quantitative reconstruction of mid to late holocene climate in ne china from peat cellulose stable oxygen and carbon isotope records and mechanistic models there has been an increasing need to reconstruct past climate from proxy records quantitatively and mechanistically the inverse proxy modeling method stands out as a novel approach to quantitative palaeoclimate reconstructions through integrating process based models and proxy records representing a major progress in quantitative palaeoclimatology it has been proposed to incorporate multiple proxy records to produce a more robust constraint on the climate parameters sought for estimation and most of the work has been conducted using pollen records in conjunction with vegetation models here i show a worked example of using paired stable oxygen and carbon isotope records of peat cellulose from one single core to infer the climate history in ne china for the last 6000 years through solving a well posed inverse problem using bayesian statistics the quantitative palaeoclimate data obtained in this study may deepen our insight into the dynamics of the east asian summer monsoon mean growing season temper

development of single crystal σ shaped quartz porphyroclasts by dissolution precipitation creep in a calcite marble shear zone abstract within a greenschist facies calcite marble shear zone isolated quartz grains change shape across the shear zone profile whereas quartz grains have a spherical to elongated shape in the coarse grained marble protolith and protomylonite they are asymmetric shaped porphyroclasts with wedge shaped appendages wings in ultramylonites in all cases quartz grains are single crystals they are sometimes twinned but never recrystallized stress induced dissolution precipitation creep is the favourable shape controlling process during deformation providing a relatively undeformed core truncation of pre existing cathodoluminescence cl patterns and syntaxial precipitation of wings the necessary fluids may have been released from fluid inclusions during dynamic recrystallization of the calcite matrix the development of shape is not related to the crystallographic orientation of the quartz porphyroclasts crystallographic orientation analysis by electron backscatter diffraction ebsd and cl analyses exclude crystal plasticity as a shape controlling mechanism of quartz grains during mylonitisation however in ultramylonites quartz clasts have a strong crystallographic preferred orientation cpo with c axes sub parallel to the shear direction this fabric is uncommon for quartz under greenschist facies conditions it might be explained by a strengthening of a pre existing weak cpo during mylonitisation by rigid particle rotation of elongated quartz grains

methodology of the last climatic cycle reconstruction in france from pollen data abstract a numerical method has been devised to reconstruct the climate of the last climatic cycle from pollen data reliable annual reconstructions have been published recently for the two french long sequences of la grande pile and les echets covering the last 140 millennia this paper gives more details on the method used it proposes new reconstructions based on an extended modern pollen data base these reconstructions are consistent with the previous ones especially detailed information is obtained on the seasonal characteristics of climate computations of gcm on the climate variations from 125 kyr to 115 kyr b p are confirmed for western europe the insolation variations have induced at that time a decrease of seasonality accompanied by an increased cyclonic activity in winter this has been the beginning of the first ice growth after the last interglacial other glacier growth phases are detected at the end of substage 5c and particularly at the end of substage 5a

inverse multiparameter modeling of paleoclimate carbon cycle indices abstract a simple linear response model describing the functional relationship between ocean carbon cycle parameters and paleoclimate tracers atmospheric p co2 13c caco3 saturation was derived from a set of sensitivity experiments performed previously using a three dimensional carbon cycle model the linear model is optimally fitted to ice and marine sediment core records for the last 120 000 yr to estimate the carbon cycle parameter changes that could have caused the observed reduction of atmospheric co2 partial pressure during the last glaciation the analysis indicates that the glacial pco2 reduction was primarily caused by a strengthening of the biological poc pump and a retardation of the oceanic circulation an increase in deep sea alkalinity and a change in the advective pattern of the ocean circulation have a smaller impact on atmospheric co2 but are necessary to explain the full set of paleoclimate tracers

meridional circulation during the last glacial maximum explored through a combination of south atlantic δ18o observations and a geostrophic inverse model 1 the vertical profile of meridional transport in the south atlantic is examined by combining paleoceanographic observations with a geostrophic circulation model using an inverse method 18ocalcite observations along the margins of the south atlantic show that upper ocean cross basin differences were weaker during the last glacial maximum lgm than the holocene the 18ocalcite observations can be explained by a shift of water mass properties without any change in the overturning circulation alternatively they may indicate a reduced lgm cross basin density difference and via the thermal wind relation a reduced vertical shear model inversions of 18ocalcite are found to require meridional transports different from the modern only after three assumptions are made temperature and salinity distributions are spatially smooth the relationship between salinity and 18owater is linear and spatially invariant and lgm temperatures are known to within 1 c along the margins the last assumption is necessary because an independent constraint on temperature or salinity is required to determine density from 18ocalcite observations 18ocalcite observations are clearly useful but before any firm constraints can be placed on lgm meridional transport it appears necessary to better determine the relationship between 18ocalcite and density

insolation values for the climate of the last 10 million years new values for the astronomical parameters of the earth s orbit and rotation eccentricity obliquity and precession are proposed for paleoclimatic research related to the late miocene the pliocene and the quaternary they have been obtained from a numerical solution of the lagrangian system of the planetary point masses and from an analytical solution of the poisson equations of the earth moon system the analytical expansion allows the direct determination of the main frequencies with their phase and amplitude numerical and analytical comparisons with the former astronomical solution ber78 are performed so that the accuracy and the interval of time over which the new solution is valid can be estimated the corresponding insolation values have also been computed this analysis leads to the conclusion that the new values are expected to be reliable over the last 5 ma in the time domain and at least over the last 10 ma in the frequency domain

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

reaction enhanced ductility the role of solid solid univariant reactions in deformation of the crust and mantle abstract in collision belts and subduction zones penetrative deformation of thrust sheets may be catalyzed by metamorphic reactions if the reactions have a significant effect on the mechanical properties of rocks reaction enhanced ductility may result if a reaction produces a significant decrease in grain size thus allowing the rock to deform superplastically the product grain size of a reaction is a function of the ratio of nucleation and growth rates this ratio varies along any pressure temperature time ptt path and only attains a significant value at a certain distance from an equilibrium boundary a comparison of rates of change of p and t along typical segments of ptt paths for crustal rocks leads to the conclusion that a high nucleation rate a small grain size and resulting superplastic deformation are more likely to be achieved when reaction boundaries are crossed during underthrusting rather than during the thermal readjustments of a perturbed geotherm following crustal thickening or during uplift an example of reaction enhanced ductility occurs in eclogite facies metagranitoids in the sesia lanzo zone western alps where medium grained plagioclase reacted to fine grained jadeite quartz during early alpine underthrusting microstructural evidence from shear zones shows that the jadeite quartz aggregates were highly ductile and it is inferred that the small grain size allowed superplastic deformation further evidence suggests that this process operated during regional deformation of metagranitoids rubie 1982 the reaction of olivine to spinel or the beta phase by metastable overstepping of the two phase stability fields in a subducting plate ringwood 1975 may result in fine grained products and thus may be analogous to the albite jadeite quartz reaction the consequent decrease in effective viscosity is likely to have important consequences for plate dynamics at and below the depths of major phase transitions

three dimensional simulation and inversion of borehole temperatures for reconstructing past climate in complex settings 1 the majority of inversion methods used for inferring past ground surface temperatures gst from borehole temperature depth profiles rely on the assumption that heat flow is in the vertical direction only this means that accounting for certain effects caused by the local terrain of a borehole is not possible and consequently many borehole profiles cannot be used with confidence here we describe a methodology to avoid this problem by solving the heat conduction forward problem in 3 d using finite elements fe in order to make the inversion approach computationally tractable we reduce the dimensions of this fe model using proper orthogonal decomposition the inverse problem is cast in a probabilistic bayesian framework for which the posterior probability distribution of the past gsts is sampled using a reversible jump markov chain monte carlo algorithm this allows the resolution of the gst history over time to be explored by varying the parameterization of the gst model synthetic examples calculated with moderate topographies demonstrate the efficacy of the bayesian 3 d inversion method and the results are compared with those using a 1 d approach for moderate topography the latter can lead to spurious gst reconstructions a further synthetic example demonstrates that the effect of incorrectly assuming lateral geological homogeneity is negligible the inversion method is also compared with a more standard inversion method a significant advantage of the bayesian approach is that uncertainties in all of the model parameters can be accounted for leading to a more realistic interpretation of the range of gst histories supported by the data the methods presented here should allow a broader range of geothermal data to be used for paleoclimate reconstruction purposes in the future

friction properties of hornblende and implications for slow slip events in subduction zones abstract in order to understand the friction properties of amphibole as a primary constituent mineral in subduction zones we used hornblende as the simulated gouge material to conduct two series of shearing experiments at temperatures from 101 to 607 c under confining pressures of 136 mpa and 83 mpa a pore pressure of 30 mpa and loading rates of 0 0488 1 22 m s steady state friction coefficients in the high confining pressure series exhibited values between 0 70 and 0 72 with an average of 0 71 without showing a systematic temperature dependence the counterpart in the low confining pressure series ranged from 0 67 to 0 73 and exhibited a temperature dependent decline for temperatures above 400 c velocity weakening behaviors were observed at 303 505 and 607 c in the high confining pressure series and at 303 and 403 c in the low confining pressure series the a b parameter associated with velocity weakening of hornblende in our high and low confining pressure experiments are 0 0005 0 0014 and 0 0014 0 0015 respectively the b values which represent the evolution effect in friction were found to increase with increasing temperature suggesting a thermally activated process that produced creep at asperity ubiquitously precipitated particles in the deformed gouge suggest that dissolution precipitation creep may be the most likely mechanism associated with the evolution effect and therefore velocity weakening the very low velocity weakening observed for hornblende a b 0 0015 provides a favorable condition for nucleation of slow slip events to occur in subduction zones over a wider range of effective normal stress

