critical pool level and stability of slopes in granular soils the influence of pore water pressure and the pool water pressure on stability of submerged slopes was investigated using the kinematic approach of limit analysis for soils with some cohesive component of strength the critical pool level is slightly below half of the slope height whereas for slopes built of purely granular soils the critical pool level is not well defined the most critical mechanism of failure for submerged granular slopes was found to have the failure surface intersecting the face of the slope with one intersection point above and the other one below the pool level the solution to the stability problem was found to be independent of the length scale slope height and equally critical mechanisms of failure can be triggered locally with any water level in the pool the safety factor associated with these mechanisms is lower than the well known factor defined by a planar failure surface approaching the slope face

distribution and mechanisms of strain within rocks on the northwest ramp of pine mountain block southern appalachian foreland a field test of theory fractures faults stylolites and strain determined from an analysis of twinning in calcite in the mississippian newman limestone at the base of the pine mountain block show that deformation was accomplished primarily by a combination of bedding plane slip and layer parallel shortening poles to joints are either parallel to strike of the thrust sheet or are in the transport plane small slip surfaces with syntaxial calcite fibers lie either parallel to bedding or parallel to the strike of the pine mountain block and dip steeply movement along the former is in the direction of transport of the block whereas movement on the latter is approximately along strike tectonic stylolites are rare but appear to be controlled by subtle changes in lithology wackestones contain more stylolites than do packstones strains in calcite from closely spaced samples show the converse relationship they are highest in units without stylolites maximum shortening strain e 1 10 4 and lowest in units with stylolites or small faults e 1 2 0 the maximum principal shortening strain directions however are identical within the error and are parallel to both bedding and the transport direction a sequence of events in this portion of the pine mountain block is 1 layer parallel shortening producing tectonic stylolites and a strong preferred orientation of compression axes 2 development of fractures parallel to the strike of the block on the lower hinge of the ramp to accommodate stretching parallel to the transport direction these strike parallel fractures can also be interpreted as having occurred quite late 3 during 2 above and continuing the start of bedding plane slip marked by syntaxial calcite fibers which trend in the direction of transport and 4 complications such as shear parallel to the strike of the pine mountain fault as a result of motion of the entire block between bounding tear faults events 2 through 4 most likely overlapped in time these data suggest that the acquisition of dip of the rocks on the ramp was primarily accomplished by bedding plane slip on the slip surfaces which experienced a shear stress of

semi brittle deformation of anhydrite halite shear zones simulating mylonite formation abstract a series of new shear experiments on similar volume mixes of anhydrite and halite have been run at 100 and 400 c at the same constant loading rate and constant confining pressure of 200 mpa increasing temperature is found to decrease the viscosity contrast between anhydrite and halite the hard and soft phases respectively the mechanical response is similar at all temperatures regardless of volume proportions of mix an initial high stress steady state portion of the stress strain curve is followed by a stress drop and then by a second steady state stress interval at a much lower value that is nearly equal to the strength of the softer phase halite individual mineral behaviours and deformation mechanisms appear to correlate with specific portions of the stress strain curve as the fabric s evolve with increasing strain mechanism s of strain accomodation at all temperatures is semi brittle deformation mechanisms change gradually with conditions with shear dominated by stable sliding along r 1 and r 2 shear fracures especially in mixes of high anhydrite content at 100 c while homogeneous ductile flow along s and c surfaces is observed at 400 c in all variations of composition these features are very similar to those observed in natural shear zones

magnetite authigenesis and diagenetic paleotemperatures across the northern appalachian basin the concentration of magnetite in the lower and middle devonian helderberg and onondaga carbonate formations varies in a distinct pattern along an east west profile across new york state magnetite concentrations are uniformly low in the western half of the profile increase sharply eastward to a peak value near syracuse and decrease farther east the pattern strongly resembles previously reported variations in the extent of clay mineral diagenesis that reflect differences in paleotemperatures along the profile previous paleomagnetic studies have documented that the magnetite carries a well defined magnetization of pennsylvanian permian age and magnetite authigenesis is therefore no younger than late paleozoic we attribute the correlation between high magnetite concentration and high illite content to temperature dependent diagenesis triggered by orogenic fluids the large proportion of secondary magnetite indicates that over most of the area the mechanism of late paleozoic remagnetization was principally chemical thermal effects played a less direct role in the remagnetization of the strata by controlling the extent of the chemical processes that resulted in overprinting of the original remanence

deformation mechanisms in a high temperature quartz feldspar mylonite evidence for superplastic flow in the lower continental crust abstract microstructures and crystallographic preferred orientations in a fine grained banded quartz feldspar mylonite were studied by optical microscopy sem and tem mylonite formation occurred in retrograde amphibolite facies metamorphism interpretation of the microstructures in terms of deformation mechanisms provides evidence for millimetre scale partitioning of crystal plasticity and superplasticity strain incompatibilities during grain sliding in the superplastic quartz feldspar bands are mainly accommodated by boundary diffusion of potassic feldspar the rate of which probably controls the rate of superplastic deformation there is evidence for equal flow stress levels in the superplastic and crystal plastic domains in this case mechanism partitioning results in strain rate partitioning fast deformation in the superplastic bands therefore dominates flow and deformation is probably best modelled by a superplastic law if this deformational behaviour is typical shearing in mylonite zones of the lower continental crust may proceed at exceptionally high rates for a given differential stress or at low differential stresses in case of fixed strain rates

oxygen diffusion in quartz diffusional oxygen exchange between quartz and water was studied by determining 18o profiles in the quartz using an ion microprobe inverse error function plots of the data are linear as required for a diffusion mechanism one natural and two synthetic samples were used and although they had different impurity concentrations oh na and al per 106 si atoms are 7 4000 35 835 and 67 127 respectively the d values were the same within experimental uncertainty diffusion parallel to c is about 2 orders of magnitude faster than that normal to c at 700 c and diffusion normal to the rhombohedron is intermediate the data indicate a change in slope on an arrhenius plot at the boundary at 100 mpa 1 kbar water pressure the preexponential factors do in square centimeters per second and activation energies q in kilojoules per mole for quartz 500 550 c are as follows do 190 and q 284 parallel to c and do 8 10 2 and q 238 normal to the rhombohedron for quartz 600 800 c do 4 10 7 and q 142 parallel to c do 9 10 7 and q 155 normal to the rhombohedron and do 1 10 4 and q 234 normal to c d increases with ph 2 o and between 25 and 350 mpa log d versus log h 2 o has a slope of approximately 1 1 these d values are all several orders of magnitude larger than previously reported values for oxygen diffusion in water free systems

the effect of fluid composition on the behavior of well cemented quartz rich sandstone during faulting abstract previous studies o kane a onasch c m farver j 2007 the role of fluids in low temperature fault related deformation of quartz arenite journal of structural geology 29 819 836 cook j dunne w m onasch c m 2006 development of a dilatant damage zone along a thrust relay in a low porosity quartz arenite journal of structural geology 28 776 792 found that quartz arenite within two fault zones in the appalachian foreland thrust belt displays very different structural styles and histories despite deforming at similar pressures and temperatures during the alleghanian orogeny a comparison of the grain scale deformation and fluid histories using transmitted and cathodoluminescence microscopy and fluid inclusion microthermometry shows that fluid composition was a controlling factor for causing these differences the cove fault zone deformed in the presence of aqueous fluids first a cacl 2 brine and then an iron rich fluid the precipitation of quartz cement from the brine kept pace with brittle deformation maintaining overall rock cohesion in the fault zone the introduction of iron rich fluids caused a switch from precipitation to dissolution of quartz along with precipitation of goethite in a damage zone along a backthrust in the cave mountain anticline early deformation occurred in the presence of an aqueous fluid from which quartz was precipitated the latest deformation however occurred in the presence of a methane rich fluid which inhibited the precipitation of quartz cement producing porous breccias and open fractures despite deformation at 6 km depth fluid composition not only affected cementation in the fault zones but also the selection of grain scale deformation mechanisms therefore it is a controlling factor in determining the behavior and strength of these fault zones

