evidence for upper mantle anisotropy beneath southern germany from love and rayleigh wave dispersion we advance evidence for the existence of seismic anisotropy in the upper mantle beneath southern germany from the dispersion of love and rayleigh waves the evidence is based upon a substantial love rayleigh discrepancy observed between periods of 40 s and 120 s an isotropic mantle model clearly fails to explain the observed dispersion curves systematic inversion experiments with transversely isotropic models show that anisotropy at depths between 70 km and 200 km is sufficient to explain the observed dispersion curves our data require neither anisotropy at greater depths nor anisotropy in the crust though we cannot exclude its presence there a search for azimuthal anisotropy of rayleigh wave propagation indicates a weak but possibly insignifant azimuthal anisotropy of about 1 for periods less than 40 s with fast directions between 20 and 50 degrees east of north at larger periods azimuthal anisotropy is less than 1 and the fast directions scatter considerably as period varies

anisotropy in the indian ocean upper mantle from rayleigh and love waveform inversion a tomographic method is applied to love and rayleigh wave seismograms in order to address the problem of upper mantle elastic anisotropy in the indian ocean the first step in our approach is a waveform inversion for each path of the study a 1 d depth dependent model compatible with the waveforms of the fundamental mode and several higher modes of love and rayleigh waves is obtained then the models related to the different paths are inverted in order to retrieve 3 d velocity heterogeneities and anisotropy in this paper both the radial anisotropy and the azimuthal anisotropy of s waves are investigated in detail we find a significant radial anisotropy in the uppermost 300 km of the mantle with an overall amplitude smaller than what is found in global studies azimuthal s wave anisotropy is also present the directions of fast s velocities show rather simple patterns from 100 to 300 km depth and strong correlations with the direction of absolute plate motion apm are found in the uppermost 100 km the pattern of fast velocity directions is complex and does not correlate simply with plate motions from 100 to 200 km depth a correlation with apm is found in most oceanic regions the main lack of correlation is located in the vicinity of la reunion and mauritius islands in this region the anisotropy exhibits a complex pattern between 100 and 150 km possibly due to a disturbing effect of the hotspot at 200 km depth and deeper azimuthal anisotropy vanishes progressively beneath most of the oceanic regions no significant azimuthal anisotropy is found beyond 300 km depth the depth extent of both azimuthal and radial anisotropy the amplitude of radial anisotropy and the pattern of azimuthal anisotropy support the idea of a preferential orientation of olivine crystals in a low viscosity zone beneath the lithosphere this region would be located between 100 and 200 km in oceanic areas and possibly deeper between 200 and 300 km in continental areas not well resolved in this study

the malpica lamego line a major crustal scale shear zone in the variscan belt of iberia abstract the malpica lamego line mll is a deformation zone in the variscan belt of nw iberia nw spain and n portugal that runs parallel to the chain for at least 275 km bearing i type granodiorite plutons along most of its length the mll affects previous structures by which high pressure and ophiolitic rocks were exhumed and emplaced on the iberian plate during earlier deformation phases correlation and reconstruction of the stratigraphy of these sheets or tectonic units at both sides of the shear zone allows a preliminary estimate of the accumulated vertical and horizontal offsets after the tectonic activity of the fault the value of the separations of crustal scale proportions reaches a maximum 15 km of vertical offset that decreases gradually to the south the structural record found in the rocks indicates a strike slip regime that in general does not fit the geometry of the offsets we suggest that the mll went through two different stages during the same orogenic cycle a first dip slip episode a reverse faulting event overprinted by a later strike slip reactivation

upper mantle structure under western europe from fundamental and higher mode surface waves using the nars array summary a generalized inversion of a new data set consisting of surface wave phase velocities and sn traveltimes has resulted in a new shear velocity and density model for the west european platform wepl 2 the surface wave phase velocity data set consists of fundamental and higher mode mode 1 6 measurements from 25 to 70mhz using the network of autonomously recording stations nars array which was specifically designed for higher mode surface wave measurements the sn traveltime data set consists of isc readings for selected european events major features of wepl 2 are a high velocity lid of 80 140 km depth underlain by a pronounced low velocity zone between 160 and 220 km depth the transition zone 400 650 km depth is characterized by high shear velocities with respect to prem the density shows a positive gradient from 60 to 140 km depth followed by an approximately constant value down to 400 km depth a model for the baltic shield scsh 2 is obtained by combination of nolet s 1977 higher mode phase velocity data set for western europe including the baltic shield and the present phase velocities for the platform this shield model shows an absence of the low velocity layer and low shear velocities in the top of the transition layer with respect to wepl 2 density although less well resolved shows lower values for the shield structure between 200 and 350 km depth