focal depths and mechanisms of shallow earthquakes in the himalayan tibetan region abstract the complexity of the himalayan tibetan lithospheric deformation is evident from widespread seismicity and diverse focal mechanism solutions here we investigate the focal depths and fault plane solutions of 97 moderate and shallow earthquakes in the himalayan tibetan region by modeling teleseismic p wave and its tailing surface reflections pp and sp earthquakes in central tibet are restricted to the upper crust and originate dominantly by strike slip faulting in agreement with the low p wave velocity layers in the lower crust and the strong s wave attenuation zones in the uppermost mantle in northern and southern tibet where the asian and indian plates descend beneath central tibet earthquakes appear to be distributed throughout the thickness of the crust and exhibit dominantly reverse faulting we incorporate well estimated focal depths of 127 additional earthquakes from previous studies to estimate the seismogenic thickness ts of the study region the resulting pattern of ts is found to be rather flat for central and northeastern tibet and highly variable along the strike of the himalayan foreland

a method for climate and vegetation reconstruction through the inversion of a dynamic vegetation model climate reconstructions from data sensitive to past climates provide estimates of what these climates were like comparing these reconstructions with simulations from climate models allows to validate the models used for future climate prediction it has been shown that for fossil pollen data gaining estimates by inverting a vegetation model allows inclusion of past changes in carbon dioxide values as a new generation of dynamic vegetation model is available we have developed an inversion method for one model lpj guess when this novel method is used with high resolution sediment it allows us to bypass the classic assumptions of 1 climate and pollen independence between samples and 2 equilibrium between the vegetation represented as pollen and climate our dynamic inversion method is based on a statistical model to describe the links among climate simulated vegetation and pollen samples the inversion is realised thanks to a particle filter algorithm we perform a validation on 30 modern european sites and then apply the method to the sediment core of meerfelder maar germany which covers the holocene at a temporal resolution of approximately one sample per 30 years we demonstrate that reconstructed temperatures are constrained the reconstructed precipitation is less well constrained due to the dimension considered one precipitation by season and the low sensitivity of lpj guess to precipitation changes

geothermobarometry in albite garnet orthogneisses a case study from the gran paradiso nappe western alps abstract the aim of this paper is to estimate syntectonic p t conditions within albite and garnet bearing orthogneisses these rocks are generally characterized by the assemblage quartz albite biotite phengite cafe garnet epidote titanite garnet contains up to 55 mole per cent of grossular k feldspar is a relict magmatic phase p t conditions are estimated using several independent methods first it is shown that exchange reactions based on the fe mg partitioning between garnet and biotite or garnet and phengite cannot be used to estimate temperatures in these rocks due to the high grossular content of garnet second maximum and minimum pressures are constrained respectively by the occurrence of albite instead of jadeite quartz and by the assemblage phengite biotite quartz third phase equilibria in albite and garnet bearing metagranites are modelled in the system k 2 o cao feo al 2 o 3 sio 2 h 2 o equilibrium curves are calculated for the observed phase compositions uncertainties in p t estimates mainly result from the choice of appropriate non ideal solution models for the garnet an application is developed for granites from the gran paradiso nappe western alps these granites show an heterogeneous deformation of alpine age expressed by mylonitic shear zones cutting across weakly deformed domains estimated p t conditions for the synkinematic assemblages are 10 16 kbar at 550 50 c

friction of foliated fault gouge with a biotite interlayer at hydrothermal conditions abstract to investigate the influence of foliation and structure within fault zones synthetic fault gouges of quartz containing various thin layers of biotite were sheared in a triaxial testing system at hydrothermal conditions to acquire the faulting behaviour along with quartz biotite mixtures tested for comparison first in series 1 experiments gouges were sheared at a temperature of 100 c with effective confining pressure of 200 mpa pore pressure of 30 mpa and loading rate of 1 22 m s the results revealed that strength of quartz biotite mixture weakened linearly with increasing biotite proportion whereas the gouges with a biotite interlayer weakened much more significantly even for biotite content as little as 5 wt series 2 experiments were performed on simulated gouge with 15 wt biotite interlayer at temperatures of 25 600 c effective normal stress of 200 230 mpa and pore pressure of 30 mpa with stepped shear rates of 0 0488 to 1 22 m s at effective normal stress of 200 mpa the simulated foliate gouge showed a transition from velocity strengthening to velocity weakening around 200 c which persisted up to 600 c stick slips above 400 c were associated with minor a b averagely of 0 0006 and submicron dc values at effective normal stress of 230 mpa and temperature of 600 c stick slip motions evolved with slip distance to viscous like behaviour at a displacement of 3 mm microstructural observation on deformed samples revealed that shear deformation mainly occurred within the biotite interlayer in most cases with surrounding quartz gouge only slightly deformed but increasingly compacted as temperature increased viscous like behaviour corresponded to migration of dominant shear deformation to the quartz gouge as indicated by the development of riedel shears therein our results may help constrain fault strength and depth range of seismogenesis within fault zones associated with biotite in form of foliations and or interconnected networks

temperature responses to quasi 100 yr solar variability during the past 6000 years based on δ18o of peat cellulose in hongyuan eastern qinghai tibet plateau china abstract during the past 6000 years the temperature variation trend inferred from 18o of peat cellulose in a peat core from hongyuan eastern qinghai tibet plateau southwestern china is similar to the atmospheric 14c concentration trend and the modeled solar output trend the general trend of hongyuan 18o during the past millennium also coincides well with the atmospheric 14c concentration trend the 10be concentration trend in an ice core from the south pole the reconstructed total solar irradiance trend as well as the modeled solar output trend in addition temperature events also correspond well to solar perturbations during the past 6000 years therefore the driving force of holocene temperature variations should be properly ascribed to solar activity the spectrum analysis further illustrates that quasi 100 yr fluctuation of solar activity was probably responsible for temperature variations in northeast qinghai tibet plateau during the past 6000 years

long lived radionuclides as chronometers and tracers of environmental processes at the xi an accelerator mass spectrometry center abstract long lived radionuclides with half lives ranging from 103 to 108 years have wide applications in geochronology and environmental tracer studies a wide range of climatic geologic and environmental records preserved in diverse natural archives can be characterized by measuring their concentrations using accelerator mass spectrometry ams the purpose of this paper is to highlight some representative works on 14c 10be 26al and 129i in these two aspects at the xi an ams center in the past ten years since a dedicated ams facility was established the improvement of the sample preparation procedures the development of the new mathematical analysis method and related applications are summarized

velocity dependence of strength and healing behaviour in simulated phyllosilicate bearing fault gouge abstract despite the fact that phyllosilicates are widespread in fault zones little is known about the strength of phyllosilicate bearing fault rocks under brittle ductile transitional conditions in this study we explored the steady state strength and healing behaviour of a simulated phyllosilicate bearing fault rock i e muscovite plus halite and brine at room temperature normal stresses of 1 9 mpa atmospheric fluid pressure and sliding velocities of 0 001 13 m s using a rotary shear apparatus while 100 halite and 100 muscovite samples exhibit rate independent frictional brittle behaviour the strength of mixtures containing 10 50 muscovite is both normal stress and sliding velocity dependent at low velocities 1 m s velocity weakening frictional behaviour occurs along with the development of a structureless intermixed cataclastic microstructure the steady state porosity of samples deformed in this regime increases with increasing sliding velocity we propose that this behaviour involves competition between dilatation due to granular flow and compaction due to pressure solution towards higher sliding velocities dilatation increasingly dominates over pressure solution compaction so that porosity increases and frictional strength decreases during periods of zero slip pressure solution compaction occurs causing a significant strength increase on reshearing our results imply that cataclastic overprinting of mylonitic rocks in natural fault zones does not require any changes in temperature or effective pressure conditions but can simply result from oscillating fault motion rates our healing data suggest that foliated aseismically creeping fault segments will remain weak and aseismic whereas segments that have slipped seismically will rapidly re strengthen and remain in the unstable velocity weakening regime

