strain heating as a mechanism for partial melting and ultrahigh temperature metamorphism in convergent orogens implications of temperature dependent thermal diffusivity and rheology 1 we explore the importance of strain heating in ductile shear zones for production of leucogranites and high temperature metamorphism in collisional orogens with temperature dependent thermal diffusivity d and rock rheology new measurements on metamorphic rocks from the bohemian massif show that d is 1 3 mm2 s at 25 c and decreases exponentially to as low as 0 4 mm2 s at 600 c this temperature dependence causes model lithospheric geotherms to be straighter compared to geotherms calculated with a constant d using power law parameters for rheology we show that deformation of quartzite at strain rate of 3 10 13 s 1 produces 100 w m3 at 550 c and 7 w m3 at 800 c deformation of stronger clinopyroxenite at this strain rate produces 8 w m3 even at 1050 c when strain heating is introduced by a 3 km thick ductile shear zone with quartz rheology at the depth of 35 km in a lithosphere that has 70 km thick crust and 60 km thick lithospheric mantle the schist solidus is reached by 8 myr in the vicinity of the shear zone deforming at the strain rate of 3 10 13 s 1 for clinopyroxenite rheology ultrahigh temperature uht metamorphic conditions are reached in 40 myr after initiation of strain heating two dimensional models that replicate the exhumation of the greater himalaya crystalline rocks above the main central thrust produce extensive partial melting and an inverted metamorphic field gradient occurrences of leucogranites within crustal shear zone systems may be evidence of the coupling between deformation and heat production in the crust

strength and anisotropy of foliated rocks with varied mica contents abstract we have shortened 15 schists and gneisses with varying compositions 15 75 mica by volume at angles of 45 and 90 to foliation s to investigate the influence of micas on the strength and anisotropy of foliated rocks at the conditions tested t 25 c p c 200 mpa and e 10 5 s 1 compressive strengths vary by a factor 4 in the 45 and 90 orientations and individual rock types exhibit directional responses ranging from isotropic to strongly anisotropic trends of decreasing strength decreasing anisotropy and increasing ductility are observed with increasing mica content strains in all samples were localized within inclined shear zones accommodated by dislocation slip and grain scale microkinking in micas and microcracking in all other silicates stress strain response and grain scale deformation microstructures both indicate that mechanical behavior is strongly influenced by the concentration and spatial arrangement of micas shear zone formation is associated either with discrete brittle fracture transitional strain softening or steady strength ductile shear in both brittle and transitional samples extensive microcracking of strong quartzo feldspathic bridges occurs and stress drop magnitudes decrease with decreasing spacing and increasing overlap of adjacent critically oriented micas steady strength ductile shear zones develop in samples containing domains of interconnected micas and isotropic mechanical response is observed in those in which micas are contiguous in nearly all directions

fluid flow and volume loss during mylonitization an origin for phyllonite in an overthrust setting north carolina u s a abstract in the western blue ridge province of the southern appalachians north carolina granite gneisses are converted to phyllitic mylonites phyllonites along the base of the rector branch thrust sheet the mylonites show evidence for fluid infiltration and large volume losses with decreasing distance from the thrust and local shear zones feldspars undergo grain size reduction by cracking followed by chemical breakdown to muscovite sericite and zoisite the following reaction was important during mylonitization 3 k feldspar 2 h muscovite 2 k 6 sio 2 quartz displays evidence for dynamic recrystallization whereas feldspar deforms brittely which together with the secondary mineral assemblages suggest that deformation occurred at temperatures of between 300 c and 500 c in the presence of a fluid the mylonites are enriched by a factor of at least 2 5 in elements such as tio 2 p 2 o 5 zr y v la ce and depleted in sio 2 in comparison to their protolith gneisses the immobile element enrichments are attributed to enrichment in residual phases such as ilmenite zircon apatite and epidote in the mylonites and are interpreted as due to minimum volume losses of 60 mass balance calculations based on major element chemistry indicate the mylonites lost large amounts of sio 2 and smaller amounts of alkalies and were infiltrated by fluid rock weight ratios of between 10 2 and 10 3 phyllonitization as a process involves several deformation mechanisms including cataclasis and solution of feldspar as well as dislocation creep of quartz and micas reaction enhanced softening was apparently important in strain localization

dislocation interactions in experimentally deformed biotite abstract biotite single crystals shortened experimentally in orientations that maximize critical resolved shear stresses on 001 in directions 110 010 and 310 have been examined by transmission electron microscopy in all samples dislocations are confined to the basal plane with burgers vectors of 1 2 110 and 100 consistent with previous determinations of mica slip systems occasional partial dislocations that bound stacking faults form extended dislocations of these same systems typically dislocations are concentrated in complex arrays in local regions of the samples isolated or widely spaced dislocations are the exception within these arrays a variety of interactions between the dislocations are suggested by the geometrical arrangements of dislocations that cross over one another on parallel 001 planes sufficiently close together for elastic interaction and dislocations on the same 001 plane in networks and parallel arrays crossing dislocations of opposite sign on separate 001 planes form stable dipole segments where they overlap attractive and repulsive interactions between overlapping dislocations of like sign are evident as well dislocation networks occur in all samples and may exhibit a variety of complexly distorted geometries the spacing of dislocations in parallel arrays do not match models for standard dislocation pile ups consistent with observations showing these arrays involve dislocation multipoles the observed dislocation arrays and interactions resemble those reported for stage i easy glide deformation of fcc and hcp metals basal shear strengths are probably largely controlled by the development of multipoles and dislocations that pile up behind them

strain path partitioning within thrust sheets microstructural and petrofabric evidence from the moine thrust zone at loch eriboll northwest scotland abstract quartz c axis fabrics and microstructures have been investigated within a suite of quartzites collected from the loch eriboll area of the moine thrust zone and are used to interpret the detailed processes involved in fabric evolution the intensity of quartz c axis fabrics is directly proportional to the calculated strain magnitude a correlation is also established between the pattern of c axis fabrics and the calculated strain symmetry two kinematic domains are recognized within one of the studied thrust sheets which outcrops immediately beneath the moine thrust within the upper and central levels of the thrust sheet coaxial deformation is indicated by conjugate mutually interfering shear bands globular low strain detrital quartz grains whose c axes are aligned sub parallel to the principal finite shortening direction z and quartz c axis fabrics which are symmetric both in terms of skeletal outline and intensity distribution with respect to mylonitic foliation and lineation non coaxial deformation is indicated within the more intensely deformed and recrystallized quartzites located near the base of the thrust sheet by single sets of shear bands and c axis fabrics which are asymmetric with respect to foliation and lineation tectonic models offering possible explanations for the presence of kinematic strain path domains within thrust sheets are considered

salt crystallization in pores quantification and estimation of damage the objective of this study is to understand and predict the alteration of porous rock by crystallization of salts samples of different rocks have been tested according to the en 12370 standard test two parameters are proposed to evaluate the alteration of a rock during these tests the alteration index ai represents the cycle in which the first damages occur the alteration velocity av represents the alteration rate at the end of the experiment when the decay has become regular these parameters can be estimated with the help of a microstructural study of the rocks the most relevant intrinsic parameters of the stones for this estimation are capillary coefficient evaporation coefficient tensile strength and p waves velocity an evaluation of the alteration pattern is also proposed depending on the eventual heterogeneities and anisotropies of the rocks the influence of the dimension and shape of the samples is also discussed

effects of mica content on rock foliation strength abstract foliation is a planar geological structure characterized by the alignment of minerals including mica grains foliated metamorphic rocks exhibit anisotropic mechanical behaviors wherein the weakest properties are usually oriented parallel to the foliation planes rock mechanics research on this subject has been focused on characterizing the full anisotropic behaviors of rocks with stresses applied parallel oblique and perpendicular to the anisotropy direction foliation planes however less effort has been given to characterizing the mechanical behaviors of isolated foliation planes and describing the influences of mineralogical properties on the weaknesses associated with such geological structures this paper presents a laboratory testing program including direct shear tests and pull off tests to characterize the influences of mica content on the shear and tensile strengths of foliation planes of the biotite gneiss which is basically composed of biotite quartz and feldspar direct shear tests were performed under constant normal load and constant normal stiffness boundary conditions wherein the foliation planes were isolated in 1 cm thick shear zones the mica content was estimated by a practical digital image analysis approach that was capable of quantifying the percentage of biotite area on the foliation surfaces that failed in shear and tension the results showed that the mica e g biotite content had substantial effects on the mechanical behaviors of isolated foliation planes especially on the peak shear and tensile strengths a practical 3d strength envelope was proposed that included the mica content as an independent variable which can be quantified from foliation surfaces on rock blocks and outcrops the results provided new insights into the influences of mica rich foliation planes on the mechanical behaviors of metamorphic rocks which is directly applicable to rock engineering problems

experimental study of shear behavior of rock joints under constant normal stiffness conditions abstract the shear behavior of synthetic soft rock joints regular saw tooth was investigated in the laboratory under constant normal stiffness condition cns a large scale shear apparatus was designed and constructed which can test joints under both constant normal load cnl and cns conditions it is observed that cnl condition overestimates joint dilation compared to cns condition and thereby underestimates the peak shear stress of joints plot of shear stress against normal stress shows that a bilinear shear strength envelope is suitable for soft rock joints subjected to cnl conditions while linear or bilinear envelopes are acceptable for cns testing depending on the asperity angles the shear behavior of infilled joints was also investigated under cns conditions and it was found that a very small thickness of bentonite infill reduced the shear strength significantly the shear strength of joints almost approached that of pure infill when the infill thickness to asperity height ratio reached 1 60