seismic anisotropy and velocity structure beneath the southern half of the iberian peninsula travel times of 11 612 pn arrivals collected from 7675 earthquakes are inverted to image the uppermost mantle velocity and anisotropy structure beneath the southern half of the iberian peninsula and surrounding regions pn phases are routinely identified and picked for epicentral distances from 200 to 1200 km the method used in this study allows simultaneous imaging of variations of pn velocity and anisotropy the results show an average uppermost mantle velocity beneath the study area of 8 0 km s the peninsular area covered by the iberian massif is characterized by high pn velocity as expected in tectonically stable regions indicating areas of the hercynian belt that have not recently been reactivated the margins of the iberian peninsula have undergone a great number of recent tectonic events and are characterized by a pronouncedly low pn velocity as is common in areas greatly affected by recent tectonic and magmatic activity our model indicates that the betic crustal root might be underlined by a negative anomaly beneath the southeastern iberian peninsula in the atlantic ocean we find a sharp variation in the uppermost mantle velocities that coincides with the structural complexity of the european and african plate boundary in the gulf of cadiz our results show a very pronounced low velocity anomaly offshore from cape san vicente whereas high velocities are distributed along the coast in the gulf of cadiz in the alboran sea and northern morocco the direction of the fastest pn velocity found is almost parallel to the africa eurasia plate convergence vector northwest southeast whereas to the north this direction is almost parallel to the main trend of the betic cordillera i e east west in its central part and north south in the curvature of the arc of gibraltar this suggests that a significant portion of the uppermost mantle has been involved in the orogenic deformation that produced the arcuate structure of the betic cordillera however we assume that the neogene extension had no major influence on a lithospheric scale in the alboran sea our results also show a quite complex pattern of anisotropy in the southwest iberian lithospheric mantle since the relationship between the direction of fastest pn velocity and major hercynian tectonic trends cannot be directly established 2004 elsevier b v all rights reserved

global upper mantle structure from finite frequency surface wave tomography 1 we report global shear wave velocity structure and radial anisotropy in the upper mantle obtained using finite frequency surface wave tomography based upon complete three dimensional born sensitivity kernels because wavefront healing effects are properly taken into account finite frequency surface wave tomography improves the resolution of small scale mantle heterogeneities especially for deep anomalies that are constrained by the longest period surface waves in our finite frequency model ffsw1 the globally averaged radial anisotropy shows a transition from positive sh sv to negative anisotropy sv sh at about 220 km consistent with a change in the dominant mantle circulation pattern from predominantly horizontal flow at shallow depths to vertical flow at greater depths the radial anisotropy beneath cratons and the old pacific plate agrees well with previous studies however our model exhibits a strong negative radial anisotropy at depths greater than 120 km beneath mid ocean ridges a feature that is not present in previous upper mantle models more interestingly the depth extent of the ridge anomalies is distinctly different beneath fast and slow spreading centers anomalies beneath fast spreading centers are stronger but the strength decreases rapidly below 250 km in contrast beneath slow spreading centers such as the northern mid atlantic ridge and the red sea anomalies extend down at least to the top of the transition zone the different depth extent of the ridge anomalies suggests that the primary driving force of slow spreading seafloor may be different from that of fast spreading seafloor and that active upwelling beneath slow spreading ridges may play a major role in the opening of the seafloor

a deep seismic sounding investigation of lithospheric heterogeneity and anisotropy beneath the iberian peninsula abstract the dimensions of the iberian peninsula the facility of firing large charges in the surrounding waters the well known and relatively uniform geology and prior knowledge of the crustal structure resulted in it being chosen as a study area for the investigation of the seismic structure of the lower lithosphere via refraction wide angle reflection seismic profiling the iberian lithosphere heterogeneity and anisotropy experiment iliha with a star shaped arrangement of six long range dss profiles was carried out in october 1989 the models derived from a first interpretation of the recorded data are presented three crustal profiles cover the same western and central part of the hercynian massif as the mantle profiles the resulting interpretations all include a middle as well as a lower crustal layer above the mantle the velocities of the layers in all three models are similar however the layer depths vary beneath the profiles interpretation of the mantle derived data suggests a layered lower lithosphere one reversed line and an intersecting unreversed line indicate the layering penetrates to at least 90 km depth the homogeneity of these layers contrasts strongly with the heterogeneous hercynian surface geology velocities derived from reflected data from the deep layers suggest the constituent materials are either anisotropic or that the layers suffer a slight regional dip

