformations occurred under UHP metamorphic conditions, and are well preserved in the eclogite bodies. D3 structures which developed shortly after the formation of granulite/amphibolite facies symplectites are characterized by imbricated associations marked by a regional, steeply dipping foliation, compositional layering, eclogite boudinage, isoclinal folds and reverse ductile shear zones. The D3 deformation was accompanied by decompressional partial melting. A regional, gently dipping amphibolite facies foliation and stretching lineation, low-angle detachments, and dome- and arc-shaped structures formed during the D4 deformation stage dominate to some degree the map pattern of the Weihai-Rongcbeng UHP domain. The last stage of deformation （Ds） gave rise to the final exhumation of the UHP rocks. Ds is characterized by development of brittle-dominated high-angle faulting associated with emplacement of large volmnes of undeformed granite plutons and dykes dated at 134-100 Ma. The deformational and metamorphic sequence followed by the UHP rocks in the Weihai-Rongcheng area is similar to that studied in the entire Dabie-Sulu UHP and HP metamorphic belts from microscopic to mapping scale. Based on structural data, combined with available petrographic, metamorphic and geochronological data, a speculative tectonic evolutionary model for the Dabie-Sulu UHP and IIP belts is proposed, involving continental subduction/collision between the Sino-Korean and Yangtze cratons and subsequent polyphase exhumation histories of the UHP and IIP metamorphic rocks.

Experimental study on the deformation behaviour,energy evolution law and failure mechanism of tectonic coal subjected to cyclic loads

Compared to intact coal,tectonic coal exhibits unique characteristics.The deformation behaviours under cyclic loading with different confining pressures and loading rates are monitored by MTS815 test system,and the mechanical and energy properties are analysed using experimental data.The results show that the stress-strain curve could be divided into four stages in a single cycle.The elastic strain and elastic energy density increase linearly with deviatoric stress and are proportional to the confining pressure and loading rate;irreversible strain and dissipated energy density increase exponentially with deviatoric stress,inversely proportional to the confining pressure and loading rate.The internal structure of tectonic coal is divided into three types,all of which are damaged under different deviatoric stress levels,thereby explaining the segmentation phenomenon of stress-strain curve of tectonic coal in the cyclic loading process.Tectonic coal exhibits nonlinear energy storage characteristics,which verifies why the tectonic coal is prone to coal and gas outburst from the principle of energy dissipation.In addition,the damage mechanism of tectonic coal is described from the point of energy distribution by introducing the concepts of crushing energy and friction energy.

Surrounding rock deformation and stress evolution in pre-driven longwall recovery rooms at the end of mining stage

Two case studies were conducted in the Shennan mining area of Shaanxi Province,China to evaluate the surrounding rock deformation and stress evolution in pre-driven longwall recovery rooms· These studies mainly monitored the surrounding rock deformation and coal pillar stress in the recovery rooms of the N1206 panel of 2-2 coal seam at Ningtiaota Coal Mine and the 15205 panel of 5-2 coal seam at Hongliulin Coal Mine.The monitoring results showed that the surrounding rock deformation of the main recovery room and the coal pillar stress in the N1206 and 15205 panels began to increase significantly when the face was 36 m and 42 m away from the terminal line,respectively.After the face entered the main recovery room,the maximum roof-to-floor convergence in the N1206 and 15205 panels was 348.03 mm and 771.24 mm,respectively,and the coal pillar stresses increased more than 5 MPa and 7 MPa,respectively.In addition,analysis of the periodic weighting data showed that the main roof break position of the N1206 and 15205 panels after the longwall face entered the main recovery room was-3.8 m and-8.2 m,respectively.This research shows that when the main roof breaks above the coal pillar,the surrounding rock deformation of the main recovery room and the coal pillar stress increase sharply.The last weighting is the key factor affecting the stability of the main recovery room and the coal pillar;main roof breaks at disadvantageous positions are the main cause of the support crushing accidents.