investigations of soil cracking and preferential flow in a weighing lysimeter filled with cracking clay soil an improved understanding of deep drainage processes in irrigated cracking soils is needed for sustainable irrigation management to investigate the effect of crack dynamics and macropore flow on drainage in cracking soils a series of irrigation experiments was carried out in a weighing lysimeter subsurface soil cracks of the initially very dry soil were investigated with a videoscope and changes in the surface expression of cracks in response to irrigation events were monitored by time lapse photography a bromide tracer was applied to one irrigation event variations in the combined soil and moisture mass and the volume of drainage out of the soil column was logged and the drainage ec and bromide content were determined no drainage occurred out of the soil column during the first 3 out of 6 irrigation events even though substantial surface runoff into the cracks occurred and at least initially soil cracks provided an uninterrupted flow path through the profile the breakthrough of the bromide tracer as well as an initially low ec of the drainage water indicate that preferential flow accounted for a substantial part of the first of the two drainage events even though the soil cracks were sealed on the surface at the onset of the irrigation causing the drainage the results show that lateral infiltration of macropore flow into the soil matrix can be substantial and should not be neglected while simulating macropore flow and deep drainage in cracking soils the results also indicate that soil cracks can remain pathways for preferential flow even after they are closed at the soil surface the type of water application appears to have an impact on the location of crack formation with flood irrigation favouring reappearance of cracks at previous crack locations and simulated rainfall resulting in shifting crack locations

basal slip and mechanical anisotropy of biotite the basal slip systems of biotite and their mechanical expressions have been investigated by shortening single crystals oriented to maximize and minimize shear stresses on 001 samples loaded at 45 to 001 exhibit gentle external rotations associated with dislocation glide high angle kink bands in these samples unlike those developed in micas loaded parallel to 001 are limited to sample corners samples shortened perpendicular to 001 show no evidence of nonbasal slip and fail by fracture over all conditions tested the mechanical response of biotite shortened at 45 to 001 is nearly perfectly elastic plastic stress strain curves are characterized by a steep elastic slope a sharply defined yield point and continued deformation at low mostly 1 stresses measured beyond the yield point are insensitive to confining pressure over the range 200 to 500 mpa and exhibit weak dependencies upon strain rate and temperature assuming an exponential relationship between differential stress d and strain rate e of the form e cexp d exp q rt the data collected over strain rates and temperatures of 10 7 to 10 4 s 1 and 20 to 400 c respectively are best fit by an exponential constant of 0 41 0 08 mpa 1 and an activation energy q of 82 13 kj mol a power law fits the data equally well with n 18 4 and q 51 9 kj mol samples oriented favorably for slip in directions 100 and 110 are measurably weaker than those shortened at 45 to 010 and 310 consistent with the reported burgers vectors 100 1 2 110 and 1 2 110 the anisotropy of biotite is further revealed by contrasting these plastic strengths with results of samples deformed parallel and perpendicular to 001 previous studies have shown that biotite loaded in the 001 plane is strong prior to the nucleation of kink bands the strength of biotite shortened perpendicular to 001 exceeds that measured parallel to 001 and is pressure dependent application of the results to deformation within the continental crust suggests that biotite oriented favorably for slip is much weaker than most other silicates over a wide range of geologic conditions its presence within foliated rocks and shear zones may limit locally the stresses that can be supported

earthquake faulting as a structural process abstract structural geology is concerned with the history of movement in the earth s crust and the processes by which displacements occur in the upper one third to one half of deforming continental crust displacement is accommodated largely by seismic slip increments on existing faults it follows that earthquakes and related processes are an integral part of structural geology traditionally structural geologists have been preoccupied with the complexity of the finite deformation within fault zones and with the stress states prevailing at the initiation of faults in intact crust future structural work should be directed more towards understanding the dynamic character of fault reactivation during incremental slip and related effects questions of interest include rheological and geometrical controls on the initiation perturbation and termination of ruptures directivity effects associated with rupture propagation the recognition of structures resulting from repeated stress cycling within seismogenic crust and identification of structural features diagnostic of shear stress levels during faulting structures arising from the inter relationships between slip episodes and induced fluid flow are of special importance because these dynamic fault processes appear influential in the development of much fault hosted mineralization mesothermal gold quartz lodes hosted in high angle reverse shear zones of mixed brittle ductile character form illustrative examples of structures that arguably can only be interpreted by seismo structural analysis embodying the concepts listed above

displacement features associated with fault zones a comparison between observed examples and experimental models abstract fault zones commonly consist of discontinuous surfaces or are composed of different kinds of en echelon fractures tension cracks r or p type fractures which give the brittle shear zone a width translation along these faults and related features can occur by sliding on the elementary planes and or by solution deposition processes with opening of transtension zones and possible dilatation of the shear zone in order to understand how fault planes develop and to investigate the mechanical conditions corresponding to natural configurations displacement along an analogue fault model was examined under conditions of direct shear the experimental fracture patterns were then compared with the natural features the structural elements of certain faults created by testing and showing transpression and transtension zones were found to be similar to natural domino structures bounded by elementary shears and could be compared with computed situations it can be inferred that stresses are reoriented inside the shear zone the angle between elementary fractures depends on their order of development transpression and transtension zones occur systematically and the shear zone undergoes dilatancy under low normal stresses

feldspar influenced rock rheologies progressive fracture subsequent cataclasis and syntectonic alteration of feldspar to phyllosilicates transformed a massive granite into a quartz mica phyllonite during early tertiary deformation in a 20 30 m wide shear zone in southeastern arizona the ductile deformation proceeded at temperatures and pressures approximating middle to upper crustal levels most of the deformation was taken up by the feldspar and its alteration products quartz deformed by both brittle fracture and crystal plastic mechanisms these results show that under certain temperature pressure strain rate conditions feldspars are weaker than quartz the observed deformation mechanisms indicate that the brittle to ductile transition in fault zones is not simply a function of the onset of temperature activated plastic deformation in quartz nor of the frictional behavior of rocks as inferred in the familiar strength vs depth curves it is more likely that the transition is complex and depends on a variety of parameters one such factor delineated in this study is the fracture and fracture facilitated syntectonic alteration of feldspar under hydrated conditions

hillslope run off thresholds with shrink swell clay soils irrigation experiments on 12 instrumented field plots were used to assess the impact of dynamic soil crack networks on infiltration and run off during applications of intensity similar to a heavy rainstorm water was seen being preferentially delivered within the soil profile however run off was not observed until soil water content of the profile reached field capacity and the apertures of surface connected cracks had closed 60 electrical resistivity measurements suggested that subsurface cracks persisted and enhanced lateral transport even in wet conditions likewise single ring infiltration measurements taken before and after irrigation indicated that infiltration remained an important component of the water budget at high soil water content values despite apparent surface sealing overall although the wetting and sealing of the soil profile showed considerable complexity an emergent property at the hillslope scale was observed all of the plots demonstrated a strikingly similar threshold run off response to the cumulative precipitation amount copyright 2014 john wiley sons ltd

estimation of the moisture supply capacity of some swelling clay soils in the netherlands abstract the growing season in the netherlands is characterized by a precipitation deficit evapotranspiration surplus in most years optimal crop development requires therefore moisture supply by the soil in addition to natural rainfall moisture can either be supplied as available water from the root zone or as an upward flux from the water table towards the root zone a computer model was used to simulate soil moisture regimes of a swelling clay soil the model uses thickness of the root zone hydraulic conductivity and moisture retention data for the soil horizons and needs depth to water table and climatic data as boundary conditions existing flow theory does not describe flow of water in swelling clay soils where dessiccation is associated with the formation of both vertical and horizontal cracks in the soil cracks strongly influence the flow regime by reducing upward fluxes to the root zone horizontal cracks and by inducing rapid downward flow of water along vertical cracks short circuiting a field technique is used which allows an estimate of the effective reduction of the hydraulic conductivity due to horizontal crack formation this reduction is a function of the pressure head the amount of short circuiting was estimated by analysing the occurrence of heavy and very heavy rains over a 30 year period since these rains are likely to partly bypass the root zone short circuiting effectively increases the precipitation deficit the simulation model was experimentally validated using field data for the growing season of 1979 calculated moisture conditions in the soil agreed only with those that were measured in situ when the effects of both horizontal and vertical cracking were considered additional runs with the validated model were made using statistically expressed climatic data and selected water table levels results allow an estimate of the amount of water which needs to be supplied to the soils so as to achieve potential evapotranspiration