the influence of skeletal micro structures on potential proxy records in a bamboo coral assessing the physicochemical variability of the deeper ocean is currently hampered by limited instrumental time series and proxy records bamboo corals isididae form a cosmopolitan family of calcitic deep sea corals that could fill this information gap via geochemical information recorded in their skeletons here we evaluate the suitability of high resolution chemical imaging of bamboo coral skeletons for temperature and nutrient reconstruction the applied elemental mapping techniques allow to verify the suitability of the chosen transect on the sample section for paleo reconstructions and enhance the statistical precision of the reconstruction we measured mg ca via electron microprobe at 1 m resolution and ba ca via laser ablation icp ms at 35 m resolution in a historic specimen of keratoisis grayi from the blake plateau off eastern florida long term growth temperatures of 7 1 3 4 c 2 sd that are in agreement with recent ambient temperature range can be reconstructed from mg ca ratios provided that anomalously mg enriched structural features around the central axis and isolated features related to tissue attachment are avoided for reconstruction skeletal ba ca measurements reflect mean seawater barium ba sw concentrations ba sw 51 24 nmol kg 1 2 sd in agreement with instrumental data 47 nmol kg 1 we show for the first time that ba ca forms concentric structures in a bamboo coral skeleton section our investigations suggest that while bamboo coral skeletons do record environmental parameters in their mean chemical composition the magnitude of environmental variability reconstructed from high resolution chemical maps exceeds that expected from instrumental time series this necessitates additional investigation of the factors driving bamboo coral skeletal composition

modeling and mechanistic interpretation of creep of rock salt below 200 c abstract upper and lower bound estimates of the steady state strain rates of rock salt from five locations are analyzed the measurements were obtained in triaxial creep tests including systematic changes in stress and temperature the various data sets are correlated in activation analyses and fitted by models and combinations of models for power law creep cross slip and dislocation glide to show that a cross slip model yields the best mechanistically most credible fit good fits for cross slip and high power law stress exponents rule out the possibility that pressure solution affected the data in a major way to the lowest recorded strain rates of order 10 10s 1

infrared microspectroscopy analysis of water distribution in deformed and metamorphosed rocks infrared microspectroscopy has been applied to thin sections of various deformed and metamorphosed rocks in order to investigate water content of quartz in these rocks the broad ir band absorbance around 3400 cm 1 probably due to fluid inclusion molecular water h2o was used to calculate water contents deformed granitic rocks from the yanazawa kamimura area near the median tectonic line mtl showed an increase of water content in quartz from about 300 ppm to 2500 ppm toward the mtl with increasing degree of deformation metacherts from sambagawa metamorphic rocks asemigawa route showed a systematic decrease of water content in quartz from about 1000 ppm to 200 ppm with increasing metamorphic degree from chlorite garnet albite biotite to oligoclase biotite zones an archaean metachert from the napier complex granulite facies has only 40 ppm water comparing this with an inuyama unmetamorphosed chert sample having water contents of 3500 to 7000 ppm a starting point of metamorphism the systematic decrease of water in quartz with increasing metamorphic grade may extend from unmetamorphosed cherts to the highest grade metacherts water contents in high pressure metamorphic rocks in japan are mostly of the order of 500 ppm 300 700 ppm except for those from kurosegawa with a water content as high as 1700 ppm these results represent an exploratory analysis of intragranular water contents in quartz in various deformed and metamorphosed rocks further micro ft ir studies of the distribution of water in crustal rocks will provide a quantitative basis for examining the geochemical cycle of water in the earth s crust

weakening of rock salt by water during long term creep the rheological properties of rock salt are of fundamental importance in predicting the long term evolution of salt based radioactive waste repositories and strategic storage caverns and in modelling the formation of salt diapirs and associated oil traps1 2 the short term high stress rheology of rock salt is well known from laboratory experiments however extrapolation to appropriately low stresses fails to predict the rapid flow seen in certain natural structures furthermore experiments have failed to reproduce the recrystallized microstructure of naturally deformed salt here we report experiments indicating that the above discrepancies can be explained by taking into account the influence of trace amounts of brine trace brine is always present in natural salt but sometimes escapes during experiments our tests on dry dilated salt show more or less conventional dislocation creep behaviour but brine bearing samples show marked weakening at low strain rates this is associated with dynamic recrystallization and a change of deformation mechanism to solution transfer creep because natural rock salt always contains some brine these results cast substantial doubt on the validity of presently accepted dislocation creep laws for predicting the long term rheological behaviour of salt in nature

cooling induced strain localization in carbonate mylonites within a large scale shear zone glarus thrust switzerland abstract the glarus thrust switzerland offers a great field example of strain localization under retrograde conditions along the thrust mylonitic microfabrics are characterized by a temperature stress controlled balance of grain size reducing mechanisms and grain growth consequently mean grain sizes decrease along the thrust with decreasing metamorphic conditions and towards the thrust contact in an opposite manner calcite twin densities increase towards the contact cpos are strongest between 0 5 and 15 m away from the thrust but become generally weaker in the last centimeters where also cataclasites occur the cpo weakening and grain size reduction towards the shear zone point to a change from predominant dislocation creep to granular flow finally ending in cataclastic deformation the microfabric changes correlate with a decrease in 13c and 18o towards the thrust contact indicating the presence of fluids during cycles of brittle and plastic deformation based on the microfabric changes variations in stable isotopes and cross cut relationships a subdivision into a low and high temperature shear zone can be made the microfabric modifications resulted from changes in deformation conditions due to ongoing thrusting and exhumation induced cooling promoting further strain localization of an existing high strain shear zone

coupling of diffusional mass transport and deformation in a tight rock abstract simple governing equations coupling diffusional transport at a macroscopic scale and deformation in a tight rock are formulated the deformation alone is described by a linear viscous rheology several deformations of geological interest are analyzed including the folding of an embedded layer a basic feature is the length scale dependence of diffusional effects interpretation of natural structures permits the estimation of parameters governing the diffusional transport and rate of deformation

small scale features of temperature and salinity surface fields in the coral sea the small scale features in sea surface temperature and salinity fields sst and sss of the coral sea are examined using high horizontal spatial and short term temporal in situ measurements these features are extracted from thermosalinographs tsgs gathered onboard commercial and research vessels and at one long term fixed station the analyses are performed along the vessel tracks and the structures of small scale features are extracted by high pass spatial filtering the original tsg data for sss it is shown that the features at the scale of mesoscale eddies approximate to 100 km vary from about 1 1 to 0 6 psu in the coral sea region processes sustaining such range include rainfall events stirring by mesoscale eddies and the latitudinal displacement of the sharp front associated with the edge of the western pacific warm pool at the seasonal time scales the tsg data have revealed the presence of a sharp front 0 4 0 6 psu between the subtropical and equatorial waters instead of a smooth gradient in the standard sss climatologies within the context of recent remotely sensed observations of salinity this could represent an important limitation for the validation and calibration of satellite products in addition to these spatial considerations temporal variations at one long term station near vanuatu show that the coupled air sea responses to intraseasonal tropical variability such as the madden julian oscillation may have a signature in both sst and sss fields however this response is found to be complex and not necessarily in phase in the coral sea region our results suggest that mjo induced variability on sst and sss exhibit little coherency at the seasonal time scales

