the pressure path of solid inclusions in minerals the retention of coesite inclusions during uplift abstract an inclusion model allows calculation of the stresses in and around minerals included in other minerals during changes in pressure and temperature the equations are applied to illustrate cooling and uplift histories of quarzo feldspathic rocks from 500 c and various pressures to ambient conditions even in the absence of pore fluid pressure microfractures may open at external pressures of 200 400 mpa and temperatures of 200 400 c due to differential volume changes of the constituent minerals coesite included in garnet cannot have formed during progressive metamorphism from quartz at lithostatic pressures below the coesite stability field because of differential volume changes coesite inclusions are captured by their host minerals at ultra high pressures and they persist to lower pressures because of the large volume increase occurring at the coesite to quartz transition the pi t path followed by the sio2 inclusion traces the boundary between the stability fields of coesite and quartz until radial fractures develop in the host at low external pressure

effects of pre existing discontinuities on the residual strength of rock mass insight from a discrete element method simulation abstract when rock failure is unavoidable the designer of engineering structures must know and account for the residual strength of the rock mass this is particularly relevant in underground coal mine openings pre existing discontinuities play an important role in the mechanical behavior of rock masses and thus it is important to understand the effects of such pre existing discontinuities on the residual strength for this purpose the present study demonstrates a numerical analysis using a discrete element method simulation the numerical results indicate that fracture intensity has no significant influence on the residual strength of jointed rock masses independent of confining conditions as confining pressures increase both peak and residual strengths increase with residual strength increasing at a faster rate the finding was further demonstrated by analyzing documented laboratory compressive test data from a variety of rocks along with field data from coal pillars a comprehensive interpretation of the finding was conducted using a cohesion weakening friction strengthening cwfs model the effect of rock bolts on rock mass strength was also evaluated by using a discrete element method model which suggested that rock bolts can significantly increases residual strength but have limited effect on increasing the peak strength of rock masses

garnets recording deep crustal earthquakes syn eclogite facies pseudotachylytes of the bergen arcs western norway were formed during co seismic faulting at a depth of 60 km during caledonian continent collision concurrent with fluid induced partial eclogitization of precambrian anorthositic granulites the pseudotachylytes contain the high pressure assemblage omphacite garnet and kyanite and formed in the metastable granulites at the border of eclogitized areas rock volumes corresponding to outcrops of 100 m2 in area were shattered by pseudotachylytes associated with ultramylonites cataclasites and shear zones the granulite facies garnets unzoned and inclusion free away from the pseudotachylyte veins display planar and curved fractures brecciation and melting with decreasing distance from the veins sieve textured garnet developed by the disintegration of granulite facies garnet crystallization of eclogite facies mineral inclusions and welding together of garnet fragments fractured granulite facies garnets trend to more almandine rich compositions with variable grossular contents in the pseudotachylyte veins a second generation of minute 10 200 m euhedral or dendritic garnets has a higher femg ratio than the granulite facies garnet and a wide range in grossular content grs11 grs89 suggesting rapid growth and cooling fracturing of garnet and its preferential disappearance in the pseudotachylyte show that garnet has a relatively low fracture toughness seismic faulting caused enhanced reaction rates during ongoing fluid induced eclogitization of the deep crust by increasing the surface to volume ratio of garnet and its dislocation density the sudden volume reduction associated with eclogitization of metastable crust may have nucleated further faulting and pseudotachylyte formation

the effect of fluid and deformation on zoning and inclusion patterns in poly metamorphic garnets within the bergen arcs of w norway caledonian eclogite facies assemblages t 650 c p 15 kbar have formed from grenvillian granulites t 800 900 c p 10 kbar along shear zones and fluid pathways garnets in the granulites grti pyr56 40 alm45 25gro19 14 are unzoned or display a weak ca 1 wt feo over 1000 m zoning the eclogite facies rocks contain garnets inherited from their granulite facies protoliths these relict garnets have certain areas with compositions identical to the garnets in their nearby granulite but can be crosscut by bands of a more almrich composition grtii pyr31 41alm40 47gro17 21 formed during the eclogite facies event these bands orientated preferentially parallel or perpendicular to the eclogite foliation may contain mineral filled veins or trails of eclogite facies minerals omphacite amphibole white mica kyanite quartz and dolomite steep compositional gradients up to 9 wt feo over 40 m separate the two generations of garnets indicating limited volume diffusion the bands are interpreted as fluid rich channels where element mobility must have been infinitely greater than it was for the temperature controlled volume diffusion at mineral interfaces in the granulites the re equilibration of granulite facies garnets during the eclogite facies event must therefore be a function of fracture density deformation and fluid availability the results cast doubts on modern petrological and geochronological methods that assume pure temperature controlled chemical re equilibration of garnets

defect microstructures of minerals as a potential indicator of extremely rapid and episodic exhumation of ultrahigh pressure metamorphic rock implication to continental collision orogens exhumation of subducted continental crust to the earth s surface was presumably rapid though at an uncertain rate to retain coesite diamond and pbo2 type tio2 here we report unique defect microstructures of minerals as a potential indicator of a rapid and episodic exhumation process in a fossil fracture zone of coesite eclogite from the sulu terrain eastern china having the most negative 18o value ever reported for eclogite facies metamorphic rock analytical electron microscopy indicates that semi brittle deformation occurred in kyanite omphacite spinel with extensive and unusual fine scale twin lamellae and that brittle deformation occurred in garnet with hardly healed 110 microcleavages these unique defect microstructures can be rationalized by a high strain rate at local weakening and deep faulting of continental collision orogens