deformation of two phase systems with contrasting rheologies abstract rheological model experiments are used as analogues for foliation development in quartz mica rocks in a regime of pure shear in situ observations involving ice containing varying proportions and distributions of naphthalene and camphor illustrated two contrasting types of behaviour a matrix controlled versus a particle controlled deformation the matrix controlled deformation accommodates shortening predominantly by intracrystalline slip in the ice accompanied by some recrystallization while the more rigid naphthalene plates undergo rotation and mechanical alignment where shortening is normal to an initial platelet preferred orientation the foliation is enhanced and the matrix material aggregates between the rigid plates whereas a conjugate foliation is produced during shortening parallel to an initial platelet preferred orientation during particle controlled deformation strain is localized in particle concentrates the matrix areas and particles isolated in the matrix show little deformation at shortenings 10 dissolution of selected particles is achieved through an artificial fluid transport mechanism to create voids further shortening does not create closure of the fluid filled holes where shape is supported by the rigid matrix

deformation mechanisms in granitic rocks at shallow crustal levels abstract microstructural observations of naturally faulted granitic gneisses show that feldspar grains are weaker than quartz grains at temperatures below 325 c and at depths of less than 8 10 km feldspar grains sustained most of the deformation by grain scale faulting slip along cleavage controlled fractures and cataclasis fracture of feldspar grains within fault zones promoted their alteration to kaolinite quartz grains also deformed by fracturing and often healed to form quartz porphyroclasts and mosaics in a comminuted matrix of feldspar and kaolinite syntectonic alteration of the feldspar grains may have weakened the fault zones over time and resulted in foliated textures within the fault zones this study of naturally deformed rocks confirms published experimental results on the behavior of granitic rocks at low temperatures and pressures and taken together these data show that the theology of the upper 10 km of the crust is greatly influenced by cataclastic processes in feldspar

dilatancy brittle strength and anisotropy of foliated rocks experimental deformation and micromechanical modeling 1 triaxial compression experiments were performed on the four mile gneiss the biotite foliation in the four mile gneiss results in dilatancy and strength anisotropies which become more pronounced with increasing confining pressure microstructural observations indicate that when there is high resolved shear stress on the macroscopic foliation dilatancy arises from extensile microcracks nucleated by frictional slip on biotite grains evolution of crack geometry and coalescence are also influenced by the biotite foliation motivated by these observations a damage mechanics model based on sliding wing cracks was adopted to analyze the anisotropic development of dilatancy and brittle fracture frictional coefficients for the sliding cracks are inferred to be comparable to those of cleavage surfaces of biotite the strength anisotropy data of the four mile gneiss can be explained by the variation of the initial damage with the foliation angle the damage derives from a set of preexisting microcracks with random orientation and a set of cleavage cracks in mica grains preferentially oriented along the foliation angle hence the initial damage is higher for the intermediate angles and consequently the strength is somewhat lower the observation that the mechanical strengths of a variety of foliated rocks decrease with increasing mica content can be explained by the same model with the implication that the initial damage and mica content are linearly related the mechanical and microstructural data show that dilatancy anisotropy may significantly influence the progressive development of borehole breakout and strain localization

a field method for measuring short circuiting in clay soils abstract a field method is described for measurement of short circuiting which is defined as vertical flow of free water along the walls of continuous macropores in unsaturated soil a cylinder with a diameter and height of 20 cm is filled with undisturbed surface soil and is placed on a perforated disk in a funnel the funnel is supported to allow periodic measurement of the volume of outflow from the soil the assembly is placed along the track of a spray gun which is commonly used for sprinkling irrigation at least four samples can be measured during one run the method is illustrated by discussing the measured short circuiting in surface soils of 1 a heavy clay soil 2 a light clay soil with two different types of structure in and adjacent to potato ridges and 3 a heavy clay soil with two types of surface microrelief short circuiting is unfavourable because water moves rapidly beyond the root zone without moistening and leaching the soil between the macropores the water may carry surface applied fertilizers

kinks in mica role of dislocations and 001 cleavage abstract kinking in natural and experimentally deformed biotite and muscovite has been investigated by transmission electron microscopy tem it is found that complex microstructures exist in the vicinity of kink band boundaries kbbs gentle bending of 001 planes plays an important role in the kinking process where 001 planes are bent several degrees edge dislocations are observed in complex walls between active slip planes together with broad bands of dislocations parallel to 001 microfracturing and dilation occur parallel to 001 planes and the kbb a model is presented to explain the origin of observed kbbs which may be applicable to other crystalline materials with only one active slip plane

the rheology of polymineralic rocks an approach deduced from empirical and theoretical work a model is proposed for the rheology of bi and polyphase rocks based on the rheology of the components their volume fractions and their geometrical distribution the model is formulated for the common case where some minerals deform by crystall plasticity at steady state and others stronger ones deform in the vincinity of the brittle ductile transition

high temperature plastic deformation of quartz plagioclase multilayers by layer normal compression it is a common practice in rheological modeling to take the extrapolated compressive flow strengths of quartzite and plagioclase rock as the bulk flow strengths of the upper and lower continental crusts respectively such a practice implies that the bulk flow strength of polyphase rocks is identical to that of the pure weak phase to test this assumption we performed deformation experiments on synthetic layered and particulate quartz anorthite 50 50 composites and aggregates of the end members in a paterson gas medium apparatus at a confining pressure of 300 mpa a constant strain rate of 10 5 s 1 and temperatures from 1273 to 1473 k under these conditions anorthite deforms by recrystallization accommodated dislocation creep while quartz is semibrittle electron backscatter diffraction measurements show a strong lattice preferred orientation lpo of anorthite developed in deformed specimens and the lpo pattern is interpreted as a result of dislocation slip on the 010 100 system our experimental results show that the bulk flow strength of layered composites increases with decreasing thickness of the layers thinlayered composites are significantly stronger than pure anorthite aggregates and a homogeneous quartz anorthite mixture i e particulate composites with the same modal composition but weaker than pure quartz aggregates our experimental results together with the theoretical overview presented previously in the materials science literature demonstrate that 1 compressive flow strength of a polyphase rock cannot be represented by that of the weak phase and 2 thin layered rocks compressed normal to the layering are rheologically stronger than homogeneous isotropic mixtures under the same deformation conditions thus weak phase based rheology will lead to an underestimation of the bulk flow strength of the continental crust in which polyphase rocks dominate

on the origin of rock fragment mulches on vertisols a case study from the ethiopian highlands abstract many vertisols in tigray ethiopia typically carry a discontinuous rock fragment rf size 0 5 40 10 2 m cover with 10 to 100 rfs m 2 such rf mulches are of agricultural and environmental significance because they influence the water balance in the underlying soils and the crop yield natural rf concentrations are mostly considered as eolian or hydraulic lag deposits or as the result of lateral transport over the soil surface from a rock outcrop upslope in cultivated areas rf mulches can develop by tillage this paper presents the case of a natural rf mulch whose lithology indicates that the rfs are up squeezed by the local vertisol the study site is located in the pass of enda maryam tigray northern ethiopia 39 8 e and 13 36 n a circular area of 10 m diameter about 200 m away from the water divide in the valley has been cleared annually between 01 1999 and 05 2003 during this period 625 rfs 17 being 7 5 10 2 m in size totalling a mass of nearly 62 kg have been collected after correction for measurement procedures the rate of rf up warping by the vertisol at enda maryam is assessed at 5 rfs m 2 in 3 years at this rate of appearance the formation of current rf concentrations on top of active valley vertisols is only a matter of 10 1 2 years provided the availability of rfs below the soil surface although important underground displacements were measured in the vertisol between 01 1999 and 05 2002 the supposed link between up squeezing of rfs and plastic deformations of chimney diapir or intrusion like type in the vertisol could not be evidenced instead rfs are clearly concentrated on the soil surface as well as in depth along the existing vertical desiccation cracks often 1 m deep which display polygonal configurations at the soil surface further bundles of slickensides containing some rfs have been mapped at the base of the vertisol the slickenside configuration suggests that the rf bearing substrate is being scraped off while the underground displacement of rfs along active slickensides seems normal the process of rfs ascending in upright position in the edge of desiccation cracks needs explanation the closure of a desiccation crack is a peristaltic like movement following ascent or descent of the capillary fringe it is hypothesized that this movement gradually pushes the rf to the surface or to another place or level in the soil profile where the crack closes in last instance the apparent young age of the valley vertisol mulches in ethiopia might indicate the very recent formation of yearly recurrent desiccation cracks of vertisols in the area available information confirms that most valleys in the study area used to be perennially marshy under these conditions no movements of rfs in the soil profile are expected to occur gullying leading to pronounced seasonal desiccation of the vertisols started in several cases not more than 50 years ago

field data and flow system response in clay vertisol shale terrain north central texas usa the water budget in clay shale terrain is controlled by a complex interaction between the vertisol soil layer the underlying fractured rock land use topography and seasonal trends in rainfall and evapotranspiration rainfall runoff lateral flow soil moisture and groundwater levels were monitored over an annual recharge cycle four phases of soil aquifer response were noted over the study period 1 dry season cracking of soils 2 runoff initiation lateral flow and aquifer recharge 3 crack closure and down slope movement of subsurface water with surface seepage 4 a drying phase surface flow predominated within the watershed 25 of rainfall but lateral flow through the soil zone continued for most of the year and contributed 11 of stream flow through surface seepage actual flow through the fractured shale makes up a small fraction of the water budget but does appear to influence surface seepage by its effect on valley bottom storage when the valley soil storage is full lateral flow exits onto the valley bottom surface as seasonal seeps well response varied with depth and hillslope position flowtube model results and regional recharge estimates are consistent with an aquifer recharge of 1 6 of annual precipitation calculated from well heights and specific yield of the shale aquifer copyright 2005 john wiley sons ltd