Evolution of the deformation field and earthquake fracture precursors of strike-slip faults

Seismic hazard analysis is gaining increased attention in the present era because of the catastrophic effects of earthquakes.Scientists always have as a goal to develop new techniques that will help forecast earthquakes before their reoccurrence. In this research,we have performed a shear failure experiment on rock samples with prefabricated cracks to simulate the process of plate movement that forms strike-slip faults. We studied the evolution law of the deformation field to simulate the shear failure experiment, and these results gave us a comprehensive understanding of the elaborate strain distribution law and its formation process with which to identify actual fault zones. We performed uniaxial compression tests on marble slabs with prefabricated double shear cracks to study the distribution and evolution of the deformation field during shear failure. Analysis of the strain field at different loading stages showed that with an increase in the load, the shear strain field initially changed to a disordered-style distribution. Further, the strain field was partially concentrated and finally completely concentrated near the crack and then distributed in the shape of a strip along the crack. We also computed coefficients of variation(CVs) for the physical quantities u, v, and exy, which varied with the load. The CV curves were found to correspond to the different loading stages. We found that at the uniform deformation stage, the CV value was small and changed slowly,whereas at the later nonuniform deformation stage, the CV value increased sharply and changed abruptly. Therefore, the precursor to a rock sample breakdown can be predicted by observing the variation characteristics of CV statistics. The correlation we found between our experimental and theoretical results revealed that our crack evolution and sample deformation results showed good coupling with seismic distribution characteristics near the San Andreas Fault.

CENOZOIC COLLISIONAL DEFORMATION AND LITHOSPHERE TECTONIC EVOLUTION OF THE EASTERN HIMALAYAN SYNTAXIS

The Eastern Himalayan Syntaxis (EHS) is one of the strongest deformation area along the Himalayan belt resulted from the collision between Indian plate and the Eurasian plate since 50～60Ma, and has sensitivity tracked and preserved the whole collisional processes. It should depend on the detail geological investigations to establish the deformational accommodate mode, and the uplift history, to elucidate the deep structure and the crust\|mantle interaction of the EHS. The Namjabarwa metamorphic complex indented into the Gangdise arc along the sinistral Pai shear fault and the dextral Aniqiao shear fault on the both sides of the Great Canyon of Yalung Zangbo river since the collision of the NE corner of the Indian plate and the Eurasian Plate at 60～70Ma [1] . The distance between Yarlung Zangbo suture and Bangong—Nujiang suture is shortened more 120km in the EHS area than that of the Lhasa block.

Deformation behavior and strength evolution of MIM compacts during thermal debinding

Effects of the debinding atmosphere,powder characteristic,solid loading and heating rate on the compact deformation were investigated.The compact strength after thermal debinding was measured by bending mode.The experimental results indicate that the vacuum atmosphere is beneficial to improving the deformation resistance compared with nitrogen atmosphere.Small particle size,irregular particle shape and high solid loading are suitable for decreasing the deformation defects.Besides,too fast heating rate may induce deformation defects.It is also indicated that effect of the factors for the deformation defects is different in different debinding stages.The strength evolution of the compacts during thermal debinding was also discussed.

Hot deformation behavior and microstructural evolution of Al-Zn-Mg-0.25Sc-Zr alloy during compression at elevated temperatures

The hot deformation behavior of Al-Zn-Mg-0.25Sc-Zr alloy and its microstructural evolution were investigated by isothermal axisymmetric hot compression tests at temperatures from 340 to 500°C and strain rates ranging from 0.001 to 10 s -1 .The steady flow stress increased with increasing the strain rate or decreasing the deformation temperature,which can be described by a hyperbolic-sine constitutive equation with the deformation activation energy of 150.25 kJ/mol.The tendency of dynamic recrystallization enhanced at high deforming temperatures and low strain rates,which corresponded to low Z values.With decreasing Z value,the main softening mechanism of the alloy transformed from dynamic recovery to dynamic recrystallization, correspondingly,the subgrain size increased and the dislocation density decreased.