radial cracks around α quartz inclusions in almandine constraints on the metamorphic history of the oman mountains radiating tensional cracks around quartz inclusions in almandine have been observed in metapelite samples from the southeastern saih hatat tectonic window northeastern oman mountains these almandines show an inclusion rich glaucophane epidote and strongly deformed core with inclusions of different mineral phases the rim of the same almandines is inclusion poor and shows only quartz apatite zircon rutile and baal phosphates as inclusions quartz and apatite inclusions in the rim are single crystals often surrounded by radial cracks these radial cracks developed during uplift by the dilation of quartz 4 5 vol without a phase transformation subsequently these cracks were filled with kaolinite phengite si content 3 4 per formula unit p f u chlorite and fe oxides we calculated the appearance of radial cracks without phase transformation using the mathematical procedure of van der molen and van roermund 1 this calculation involves terms for thermal expansion isothermal compressibility and shear modulus for the example of quartz and almandine for the same p and t interval during a retrograde path published geothermobarometric estimates give pressures of between 1 0 and 2 0 gpa and temperatures of between 450 and 600 c for the peak conditions for these rocks of the saih hatat tectonic window on the basis of these p t data we calculated different retrograde p t paths in the quartz domain initiation of garnet fracturing is dependent on the p t starting conditions and the component of isothermal compression of the retrograde path the calculations yield a set of smooth monotonic curves whose exact position on the p t plane between 0 1 and 0 6 gpa and 40 and 500 c depends on the initial p t conditions and the component of isothermal compressibility of the retrograde p t paths this model can be used in general terms to estimate pressure and temperature for the following cases 1 if independent evidence such as petrological data allow the determination of the final pressure at which radial cracks appeared the initial inclusion pressure can be recalculated 2 if the initial inclusion pressure is known e g from petrological data the conditions of radial cracking can be calculated and the pair initial pressure final pressure leads to an estimate of the shape of the retrograde p t path as a function of its component of isothermal decompression in the example from the northeastern saih hatat tectonic window the late syntectonic growth of albite phengite kaolinite suggests that the final pressure for fracturing ranged between 0 4 gpa and 0 5 gpa at temperatures of 300 c these values correspond to high initial pressures of at least 2 0 gpa at a temperature of 550 c the following geodynamic model is suggested a regionally extended metamorphism led to the growth of inclusion rich garnets in the rocks from the northeastern saih hatat tectonic window at depths of about 30 km 0 1 gpa about 450 c continuing prograde metamorphism at a depth of more than 60 km with p 2 0 gpa and t 550 c affected a metapelite unit that is only exposed immediately south of as sifah village in this area clear rims of almandine grew around the older garnets and entrapped mainly quartz and apatite during uplift along a retrograde p t path with a large component of isothermal decompression radial cracks around quartz inclusions developed in the rims of almandines at a depth of about 12 km 0 4 0 5 gpa 300 c

numerical simulation of cumulative damage and seismic energy release during brittle rock failure part i fundamentals abstract this paper presents a numerical approach for the simulation of damage initiation and propagation causing seismic energy release during unstable failure of brittle rock with a newly developed numerical code rfpa2d rock failure process analysis the progressive failure process leading to the development of a shear or fault zone and the eventual collapse of a heterogeneous rock sample is modeled since the constitutive law for each element in the model is elastic brittle seismic energy is radiated whenever an element fails it is assumed that the radiated energy is equal to the energy stored in the element before failure is triggered due to the heterogeneity of rock properties seismic quiescence may occasionally occur within the nucleation zone the cumulative seismic damage calculated based on the seismic event rate from the simulation can be used as a damage parameter to describe the damage evolution it was found that significant decreases followed by sudden increases in radiated seismic energy may be an indicator of potentially unstable nucleation

sub critical fracture and associated retrogression of garnet during mylonitic deformation garnets from the alpine fault mylonites are fractured most fractures have a retrogressive fracture fill a small number have garnet fill a detailed sem study has been carried out to elucidate the mechanisms of fracture and associated retrogression wide fracture zones contain free floating islands of garnet in a retrogressive matrix electron channelling patterns show that segments of garnet across such fracture zones rarely show any relative rotations where rotations are observed they are small and systematic some large fractures show clearly that fracture and retrogression occurs by a replacement process fracture surface morphologies are indicative of surface dissolution a model is established where crack tips advance by a process of dissolution at a high stress crack tip whilst precipitation occurs as the tip and its associated stress field advance precipitation of retrogressive fracture fill occurs if fracture occurs out of the field of stability of garnet

calcium depletion halos and fe mn mg zoning around faceted plagioclase inclusions in garnet from a high grade pelitic gneiss

low energy phase boundary pairs and preferred crystallographic orientations of olivines in nanometer sized ultrapotassic fluid inclusions of aykhal diamond abstract the healed internal conjugated cleavages at the core of aykhal octahedral diamond sample ah2 were decorated with 111 dia facetted ultrapotassic fluid melt inclusion pockets containing nanosized graphite phlogopite and olivine fo92 inclusions these olivines are either rounded in pockets with ample fluid or facetted by the 111 dia mold in the pockets with a fluid film transmission electron microscopy revealed two distinct crystallographic characteristics of olivine inclusions 1 pronounced crystallographic texture of olivines grouped in specific diamond domain and 2 frequent parallelism or sub parallelism of specific low energy faces of the two phases mainly 010 ol 120 ol 001 ol and 111 dia 110 dia 100 dia in the order of decreasing preference forming prominent 010 ol 111 dia 010 ol 110 dia 001 ol 110 dia 120 ol 111 dia and 120 ol 110 dia low energy phase boundaries with thin liquid film of 1 2 nm in between these findings not only testify to the extremely low adhesion energies of olivine diamond boundary pairs but also imply that in the presence of a fluid phase the interfacial energetics and the energetically favored crystallographic orientations of olivine inclusions in diamond can be controlled simply by the settlement attachment of low energy facets of olivine crystals precipitating from the parental fluid upon the low energy 111 dia or 110 dia surfaces of diamond such interfacial energetics control and the resultant low energy boundary pairs are characteristically distinct from the common topotaxy or epitaxy between oxide silicate mineral pairs but are in a sense like the van der waals heteroepitaxy in artificial systems