anisotropy beneath the pyrenees range from teleseismic shear wave splitting results from a test experiment we have investigated the seismic anisotropy from sks and skks wave splitting along a n s profile perpendicular to the pyrenean mountain belt the line crossed the north pyrenean fault npf which probably represents the plate boundary between the european and the iberian plates we observed large delay times t 1 3 to 1 5 s and uniform fast polarization directions n100e at three stations located on the iberian plate on the other hand t are smaller 0 5 1 0 s and the scattered at stations located north of the npf the small scale variability the relation with surface geology and the correlation of the t with lithospheric thickness suggest that the anisotropy could be predominantly of lithospheric origin however an asthenospheric contribution cannot be ruled out in the north pyrenean zone an important thermal event before the pyrenean compression has likely erased the former mantle fabric the observed anisotropy is then likely related to the pyrenean orogeny on the iberian plate our splitting parameters are similar to those obtained at two stations located on hercynian structures in central spain this suggests that two contributions are likely superposed to that of the pyrenean built up one related to the hercynian orogeny and the other one related to the rotation of the iberian plate

on mantle chemical and thermal heterogeneities and anisotropy as mapped by inversion of global surface wave data 1 we invert global observations of fundamental and higher order love and rayleigh surface wave dispersion data jointly at selected locations for 1 d radial profiles of earth s mantle composition thermal state and anisotropic structure using a stochastic sampling algorithm considering mantle compositions as equilibrium assemblages of basalt and harzburgite we employ a self consistent thermodynamic method to compute their phase equilibria and bulk physical properties p s wave velocity and density combining these with locally varying anisotropy profiles we determine anisotropic p and s wave velocities to calculate dispersion curves for comparison with observations models fitting data within uncertainties provide us with a range of profiles of composition temperature and anisotropy this methodology presents an important complement to conventional seismic tomography methods our results indicate radial and lateral gradients in basalt fraction with basalt depletion in the upper and enrichment of the upper part of the lower mantle in agreement with results from geodynamical calculations melting processes at mid ocean ridges and subduction of chemically stratified lithosphere compared with preliminary reference earth model prem and seismic tomography models our velocity models are generally faster in the upper transition zone tz and slower in the lower tz implying a steeper velocity gradient while less dense than prem density gradients in the tz are also steeper mantle geotherms are generally adiabatic in the tz whereas in the upper part of the lower mantle stronger lateral variations are observed the retrieved anisotropy structure agrees with previous studies indicating positive as well as laterally varying upper mantle anisotropy while there is little evidence for anisotropy in and below the tz

using incremental elongation and shearing to unravel the kinematics of a complex transpressional zone abstract this study presents in depth geometric and kinematic analyses of a complex transpressional shear zone fellos shear zone fsz that integrates structural mapping with microstructural and quartz crystallographic texture data the fsz strikes ne sw and formed in the short limb of a map scale antiform the foliation pattern within the zone indicates dextral shearing whereas the macroscopic object lineation is dispersed over a half great circle girdle along the mean mylonitic foliation based on this deformation pattern the fsz could be interpreted as a dextral ne directed triclinic transpressional zone however the integration of field based with microtectonic data reveal a more complicate kinematic history we show that the elongation trend is dispersed along an entire great circle girdle when we take into account the trends of incremental elongations recorded by fabrics with different strain memories mapping of incremental shear directions implies that the fsz initiated as a ne directed dextral transpressional shear zone and progressively evolved into a nw directed dextral zone the passage from ne to nw directed shearing was accompanied by transpression whilst local transtension likely occurred during the last stages of ductile deformation deformation in the fsz ended up at semi ductile conditions with localized ne directed dextral shearing our study demonstrates that the integration of field observations and fabrics microstructures that have different strain memories is a powerful tool for unravelling the complex kinematics of high strain zones

anisotropy beneath the iberian peninsula the contribution of the iliha nars broad band experiment the presence of anisotropy beneath the iberian peninsula and its main distinctive features can be established through the analysis of teleseismic shear wave splitting observed in the iliha nars experiment in this experiment an homogeneous data set is provided by a network of 14 broad band stations deployed over the entire peninsula for about one year even if technical problems led to an amount of data smaller than expected significant variations in the inferred fast velocity direction are observed for stations located in different iberian domains the stations in central and east iberia show a fast velocity direction oriented roughly e w coincident with previous results in toledo a clearly different ne sw direction is observed in the ossa morena zone supporting the image from a previous regional experiment the observed delay times lie between 0 5 and 1 s although large scale mechanisms such as the absolute plate motion of eurasia can be invoked to explain the origin of anisotropic features in many sites the regional variations observed in some domains imply that differentiated origins of the anisotropy have to be considered probably related to the particular tectonics in the area an interesting example of this fact is provided by the stations in the betic chain the fast velocity direction inferred for a station located in the limit of the external betics south iberian domain oriented n80 e is clearly different from the n15 35 e direction observed in the internal betics alboran crustal domain the origin of which has to be related to the alpine building of the chain