simple shear experiments on calcite rocks rheology and microfabric ideal simple shearing of carrara marble and solnhofen limestone was achieved by inserting calcite rock slices into sandstone cylinders precut at 35 the experiments covered a wide range in temperatures 25 900 c at confining pressures of 200 and 250 mpa and at strain rates between 10 3 and 10 5 s 1 shear strains of up 2 7 were achieved the stress strain data for simple shear favourably compare with predictions on the basis of existing flow laws established in coaxial testing this comparison demonstrates that the simple shear experiments covered most of the previously established flow regimes for calcite rocks at the highest temperatures carrara marble exhibited substantial work softening after high shear strains a complete texture analysis was carried out with the u stage and a texture goniometer the following four distinct microfabric regimes were found 1 twinning regime an oblique c axis maximum deflected from the pole to the flattening plane towards 1 and against the imposed sense of shear results directly from e twinning extensive twinning some grains are completely twinned rapidly rotates the c axes into near parallelism with 1 this regime was observed for carrara marble deformed at temperatures below 700 c and for solnhofen limestone at room temperature 2 intracrystalline slip regime three c axis maxima were observed in both rock types at more elevated temperatures and in the absence of twinning these c axis orientations result from an alignment of slip planes and slip directions into parallelism with the shear zone boundary and the shear direction respectively this finding supports the idea of an orientation for easy slip resulting from simple shearing in addition to r and f glide basal glide is inferred to have been operative 3 grain boundary sliding regime a great circle distribution of c axes approximately perpendicular to the direction of finite shortening is observed this texture is weaker compared to the other regimes it is interpreted to result from minor contributions of f slip towards total strain this regime is restricted to fine grained solnhofen limestone deformed at the highest temperatures 4 grain boundary migration regime only in carrara marble deformed at the highest temperatures is there substantial grain boundary migration recrystallization the texture consists of a dominant c axis maximum oriented perpendicular to the shear zone boundary this single maximum corresponds to an orientation for easy slip for basal slip grain boundary migration assists rapid lattice reorientation and leads to geometrical work softening quantitative analysis of grain boundary surface orientations gave the following results within the twinning and the intracrystalline slip regimes the characteristic grain shape is elliptical for both rock types the strain ellipses derived from this analysis closely correspond to the known finite strain at the lowest temperatures at intermediate temperatures and especially in carrara marble there is a consistent trend for the aspect ratios to indicate too little flattening and for the angles between the long axis of the strain ellipse and the shear zone boundary to be too small in the absence of grain boundary migration recrystallization this finding indicates minor translations of grains with respect to one another grain boundary sliding or translations accommodated in the mantle regions of grains at the highest temperatures where extensive grain boundary migration occurs in carrara marble grain boundary migration regime two preferred orientations of grain boundaries are observed 1 parallel to the shear zone boundary and 2 parallel to an oblique direction deflected 20 away from the normal to the shear zone boundary in the sense of the imposed shear the same pattern of grain boundary alignment is observed in solnhofen limestone deformed in the grain boundary sliding regime the geological applications of this experimental work are discussed in terms of calcite tectonites in particular and sheared rocks in general

reconstruction of the grande pile eemian using inverse modeling of biomes and δ13c abstract a new method to reconstruct past climatic conditions between 130 and 100 ka bp from pollen and isotopic data is applied to a previously unanalyzed grande pile core gpxxi we applied the inverse mode to the biome4 vegetation model the method utilizes 13 c measured in parallel to the pollen samples as a constraint for the model first the biomes and the 13 c simulated by the model are compared with the biome allocation of the pollen data the 13 c to be simulated takes into account the degradation effect on the preserved organic matter this procedure allows the reconstruction of the mean annual temperature and precipitation as well as the mean temperatures of the warmest and coldest months we show that during the eemian sensu stricto the reconstructed precipitation is similar to modern values with low variability the cold stadials and the penultimate glaciation are characterized by very low precipitation amounts the temperature estimates however indicate differences with several oscillations identified the peak values are reached at about 124 125 ka bp but two other warm intervals are also identified the variations in temperature appear to be related to sea surface temperature oscillations in the north atlantic region and are also in agreement with the timing of ice sheet build up in the northern hemisphere seasonal variations are also identified in the estimated temperatures of the warmest and coldest months

the coexistence approach a method for quantitative reconstructions of tertiary terrestrial palaeoclimate data using plant fossils abstract the coexistence approach is introduced as a method for quantitative terrestrial palaeoclimate reconstructions in the tertiary it is based on the assumption that tertiary plant taxa have similar climatic requirements to their nearest living relatives the aim of the coexistence approach is to find for a given fossil flora and a given climate parameter the climatic interval in which all nearest living relatives of the fossil flora can coexist for this purpose we have developed a data base climbot containing for over 800 tertiary plant taxa the nearest living relatives and their climatic requirements and an algorithm for analysis climst for all types of fossil floras the coexistence approach thus allows the rapid quantitative reconstruction of 10 different climate parameters including the mean annual temperature temperature of the warmest month temperature of the coldest month mean annual precipitation maximum monthly precipitation minimum monthly precipitation precipitation of the warmest month relative humidity potential evaporation as well as the ratio of mean annual precipitation over potential evaporation the reliability and resolution of the coexistence approach are tested with various techniques and proved to be reasonably good for instance the resolution with respect to the mean annual temperature can be up to 1 c applications to various modern and fossil floras are illustrated and the advantages and disadvantages of the coexistence approach are discussed

can oxygen stable isotopes be used to track precipitation moisture source in vascular plant dominated peatlands a b s t r a c t variations in the isotopic composition of precipitation are determined by fractionation processes which occur during temperature and humidity dependent phase changes associated with evaporation and condensation oxygen stable isotope ratios have therefore been frequently used as a source of palaeoclimate data from a variety of proxy archives which integrate this signal over time applications from ombrotrophic peatlands where the source water used in cellulose synthesis is derived solely from precipitation have been mostly limited to northern hemisphere sphagnum dominated bogs with few in the southern hemisphere or in peatlands dominated by vascular plants new zealand nz provides an ideal location to undertake empirical research into oxygen isotope fractionation in vascular peatlands because single taxon analysis can be easily carried out in particular using the preserved root matrix of the restionaceous wire rush empodisma spp that forms deep holocene peat deposits throughout the country furthermore large gradients are observed in the mean isotopic composition of precipitation across nz caused primarily by the relative influence of different climate modes here we test whether 18o of empodisma cellulose from ombrotrophic restiad peatlands in nz can provide a methodology

dissolution and replacement creep a significant deformation mechanism in mid crustal rocks abstract zoning patterns and zoning truncations in metamorphic minerals in a granodioritic orthogneiss indicate that strain and s c fabrics in these rocks were produced by dissolution precipitation and replacement processes even at epidote amphibolite facies metamorphic conditions the metamorphic fabric is defined by alternating layers and folia dominated by quartz feldspars and biotite epidote zoning patterns in most metamorphic plagioclase orthoclase epidote and sphene are truncated at boundaries normal to the shortening direction suggesting dissolution interfaces of relict igneous orthoclase phenocrysts that face the shortening direction are embayed and replaced by biotite epidote and myrmekitic intergrowths of plagioclase and quartz metamorphic plagioclase grains are also replaced by epidote we interpret these microstructures to reflect strain enhanced dissolution the cores of many grains show asymmetric overgrowths with at least two generations of beards all oriented on the ends of grains that face the extension direction we interpret these textures to reflect precipitation of components dissolved by deformation enhanced dissolution while biotite and quartz probably deformed by dislocation creep the overall deformation was accommodated by dissolution perpendicular to the shortening direction and precipitation parallel to it these chemical processes must have been activated at lower stresses than the dislocation creep predicted from extrapolations of data from experiments in dry rocks thus wet crust is likely to be weaker than calculated from these experimental studies

quantitative measure of the variation in fault rheology due to fluid rock interactions we analyze friction data from two published suites of laboratory tests on granite in order to explore and quantify the effects of temperature t and pore water pressure pp on the sliding behavior of faults rate stepping sliding tests were performed on laboratory faults in granite containing gouge granite powder both dry at 23 to 845 c lockner et al 1986 and wet pp 100 mpa at 23 to 600 c blanpied et al 1991 1995 imposed slip velocities v ranged from 0 01 to 5 5 m s and effective normal stresses were near 400 mpa for dried granite at all temperatures and wet granite below 300 c the coefficient of friction shows low sensitivity to v t and pp for wet granite above 350 drops rapidly with increasing t and shows a strong positive rate dependence and protracted strength transients following steps in v presumably reflecting the activity of a water aided deformation process by inverting strength data from velocity stepping tests we determined values for parameters in three formulations of a rate and state dependent constitutive law one or two state variables were used to represent slip history effects each velocity step yielded an independent set of values for the nominal friction level five constitutive parameters transient parameters a b1 and b2 and characteristic displacements dc1 and dc2 and the velocity dependence of steady state friction ss ln v a b1 b2 below 250 data from dry and most wet tests are adequately modeled by using the slip law ruina 1983 and one state variable a 0 003 to 0 018 b 0 001 to 0 018 dc 1 to 20 m dried tests above 250 can also be fitted with one state variable in contrast wet tests above 350 require higher direct rate dependence a 0 03 to 0 12 plus a second state variable with large negative amplitude b2 0 03 to 0 14 and large characteristic displacement dc2 300 to 4000 m thus the parameters a b1 and b2 for wet granite show a pronounced change in their temperature dependence in the range 270 to 350 c which may reflect a change in underlying deformation mechanism we quantify the trends in parameter values from 25 to 600 c by piecewise linear regressions which provide a straightforward means to incorporate the full constitutive response of granite into numerical models of fault slip the modeling results suggest that the succeptibility for unstable stick slip sliding is maximized between 90 and 360 c in agreement with laboratory observations and consistent with the depth range of earthquakes on mature faults in the continental crust