the geomorphic evolution of slopes and sediment chutes on forereefs abstract frequent slope failures of the forereef dropoff occur in living coral reefs on the island of bonaire in the southern caribbean topographic profiles of ten sites were taken perpendicular to shore followed by an estimation of coral ages m annularis along the topographic profiles the coral ages were estimated from published rates of growth and sizes of the sampled corals comparisons of coral age and adjacent slope angle indicated that the steeper slopes are older and that mass failure of the slope reduces the steepness of the forereef front and destroys the coral community along the disturbed slope slopes grow until reaching a critical steepness after which underwater sliding of the over steepened forereef front results in observed slides the mechanical weakness in the reef structure that facilitates a slide failure was the result of a weak mud and coral rubble layer deposited 2 m below the living coral cover the remaining slide scarp evolves into a sediment chute that conveys the resulting flow of biogenic sands from the shallow forereef terrace down the forereef edge because of the constant flow of sand down these channels no corals can recolonize the sediment chutes and the chutes become stable topographic features in addition these indentations in the forereef front also serve as channels for the vertical density mixing of water of varying salinities and temperatures

characterization of strain burst rock fragments under a scanning electron microscope an illustrative study abstract fractures around excavations in hard fine grained brittle rock sometimes display unique patterns from which an interpretation of the manner of failure fracture propagation can be made igneous rock fragments from a strain burst event at a site in western australia have been studied under a scanning electron microscope sem in order to characterize their surficial features sem image analysis indicates that anisotropy a contrast in geomechanical properties geometry and contact patterns present at the micro scale as they do at the large mine drive scale it is proposed that these micro scale features can lead to anisotropic material behaviour and stress concentrations that manifest as strain burst events

modeling of radial microcracks at corners of inclusions in garnet using fracture mechanics radial microcracks around inclusions in garnet are important indicators of ultrahigh pressure metamorphism and have been used to interpret changes in pressure as a function of temperature during decompression of metamorphic terrains we investigate the growth of microcracks from inclusion corners using a two dimensional fracture mechanics based boundary element method code and propose that microcracks emanating from inclusions are primarily controlled by inclusion shape and size and do not require high confining lithostatic pressure or significant decompression to initiate results suggest that inclusions 100 m diameter develop microcracks during modest decompression the magnitude of decompression required to initiate microcracks decreases with increased degree of faceting and increased inclusion size the potential for crack growth at each corner depends on the corner sharpness and the overall shape of the inclusion we integrate model results with petrographic observations to understand mechanisms and conditions of garnet microcracking during regional metamorphism

rockburst mechanism and prediction based on microseismic monitoring abstract in this study the rockburst definition is comprehensively described and several main rockburst theories the strength theory the energy theory the bursting liability theory the rigidity theory and the instability theory are analyzed the two body interaction theory based on the newton s law can explain the rockburst mechanism most reasonably the rockburst development process is a static process and the rockburst occurrence process is within the scope of dynamics in addition some precursors exist before rockburst occurrence reflected by the consistency between acoustic emissions and damage variables in rock mass which can be summarised as three seismogenic models according to the tempo spatial distribution by utilizing the 3s stress buildup stress shadow and stress transfer principle in seismology three rockburst criteria are proposed in this paper namely the stress tempo spatial evolution the magnitude energy and concentration degree of microseismic events sudden change of apparent volume finally by comparing the results obtained by microseismic monitoring and landsonar positioning it is shown that the root cause of rockburst occurrence is rock heterogeneity and the existence of joints and fractures the fracture intersection points are the locations for rockburst initiation it is proven that the two body interaction principle can perfectly explain the rockburst mechanism

a zoning model for coal mining induced strata movement based on microseismic monitoring a microseismic monitoring technique is adopted to investigate the distribution regularity of microseismic events released by the coal mining induced roof rock mass along the vertical and horizontal directions in combination with mine geological data on the basis of the quantity and energy distributions of the microseismic events recorded using the microseismic monitoring technique a zoning method is first established for the roof strata movement in the vertical and horizontal directions the vertically zoning method is then applied to analyze the microseismic monitoring results obtained in the dongjiahe coal mine which divides rock mass into six zones along the vertical direction i e the caved zone the block zone the vertical fracture through going zone the vertical fracture zone the separation zone and the continuous zone the horizontally zoning model divides the roof strata movement into three zones i e the calm zone the generation zone impacted by working face and the historical generation zone after that based on the horizontally zoning model a method is developed to determine the displacement angle using the microseismic monitoring data which has been verified in the dongjiahe coal mine

garnets as open systems during regional metamorphism if a garnet fractures during metamorphism its interior will be in chemical communication with matrix phases solids and fluids and may participate in late prograde or retrograde metamorphic reactions the core of a growth zoned garnet is unlikely to be in equilibrium with matrix phases and may react locally in the vicinity of fractures or extensively resulting in dissolution and reprecipitation of the garnet interior and or production of new phases the results of petrologic techniques such as thermobarometry pressure temperature path calculations and geochronometry may be misinterpreted if sites of garnet and mineral inclusion compositional modification are not identified brittle fracturing of garnet during regional metamorphism may be facilitated by the presence of mineral inclusions the conditions at which differential expansion of an inclusion relative to its host garnet are sufficient to cause radial cracking around the inclusion vary as a function of peak pressure retrograde pressure temperature path and thermoelastic properties of the inclusion and garnet inclusion induced fracturing is favored by nearly isothermal decompression a common metamorphic pressure temperature path other fractures may form as a result of propagation of an inclusion host boundary or by mechanisms external to the garnet