a non linear statistical downscaling model el nino southern oscillation impact on precipitation over new caledonia a new multivariate non linear non parametric regression method called mars is used in a statistical downscaling problem for simulating new caledonian rainfall anomalies induced by el nino southern oscillation enso the use of a non linear method was motivated by wavelet analyses pointing to a complex interaction between interannual and intraseasonal rainfall variability the proposed method is very flexible and computationally efficient it can be applied to a wide range of problems and its use is not limited to spatial downscaling applications furthermore the method provides great potential for comprehensive diagnostics of multivariate problems in climate research it is shown that this method can take into account the asymmetry between el nino and la nina periods and also the type of el nino

brittle deformation events at the western border of the bohemian massif germany investigations of brittle deformation structures present within the crystalline rocks of the bavarian oberpfalz reveal a complex late to post variscan crustal evolution upper carboniferous mainly westphalian granites were emplaced into semibrittle to brittle rocks of the zev zone of erbendorf vohenstraus and the egz erbendorf greenschist unit respectively from both the alignment of the granites and the direction of granite related tension gashes a north east south west extension must be assumed for the period of magmatic activities apart from the granite intrusions rapid crustal uplift about 1 5 km my led to an increase in the geothermal gradient from 40 c km late variscan post granitic the increased geothermal gradient persisted during the succeeding reverse faulting which results from late carboniferous probably stephanian east west and northeast south west compression although not evidenced directly in the area considered strike slip faults seem to have played an important part during the late variscan crustal evolution particularly in the early permian the strike slip events indicate further crustal shortening and indentation under north south compression a similar indentation was present in cretaceous time after a weak phase of early cretaceous reverse faulting which results from north south compression strike slip faults formed under north west south east and north south compression all these faults in particular the strike slip faults seem to be related to the cretaceous and lowermost tertiary convergence of the alpine carpathian orogeny a late stage of crustal extension characterized by a radial stress tensor 2 3 is indicated through high angle normal faults which probably formed during the subsidence of the adjacent neogene eger graben

deep fluid circulation in fault zones massive fluid circulation in retrogressive ductile shear zones is a well established but poorly understood phenomenon in some cases surface derived fluids which must initially have been at hydrostatic pressures can be shown to have entered shear zones in which fluids would normally be expected to be at lithostatic pressure in these circumstances thermal convection is an unlikely driving force for fluid movement underthrusting of a surficial fluid reservoir beneath shear zones is a viable mechanism in some cases but not for metasomatic shear zones in the pyrenees where insufficient underthrusting has occurred seismic pumping provides an alternative mechanism to explain the paradox of fluid access into ductile shear zones a kinematic analysis of a hypothetical fault zone shows that stress and dilatancy cycles will be out of phase above and below the frictional quasiplastic transition if this effect is sufficiently large hydraulic gradients may force fluid downward across the transition immediately after earthquake rupture through highly permeable microcrack networks between earthquake cycles plastic creep in mylonites will overprint microcrack networks increase fluid pressure and promote slow upward movement of fluid at low permeability for smaller shear zones such as those in the pyrenees seismic pumping could occur down a shallow decollement with subsequent upward fluid flow through shear zones in the hanging wall of the decollement

constraints on the mechanism of deformation of olivine imposed by defect chemistry abstract more is known about diffusion electrical conductivity and creep in forsterite and olivine than any other mineral this paper examines these data to see what constraints are placed on the mechanisms of deformation in these minerals experimental observations show a creep rate for forsterite independent of the activity of oxygen a o 2 in olivine the creep rate is proportional to a 1 6 o 2 and in addition is ten times faster for the enstatite excess situation than for the magnesiowustite excess situation these data are consistent with positively charged kinks being the rate controlling species in olivine the data for forsterite are also compatible with a kink controlled mechanism although some other jog and diffusion controlled mechanisms remain as possibilities the activation energy for creep is not related to that for diffusion of silicon or oxygen for kink controlled mechanisms the activation energy is approximately given by the sum of the fermi level and the activation energy for charged kink migration minus the ionization energy of the kink the fermi level can be changed by minor changes in impurities and by changes in the imposed thermodynamic environment so unless these parameters are controlled during deformation variations in observed activation energies for creep are to be expected from one set of experiments to another

nucleation of ductile shear zones on dilatant fractures small shear zones in granitic rocks of the sierra nevada california and near roses rosas northeast spain display features which indicate that dilatant fracturing preceded the localization of ductile shear deformation many zones have sharp nearly planar boundaries between their highly deformed interiors and the undeformed wall rock the roses shear zones narrow continuously to hairline fractures at their ends mineralized microcracks oriented parallel to the shear zones cluster near the zone boundaries and are interpreted as relicts of the earlier fracturing episode dynamic recrystallization of minerals filling these microcracks demonstrates that fracturing predated the ductile deformation gradients in ductile strain suggest that deformation spread laterally into the wall rocks after nucleation of the shear zones we suggest that cracks enhance the wall rock ductility by increasing local fluid fluxes thereby promoting chemical alteration and or hydrolytic weakening

magma accumulation rates and thermal histories of plutons of the sierra nevada batholith ca zircon u pb geochronology results indicate that the john muir intrusive suite of the central sierra nevada batholith california was assembled over a period of at least 12 ma between 96 and 84 ma bulk mineral thermochronology u pb zircon and titanite 40ar 39ar hornblende and biotite of rocks from multiple plutons comprising the muir suite indicates rapid cooling through titanite and hornblende closure following intrusion and subsequent slow cooling through biotite closure assembly of intrusive suites in the sierra nevada and elsewhere over millions of years favors growth by incremental intrusion estimated long term pluton assembly rates for the john muir intrusive suite are on the order of 0 001 km3 a 1 which is inconsistent with the rapid magma fluxes that are necessary to form large volume magma chambers capable of producing caldera forming eruptions if large shallow crustal magma chambers do not typically develop during assembly of large zoned intrusive suites it is doubtful that the intrusive suites represent cumulates left behind following caldera forming eruptions

an experimental study of hydroxyl in quartz using infrared spectroscopy and ion microprobe techniques we have measured the concentrations of hydroxyl deuterium al fe li na k and rb in a natural quartz crystal before and after hydrothermaltreatment at 1 5 gpa and 800 degree 1050 degree c we employed microbeam infraredspectroscopy and ion probe techniques to avoid impurities trapped in healedcracks and fluid inclusions that might bias a normal bulk analysis the ital f sub h sub 2 of our experiments were buffered to thehematite magnetite oh fluid nickel nickel oxide oh fluid oriron wustite oh fluid phase assemblages after hydrothermal treatment the samples contained local concentrations of hydrogen or deuterium ofseveral hundred atoms 10 sup 6 si the starting crystal contained 45 h 10 sup 6 si we did several experiments with al sub 2 o sub 3 or rbcl added to the sample chargeand found local al enrichment where the deuterium concentration was highbut no rb enrichment finally we measured trace elements and hydroxyl in aquartz sample after plastic deformation in a talc furnace assembly inregions of the sample containing basal and prismatic deformation lamellae but no visible healed microcracks at 400 times optical magnification hydroxyl had increased to similar to 200 oo 10 sup 6 si with no increase in al or fe samples enriched in hydroxyl but not al including the plastically strainedsample gave infrared spectra resembling natural amethyst crystals

deformation mechanisms in the southeastern ramp region of the pine mountain block tennessee a field and petrofabric study of the southwestern part of the pine mountain thrust sheet shows that most deformation features may be attributed to one of two processes the first layer parallel compression is responsible for a a layer parallel maximum shortening direction in the mechanically twinned fabric of the limestone and dolomite country rock b transport parallel extension fractures and joints c transport normal stylolite surfaces and d some small thrusts the second bending at thrust ramp hinges is responsible for a non bedding parallel maximum shortening directions in mechanically twinned calcite from fracture fillings b transport normal extension fractures and joints and c small normal faults possible explanations for the failure of calcite in the country rock to twin in response to bending at the ramp include both 1 an early imposed pre thrusting calcite twin strain hardening and 2 deformation of the country rock by competing mechanisms such as pressure solution small normal faults are parallel to the strike of the thrust sheet and seem to have evolved from strike parallel extension fractures in response to continued extension both small thrusts and stylolite surfaces are rare in outcrop there seems to be no major change in deformation of rocks which have traveled through different fractions of the total ramp length so long as the rocks have passed onto the ramp

