structural characterization of natural loess and remolded loess under triaxial tests this paper characterizes the microstructural evolution of saturated natural loess from a site in jingyang china during triaxial test along two stress paths for comparison the same soil in remolded state is also characterized mercury intrusion porosimetry mip scanning electron microscopy sem and environmental scanning electron microscopy esem were used for the microstructure investigation results show that the microstructure of natural loess is similar to that of remolded loess before the consolidated undrained cu triaxial tests including conventional triaxial compression ctc test and reduced triaxial compression rtc test on the contrary their microstructures are different after the tests deeper examination shows that loading led to a significant change of inter aggregate pores without modifying the intra aggregate pores in addition the volume of inter aggregate pores after the rtc test is greater than that after the ctc test under the same consolidation stress the microstructure features of natural and remolded loess after the tests are further used to analyze the macro mechanical behavior for better understanding the relationship between them the results show that it is the cementation bonds of which breakage is influenced by stress path and confining pressure that play important roles in the strength and deformation behavior

experimental calibration of the aluminum in hornblende geobarometer with application to long valley caldera california volcanic rocks a new geobarometer based on the al content of igneous hornblendes in equilibrium with melt fluid biotite quartz sanidine plagioclase sphene and magnetite or ilmenite has been calibrated experimentally the calibration was performed by equilibrating the required phase assemblage over the pressure range 2 8 kbar at 740 780c and then analyzing euhedral hornblendes in equilibrium with glass melt experiments were performed on natural samples of both volcanic and plutonic rocks earlier empirical calibrations of this geobarometer relied on analyzing natural hornblendes from plutons with the required phase assemblage and inferring pressure from nearby metamorphic country rocks the experimental calibration differs from the empirical calibrations especially above 5 kbar and shows that the al content of hornblendes in equilibrium with the required phase assemblage is greater for a given total pressure than previously thought the geobarometers uncertainty is dramatically reduced the derived equation is p plus minus 0 5 kbar 3 minus 3 46 plus minus 0 24 4 23 plus minus 0 13 al sup t the geobarometer is applied to post bishop tuff volcanic rocks from long valley caldera california and reveals that most rhyodacites in this complex erupted from depths of about 6 km these eruptions occurred over 500 000 yr suggesting that the rhyodacitic magma reservoir beneath longmore valley had reached a steady p depth t state less

centrifuge model study on settlement of strip footing subject to rising water table in loess owing to man made activities and natural conditions the groundwater table experiences considerable changes in lanzhou centrifugal model tests were performed to investigate the settlement of strip

a melt inclusion study of the toba tuffs sumatra indonesia the toba caldera in northern sumatra indonesia is the site of earth s largest quaternary volcanic eruption this eruption dated at 74 ka produced the 2800 km3 youngest toba tuff ytt and ash fall quartz bearing silicic pumices ranging from 68 to 77 wt sio2 indicate that the ytt magma was zoned compositionally and mineralogically prior to the ytt eruption two other silicic quartz bearing tuffs known as the middle toba tuff mtt and the oldest toba tuff ott were erupted from toba at 0 501 ma and 0 840 ma respectively although the volatile contents of the toba magmas are poorly constrained aerosols generated by the ytt eruption are generally thought to have caused a global volcanic winter an evaluation of the pre eruptive dissolved gas contents of the ytt magma is fundamental to understanding the global effects of this eruption we used melt inclusions in quartz crystals to determine the dissolved h2o co2 s cl and f contents of the ytt mtt and ott magmas quartz crystals selected from pumice blocks and welded tuffs that spanned the compositional ranges of the three units were chosen for study major and trace element analyses of melt inclusions were also conducted to characterize melt evolution and provide context to the volatile data melt inclusions from the ytt mtt and ott are rhyolitic in composition 73 77 wt sio2 and have overlapping indistinguishable major element trends inclusions from the large eruptions ytt and ott have similar geochemical relationships where the most evolved melt inclusions occur in the least silicic bulk rock samples and are more evolved than their matrix glasses in contrast the least evolved melt inclusions occur in the most silicic samples and either overlap with or are less evolved than their matrix glasses these patterns can be explained if quartz crystals in the least silicic magmas were inherited from more evolved melt while those in the most silicic melt formed in situ several lines of evidence suggest that crystal settling of early formed quartz crystals in long lived magma bodies was an important process in the ytt and ott magmas trace element data from the ytt melt inclusions have wide ranges rb 250 830 ppm ba 10 485 ppm and mostly support these models however incompatible trace elements are enriched 2 3 over their matrix glass compositions in all samples in the smaller mtt melt inclusions overlapped with the compositional range of the bulk rock samples and are consistent with in situ crystallization ftir analyses indicate that the ytt mtt and ott melts contained about 4 0 5 5 2 0 5 5 and 2 0 5 5 wt h2o respectively co2 contents in all units are generally 100 ppm and cl is 2000 ppm water gradients occur in all 3 tuffs cl gradients are evident only in the ytt and the least silicic samples from all units had no detectable co2 sulfur contents in melt inclusions are low in all samples 32 ppm and overlap with matrix glass s contents applying broad degassing constraints about 1014 g of h2so4 aerosols were likely loaded into the atmosphere during the ytt eruption 2 orders of magnitude less than previous petrologic estimates considerably more cl and f about 1015 g of each may have been part of the ytt aerosol cloud

active seismic monitoring of hydraulic fractures in laboratory experiments in scaled laboratory tests we perform acoustic measurements in a time lapse sequence to separate the fracture response from the background signal using both compressional and shear waves that are very sensitive to fluid filled fractures we can not only detect the hydraulic fracture but also characterize its shape and geometry during its growth we show the application of the technique to propagation and reopening of hydraulic fractures during fracture growth the acoustic waves excite diffractions at the tip of the fracture depending on the acquisition geometry we detect many events related to surface waves propagating along the fracture also we observe that shear waves detect the migration of the fluid front during reopening of a pre existing hydraulic fracture in contrast with the compressional waves which are insensitive to the fluid front during reopening

engineering geology of loess and loess like deposits a commentary on the russian literature loess and loess like deposits were much studied in the soviet union and are currently under investigation in russia and surrounding countries there is a vast literature in russian which touches on all aspects of loess science and technology in particular the studies of the origin of collapsibility are almost totally in russian and of course studies on the various regions of russia and the countries of the former soviet union fsu appear in russian this review looks at the literature in russian and attempts to pick out key contributors major topics and works and to identify the critical regions and zones of investigation because so many regions of the fsu had people living on loess ground there is a vast literature on engineering geology and ground engineering topics and this tends to dominate all the literature on loess in russian following russian practice the fine grained deposits under consideration are divided into loess and loess like deposits three main topics are recognised across the whole spectrum of loess research formation and distribution of loess deposits stratigraphy cyclicity and palaeoclimatology and engineering topics in particular hydrocollapse and subsidence and we concentrate on the engineering geology topics an attempt is made based on the map of abelev and abelev abelev yu m abelev m yu 1968 fundamentals of design and construction on collapsible macroporous soils 2nd ed stroiizdat moscow 431 pp in russian of collapsing loess deposits to define seven loess regions within the geographical limits of the old ussr the seven regions are those where geotechnical problems might be expected

monitoring the width of hydraulic fractures with acoustic waves during scaled hydraulic fracturing experiments in our laboratory the fracture growth process is monitored in a time lapse experiment with ultrasonic waves we observe dispersion of compressional waves that have propagated across the hydraulic fracture this dispersion appears to be related to the width of the hydraulic fracture this means that we can apply the dispersion measurements to monitor the width of the hydraulic fracture in an indirect manner for a direct determination of the width the resolution of the signal is required to distinguish the reflections that are related with two distinct fluid solid interfaces delimiting the hydraulic fracture from its solid embedding to make this distinction the solid fluid interfaces must be separated at least one eighth of a wavelength and represent sufficient impedance contrast the applicability of the indirect dispersion measurement method however extends to a fracture width that is in the order of 1 of the incident wavelength the time lapse ultraso

slow waves in fractures filled with viscous fluid stoneley guided waves in a fluid filled fracture generally have larger amplitudes than other waves and therefore their properties need to be incorporated in more realistic models in this study a fracture is modeled as an infinite layer of viscous fluid bounded by two elastic half spaces with identical parameters for small fracture thickness i obtain a simple dispersion equation for wave propagation velocity this velocity is much smaller than the velocity of a fluid wave in a biot type solution in which fracture walls are assumed to be rigid at seismic prospecting frequencies and realistic fracture thicknesses the stoneley guided wave has wavelengths on the order of several meters and an attenuation q factor exceeding 10 which indicates the possibility of resonance excitation in fluid bearing rocks the velocity and attenuation of stoneley guided waves are distinctly different at low frequencies for water and oil the predominant role of fractures in fluid flow at field scales is supported by permeability data showing an increase of several orders of magnitude when compared to values obtained at laboratory scales these data suggest that stoneley guided waves should be taken into account in theories describing seismic wave propagation in fluid saturated rocks

characterisation of collapsing loess by seismic dilatometer abstract structural collapse and sudden volume changes represent a major geotechnical issue particularly in loess soils there are different criteria for assessing collapse potential based on laboratory test results which require the collection of undisturbed samples from test pits this can be a complicated and costly procedure often financially unjustified for smaller projects this paper presents the results of seismic dilatometer tests sdmt performed at a single location in a loess soil in belgrade in addition to the results of single oedometer collapse tests performed on high quality samples from test pits after comparing laboratory test results it was possible to determine that in samples collected from boreholes dry unit weight is approximately 20 higher than in block samples taken from test pits while moisture content is between 1 and 4 higher unit weight estimated from dmt is on average 15 higher than the unit weight obtained from block samples the constrained modulus mdmt determined by dmt are highly compatible with oedometer modulus eoed obtained from samples at natural moisture content this paper presents two possible ways of identifying collapsing loess based on intermediate dmt parameters and the ratio of g0 mdmt the tests results indicate that if the ratio between the material index id and the horizontal stress index kd is greater than 5 the danger of collapse is imminent simultaneous observation of the changes of id and kd with depth on a semi log graph in the same scale is recommended in this way the relative distance between them may be clearly noticed the larger the distance becomes the greater the risk of collapse in the collapsing loess ratio g0 mdmt is found to be higher than 21 for kd less than 0 6 while in non collapsing loess g0 mdmt is less than 21 for higher values of kd in terms of dmt loess is considered as underconsolidated soil which is one of the most common definitions of loess