in situ monitoring of rockburst nucleation and evolution in the deeply buried tunnels of jinping ii hydropower station abstract rockbursts occurred frequently during the excavation of several parallel tunnels in the jinping ii hydropower station under a maximum overburden of 2525 m over an average length of 17 5 km in order to investigate the nucleation and evolution mechanism of rockbursts a comprehensive monitoring campaign consisting of a digital borehole camera cross hole acoustic apparatus and sliding micrometer was undertaken for in situ measurements in two specially excavated test tunnels b and f this paper presents the comprehensive monitoring methods applied and results of numerical analysis applied to a typical rockburst that fortuitously occurred during the testing period precursory characteristics preceding rockbursts are a abundant crack initiation propagation and coalescence b deformation of surrounding rock mass involving an accelerated deformation stage quiescence stage and reaccelerated deformation stage and c decrease of the characteristic elastic wave velocity of the rock mass the nucleation and evolution of rockbursts discussed consist of four stages a stress adjustment b energy accumulation c crack initiation propagation and coalescence and d fractured rock collapse and ejection the results provide a direct case history to assist the prediction and support of rockburst disasters and contribute to field excavation of deeply buried tunnels

fault creep growth model and its relationship with occurrence of earthquakes summary a fault model is used to analyse creep growth process of microcracks in damage zone near the tips of fault by means of the rheology fracture mechanics when microcracks in the zone link each other and their deformation quickly intensifies it means that an earthquake is taking place to a certain degree the relationships among some key parameters that are correlated to the growth of microcracks are analysed theoretically these parameters include failure time of fault number of microcracks in unit area stresses field yield strength and rheological properties of medium the results indicate that the model proposed here is reasonable to describe the pregnant process of an earthquake in the meantime this research shows that with the results of in situ surveys and lab experiments it is possible to estimate the time span for a fault expanding

development of a comparative index for the assessment of the severity of violent brittle failures around underground excavations abstract in order to assess the severity of a violent brittle failure strain burst around the vicinity of complex underground excavations an index parameter has been developed the index incorporates measures of the induced stress path and accumulated plastic strain and is calculated after brittle failure conditions are identified by the established damage initiation threshold and spalling limit dit sl the comparative index developed provides guidance to minimize strain burst hazard for geotechnical design application of the index to a conceptual model shows that strain burst hazard can be related to geological boundaries and their exposure in excavation faces the potential violence of these strain burst failures can be quantified by changes in principal stress and plastic strain within a numerical model

coupled disaster causing mechanisms of strata pressure behavior and abnormal gas emissions in underground coal extraction the generalization and application of fully mechanized caving with super great mining height sgmh face a series of new issues of which strata pressure behavior and abnormal gas emissions are the most prominent disasters and display a close relationship the tashan coalmine was chosen as the experiment base because of its sgmh and the overlying hard and thick main roof htmr this coalmine had experienced many damaging hydraulic support and abnormal gas emission accidents induced by strata pressure behavior the key strata theory and the fracture failure process analysis model established by 3dec were used to analyze the structural characteristics and fracture failure process of the htmr the geostress reduction and permeability enhancement redistribution of the adjacent coal measure strata were studied by the geostress and permeability distribution model established by flac 3d the htmr controlled the failure extent and the movement evolution of the entire overburden stratum the htmr acted as a large double sided embedded rock beam during primary fracturing and a cantilever articulated rock beam during periodic fracturing and it generated a huge hanging space above the gob the fully mechanized caving with sgmh caused large scale disturbances and permeability enhancements in the adjacent rock and coal strata then the substantial amounts of gas stored in the remaining coal surrounding rock strata and adjacent coal seam rushed out and aggregated in the caved and fissured zones of the gob forming a huge gas warehouse the strata pressure behavior and abnormal gas emission disasters primarily occurred after the primary and periodic fracturing of the htmr these disasters are predominantly caused by the escaping of the abundant gas that existed in the gob during mine pressure behavior processes when the ultimate broken span was reached as the htmr rotated and collapsed the substantial amounts of gas that accumulated in the gob escaped into the working face which easily caused abnormal gas emissions hydraulic presplitting and gas drainage technologies are proposed to solve these disasters

scaling of ground motion parameters state of stress and focal depth the ground motion parametersrv and ra where r is hypocentral distance v is peak velocity is density and a is peak acceleration are found observationally to be strong functions of stress state and linearly related to focal depth z if the stress state and focal depth are properly taken into account then the ground motion parameters depend on the seismic moment m0 as expected from basic scaling principles that is rv m01 3 and ra is independent of earthquake size regression lines fitted to observations covering broad ranges in seismic moment and focal depth indicate that for extensional and compressional tectonic regimes corresponding to normal and thrust or reverse faulting earthquakes respectively peak acceleration is given by ra 1 08 mpa 3 06 mpa km z normal and ra 5 65 mpa 8 76 mpa km z thrust and for peak velocity rv m01 3 10 4 m2 s n m 1 3 3 00 0 69 km 1 z normal and rv m01 3 10 4 m2 s n m 1 3 4 63 1 82 km 1 z thrust for strike slip earthquakes the data currently are insufficient to define regression fits but such lines would definitely lie between those for the normal and thrust stress regimes these equations are appropriate for ground motion at small hypocentral distance as recorded in a whole space it follows that for comparable hypocentral depth peak acceleration in a compressional tectonic regime for example much of the eastern united states is a factor of about 3 greater than in an extensional regime such as nevada and for peak velocity a similar comparison yields a factor of 2 difference the similarity in behavior of the peak acceleration parameter to crustal strength estimated from byerlee s law of friction with respect to depth and stress state indicates that crustal strength is probably the factor governing the seismic source processes that give rise to the high frequency peak ground motion analysis of the peak acceleration data in the context of crustal strength suggests bounds on this ground motion parameter as recorded at a typical surface site that depend on stress state specifically a normal 0 5 g and a thrust 1 9 g thus the state of stress as well as the focal depth clearly is an important factor to be taken into account in the prediction of seismic ground motion