fluid participation in deep fault zones evidence from geological geochemical and 18o 16o relations fluid incursion into fault zones and their deeper level counterparts brittle ductile shear zones is examined in a number of different crustal environments at the grenville front translation was accommodated along two mylonite zones and an associated boundary fault the high mz ii and low temperature mz i mylonite zones formed at 580 to 640 c and 430 to 490 c respectively in the presence of fluids of metamorphic orgin indigenous to the immediate rocks a population of posttectonic quartz veins occupying brittle fractures were precipitated from fluids with extremely negative 18o at 200 to 300 c the water may have been derived from downwards penetration into fault zones of low 18o precipitation on a mountain range induced by continental collision with uplift accommodated at deep levels by the mylonite zones coupled with rebound on the boundary faults at lagoa real brazil archaean gneisses overlie proterozoic sediments along thrust surfaces and contain brittle ductile shear zones locally occupied by uranium deposits following deformation at 500 to 540 c in the presence of metamorphic fluids and under conditions of low water to rock ratio shear zones underwent local intense oxidation and desilicification all minerals undergo a shift of 10 indicating discharge of meteoric water recharged formation brines in the underlying proterozoic sediments up through the archaean gneisses during overthrusting about 1000 km3 of solutions passed through these structures at yellow knife a series of large scale shear zones developed by brittle ductile mechanisms involving volume dilation with migration of 5 wt volatiles into the shear zone from surrounding metabasalts this early deformation involved no departures in redox state or whole rock 18o from background states of fe2 fe 0 72 and 7 to 7 5 respectively attesting to conditions of low water rock shear zones subsequently acted as high permeability conduits for pulsed discharge of 9 km3 of reduced metamorphic hydrothermal fluids at 360 450 c the west bay fault a late major transcurrent structure contains massive bull quartz that grew at 200 300 c from fluids of 2 to 6 possibly formation brines in general flow regimes in these fault and shear zones follow a sequence from conditions of high temperature and pressure with locally derived fluids at low water to rock ratios during initiation of the structures to high fluxes of reduced formation or metamorphic fluids along conduits as the structures propagate and intersect hydrothermal reservoirs later in the tectonic evolution and at shallower crustal levels there was incursion of oxidizing fluids from near surface reservoirs into the faults

brittle ductile deformation in the glarus thrust lochseiten lk calc mylonite the glarus thrust accommodated at least 30 km of northward displacement strongly localized within a 1 m layer of lochseiten lk calc mylonite this layer displays veins in various states of plastic deformation and a wildly refolded foliated gouge texture lattice and shape preferred orientations are observed within the fine grained recrystallized matrix these features indicate the alternate activity of brittle and ductile deformation mechanisms in contrast to the classical view that grain boundary sliding superplasticity is the dominant deformation mechanism it is advocated that fluids derived from the footwall and expelled along the thrust are responsible for hydrofracturing and cataclastic deformation in periods between fracture events deformation was ductile in this new interpretation a substantial amount of the total thrust displacement was accommodated by numerous short lived and strongly localized fracture events at the base of the verrucano thrust sheet rather than a permanently weak decollement lithology

the origin of large or great thrust type earthquakes along subducting plate boundaries abstract seismicity deformation state of stress and abundance of fluids along subducting plate boundaries are reviewed and the origin of large or great thrust type earthquakes is discussed based on the recent experimental results on the slip behavior of halite and serpentine gouges shallow subducting plate boundaries above 20 25 km in depth are characterized by low seismicity low tectonic stress inter plate decoupling ductile deformation associated with the formation of metamorphic schistosity except at very shallow depths metamorphism suggesting solution processes on massive scale and presence of abundant h 2 o it is argued that these unique features are due to pressure solution processes to high fluid pressure to low strength and stable behavior of clayey sediments under wet environments and or to the deformation of soft unconsolidated sediments at very shallow depths the low seismicity in this zone is in marked contrast with major strike slip faults along which large earthquakes occur at depths shallower than 15 20 km it is emphasized that these unique features are expected only for restricted regions where there is constant supply of h 2 o due to progressive metamorphism or where fluids in the rocks are trapped and cannot escape to the surface large or great thrust type earthquakes in subduction zones initiate at depths of 30 50 km below the shallow decoupled zone in this focal depth range the supply of h 2 o during progressive metamorphism perhaps diminishes downwards the overriding and subducting plates are coupled and stick to each other during much of the inter seismic period and the resistance to slip or shear stress is presumably high it is suggested that these earthquakes begin to occur at a depth where the plate boundary zone becomes fairly dry deformation at these depths appears to be predominantly ductile so that the earthquakes cannot be regarded simply as a brittle phenomenon 1 creep instability i e instability associated with plastic deformation and 2 dehydration induced instability are the most likely mechanisms for initiating the earthquakes and both have some experimental support stick slip of halite gouge while undergoing ductile deformation primarily by intracrystalline gliding is described and discussed as a supporting evidence for 1 shear resistance of halite gouge increases with increasing confining pressure in stick slip regimes hence the observed stick slip may be a semi brittle phenomenon with respect to the pressure dependence of the shear resistance although the deformation texture cannot be distinguished from that formed by pressure insensitive flow serpentine gouge exhibits violent stick slip upon its decomposition under dry not wet environments supporting the mechanism 2 above exact mechanisms which lead to the unstable fault motion are poorly understood as yet but stick slip of both halite and serpentine gouges is recognized only when the slip rate dependence of friction is negative i e lower friction at faster slip rate consistent with the theoretical prediction of rice and ruina 1983 there is a possibility that the thrust type earthquakes can be explained essentially within the framework of fault constitutive laws developed by dieterich 1979 and ruina 1983

concretion morphology classification and genesis abstract a discussion of the most relevant morphological features of concretionary bodies and the different classifications and the criteria involved in these classifications is presented together with suggestions for improvements to the various classification schemes the meaning of syngenetic diagenetic and epigenetic related to the relative timing and environment of growth of concretionary bodies is also reviewed and discussed the replacement of mixed morphogenetic classifications which lead to conflicting results by classification categories based on textural features is proposed because the identification of the genetic environment of a concretionary body tells little about its history i recommend defining growth patterns in which the successive steps associated with changes in composition and or texture and the development of new structures are recorded a new path is presented that accounts for the contradiction between textural and isotope features which suggests respectively syngenetic and diagenetic or even epigenetic signatures this new path is characterized by the preservation of large porosities over very long time spans and down to depths that are somewhat greater than expected due to the inhibition of normal compaction caused by early overpressuring this overpressuring is the result of the development of hydraulic seals since approximately the syngenetic phase times the concepts of force of crystallization and displacive growth are also reviewed it is being suggested to discard some controversial interpretations of their actual importance for true concretionary displacive growth under epigenetic conditions in accordance with other authors the conclusion is reached that displacive growth is only possible if the shear strength of the host is very low and the stress field within the host is almost hydrostatic a new model the symcompactional concretionary growth model is proposed which explains how a concretionary body generally a nodule can grow while its host thins down by compaction this overpressured undercompacted model will be useful for the interpretation of an assemblage of features such as injection dikes hydraulic breccias cone in cone structures among others that are thought to be representative of the former presence of overpressured horizons these overpressured horizons could serve as detachment planes in paleotectonically active basins seals that could have controlled the movement of brines and hydrocarbons during the diagenetic evolution of the basin can also be assessed this is relevant for the identification of maturation conditions the potential development of secondary fracture permeability due to hydraulic fracturing in buried areas of the basin can also be evaluated based on the identification of formerly overpressured horizons in outcrops the origin of concretions is generally a geological puzzle clifton 1957