the effect of material properties on growth rates of folding and boudinage experiments with wax models abstract the growth of unstable structures was studied experimentally in layered wax models the rheological properties of the two wax types were determined independently by a series of cylinder compression tests both waxes enhibited 1 a non newtonian stress vs strain rate relationship 2 strain softening and 3 temperature dependent viscosity the stress strain rate relationships approximated a power law with stress exponents of 5 for the microcrystalline wax and 1 8 for paraffin wax blocks of paraffin with a single embedded layer of microcrystalline wax were deformed in two dimensional pure shear with the layer oriented either parallel to the compressive strain axis so that it shortened and folded or perpendicular to that axis so that it would stretch and boundinage would form the growth rates of tiny initial disturbances were measured the growth rates for folding and boudinage were much higher than could be accounted for by theories assuming newtonian material properties theories taking non newtonian behaviour into account smith r b 1975 bull geol soc am 86 1601 1609 fletcher r c 1974 am j sci 274 1029 1043 better describe the folding growth rates boudinage however grew almost three times faster than would be predicted even by existing non newtonian theory a possible reason for this discrepancy is that the waxes do not exhibit steady state creep as assumed in the theory we therefore extend the theory to include strain softening the crucial step in this theory is the use of a scalar measure of the deformation as a state variable in the constitutive law in this way the isotropic manifestation of strain softening can be taken into account the analysis shows that strain softening can lead to greatly increased boudinage growth rates while having little influence on the growth rates of folds which is in agreement with the experiments

an upper mantle s wave velocity model for northern europe from love and rayleigh group velocities summary a model of upper mantle s wave velocity and transverse anisotropy beneath northwestern europe is presented based on regional surface wave observations group velocities for both love and rayleigh surface waves are measured on waveform data from international and regional data archives including temporary deployments and then inverted for group velocity maps using a method accounting for fresnel zone sensitivity the group velocity variations are larger than in global reference maps and we are able to resolve unprecedented details we then apply a linear inversion scheme to invert for local 1 d shear wave velocity profiles which are consequently assembled to a 3 d model by choosing conservative regularization parameters in the 2 d inversion we ensure the smoothness of the group velocity maps and hence of the resulting 3 d shear wave speed model to account for the different tectonic regimes in the study region and investigate the sensitivity of the 1 d inversions to inaccuracies in crustal parameters we analyse inversions with different reference models of increasing complexity pure 1 d 3 d crust 1 d mantle and pure 3 d we find that all inverted models are very consistent at depths below 70 km at shallower depths the constraints put by the reference models primarily moho depth which we do not invert for remain the main cause for uncertainty in our inversion the final 3 d model shows large variations in s wave velocity of up to 12 per cent we image an intriguing low velocity anomaly in the depth range 70 150 km that extends from the iceland plume beneath the north atlantic and in a more than 400 km wide channel under southern scandinavia beneath southern norway the negative perturbations are around 10 per cent with respect to ak135 and a shallowing of the anomaly is indicated which could be related to the sustained uplift of southern scandinavia in neogene times furthermore our upper mantle model reveals good alignment to ancient plate boundaries and first order crustal fronts around the triple junction of the baltica avalonia laurentia collision in the north sea

complex lithospheric structure under the central baltic shield from surface wave tomography complex lithospheric structure under the central baltic shield from surface wave tomography

package fluids 1 computer programs for analysis of fluid inclusion data and for modelling bulk fluid properties the computer package fluids contains five sets of computer programs written in c for the calculation of fluid properties both model fluids and data from fluid inclusions can be analysed in the programs bulk density molar volume and composition of fluid inclusions are calculated with the program bulk which uses microthermometric data micro raman spectroscopic data cation ratios and volume fraction estimations as input the program offers a broad variety of equations of state which are selected according to the fluid system or the temperature and pressure conditions of interest the isochores that correspond to the output or test v x properties of fluid inclusions are calculated by the program isoc in calculating the isochores this program takes account of the compressibility and expansion of selected host minerals the program test allows different equations of state to be compared directly with experimental data thereby facilitating selection of the most adequate model in the programs bulk and isoc loner is a group of programs that handle individual equations of state eos for all fluid systems presented in the programs bulk and isoc aqso is a group of programs that allows purely empirical modelling of electrolyte bearing aqueous solutions henry s law for dilute gas bearing aqueous solutions and osmotic coefficients for dilute electrolyte bearing aqueous solutions the programs are available on the university of leoben web site at http www unileoben ac at buero62 minpet ronald