influence of tunneling methods on the strainburst characteristics during the excavation of deep rock masses abstract it is widely known that blasting and tbm are the general methods for the deep rock mass excavation and can respectively induce transient release of in situ stress tris and quasi static unloading of in situ stress qsuis on the excavation boundary as one of the most important triggers the unloading of in situ stress caused by excavation frequently induces strainbursts however little attention has been focused on the influence of the tunneling methods on the strainburst characteristics in this paper the cracking of surrounding rock masses and associated energy dissipation under the different tunneling methods was analyzed the influence of different tunneling methods on the evolution characteristics of strainburst was also discussed results show that compared with the tbm excavation the blasting excavation aggravates the cracking of surrounding rock masses and enlarges the energy dissipation during the cracking process during the unloading process of in situ stress the total energy and the releasable strain energy for the case of blasting excavation are much higher than that for the tbm excavation this makes that the intensity and frequency of immediate strainbursts induced by blasting excavation are much greater than that caused by tbm excavation while after the unloading of in situ stress as the surrounding rock masses dissipate larger energy during its cracking process the releasable strain energy for the case of blasting excavation is lower than that for the tbm excavation this brings down the risk of time delayed strainbursts for the blasting excavation in addition a case study at diversion tunnels in jinping ii hydropower project was presented as a verification

numerical and experimental study on progressive failure of marble this study presents a framework for numerical simulations based upon micromechanical parameters in modeling progressive failures of heterogeneous rock specimens under compression in our numerical simulations a weibull distribution of the strength and elastic properties of the finite elements is assumed and the associated weibull parameters are estimated in terms of microstructural properties such as crack size distribution and grain size through microscopic observations of microcracks the main uncertainty in this procedure lies on the fact that various ways can be used to formulate a microcrack size distribution in relating to the weibull parameters as one possible choice the present study uses the number of counted cracks per unit scanned volume per grain size to formulate the crack distributions finally as a tool the rock failure process analysis code rfpa2d is adopted for simulating the progressive failure and microseismicity of heterogeneous rocks by using an elastic damage finite element approach to verify our framework compression tests on marble specimens are conducted and the measured acoustic emissions ae are compared with those predicted by the numerical simulations the mode of failure compressive strength and ae pattern of our simulations basically agree with experimental observations

numerical simulation of the dynamic impact breakage testing of rock laboratory drop weight tests and numerical modelling have been used to study the effect of impact energy on the degree of fragmentation of cylindrical granite specimens the drop weight tests indicated that the degree of fragmentation of the granite formed a non linear relation with impact energy in the modelling of the drop weight test the shear localisation developed in the granite was assumed to represents discrete fracture planes image analysis of the model outputs was undertaken to determine particle size distributions corresponding grading curves from the numerical modelling were then validated against the laboratory derived curves indicating the potential of numerical modelling to simulate the fragmentation process of brittle rocks

shock metamorphic features and their zoning and orientation in the precambrian rocks of the manicouagan structure quebec canada abstract the manicouagan structure of impact origin is located in eastern quebec about 300 km north of the st lawrence river the complex is of triassic age the shock deformation of the more important rock forming minerals of the autochthonous or at least parautochthonous rocks within the structure is described four zones of shock metamorphism are delineated based on the deformation features of plagioclase 1 plagioclase without planar features 2 plagioclase with planar features 3 first occurrence of plagioclase with partial isotropization and 4 first occurrence of plagioclase with total isotropization these four zones are more or less concentric and indicate a general increase in the grade of shock metamorphism towards the centre of the structure however several small areas probably underlain by allochthonous rocks appear not to fit this general picture biotite and garnet show evidence of a shock orientation of their deformation features an impact origin for the structure is favoured the impact possibly triggering volcanism

the shift of the α β transition temperature of quartz associated with the thermal expansion of granite at high pressure abstract measurements are presented of volume changes in granite during room temperature compression to 100 200 and 300 mpa confining pressure followed by temperature increase to 900 c comparison with thermal expansion and compressibility data for the constituent minerals allows changes in porosity to be estimated under confining pressure porosity is found to decrease with heating to 200 c through expansion of the minerals into cracks which are thought to be related to the geological cooling history of the rock between 200 c and 840 c porosity increases as a result of differential thermal expansion of the constituent minerals but crack opening is increasingly suppressed at higher confining pressures extrapolation of the results indicates that differential thermal expansion can no longer cause crack opening in dry granite at confining pressures in excess of 450 mpa the quartz transition temperature in granite is marked by a kink in the thermal expansion curve of the rock and it is found to increase by 60 c 70 c per 100 mpa confining pressure as opposed to the published value of 26 c per 100 mpa for single crystals of quartz equations are presented which allow calculation of the effects of confining pressure and temperature on the stresses and displacements in and around a spherical inclusion embedded in a matrix of different elasticity and thermal expansion the theory together with a simple self consistent model for granite accounts semiquantitatively for the observations of thermal expansion and the effect of confining pressure thereon and for the observed transition temperatures for quartz in granite

diamond former coesite and supersilicic garnet in metasedimentary rocks from the greek rhodope a new ultrahigh pressure metamorphic province established abstract we report here the first discovery of ultrahigh pressure uhp indicator minerals and textures from the rhodope metamorphic province rmp northern greece in particular we document the exsolution of quartz rutile and apatite in sodic garnet from metapelites garnet biotite kyanite gneisses which attests to the presence of a si ti na p rich precursor garnet phase similar textures in garnet have been reported in the literature only once before for eclogites from the su lu uhp metamorphic province china we also document the presence of microdiamonds and multicrystalline quartz pseudomorphs after coesite included in garnet from both eclogites and metapelites we then argue that these rocks had once been transported to depths exceeding 220 km well into the upper mantle thus establishing the rmp as another important uhp metamorphic belt in the world