grain size sensitive deformation of upper greenschist to lower amphibolite facies metacherts from a low p high t metamorphic belt abstract to identify the dominant deformation mechanism in continental middle crust at an arc trench system we used an sem ebsd system to measure the lattice preferred orientations of quartz grains in fine grained metachert from the low grade chlorite and chlorite biotite zones part of the low p high t ryoke metamorphic belt sw japan quartz c axis fabrics show no distinct patterns related to dislocation creep although the strain magnitudes estimated based on deformed radiolarian fossils are high enough that a distinct fabric might be expected to have formed during deformation fabric intensities are very low indicating a random distribution of quartz c axes quartz grains are equant in shape and polygonal and free of intracrystalline plasticity these observations suggest that the dominant deformation mechanism in the metacherts was grain size sensitive flow diffusion creep accompanied by grain boundary sliding rather than dislocation creep possibly reflecting the relatively low strain rate or low flow stress compared with that in high strain zones the development of grain size sensitive flow in metamorphic tectonites at mid crustal conditions would result in a significant decrease of the rocks strength of the continental middle crust

the origin of vertisols and their relationship to acid sulfate soils in the senegal valley in the senegal valley it is commonly considered that the acid sulfate soils of the delta are fossil soils overlain by more recent sediments and that the vertisols which abruptly overlie a thick sandy horizon result from a change in the sedimentation mode of the river however we show that both soils belong to the same pedological system extending from the delta to the limit of the last marine transgression this conclusion is based on 1 the study of soil profiles intermediate between acid sulfate soils and vertisols along a 100 m sequence in the delta 2 the mineralogy of the clay fraction 2 am in a 200 km transect along the river and 3 the similarity of the sand size distribution across the textural discontinuity between the horizons the following processes are involved in the pedological transformations 1 development of acidity by oxidation of pyrite 2 neutralization of acidity initially by the carbonate in shell beds and later by the hydrolysis of easily weatherable silicate clays the slightly alkaline river water precipitates kaolinite and later smectite at the contact between the strongly acidic and slightly alkaline environments this results in the formation of a superficial vertic clay horizon surmounting a sandy horizon therefore we emphasize that the soil morphology results from development and control of acidity and not from changes in past climates

analogies between the high temperature deformation of polyphase rocks and the mechanical behavior of porous powder metal abstract in some rock types one or more mechanically similar minerals may constitute a loadcarrying framework while other subordinate phases carry little load if incompetent phases are more than one or two orders of magnitude weaker than the competent phases the load carrying framework behaves much like a porous solid the deformational properties of porous powder metal provide analogies for the deformation of such porous like rock types 1 the yield strength of porous powder metal is analogous to the power law flow stress for rock deformed at high temperatures 2 the correspondence principle relating elastic and viscoelastic deformation may be used to relate the young s modulus of porous powder metals to the flow stress for nabarro herring creep in rock where the incompetent fraction is 15 of the rock there should be a 50 reduction in power law flow stress for an incompetent fraction of 40 the power law stress is reduced by an order of magnitude and the nabarro herring creep stress is reduced by 80

origin of reflections from the brevard fault zone the brevard fault zone is a belt of mylonitic metamorphic rocks that extends northeast over 700 km from alabama into virginia seismic reflection studies show that the fault zone produces excellent reflections which dip gently to the southeast and sole at depth the origin of these reflections has been investigated by measuring compressional wave velocities to 800 mpa confining pressure in 127 samples obtained from drill core which continuously sampled the fault zone to a depth of over 300 m densities are reported as well as chemical analyses at selected depths anisotropy at elevated pressures ranges within the fault zone from less than 5 to over 26 similarly the fault zone rocks show significant chemical variability with sio2 ranging from 58 0 to 70 4 by weight synthetic seismograms generated from the velocity and density measurements show that the reflections originate within the brevard fault zone from the complex interaction of compositional variations and seismic anisotropy resulting from ductile strain essential to this study has been the continuous coring of a major section of the brevard fault zone which has provided the necessary stratigraphic control as well as unweathered samples for laboratory studies

shrink swell behavior of soil across a vertisol catena summary an accurate estimate of the degree of soil cracking is important in partitioning rainfall into soil infiltration and runoff in watersheds with clay soils that shrink and swell usually in the application of surface hydrology models cracking is considered to be predicted by assuming equidimensional shrinkage and a 1 3 ratio of change in soil profile thickness to depth of water loss our objective was to use in situ measurements of soil profile subsidence with loss of water in an apparently uniform vertisol to determine 1 whether or not the soil profile subsidence followed the 1 3 ratio of change in thickness to depth of water loss and 2 how the ratio of subsidence to water loss varies with the coefficient of linear extensibility cole the research was conducted on a catena of houston black and heiden clays vertical soil shrinkage and swelling along with soil water content were measured at the summit shoulder backslope and footslope positions of the catena change in soil water content along with spatial variability in cole were the primary drivers of temporal and spatial variability of shrinkage and swelling on the catena the rate that soil shrank or swelled with change in the amount of water stored in the soil was related to cole which was negatively correlated with carbonate content of the soil shrinkage of the soil profile with water lost was less than the commonly used 1 3 ratio our data supported using cole to predict the degree to which the ratio is less than 1 3 incorporating cole values into a hydrology model to simulate soil shrinkage with water loss is a useful approach because cole values have been measured for soils with shrink swell potential and that data is available in usda nrcs soil survey databases

experimental investigation into the microstructural and mechanical evolution of phyllosilicate bearing fault rock under conditions favouring pressure solution abstract mature crustal fault zones are known to be zones of persistent weakness this weakness is believed to result from microstructural modifications during deformation such as grain size reduction and foliation development around the brittle ductile transition phyllosilicates are expected to have a significant effect on fault strength in particular under conditions favouring pressure solution to study such effects we performed rotary shear experiments on brine saturated halite kaolinite mixtures aimed at investigating the relation between microstructural and mechanical evolution in a system where pressure solution and cataclasis dominate the results show significant strain weakening and a transition with progressive strain towards more rate sensitive and less normal stress sensitive behaviour this was accompanied by a microstructural evolution from a purely cataclastic microstructure to a mylonitic microstructure consisting of elongate asymmetric clasts in a fine grained foliated matrix the results demonstrate that strain weakening and the development of a typical mylonitic microstructure can occur as a consequence of grain size reduction by cataclasis and a transition to pressure solution accommodated deformation even in the absence of dislocation creep the data raise questions regarding the reliability of microstructures as rheology indicators as well as on the use of low strain monomineralic flow laws for modelling crustal dynamics

variation of schmidt hammer values with imbrication direction in clastic sedimentary rocks abstract in this study schmidt hammer rebound hr values of clast supported conglomerates matrix supported conglomerates and normally graded gravelly sandstones were measured to investigate the effect of such anisotropy on strength the highest schmidt hr values were obtained from the gravelly sandstones with an average value of 39 decreasing with gravel content in clast supported conglomerates the average hr values were 34 and 38 parallel and perpendicular to the palaeocurrent direction respectively similar measurements were also made over the matrix supported conglomerates average hr values of matrix supported conglomerates were determined as 37 and 41 parallel and perpendicular to the palaeocurrent direction respectively in the clast supported conglomerates average hr value on perpendicular palaeocurrent side was 12 higher than those parallel to palaeocurrent this ratio was 9 for matrix supported conglomerates preferred orientation or clast imbrication creates more gravelly and less matrix covered area parallel to the palaeocurrent than the other directions this visible difference in the gravel matrix ratio is considered to be the basis of the strength anisotropy in clastic sedimentary rocks this study demonstrates the potential of the schmidt hammer for quantifying the degree of anisotropy in such rocks

the effect of composition and strain on quartz fabric intensity in pebbles from a deformed conglomerate twenty eight quartz c axis fabrics from individual pebbles from a single outcrop of deformed conglomerate have been measured these pebbles vary in composition and have undergone different amounts of strain contrary to expectations based on published results of computer simulated deformation by intracrystalline slip of pure quartzites it is observed that fabrics are not stronger in the more highly deformed pebbles instead the fabric strength is related to the quartz content of the pebbles pure quartzites show the strongest fabrics as the percentage of non quartz minerals increases up to 25 the strength of the fabrics rapidly decreases though the influence of composition becomes less marked when impurities exceed 25 these observations can be explained if the deformation of the impure quartzites included a contribution from a non intracrystalline mechanism such as grain boundary sliding

experimental deformation of muscovite abstract the strength and mechanical anisotropy of muscovite have been investigated by shortening single crystals at 45 0 and 90 to the basal plane 001 at temperatures t from 20 to 400 c confining pressures pc from 10 to 400 mpa and strain rates e from 2 5 10 7 to 2 3 10 4 s 1 samples deformed as 45 to 001 exhibit smooth undulatory extinction in thin section associated with dislocation glide with few well developed low angle kink boundaries basal shear strengths depend on confining pressure at pc e a exp a exp q rt results from temperature and strain rate stepping experiments performed at pc 200 mpa yield an activation energy q of 47 19 kj mol 1 and an exponential constant a of 0 5 0 2 mpa 1 samples loaded parallel to the basal plane shorten by the development of sharply defined kink bands strengths associated with kink band formation are higher than those associated with glide in samples compressed at 45 to 001 and exhibit significant pressure dependence 0 8 up to confining pressures of 200 mpa kink bands are generated at the ends of samples where contact is made with the pistons samples loaded at 90 to 001 are much stronger than samples of all other orientations and deformation is accomplished by fracture fracture strengths exhibit a strong dependence on confining pressure 0 9 similar in magnitude to other silicates that are brittle at the same conditions by comparison with biotite muscovite is weaker in shear on 001 at the experimental conditions tested with an activation energy for glide q that is significantly smaller than that for glide in biotite