loess improvement methods abstract evstatiev d 1988 loess improvement methods eng geol 25 341 366 the paper deals with the present day state of the methods of improvement of loess soils as a base and material for engineering constructions the experience of the soviet union bulgaria the united states china and other countries where loess is widespread has been taken into account the classification of loess bases into 2 types and 4 sub types has been suggested depending on the thickness of the loess and total overburden collapse the improvement methods have been classified into 8 groups depending on their nature and the results achieved 1 compaction by rollers heavy tampers soil piles moistening and by explosions or vibrations and other similar methods 2 modification of the granulometric composition by the addition of coarser material 3 stabilization on the surface or in depth by means of injection or mixing with various binders and chemical reagents 4 loess improvement by replacement with various cushions or jet grouting 5 reinforcement comprising methods in which the strength of loess is improved by putting bodies of tensile resistance into it 6 geomembranes 7 desiccation by different draining systems electro osmosis or hygroscopic materials and 8 correction terracing grassing and afforestation of slopes the applicability of the methods their recent development as well as typical case histories have been discussed

late magmatic controls on the origin of schorlitic and foititic tourmalines from late variscan peraluminous granites of the arbus pluton sw sardinia italy crystal chemical study and petrological constraints abstract tourmalines from the late variscan arbus pluton sw sardinia and its metamorphic aureole were structurally and chemically characterized by single crystal x ray diffraction electron and nuclear microprobe analysis mossbauer infrared and optical absorption spectroscopy to elucidate their origin and relationships with the magmatic evolution during the pluton cooling stages the arbus pluton represents a peculiar shallow magmatic system characterized by sekaninaite fe cordierite bearing peraluminous granitoids linked via afc processes to gabbroic mantle derived magmas the fe2 al dominant tourmalines occur in a pegmatitic layers and pods as prismatic crystals b greisenized rocks and spotted granophyric dikes as clots or nests of fine grained crystals in small miaroles locally forming orbicules c pegmatitic veins and pods close to the contacts within the metamorphic aureole structural formulae indicate that tourmaline in pegmatitic layers is schorl whereas in greisenized rocks it ranges from schorl to fluor schorl tourmalines in thermometamorphosed contact aureole are schorl foitite and mg rich oxy schorl the main substitution is na fe2 al which relates schorl to foitite the homovalent substitution oh f at the o1 crystallographic site relates schorl to fluor schorl while the heterovalent substitution fe2 oh f al o relates schorl fluor schorl to oxy schorl tourmaline crystallization in the arbus pluton was promoted by volatile b f and h2o enrichment low oxygen fugacity and fe2 activity the mineralogical evolutive trend is driven by decreasing temperature as follows sekaninaite quartz schorl quartz fluor schorl quartz foitite quartz the schorl foitite evolution represents a distinct trend towards al increase and unit cell volume decrease these trends are typical of granitic magmas and consistent with li poor granitic melts as supported by the absence of elbaite and other li minerals in the arbus pluton tourmaline bearing rocks reflect the petrogenetic significance of contribution from a metapelitic crustal component during the evolution of magmas in the middle upper crust

geological and geotechnical characteristics of some loess and loessic soils from china and britain a comparison abstract derbyshire e and mellors t w 1988 geological and geotechnical characteristics of some loess and loessic soils from china and britain a comparison eng geol 25 135 175 loess and loessic deposits cover some 630 000 km 2 of the surface of mainland china the loess plateau of shanxi shaanxi gansu and ningxia being the type region of this formation loess thickness generally exceeds 100 m over large areas of the loess plateau the maximum recorded thickness being 335 m in eastern gansu province near the city of lanzhou in britain loess and loessic deposits form part of a group of materials collectively known as brickearth they occur predominantly as sporadic accumulations in the southeast of england and rarely attain a thickness of more than four metres despite their geographical separation the deposits from china and britain have a remarkable similarity in some of their physical and geotechnical characteristics samples from both locations have been examined and tested in the laboratory and the results are presented the scope of the testing programme involved mineralogical analyses soil microfabric studies using a scanning electron microscope index testing including plasticity grading and density measurements and the investigation of the compressibility characteristics of the soils with particular reference to their susceptibility to collapse a soil structure model based on scanning electron microscope studies is presented and discussed in relation to the perceived mode of formation of the soils and their postdepositional history

seismic detection of a hydraulic fracture from shear wave vsp data at lost hills field california a shear wave s wave vsp experiment was performed at lost hills field california in an attempt to detect hydraulic fractures induced in a nearby well the hydrofrac well was located between an impulsive s wave source on the surface and a receiver well containing a clamped three component geophone both direct and scattered waves were detected immediately after shut in when the hydraulic pumps were shut off and recording started the scattered energy disappeared within about an hour which is consistent with other measurements that indicate some degree of fracture closure and leak off within that period although s wave splitting was evident no change was detected in the fast wave polarized parallel to the fracture however the slow wave polarized perpendicular to the fracture did change over a period of about an hour after which the prehydrofrac wavelet shape was recovered the fact that only the wave polarized perpendicular to the fracture was affected is a dramatic confirmation of both theoretical predictions and laboratory observations of s wave behavior in a fractured medium subtracting the prehydrofrac wavelet from the wavelets recorded within the first hour after shut in revealed scattered wavelets that were diminished and phase rotated versions of the incident prehydrofrac wavelet arrival times of the direct and scattered waves were matched by ray tracing we accounted for the scattered wave amplitudes by using numerical solutions of s wave diffractions off of ribbon shaped fractures amplitudes derived from full wavefield born scattering however did not match recorded amplitudes the phase of the scattered wavelets was matched very well by born scattering when the incident wavelet was input but only for fracture lengths no larger than half those predicted from fracture simulator models these results show that a carefully controlled experiment combined with accurate modeling can provide important information about the geometry of induced fractures

loessification and hydroconsolidation there is a connection abstract loessification can be defined as the acquisition of loessic characteristics by ground systems hydroconsolidation in this context is the collapse of the loess ground structure under the influence of loading and wetting loess on aeolian deposition is metastable a pre requisite for eventual collapse the actual collapse mechanism is dependent on the presence of a critical amount of clay mineral material at major particle contacts this clay accumulates via post depositional processes processes which can be described as part of loessification and as a contribution to collapsibility studies at ospringe in kent england support observations made in the bohemian massif in the czech republic about the nature of the loess ground system and the role of clay minerals and calcite crystals fragipan formation another important post deposition event could depend on hydroconsolidation in loess ground

engineering properties of loess in algeria loess in north africa has been investigated using samples from algeria the specific gravity atterberg limits grain size distribution and dry density were determined the hydro collapsibility properties due to wetting under different stress levels were measured in single oedometer tests the results of this investigation indicate that the properties of algerian loess are similar to those of loess from many parts of the world such as iowa and libya they can be classified as silty loess

phase equilibrium geobarometers for silicic rocks based on rhyolite melts part 3 application to the peach spring tuff arizona california nevada usa establishing the depths of magma accumulation is critical to understanding how magmas evolve and erupt but developing methods to constrain these pressures is challenging we apply the new rhyolite melts phase equilibria geobarometer based on the equilibrium between melt quartz and two feldspars to matrix glass compositions from peach spring tuff arizona california nevada usa high silica rhyolite we compare the results to those from amphibole geothermobarometry projection of glass compositions onto the haplogranitic ternary and glass sio2 geobarometry quartz 2 feldspar rhyolite melts pressures span a relatively small range 185 230 mpa consistent with nearly homogeneous crystal compositions and are similar to estimates based on projection onto the haplogranitic ternary 250 50 mpa and on glass sio2 255 275 mpa amphibole geothermobarometry gives much wider pressure ranges temperature independent 65 300 mpa temperature dependent 75 295 mpa amphibole only 80 950 mpa average anderson and smith am mineral 80 549 559 1995 blundy and holland contrib miner petrol 104 208 224 1990 or holland and blundy contrib miner petrol 116 433 447 1994 thermometer a b pressures are most similar to phase equilibria results 220 210 190 mpa respectively crystallization temperatures determined previously with rhyolite melts 742 c zr in sphene 769 20 c and zircon saturation 770 780 c geothermometry are similar but temperatures from amphibole geothermometry 450 955 c are notably different the average anderson and smith holland and blundy 1994 thermometer b 710 c temperature is most consistent with previous estimates the rhyolite melts geobarometer effectively culls glass compositions affected by alteration or analytical issues peach spring glass compositions that yield pressure estimates reveal a tight range of plausible na2o and k2o contents suggesting that low na2o and high k2o contents of many peach spring samples are due to alteration use of altered whole pumice compositions in rhyolite melts simulations is likely the cause of the incorrect crystallization sequence reported previously for peach spring compositions using the rhyolite melts geobarometer we estimate a more realistic composition for peach spring tuff high silica rhyolite and the calculated composition finds close matches with some analyzed rocks and results in the expected sequence of crystallization

hydroconsolidation and subsidence of loess studies from china russia north america and europe abstract various approaches to the widespread problem of the hydroconsolidation and subsidence of loess have been suggested these include considerations of rheology thermodynamics phase movements particle packing interparticle bonding pore structure and distribution catastrophe theory topology and simple structural frameworks chinese north american and most european investigators tend to concentrate on mechanisms of loess collapse the russian literature however retains an extra dimension two approaches the syngenetic and the epigenetic approach to the formation of subsiding loess have been defined in the literature most investigators follow a syngenetic approach which appears to be a consequence of the aeolian idea of loess deposition some russian writers in contrast promote an epigenetic approach in which collapsibility can develop in an originally noncollapsible material which can then suffer from hydroconsolidation and subsidence the basis of the phenomenon is a change in the packing structure of the major loess particles and this can be modelled using simple monte carlo methods to develop appropriate structures this paper aims to review the work done on this important subject serious investigation of hydroconsolidation and subsidence of loess began in the early nineteen forties fifty years ago and this has been reported in a piecemeal manner a detailed critical review of this diverse work is now overdue and this is presented herein in the light of recent work in the united kingdom an attempt is made to describe the process in a phenomenological and a structural sense inherent in this the role of n ya denisov as subsidence pioneer is considered

centrifuge model testing of a loess landslide induced by rising groundwater in northwest china abstract considerable artificial irrigation in the heifangtai area has caused the continued rise of groundwater levels which has resulted in several large scale landslides in the loess platform area considering the no 13 landslide of jiaojia in the heifangtai area as a geological archetype a series of centrifuge tests was conducted to study the deformation and failure characteristics of the slope due to the continuous rise in the groundwater level meanwhile the pore water pressure earth pressure deformation and evolution characteristics of the slope were monitored and recorded in real time furthermore isotropically consolidated undrained triaxial testing icu was conducted to investigate the static liquefaction of loess specimens which was related to the slope instability the centrifuge test results showed that a series of parallel and steep tension cracks at the top of the slope were present before the landslide which was caused by the rising groundwater the icu experimental results showed that as the pore water pressure increased strong strain softening and static liquefaction of saturated loess soils were found which was related to the sudden destruction of the slope