on the mechanism of resorption zoning in metamorphic garnet an analytical electron microscope study of almandine garnet from a metamorphosed al fe rich rock revealed detailed composition profiles and defect microstructures of resorption zoning along fluid infiltrated veins and even into the garnet ilmenite inclusion interface this indicates a limited volume diffusion for the cations in substitution mainly ca and fe and an interface controlled partition for the extension of a composition invariant margin a corrugated interface between the ca rich margin zone and the almandine garnet core is characterized by dislocation arrays and recovery texture further suggesting a resorption process facilitated by diffusion induced recrystallization diffusion induced dislocation migration and diffusion induced grain boundary migration integrated microstructural and chemical studies are essential for understanding the underlying mechanisms of processes such as garnet zoning and its modification without this understanding it will not be possible to reliably use garnet compositions for thermobarometry and other applications that rely on garnet chemical information

tio2 exsolution from garnet by open system precipitation evidence from crystallographic and shape preferred orientation of rutile inclusions we investigated rutile needles with a clear shape preferred orientation in garnet from ultra high pressure metapelites from the kimi complex of the greek rhodope by electron microprobe electron backscatter diffraction and tem techniques a definite though complex crystallographic orientation relationship between the garnet host and rutile was identified in that rt 001 is either parallel to grt or describes cones with opening angle 27 6 around grt each rt 001 small circle representing a cone on the pole figure displays six maxima in the density plots this evidence together with microchemical observations in tem when compared to various possible mechanisms of formation corroborates a precipitate origin a review of exchange vectors for ti substitution in garnet indicates that rutile formation from garnet cannot occur in a closed system it requires that components are exchanged between the garnet interior and the rock matrix by solid state diffusion a process we refer to as open system precipitation osp the kinetically most feasible reaction of this type will dominate the overall process the perhaps most efficient reaction involves internal oxidation of fe2 to fe3 and transfer from the dodecahedral to the octahedral site just vacated by text ti 4 6 text m 2 3 text tial left text alsi 2 right text o 1 2 6 text m 2 2 5 text tialsi 3 text o 1 2 10 text m 2 3 0 text al 1 8 text fe 0 2 text si 3 text o 1 2 text m 2 2 text e 1 2 text tio 2 osp is likely to occur at conditions where the transition of natural systems to open system behaviour becomes apparent as in the granulite and high temperature eclogite facies

shear promoted phase transitions in fe2sio4 and mg2sio4 and the mechanism of deep earthquakes phase transformations in end member olivines have been investigated in the temperature range comparable to the interior of subducting slabs this work constitutes the experimental evidence that the kinetics of transformation of silicate olivine phase to modified spinel and spinel phases is enhanced by shear deformation natural fayalite fe2sio4 subjected to a pressure gradient from 0 to 25 gpa at 380 c in the diamond anvil cell dac developed a ring of phase where the pressure was in the stability field of the phase and shear stress was large enough to promote the transition the sample inside the ring despite being at higher pressure remained dominantly as phase the outermost lower pressure region of the sample also remained as phase in the mg2sio4 system the transition from to was observed at 575 c in runs in which pressure covered the stability fields of phase phase and mixed oxides these results show that the characteristic transformation temperature tch can be lowered as much as 200 c by shear deformation on the basis of these observations we propose a nonhydrostatic kinetic boundary for the and transitions in mantle olivine for temperatures below this boundary the transformations are kinetically inhibited while above it the transformations can be promoted by shear deformation therefore olivine carried to a depth of several hundred kilometers in a subducting slab can remain as metastable phase until shear deformation causes its transformation we suggest that this region of shear promoted transformation in the cold interior of the subduction zone is responsible for the generation of deep earthquakes

information entropy of earthquake populations in northeastern italy and western slovenia abstract the spatio temporal evolution of eight seismicity populations preceding and following moderate earthquake sequences occurred in ne italy and w slovenia are investigated by means of the normalized shannon entropy and the fractal dimension three phases are recognized in the temporal seismic series the period preceding the mainshock is characterized by oscillations of the shannon entropy around a nearly constant level and by fluctuations of the fractal dimension the phase of mainshock and aftershock sequences is characterized by a significant decrease of the shannon entropy a simultaneous marked decrease of the fractal dimension is observed in five cases after the sequence the entropy recovers the nearly constant trend before the mainshock and the fractal dimension is characterized by fluctuations we interpreted the fluctuations of the normalized shannon entropy and the fractal dimension caused by the coupling between the stress field and the mechanical heterogeneities of the crust that results in spatial and temporal fluctuations of the strain energy

evidence for submarine weathering from metamorphosed weathering profiles on basaltic rocks tananao metamorphic complex taiwan the metamorphosed paleo weathering horizon s developed on basaltic rocks in the tananao metamorphic complex forms distinct al fe rich rocks and occurs as two parallel belts demonstrating its potential as a stratigraphic correlation unit in this structurally complicated metamorphic terrain these al fe rich rocks have been metamorphosed under amphibolite greenschist facies conditions leading to the formation of garnet chloritoid rocks chloritoid rich rocks the chemical changes along three profiles from metabasite to garnet chloritoid rock show prominent k rb cs and ba enrichment yet also a large depletion of other elements if it is assumed that ti zr nb ta and hf remained relatively immobile the ree s however behaved non coherently these chemical characteristics are attributed to pre metamorphic processes and are shown to be similar to those observed with submarine weathering of basaltic rocks in contrast the chloritoid rich rocks reveal distinct k rb cs and ba depletion it is suggested that this resulted from subaerial weathering processes k enrichment is not an uncommon feature in paleozoic precambrian paleosols the present case study demonstrates that submarine weathering should be considered as a probable cause