Microstructure evolution and deformation features of single crystal nickel-based superalloy containing 4.2% Re during creep

By means of microstructure observation and measurement of creep properties,the high temperature creep behaviors of a single crystal nickel-based superalloy containing Re were investigated.Results show that the single crystal nickel-based superalloy containing 4.2% Re possesses a better creep resistance at high temperature.After being crept up to fracture,the various morphologies are displayed in the different areas of the sample,and the γ＇ phase is transformed into the rafted structure along the direction vertical to the applied stress axis in the regions far from the fracture.But the coarsening and twisting extents of the rafted γ＇ phase increase in the regions near the fracture,which is attributed to the occurrence of the larger plastic deformation.In the later stage of creep,the deformation mechanism of the alloy is that the dislocations with [01^-1]and [011] trace features shear into the rafted γ＇ phase.The main/secondary slipping dislocations are alternately activated to twist the rafted γ＇ phase up to the occurrence of creep fracture,which is thought to be the fracture mechanism of the alloy during creep.

The Geochemical Evolution of the Proterozoic Continental Crust in Northwestern Jiangxi and Western Zhejiang,China

The pertochemistry and Sm-Nd isotopic compositions and the geochemical characteristics of REE,U,Th,etc..in the Late Proterozoix and Early Palaeozoic strata in northwestern Jiangxi and western Zhejiang provinces are described in this paper.It seems to be sure that the middle Proterozoic strata of southeastern China are low in the degree of matrration .The strata contain much mantle-derived material.At the end of Late Proterozoic there was an abrupt turn with respect to the crustal geochemical evolution of the eastern part of South China .Since then ,the geochemical environment has undergone a change from a simple reducing environment to a complex oxidizing-reducing environ-ment, which would be geochemically beneficial to the formation of Late Sinian to Early Cambrian U-bearing formations.

Research on the Dynamic Evolution of Deformation Field and the Acquisition of Seismogenic Information Before Lijiang Earthquake With Ms7.0

By using the integral dynamic adjustment of the "segmentation rate," this paper processes the leveling repetition measurement data of the Dianxi(western Yunnan)area since the 1980s,makes the fitting of the velocity surface for vertical deformation with multi-surface function,and splits information of the vertical deformation field.The dynamic evolution of the deformation field and vertical deformation information norm-shear deformation,extension deformation,volumetric deformation,and quasi acceleration,which are the distribution characteristics of variation,are studied by using the information split before the Lijiang earthquake with MS7.0(February 3,1996)in the north of the Dianxi(western Yunnan)leveling network.The results indicate that in Dianxi(western Yunnan)area,the acute vertical differential movement of the large-scale deformation velocity high gradient belt and high information norm distribution in the Lijiang,Yongsheng,and its adjacent areas in the middle stage of the 1980s is the reflection

EVOLUTION OF THE CONTINENT CRUST AND URANIUM MINERALIZATION

Uranium is a typical lithophile element, having outstanding geo-chemical characteristics of association whith high SiO2, peraluminousand marginally peralkalic rocks. In evolution process of all geologicalhistory, uranium gathers without interruption in upper crust. Urani-um mineralization is closely realted with evolution characteristics of thecontinent crust.1. It was not until the continent crust evolved to certain maturedegree that uranium began metallization. The oldest uranium depositon the earth occurred in the Delanshiwa （Kapuwaer） district,

FORMATION OF THE CRUSTAL MELTING LAYER AND ITS RELATIONS TO THE DEFORMATION OF CONTINENTAL CRUST:AN EXAMPLEFROM SOUTHEAST CHINA

Unlike the magma intrusion model,the in- situ melting hypothesis advanced in the lastdecade regards the upper crustas a closed system,and granite as the resultof the materialswithin system changing from order (protolith) to disorder (melts) and to new order(granite) with the variations of entropy of the system.The various geological and geochemi-cal data from the Mesozoic granitesof southeast China are explained logically and systemical-ly by the hypothesis,concluding that they should be originated from the melting of pro-toliths.According to the hypothesis,melts generated from in- situ melting are of layer- likewithin the crustand batholithsare the protruding parts of the uppersurface of the layer (de-fined as the Melting Interface,MI for short) .On the basis the author tries to discuss thesource of heatfor the Mesozoic crustal melting in southeast China.