first results regarding the influence of mineralogy on the mechanical properties of seafloor massive sulfide samples abstract seafloor massive sulfides sms are increasingly accepted as important marine raw material resources for the future in particular because of their polymetallic character many industrial nations are researching not only on the scientific importance of these deposits but also on their economic value regarding the current state of the international exploration mainly two dimensional surface close observations are accessible whereas only some core data and measurements are publicly available to date in fact there are few successful drilling campaigns containing information about the size and shape which also give information on the structure and content of modern massive sulfide ore bodies in their third dimension regarding the mechanical properties of sms samples only few data are available geotechnical data of these deposits are important in order to develop an efficient mining technology for exploitation in this research 12 sms samples from two different locations were investigated based on the mineralogical characterization of the studied samples the geotechnical properties were preliminary correlated with the mineralogical results the comparative study indicates how far the geotechnical data are controlled by mineral type and composition including the porosity a regression relation between compressive strength and the porosity based on the mineralogy shows a distinct relation between these parameters therefore the geomechanical and mineralogical features have a strong importance for deep sea mining applications and this should be kept in mind considering the hyperbaric effects on the rock cutting

water movement and soil swelling in a dry cracked vertisol abstract vertisols are widely used for irrigated rice in the senegal river basin where farmers are increasingly reporting problems with soil salinization water movement at the onset of the growing season when soils are dry and cracked may have a large impact on soil salinity and water economy water movement and soil swelling processes were studied in a dry cracked vertisol in the senegal river valley surface irrigation and simulated rainfall intensity 88 mm h 1 on cracked 2 25 m 2 plots crack width 0 01 0 02 m crack depth 0 3 m resulted in crack closure within 4 5 h starting at the soil surface soil swelling was separated into two components 1 swelling of the 0 01 0 02 m border zone of a soil island soil mass distinctively separated by cracks and 2 swelling of the rest of the soil island as a whole soil swelling was heterogeneous with a very rapid expansion of the border zone at the moment of crack closure the relative contributions of these two components to crack closure were respectively 80 90 and 10 20 24 h later these percentages changed slightly only maximum bulk linear shrinkage determined at the field level was only 7 results indicate the importance of rapid local heterogeneous swelling processes to water flow into cracked vertisol resulting in limited bypass flow use of bulk shrinkage curves and assumptions on isotropy of shrinkage and swelling processes when modelling water and solute flow in cracked vertisols should therefore be done with great care

strain discontinuities within the seve koli nappe complex scandinavian caledonides this paper utilizes the results of a regional survey of the state of finite strain carried out in an area built up of stacked thrust sheets to draw conclusions about the relative timing of penetrative deformation and thrust motion and to place constraints on the deformation models devised to explain the geometry of the individual thrust sheets a strain survey within the seve koli nappe complex reveals abrupt changes which represent discontinuities in the strain pattern one of these discontinuities coincides with the boundary between the seve and koli nappes and separates intense transversal stretching strain within the seve nappe from the longitudinal strains of lower intensity within the koli nappe the weight of geological evidence favours the interpretation of this strain discontinuity as a unconformity with significant deformation of the seve nappe occurring before rocks of the overlying koli nappe were deposited middle ordovician a second discontinuity marks the junction between the krutfjell nappe and the underlying lower grade koli rocks the strain distribution is incompatible with a previous interpretation of the discontinuous krutfjell nappe as a string of mega boudins an interpretation which implies considerable post thrust flattening of the nappe pile the strain results and other evidence favour earlier deformation of the krutfjell nappe before these rocks were thrust over the underlying tectonic units the lens shaped outcrop configuration of the krutfjell nappe is explicable in some cases if the geometry of this nappe is a westerly thinning wedge within the low grade koli nappe rocks north of the grong culmination the longitudinal stretching is difficult to explain in terms of easterly directed nappe movements whereas the clear transverse strains in other tectonic units appear to predate the main silurian thrusting event

quartz preferred orientations within a deformed pebble conglomerate from new hampshire u s a abstract the orientations of quartz c axes within a deformed pebble conglomerate from piermont new hampshire have been measured and compared to finite strain estimates for both the pebbles and the surrounding matrix quartz grains within the relatively pure orthoquartzite pebbles show a strong c axis preferred orientation while quartz grains within the matrix show a random distribution of c axes comparisons of the preferred orientation of the pebbles with computer simulated fabrics of lister and hobbs 1980 yield estimates of the principal finite strains i 1 00 0 00 0 50 which are consistent with previous strain estimates rumble and oertel 1979 derived from the pebble shapes 1 22 0 13 0 48 the random c axis pattern within the matrix however is inconsistent with the strain estimates derived from fabric analysis of matrix phyllosilicates using the march model while it is believed that intracrystalline slip of quartz was as prevalent in the matrix as in the pebbles the presence of phyllosilicates in the matrix appears to have prevented the development of a quartz preferred orientation it is proposed that slip and or grain boundary sliding of phyllosilicates in the matrix may have been responsible for quartz grain rotations which were random with respect to quartz c axes

physical modeling of an underground roadway excavation in geologically 45 inclined rock using infrared thermography abstract physical modeling of excavation of a roadway tunnel in the geologically 45 inclined rock strata by using a newly developed physical modeling approach the so called physically finite elemental slab assemblage pfesa together with infrared ir thermography were conducted for visualization and observation of the progressive development of the excavation damaged zone edz the excavation was schemed as two phases i e phase 1 the full face excavation and phase 2 the staged excavation the experiment was performed under unbalanced confinement found in underground coal mining the relative temperatures of the excavation zone were mapped by the ir camera in real time and over the entire field into thermography series which were processed using such procedures as statistics noise removal and spectral frequency analysis for image feature extraction irt defined as the statistical mean of the thermography matrix was used as a measure of rock responses characterizing the full face excavation and the staged excavation as a multi linearity and nonlinearity processes respectively by its time marching scheme the temporal and spatial evolutions of the edz were described in detail by the denoised thermographies directional propagations of the excavation induced stress wave were characterized by the spectral frequency analysis of the resultant thermographies

texture development in experimentally deformed two phase aggregates of calcite and anhydrite abstract fully quantitative textures have been measured from experimentally deformed two phase aggregates of calcite and anhydrite two sets of deformation experiments were performed firstly to investigate the development of microstructure and texture with composition samples with varying volume proportions of calcite and anhydrite were deformed to 20 strain at identical conditions secondly to study the texture development of the two materials with strain and explore the possible use of texture index as a strain gauge in polyphase materials pure calcite and pure anhydrite were deformed at the same conditions as the two phase rocks to strains of 6 12 and 20 the textures in both calcite and anhydrite were found to be similar but not identical to those reported in previous studies for pure samples our experimental investigations and measured textures show that the textures both of the pure materials and of the two phase rocks depend not only on strain but also on stress and grain size through their influence on the deformation mechanisms the dependence of texture index with change in deformation mechanism is particularly pronounced in the anhydrite component where the texture index decreases with grain size which decreases with anhydrite content the texture in the pure calcite and in the calcite component of the two phase rocks was influenced by a preexisting fabric the intensity of the texture in the deformed samples seems to correlate with the stress in the calcite rather than with strain

engineering geological and geotechnical responses of schistose rocks from dam project areas in india abstract for a rational and safer design of civil and mining engineering structures in or on rocks a proper understanding of the quality of rock mass is required to assess the rock mass quality evaluation of physical and mechanical characteristics of the intact rocks is essential especially if the rock is anisotropic in nature the genetic complexity associated with its petrofabric makes it more difficult to predict its behaviour in this paper a comprehensive study of the compositional physical and geotechnical responses of four varieties of schists i e quartzitic chlorite quartz mica and biotite schists obtained from two hydroelectrical project sites in the foot hills of himalayas india has been presented anisotropic strength behaviour of the schists has been brought out through the testing of specimens with varying orientation of schistosity with respect to the major principal stress under uniaxial and triaxial conditions the significance of anisotropic response for consideration in the design is emphasized

phase boundary mobility in naturally deformed high grade quartzofeldspathic rocks evidence for diffusional creep abstract grain shape fabrics and optical microstructures of some quartzofeldspathic rocks deformed under upper amphibolite facies conditions in the southwestern grenville province ontario canada suggest that quartz and feldspar have accommodated intracrystalline plastic strains by both diffusional and dislocation creep in these rocks quartz and feldspar form polycrystalline domains separated by gently curved and locally cuspate phase boundaries whose morphology is similar in certain respects to the phase boundary morphology of rocks annealed experimentally under hydrostatic stress conditions in the naturally deformed rocks however phase boundary cusps consistently point along the foliation and parallel to the mineral fibre lineation i e in directions of inferred finite extension which implies that phase boundary motion and cusp formation occurred during deformation optical microstructures in feldspar and crystallographic preferred orientations in quartz are consistent with the accommodation of some intracrystalline plastic strains by dislocation creep however the morphology of quartz feldspar phase boundaries cannot be explained by either dislocation creep or static annealing alone we propose that phase boundary motion resulted from a diffusion assisted process involving dissolution at foliation parallel quartz feldspar phase boundaries mass transfer over length scales of the order of feldspar domain size 200 m or greater and precipitation at quartz feldspar phase boundary cusps this study extends the range of natural deformation conditions under which diffusional creep has been identified in quartzofeldspathic rocks it also has important implications for the natural rheological behavior of the mid and lower continental crust