tio2nanoparticle trails in garnet implications of inclusion pressure induced microcracks and spontaneous metamorphic reaction healing during exhumation a new mechanism of cleaving healing of garnet in metamorphic rocks during exhumation is reported almandine garnet with submicron multiple phase inclusions characteristic of the grail reaction garnet rutile kyanite ilmenite low quartz was found by analytical electron microscopy to have non epitaxial rutile nanoparticles distributed along internal 110 microcrack trails at the acute corner of submicron multiple phase inclusions defined by the intersecting 110 and 011 mould surfaces such garnet microcracks were formed during lithostatic decompression due to a relatively high compressibility of quartz in the inclusion pockets and stress concentration at the acute corner spontaneous healing with accompanied formation of non epitaxial rutile nanoparticles was activated predominantly via the grail reaction due to high surface tension at the tip of microcracks and to a lesser extent decreasing lithostatic pressure or increasing inclusion pressure upon exhumation this new mechanism of microcracking and healing involves stress build up fracture propagation mineral reaction transport of elements to the reaction site and lowering of reaction boundaries by capillarity effect all under the influence of thermodynamic and kinetic factors at the submicron scale thus tio2 nanoparticle trails in garnet provide additional information on the p t path and may shed light on exhumation rates mechanisms and metamorphic reactions processes careful scrutiny of host minerals on the submicron scale is required to tell whether there are other metamorphic reaction facilitated healing processes being overlooked by inappropriate techniques or being obliterated by the predominant healing processes of fluid infiltration and resorption zoning

estimating in situ rock stress from spalling veins a case study stress induced failures have typically been considered as engineering disasters in deep underground excavations this paper highlights the importance of stress driven rock failures as a means to estimate the in situ rock stress at the depth the method which is based on the observation and documentation of a failure mode referred to here as spalling in deep tunnels or caverns is put forward and presented to estimate the macro scale rock stress using the proposed method the orientation of the principal stresses in situ can be deduced by the spalling intensity and associated stress induced spalling veins in the rock mass surrounding the opening and the magnitude of the principal stresses can be estimated by the assumed crack initiation stress required to generate spalling in the given rock by careful documentation of spalling failure characteristic in the field a real case study at baihetan powerhouse site has been carried out and indicates that the proposed method is an available way to enriching recognition of in situ rock stress and a helpful supplement to traditional methods of stress measurements after strictly numerical verification analysis of the regional tectonic setting as well as measurements of in situ stress supports the results by the suggested approach

microseismic monitoring and stability evaluation for the large scale underground caverns at the houziyan hydropower station in southwest china abstract the stability of underground caverns and the excavatability of rock masses are important for geotechnical engineering practices during the design and construction stages the risks associated with underground caverns at the houziyan hydropower station in southwest china are growing due to excavation induced unloading to assess the instability of underground caverns and resolve the complex subsurface conditions of the highly fractured rock mass a high resolution microseismic monitoring system was established in deep underground caverns this system was used to determine the relationship between the measured microseismic activities and the excavation damage zones of the surrounding rock mass the excavation damage zones and potential risk regions in the underground caverns were identified by analyzing the tempo spatial distribution of microseismic activities in addition the correlation between microseismic activities and pre existing geological structures was determined and traditional monitoring results were analyzed to validate the correlation between seismicity and the excavation damaged zones of the underground caverns a numerical model was employed to further evaluate the deformation and stability of the surrounding rock mass the monitoring results demonstrate that microseismic events mainly occurred in high stress concentration regions corresponding with the results obtained from the numerical analysis therefore this comprehensive method which incorporates microseismic monitoring numerical analysis traditional monitoring and field observations is promising for predicting the deformation and instability of surrounding rock masses in the underground caverns subjected to excavation

simulating electropulse fracture of granitic rock abstract electropulse treatments employ a series of high voltage discharges to break rock into small fragments as these methods are particularly suited to fracturing hard brittle rocks electropulse treatments can serve to enhance or substitute for more traditional mechanical approaches to drilling and processing of these materials nevertheless while these treatments have the potential to improve hard rock operations the coupled electro mechanical processes responsible for damaging the rock are poorly described the lack of accurate models for these processes increases the difficulty of designing controlling and optimizing tools that employ electropulse treatments and limits their range of application this paper describes a new modeling method for studying electropulse treatments in geotechnical operations the multiphysics model simulates the passage of the pulse electrical breakdown in the rock and the mechanical response at the grain scale it also accounts for the contributions from different minerals and porosities allowing the effect of material composition to be considered in so doing it provides a means to investigate the different physical and operational factors influencing electropulse treatments

on oriented ilmenite needles in garnet porphyroblasts from deep crustal granulites implications for fluid evolution and cooling history abstract garnet porphyroblasts from a litho assemblage containing aluminous granulite and quartzofeldspathic gneisses of the eastern ghats granulite belt india contain nanometer to micrometer thick ilmenite needles oriented crystallographically petrographic and chemical analyses reveal that garnet was formed by dehydration melting reaction s of titaniferous biotite in an oxidized condition elevated oxygen fugacity might have promoted enrichment of ti bearing andradite component of garnet porphyroblasts formed during pre to peak metamorphic condition in appropriate bulk chemistry during the post peak cooling history ti bearing components in garnet decomposed to rhombohedral oxide solid solution ilmenite hematite detailed transmission electron microscopic study of the host garnet and ilmenite solid solution indicates that though there is an overall parallelism of 011 plane of host garnet and 011 plane of ilmenite structural coherence between the two phases was progressively lost during growth from thin to thick needles appropriate cooling rate from high temperature peak metamorphic condition arguably promoted growth of ilmenite solid solution through reaction exsolution process within garnet porphyroblasts