estimation of crystallization pressure of granite intrusions abstract a numerical method is presented to estimate the crystallization pressure of granite intrusions based on two polynomial equations obtained by an analysis of the existing haplogranite ternary phase diagram and associated dataset the results indicate that the pressure is correlated respectively with normative quartz qtz content and with normative albite ab plus orthoclase or contents of granitic rocks as follows 1 p 0 2426 qtz 3 26 392 qtz 2 980 74 qtz 12563 2 p 0 2426 ab or 3 46 397 ab or 2 2981 3 ab or 64224 r 2 0 9943 where p is pressure in mpa and r denotes correlation coefficient it is noted that the procedure of normalizing the sum of cipw norm quartz albite orthoclase contents to 100 is required before using eqs 1 and 2 the difference in pressure calculations between these two equations is 16 mpa for the range of normative quartz contents from 15 to 40 wt an example of how to use these equations to estimate the crystallization pressure of a granite intrusion is also provided to show the validity and convenience of this method the uncertainty of such pressure estimation is not well known although it must fall into the uncertainty range of the existing experimental work on pressure constraints the simplicity of this empirical method is appreciable although its applicability to natural granitoids needs further test more experimental work is required to constrain the effects of components such as cao feo mgo f cl co2 on the granite phase equilibria these equations however can be used for estimating crystallization pressures of water saturated and quartz oversaturated granitic systems

phase equilibrium geobarometers for silicic rocks based on rhyolite melts part 1 principles procedures and evaluation of the method constraining the pressure of crystallization of magmas is an important but elusive task in this work we present a method to derive crystallization pressures for rocks that preserve glass compositions either glass inclusions or matrix glass representative of equilibration between melt quartz and 1 or 2 feldspars the method relies on the well known shift of the quartz feldspar saturation surface toward higher normative quartz melt compositions with decreasing pressure the critical realization for development of the method is the fact that melt quartz and feldspars need to be in equilibrium at the liquidus for the melt composition the method thus consists of calculating the saturation surfaces for quartz and feldspars using rhyolite melts over a range of pressures and searching for the pressure at which the expected assemblage quartz 1 feldspar or quartz 2 feldspars is found at the liquidus we evaluate errors resulting from uncertainties in glass composition using a series of monte carlo simulations for a quartz hosted glass inclusion composition from the bishop tuff which reveal errors on the order of 20 45 mpa for the quartz 2 feldspars constraint and on the order of 25 100 mpa for the quartz 1 feldspar constraint we suggest actual errors are closer to the lower bounds of these ranges we investigate the effect of fluid saturation in two ways 1 by applying our procedure over a range of water contents for three glass compositions we show that the effect of fluid saturation is more important at higher pressures 300 mpa than at lower pressures 100 mpa but reasonable pressure estimates can be derived irrespective of fluid saturation for geologically relevant h2o concentrations 3 wt and 2 by performing the same type of pressure determinations with a preliminary version of rhyolite melts that includes a h2o co2 mixed fluid phase we use a range of h2o and co2 concentrations for two compositions characteristic of early erupted and late erupted bishop tuff glass inclusions and demonstrate that calculated pressures are largely independent of co2 concentration for co2 1 000 ppm at least for relatively high h2o contents as expected in most natural magmas such that co2 concentration can be effectively neglected for application of our method finally we demonstrate that pressures calculated using the rhyolite melts geobarometer compare well with those resulting from h2o co2 glass inclusion barometry and al in hornblende barometry for an array of natural systems for which data have been compiled from the literature the agreement is best for quartz hosted glass inclusions while matrix glass yields systematically lower rhyolite melts pressures suggestive of melt evolution during eruptive decompression

silt 2 62 μm 9 4φ the particles in finer grained detrital sediments are usually composed of quartz they fall into two size grades sand 2 mm 62 m and silt 62 m 2 m these size gradings conceal important geological processes since there are geological controls on both the quartz sand and silt populations sand nature is largely controlled by geochemical reactions for example in cooling granite from which it is eventually released by weathering action the quartz is among the last part of the rock system to solidify and the eutectic like reaction which occurs ensures that the quartz exists as small crystalline units each suffering considerable cooling and recrystallisation stresses silt is broken quartz and has traditionally been considered to lack a specific geological control the situation is confused by the large range of materials that fall into the size category but there do seem to be distinguishable modes and possibly comminution limits within the 60 m span the controls operating in this size range are probably the critical concentration of moss defects in the quartz particles moss postulated the formation of specific crystal defects in the quartz formed in granites these affect sand formation and it is possible that they also control the mode size of silt particles within the silt range there may be several usefully definable populations as moss proposed for sand the quaternary appears to be a silt rich period due to tectonic and glacial activity but silt production is apparent throughout the sedimentary record very long term silt producing processes are required to produce silt in nature on a large scale very energetic processes are required many processes that are believed to generate silt particles have been listed however large scale production is essentially due to glacial grinding or to intense weathering processes in high cold tectonically active mountain regions the region of high asia of crustal overlap is a major generator of silt particles these form the productive alluvial soils of north india most of the nation of bangladesh the loess deposits along the syr darya and amu darya rivers in central asia and the great loess deposits of north china some claims have been made for silt production in hot deserts large amounts of very fine aerosolic dust are produced but in terms of loess sized particles this is a small scale process and leads to modest disputed deposits the loess deposits around the sahara usually have smaller mode sizes e g nigeria or larger mode sizes e g libya tunisia than the true chinese mode at 25 m this paper aims to introduce the distinguishing properties of sand and silt discuss in detail the possible processes of silt formation in relation to the evidence of what is produced describe the major silt populations and conclude on the most likely formation process es in particular three silt ranges are discussed in relation to the r size diagram c 2 5 m d1 20 30 m and d2 60 m these can represent canadian quickclay qq chinese loess and the ideal loughborough loess ll and north african loess nal it is intended that this paper will put into context the diverse work in the area and in so doing shed light on what is an often overlooked subject

active and passive imaging of hydraulic fractures hydraulic fracturing is a method commonly used to stimulate production in low permeability reservoirs with this method a viscous polymer based fluid is injected into the formation opening a fracture perpendicular to the direction of least principal stress this is followed by injection of a suspension of sand in liquid proppant which prevents the fracture from closing after the fluid pressure is allowed to bleed off after a fracture treatment the reservoir can be produced from the vicinity of a fracture surface which is substantially larger than the surface of the borehole

effects of filling fluid type and composition and joint orientation on acoustic wave propagation across individual fluid filled rock joints abstract wave propagation and attenuation in subsurface rock masses could be highly affected by rock joints filled with fluids however the understanding of acoustic behaviours across fluid filled rock joints is still at its infancy to determine the effects of the type and composition of filling fluids as well as joint orientation on compressional wave propagation and attenuation across individual fluid filled rock joints extensive laboratory acoustic tests were conducted in this paper results showed that the existence of water in fluid filled rock joints results in higher wave velocity more wave transmission and less wave attenuation compared to light oils in most circumstances increasing liquid content in a single liquid filled joint enhances wave velocity and wave transmission for dual liquid filled joints both wave velocity and wave transmission increase with increasing water content joint orientation significantly affects wave characteristics of rock joints partially filled with liquids while it has slight influences on wave attributes of rock joints fully filled with liquids in addition wave velocity and attenuation across fluid filled rock joints increases with increasing central frequency of incident compressional waves

melts_excel a microsoft excel based melts interface for research and teaching of magma properties and evolution the thermodynamic modeling software melts is a powerful tool for investigating crystallization and melting in natural magmatic systems rhyolite melts is a recalibration of melts that better captures the evolution of silicic magmas in the upper crust the current interface of rhyolite melts while flexible can be somewhat cumbersome for the novice we present a new interface that uses web services consumed by a vba backend in microsoft excel the interface is contained within a macro enabled workbook where the user can insert the model input information and initiate computations that are executed on a central server at ofm research results of simple calculations are shown immediately within the interface itself it is also possible to combine a sequence of calculations into an evolutionary path the user can input starting and ending temperatures and pressures temperature and pressure steps and the prevailing oxidation conditions the program shows partial updates at every step of the computations at the conclusion of the calculations a series of data sheets and diagrams are created in a separate workbook which can be saved independently of the interface additionally the user can specify a grid of temperatures and pressures and calculate a phase diagram showing the conditions at which different phases are present the interface can be used to apply the rhyolite melts geobarometer we demonstrate applications of the interface using an example early erupted bishop tuff composition the interface is simple to use and flexible but it requires an internet connection the interface is distributed for free from http melts ofm research org

summary of collapsible behaviour of artificially structured loess in oedometer and triaxial wetting tests this paper summarizes experimental studies on wetting induced collapsibility in loess using single oedometer double oedometer and triaxial wetting tests artificially structural loess samples with interparticle bonding calcite caco3 and a large void ratio were tested in the laboratory to avoid sampling disturbance of natural loess the comparison between the single and double oedometer tests confirms that the wetting induced deformation is independent of the sequence of wetting and loading the conventional triaxial apparatus was enhanced for investigating the collapse deformation in response to different water content increments when subjected to different stress levels the wetting induced strain subjected to high confining pressure develops in two steps it increases with increasing water content and reaches a relatively stable plateau and then increases rapidly again until a final stable state is reached the initial collapse surface was found by plotting the wetting induced strain vectors obser

phase equilibrium geobarometers for silicic rocks based on rhyolite melts part 2 application to taupo volcanic zone rhyolites constraining the pressure of crystallisation of large silicic magma bodies gives important insight into the depth and vertical extent of magmatic plumbing systems however it is notably difficult to constrain pressure at the level of detail necessary to understand shallow magmatic systems in this study we use the recently developed rhyolite melts geobarometer to constrain the crystallisation pressures of rhyolites from the taupo volcanic zone tvz as sanidine is absent from the studied deposits we calculate the pressures at which quartz and feldspar are found to be in equilibrium with melt now preserved as glass the quartz 1 feldspar constraint of gualda and ghiorso contrib mineral petrol 168 1033 doi 10 1007 s00410 014 1033 3 2014 we use glass compositions matrix glass and melt inclusions from seven eruptive deposits dated between 320 and 0 7 ka from four distinct calderas in the central tvz and we discuss advantages and limitations of the rhyolite melts geobarometer in comparison with other geobarometers applied to the same eruptive deposits overall there is good agreement with other pressure estimates from the literature amphibole geobarometry and h2o co2 solubility models one of the main advantages of this new geobarometer is that it can be applied to both matrix glass and melt inclusions regardless of volatile saturation the examples presented also emphasise the utility of this method to filter out spurious glass compositions pressure estimates obtained with the new rhyolite melts geobarometer range between 250 to 50 mpa with a large majority at 100 mpa these results confirm that the tvz hosts some of the shallowest rhyolitic magma bodies on the planet resulting from the extensional tectonic regime and thinning of the crust distinct populations with different equilibration pressures are also recognised which is consistent with the idea that multiple batches of eruptible magma can be present in the crust at the same time and can be tapped simultaneously by large eruptive events