comparing dry and wet friction of plagioclase implication to the mechanism of frictional evolution effect at hydrothermal conditions to understand mechanism for unstable velocity weakening slip behavior of plagioclase at hydrothermal conditions in the lower crust we employed nominally dry experiments on plagioclase gouge to isolate fluid assisted processes that may be activated at hydrothermal conditions and obtained constitutive parameters fitted to rate and state friction laws with temperatures of 99 617 c and confining pressure of 150 mpa allowing comparison to the hydrothermal counterpart while the direct effect a value has relatively high values of 0 007 0 01 in the high temperature range above 300 400 c the evolution effect b value shows a diminishing trend from peak values of 0 0075 and 0 0057 respectively at 305 c and 400 c down to 0 at 617 c in contrast to the increasing trend in both effects at hydrothermal conditions the evolution effect in the dry experiments may be controlled by structural changes related to degrees of shear localization and evolution of porosity change rate in response to a change in loading rate the evolution effect in dry friction compared to the thermally enhanced much stronger one at hydrothermal conditions suggests activation of fluid assisted time dependent mechanism operating in the wet experiments

quartz grain size reduction in a granitoid rock and the transition from dislocation to diffusion creep abstract in the gran paradiso metagranodiorite western alps small scale lower amphibolite facies shear zones record the transition from a mylonite composed of polycrystalline mineral aggregates to a homogeneous ultramylonite with a grain scale phase mixture polycrystalline quartz aggregates in the mylonite deform by dislocation creep developing a crystallographic preferred orientation cpo and a monoclinic surface orientation distribution function odf the polymineralic matrix of the mylonite and the ultramylonite deform by diffusion creep in the ultramylonite the quartz cpo is randomized and the surface odf becomes orthorhombic the transition from mylonite to ultramylonite is accompanied by a grain size decrease and a disintegration of quartz aggregates concomitant with the precipitation of k feldspar biotite between quartz grains in quartz reduction from the dynamically recrystallized grain size in the aggregates 110 m to the size of the dispersed grains in the ultramylonite 25 m occurs through the following processes k feldspar precipitates at opening sites along grain boundaries strain incompatibility pinning the grain size in quartz aggregates coalescence of k feldspar leads to enhanced grain boundary sliding and disintegration of the quartz aggregates solution precipitation reduces the size of the dispersed grains to less than subgrain size 45 m

earthquake nucleation on rate and state faults aging and slip laws we compare 2 d quasi static earthquake nucleation on rate and state faults under both aging and slip versions of the state evolution law for both versions mature nucleation zones exhibit 2 primary regimes of growth well above and slightly above steady state corresponding respectively to larger and smaller fault weakening rates well above steady state aging law nucleation takes the form of accelerating slip on a patch of fixed length this length is proportional to b 1 and independent of a where a and b are the constitutive parameters relating changes in slip speed and state to frictional strength under the slip law the nucleation zone is smaller and continually shrinks as slip accelerates the nucleation zone is guaranteed to remain well above steady state only for values of a b that are low by laboratory standards near steady state for both laws the nucleation zone expands the propagating front remains well above steady state giving rise to a simple expression for its effective fracture energy g c this fracture energy controls the propagation style for the aging law g c increases approximately as the square of the logarithm of the velocity jump this causes the nucleation zone to undergo quasi static crack like expansion to a size asymptotically proportional to b b a 2 for the slip law g c increases only as the logarithm of the velocity jump and crack like expansion is not an option instead the nucleation zone grows as an accelerating unidirectional slip pulse under both laws the nucleation front propagates at a velocity larger than the slip speed by roughly b divided by the logarithm of the velocity jump where is the effective elastic shear modulus for this prediction to be consistent with observed propagation speeds of slow slip events in subduction zones appears to require effective normal stresses as low as 1 mpa

frictional behavior of simulated biotite fault gouge under hydrothermal conditions abstract we investigated frictional properties of biotite under hydrothermal conditions by shearing simulated biotite gouge sandwiched between saw cut driving blocks using a testing system with argon as confining medium experiments were conducted under an effective normal stress of 200 mpa with pore pressure of 30 mpa temperatures were varied from room temperature to 600 c with shear displacement rate stepped at standard velocities 1 22 0 122 m s and slow velocities 0 244 0 0488 m s to acquire rate dependence of friction our results show that the friction coefficient of biotite ranges from 0 25 to 0 44 significantly lower than that of muscovite documented in previous studies the steady state rate dependence shows velocity strengthening at temperatures of 25 c to 200 c and transitions to velocity weakening at temperatures above 300 c the velocity weakening is quite minor with a b ranging from 4 10 4 to 9 10 4 and stick slip motions at temperatures from 400 c to 600 c are found to be related to submicron dc values corresponding to critical stiffness higher than the actual stiffness surrounding the fault thus leading to unstable slips microstructures of deformed samples show three types corresponding respectively to three different temperature ranges while brittle structures are dominantly associated with deformation at 100 c significant plastic deformation occurred at higher temperatures deformation at temperatures of 200 c to 400 c are characterized with shear fracture zones accompanied with plastic deformation mostly associated with basal glide intensively deformed zones are the characteristic structures for samples deformed at 500 c to 600 c accompanied with shear fracture zones and moderately deformed zones it is evident that biotite alone is not weak enough to explain a weak fault like the san andreas fault thus overpressured pore fluid or another weaker mineral is needed to produce a weak fault with apparent friction coefficient of 0 1 0 2 the around neutral velocity weakening found for biotite may be appropriate in modeling fault creep transients in the mid crust

regional scale palaeoclimate modelling on soft proxy data basis an example from the upper miocene of the lower rhine embayment abstract a new method in palaeoclimatology initially proposed by mosbrugger and schilling 1992 which makes it possible to extract a maximum of information from the available proxy data is tested it possesses a capacity to produce a detailed palaeoclimate reconstruction which is consistent with both proxy data and the physics of atmospheric models since proxy data information is particularly poor on a global scale our method focuses on smaller scale regions of better proxy data coverage it consists of an iterative coupling of inverse mesoscale atmospheric modelling with proxy based palaeoclimate reconstruction using this method the palaeoclimate of the tortonian upper miocene of the lower rhine embayment northwest germany is reconstructed with a high spatial resolution the results include a physically consistent inter and extrapolation of proxy derived palaeoclimate data in space and onto variables not accessible from geological palaeontological proxies alone moreover the method delivers statistics of the large scale atmospheric flows as information on the coupling of the regional climate to global fields

palaeoprecipitation reconstruction by inverse modelling using the isotopic signal of loess organic matter application to the nusloch loess sequence rhine valley germany a modified version of the biome4 vegetation model for simulation of the mean 13c of plant communities is presented and used to reconstruct palaeoprecipitation we treat all fractionations by c3 and c4 plants in all coexistent plant functional types weighted by their respective net primary production we constrain the range of variation in the intracellular versus atmospheric co2 concentration by fixing a lower limit finally we replace some constant parameters by functions of external forcing to account for their responses to environmental variation the new version of biome4 was applied as an inverse model and tested on three modern data sets the fit between observations and simulations is very close to the 1 1 relationship with respective slopes of 0 90 0 02 r2 0 98 n 29 for 13c and 0 97 0 06 r2 0 90 n 29 for precipitation inverse modelling was applied using the metropolis hastings algorithm to the nusloch loess sequence over the last glaciation simulated palaeoprecipitation varies between 240 mm year 1 and 400 mm year 1 this study clearly demonstrates atmospheric teleconnections with the greenland ice sheet extension by matching dansgaard oeschger events with precipitation increase of ca 100 200 mm year 1

can paleoceanographic tracers constrain meridional circulation rates abstract the ability of paleoceanographic tracers to constrain rates of transport is examined using an inverse method to combine idealized observations with a geostrophic model considered are the spatial distribution accuracy and types of tracers required to constrain changes in meridional transport within an idealized single hemisphere basin measurements of density and radioactive tracers each act to constrain rates of transport conservative tracers while not of themselves able to inform regarding rates of transport improve constraints when coupled with density or radioactive observations it is found that the tracer data would require an accuracy one order of magnitude better than is presently available for paleo observations to conclusively rule out factor of 2 changes in meridional transport even when assumed available over the entire model domain when data are available only at the margins and bottom of the model radiocarbon is unable to constrain transport while density remains effective o