vlf emission bursts in the terrestrial and venusian nightside troughs the existence of very low frequency 100 hz electric field bursts in the nightside venus ionosphere has been commonly assumed to be evidence for lightning by analogy to the earth where some of the whistler mode radiations above the ionosphere originate from lightning1 3 non lightning sources for venus whistler mode waves have been ignored vlf emission bursts not associated with lightning are frequently observed over the terrestrial polar ionosphere4 6 one type saucers are whistler mode wave emissions that propagate upwards along magnetic field lines5 6 here we show that the 100 hz emission bursts in the venusian nightside ionosphere are remarkably similar to those of the terrestrial vlf saucer emissions in terms of their spatial and temporal characteristics and the properties of their magnetoplasma environment we therefore propose that the generation mechanism for such vlf saucers6 7 should be considered as a viable alternative to lightning as a source of venusian ionospheric whistler mode emissions

c slip in quartz from subsolidus deformed granite abstract the slip behaviour of quartz from a granite and granitic veins during subsolidus high temperature conditions 700 800 c of deformation is studied by lattice preferred orientation lpo and microstructural techniques lpos with a point maximum of c axes parallel to the shear direction which is close to the stretching lineation are presented and interpreted with the aid of light and electron microscopy in terms of c as the dominant slip direction during plastic deformation microscopy of such samples reveals the presence of 0001 tilt boundaries and free 0001 burgers vector dislocations in edge orientations a change in lpo in a decreasing temperature environment from c axes parallel to the shear direction to c axes normal to the shear direction documents a fabric transition from the rare c slip to the more common a slip fabric it is concluded that conditions of high temperature and partial pressure of water are required to initiate dominant c slip during deformation at geological strain rates

the fractal shape of sutured quartz grain boundaries application as a geothermometer along grain boundaries of quartz from metamorphic and igneous rocks complex interfingering sutures may occur under the light microscope the lengths of the sutures range from approximately 10 1000 m the sutured grain boundaries are statistically self similar over one to two orders of magnitude they represent fractals their mathematical counterpart are koch curves which are developed after two to four iterations the fractal hausdorff besicovitch dimensions d of sutured quartz grain boundaries from different grades of metamorphism are between ca 1 05 and 1 30 the d value decreases with increasing temperature during formation of the sutures on a statistical basis d can be used as a measure of this temperature and therefore as a deformation related thermometer

upper mantle anisotropy in sw iberia from long range seismic profiles and teleseismic shear wave data abstract deep seismic profiles of the iliha experiment have provided evidence for the presence of anisotropy in the deeper levels of the lithosphere beneath the ossa morena zone of the hercynian domain of sw iberia allowing estimation of its main characteristics a n15 e fast p wave velocity direction and a degree of anisotropy of around 4 the consistency of these results is tested against an anisotropy analysis using teleseismic shear waves data recorded in a dense network of up to 13 digital three component stations deployed in the area for about 2 months are used to study the spatial coherence of wave fields in particular of shear wave splitting observations over an array significant small scale lateral variations are observed in the data suggesting that care should be taken in using single station results as representative for geodynamical interpretations in spite of the short duration of the test a few teleseismic events provide useful data the analysis of sks and s phases shows evidence of the presence of anisotropy the results from the different events depict a rather consistent anisotropic structure with roughly a ne sw to east west fast velocity direction the anisotropic patterns derived from dss crossing profiles and shear wave splitting over the ossa morena zone are compared mechanisms classically suggested to be responsible for the origin of the anisotropy such as past deformations of the lithosphere or relative motion between lithosphere and asthenosphere are discussed to test their consistency with the geophysical and geological data available in the area

processing and inversion of long period surface wave data collected in the iberian peninsula summary several filtering techniques have been used to remove the effects of multipathing and modal contamination and to isolate the fundamental mode from rayleigh wavetrains group velocity data are obtained by means of the multiple filter technique a time variable filter has allowed the influence of noise as well as the interference produced by higher modes to be removed multiple filtering is then used again to compute group velocities at each station the interstation group velocity for the fundamental mode rayleigh wave is estimated according to the velocities at two stations frequency domain wiener deconvolution is used to compute the phase velocity between two stations the well known three station method is applied to correct the distances travelled by the waves across the array and therefore to determine interstation phase and group velocities in a more accurate manner on the other hand lateral refraction at the atlantic continental edge of the peninsula is also studied phase velocities are corrected for the anelastic effect inversion of the interstation rayleigh wave phase velocities is then made in accordance with generalized inversion theory to obtain theoretical 2 d layered earth models in this paper these methods are applied to rayleigh waves generated by teleseismic events propagating across the iberian peninsula and recorded at wwssn stations as a consequence new and principal features for the iberian lithosphere asthenosphere system are obtained a very interesting feature of the the iberian lithosphere was found a low velocity layer directly under the moho between 39 and 64 km depth with shear velocities ranging from 4 12 to 4 37 km s 1 the iberian asthenosphere which lies between 100 and 180km depth is not an homogeneous layer and shows a negative velocity gradient from top to bottom together with a sudden increase in shear velocity beneath the low velocity zone