high sr y magmas reflect arc maturity high magmatic water content and porphyry cu mo au potential examples from the tethyan arcs of central and eastern iran and western pakistan the temporal and geochemical evolution of arc magmatism that culminated in porphyry cu mo au deposit formation has been studied in three separate neo tethyan arc systems in central and eastern iran and western pakistan porphyry cu au deposits in the lut block of eastern iran formed in the middle eocene at the end of a period of extensive paleocene eocene volcanism porphyry cu mo deposits in the kerman belt of central iran formed in the middle miocene at the end of a period of voluminous eocene oligocene volcanism and porphyry cu au deposits in the chagai belt of western pakistan formed in four pulses during the eocene early miocene middle late miocene and late miocene pliocene after a prolonged period of arc magmatism that began in the late cretaceous and is still active in each region the late porphyry related magmas are more geochemically evolved and more hydrous as evidenced by the presence of hornblende phenocrysts than the preceding volcanic rocks we suggest that this reflects maturation of the arc magmatic system over a period of tens of millions of years leading to the generation of more evolved volatile rich magmas at later stages of the arc s history high magmatic water contents are a prerequisite for the shallow crustal emplacement of arc magmas and the subsequent generation of potentially ore forming subvolcanic magmatic hydrothermal systems it is thus suggested that the fertility of arc magmas within a given arc terrane can be assessed by observing the relative timing of plutonic suites later suites are more prospective noting the common presence of hornblende or biotite phenocrysts indicating high magmatic water contents and through lithogeochemical fingerprinting of magmatic fractionation processes relatively high sr y and la yb ratios and eun eu ratios 1 indicating abundant early hornblende fractionation and suppression of plagioclase crystallization in hydrous magmas

the physical and chemical evolution of fluids in rare element granitic pegmatites associated with the lacorne pluton quebec canada abstract co magmatic rare element be li nb ta granitic pegmatites associated with the lacorne monzogranite pluton of the preissac lacorne batholith quebec range from a least evolved beryl type in the pluton through a transitional beryl spodumene type to a most evolved spodumene type in mafic country rocks they possess internal lithologic fabrics and primary fluid inclusions that provide evidence for saturation of the magma with aqueous fluids immediately after the formation of aplite in the beryl pegmatite and pene contemporaneously with formation of the beryl spodumene and spodumene pegmatites the early fluids are represented by aqueous liquid vapor type 1a and aqueous liquid vapor solid type 2 inclusions in beryl from beryl and beryl spodumene pegmatites and are estimated to have been trapped between 500 and 550 c and at 3 5 kb on the basis of microthermometric measurements analyses of the compositions of the precipitates from decrepitated inclusions and the nature of the solids trapped these fluids are interpreted to have been nacl dominated 16 wt nacl eq and to have contained appreciable fe and dissolved co2 in spodumene pegmatite the equivalent fluid which was trapped at 450 to 500 c contained significant mn li and cs in place of fe consistent with corresponding trends in the chemical evolution of the host rock volatile rich mainly secondary aqueous fluid inclusions type 1b trapped in beryl are interpreted to reflect temporary sharp drops in pressure later in the crystallization history of the beryl bearing pegmatites due to local fluid overpressures that led to brecciation and consequent pressure release these inclusions have high salinity are cacl2 rich and are considered to represent magmatic hydrothermal fluids that acquired their calcium as a result of their interaction with the host lacorne pluton incursion of cacl2 rich fluids into the spodumene pegmatites is interpreted to have occurred earlier in their crystallization history i e upon emplacement of the pegmatites as shown by the fact that a high proportion of primary inclusions in spodumene in these pegmatites contains considerable calcium and calcium contents are generally higher in inclusions in spodumene than in beryl the inclusions in the spodumene pegmatites are thought to have acquired their calcium through interaction of the fluids with the amphibolites metabasalts that host these intrusions the crystallization of the pegmatites terminated with the entrapment of low salinity aqueous carbonic fluids type 3 inclusions in quartz 6 10 wt nacl eq which most likely formed as a result of the unmixing of the magmatic fluid into separate aqueous and carbonic fluids probably at temperatures between 250 and 350 c the results of this study show that aqueous fluid saturation can take place at an early stage of pegmatite emplacement and that magma evolution is matched by changes in the solute chemistry of the exsolving aqueous fluid they also show that evolution to a more volatile rich composition h2o f li may have contributed to the increased mobility of later magma batches thereby helping to explain the regional zonation of the pegmatites from beryl type within the pluton to spodumene type in the adjacent amphibolite

granite magma formation transport and emplacement in the earth s crust the origin of granites was once a question solely for petrologists and geochemists but in recent years a consensus has emerged that recognizes the essential role of deformation in the segregation transport and emplacement of silica rich melts in the continental crust accepted petrological models are being questioned either because they require unrealistic rheological behaviours of rocks and magmas or because they do not satisfactorily explain the available structural or geophysical data provided flow is continuous mechanical considerations suggest that far from being geologically sluggish granite magmatism is a rapid dynamic process operating at timescales of or 100 000 years irrespective of tectonic setting

low pressure origin of high silica rhyolites and granites abstracthigh silica rhyolites and granites 75 wt sio2 anhydrous basis are common features of the crust as part of both the volcanic and the plutonic records while low crystallization pressure 500 mpa we use glass compositions derived from the earthchem portal selected natural examples from the literature and rhyolite melts calculations to show that the phase relations in the quartz albite orthoclase ternary dictate the silica content of silicic melts in particular we show that silica content of melts increases with decreasing pressure as a result of the displacement of the quartz sanidine cotectic toward the qz apex with decreasing pressure it follows from our analysis that 1 the crust is expected to be stratified in terms of the silica content of residing melts 2 high silica glasses form at low pressure requiring shallow level cryst

geochemistry of the highly evolved sn w mo bearing mount douglas granite new brunswick canada implications for origin and mineralization abstract the late devonian 368 1 ma post orogenic peraluminous mount douglas granite located in southwestern new brunswick canada forms the eastern part of the saint george batholith the batholith was emplaced following the accretion of the gander and avalon zones of the northern appalachians during the neoacadian orogeny the mount douglas granite is divided into three units dmd1 dmd2 and dmd3 that formed by progressive high degrees of fractional crystallization the two most fractionated units i e dmd2 and dmd3 are locally associated with greisen sheeted veins related endogranitic sn w mo mineralization whole rock 18o values of 6 0 to 7 3 high initial 87sr 86sr ratios of 0 70550 to 0 71665 slightly positive end 368 ma values 0 3 to 1 1 and pb isotopic data indicate that the granite was derived dominantly from partial melting of juvenile avalonian crust contaminated by supracrustal rocks petrochemical features support the idea of multiple periods of fractional crystallization at lower temperatures producing compositionally more evolved magmas this is supported by estimated zircon saturation temperatures that decrease from dmd1 747 826 c dmd2 733 817 c dmd3 729 816 c the estimated crystallization pressure based on normative quartz and feldspar albite orthoclase contents also decreases with increasing silica content from 2 3 kbar 7 7 km in dmd1 to 0 3 kbar 1 km in dmd3 whole rock geochemical characteristics of this system show that unit dmd3 is the most highly evolved unit it has the highest sio2 avg 76 4 wt lile contents e g li rb cs rb sr mean 42 certain hfse ta th u including y 138 ppm and ree and has the most pronounced negative eu anomalies avg eu eu 0 08 and the lowest k rb 70 127 nb ta mean 4 9 and zr hf mean 23 5 therefore unit dmd3 with the highest content of incompatible elements is the most prospective for sn w zn bi and u mineralization and then dmd2

changes in tensile strength and microstructure of loess due to vibration abstract loess soils typically have an open and metastable structure humidification and vibration can modify their microstructure and thus influence their mechanical behavior in the present study to investigate the influence of train vibration on the tensile strength behavior of loess the tensile tests were performed on loess specimens that had been vibrated at a low amplitude for a long period using a modified horizontal extensograph in addition the microstructures of vibrated and non vibrated loess specimens before and after the tensile tests were characterized changes in the loess microstructure due to vibration and that in the tensile test were analyzed the results show that the relationship between uniaxial tensile strength and water content in soil specimen could be represented using a power function the axial displacement at failure varies at the same manner as tensile strength with respect to water content in comparison to intact loess occurrence of less clay bridges and clay buttresses between aggregates or coarse particles is identified in the disturbed specimens while aggregates are seen to be a very little more loose in vibrated specimens after the tensile tests than that before the tensile tests this indicates that vibration reduces the tension resistance and ductility of loess soil structure which could be attributed to loss of bonding strength as a result of breakage of clay cementations and disintegration of aggregates in the tensile test the soil structure goes through two distinct phases of change i e stretching phase and cracking phase in the stretching phase the tensile deformations take place throughout the specimen without altering the contacts between soil particles significantly in the cracking phase weak cementations fail to resist tensile deformation and suffer from breakage once a through crack is developed the specimen breaks in two leading to a catastrophic drop of tensile stress

collapsibility and seismic settlement of loess loess collapsibility and seismic settlement have proven to be costly geotechnical hazards in china since collapsibility assessment and mitigation are now conventional practices in chinese design codes some previous efforts have been made to relate collapsibility and seismic settlement in order to simplify assessment of the latter however these works have neglected mechanical difference between the two phenomena in this study the similarity and difference between collapsibility and seismic settlement of loess are analyzed which shows that both are based on the metastable microstructure of loess but their triggering mechanisms are different collapsibility is primarily driven by suction loss whereas seismic settlement is caused by shear failure of the loess matrix during dynamic loading though both of them result in collapse of trellis structure pores consequently the lack of a common mechanism demonstrates there is no tenable physical basis to relate collapsibility and seismic settlement

collapsibility composition and microstructure of loess in china the collapse potential mineralogy microstructure and particle morphology of a loess from the loess plateau china were characterized by double oedometer testing x ray diffraction scanning ele

s type granites in the western superior province a marker of archean collision zones detailed field observations indicate that neoarchean s type granites were emplaced along and or proximal to some terrane tectonic boundary zones in the western superior province southeastern m

stability of loess abstract lutenegger a j and hallberg g r 1988 stability of loess eng geol 25 247 261 the natural stability of loess soils can be related to fundamental geotechnical properties such as atterberg limits water content and void ratio field observations of unstable conditions in loess deposits in the upper midwest u s a show relationships between instability and the in situ moisture content and the liquidity index of the loess unstable loess can attain natural moisture contents equal to or greater than its liquid limit implications of these observations for applied engineering works are described