brittle ductile transition and associated seismicity experimental and numerical studies and relationship with the b value the acoustic emission ae and the mechanical behavior of granite samples during triaxial compression tests have been analyzed the size of ae events displays power law distributions conforming to the gutenberg richter law observed for earthquakes which is characterized by the b value as the confining pressure increases the macroscopic behavior becomes more ductile for all different stages of the rock mechanical behavior linear nonlinear prepeak nonlinear postpeak shearing there is a systematic decrease of the b value with increasing confining pressure a numerical model based on progressive elastic damage and the finite element method allows simulations of the main experimental observations on ae and of a wide range of macroscopic behaviors from brittleness to ductility the model reproduces a decrease in the b value that appears to be related to the type of macroscopic behavior brittle ductile rather than to the confining pressure both experimental and numerical results suggest a relationship between the b value and the brittle ductile transition moreover these results are consistent with recent earthquake observations and give new insight into the behavior of the earth s crust

submicron polyphase inclusions in garnet from the tananao metamorphic complex taiwan a key to unravelling otherwise unrecognized metamorphic events kyanite and staurolite occur in the tananao metamorphic complex as submicron inclusions in almandine rich garnet from a metamorphosed palaeosol weathering horizon near hoping eastern taiwan quartz rutile brookite and zircon are also found as associated submicron inclusions in garnet employing the reaction ilmenite kyanite quartz almandine rutile and the breakdown of staurolite and quartz as thermobarometers these submicron scale minerals formed at 8 3 8 8 kbar and 660 690 c this p t estimate is different from that i e 5 7 kbar and 530 550 c derived from matrix minerals which include almandine rich garnet muscovite chlorite chloritoid plagioclase quartz and ilmenite these results suggest that submicron inclusions in garnet like materials may record portions of the otherwise undocumented prograde path or provide information about previous metamorphic events and thus yield new insights into orogenic belts

a new method to estimate location and slip of simulated rock failure events abstract at the laboratory scale identifying and locating acoustic emissions aes is a common method for short term prediction of failure in geomaterials above average ae typically precedes the failure process and is easily measured at larger scales increase in micro seismic activity sometimes precedes large earthquakes e g tohoku l aquilla oceanic transforms and can be used to assess seismic risk the goal of this work is to develop a methodology and numerical algorithms for extracting a measurable quantity analogous to ae arising from the solution of equations governing rock deformation since there is no physical property to quantify ae derivable from the governing equations an appropriate rock mechanical analog needs to be found in this work we identify a general behavior of the ae generation process preceding rock failure this behavior includes arbitrary localization of low magnitude events during pre failure stage followed by increase in number and amplitude and finally localization around the incipient failure plane during macroscopic failure we propose deviatoric strain rate as the numerical analog that mimics this behavior and develop two different algorithms designed to detect rapid increases in deviatoric strain using moving averages the numerical model solves a fully poro elasto plastic continuum model and is coupled to a two phase flow model we test our model by comparing simulation results with experimental data of drained compression and of fluid injection experiments we find for both cases that occurrence and amplitude of our ae analog mimic the observed general behavior of the ae generation process our technique can be extended to modeling at the field scale possibly providing a mechanistic basis for seismic hazard assessment from seismicity that occasionally precedes large earthquakes

pseudotachylytes generated during seismic faulting and eclogitization of the deep crust pseudotachylytes are typically interpreted to have formed by frictional melting during coseismic faulting within the upper to middle crust pseudotachylytes in the bergen arcs of western norway contain microlites including omphacite garnet plagioclase and quartz this eclogite facies assemblage is stable at temperatures of about 800 c and pressures of 18 to 19 kilobars corresponding to depths of 60 kilometers or more the pseudotachylytes are exposed in grenvillian granulites that locally underwent fluid induced eclogitization and corresponding volume reduction of approximately 10 percent during the caledonian continental collision the pseudotachylytes may have formed as a result of the rapid relaxation of stresses caused by the eclogitization process

origin of rutile needles in star garnet and implications for interpretation of inclusion textures in ultrahigh pressure metamorphic rocks the asterism effect of star garnet has been attributed to the oriented distribution of needle like rutile inclusions rutile needles occur in garnet from a wide range of metamorphic settings and rock bulk compositions and their origin has been ascribed to different mechanisms such as exsolution and used to interpret petrological and tectonic processes results from an optical and transmission electron microscopy of idaho star garnet indicate a co precipitation origin it was found that rutile needles are predominantly oriented along the rt grt and rt grt directions following multiple crystallographic orientation relationships cors i e cor 1 2 2 3 4 and 5 in 6 ray star garnet and are oriented solely along the rt grt directions following exclusively cor 2 in 4 ray star garnet the sole presence of cor 2 grt needles in the common 4 ray star garnet in contrast to the presence of both grt and grt needles with multiple cors in the rare 6 ray star garnet suggests that the cor 2 grt needle probably is the energetically most favoured variant as is also supported by the coincidence site lattice considerations the unique crystallography controlled microstructures of 4 ray star garnet including the cloudy domains behind the 111 grt or 100 grt fronts with abundant inclusions of rutile needle rutile compound needle and multiple phase inclusion as well as the clear domains behind the 110 grt fronts with only a few above inclusions concentrated exclusively within the linear grt oriented continuous tube like domains further suggest that the cor 2 grt needles in 4 ray star garnet most likely have a growth in origin co precipitating with garnet at its growth fronts close to thermodynamic equilibrium conditions the 6 ray star garnet on the other hand most likely formed under far from equilibrium conditions thereby yielding a maximum of 99 crystallographic variants of rutile needles with multiple cors in a single crystal in the light of these findings along with the common occurrences of the sole cor in many inclusion host systems owing to the requirement to minimize the energy barrier in an exsolution process the presence of both rt grt and rt grt needles with multiple cors in garnet of sulu eclogite and erzegebirge quartzofeldspathic rock would therefore cast doubt on the assertion of an exsolution origin of rutile needles in garnet from these ultrahigh pressure rocks