lightning measurements from the pioneer venus orbiter the plasma wave instrument on the pioneer venus orbiter frequently detects strong and impulsive low frequency signals when the spacecraft traverses the nightside ionosphere near periapsis these particular noise bursts appear only when the local magnetic field is strong and steady and when the field is oriented to point down to the ionosphere thus the signals have all characteristics of lightning whistlers we have tried to identify lightning sources between the cloud layers and the planet itself by tracing rays along the b field from the orbiter down toward the surface an extensive data set consisting of measurements through orbit 1185 strongly indicates a clustering of lightning sources near the beta and phoebe regios with an additional significant cluster near the atla regio at the eastern edge of aphrodite terra these results suggest that there are localized lightning sources at or near the planetary surface

recently formed elastic anisotropy and petrological models for the continental subcrustal lithosphere in southern germany this paper advances new evidence for elastic anisotropy in the continental subcrustal lithosphere in southern germany the range of petrological models compatible with the observed azimuthal variation of seismic p wave velocity is explored the azimuthal distribution of amplitudes of mantle phases and the observed increase of p velocity with depth both indicate a continuation of anisotropy with depth together with an increase of preferred orientation even depletion of the upper mantle in basaltic components as suggested by mantle xenoliths from various parts of germany cannot explain the velocity depth and azimuthal amplitude observations without an increase of anisotropy with depth preferred orientation of olivine is the most likely mechanism for the observed phenomena its fast a axis at the moho level is directed towards n22 5 e the b axis is also required to be horizontal i e the b plane one of the preferred glide planes of olivine is vertical with a strike of n22 5 e therefore this preferred glide plane of olivine practically coincides with the plane of maximum horizontal shear stress deduced from fault plane solutions of earthquakes in western germany this is a strong indication that the preferred orientation of olivine is formed in the recent west european crustal stress field leaking into the upper mantle the distribution of velocities to a depth of at least 50 km requires slight horizontal rotation of the a axis with depth by 10 towards n32 e and a change in the modal composition towards a depletion increasing with depth compatible with the composition of mantle xenoliths from western germany further experiments are needed to substantiate this suggestion which could lead to a better understanding of the interaction of crustal and upper mantle stress strain fields

crustal parameters in the iberian peninsula abstract the structure of the crust in the iberian peninsula has been investigated for the last 15 years by spanish and portuguese groups in close collaboration with other european institutions the first experiments were carried out in portugal mueller et al 1973 with the aim of investigating the crustal structure of the hercynian belt in the southwest corner of the iberian peninsula other experiments have been subsequently realized to study different aspects of the crust in various regions of portugal in spain the main effort has been focused in alpine areas with the first experiments in the alboran sea and the betic cordilleras working group for deep seismic sounding in spain 1974 1975 1977 working group for deep seismic sounding in the alboran sea 1974 1975 1978 follow up experiments until 1981 completed the work in the betic cordillera extensive experiments were carried out in the pyrenees in 1978 further surveys covered the balearic islands in 1976 the valencia trough in 1976 and 1983 and the celtiberian chain or iberic system in 1981 the hercynian belt has only been studied in detail in the northwest corner of spain in 1982 with smaller studies in the central iberian massif in 1976 and 1986 mostaanpour 1984 has compiled some crustal parameters crustal thickness average crustal velocity and pn velocity for western europe meanwhile more complete data are available for the iberian peninsula the results presented here were derived from a large number of seismic refraction experiments which have been carried out mostly along or close to coastal areas of the iberian peninsula offshore explosions of various sizes were used as the energy source in most cases in addition to some quarry blasts unfortunately this leaves most of the inner part of the iberian peninsula unsurveyed our purpose is to summarize some of the crustal parameters obtained so far and to detail the appropriate literature for the interested reader