microstructure and soil water retention behavior of compacted and intact silt loess abstract there are an increasing number of mega engineering projects of removing the top of hills to fill in the valley for new land creation in the loess plateau of china which significantly changes the hydrological and geological equilibrium state of the site the formation of a new hydrological equilibrium state is associated with the water movement in the compacted and intact loess layers most disasters occurring in the loess area are related to water the soil water retention curve swrc is the key to the implementation of unsaturated soil mechanics in engineering practice and is required to numerically model the movement of water in the soil in this study the swrcs and microstructure of intact and compacted specimens from lanzhou and yan an two typical cities that have new land creation projects are investigated the swrc is obtained using the filter paper method the mercury intrusion porosimetry mip and scanning electron microscope sem techniques are used to explore the microstructure the results highlight that the intact loess has a higher air occlusion value aov and a similar slope of swrc in the transition zone compared with the remolded specimens that compacted at the natural water content the normalized swrc i e degree of saturation versus suction avo of the intact specimen is approximately the same as the remolded specimens compacted as the natural water content the difference in the microstructure between intact and compacted specimens originates from different existing states of the clay particles and further contributes to the variation of the swrc

fractured micro granitoid enclaves a stress marker abstract systematic parallel and steeply dipping tensile fractures within rounded to sub rounded micro granitoid enclaves are analyzed to decipher the stress condition at chitradurga granite dharwar craton south india the study is performed in two steps 1 assessing the fracturing condition through thermo mechanical model as fractures in granite may be related to thermal stresses during its cooling or to tectonics stresses 2 performing the plane strain mechanical solution for circular rigid inclusions to fractured enclaves where rock mechanics concepts of fracturing are integrated with kinematic analysis we interpret that the parallel systematic fractures in the micro granitoid enclaves developed due to the stress amplification inside enclaves when the host pluton was at shallow depth of 2 4 km the derived paleostress orientation fits well with the orientation and sense of movement to the adjacent chitradurga shear zone the deduced paleostress conditions from fractured micro granitoid enclaves are also in a good agreement with the previously revealed regional tectonics we conclude that the fractured micro granitoid enclaves are reliable stress indicator

petrology and geochemistry of the late eocene harrison pass pluton ruby mountains core complex northeastern nevada which suggest a single mixing event before emplacement in the upper the late eocene harrison pass pluton was emplaced in the crust late stage activity consisted of three pulses of monzogranitic transition zone between the infrastructure and suprastructure of the magma plus sparse mafic dikes the largest and youngest of these ruby mountains core complex emplacement was at 3 kbar pulses the two mica monzogranite of green mountain creek is pressure and was in two stages early stage tonalitic to monzogranitic distinct from all other units in the presence of restitic enclaves low magmas followed by late stage monzogranites and mafic dikes nd and high initial sr sr pod like bodies of leucocratic biotite the early stage began with emplacement of biotite hornblende amphibole monzogranite and sheets and dikes of leucocratic granodiorite of toyn creek followed by the biotite monzogranite of two mica monzogranite make up the other late stage granites these corral creek quenched equivalents of these units are preserved as rocks display deep negative eu anomalies and show wide nonporphyritic dikes in the roof leucocratic monzogranite that forms systematic concentrations of high field strength elements however cupolas in the roof zone represents the product of fractional crystheir isotopic compositions are identical to those of the early stage tallization of the early magmas al in hornblende barometry and rocks they are thought to be small melt fractions of the lower to the presence of magmatic epidote suggest that early stage magmas middle crust their elemental compositions are thought to result resided at a pressure of 5 6 kbar before emplacement in the from the effects of residual plagioclase and accessory minerals the upper crust compositional variation in the toyn creek and corral variable and non systematic isotopic compositions of all granitic creek units is essentially linear and can be explained by mixing units in the pluton suggest a heterogeneous source region such as of a tonalitic end member with a monzogranitic end member such the proterozoic mojave province as evolved samples of the monzogranite of corral creek the tonalitic end member was itself a hybrid that formed by interaction

chemical composition of rock forming minerals in gold related granitoid intrusions southwestern new brunswick canada implications for crystallization conditions volatile exsolution and fluorine chlorine activity chemical composition of rock forming miner als in appalachian siluro devonian granitoid intru sions southwestern new brunswick was systematically determined by electron microprobe the mineral chem ical data together with petrographic examination was used to test magmatic equilibration and to constrain crystallization conditions volatile exsolution and fluo rine chlorine activity of fluids associated with these intrusions mineralogical distinction between late silu rian to early devonian granodioritic to monzogranitic series gms and late devonian granitic series gs rocks is evident although both are subsolvus i type to evolved i type granitoids oxidized to reduced gms rocks consist of quartz plagioclase an 10 k feld spar biotite apatite titanite zircon monazite hornblende pyroxene magnetite ilmenite and sulfide gs rocks comprise quartz k feldspar pla gioclase an 10 mica group minerals zircon mon azite apatite sulfide ilmente magnetite topaz columbite and xenotime inter intrusion and intra intrusion variations in mineral chemistry are in terpreted to reflect petrogenetic processes e g assim ilation and fractional crystallization during granitoid evolution although magmatic equilibration among rock forming minerals are disturbed by subsolidus hy drothermal processes gms rocks appear to have higher magmatic temperatures variable levels of emplacement a range of fo2 i e reduced intrusions 10 16 7 10 13 4 and oxidized intrusions 10 14 0 10 10 5 bars and rela tively low fhf fhcl ratios 10 3 0 10 1 0 in exsolved fluids compared to gs rocks reduced gms intrusions bear higher gold potential and thus may be prospective targets for intrusion related gold systems

engineering geological problems of loess in poland abstract grabowska olszewska b 1988 engineering geological problems of loess in poland eng geol 25 177 199 in poland loess covers are limited to a latitudinal belt in the southern part of the country the covers vary from 2 to 30 m in thickness and the loesses are developed in three major facies eolian deluvial and alluvial stratigraphically they represent four major horizons correlated with the vistulian wurm glaciation and some older ones the paper presents characteristics of granulometric mineral and chemical compositions with reference to origin facies and stratigraphic position of these soils as well as their lithofacies classification the classification gives the basis for analysis of local and regional variability in engineering geological properties of the loess

pleistocene loess in the humid subtropical forest zone of east asia 1 loess deposits in asia have been used as indicators of palaeoclimate because they are usually found bordering deserts this paper reports extensive and thick deposits of loess in tropical southwest china between latitudes 18 and 23 30 n which is 1300 km south of known and extensively researched loess deposits in north china the present climate of the reported loess areas is hot and humid with mean annual rainfall of 1000 2000 mm and vegetation of subtropical evergreen broadleaf forest this compares with less than 400 mm rainfall and vegetation of semi desert steppe in areas of current loess accumulation on desert margins in north china the source area of the loess which is dated by optical luminescence to the late pleistocene from 90 222 ka is thought to be the exposed east asian shelf which was up to 140 m below present sea level during quaternary arid phases recent research on the nature of the shelf environment and the relatively large particle size of the loess suggests a local origin the reported loess is not interbedded with palaeosols and small amounts of soil cover the loess compared with well developed soils in loess in semiarid regions in north china this is explained by elimination of the supply source by sea level rise following each arid phase as continued dust supply appears necessary for soil to form this preliminary report of loess in southwest china conflicts with palynological evidence and suggests that recent reconstructions of pleistocene aridity in east asia may be conservative

fragipan formation in loess soils development of the bryant hydroconsolidation hypothesis abstract the formation of fragipans is still a matter for investigation and discussion bryant soil sci soc am spec publ 24 1989 pp 141 150 suggested that the hydroconsolidation process structure collapse when loaded and wetted may contribute to fragipan formation experimental studies of the collapse behaviour of both undisturbed and model loess soils are reported these demonstrate that the small clay model of hydroconsolidation advanced by rogers et al eng geol 37 1994 83 113 appears to explain many aspects of the collapse of loess soils when loaded and wetted this small clay model can reconcile the bryant suggestion with collapse observations and in so doing can satisfy all of the important criteria governing the formation of fragipans in particular it can explain the constant depth of occurrence the small clay model requires the soil structure to collapse under the control of a critical and limited clay mineral content too much or too little clay does not allow collapse to occur as indicated by oedometer test data for both undisturbed and reconstituted loess soils under simulated field conditions the fragipan should form in a metastable soil one capable of some linear collapse

scattering by hydraulic fractures finite difference modeling and laboratory data reservoir production can be stimulated by creating hydraulic fractures that effectively facilitate the inflow of hydrocarbons into a well considering the effectiveness and safety of the operation it is desirable to monitor the size and location of the fracture in this paper we investigate the possibilities of using seismic waves generated by active sources to characterize the fractures first we must understand the scattering of seismic waves by hydraulic fractures for that purpose we use a finite difference modeling scheme we argue that a mechanically open hydraulic fracture can be represented by a thin fluid filled layer the width or aperture of the fracture is often small compared to the seismic wavelength which forces us to use a very fine grid spacing to define the fracture based on equidistant grids this results in a large number of grid points and hence computationally expensive problems we show that this problem can be overcome by allowing for a variation in grid spacing in the finite

seismic reflection coefficients of faults at low frequencies a model study we use linear slip theory to evaluate seismic reflections at non welded interfaces such as faults or fractures sandwiched between general anisotropic media and show that at low frequencies the real parts of the reflection coefficients can be approximated by the responses of equivalent welded interfaces whereas the imaginary parts can be related directly to the interface compliances the imaginary parts of low frequency seismic reflection coefficients at fault zones can be used to estimate the interface compliances which can be related to fault properties upon using a fault model at normal incidence the expressions uncouple and the complex valued p wave reflection coefficient can be related linearly to the normal compliance as the normal compliance is highly sensitive to the infill of the interface it can be used for gas fluid identification in the fault plane alternatively the tangential compliance of a fault can be estimated from the complex valued s wave reflection coefficient the tangential compliance can provide information on the crack density in a fault zone coupling compliances can be identified and quantified by the observation of ps conversion at normal incidence with a comparable linear relationship

the mechanics of a saturated silty loess and implications for landslides the results from an intensive experimental investigation on a loess that was retrieved from a typical silty loess zone in the north western chinese loess plateau are presented and interpreted triaxial and oedometer tests were performed on intact and reconstituted samples in a saturated condition the soil behavior was found to be strongly affected by structure the compression paths of the intact samples crossed the intrinsic compression line of the reconstituted soil and reached well defined gross yield points after which the compression paths converged towards the intrinsic compression lines two critical state lines were defined for the intact and reconstituted soils in the volumetric plane as a result of a robust element of natural structure comparisons were made with a structured clayey loess retrieved from the south eastern loess plateau it was found that the effects of structure on the behavior of the two loess soils are similar though they are very different in natural properties this indicates that their natural structures might have experienced similar forming processes perhaps related to their common origin catastrophic flowslides commonly occur in the study area and the patterns of behavior observed in the laboratory tests may create some new insights into mechanisms of landslide initiation and subsequent movement as discussed in the study