deformation of biotite and muscovite tem microstructure and deformation model abstract growth and deformation defects have been observed in 1m and 2m 1 biotites and 2m 1 muscovites using transmission electron microscope tem techniques these have been related to optical observations in deformed biotite the dislocation density increases as the strain increases the density of stacking faults also increases with strain the spatial ordering of stacking faults decreases as the strain increases in muscovites selected from the same areas as the biotites stacking fault and dislocation densities show little or no variation with deformation the different responses of biotite and muscovite to deformation are explained in part by the physical and chemical differences between 1m biotite and 2m 1 muscovite there is strong evidence in both the biotites and muscovites that stacking faults may be result of deformation as well as a crystal growth process the grain size of the deformed mica aggregates is reduced by the nucleation of new micas there is also evidence for a grain size reduction mechanism segmentation in biotites this mechanism appears to achieve the same result as recovery recrystallization mechanisms but not by the same method segmentation may be a mechanism which is favoured in strongly anisotropic minerals with a limited number of slip systems a model is proposed that attempts to correlate response of the biotite to deformation the deformation is synchronous with and post dates the nucleation of the new metamorphic micas

the movement of water through cores of a dry cracked clay loam grassland topsoil abstract water bypassed the soil matrix through cracks and other large voids when applied to cores of dry cracked clay loam grassland topsoil at rates in excess of 2 2 mm hr 1 the bypassing ratio increased from 0 to 0 55 as the application rate rose from 2 2 to 21 2 mm hr 1 it was estimated that 10 20 of rainfall bypassed the top 0 09 m of a grassland soil at wytham near oxford england during periods of summer soil moisture deficit

rheology and deformation mechanisms of an isotropic mica schist we have investigated the transitional semibrittle deformation of a mica schist 75 biotite by shortening cylinders cored at 0 45 and 90 to foliation to varying strains at confining pressures pc to 500 mpa constant strain rates e from 1 5 10 7 to 1 6 10 4 s 1 and temperatures t from 25 to 400 c deformation is concentrated within one or more throughgoing millimeter wide shear zones at all conditions these localize at low strains e 2 through the nucleation and coalescence of dense sets of intragranular microkink bands mkbs despite distinct differences in the relative number of mica grains oriented favorably for slip and kinking in different loading directions the differential stresses required for shear zone development vary little with fabric orientation biotite schist undergoes a transition from strain softening to steady strength mechanical response at confining pressures in the range 75 to 150 mpa the pressure sensitivity of strength characterized by the slope of the mohr envelope decreases from 0 5 at pc 100 mpa to 0 1 at pressures greater than 200 mpa reflecting the increasing contribution of glide and kinking in biotite at higher pressures however dilatancy associated with microcracking and void formation along mkb boundaries persists to at least 500 mpa within the pressure insensitive regime 200 pc 500 mpa temperature and strain rate dependencies of strength determined in stepping tests reveal a strong history dependence to flow that cannot strictly be described by a steady state constitutive law samples deformed in steps from low to high temperatures or fast to slow strain rates consistently exhibit stronger temperature and strain rate sensitivities than those deformed along t decreasing or e increasing paths path dependent effects may reflect differences in the degree to which inherited dislocation substructures are utilized or overprinted during later deformation increments by assuming an exponential relationship between differential stress d and strain rate e of the form e c exp d exp q rt we fit the data with two end member flow laws with a single activation energy q 89 kj mol and exponential constants ss 0 15 0 01 mpa 1 and ws 0 55 0 04 mpa 1 that account for the different responses observed along stepping paths that are strongly sensitive or weakly sensitive to t and e respectively application of the results to crustal deformation suggests that mica rich aggregates are weaker than other common rock types throughout a broad midcrustal depth range supporting the inference that retrograde reaction to phyllosilicates may be important in localizing crustal deformations within large faults and shear zones

grain size reduction and foliation development in a deformed granitoid batholith abstract the predominantly peraluminous wologorong batholith in eastern new south wales australia has undergone heterogeneous deformation it always has at least one gneissic foliation but in strongly deformed zones it has two foliations one of these is a gneissic foliation s 1 consisting of relatively discontinuous fine grained micaceous and feldspathic folia anastomosing between feldspar relics and elongate aggregates of recrystallized quartz the other foliation s 2 is more continuous than s 1 and the folia are fine grained and commonly laminated as in mylonites the two foliations could have formed siimultaneously or sequentially during a single deformation s 2 formed oblique up to 30 to s 1 in order to accommodate an imposed shear component of the strain in strongly deformed parts of the batholith s 2 folia appear to have initiated on suitably oriented parts of anastomosing s 1 folia continued deformation locally reduced the angle between s 1 and s 2 and resulted in the development of mylonite zones grain size reduction by recrystallization and or neocrystallization occurred in all minerals during the deformation but quartz appears to have attained a steady state grain size of around 0 15 mm which was not reduced during more intense deformation deformation mechanisms are difficult to determine but microfracturing associated with offsetting and microboudinage intragranular slip and solution transfer of material may have operated in the earlier stages of deformation and grain boundary sliding and or solution transfer of material may have dominated the later stages the material transfer may have been associated with chemical and mineralogical changes that accompanied neocrystallization

deformation of chlorite in naturally deformed low grade rocks the intracrystalline deformation of chlorite in naturally deformed low grade rocks was investigated with transmission electron microscopy tem as in other phyllosilicates the deformation of chlorite is dominated by the 001 slip plane slip along this plane is very easy through the generation and movement of partial dislocations with burgers vector b 1 n uv0 after initial bending of the 001 planes through a flexural slip mechanism accommodated by slip along 001 the misorientation is concentrated in tiltwalls subnormal to 001 which are formed by partial dislocations with b 1 n uv0 tiltwalls subparallel to 001 are formed by arrays of dislocations with a total burgers vector 001 these boundaries are either initiated at the grain boundary and move inwards by dislocation climb or form by movement of free dislocations towards the tip of propagating boundaries by glide along planes inclined to 001 once a boundary is formed the increasing misfit is accommodated by climb of these dislocations along 001 due to the combination of very easy slip along 001 and the ability to form subgrain boundaries subparallel to 001 by dislocation climb and activation of hard slip systems chlorite deforms plastically even at temperatures below 300 c

characterizing ponded infiltration in a dry cracked clay soil ponded infiltration in a dry cracked clay soil was studied in large blocks of soil upper surface area 1500 cm2 height 25 40 cm using physical and morphological methods blocks were encased in gypsum physical measurements included 1 infiltration rates into the block and into subsoil below the block during shallow ponding 2 d relations of soil in the block and 3 depth and degree of wetting in soil adjacent to the cracks cracks in the block were then filled with a gypsum slurry morphological measurements included quantimet counts of the surface area a and the peripheral length l of the gypsum filled cracks using in situ drawings simulation of horizontal infiltration from the cracks using d and l values yielded results that agreed well with in situ measurements demonstrating the mutual compatibility of the morphological and physical methods

the effect of hydrous mineral content on competitive strain localization mechanisms in felsic granulites abstract this study investigates the grain scale mechanisms that facilitated strain localization in the lower crust within the east athabasca mylonite triangle of northern saskatchewan canada there two distinct lithotectonic units the upper deck and northwestern domain are juxtaposed across a km scale shear zone that has been previously interpreted to record thrust and or normal sense displacement our study reports new quartz c axis opening angle ti in biotite and ti in quartz geothermometry and amphibole plagioclase geothermobarometry within syn kinematic phases indicating that both units were deformed and metamorphosed at upper amphibolite to granulite facies 725 c and 0 8 gpa while sharing similar conditions the dominant mechanisms of deformation across the two units are strongly linked to modal proportion of syn kinematic hydrated mineral phases detailed microstructural and crystallographic preferred orientation cpo analyses reveals that specimens poor in hydrated minerals 10 pressure solution and re precipitation processes enhanced phase mixing and promoted grain boundary sliding resulting in weakly developed or absent quartz cpo these results indicate a strong mineralogical and fluid control on deformation and therefore which strain softening process es may dominate in lower crustal shear zones