Tensile deformation of fine-grained Mg at 4K,78K and 298K

The impact of grain size, ranging from 0.9 μm to 9 μm, on the mechanical properties of commercially pure Mg is investigated at temperatures of 4K, 78K, and 298K. The mechanisms governing plastic flow are influenced by both grain size and temperature. At 4K and 78K, dominant deformation modes in Mg involve dislocation glide and extension twinning, regardless of grain size. The interactions between basal and non-basal dislocations and dislocations with grain boundaries promote an unusually high rate of work hardening in the plastic regime, leading to premature failure. The yield stress follows the Hall-Petch relationship σy~ k/√d, with the slope k increasing with decreasing temperature. At 298K, in addition to dislocation glide and twinning, grain boundary sliding(GBS) becomes significant in samples with grain sizes below 3 μm, considerably enhancing the material's deformability. GBS activation provides an additional recovery mechanism for dislocations accumulating at grain boundaries, facilitating their absorption during sliding and rotation. Analysis of σ Θ relationship suggests that the basal slip is the dominant dislocation mode in Mg at 298K. Decreasing grain size suppresses dislocation activity and twinning and increases GBS, resulting in lower Θ and σ Θ values. Suppressing conventional deformation modes coupled with enhanced GBS yields stress softening, breaking down the Hall-Petch relationship in Mg below 3 μm grain size, leading to an inverse Hall-Petch behaviour. The work reports new data on the strength, ductility, work hardening and fracture behaviour, and their variations with Mg grain size across different temperature regimes.

Hot deformation behaviors of a 9Cr oxide dispersion-strengthened steel and its microstructure characterization

The hot deformation behaviors of a 9 Cr oxide dispersion-strengthened(9 Cr-ODS) steel fabricated by mechanical alloying and hot isostatic pressing(HIP) were investigated. Hot compression deformation experiments were conducted on a Gleeble 3500 simulator in a temperature range of 950–1100°C and strain rate range of 0.001–1 s^(-1). The constitutive equation that can accurately describe the relationship between the rheological stress and the strain rate of the 9 Cr-ODS steel was established, and the deformation activation energy was calculated as 780.817 kJ/mol according to the data obtained. The processing maps of 9 Cr-ODS in the strain range of 0.1–0.6 were also developed. The results show that the region with high power dissipation efficiency corresponds to a completely recrystallized structure. The optimal processing conditions were determined as a temperature range of 1000–1050°C with strain rate between 0.003 and 0.01 s^(-1).

Triassic Collisional Structures and Post-CollisionalDeformation of Bixiling UHP Rock Stack: Insightsfor Tectonic Evolution of UHP MetamorphicBelt in Dabie Massif, Central China