time lapse velocity analysis application to onshore continuous reservoir monitoring in 4d seismic the velocity model used for imaging and reservoir characterization can change as production from the reservoir progresses this is particularly true for heavy oil reservoirs stimulated by steam injection in the context of sparse and low fold seismic acquisitions conventional migration velocity analyses can be inadequate because of a poorly and irregularly sampled offset dimension we propose to update the velocity model in the context of daily acquisitions with buried sources and receivers the main objective is to demonstrate that subtle time lapse effects can be detected over the calendar time on onshore sparse acquisitions we introduce a modified version of the conventional prestack time migration to detect velocity changes obtained after cross correlation of the base and monitor surveys this technique is applied on a heavy oil real data set from the netherlands and reveals how the steam diffuses over time within the reservoir

the nature origin and accumulation of loess abstract loess can be defined simply as a terrestrial clastic sediment composed predominantly of silt size particles which is formed essentially by the accumulation of wind blown dust there are three fundamental requirements for its formation 1 a sustained source of dust 2 adequate wind energy to transport the dust and 3 a suitable accumulation site most loess has been modified to some degree by local reworking bioturbation and syn depositional weathering but a process of loessification is not necessary for a dust deposit to qualify as loess the terms primary loess and secondary loess have previously been used to described wind deposited loess and redeposited loess respectively but it is more accurate to describe material reworked and redeposited by non aeolian processes as loess derived colluvium or loess derived alluvium during the quaternary loess formed in three main situations 1 mid continental shield areas beyond the limits of ice sheets periglacial loess 2 on the margins of high mountain ranges perimontane loess and 3 on the semi arid margins of some lowland deserts peridesert loess peridesert loess is relatively poorly developed partly due to the limited efficiency of silt generating mechanisms in low land deserts compared with glaciation but also important is the tendency in arid areas for dust to be dispersed over a wide area and to be rapidly reworked after deposition particularly in areas which experience frequent climatic changes the remarkably thick loess of china and central asia results from an unusual combination of conditions which has persisted for much of the last 2 3 million years namely rapid uplift of the tibetan plateau and surrounding mountain ranges high rates of sediment production and supply to adjacent basins a strong northwesterly and westerly wind regime and the existence of effective dust traps downwind of the source regions

collapse and strength characteristics of loess in thailand abstract collapse and strength characteristics of loess of thailand are presented the metastable loose structure of the soil which makes it susceptible to collapse is mainly attributed to clay bridge bonds collapsibility of the loess is strongly governed by water content and the magitude of applied stress under an increasing load the critical pressure at which collapse started to occur was greater for the loess with a lower water content at natural water content the critical pressure was greater than the overburden pressure collapse caused by wetting at a given applied stress always resulted in approximately the same final porosity regardless of the initial water content this reflected the existence of a unique post wetted relationship between void ratio and applied stress the predicted collapse settlement based on the double consolidation test results compared reasonably well with the settlements measured in the field plate bearing tests for shear strength besides the initial water content and consolidation pressure drainage condition is an important influencing factor loose structure could remain after initial saturation and consolidation at pressure as high as 400 mpa leading to a much lower undrained strength than drained strength

the structure degradation of a silty loess induced by long term water seepage abstract loess is a typical silt sized aeolian soil that is widely deposited and possesses a fragile soil structure susceptible to collapse upon wetting the instability of shallow loess slopes is well documented but deeper failures triggered by rainfall and irrigation can also occur in the case of long term seepage clay particles and salts have been observed to leach out of the loess slopes this paper presents a systematic laboratory study of the effects of water conditions on the mechanical behaviour of silty loess with isotropic compression and bender element tests carried out on natural and reconstituted loess recovered at 10 m depth from a site in china the results show that saturation causes reduction in both the compression yield stress and small strain stiffness of the soil and that after being exposed to seepage they decrease further the possible mechanism of structure degradation is investigated by means of microscopic and chemical analyses and it is found that seepage will cause the pore ions concentration to reduce with a loss of clay mineral bonding strength resulting in the detachment of silt particles from aggregates this work highlights the importance of monitoring the water outflow in the field at the loess slope edge since it may causes large deformation in the long term

avo inversion for a non welded interface estimating compliances of a fluid filled fracture though well known for layer boundaries the use of amplitude versus offset avo variations for non welded boundaries like fractures is not yet investigated depending on the seismic wavelength used fractures can be regarded as thin compliant zones in rocks in different scales we explore the potential of multiangle avo inversion of p p and p s reflections from a fracture to estimate fracture properties we conduct laboratory experiments to measure reflection responses of dry and wet fractures the observed p p reflections of the wet fracture and the fracture aperture are very well predicted by the non welded interface model we invert the angle dependent p p reflectivity of the fracture to estimate both normal and tangential fracture compliances the estimated value of the normal compliance is accurate and it is also possible to obtain the value of the non zero tangential compliance we find that supplementing the information of converted p s reflections in theavoinversion greatly improves the estimate of the tangential compliance the calculated compliance ratio clearly shows the existence of fluid in the fracture this finding can be crucial for new applications in a wide range of scale from earthquake seismology deep and shallow seismic exploration to non destructive material testing

temporal variation in the permeability anisotropy behavior of the malan loess in northern shaanxi province china an experimental study by analyzing a fresh soil section and soil samples from yan an new area northwest china an engineering shallow loess slope was investigated temporal variation in the saturated horizontal hydraulic conductivity kh and saturated vertical hydraulic conductivity kv of loess samples were measured using variable head permeability tests the kh and kv values indicate that the loess exhibited permeability anisotropy in space and time and kh and kv at different depths decreased as seepage time increased kh time showed an exponentially decreasing trend and kv time showed a linearly decreasing trend analysis of the initial state and micromorphological features of the loess indicate that the orientation of soil particles in the deposition process may be inherently anisotropic the kh and kv values of the loess tended to decrease with depth as described by an exponential decay model

equivalent medium representation of fractured rock a similarity may be found between various approaches for determining the effects of parallel fractures or aligned cracks on seismic wave propagation at wavelengths that are long compared with the scale length of the cracks fractures can be modeled using an empirical linear slip condition however natural fracture surfaces can also be simulated directly as planar distributions of small isolated areas of slip cracks model 1 or conversely as planar distributions of imperfect interfacial contacts model 2 an alternative is plane surfaces separated by thin continuous layers of viscous fluid or a soft material model 3 we present analytic expressions for the fracture compliances for these three models and using these analytic results compute the effective compliances and stiffnesses of the fractured material as a result it is possible to relate the measured compliances or stiffnesses directly to the statistics of the microstructural details of a fracture given appropriate a priori information on the fracture surfaces the results for model 1 are equivalent to a volume distribution of cracks as studied by hudson 1980 1981 for small crack density the results for model 2 are basically the same as those given by white 1983 for a packing of spheres and finally the results for model 3 are in agreement with those given by backus 1962 for combinations of two constituent layers these results can be extended to the case of nonaligned fractures and to allow for fluid flow between cracks and into a porous matrix rock finally it is shown that the ratio of the normal to shear fracture compliance is a good indicator of the properties of the fracture infill

experimental constraints on rhyolite melts and the late bishop tuff magma body thermodynamic models are vital tools to evaluate magma crystallization and storage conditions before their results can be used independently however they must be verified with controlled experimental data here we use a set of hydrothermal experiments on the late erupted bishop tuff lbt magma to evaluate the rhyolite melts thermodynamic model a modified calibration of the original melts model optimized for crystallization of silicic magmas experimental results that are well captured by rhyolite melts include a relatively narrow temperature range separating the crystallization of the first felsic mineral and the onset of the ternary minimum quartz plus two feldspars and extensive crystallization over a narrow temperature range once the ternary minimum is reached the model overestimates temperatures by 40 c a known limitation of rhyolite melts at pressures below 110 mpa model and experiments differ in the first felsic phase suggesting that caution should be exercised when applying the model to very low pressures our results indicate that for quartz sanidine plagioclase magnetite and ilmenite to crystallize in equilibrium from lbt magma magma must have been stored at 740 c even when a substantial amount of co2 occurs in the coexisting fluid such temperatures are in conflict with the hotter temperatures retrieved from magnetite ilmenite compositions 785 c for the sample used in the experiments consistent with other recent studies we suggest that the fe ti oxide phases in the late bishop tuff magma body are not in equilibrium with the other minerals and thus the retrieved temperature and oxygen fugacity do not reflect pre eruptive storage conditions

an experimental study on the compaction and collapsible behaviour of a flood defence embankment fill with renewed interest in the performance of flood embankments globally it is important that the performance of fills in conditions similar to as constructed are scrutinised the fill material investigated in this study was sampled from flood embankments located along the bengawan solo river in east java indonesia the recurrent history of overtopping and stability issues in these embankments provided the motivation for developing a better understanding of the behaviour of this compacted fill under different loading and wetting conditions the site investigation revealed that the embankment fill was compacted at low dry densities and that there was local variation in the dry densities determined a detailed study highlighted that at low compactive efforts this fill material exhibits an irregular double peak compaction curve which can be explained by the tendency of this fill to form aggregates on wetting to cover different plausible operational conditions of these embankments saturated and unsaturated compression oedometer tests and one dimensional collapse tests were performed under different initial conditions specimens compacted at conditions similar to as constructed exhibited significant collapse deformation up to 13 6 on wetting evolution of the microstructure during loading and wetting paths was investigated using mip and esem a physically based framework proposed by romero 2013 was used to explain the changes in the macroscale collapse behaviour observed in the oedometer tests based on the evolution of microporosity using this model the evolution of the microporosity with dry density and water content was presented this microstructural approach could be used as a tool for specifying appropriate compaction conditions for earthworks where fill material is susceptible to volumetric collapse

the invisible hand tectonic triggering and modulation of a rhyolitic supereruption identifying the processes that initiate and control large explosive eruptions on time scales of human interest is challenging we present evidence for syneruptive subsurface interactions between rhyolite magmas derived from distinctive sources that reflect tectonic processes starting then temporarily stopping the 27 ka oruanui supereruption 530 km 3 magma taupo new zealand subordinate 3 16 biotite bearing pumice lapilli occur in fall deposits from phases 1 and 2 of 10 among the biotite free normal pumices in the oruanui deposits the biotite bearing magma is sourced to an independent magmatic system 10 15 km northeast of taupo lateral migration of the biotite bearing magma was initiated during a rifting episode that also triggered the oruanui eruption limited physical mingling indicates that the biotite bearing and oruanui biotite free magmas interacted in the conduit simultaneously with eruption after phase 1 a time break of months elapsed before phase 2 explosive activity resumed from the same vent again with intermixed biotite bearing magma a rift related tectonic event with its accompanying stress change is inferred to have initiated diking from northeast to southwest transporting biotite bearing magma and triggering the oruanui eruption stress relaxation following the rifting event terminated phase 1 before a tectonic event caused renewed diking and activity in phase 2 tectonics may trigger large silicic eruptions through rupturing of shallow crustal magma chambers and lateral magma transport especially in extensional regimes without necessarily leaving any discernible geological imprint only the presence of a foreign magma in the oruanui deposits allows the tectonic control to be identified