crustal earthquake instability in relation to the depth variation of frictional slip properties recent stability studies using constitutive relations of the type found by dieterich ruina and others to describe frictional slip of rocks in the laboratory have provided a new explanation of the depth cutoff of shallow crustal earthquakes the class of friction laws discussed has the property that the sliding stress depends on normal stress temperature slip rate and slip history for sliding at a fixed slip rate v and fixed environment e g normal stress temperature etc the shear strength evolves toward a steady state value ss v stability analysis show that for d ss v dv 0 velocity strengthening implies stable steady state sliding at least for a broad class of constitutive laws more fully described in the paper experiments by dieterich and by tullis and weeks on westerly granite with mature sliding surfaces indicate that d ss v dv is negative at room temperature whereas higher temperature experiments by stesky show that d ss v dv becomes positive above approximately 300 c therefore in the case of the earth where temperature increases with depth the above observations seem to suggest that the depth cutoff of crustal earthquake activity can be understood in terms of the variation of the frictional response with depth from a regime with d ss v dv 0 this is not inconsistent with but rather refines the suggestion by sibson and others that the depth cutoff is due to a transition from brittle friction to ductile flow further our results show definitively that the shallow depth confinement of seismicity is compatible with a model in which deformation is localized to a fault zone extending well below the seismogenic depth the depth confinement does not require a model showing transition to a zone of broadly distributed creep flow beneath the seismogenic zone following mavko a two dimensional quasi static strike slip fault model is analyzed but using different numerical procedures and a depth variation of frictional properties based on the laboratory data mentioned above and the lachenbruch sass depth variation of temperature for the san andreas fault the resulting predictions of such features as the confinement of crustal earthquakes to shallow depths the development of locked patches the recurrence time for the seismic cycle the seismic stress drop and displacement etc are generally in agreement with the observed characteristics of large scale strike slip earthquakes along the san andreas fault calculations based on the laboratory data predict for example that stick slip nucleates around 5 7 km that large seismic motion occurs around the nucleation depth and above but diminishes gradually to zero at 13 15 km depths that rapid postseismic creep occurs over another 3 4 km depth and that at greater depths steady slip consistent with the average plate velocity is only modestly perturbed by the earthquakes occurring above the most uncertain parameter is the slip weakening distance l for evolution of fault surface state we illustrate how features of the predicted earthquake cycles vary with l over the range for which calculations are feasible

effects of temperature and sliding rate on frictional strength of granite layers of artificial granite gouge have been deformed on saw cut granite surfaces inclined 30 to the sample axes samples were deformed at a constant confining pressure of 250 mpa and temperatures of 22 to 845 c the velocity dependence of the steady state coefficient of friction ss was determined by comparing sliding strengths at different sliding rates the results of these measurements are consistent with those reported bysolberg andbyerlee 1984 at room temperature andstesky 1975 between 300 and 400 c stesky found that the slip rate dependence of ss increased above 400 c in the present study however the velocity dependence of ss was nearly independent of temperature

a re assessment of focal depth distributions in southern iran the tien shan and northern india do earthquakes really occur in the continental mantle summary we investigate the depth distribution of earthquakes within the continental lithosphere of southern iran the tien shan and northern india by using synthetic seismograms to analyse p and sh body waveforms in the zagros mountains of southern iran earthquakes are apparently restricted to the upper crust depths of 20 km whereas in the tien shan and northern india they occur throughout the thickness of the continental crust to depths of 40 45 km we find no convincing evidence for earthquakes in the continental mantle of these regions in spite of previous suggestions to the contrary and question whether seismicity in the continental mantle is important in any part of the world in some regions such as iran the aegean tibet and california seismicity is virtually restricted to the upper continental crust whereas in others including parts of east africa the tien shan and northern india the lower crust is also seismically active although usually less so than the upper crust such variations cannot reliably be demonstrated from published catalogue or bulletin locations even from ones in which depth resolution is generally improved in contrast to the oceanic mantle lithosphere in which earthquakes certainly occur the continental mantle lithosphere is we suggest virtually aseismic and may not be significantly stronger than the lower continental crust these variations in continental seismogenic thickness are broadly correlated with variations in effective elastic thickness suggesting that the strength of the continental lithosphere resides in the crust and require some modification to prevalent views of lithosphere rheology

constraints from paleotracer data on the north atlantic circulation during the last glacial maximum we investigate the extent to which the paleotracers 13c and 18o constrain the north atlantic ocean general circulation during the last glacial maximum lgm the distinction is made in this work between the depiction of water mass distributions and the inference of the oceanic circulation the 13c data indicate that water masses formed in the north atlantic and in the southern ocean were distributed differently during the lgm but the extent of the differences cannot be quantified because of uncertainties in the end member composition reasonable choices of values for the end members produce volumes of lower north atlantic deep water nadw significantly smaller than in the modern atlantic in agreement with previous studies to explore the range of circulations consistent with this water mass distribution a coarse resolution inverse model of the north atlantic is constrained with 13c and 18o paleodata the model shows that the glacial period tracer distribution is fully consistent with the circulation rates estimated for the modern ocean however the paleodata are also consistent with a circulation rate of one half the modern flux of nadw and indeed there are an infinite number of rates of deep water movement that are possible to remove this ambiguity the central need is for a data type capable of setting the overall rates of water movement i e a clock such as that provided by geostrophy or a well sampled radioactive tracer

holocene temperature changes in northern fennoscandia reconstructed from chironomids using bayesian modelling the recently developed bayesian multinomial calibration model bummer was applied to the fossil chironomid assemblages of a lake situated at the present tree line in northern fennoscandia to reconstruct patterns in holocene climates the results are compared with inferences derived using non bayesian weighted averaging partial least squares regression the reconstruction exhibits both long term trends as well as a series of shorter term oscillations abrupt climatic excursions were particularly characteristic for the early holocene period with cooling episodes around 9200 8600 and 8200 cal yr bp the interval from ca 8000 to 5800 cal yr bp appeared to be warm and stable but was followed by a pronounced climatic cooling around 5800 cal yr bp leading to a relatively long lasting mid holocene temperature minimum between ca 5800 and 4000 cal yr bp the reconstruction during the latter part of the holocene is relatively featureless which may partly be due to gradual shallowing of the lake by sedimentation that may have affected chironomid compositions thereby masking the climate signal the major climatic patterns in our reconstruction agree well with inferences from greenland ice and marine sediments and are also in line with the previous reconstructions based on diatoms and pollen from the same core although the finer scale variations reflected by the three proxies do not always match the overall results provide evidence for climatic complexity during the holocene epoch and demonstrate that bayesian modelling is highly suitable for reconstruction purposes

grain growth in synthetic marbles with added mica and water evolution of grain size in synthetic marbles was traced from compaction of unconsolidated powder through primary recrystallization and normal grain growth to a size stabilized by second phases to form the marbles reagent grade caco3 was mixed with 0 1 and 5 volume mica and heat treated under pressure with added water densification with negligible recrystallization occurred within one hour at 500 c and 500 mpa confining pressure primary recrystallization occurred at 500 550 c causing increases of grain size of factors of 2 5 resulting samples had uniform grain size gently curved grain boundaries and near equilibrium triple junctions they were used subsequently for normal grain growth studies normal grain growth occurred above 550 c at 800 c grain size d increased from 7 m d0 to 65 m in 24 hours growth rates fit the equation d n d 0 n kt where k is a constant and n 2 6 minor amounts of pores or mica particles inhibit normal grain growth and lead to a stabilized grain size dmax which depends on the size of the second phases and the inverse of their volume fraction raised to a power between 0 3 and 1 once dmax is reached normal growth continues only if second phases are mobile or coarsen or if new driving forces are introduced that cause unpinning of boundaries normal grain growth in solnhofen limestone was significantly slower than in pure synthetic marble suggesting that migration is also inhibited by second phases in the limestone

crystallographic preferred orientation development by dissolution precipitation creep abstract crystallographic preferred orientations cpos in deformed rocks are commonly interpreted as resulting from crystal plastic deformation mechanisms where deformation is achieved by the movement of dislocations in this paper we investigate the possibility of cpo development by dissolution precipitation creep or pressure solution a numerical model is presented which simulates the development of a grain aggregate that deforms by reaction controlled dissolution precipitation creep grains are simulated as rectangular boxes that change their shape by growth or dissolution of their surfaces depending on the normal stresses acting on the individual surfaces grains can also rotate due to an applied vorticity for non coaxial deformation and if they have a non equidimensional shape for each strain increment stress that is applied to the grains is the same for all grains while individual grains deform and rotate by different amounts a variety of cpos develop at moderate strains depending on the reaction rates of the different crystal surfaces and type of deformation uni axial shortening plane strain pure shear and simple shear the modelling results confirm that dissolution precipitation creep may play a role in cpo development in rocks

the instantaneous rate dependence in low temperature laboratory rock friction and rock deformation experiments 1 earthquake occurrence probabilities that account for stress transfer and time dependent failure depend on the product of the effective normal stress and a lab derived dimensionless coefficient a this coefficient describes the instantaneous dependence of fault strength on deformation rate and determines the duration of precursory slip although an instantaneous rate dependence is observed for fracture friction crack growth and low temperature plasticity in laboratory experiments the physical origin of this effect during earthquake faulting is obscure we examine this rate dependence in laboratory experiments on different rock types using a normalization scheme modified from one proposed by tullis and weeks 1987 we compare the instantaneous rate dependence in rock friction with rate dependence measurements from higher temperature dislocation glide experiments the same normalization scheme is used to compare rate dependence in friction to rock fracture and to low temperature crack growth tests for particular weak phyllosilicate minerals the instantaneous friction rate dependence is consistent with dislocation glide in intact rock failure tests for each rock type considered the instantaneous rate dependence is the same size as for friction suggesting a common physical origin during subcritical crack growth in strong quartzofeldspathic and carbonate rock where glide is not possible the instantaneous rate dependence measured during failure or creep tests at high stress has long been thought to be due to crack growth however direct comparison between crack growth and friction tests shows poor agreement the crack growth rate dependence appears to be higher than the rate dependence of friction and fracture by a factor of two to three for all rock types considered

quantitative palaeoclimate reconstruction as an inverse problem a bayesian inference of late holocene climate on the eastern tibetan plateau from a peat cellulose δ18o record there has been a sustained need to quantify past climate changes from proxy records to better understand the driving mechanisms and thus to improve the prediction of the future transfer function is an intuitive and frequently used method in this regard however this method is unable to provide interpretive and predictive results from proxy records because physical processes are not included the inverse proxy modelling method opened up a new avenue for quantitative palaeoclimate reconstructions through the integration of proxy records with deterministic models it is fundamentally different from the statistical approach representing a conceptual advance in quantitative palaeoclimatology here we demonstrate the potential of this method by placing a mechanistic model and a 6000 year long peat cellulose 18o record obtained from the high cold and monsoonal eastern tibetan plateau c 3500 m a s l in a bayesian paradigm in this worked example the marginal posterior probability distributions of palaeo