seasonal to decadal modulation of the impact of el nino southern oscillation on new caledonia sw pacific rainfall 1950 2010 1 new caledonia nc 166 e 22 s rainfall anomalies are more sensitive to central pacific cp el nino and la nina events than to those exhibiting highest sea surface temperature sst anomalies in the eastern pacific ep the linear relationship between nc rainfall anomalies and cp sst indices peaks from september to march s m the seasonal s m atmospheric anomalies observed in the south west sw pacific during the warm cp events are highly dissimilar to the ep ones while there are more similarities during the cold events with a higher amplitude during the cp ones the warm cp events strengthen the southern hadley cell around nc longitudes with positive rainfall anomalies in the equatorial pacific leading to an anomalous release of latent heat in the upper troposphere and an increased subsidence in the sw pacific atmospheric anomalies are strongest in september november because of a combination of a rather strong zonal sst gradient with the warmest sst in the equatorial pacific just west of the dateline the cold cp and ep events are associated with a southwestward shift of the south pacific convergence zone with strongest atmospheric anomalies during the cp events squared wavelet coherence between nc rainfall and nino 4 sst index shows that their negative correlations are mostly carried by two distinct timescales the classical el nino southern oscillation i e 3 6 years variability and a quasi decadal one i e 10 12 years the high frequency 1 8 cycle per year correlations peak around christmas and are quasi stationary since 1950 whereas the low frequency ones 1 8 cycle per year peak from the austral autumn to the austral spring and have strengthened from 1975 to 1980 onward with a subtle warming trend in the equatorial pacific near the dateline

the role of fluids in low temperature fault related deformation of quartz arenite abstract the microstructural and fluid histories in quartz arenite deformed in a regional scale fault zone were investigated to determine the role of fluids in the selection of grain scale deformation mechanisms using cathodoluminescence fluid inclusion microthermometry and stable isotope geochemistry of quartz cements three chemically distinct aqueous fluids were identified that affected the rock at different times during deformation the earliest deformation microstructures are distributed cataclasites which were cemented by reddish brown luminescing quartz precipitated from an aqueous cacl 2 brine fluid i once cemented brittle deformation continued but localized along discrete shear surfaces in narrow zones 20 1000 m wide and on discrete microfractures microveins associated with this phase were cemented with bluish green luminescing quartz precipitated from an aqueous cacl 2 brine fluid ii water channelized along dissolution surfaces and in pervasive microfracture networks that formed at this time promoted hydrolytic weakening and crystal plastic deformation especially near fluid pathways temperatures during deformation associated with fluids i and ii were 225 235 c as determined from fluid inclusion data in the later stages of deformation an influx of iron bearing aqueous fluid fluid iii greatly accelerated the rate of quartz dissolution and filled fractures stylolites and vugs with goethite the progression of deformation mechanisms indicated by the microstructures and their relationship to the different fluids show that the selection of grain scale deformation processes is affected not only by the presence of fluids but also by their chemistry

3 d rock salt fabrics in a shear zone suria anticline south pyrenees abstract the internal geometry of the evaporitic horizons serves as a good indicator of their large scale behaviour however the determination of the strain ellipsoid inside the deformed salt bodies can often be difficult moreover the relationship between the bulk strain ellipsoid and the grain shape ellipsoid is not straightforward and two parameters orientation and the dimension of the grain shape ellipsoid need evaluation the grain shape ellipsoid is not an indicator of the dimensions of the bulk strain ellipsoid the increase in shear strain led initially to a growth in grain volume followed by a reduction to a value near the original volume specifically due to the long axis change the orientation of the grain shape ellipsoid runs parallel to that of the strain ellipsoid after a certain amount of deformation these changes were accompanied by the growth of a new tectonically oriented grain population the rapid spatial changes in morphology contrast with the constant and strong 100 texture the intracrystalline deformation mechanism consistent with this texture is the 110 1 1 0 slip system nevertheless a mechanism such as fluid assisted grain boundary migration might have also taken place to account for the grain volume changes

fluids and thrusting abstract recent studies of the structure of the continental crust by cocorp and birps have shown that major thrust structures in the lower crust are ubiquitous plate tectonic processes of continental crust destruction or construction at sites where subduction or collision occurs the himalayas or the andes involve thrusting of continental materials or ocean crust beneath continents and local overthrusting may accompany transcurrent motion in all such cases massive fluid flow must occur as first stressed by m k hubbert and w w rubey thrusting mechanisms require that fluid pressures are close to or greater than lithostatic pressures when thrusting occurs compaction of the underplate must occur rapidly expelling pore water crustal thickening leads to gradual heating of the underplate with prograde metamorphism near the top and even melting at the base if the overthrust plate is thick and hot at the base retrograde metamorphism will occur at the base of the overthrust plate and rising fluids will encounter inverted thermal gradients in such a region veins need not occur but leaching phenomena may dominate if an underthrust plate is hydrated and or contains sedimentary aquifers large fluid volumes are expelled through shear zones into the overthrust plate the scale of fluid release processes can be large thus in thin skinned tectonics where the overthrust plate is 10 15 km thick induced fluid release can easily reach 4 109 g m 2 of thrust surface the flow of such fluids will be controlled by the thrust surface and lithology both of which will influence hydraulic fracture mechanisms and spacing of fractures the chemistry of thrust derived fluids may be highly variable depending on lithology and the time constants of thrusting vertical thermal and redox environments will be similarly dependent in the subduction process impressive quantities of fluids must pass back up the thrust surface and such fluids have recently been directly observed during drilling dewatering of spilites serpentinites and sediment layers of the underthrust oceanic lithosphere must produce massive fluid flow back to the surface but some of these fluids may form hydrated minerals in the overlying mantle and at great depth flux mantle melting extreme metasomatism in blueschist belts must result from such fluids a case of particular interest involves the cessation of subduction when a high level slab reaches thermal equilibrium in general flow regimes in the thrust and fault zones associated with collisions follow a sequence from conditions of high t p with locally derived fluids at low water rock ratios during initiation of the structures to high fluxes of reduced metamorphic fluids along conduits as the structures propagate and intersect hydrothermal reservoirs later in the tectonic evolution and at shallower crustal levels there may be incursion of oxidizing near surface fluid reservoirs into the faults these fluids may have extremely low 18o values where mountain ranges form on rebound faults and high altitude depleted fluids penetrate down the rebound structure extensive mineralization may be associated with such thrust derived fluids examples which will be discussed include the mother lode au deposits of california u s a and the large u deposits of lagoa real brazil

limit analysis of submerged slopes subjected to water drawdown a rapid draw of water from a reservoir can cause a temporary increase in the hydraulic gradient that may not be tolerated by the slope of an earth dam the increased seepage forces may lead to slope instability causing the collapse of the structure the kinematic approach of limit analysis is used to examine stability of slopes subjected to a rapid or slow drawdown combinations of slope inclination soil properties and hydraulic conditions are found for which the slope becomes unstable the results are presented in the form of charts for convenient practical use and the safety factors can be obtained from the charts without the need for iteration for granular slopes particularly if shallow subjected to drawdown a simple translational mechanism with a shallow failure surface is not the most adverse mechanism for all water draw regimes key words slopes stability rapid drawdown limit state analysis