a theoretical model for rock joints subjected to constant normal stiffness direct shear abstract the authors have conducted an investigation into the behaviour of rock joints subjected to direct shear both concrete rock and rock rock joints were investigated the behaviour of rock rock joints is important for the assessment of stability issues involving rock masses e g rock slope stability concrete rock joints are vital to the assessment of performance of concrete piles socketed into rock rock anchors and concrete dam foundations this investigation included an extensive series of direct shear tests under a range of stress boundary conditions the rock used for the tests was a soft artificial siltstone called johnstone the results from the tests on concrete johnstone joints have been presented in seidel and haberfield geotech testing j 2002 accepted for publication and on johnstone johnstone joints in fleuter mengsc dissertation department of civil engineering monash university australia 1997 and pearce ph d dissertation department of civil engineering monash university australia 2001 in preparation this paper describes the theoretical models developed to simulate the observed behaviour including asperity sliding asperity shearing post peak behaviour asperity deformation and distribution of stresses on the interface these models have been combined into a micro mechanical simulation of joint shear comparisons between program predictions and measured performance are presented and discussed

an experimental study of vaporous water migration in unsaturated lime treated expansive clay to ensure safety of lime treatment for expansive clay foundation investigation of vaporous water migration features is of great significance since moisture migration leads to changes in engineering behaviors of the lime treated expansive clay herein a novel model was described to perform the vaporous water migration tests of unsaturated lime treated expansive clays and effects of initial water content lime dosage curing time migration period and transfer distance on vaporous moisture migration were discussed the soil water characteristic curves swccs and textures of expansive clay and the corresponding improved soil treated with 7 lime were determined to further investigate changes in hydraulic characteristics by means of the geotechnical digital system gds and scanning electron microscopy sem tests the results indicated vaporous water migration between two soil columns of different initial water contents increased as migration time went by and moisture content variation mostly occurred in the first 30 days for the cases of same 24 initial water content in the left soil column variation of moisture content in the case of 0 initial water content in the right soil column after 90 days migration was about 3 times and 78 times respectively bigger than that for the cases of 6 and 12 initial water content in the right soil column besides as migration distance increased it took longer time to reach the water migration balance moreover the left and right soil columns behaved different migration characteristics and transfer speeds of mixing water within the soil columns and vaporous water between columns were different

development of a shear zone in brittle rock subjected to direct shear abstract laboratory direct shear tests were carried out on a brittle synthetic rock at various normal loads the observed fracture patterns changes as the normal load increased a discrete element code was used to simulate the direct shear tests the simulation results clearly showed that cracks that developed during the test were predominantly tension cracks these cracks started to grow from the upper edge of the shear box due to the highly non uniform stress distribution along the shear plane the fracture development observed in discrete element simulation models showed that inclined fractures developed parallel to the maximum principal stress direction en echelon type extensile fractures were also generated and assemblies of theses fractures formed shear bands similar to the process observed in conventional triaxial test using brittle rocks the discrete element simulations showed that the macro scale shear band in the direct shear tests resulted from progressive failure of tension induced micro cracks

nucleation and growth of retrograde shear zones an example from the needle mountains colorado u s a abstract brittle and ductile deformation features are heterogeneously developed in late proterozoic retrograde normal slip shear zones that cross cut amphibolites and quartzo feldspathic gneisses in the needle mountains replacement of amphibolite grade minerals by greenschist facies assemblages is spatially related to transgranular fractures that cross cut the older gneissosity steeply dipping chlorite lined slip surfaces are associated with chlorite quartz muscovite filled dilational jogs and narrow breccia zones arrays of slip surfaces are transitional into similarly oriented phyllonite zones within which the foliation locally overprints early cataclastic zones the nucleation of these shear zones under greenschist facies conditions involved fluid infiltration along early transgranular fractures and hydration of fe mg bearing minerals initial displacement occurred by slip along these fractures and local cataclasite development fluids were episodically drawn into dilatant sites along these slip surfaces a transition to plastic deformation resulted directly from the metamorphic breakdown of feldspars and amphiboles to phyllosilicates which allowed strain localization into narrow phyllonite zones thus dilatancy produced by early brittle deformation appears to be the main process by which fluids infiltrate into developing greenschist grade retrograde shear zones reaction softening via hydration reactions causes a brittle to plastic transition and results in strain localization

tracking progressive deformation of an orogenic wedge through two successive internal thrusts insights from structure deformation profile strain and vorticity of the main central thrust mct and the pelling munsiari thrust pt sikkim himalayan fold thrust belt abstract we compare and contrast the structural evolution of two successive internal thrusts the main central thrust mct and the pelling munsiari thrust pt from the crystalline core of the sikkim himalaya in the context of progressive deformation involving a footwall lesser himalayan duplex the pt is its roof thrust the mylonitic foliations in both the shear zones are overprinted by successive cleavages the youngest cleavage from the pt zone continues within the hangingwall mct sheet that records one additional cleavage possibly indicating time transgressive cleavage development the cleavages become steeper while their intensity decreases structurally higher up within individual thrust sheets the rs values and angular shear strain decrease from the mylonite zones to structurally higher up within the sheets both the shear zones are type ii with decelerating strain paths rs relationships and microstructures indicate thrust parallel stretch is greater than thrust perpendicular component both the shear zones record strain partitioning with lesser competent mylonite domains recording higher rxz and a greater proportion of simple shear than the protomylonite domains the shear zones recorded the growth of the duplex during progressive deformation that contributed to pure shear dominated general shear higher flattening strain and greater translation on its roof thrust the pt than the overlying mct

textural evolution of synthetic anhydrite halite mylonites the rheology and textural evolution of mylonites for both crustal and mantle rocks are generally poorly understood stress and strain partitioning between shear zones and wall rock foliation development flow mechanisms and constitutive relations are little known to address these problems we have begun an experimental study in which anhydrite and halite aggregates are deformed in simple shear homogeneous mixes at intervals of 10 vol of anhydrite and halite powders of 90 to 180 m grain size comprise the 1 mm thick zone between the 35 precut surfaces in 2 by 4 cm right circular cylinders of anhydrite all specimens are confined under 200 mpa pc and tested at 300 c t producing an aggregate of near zero porosity all specimens are shortened at an axial displacement rate of 5 l0 6 cm s to shear strains of about 2 0 most stress strain curves have a similar form they are characterized by an initial linear response that is followed by a work hardening region that leads to a plateau of constant stress whilst strain continues to accumulate this apparent steady state behavior is followed by a drop in stress to a second apparent steady state stress the strain at this stress drop and the magnitude of the drop increase with increasing anhydrite content the second lower steady state stress for all mixes approaches that of sheared pure halite optical examination of the fabrics shows that straining under the initial apparent steady state is accommodated by both mineral phases a foliation evolves as defined by mineral segregation and grain elongation of halite at 15 to 30 to the shear zone walls anhydrite grains rotate until their 001 010 slip system parallels the foliation the anhydrite also exhibits twin lamellae kinks and microfractures following the stress drop rheologic behavior is dominated by dynamic recovery in halite the recrystallized grain size increasing consistent with the lower stress level

shearing of magma along a high grade shear zone evolution of microstructures during the transition from magmatic to solid state flow abstract syntectonic plutons may record short lived geological events related to crustal melting and deformation of the continental crust therefore interpretation of microstructure and orientation of fabrics is critical in order to constrain space time temperature deformation relationships during pluton crystallization here we describe the transition from magmatic to solid state deformation in the late variscan diorite granite suite dgs emplaced along the santa lucia shear zone the systematic collection of meso microstructural and quartz axis data allow us to examine the spatial distribution and the mode of superposition of different fabrics we identify three magmatic microfabric types thought to reflect the microstructural evolution at decreasing melt content during pluton crystallization our data suggest that diffusion creep dislocation creep and grain scale fracturing cooperated in accommodating the shearing of the partially molten quartzofeldspathic aggregate we suggest that the switch from upward to horizontal magmatic flow occurred at melt fractions gt 0 40 and that most of the hypersolidus fabrics formed during horizontal flow reflecting the stress field imposed by the shear zone and preserving no memory of the ascent stage

the deformational behaviour of bimineralic limestone halite aggregates abstract a compositional foliation banding develops within synthetic limestone halite aggregates experimentally deformed in axially symmetric compression and in simple shear the strength of the bulk aggregate decreases as the foliation becomes stronger foliation weakening in calcite rich specimens the development of foliation starts with the formation of cataclastic shear systems in calcite domains between isolated halite domains with increasing deformation halite is sheared into these systems the halite domains coalesce into halite rich shear systems and accommodate an increasing amount of the bulk deformation the bulk strength of bimineralic aggregates at a given amount of strain increases with decreasing halite content the influence of halite on the bulk strength is much greater than would be expected from its volume fraction and becomes dominant with increasing deformation due to the development of the foliation it is postulated that such processes also occur during natural deformation of polyphase rocks competent clasts within a weaker ductile matrix showing no recrystallization differ in shape and rotational behaviour from recrystallizing clasts such as feldspar augen these competent clasts denoted as type clasts may cause problems in deducing the sense and direction of shear when formed as almost exact mirror images of type recrystallizing clasts

water vapor sorption and its mechanical effect on clay bearing conglomerate selected from china abstract water sorption is one of the most important causes for rock deformation and failure in the present study water vapor sorption experiment was carried out on clay bearing conglomerate rock samples collected from northeast china to investigate dynamics of water vapor sorption and vapor induced strength softening effect the experimental results have shown that the amount of water vapor sorbed by each conglomerate sample kept increasing with time until finally reached to a plateau generally following an exponential law the greater abundance of clay minerals especially smectite allowed more water sorption by analyzing correlation relationships between the porosity characteristic parameters of conglomerate samples and the sorbed water content it was found that vapor sorption was positively correlated with rock porosity diameter 0 2 m this result indicated that the total volume of pores with diameter 0 2 m was an important factor influencing water sorption of conglomerate rocks negative correlations between water content and uniaxial compressive strength ucs as well as modulus of elasticity suggested that with increasing water content induced by vapor sorption conglomerate rock strength tended to decrease and meanwhile it was more prone to deformation furthermore microstructure images of scanning electron microscope sem analyses for conglomerate rocks before and after water vapor sorption showed that after vapor sorption conglomerate rocks have undergone significant changes in microscopic morphology which may be an important cause for rock softening and deterioration