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

local shear zone pattern and bulk deformation in the gran paradiso metagranite nw italian alps the gran paradiso nappe of the northwestern alps mostly consists of augen gneisses derived from the alpine deformation of permian granitoids the regional foliation of the augen gneisses developed at lower amphibolite facies conditions and is associated with a top to west sense of shear the granitoid protolith is preserved in the kilometre scale low strain domain of the piantonetto valley and mainly consists of a porphyritic metagranite including joints leucocratic dykes and biotite rich schlieren in this low strain domain the alpine deformation is mainly localized in discrete ductile shear zones within weakly foliated metagranite the shear zones mostly dip towards s se in a shallow shear zones1 to steep inclination shear zones2 the shear zones show typical features that can be explained by reactivation of pre existing joints and planar compositional heterogeneities palaeostress and strain analysis indicate that shear zones and the metagranite foliation both formed in the presence of a strong component of flattening the kinematics of individual shear zones depends on the orientation of the original heterogeneities acting as nucleation planes and by partitioning of strain components at the kilometre scale with concentration of the flattening component to the piantonetto low strain domain the strain geometry and the kinematics of individual shear zones within piantonetto are not directly connected to the top to west sense of tectonic transport observed elsewhere in the gran paradiso nappe however the bulk stress ellipsoid reconstructed for the incipient shear zone network within very weakly deformed granites is oriented consistently with the bulk direction of tectonic transport within the gran paradiso massif we conclude that the shear zone network of the piantonetto valley is representative of the incipient stages of ductile deformation of a granite nappe even if its architecture is determined by the arrangement of pre existing structural and compositional heterogeneities aspects of the large scale bulk strain can be derived from this local shear zone pattern

fracture toughness and subcritical crack growth during high temperature tensile deformation of westerly granite and black gabbro abstract the double torsion testing method has been used to determine catastrophic and subcritical crack propagation parameters for pre cracked specimens of westerly granite and black gabbro under a number of environmental conditions the critical stress intensity factor for catastrophic crack propagation fracture toughness of granite and gabbro has been measured at temperatures from 20 to 400 c in a vacuum at 20 c the fracture toughness of westerly granite was 1 79 0 02 mpa m 1 2 and for two blocks of black gabbro it was 3 03 0 08 mpa m 1 2 and 2 71 0 15 mpa m 1 2 respectively these values are very close to those reported by other investigators for tests conducted in air of ambient humidity at room temperature for both rocks fracture toughness at first increased slightly and then decreased steadily on raising the temperature above ambient conditions this behaviour is explained in terms of the density and distribution of thermally induced microcracks as determined by quantitative optical microscopy subcritical crack growth behaviour has been studied at temperatures up to 300 c and under water vapour at pressures of 0 6 to 15 kpa both the load relaxation and incremental constant displacement rate forms of the double torsion testing method were utilised to generate stress intensity factor crack velocity diagrams crack growth was measured over the velocity range 5 10 3 to 10 7 m s 1 increasing both temperature and water vapour pressure resulted in substantially higher crack growth rates the overall effect of raising the temperature over the range studied here 20 300 c was to increase the crack growth rate in granite and gabbro by 5 and 7 orders of magnitude respectively at constant stress intensity factor and vapour pressure of water for both rocks the slopes of stress intensity factor crack velocity curves were sensitive to changes in both temperature and water vapour pressure at low values of the latter parameter slopes fell substantially on raising the water vapour pressure but were relatively insensitive to changes in temperature at these higher pressures no subcritical crack growth limit was encountered estimates of the uncertainty in our experimental data are given from the results of multiple load relaxation experiments on westerly granite specimens we estimate the uncertainty in position of stress intensity factor crack velocity curves along the stress intensity axis to be c 10 of the fracture toughness and the uncertainty in slope of such curves to be c 12 problems associated with the extrapolation of our experimental data to regions of higher effective confining pressure in the earth s crust are discussed

abrupt changes in the asian southwest monsoon during the holocene and their links to the north atlantic ocean during the last ice age the indian ocean southwest monsoon exhibited abrupt changes that were closely correlated with millennial scale climate events in the north atlantic region1 2 3 suggesting a mechanistic link in the holocene epoch which had a more stable climate the amplitude of abrupt changes in north atlantic climate was much smaller and it has been unclear whether these changes are related to monsoon variability here we present a continuous record of centennial scale monsoon variability throughout the holocene from rapidly accumulating and minimally bioturbated sediments in the anoxic arabian sea our monsoon proxy record reveals several intervals of weak summer monsoon that coincide with cold periods documented in the north atlantic region4 including the most recent climate changes from the medieval warm period to the little ice age and then to the present we therefore suggest that the link between north atlantic climate and the asian monsoon is a persistent aspect of global climate

precise tremor source locations and amplitude variations along the lower crustal central san andreas fault 1 we precisely locate 88 tremor families along the central san andreas fault using a 3d velocity model and numerous p and s wave arrival times estimated from seismogram stacks of up to 400 events per tremor family maximum tremor amplitudes vary along the fault by at least a factor of 7 with by far the strongest sources along a 25 km section of the fault southeast of parkfield we also identify many weaker tremor families which have largely escaped prior detection together these sources extend 150 km along the fault beneath creeping transitional and locked sections of the upper crustal fault depths are mostly between 18 and 28 km in the lower crust epicenters are concentrated within 3 km of the surface trace implying a nearly vertical fault a prominent gap in detectible activity is located directly beneath the region of maximum slip in the 2004 magnitude 6 0 parkfield earthquake

the climate record inverted from borehole temperatures in slovenia abstract temperature profiles from nine boreholes in slovenia located mostly in the northeastern part of the country have been studied for evidence of past climatic changes the reconstruction of the ground surface temperature gst history based on 1 d theory of heat conduction was accomplished using the functional space inversion fsi method because of the paucity of quality thermal conductivity data and because the nature of heat conduction is such that information about gst changes decay with the passage of time the a priori standard deviations of the thermal conductivity model 1 w m 1 k 1 and measured temperature 0 2 k were chosen large enough so that the gst histories older than 200 years are considerably smoothed and essentially merge with the long term mean the average gst history based on consistent results from seven boreholes starts to rise at the end of the last century the amplitude of the warming is about 0 6 to 0 7 k in the past 100 years two boreholes were rejected the long term mean gsts lie between 9 4 and 11 1 c the mean annual air temperatures from the ljubljana meteorological station are in good agreement with the average gst solution the gst history of the past 20 30 thousand years ka was reconstructed from the almost 2 km deep ljutomer temperature profile the history evidences climate variations during the wurm weichselian ice age it places the glacial minimum of about 3 c at 13 14 ka ago and the postglacial maximum of 10 5 c roughly at 2 3 ka ago

velocity weakening behavior of plagioclase and pyroxene gouges and stabilizing effect of small amounts of quartz under hydrothermal conditions 1 we investigated properties of frictional sliding of plagioclase pyroxene and their mixture gouges with a small amount of hornblende biotite and quartz as accessory minerals under hydrothermal conditions with an effective normal stress of 200 mpa pore pressure of 30 mpa and temperatures from 100 c to 600 c axial loading rate was stepped between 0 001 and 0 0001 mm s to acquire the rate dependence both plagioclase and pyroxene gouges showed velocity weakening behavior in the whole temperature range except the velocity strengthening behavior of pyroxene at 200 c for temperatures above 400 c both plagioclase and pyroxene gouges showed oscillatory slips as a result of small dc values of 3 4 m which make the critical stiffness rise remarkably and approach the system stiffness above 300 c the direct effect of plagioclase shows an increasing trend with temperature indicating control of the deformation process by thermally activated mechanisms as the difference of a and b values here are only 20 at most this trend also applies to the evolution effect our analytical derivation based on the theory of pressure solution shows a log linear contact area growth with time that corresponds to an evolution effect and estimations based on this encompass the plagioclase data though the identification of actual mechanisms is not easy finally it is found that a little quartz 3 5 added to the plagioclase 60 62 pyroxene 35 mixture has a strong stabilizing effect leading to a transition from velocity weakening to velocity strengthening these results may help constrain the depth range of seismic slips on deep faults in the lower crust of gabbroic composition