continental fault structure and the shallow earthquake source plate boundaries in continental crust are generally less sharply defined than in the oceans with seismicity spread over broad areas interplate displacements appear to be largely accommodated by networks of major fault zones a simple 2 level model for these important structures accounts for the depth distribution of most continental earthquakes and for the observed range of faulting styles and associated rock deformation textures the model consists of a seismogenic frictional slip regime overlying quasi plastic mylonite belts wherein shearing is largely accommodated aseismically due mainly to the changing response of quartz to deformation with increasing temperature shear resistance increases with depth to a peak value in the vicinity of the frictiona1 quasi plastic transition and then decreases rapidly the depth to which microseismic activity extends appears inversely related to regional heat flow and can be satisfactorily modelled as the frictional quasi plastic transition for different geotherms using laboratory determined flow laws for quartz bearing rocks larger earthquake ruptures m 5 5 tend to nucleate near the base of the seismogenic regime in the region inferred to have the highest shear resistance and concentration of distortional strain energy consideration is also given to the depression of isotherms and seismic activity in regions of thrusting and to the question of the downward continuation of major fault zones through the lithosphere decoupling of the upper crust on flat lying shear zones may accompany higher level dip slip and perhaps in some circumstances strike slip faulting being favoured by above average continental heat flow and a high quartz content in the middle or deep crust the average level of deviatoric stress within the seismogenic regime remains an outstanding problem

influence of filling drawdown cycles of the vajont reservoir on mt toc slope stability abstract in the present work the 1963 vajont landslide has been back analyzed in detail to examine the influence of reservoir operations filling and drawdown on mt toc slope stability the combined seepage slope stability analyses carried out show that the main destabilizing factor that favored the 1963 vajont landslide was the reservoir induced water table that formed as a consequence of rapid seepage inflow within the submerged toe of the slope decrease in the factor of safety fos up to 12 compared to the initial slope stability condition i e in the absence of the vajont reservoir rainfall would only have been a decisive factor if the initial stability condition of the mt toc slope had already been very close to failure decrease in fos caused by heavy or prolonged rainfall is about 3 4 for the worst case scenario analyzed the permeability of the shear zone material occurring at the base of the prehistoric vajont rockslide has been evaluated at 5 10 4 m s and back calculated values of the friction angles range from 17 5 to 27 5 when considering mountain reservoirs slope failures can occur during both filling and drawdown phases in the vajont case owing to the highly permeable materials of the shear zone slope stability decreased during filling and increased during drawdown another displacement dependent phenomenon of a mechanical nature progressive failure of the ne landslide constraint has to be considered to understand the slope collapse that occurred during the last drawdown 26 september 9 october 1963 the results of the combined seepage slope stability models indicate that permeability of bank forming material and filling drawdown rates of reservoirs can strongly influence slope stability slow lowering of the reservoir level is a necessary measure to reduce the occurrence of very dangerous transient negative peaks of fos

rheology of the lithosphere selected topics we review recent results concerning the rheology of the lithosphere with special attention to the following topics 1 the flexure of the oceanic lithosphere 2 deformation of the continental lithosphere resulting from vertical surface loads and forces applied at plate margins 3 the rheological stratification of the continents 4 strain localization and shear zone development and 5 strain induced crystallographic preferred orientations and anisotropies in body wave velocities we conclude with a section citing the 1983 1986 rock mechanics literature by category

brittle ductile transition semi brittle behavior abstract in central british columbia mesoscopic and microscopic deformation mechanisms within metamorphic rocks ranging from greenschist facies through upper amphibolite facies have been examined to evaluate the applicability of single mechanism flow laws at different crustal levels throughout the entire sequence regardless of metamorphic grade the processes of regional strain accommodation were dominantly semi brittle in the presence of an aqueous fluid phase no sign was found of abrupt brittle ductile transition and caution against calculating such a transition through the intersection of single mechanism flow laws with friction law s that on the regional and local scales do not appear to describe the mechanisms whereby regional strain is accommodated is advised

rock mechanics observations pertinent to the rheology of the continental lithosphere and the localization of strain along shear zones emphasized in this paper are the deformation processes and rheologies of rocks at high temperatures and high effective pressures conditions that are presumably appropriate to the lower crust and upper mantle in continental collision zones much recent progress has been made in understanding the flexure of the oceanic lithosphere using rock mechanics based yield criteria for the inelastic deformations at the top and base at mid plate depths stresses are likely to be supported elastically because bending strains and elastic stresses are low the collisional tectonic regime however is far more complex because very large permanent strains are sustained at mid plate depths and this requires us to include the broad transition between brittle and ductile flow moreover important changes in the ductile flow mechanisms occur at the intermediate temperatures found at mid plate depths two specific contributions of laboratory rock rheology research are considered in this paper first the high temperature steady state flow mechanisms and rheology of mafic and ultramafic rocks are reviewed with special emphasis on olivine and crystalline rocks rock strength decreases very markedly with increases in temperature and it is the onset of flow by high temperature ductile mechanisms that defines the base of the lithosphere the thickness of the continental lithosphere can therefore be defined by the depth to a particular isotherm tc above which at geologic strain rates the high temperature ductile strength falls below some arbitrary strength isobar e g 100 mpa for olivine tc is about 700 800 c but for other crustal silicates tc may be as low as 400 600 c suggesting that substantial decoupling may take place within thick continental crust and that strength may increase with depth at the moho as suggested by a number of workers on independent grounds put another way the moho is a rheological discontinuity a second class of laboratory observations pertains to the general phenomenon of ductile faulting in which ductile strains are localized into shear zones ductile faults have been produced in experiments of five different rock types and is generally expressed as strain softening in constant strain rate tests or as an accelerating creep rate stage at constant differential stress a number of physical mechanisms have been identified that may be responsible for ductile faulting including the onset of dynamic recrystallization phase changes hydrothermal alteration and hydrolytic weakening microscopic evidence for these processes as well as larger scale geological and geophysical observations suggest that ductile faulting in the middle to lower crust and upper mantle may greatly influence the distribution and magnitudes of differential stresses and the style of deformation in the overlying upper continental lithosphere

fluid history of the blue ridge anticlinorium in the central appalachians abstract analysis of fluid inclusions in quartz veins of the blue ridge anticlinorium in the central appalachians was undertaken to determine the relationship between the fluid history and structural evolution of the anticlinorium samples were collected from three generations of veins defined by their age relative to the alleghanian cleavage associated with formation of the anticlinorium and from different stratigraphic units on both limbs of the fold all fluid inclusions observed were two phase l v aqueous inclusions they were separated into four types based on their homogenization temperatures t h salinity and salt composition modal t h varies from 235 c for the oldest group to 135 c for the youngest corresponding salinities decrease progressively from 19 to 6 5 wt nacl equivalent predominant salt compositions are nacl cacl 2 mgcl 2 for older inclusions and nacl for the youngest based on the characteristics of these inclusion types along with the age of the vein and stratigraphic unit in which they occur four fluids were defined that were present in different parts of the anticlinorium at different times during its development the primary control on the occurrence of the different fluids was temporal with different fluids occurring in different age veins a secondary control was the stratigraphy with most of the fluid flow being focused in the catoctin and harpers formations structural location position on the fold and location relative to major faults played minor roles the temporal and stratigraphic controls on fluid occurrence along with an absence of ch 4 and co 2 which are common in fluids in the adjacent piedmont and valley and ridge provinces indicate that the fluids in the blue ridge were locally derived and not part of the late paleozoic regional fluid migration recorded elsewhere in the appalachians