late palaeozoic deformation of post variscan lower crust shear zone widening due to strain localization during retrograde shearing the santa lucia shear zone slsz corsica is a granulite facies permian shear zone that developed after the emplacement of a deep seated gabbroic intrusion new structural data shows that the slsz results from the juxtaposition of three spatially distinct mylonite belts which are the product of the interaction between magmatism metamorphism and shearing over a temperature range from 800 to 400 c during the earlier high grade deformation stage which was accompanied by decompression from 7 to 5 kb at 800 c the slsz has accommodated high finite strain on a shear zone 1 km wide strain became increasingly localized as temperature decreased but rather than reactivating pre existing shear zones as commonly expected younger mylonites expanded into previously unsheared rock extending the total width of the shear zone the zonation of different fabrics across the slsz suggests that pre existing compositional and grain size heterogeneities in the starting material played a key role in governing superposed generations of shear zones

quartz and sheet silicate preferred orientations of low symmetry pikikiruna schist new zealand abstract the pikikiruna schist of nelson new zealand displays a fabric in which the patterns of quartz c axes the poles to planes of inequidimensional quartz grains and the statistical maxima of poles to sheet silicate cleavages are oblique to each other the quartz c axes patterns consist of type 1 and type 2 crossed girdles the triclinic fabric can be explained in terms of one complex rotational deformation of an essentially plane strain nature rotation of approximately 90 about the intermediate strain axis was combined at a late stage with subsidiary rotations about the extension axis the quartz c axes patterns can be related to the kinematic framework rather than the finite strain axes on the other hand the dimensional quartz preferred orientation may be closely related to the finite strain axes though the quantity of strain can not be measured because of recrystallisation

microstructure of deformed biotite defining foliation in cataclasite zones in granite central japan abstract foliated cataclasite occurs along both left lateral faults striking n10 40 w and right lateral faults striking n10 25 e formed in the late cretaceous naegi agematsu granite along and near the atera fault in central japan quartz and feldspars in the cataclasite are angular to subangular in shape biotites which are granular or elongate exhibit kink bands and cleavage separation or cleavage steps and biotite fish arrays of deformed biotite define a p foliation that formed in the fault zones the angle between the p foliation and the 001 biotite cleavage and the ratio w l of apparent width w to length l of deformed biotites are related to the type of biotite microstructure developed in the samples studied there were no values of in the ranges 30 75 and 105 150 the cleavage step microstructure exhibits an angle of less than 30 with w l less than 0 2 kink band and or cleavage separation microstructures have an angle of 75 105 with w l between 0 5 and 1 5 biotite fish have an angle of more than 150 with w l less than 0 2 these data imply that the orientation of cleavage in biotite with respect to the plane of shear strongly controlled the response of biotite to deformation the resulting microstructures provide good kinematic indicators in biotite bearing shear zones and faults

comparison of quartz microfabric with strain in recrystallized quartzite abstract the relationship between quartz c axis microfabric and strain is examined in six specimens of recrystallized quartzite conglomerate in which strain was measured using pebble shapes four rocks subjected to plane strain display a direct relationship between the strength of preferred orientation and the strain intensity the c axis distributions in these rocks as well as a rock subjected to moderate extensional strain are crossed girdles with maxima near the intermediate principal strain axis and connecting girdles at acute angles to the direction of maximum shortening a rock subjected to moderate flattening strain has several maxima clustered near the direction of maximum shortening and a weak connecting girdle through the intermediate principal strain axis these results are generally similar to those of other studies comparing strain and tectonite fabrics and also with experimental and computer simulation studies of fabrics the degree of preferred orientation is related to total strain and therefore microfabrics in quartzites may be cautiously interpreted as qualitative indicators of strain intensity uncertainties are greater however for correlations of fabric patterns with shapes of the strain ellipsoid an observed increase in recrystallized grain sizes with increasing strain suggests that flow stress was lower in the more strained rocks

effects of anhydrite and pressure on the mechanical behavior of synthetic rocksalt bimineralic polycrystalline rocksalt specimens ranging in composition from pure halite to pure anhydrite have been fabricated in hydrostatic compression at 150 mpa and 100 sup 0 c for 15 minutes resulting porosities of the compacted samples increased with increasing anhydrite content ranging from 02 for pure halite to 14 for pure anhydrite twenty three compacted samples were then deformed in triaxial compression experiments at confining pressures of 10 100 and 200 mpa a nominal strain rate of 10 sup 4 sec sup 1 and a temperature of 200 sup 0 c sample strength at 10 percent axial strain was directly related to both anhydrite content and pressure relatively small strength increases were observed for increases in anhydrite content up to 75 percent by weight and for all pressure increases much larger increases in strength were observed when the anhydrite content was increased from 75 to 100 percent ductilites of less than 10 percent were seen in only two sets of data the 100 and 75 percent anhydrite samples run at 10 mpa confining pressure and these data indicated a trend of increasing ductility with increasing halite content and or confining pressure all samples exhibited strain hardening except for the 75 percent halite samples at all three pressures andmore the 50 percent sample of 10 mpa which exhibited slight strain softening less

quantitative description theory of water migration in rock sites based on infrared radiation temperature abstract in order to solve the problem of quantitative description of water migration in a stone artifacts site we have investigated the dynamic migration process of water and established a quantitative descriptive theory system based on infrared radiation temperature through the infrared thermal imaging method we propose the criterion of water movement initiation based on entropy theory a quantitative relationship equation between infrared radiation temperature and water content is established using the first law of thermodynamics a method of identifying the moisture migration wetting front is proposed the above theory is verified by laboratory experimental thermal imaging results of moisture migration of siltstone from the mogao grottoes cliff therefore our method can quantitatively describe the start and migration of water at a rock site using our theoretical system and infrared thermography in a non destructive and real time manner here we provide a new method for quantitative description of moisture migration in a stone artifacts site

fabric induced weakness of tectonic faults 1 mature fault zones appear to be weaker than predicted by both theory and experiment one explanation involves the presence of weak minerals such as talc however talc is only a minor constituent of most fault zones and thus the question arises what proportion of a weak mineral is needed to satisfy weak fault models existing studies of fault gouges indicate that 30 of the weak phase is necessary to weaken faults a proportion not supported by observations here we demonstrate that weakening of fault gouges can be accomplished by as little as 4 wt talc provided the talc forms a critically aligned through going layer observations of foliated fault rocks in mature large offset faults suggest they are produced as a consequence of ongoing fault displacement and thus our observations may provide a common explanation for weakness of mature faults

evaluating the stability of anti dip slate slope using an innovative failure criterion for foliation abstract toppling failure is one main failure types of anti dip slate slopes and is strongly affected by the mechanical properties of foliation this study conducted a series of pull off tests and direct shear tests on slate foliation to obtain its failure envelope and an innovative failure criterion was accordingly proposed the proposed failure criterion exhibits a nonlinear trend in the low normal stress range considers both tensile and shear strengths and has three material parameters tensile strength t 0 and parameters and are related to the slope variation of the failure criterion to investigate the effectiveness of the proposed failure criterion on the evaluation of slope stability it is implemented in a discrete element code udec and a simulation was carried out to evaluate the deformation and failure pattern of an anti dip slate slope the results of the udec analysis demonstrate that the simulated failure pattern and deformation characteristics agree with that of an actual anti dip slate slope the proposed failure criterion of foliation and the mohr coulomb criterion are further compared in slope stability analysis the proposed failure envelope accurately reflects the tensile strength and shear strength under low normal stress but the mohr coulomb criterion apparently overestimates the strength in this stress range therefore the proposed criterion is more effective than the existing criteria in predicting the toppling failure of slate slopes

intracrystalline folding and cataclasis in biotite of the santa rosa mylonite zone hvem and tem observations abstract high voltage electron microscope hvem and transmission electron microscope tem analyses indicate that grain size reduction of biotite in deformed granodiorite of the santa rosa mylonite zone southern california was in part accomplished by intracrystalline folding and cataclasis through this process deformation takes place within discrete parallel sided or lens shaped zones up to 6 m wide within the zones deformation begins with the opening of cavities along cleavage planes further deformation causes layers parallel to 001 to become detached from the surrounding crystal along cleavage planes or ruptured along micro shear zones at an angle to 001 the layers may be strongly folded branching or completely fragmented the latter suggesting cataclastic behavior the smallest measured lens of cataclasite is 0 05 m in width high resolution tem images show that 001 lattice fringes fold into these regions zones of intracrystalline folding and cataclasis are visible petrographically because of the many orientations of biotite within these regions the optical properties are effectively averaged the zones are characterized by little or no change in color with rotation of the optical microscope stage and in most orientations by higher refractive indices than the surrounding crystal