Detailed three-dimensional structural studies indicate that the Bixiling area, Dabie massif, central China shows the deepest exposed levels of the orogenic wedge formed during the Triassic Yangtze -Sino-Korean continental collision. New 1 : 10 000 scale structural mapping, combined with detailed petrological analysis in this area, has enabled us to accurately distinguish structures related to the Triassic continental collision from those related to post-collisional deformation in the ultrahigh pressure (UHP) metamorphic unit. The collisional or compressional structures include the massive eclogite with a weak foliation, foliated eclogite or UHP ductile shear zones, as well as upper amphibolite facies shear zones, whereas the post-collisional deformation is characterized by a regionally, flat-lying foliation containing stretching lineations and common reclined folds. The former is present exclusively in the eclogite lenses and their margins, representing orogenic thickening or syn-collisional events, while the latter was best occurred on variable scales under amphibolite facies conditions, showing sub-vertical, extreme shortening and ductile thinning of the metamorphic rock stack. The eclogite facies tectonites that have a marked fabric discordance to the penetrative amphibolite facies extension flow fabric are common. It is emphasized that an extensional tectonic setting following the collision-orogenic thickening stage was, at least partly, responsible for exhumation of the UHP metamorphic rocks in the Dabie massif. A new tectonic evolution model is proposed for the UHP metamorphic belt on the scale of the Dabie massif. The Bixiling area thus provides a window, from which the dynamic processes concerning the formation and exhumation of the UHP rocks can be observed. Regional studies in the Dabie Mountains have confirmed this interpretation.

Earthquake-related Tectonic Deformation of Soft-sediments and Its Constraints on Basin Tectonic Evolution

The authors introduced two kinds of newly found soft-sediment deformation-synsedimentary extension structure and syn-sedimentary compression structure, and discuss their origins and constraints on basin tectonic evolution. One representative of the syn-sedimentary extension structure is syn-sedimentary boudinage structure, while the typical example of the syn-sedimentary compression structure is compression sand pillows or compression wrinkles. The former shows NW-SE-trendlng contemporaneous extension events related to earthquakes in the rift basin near a famous Fe-Nb-REE deposit in northern China during the Early Paleozoic （or Mesoproterozoic as proposed by some researches）, while the latter indicates NE-SW-trending contemporaneous compression activities related to earthquakes in the Middle Triassic in the Nanpanjiang remnant basin covering south Guizhou, northwestern Guangxi and eastern Yunnan in southwestern China. The syn-sedimentary boudinage structure was found in an earthquake slump block in the lower part of the Early Paleozoic Sailinhudong Group, 20 km to the southeast of Bayan Obo, Inner Mongolia, north of China. The slump block is composed of two kinds of very thin layers-pale-gray micrite （microcrystalline limestone） of 1-2 cm thick interbedded with gray muddy micrite layers with the similar thickness. Almost every thin muddy micrite layer was cut into imbricate blocks or boudins by abundant tiny contemporaneous faults, while the interbedded micrite remain in continuity. Boudins form as a response to layer-parallel extension （and/or layer-perpendicular flattening） of stiff layers enveloped top and bottom by mechanically soft layers. In this case, the imbricate blocks cut by the tiny contemporaneous faults are the result of abrupt horizontal extension of the crust in the SE-NW direction accompanied with earthquakes. Thus, the rock block is, in fact, a kind of seismites. The syn-sedimentary boudins indicate that there was at least a strong earthquake belt on the southeast side of the basin during the early stage of the Sailinhudong Group. This may be a good constraint on the tectonic evolution of the Bayan Obo area during the Early Paleozoic time. The syn-sedimentary compression structure was found in the Middle Triassic flysch in the Nanpanjiang Basin. The typical structures are compression sand pillows and compression wrinkles. Both of them were found on the bottoms of sand units and the top surface of the underlying mud units. In other words, the structures were found only in the interfaces between the graded sand layer and the underlying mud layer of the flysch. A deformation experiment with dough was conducted, showing that the tectonic deformation must have been instantaneous one accompanied by earthquakes. The compression sand pillows or wrinkles showed uniform directions along the bottoms of the sand layer in the flysch, revealing contemporaneous horizontal compression during the time between deposition and diagenesis of the related beds. The Nanpanjiang Basin was affected, in general, with SSW-NNE compression during the Middle Triassic, according to the syn-sedimentary compression structure. The two kinds of syn-sedimentary tectonic deformation also indicate that the related basins belong to a rift basin and a remnant basin, respectively, in the model of Wilson Cycle.