creep of rocksalt abstract a review is presented of the fundamental flow properties and processes in experimentally deformed natural and synthetic halite single crystals and polycrystalline aggregates included in the summary are discussions of a microstructures induced during steady state creep b creep rupture of rocksalt c experiments associated with project salt vault and more recent field studies and d brine migration a representative steady state flow law determined for natural aggregates and maximum natural deviatoric stresses deduced from subgrain sizes are applied briefly to considerations of creep in waste repositories and of salt dome dynamics while the mechanical behavior of rocksalt is probably better understood than for all other rock types further investigations especially on load path stress history and creep rupture are clearly mandated furthermore additional investigations of brine migration and of bench and field scale deformations are needed the latter incorporating realistic rocksalt flow properties into numerical simulations of natural rock mass response

evidence for impact induced pressure gradients on the allende cv3 parent body consequences for fluid and volatile transport carbonaceous chondrites such as those associated with the vigarano cv parent body exhibit a diverse range of oxidative reduced alteration mineralogy mcsween 1977 although fluids are often cited as the medium by which this occurs rubin 2012 a mechanism to explain how this fluid migrates and why some meteorite subtypes from the same planetary body are more oxidized than others remains elusive in our study we examined a slab of the well known allende cv3oxa meteorite using several petrological techniques e g fry s and flinn and computerized tomography ct we discover it exhibits a strong penetrative planar fabric resulting from strain partitioning among its major components calcium aluminum rich inclusions cais 64 5 ct matrix 21 5 fry chondrules 17 6 ct in addition to the planar fabric we found a strong lineation defined by the alignment of the maximum elongation of flattened particles interpreted to have developed by an impact event the existence of a lineation could either be non coaxial deformation or the result of a mechanically heterogeneous target material in the later case it could have formed due to discontinuous patches of sub surface ice and or fabrics developed through prior impact compaction macpherson and krot 2014 which would have encouraged preferential flow within the target material immediately following the impact compacting pore spaces we suggest that structurally controlled movement of alteration fluids in the asteroid parent body along pressure gradients contributed to the formation of secondary minerals which may have ultimately lead to the different oxidized subtypes

subseasonal to interannual variability of rainfall over new caledonia sw pacific daily rainfall occurrence and amount at 55 stations over new caledonia nc 20 s 166 e are examined throughout the calendar year during 1980 2010 using a hidden markov model hmm daily rainfall variability is described in terms of six discrete rainfall states identified by the hmm three states are interpreted as trade wind regimes associated with persistent low level anticyclonic conditions and weak to strong easterlies the most prevalent state state 1 36 of days is dry everywhere and is characterized by an elongated anticyclone centered around australia nc is located on the eastern edge of this anticyclone this state is predominant from mid may to mid december and peaks in september the second most prevalent state state 2 27 of days and the last trade regime state 4 12 of days are most frequent in austral summer states 2 and 4 are associated with the subtropical anticyclone centered south of nc close to its climatological location in austral summer and light state 2 to moderate state 4 rainfall mostly along the windward coast a distinct state state 3 11 of days is mostly associated with wintertime extratropical eastward traveling troughs between new caledonia and new zealand inducing light rainfall over the sw of the main island of new caledonia the two last states 5 and 6 are infrequent 15 of days but account for almost 70 of total rainfall across the archipelago they occur mostly in austral summer with their frequency of occurrence peaking in late february early march these states are associated with synoptic wave traveling eastward from eastern australia leading to a strong influx of moisture from the equatorial latitudes when the associated cyclonic centre is located west of new caledonia the wettest state is also strongly modulated by intra seasonal 15 80 days variability these events contribute to intermittent southwestward shifts of the south pacific convergence zone from its mean location northeast of new caledonia on interannual timescales the occurrence of the rainfall states is modulated by el nino southern oscillation enso events the enso impact is strongest from mid august to march with more less frequent trade regimes 1 2 and less more frequent unstable trade regime 4 and states 5 6 during central pacific warm cold enso events stochastic simulations of daily rainfall occurrence and amount at the 55 stations are generated by using predictors based on nino 4 sea surface temperature index and a local intra seasonal 15 80 days olr index superimposed on a climatological annual cycle the cross validated skill peaks in september november

structural controls and evolution of gold silver and ree bearing copper cobalt ore deposits blackbird district east central idaho epigenetic origins the cu co au ag ni ree ore deposits of the blackbird district east central idaho have previously been classified as besshi type vms sedex and iocg deposits within an intact stratigraphic section new studies indicate that across the district mineralization was introduced into the country rocks as a series of structurally controlled vein and alteration systems quartz rich and biotite rich veins and alteration zones and minor albite and siderite veinlets maintain consistent order and sulfide mineral associations across the district both early and late quartz veins contain chalcopyrite and pyrite whereas intermediate stage tourmaline biotite veins host the cobaltite barren early and late albite and late carbonate generally siderite form veins or are included in the quartz veins ree minerals principally monazite allanite and xenotime are associated with both tourmaline biotite and late quartz veins the veins are in mineralized intervals along axial planar cleavage intrafolial foliation and shears mineralized intervals are hosted by a variety of metasedimentary rocks including three phyllitic units of mesoproterozoic age and two schistose units all of these units are s tectonites in the footwall of a regional thrust fault specifically the district lies within an oblique thrust ramp containing a series of structural horses three domains in a duplex system the deposits span the three domains and are hosted by metamorphic rocks that range from lower amphibolite facies in the structurally upper domain to lower middle greenschist facies in the lower domain an inverted metamorphic sequence early quartz and biotite veins were introduced during progressive folding and prolonged peak metamorphic conditions and they underwent late tectonic retrograde recrystallization and metamorphic mineral growth to the same extent as the country rocks in each domain where little subsequent deformation occurred early veins are discordant to bedding but where folding was polyphase and fabrics are penetrative mineralized zones are concordant with metamorphic compositional layering late quartz veins in the zones are associated with retrograde minerals and textures and are only locally deformed 40 ar 39 ar dating of unoriented muscovite from the selvage of a late quartz vein yields a late cretaceous age of about 83 ma the time of retrograde metamorphism associated with introduction of late quartz veins textural data at all scales indicate that the host sites for veins and the tectonic evolution of both host rocks and mineral deposits were kinematically linked to late cretaceous regional thrust faulting heat fluids and conduits for generation and circulation of fluids were part of the regional crustal thickening the faulting also juxtaposed metaevaporite layers in the mesoproterozoic yellowjacket formation over blackbird district host rocks we conclude that this facilitated chemical exchange between juxtaposed units resulting in leaching of critical elements cl k b na from metaevaporites to produce brines scavenging of metals co cu etc from rocks in the region and finally concentrating metals in the lower plate ramp structures although the ultimate source of the metals remains undetermined the present cu co au ag ni ree blackbird ore deposits formed during late cretaceous compressional deformation

fluid infiltration into fault zones chemical isotopic and mechanical effects fluid infiltration into fault zones and their deeper level counterparts brittle ductile shear zones is examined in diverse tectonic environments in the 2 7 ga abitibi greenstone belt major tectonic discontinuities with lateral extents of hundreds of kilometres initiated as listric normal faults accommodating rift extension and acted as sites for komatiite extrusion and locally intense metasomatism during reverse motion on the structures accommodating shortening of the belt these transcrustal faults were utilised as a conduit for the ascent of trondhjemitic magmas from the base of the crust and of alkaline magmas from the asthenosphere and for the discharge of thousands of cubic kilometres of hydrothermal fluids such fluids were characterised by 18o 6 2 d 50 20 13c 4 4 and temperatures of 270 to 450 c probably derived from devolatilisation of crustal rocks undergoing prograde metamorphism hydrothermal fluids were more radiogenic 87sr 86sr 0 7010 to 0 7040 and possessed higher than did contemporaneous mantle komatiites or tholeiites and thus carried a contribution from older sialic basement a provinciality of87sr 86sr and 13c is evident signifying that fault plumbing sampled lower crust which was heterogeneous at the scale of tens of kilometres mineralised faults possess enrichments of large ion lithophile lil lil elements including k rb ba cs b and co2 and rare elements such as au ag as sb se te bi and w fluids were characterised by xco2 0 1 neutral to slightly acidic ph low salinity 3 wt k na 0 1 they carried minor ch4 co and n2 and they underwent transient effervescence of co2 during decompression clastic sediments occupy graben developed at fault flexures the40ar 39ar release spectra indicate that fault rocks experienced episodic disturbance on time scales of hundreds of millions of years