sagging of loesses and its problems abstract there exists disagreement in the world literature with regard to the characterization of sagging the term sagging should be used solely in relation to loesses and we define it as the process in which a sudden decrease of soil volume takes place the factors which cause sagging are internal genesis geomorphological position grain size content of soluble components porosity etc and external shear stress natural moisture groundwater table infiltration flow etc the mechanism of sagging is a very complicated process which depends on many factors in principle the process of sagging can be divided into three time phases which succeed each other gradually in the first phase there occurs the destruction of the original microstructure the clay envelopes bridges and buttresses are disintegrated in the second phase the collapse of the microstructure takes place meanwhile the clay minerals as well as the soluble salts and partly the oxides of metals are leached from the soil after sagging i e in the third phase the soil acquires a heterogeneous structure compared to the original homogeneous one the relationships are changed between the individual structural elements the size and the percentual representation of pores changes

a method for calculation of soil structural pressure values abstract the values of soil structural pressures may serve as identifiers of boundaries of deformation zones below foundations under soil structural pressure sz we will understand the maximum stress value for which only recoverable deformations may be observed the paper presents a method for determination of structural pressures using oedometer test results experimental data published in literature were used for demonstration of the proposed method

coupling of remote sensing data aided with field investigations for geological hazards assessment in jazan area kingdom of saudi arabia the city of jazan is situated on the eastern flank of the read sea and considered as one of the fastest growing cities in the kingdom of saudi arabia this zone attracts a lot of investors for various development projects recently many new projects have been implemented and constructed in this region including new urban areas infrastructures and industrial projects however historically this area has been challenged from different types of geological hazards these geological hazards are catastrophic events that can cause human injury loss of life and economic devastation the current study is aimed at evaluating the different types of geological hazards in jazan city this study is based on interpretation of satellite data such as landsat and quickbird images existing geological maps and physiographical characteristics with the help of field and laboratory analyses the results of the analysis indicate that there exist various types of geological hazards in the study area mostly related to the natural factors which include 1 sabkha soil 2 salt dome 3 loess soil and 4 sand dune drift further the findings of this study revealed that most of these geological hazards have a severe impact on the ongoing development activities in jazan area

spatial analysis of surface deformation distribution detected by persistent scatterer interferometry in lanzhou region china persistent scatterer synthetic aperture radar interferometry ps insar is a remote sensing method that can be used to detect surface deformation which is an indicator of potential geohazards by capturing such deformations over time it is possible to obtain valuable information regarding geohazards such as landslides this study focused on the use of ps insar to investigate the distribution and causes of surface deformation in the lanzhou region of gansu province in china between 2003 and 2010 41 advanced synthetic aperture radar images were captured by the envisat satellite and analyzed using ps insar and the correlation between the observed surface deformation and topographic geologic and anthropogenic factors was derived based on a geographic information system platform it was found that the largest number and highest density of surface deformations occurred at elevations of 1486 1686 m it was also established that slope ranges of 25 30 and 35 40 are threshold values at which surface deformation changes abruptly and that slopes with north and northwest aspects are most prone to surface deformation the lithologies most susceptible to surface deformation are clay sandy soil and loess the normalized difference vegetation index indicated that surface deformation occurred most often in areas with sparse vegetation anthropogenic activities e g construction and wastewater discharge could be inferred as causal mechanisms of surface deformation comparison of the distributions of geohazards and surface deformation showed considerable consistency which proves surface deformation can induce geohazards these results could help governments improve urban planning and geohazard mitigation

a review of shallow ore related granites textures volatiles and ore metals shallow texturally complex granites can be associated spatially introduction and temporally with hydrothermal alteration and mineralization granite related ore deposits include porphyry and skarn the formation of a granite related ore deposit represents the confluence type ores and other hydrothermal deposits that are of many chemical and physical geological factors including magma spatially and temporally associated with granitic sensu composition e g concentrations of ore metals chlorine and water lato rocks in this paper i emphasize characteristics magma oxidation state the relative timing of crystallization magma found in porphyry style cu mo au deposits and some ascent magmatic volatile phase exsolution and the depth of em related systems however my treatment here is not meant placement early magmatic crystallization of ore metal rich minerals to cover the full range of granitic rocks and mineralization coupled with late exsolution of the magmatic volatile phase is that make up the granite related ore systems the forpromoted by deeper emplacement levels and lower magmatic water mation of granite related ore deposits by orthomagmatic concentrations and leads to low eyciencies of removal of compatible hydrothermal processes is dependent upon many physical elements from melts into the magmatic volatile phase s water and chemical magmatic factors including but not limited concentrations in the melt and pressures of crystallization can be to the composition and evolution of the associated estimated from phase equilibria and textural relationships of horn magmas the rate of magma ascent the depth and blende in some felsic systems physical factors avect the dynamics geometry of magma emplacement and the local temof fluid magma melt and volatile phase movement which in turn perature and stress fields at the site of magma emavect the size of zones of alteration and mineralization granite placement detailed studies of the igneous rocks textures can record the partial history of some dynamic processes associated with ore deposits can therefore yield critical miarolitic cavities are good evidence for magmatic volatile phase information regarding the source of metals and ligands exsolution both miarolitic cavities and pegmatitic texture exhibit in the ore generative hydrothermal solutions that are evidence for external nucleation of crystals nucleation controlled operative in the formation of granite related ores in this phenomena expressed as variations in granite textures can result review i will present a series of narratives consistent in from a multiplicity of causes including undercooling of the melt my view with prevailing field and experimental data on textural elements such as pegmatite aplite skeletal crystals and the orthomagmatic hydrothermal theory for the genesis graphic textures can form as a result of undercooling interconnected of some granite related deposits volumes of the magmatic volatile phase allow for advection of some high level granites i e those that are emplaced hydrothermal ore fluids through the magma in shallow granitic at depths of 8 km or less represent the crystallized systems miarolitic cavities can be interconnected consistent with remains of magmas that were associated with subvolcanic this hypothesis ore generative hydrothermal systems therefore studies of shallow granites aimed at understanding magmatic evolution and volatile phase exsolution at shallow levels are necessary if we are to understand ore genesis and the deep inputs to present day geothermal systems as well as evaluate hazards associated with the volcanic

fundamental properties of loess from northwestern china abstract in view of the industrialisation of northwestern china widespread research was undertaken on the properties of loess in this area this paper deals with a part of these investigations a brief report is given on the distribution of loess in china and their aeolian origin a microstructure model of chinese loess is suggested which can explain its collapsible behaviour and the sensitivity of the mechanical properties of macroporous loess to slight changes of the water content it is emphasised that the physico chemical and mechanical properties of loess are mainly governed by the granular fraction which contains illites montmorillonites and soluble salts results of physico chemical and mineralogical investigations are presented and analysed the fundamental mechanical properties of loess were determined by oedometer triaxial rheological and permeability testing conclusions and suggestions are presented for practical engineering

formation and development of the structure of collapsing loess in china abstract gao g 1988 formation and development of the structure of collapsing loess in china eng geol 25 235 245 it is well known that in china the regional variations in microstructure of loess are in phase with the overall tendency for collapsibility gradually decreasing from the northwest to the southeast these differences are consistent with variations in climatic conditions this indicates that the structure of collapsing loess is closely related to the climatic condition and geological environment based on the microstructure analyses it can be assumed that the formation and development of the structure of collapsing loess in china has undergone five stages the loessization stage the formation stage the development stage the degeneration stage and the clayization stage the five stages of loess regularly exist in different regions of the loess plateau this also shows that under the modern climatic condition the collapsing loess in the northwest of the loess plateau in china is still developing however the feature of collapsing loess is gradually disappearing in the southeast of the loess plateau

time lapse reconstruction of the fracture front from diffracted waves arrivals in laboratory hydraulic fracture experiments 4d acoustic imaging via an array of 32 sources 32 receivers is used to monitor hydraulic fracture propagating in a 250 mm cubic specimen under a true triaxial state of stress we present a method based on the arrivals of diffracted waves to reconstruct the fracture geometry and fluid front when distinct from the fracture front using bayesian model selection we rank different possible fracture geometries radial elliptical tilted or not and estimate model error the imaging is repeated every 4 seconds and provide a quantitative measurement of the growth of these low velocity fractures we test the proposed method on two experiments performed in two different rocks marble and gabbro under experimental conditions characteristic respectively of the fluid lag viscosity marble and toughness gabbro dominated hydraulic fracture propagation regimes in both experiments about 150 to 200 source receiver combinations exhibit clear diffracted wave arrivals the results of the inversion indicate a radial geometry evolving slightly into an ellipse towards the end of the experiment when the fractures feel the specimen boundaries the estimated modelling error with all models is of the order of the wave arrival picking error posterior estimates indicate an uncertainty of the order of a millimeter on the fracture front location for a given acquisition sequence the reconstructed fracture evolution from diffracted waves is shown to be consistent with the analysis of 90 circ incidence transmitted waves across the growing fracture

stoneley wave generation by an incident p wave propagating in the surrounding formation across a horizontal fluid filled fracture abstract this study investigates the generation of the low frequency borehole stoneley wave tube wave by a plane p wave propagating through the surrounding elastic formation which is intersected by a fluid filled fracture a model is constructed taking into account the dynamic fluid coupling between the borehole interior and the fluid filled fracture of infinite extent with parallel walls the basic mechanism of such coupling is due to the contraction of the fracture walls by the incident p wave leading to seismic radiation into the fracture the dynamic fluid flux from the fracture into the borehole interior and vice versa is the source of the low frequency stoneley wave an expression for the monopole pressure source exciting the tube wave is obtained the tube wave equation in the long wave approximation is derived in the presence of a fluid filled fracture of infinite extent amplitudes and waveforms of stoneley waves are analysed in the seismic wavelength range for p wave pulses of various shapes it is shown that the amplitude and waveform of the stoneley wave depends significantly on the two dimensionless parameters of the problem 1 the ratio of the borehole radius to the dominant wavelength of the incident pulse 2 the ratio of the fracture width to the borehole radius it is found that the amplitude of the generated stoneley wave can be of the order of the p wave amplitude in the borehole fluid stoneley waveforms are found to be completely different from those of the incident pulse