variations of 18o 16o in plants from temperate peat bogs switzerland implications for paleoclimatic studies despite the great potential of peat bogs as climatic archives to date only few studies have focused on the climatic controls on cellulose isotopic composition in modern bog plants this study attempts to calibrate plant climate relationships by sampling a set of modern plant species both vascular plants and mosses and bog surface waters along an altitude transect in switzerland isotopic analyses of water samples show that the 18o values of surface bog waters follow the trend of precipitation despite significant scatter in the data set detailed sampling of surface waters within one bog shows that 18o values vary widely and are closely related to the micro topography of the bog surface more enriched 18o 16o ratios in water samples collected from small raised hummocks than the ones collected from hollows are documented in both horizontal and vertical profiles a 18o d plot indicates that the process leading to the isotopic enrichment of the uppermost surface waters is evaporation greater above sphagnum covered hummocks than above open pools to investigate the implications of such high variability of source water for plant cellulose 18o values a detailed study of both surface water and cellulose 18o values within one site is conducted the large 18o variability observed in surface waters is found to be considerably smoothed in cellulose by a factor of 5 10 depending on the plant species this indicates that the water used by plant photosynthetic processes reflects the isotopic composition of the average annual precipitation this points to a source water level for plants of a few decimeters where the variations are smaller than at the air water interface the response of the cellulose 18o to the environmental gradient along the altitude transect varies considerably from species to species for most of the species studied the 18o values decrease with altitude following the trends of 18o values in precipitation and in surface water samples some species the cotton sedge eriophorum vaginatum and the moss sphagnum capillifolium show statistically significant 18o relationships to an altitude of 1 8 km and 2 9 km respectively however some other plant species calluna vulgaris vaccinium uliginosum andromeda poliflora carex pauciflora sphagnum cuspidatum and sphagnum magellanicum do not or only partially reflect changes in climatic parameters associated with an altitude increase furthermore changes in relative humidity which are not correlated with altitude are found to explain a large part of the variability in 18o values for the sedge carex pauciflora and the moss sphagnum cuspidatum therefore this study confirms the importance of species specific studies when interpreting 18o 16o ratios of macrofossils along a fossil peat sequence as a record of past climate changes our study allows to extend the mechanistic model that isotopically links source water and cellulose to the physiological specificities of sedges and mosses a comparison of the modeled and calculated net biological fractionation factors for eriophorum vaginatum and sphagnum capillifolium reveals that these two species appear to have a more homogeneous leaf reservoir than trees

preferred orientation of anorthite deformed experimentally in newtonian creep abstract synthetic anorthite aggregates were deformed in a paterson gas deformation apparatus at confining pressures up to 400 mpa in torsion and axial compression at temperatures between 950 c and 1200 c samples deformed in torsion under newtonian creep display development of texture or crystallographic preferred orientation as documented with synchrotron x ray diffraction measurements complex diffraction patterns were deconvoluted with the rietveld method to obtain quantitative texture information torsion samples deformed up to shear strains of 4 and samples deformed in compression at higher stresses to total strains of 0 3 develop clear textures texture and shape preferred orientation spo of torsion samples display a monoclinic pattern with an asymmetry inclined against the sense of shear consistent with polycrystal plasticity simulations that assume the deformation is accomplished by dislocation glide these results show that a material deforming in linear viscous creep can develop a strong texture in striking contrast to the paradigm that the presence of a texture precludes low stress newtonian behavior our observations show that the presence or absence of crystallographic preferred orientation is not sufficient to uniquely infer the dominant rheological mechanical regime as sometimes applied for interpretation of seismic anisotropy in the earth

physiological significance of low atmospheric co2 for plant climate interactions abstract methods of palaeoclimate reconstruction from pollen are built upon the assumption that plant climate interactions remain the same through time or that these interactions are independent of changes in atmospheric co 2 the latter may be problematic because air trapped in polar ice caps indicates that atmospheric co 2 has fluctuated significantly over at least the past 400 000 yr and likely the last 1 6 million yr three other points indicate potential biases for vegetation based climate proxies first c 3 plant physiological research shows that the processes that determine growth optima in plants photosynthesis mitochondrial respiration photorespiration are all highly co 2 dependent and thus were likely affected by the lower co 2 levels of the last glacial maximum second the ratio of carbon assimilation per unit transpiration called water use efficiency is sensitive to changes in atmospheric co 2 through effects on stomatal conductance and may have altered c 3 plant responses to drought third leaf gas exchange experiments indicate that the response of plants to carbon depleting environmental stresses are strengthened under low co 2 relative to today this paper reviews the scope of research addressing the consequences of low atmospheric co 2 for plant and ecosystem processes and highlights why consideration of the physiological effects of low atmospheric co 2 on plant function is recommended for any future refinements to pollen based palaeoclimatic reconstructions

mylonitic deformation of gabbro in the lower crust a case study from the pankenushi gabbro in the hidaka metamorphic belt of central hokkaido japan abstract the mylonitization of the pankenushi gabbro in the hidaka metamorphic belt of central hokkaido japan occurred along its western margin at 600 mpa and 660 700 c through dynamic recrystallization of plagioclase and a retrograde reaction from granulite facies to amphibolite facies orthopyroxene clinopyroxene plagioclase h2o hornblende quartz the reaction produced a fine grained 100 m polymineralic aggregate composed of orthopyroxene clinopyroxene quartz hornblende biotite and ilmenite into which strain is localized the dynamic recrystallization of plagioclase occurred by grain boundary migration and produced a monomineralic aggregate of grains whose crystallographic orientations are mostly unrelated to those of porphyroclasts the monomineralic plagioclase aggregates and the fine grained polymineralic aggregates are interlayered and define the mylonitic foliation while the latter is also mixed into the former by grain boundary sliding to form a rather homogeneous polymineralic matrix in ultramylonites however in both mylonite and ultramylonite plagioclase aggregates form a stress supporting framework and therefore controlled the rock rheology crystal plastic deformation of pyroxenes and plagioclase with dominant 100 001 and 001 1 2 1 1 0 slip systems respectively produced distinct shape and crystallographic preferred orientations of pyroxene porphyroclasts and dynamically recrystallized plagioclase grains in both mylonite and ultramylonite euhedral to subhedral growth of hornblende in pyroxene porphyroclast tails during the reaction and its subsequent rigid rotation in the fine grained polymineralic aggregate or matrix produced clear shape and crystallographic preferred orientations of hornblende grains in both mylonite and ultramylonite in contrast the dominant grain boundary sliding of pyroxene and quartz grains in the fine grained polymineralic aggregate of the mylonite resulted in their very weak shape and crystallographic preferred orientations in the fine grained polymineralic matrix of the ultramylonite however pyroxene and quartz grains became scattered and isolated in the plagioclase aggregate so that they were crystal plastically deformed leading to stronger shape and crystallographic preferred orientations than those seen in the mylonite

climatic changes in eurasia and africa at the last glacial maximum and mid holocene reconstruction from pollen data using inverse vegetation modelling in order to improve the reliability of climate reconstruction especially the climatologies outside the modern observed climate space an improved inverse vegetation model using a recent version of biome4 has been designed to quantitatively reconstruct past climates based on pollen biome scores from the biome6000 project the method has been validated with surface pollen spectra from eurasia and africa and applied to palaeoclimate reconstruction at 6 cal ka bp calendar years the climate was generally wetter than today in southern europe and northern africa especially in the summer winter temperatures were higher 1 5 c than present in southern scandinavia northeastern europe and southern africa but cooler in southern eurasia and in tropical africa especially in mediterranean regions summer temperatures were generally higher than today in most of eurasia and africa with a significant warming from 3 to 5 c over northwestern and southern europe southern africa and eastern africa in contrast summers were 1 3 c cooler than present in the mediterranean lowlands and in a band from the eastern black sea to siberia at 21 cal ka bp a marked hydrological change can be seen in the tropical zone where annual precipitation was 200 1 000 mm year lower than today in equatorial east africa compared to the present a robust inverse relationship is shown between precipitation change and elevation in africa this relationship indicates that precipitation likely had an important role in controlling equilibrium line altitudes ela changes in the tropics during the lgm period in eurasia hydrological decreases follow a longitudinal gradient from europe to siberia winter temperatures were 10 17 c lower than today in eurasia with a more significant decrease in northern regions in africa winter temperature was 10 15 c lower than present in the south while it was only reduced by 0 3 c in the tropical zone comparison of palaeoclimate reconstructions using lgm and modern co2 concentrations reveals that the effect of co2 on pollen based lgm reconstructions differs by vegetation type reconstructions for pollen sites in steppic vegetation in europe show warmer winter temperatures under lgm co2 concentrations than under modern concentrations and reconstructions for sites in xerophytic woods scrub in tropical high altitude regions of africa are wetter for lgm co2 concentrations than for modern concentrations because our reconstructions account for decreased plant water use efficiency