expanding collapse in partially submerged granular soil slopes the traditional approach to stability analysis of granular slopes leads to the safety factor that is associated with a planar failure surface approaching the slope face whether the slope is dry or submerged however for partially submerged slopes a more critical nonplanar failure surface can be formed a family of geometrically similar surfaces can be found that is characterized by the same safety factor if the safety factor drops down to unity and the slope becomes unstable then a mechanism of any size can form alternatively the failure may start at some small region and then the volume of the mechanism of failure can expand giving rise to a progressive failure of a different kind that is typically associated with slopes this progression has the character of a disturbance or a shock like kinematic discontinuity propagating into the soil at rest a quantitative analysis is presented and it is demonstrated that the soil dilates while the mechanism expands leaving the slope weakened and susce

semi brittle deformation within the alpine fault zone new zealand abstract this paper reports the results of an attempt to identify the deformation micromechanisms in the brittle ductile transition zone of the alpine fault new zealand characterization of sequentially developed microstructures was carried out using optical microscopy hvem and stem analysis it was found that the transition zone corresponds to a broad zone of retrogression produced initially by microcracking and fluid infiltration the non catastropic nature of the fracturing indicates that fluid enhanced sub critical cracking is a significant crustal deformation mechanism after the initial phase of retrogression both ductile and brittle processes coexist and cyclically alternate in response to stress cycling the relative importance of macroscopic brittle processes may decrease with time as more ductile minerals especially phyllosilicates develop during continued retrogression

stability charts for 3d failures of steep slopes subjected to seismic excitation design of slopes and analysis of existing slopes subjected to seismic shaking are carried out routinely using approximations of plane strain and substitution of a quasi static load for the seismic excitation a three dimensional 3d analysis of slopes is carried out based on the kinematic theorem of limit analysis a rotational failure mechanism is used with the failure surface in the shape of a curvilinear cone sector passing through the slope toe typical of steep slopes a quasi static approach is used to develop stability charts allowing assessment of the factor of safety of slopes without the need for an iterative procedure the charts are of practical importance in cases of excavation slopes and whenever a slope is physically constrained preventing a plane failure

the role of tectonic grain size reduction in the rheological stratification of the lithosphere with the aid of published constitutive flow laws for common crustal and upper mantle rock types it is possible to construct curves showing variation of rock strength with depth in the continental lithosphere assuming a particular crustal stratification of rock types and a particular geothermal gradient such exercises lead to the conclusion that marked changes in strength can occur at major petrological interfaces such as the moho discontinuity which are therefore likely to be associated with a tendency for major sub horizontal detachments to form constitutive flow laws used for such purposes are usually assumed to represent steady state flow at constant rock microstructure

structural aspects of fluid rock interactions in detachment zones metamorphic core complexes and associated detachment faults of the north american cordillera represent gently dipping normal displacement shear zones detachment zones along which hot deeper levels of the crust were transported upward and outward from underneath a brittlely distended upper plate structures that formed during the ductile to brittle evolution of detachment zones can be used to reconstruct the relative magnitudes of fluid pressure and deviatoric stress at different levels within the shear zones mylonitization which occurred along deeper segments of detachment zones below the brittle ductile transition was locally accompanied by tensile failure indicative of low deviatoric stress and high fluid pressure this condition persisted into the earliest phases of brittle deformation after which shear fractures formed due to both a reduction in fluid pressure and an increase in deviatoric stress brittle deformation of upper plate rocks occurred largely under conditions of low fluid pressure structural and geochemical data suggest that normal displacement on detachment zones results in establishment of two fluid systems 1 an upper plate system driven by convection and dominated by meteoric and connate fluids at near hydrostatic pressures and 2 a system within deeper levels of the shear zone where fluids are largely derived from igneous sources and fluid migration is aided by dilatancy pumping the late phases of normal displacement on detachment zones structurally juxtaposed rocks affected by the two fluid systems and locally caused the shear zone rocks to be overprinted by mineralization related to the upper plate fluid system

the role of water in the deformation of dunite specimens of two natural dunites anita bay of 100 m grain size and aheirn of 900 m grain size have been deformed in experiments at temperatures between 1200 and 1400 c and constant strain rates between 10 4 and 10 6 s 1 in a gas medium deformation apparatus at 300 mpa confining pressure prior to these experiments the specimens were given a heat treatment in a controlled oxygen fugacity furnace at 1200 c for 60 hours to dehydrate the trace layer silicate minerals present and drive off adsorbed water the predried specimens are much stronger than specimens tested under wet conditions in an earlier study the predried specimens also do not show the apparent grain size dependence seen under wet conditions infrared absorption measurements on the present specimens and those of the earlier study indicate that for a given rock flow stress can be correlated with the intensity of a residual water related broad absorption the addition of water to a predried specimen results in both a mechanical reweakening and an intensifying of the broadband infrared component the weakening of the dunites under wet conditions is probably strongly influenced by the presence of small amounts of a water related species in the grain boundaries but intragranular weakening may also be contributing it is suggested that the concentration of the water related species in the grain boundaries is governed by its concentration in the small melt fraction present the amounts of water that have been found to be of importance for the strength of these dunites are of the order of 0 01 wt amounts much less than most estimates of the water content of the earth s undepleted upper mantle such water may have an important role in determining upper mantle flow behavior stress strain curves for all experiments are available with entire manuscript on microfiche order from american geophysical union 2000 florida avenue n w washington dc 20009 document b84 008 2 50 payment must accompany order

oxygen self diffusion in quartz under hydrothermal conditions oxygen self diffusion dox has been monitored in single crystal quartz in the temperature range 515 850 c under hydrothermal conditions in the beta field between 700 and 850 c the data are represented by two linear arrhenius relations for transport parallel and perpendicular to c values for do m2 s 1 are 2 09 10 11 parallel to c and 3 16 10 10 perpendicular to 101 0 values for h kj mol 1 are 138 54 parallel to c and 203 72 perpendicular to 101 0 at 700 c in the total pressure range 11 5 100 mpa dox is independent of water f h2o and oxygen f o2 fugacities between the ni nio and fe3o4 fe2o3 buffers the results are consistent with diffusion via a simple charged vacancy mechanism under an extrinsic point defect regime further experiments are required to confirm the nature of the mobile oxygen defect a key aspect of the results is the observation that at the low water fugacities of the present experiments a hydrogen containing defect appears to play no role in the oxygen transport mechanism this is in contrast to other published sets of data and leads directly to the requirement for detailed interlaboratory comparisons

atmospheric circulation cells associated with the el nino southern oscillation abstract atmospheric circulation cells associated with the el nino southern oscillation enso are described and examined using the ncep ncar reanalysis field and the ncep sea surface temperature sst from january 1950 to december 1999 the divergent wind and pressure vertical velocity are employed for the identification of atmospheric circulation cells the warm phase of enso shows positive sst anomalies in the equatorial eastern pacific and along the east coast of asia and the west coast of north america and negative sst anomalies in the off equatorial western pacific and in the central north pacific associated with this sst anomaly distribution are variations of atmospheric zonal and meridional circulation cells over the pacific the equatorial zonal walker circulation cell is weakened consistent with previous schematic diagrams the anomalous meridional hadley circulation cell in the eastern pacific shows the air rising in the tropics flowing poleward in the upper troposphere sinking in the subt