quartz c axes parallel to stretching directions in very low grade metamorphic rocks abstract quartz preferred orientations with c axes parallel to stretching directions are widespread in slates phyllites and very low grade schists of the south island new zealand in general these rocks lack evidence for plastic deformation of quartz and often preserve the original clastic quartz which naturally tends to be elongate parallel to the c axis the c axis preferred orientation can be explained therefore by mechanical rotation of clastic grains during deformation so that long axes became parallel to the stretching direction plastic deformation does however play a role in some very quartz rich layers which display a preferred orientation due to basal slip with c axes at high angles to the stretching direction solution transfer is important in enhancing the contrasts between pelitic and quartz rich lithologies but its role in producing c axis preferred orientations by competitive anisotropic growth or solution seems important only in slickenfibres and in fibrous quartz veins of shear zones where quartz displays very strong preferred orientations with c axes parallel to the local stretching direction in contrast the non fibrous quartz pressure shadows in some muscovite rich layers display a c axis preferred orientation similar to adjacent quartz rich sand layers and it probably results from nucleation of pressure shadow quartz on pre existing mechanically oriented quartz clasts

the source of uranium within hydrothermal uranium deposits of the motianling mining district guangxi south china abstract uranium deposits are diverse as a result of their formation in a wide variety of geological environments however the source of the uranium within these deposits is difficult to identify and as a result it is usually poorly understood this study focuses on the hydrothermal sanqiliu and sanqisi uranium deposits both of which formed within ne sw striking shear zones that cross cut the sanfang batholith and low grade metasedimentary rocks of the motianling district southern china the deposits contain vein hosted pitchblende quartz pyrite chlorite mica orebodies fluid inclusions within quartz in the orebodies in the district homogenize at temperatures between 205 c and 222 c indicating the deposit formed as a result of low to intermediate temperature hydrothermal activity pitchblende associated hydrothermal pyrite within the sanqiliu and sanqisi deposits has 34s values from 24 7 to 19 7 and from 6 0 to 13 6 respectively quartz separates from the sanqiliu deposit yield 18o values of 1 4 11 5 mean of 5 8 for syn ore hydrothermal fluids these stable isotope data indicate that the fluids that formed these deposits were derived from the sanfang granites sediments of the sibao group and meteoric sources in addition uraninite from the host sanfang granite yields u pb ages of ca 732 773 ma combining these data with the geology of the ore deposits in this region suggests that these deposits were generated from deeply circulating meteoric water and the uraninite within the highly fractionated sanfang granite is the source of the uranium within the sanqiliu and sanqisi uranium deposits

upper mantle anisotropy a preliminary model seismic anisotropy in the upper mantle can be explained by crystallographic mineral alignment achieved through dislocation motion the physical mechanism of mineral alignment requires upper mantle shear flow which reorients and aligns minerals by dislocation glide and climb governed by the dominant glide system of each mineral the dominant glide systems are assumed to be 100 0l0 for olivine and 001 100 for the pyroxenes these yield a predominantly orthorhombic fabric with the olivine 100 and the pyroxene 001 axes aligned in the upper mantle flow direction and the olivine 010 and the pyroxene 100 axes aligned normal to the upper mantle flow plane these glide systems have a threshold temperature of enhanced mobility of 1100 1200 k which yields a solid state thermally defined lithosphere asthenosphere boundary in an olivine pyroxene mantle consistent with recent seismic determinations of the thickness of the lithosphere mantle anisotropy due to mineral alignment is then actively maintained below this boundary asthenosphere and mesosphere and is a fossil state above this boundary lithosphere we use the dominant glide systems to establish the crystallographic orientation of olivine and pyroxene in calculating the maximum seismic anisotropy of two petrologic models pyrolite and piclogite for the upper mantle by an extrapolation of single crystal anisotropic mineral elastic properties to a depth of 400 km the real earth seismic anisotropy will be bound by the limits of maximum anisotropy from perfect mineral alignment and minimum anisotropy isotropy from random mineral alignment the seismic anisotropy of the upper 220 km is best represented by the pyrolite model which reduces to quasi hexagonal symmetry with the unique axis in the direction of mantle flow the lehmann discontinuity is conjectured to be due to a change in composition from pyrolite to piclogite and therefore may represent a change in anisotropy the piclogite model has orthorhombic symmetry distinctly different from that of the pyrolite the piclogite anisotropy model can appear quasi isotropic when measured by transverse isotropy parameterization if the mantle flow is mainly horizontal with a horizontal shear plane that is the shear flow gradient duh dr dominates

comment on venus nightside ionospheric troughs implications for evidence of lightning and volcanism by h a taylor jr j m grebowsky and p a cloutier

kinematic interpretation of shearband boudins new parameters and ratios useful in ht simple shear zones partial funding to jp was provided by the centro de investigacao geolugica ordenamento e valorizacao de recursos that is supported by the pluriannual program of the fundacao para a cilncia e a tecnologia funded by the european union feder program and the national budget of the portuguese republic very insightful and helpful reviews were done by c fernandez university of huelva and two reviewers for which we are grateful we want to acknowledge to t valente university of minho for her suggestions that helped to simplify the manuscript structure and to a mccaig university of leeds for his final comments and english revision that significantly improved this manuscript