determining paleoceanographic circulations with emphasis on the last glacial maximum the inference from radiocarbon and other data that the north atlantic ocean circulation during the last glacial maximum was reduced is examined because glacial periods are thought to be windier than non glacial ones a reduced circulation is difficult to rationalize a first step is to note that the circulation of mass is unlikely to correspond simply to the circulation of heat or freshwater salt by merely permitting an enhanced input of southern hemisphere water into the north atlantic one can accommodate significantly increased radiocarbon ages such an input is equally interpretable as owing to an increased mass circulation rather than a decreased one inferred estimates from paleo shear estimates in the florida current are re interpreted as producing an indeterminate net flow there determination of the paleocirculation rates is not simpler than the problem in the modern ocean it is fully three dimensional and requires an adequate data base to determine the mass flux rates

earthquake nucleation on faults with rate and state dependent strength abstract dieterich j h 1992 earthquake nucleation on faults with rate and state dependent strength in t mikumo k aki m ohnaka l j ruff and p k p spudich editors earthquake source physics and earthquake precursors tectonophysics 211 115 134 faults with rate and state dependent constitutive properties reproduce a range of observed fault slip phenomena including spontaneous nucleation of slip instabilities at stresses above some critical stress level and recovery of strength following slip instability calculations with a plane strain fault model with spatially varying properties demonstrate that accelerating slip precedes instability and becomes localized to a fault patch the dimensions of the fault patch follow scaling relations for the minimum critical length for unstable fault slip the critical length is a function of normal stress loading conditions and constitutive parameters which include dc the characteristic slip distance if slip starts on a patch that exceeds the critical size the length of the rapidly accelerating zone tends to shrink to the characteristic size as the time of instability approaches solutions have been obtained for a uniform fixed patch model that are in good agreement with results from the plane strain model over a wide range of conditions above the steady state stress the logarithm of the time to instability linearly decreases as the initial stress increases because nucleation patch length and premonitory displacement are proportional to dc the moment of premonitory slip scales by d3c the scaling of dc is currently an open question unless dc for earthquake faults is significantly greater than that observed on laboratory faults premonitory strain arising from the nucleation process for earthquakes may by too small to detect using current observation methods excluding the possibility that dc in the nucleation zone controls the magnitude of the subsequent earthquake then the source dimensions of the smallest earthquakes in a region provide an upper limit for the size of the nucleation patch

paleoclimatic estimates from tertiary leaf assemblages a primary obstacle to evaluating numerical modeling of tertiary nonmarine climates has been the significance and reliability of proxy data sloan barron 1990 lacking direct measurements of paleoclimatic parameters inferred paleoclimatic values are based on substitute proxy sources such as fossils or isotopes are proxy data significant that is have they been calibrated in modern environments and to what level is the calibration this is the problem of accuracy validity in the statistical sense second are the proxy data reliable can two workers or even the same worker consistently arrive at the same estimates using the same data set this is the problem of precision repeatability can these two problems be resolved quaternary palynologists have used the concept of transfer functions a methodology originally developed for foraminifera imbrie kipp 1971 applied in palynology a response surface for each palynomorph taxon is constructed for the environmental variables under consideration these transformations can then be subjected to a number of different kinds of multivariate analyses including ordination methodologies bartlein et al 1986 webb bryson 1972 these transfer functions can work for quaternary and especially the lateand post glacial of the last 20 to 30 thousand years pollen assemblages because in most regions where the methodology has been applied the flora is of known diversity and the equivalency of a given palynomorph species to one or a few extant species can be reasonably assumed even in the late neogene 1 5 to 10 million years ago however this assumption can no longer be made we know that the palynomorph assemblages contain exotic genera mccartan et al 1990 and the presence of exotic and or extinct species

evidence for dominant grain boundary sliding deformation in greenschist and amphibolite grade polymineralic ultramylonites from the redbank deformed zone central australia abstract microstructural and textural investigations by scanning sem and transmission electron microscopy tem techniques have been performed on samples taken across two quartzo feldspathic mylonite zones from the redbank deformed zone central australia one has been deformed at greenschist facies gs the second at amphibolite facies am conditions with increasing strain the rock type changes from protomylonite to mylonite to ultramylonite the protomylonites and mylonites consist of alternating quartz and polymineralic quartz feldspar bands at the highest strains a homogeneous fine grained polymineralic ultramylonite occurs shear zone geometry and microscale structures indicate that these ultramylonites experienced higher strains and were weaker than the encapsulating protomylonites and mylonites tem and sem studies of the ultramylonites reveal a rectangular to square grain shape a continuous alignment of grain and interphase boundaries across several grain diameters a grain size gs 0 5 m am 5 11 m less than the equilibrium subgrain size and open and void containing grain and interphase boundaries analysis of local textures by electron back scatter diffraction ebsd in the sem showed a very weak crystallographic preferred orientation cpo for the quartz the grain misorientation relationships are not consistent with dislocation creep being the dominant deformation mechanism all structures are of the type expected if grain boundary sliding processes had contributed significantly to the deformation consequently the deformation of such quartzo feldspathic rocks and by implication the rheology of the redbank deformed zone must have been controlled by the mechanical properties of these fine grained polymineralic ultramylonites deforming by grain boundary sliding processes this is in contrast to the pure quartz bands which deformed by dislocation creep mechanisms and were less important in the rheology of the redbank deformed zone

the misorientation index development of a new method for calculating the strength of lattice preferred orientation abstract using orientation data from experimentally deformed olivine we explore some practical problems with the j index a commonly applied measure of fabric strength we show that the j index is highly dependent on several factors including the number of discrete data in the orientation distribution function odf and arbitrary numerical parameters specified for its calculation because of this non uniqueness we conclude that the j index is difficult to interpret and should only be applied with caution as an alternative to the j index we propose a new measure of fabric strength that is based on the distribution of uncorrelated misorientation angles this m index is shown to be insensitive to the parameters specified for its calculation for typical deformed olivine samples we show that 150 discrete data are adequate to quantify fabric strength using the m index technique the m index correlates well with seismic anisotropy particularly for materials of the same fabric type therefore we conclude that the m index technique is well suited for the quantification of fabric strength and the comparison of like materials

grain boundary migration microstructures in a naturally deformed quartzite abstract in this study several grain scale microstructures are presented that are thought to demonstrate the migration direction of once mobile grain boundaries in a naturally deformed quartzite an analysis is presented of the sense of migration of the boundaries and the characteristics of the patterns of relative grain growth and shrinkage grain boundary migration seems to be correlated with the relative crystallographic orientations of neighbouring grains for the quartz quartz grain boundaries and the pattern of preferred grain growth is roughly symmetrical about the mica foliation plane

a comparison between rate and state friction and microphysical models based on numerical simulations of fault slip rate and state friction rsf is commonly used for the characterisation of laboratory friction experiments such as velocity step tests however the rsf framework provides little physical basis for the extrapolation of these results to the scales and conditions of natural fault systems and so open questions remain regarding the applicability of the experimentally obtained rsf parameters for predicting seismic cycle transients as an alternative to classical rsf microphysics based models offer means for interpreting laboratory and field observations but are generally over simplified with respect to heterogeneous natural systems in order to bridge the temporal and spatial gap between the laboratory and nature we have implemented existing microphysical model formulations into an earthquake cycle simulator through this numerical framework we make a direct comparison between simulations exhibiting rsf controlled fault rheology and simulations in which the fault rheology is dictated by the microphysical model even though the input parameters for the rsf simulation are directly derived from the microphysical model the microphysics based simulations produce significantly smaller seismic event sizes than the rsf based simulation and suggest a more stable fault slip behaviour our results reveal fundamental limitations in using classical rate and state friction for the extrapolation of laboratory results the microphysics based approach offers a more complete framework in this respect and may be used for a more detailed study of the seismic cycle in relation to material properties and fault zone pressure temperature conditions

microstructural shear criteria associated with grain boundary sliding during ductile deformation abstract experimental studies on rock analogues are described which establish that certain microstructures diamond grain structures tabular grain structures and asymmetric grain boundary bulges can be used to determine i if deformation was coaxial or non coaxial and ii the sense of shear in zones of non coaxial deformation mechanisms for the development of the structures are described which involve the linked operation of grain boundary sliding and migration

a microphysical model for strong velocity weakening in phyllosilicate bearing fault gouges 1 previous rotary shear experiments performed on a halite muscovite fault gouge analogue system have shown that the presence of phyllosilicates under conditions favoring the operation of cataclasis and pressure solution in the matrix phase can have major effects on the frictional behavior of gouges while 100 halite and 100 muscovite samples exhibit rate independent frictional brittle behavior the strength of mixtures containing 10 30 muscovite is both normal stress and sliding velocity dependent at high sliding velocities 1 m s 1 such mixtures show unusually marked velocity weakening along with the development of a structureless cataclastic microstructure in the present paper a micromechanical model is developed in an attempt to explain this behavior the model assumes a granular flow process involving competition between intergranular dilatation and compaction by pressure solution the predictions of the model agree favorably with the experimental results extension of the model to quartz mica systems implies that the presence of phyllosilicates plus the operation of pressure solution can strongly promote unstable velocity weakening behavior at rapid slip rates on natural faults under midcrustal conditions static stress drop predictions based on the model agree reasonably well with estimates from seismic observations our results may help explain the discrepancy between laboratory derived rate and state friction parameter values obtained for dry low strain and or single phase rock systems and the values for natural fault rocks inferred from seismological data