numerical modelling of seismic waves scattered by hydrofractures application of the indirect boundary element method summary we use a numerical method that can model the seismic waveforms scattered from an arbitrary number of fractures that are either empty or contain elastic or fluid material the indirect boundary element method bem is capable of generating the full elastic wavefield and is programmed in 2 d the governing equations and discrete implementation of the technique are described we explain in detail a new approach for evaluating the improper boundary integrals the method is shown to be highly accurate from a comparison with mode summation subsequently the bem is applied to modelling hydrofractures synthetic examples calculated for cross well and single well geometries demonstrate the effects of crack length opening and infill on recorded displacements it is shown that diffractions from the tips can in principle be used to locate and determine the hydrofracture size these arrivals depart from ray theoretical travel times due to defocusing over a fresnel zone s wave diffractions generally have a larger amplitude than the diffracted p waves and so may provide a better indication of fracture size energy which is converted to interface waves and subsequently diffracted from the crack tips is also observed the presence of water allows energy to pass through the fracture this is clearly evident on the cross well seismograms closure of the fracture causes a further increase in transmission amplitude as less energy is attenuated through internal multiples

ascent driven crystallisation of dacite magmas at mount st helens 1980 1986 we introduce a novel scheme that enables natural silicic glasses to be projected into the synthetic system qz ab or h2o in order to relate variations in volcanic glass chemistry to changing pressure p and temperature t conditions in the sub volcanic magma system by this means an important distinction can be made between ascent driven and cooling driven crystallisation under water saturated or undersaturated conditions in samples containing feldspar and a silica phase quartz or tridymite quantitative p t estimates of the conditions of last equilibrium between crystals and melt can be made formation of highly silicic melts i e 77 wt sio2 is a simple consequence of the contraction of the silica phase volume with decreasing pressure such that high silica glasses can only form by crystallisation at low pressure resorption of quartz crystals appears to be a further diagnostic feature of decompression crystallisation groundmass and inclusion glasses in dacites from the 1980 1986 eruption of mount st helens volcano wa span a wide range in sio2 68 80 wt anhydrous the compositions of the least evolved sio2 poor inclusions in amphibole phenocrysts record entrapment of silicic liquids with 5 4 wt water corresponding to a water saturation pressure of 200 mpa at 900 c the compositions of more evolved higher sio2 plagioclase hosted inclusions and groundmass glasses are consistent with extensive ascent driven fractional crystallisation of plagioclase oxide and orthopyroxene phenocrysts and microlites to low pressures during this polybaric crystallisation plagioclase phenocrysts trapped melts with a wide range of dissolved water contents 3 5 5 7 wt magmas erupted during the plinian phase of the 18 may 1980 eruption were derived from a large reservoir at depths of 6 km subsequent magmas ascended to varying depths within the sub volcanic system prior to extraction from glass chemistry and groundmass texture two arrest levels have been identified at depths of 0 5 1 and 2 4 km a single dome sample from february 1983 contains groundmass plagioclase tridymite and quartz testifying to temperatures of at least 885 c at 11 mpa these shallow storage conditions are comparable to those in the cryptodome formed during spring 1980 the corresponding thermal gradient 0 2 c mpa 1 is consistent with near adiabatic magma ascent from 8 km we argue that the crystallisation history of mount st helens dacite magma was largely a consequence of decompression crystallisation of hot magma beyond the point of water saturation this challenges the conventional view that phenocryst crystallisation occurred by cooling in a large magma chamber prior to the 1980 1986 eruption because the crystallisation process is both polybaric and fractional it cannot be simulated directly using isobaric equilibrium crystallisation experiments however calculation of the phase proportions in water saturated 910 15 c experiments by rutherford et al 1985 over the pressure range 220 125 mpa reproduces the crystallisation sequence and phenocryst modes of mount st helens dacites from 18 may 1980 by allowing for the effects of fractional versus equilibrium crystallisation entrained residual source material and small temperature differences between nature and experiment phase compositions can also be matched to the natural samples we conclude that decompression of water saturated magma may be the dominant driving force for crystallisation at many other silicic volcanic centres

meso and neoarchean evolution of the island lake greenstone belt and the northwestern superior province evidence from lithogeochemistry nd isotope data and u pb zircon geochronology abstract the island lake greenstone belt is located on the northern margin of the north caribou terrane a large reworked mesoarchean crustal block in the northwestern superior province the belt experienced a long and complex geological history manifested by an older mesoarchean 2 897 2 852 ga and a younger neoarchean 2 744 ga volcanic assemblages comprising chronologically and geochemically distinct mafic and felsic volcanic rocks and associated plutonic rocks the mafic volcanic rocks in these assemblages are subdivided into two groups with distinct geochemical signatures 1 enriched in th and lree and with pronounced negative nb ta and ti anomalies and 2 with broadly flat ree patterns without apparent nb ta and ti anomalies the geochemical characteristics of these mafic volcanic rocks are interpreted to have formed in magmatic arc settings with a protracted history consistent with nd isotope data that require variable inputs of an older ca 3 0 ga crustal source i e the north caribou terrane for their formation crustal contamination appears to decrease with decreasing age in the volcanic assemblages and associated plutonic rocks together these data suggest that the meso and neoarchean volcanic assemblages are parts of a primary volcanic stratigraphic sequence built on the same ca 3 0 ga basement and have autochthonous relationships with each other u pb zircon id tims geochronology constrained the ages of two episodes of deformation d 1 and d 2 in the belt two dykes crosscutting an older foliation place a minimum age of ca 2 723 ga on the d 1 deformation and two syn kinematic dykes dated movement along d 2 transpressional shear zones at ca 2 70 ga geological geochemical and geochronological data indicate that the tectonic evolution in the island lake greenstone belt and in the northwestern superior province took place in three main stages the first two stages involved the generation of meso and neoarchean volcanic assemblages and contemporaneous plutonic rocks which is interpreted to be due to southward dipping subduction under the north caribou terrane this plate tectonic model is in contrast with well documented northward dipping subduction south of the north caribou terrane the third stage involved movement along late transpressional shear zones at ca 2 70 ga at the end of this geodynamic process the hudson bay terrane was terminally docked to the north caribou terrane along the north kenyon fault

an approach to the problem of loess deposit formation some comments on the in situ or soil eluvial hypothesis abstract the problem of loess formation has been widely discussed for a long time and in many languages at the beginning of the 21st century some parts of this debate are still going on a case is still being made for the in situ approach and there are problems of terminology and mechanism for the central asian loess consideration of the origin of loess material has now replaced the discussion on deposit formation as the major intrinsic problem and in the world of ground engineering there is still much investigation on the origins of collapsibility which is in effect a discussion of loess origins there remain some interesting and useful observations to be made on the north african loess and the loess like materials in australia and the desert loess controversy is still running connections of loess to chernozems fragipans and rendzinas are becoming clearer and it seems that it may be possible to appreciate a loess landscape in which the loess contribution is not immediately apparent recent sem observations suggest that collapsibility develops after metastability as the in situ theory appears to imply

influence of environmental factors on the wetting front depth a case study in the loess plateau abstract reliable information on the wetting front depth and variation of water contents within the zone of wetting is required for addressing geotechnical problems in loess deposits such as estimation of the collapse deformation and assessment of the slope stability for this reason a field test was conducted at a site in the loess plateau of china to obtain data on soil water contents and temperatures at different depths for a period of one year the variation of water contents was interpreted from the influence of environmental factors and soil temperature and used to determine the maximum wetting front depth in the loess soils in the study region in addition a commercial software vadose w was used to simulate the flow behaviour in unsaturated loess taking account of the influence of environmental factors a reasonable agreement was found between the results of field investigations and numerical simulations the study results are useful as they provide valuable information about the wetting front depth and water content variation in unsaturated loess in response to environmental factors the field investigations and numerical simulations summarized in this paper can serve as a reference for future studies on other soils

transmission of seismic waves across single natural fractures fractures and other nonwelded contacts are important mechanical and hydrological features of rock masses their effects on seismic wave propagation can be modeled as a boundary condition in the seismic wave equation seismic stress is continuous across such a boundary but seismic particle displacement and seismic particle velocity are not the complete solutions for seismic wave reflection conversion and transmission across a displacement and velocity discontinuity between two half spaces with different densities and elastic properties are derived for all angles of the incident wave the ratio between the seismic stress across this boundary and the seismic particle displacement and velocity are described by a specific stiffness and a specific viscosity respectively a displacement discontinuity results in frequency dependent reflection and transmission coefficients and a frequency dependent group time delay the velocity discontinuity results in frequency independent coefficients and zero delay results of laboratory experiments on compressional and shear wave transmission across three different natural fractures in a quartz monzonite are described measurements were made at different effective stresses under dry and saturated conditions at room temperature it is shown that the effect of these fractures on the spectral amplitudes for compressional and shear pulses transmitted across these fractures are described well by a displacement discontinuity for compressional pulses under dry and saturated conditions and by a combined displacement and velocity discontinuity for shear wave pulses under dry and saturated conditions values of specific stiffness and specific viscosity vary between fractures and increase with increasing effective stress as does the static specific stiffness of these fractures changes in the spectral amplitudes of transmitted pulses are also analyzed in terms of attenuation using the seismic quality factor q which is found to be a function of frequency

origin of ground fissures in the shanxi graben system northern china abstract since the 1950s hundreds of ground fissures have occurred in the shanxi graben system in northern china the fissures and related subsidence and differential settlement have caused and are causing substantial damage to homes agricultural land roads canals and other infrastructure although generally similar in appearance the fissures have different origins 1 some fissures coincide with northeast trending faults trenching shows that the fissures extend into the near surface faults increasing vertical offset clay beds and other stratigraphic markers at depth and therefore are probably the surface expression of fault movements 2 some fissures are demonstrably related to accelerated groundwater withdrawal this is particularly apparent in xi an city where groundwater levels have declined by about 15 m within 4 years 3 other fissures owe their origin to the well known process of soil collapse this is particularly common in the silty loessial sediments that occur within most of the valleys that comprise the shanxi graben system

the formation of loess deposits in the tashkent region and parts of central asia and problems with irrigation hydrocollapse and soil erosion abstract there are large problems of irrigation hydrocollapse and soil erosion associated with the loess deposits of central asia to get to grips with these we need a clear view of the nature and formation of the loess and in this region there are still disputes and disagreements and controversies important events in the loess deposit formation process can be identified and studied and relative significances assigned there are large loess deposits in the vicinity of tashkent in the north east of uzbekistan these were mapped and studied for many years by g a mavlyanov and associates they used a terminology which appears to be based on pavlov s nineteenth century usage and developed a polygenetic formation theory for loess deposits this was a formation theory very much associated with central asia and essentially favouring a proluvial mechanism a speculative look at the deposits near tashkent allows alternative terminologies and formation mechanisms to be considered in particular the widespread soviet antipathy to aeolian deposition can be examined the deposits associated with the chirchik river upstream of tashkent might be affected by the pavlov mechanisms but could be topped by aeolian deposits the collapse of loess when wetted is controlled by the nature of the ground and is a very significant interaction of soil and water in particular in central asia hydrocollapse and water erosion are closely related and are controlled by the complex nature of loess ground dust clouds in eastern uzbekistan are largely loess related but in the west dust material is raised from the drying aral sea bed this is often clay mineral agglomerate material and can carry dangerous pollutants