comment on further evidence for lightning at venus in contradiction to the findings of singh and russell 1986 the pioneer venus orbiter pvo electric field data are not found to provide evidence for either lightning or volcanism at venus it is suggested that the noise considered by singh and russell to be clustered at low altitudes actually appears frequently at high altitudes the frequent appearance of the broadband noise in the upper ionosphere indicates that this noise like that attributed to lightning by scarf et al 1980 is actually generated within the ionosphere near the pvo by the solar wind interaction with the ionosphere

area perimeter relation for rain and cloud areas following mandelbrot9s theory of fractals the area perimeter relation is used to investigate the geometry of satellite and radar determined cloud and rain areas between 1 and 1 2 x 106square kilometers the data are well fit by a formula in which the perimeter is given approximately by the square root of the area raised to the power d see equation in the pdf where d is interpreted as the fractal dimension of the perimeter it is concluded that rain and cloud perimeters are fractals they have no characteristic horizontal length scale between 1 and 1000 kilometers

u pb zircon and monazite geochronology of post collisional hercynian granitoids from the central iberian zone northern portugal abstract in the central iberian zone ciz of the iberian massif large volumes of granitoids were emplaced during the post collisional stage of the hercynian orogeny syn to post d3 the last ductile deformation phase twelve granitic units and a quartz monzodiorite were selected for a u pb zircon and monazite geochronological study they represent successive stages of the d3 event the ucanha vilar lamego sameiro and refoios do lima plutons are coeval 313 2 ma 319 4 ma 316 2 ma and 314 2 ma respectively and belong to the earliest stage later on the braga massif was emplaced its different units yielding the same age 309 3 ma for the braga granite 309 1 ma for the gonca granite and 311 5 ma for a related quartz monzodiorite the braga massif is subcontemporaneous with the agrela and celeiros plutons 307 3 5 ma and 306 2 ma respectively in agreement with field data the briteiros granite is younger 300 1 ma followed by the emplacement of the peneda geres massif geres paufito illa and carris granites the geres granite emplaced at 296 2 ma seems to represent a first magmatic pulse immediately followed by the intrusion of the paufito granite at 290 2 5 ma for the carris granite a minimum emplacement age of 280 5 ma was obtained based on these results the following chronology is proposed 1 syn d3 biotite granitoids 313 319 ma 2 late d3 biotite dominant granitoids 306 311 ma 3 late to post d3 granitoids ca 300 ma 4 post d3 granitoids 290 296 ma these chronological data indicate that successive granitic intrusions were emplaced in the ciz during a short time span of about 30 ma that corresponds to the latest stages of the hercynian orogeny a rapid and drastic change occurred at about 300 ma between a compressive ductile tectonic regime d3 ca 300 320 ma associated to calc alkaline monzonitic and aluminopotassic plutonism and a fragile phase of deformation d4 which controlled the emplacement of the subalkaline ferro potassic plutonism at 290 296 ma

seismic constraints on dynamics of the mantle of the kaapvaal craton abstract shear wave splitting in the upper mantle of the kaapvaal craton in southern africa is measured by applying the sks technique to the records of a portable array of digital broad band seismographs the data are interpreted in terms of lattice preferred orientation in olivine fast wave polarization directions at all stations of the array are close to the absolute plate motion apm direction of southern africa since the end of the jurassic this alignment is similar to that previously reported for the north american craton and suggests that the large scale component of mantle anisotropy on both sides of the atlantic can be related to resistive drag at the base of the plates a likely depth range of the corresponding deformation is 150 400 km analysis of the mantle converted phases suggests that the high velocity mantle root of the kaapvaal craton which translates coherently with the plate resides in the same depth range the bottom of the root is found at a depth close to 380 km we conclude that the root is deformed by the recent plate motion but the deformations are not strong enough to be seen in the available tomographic models

venus nightside ionospheric troughs implications for evidence of lightning and volcanism ionization troughs are frequently observed in the venus nightside ionosphere by the orbiter ion mass spectrometer oims on the pioneer venus orbiter pvo these events typically exhibit density depletions which may range from a factor of 2 to an order of magnitude or more often feature sharp density gradients and frequently are associated with superthermal ion fluxes although their full spatial extent cannot be determined the ion trough dimensions as perceived along the pvo orbit track extend from 1 to more than 10 in latitude and longitude troughs have been encountered at altitudes ranging from more than 1000 to less than 250 kilometers the nightside trough boundaries are similar to both the ionization gradients which mark the venus dayside ionopause and the ionization gradients which define the high latitude ionization trough in the earth ionosphere in each of these venus and earth phenomena there is a close association between sharp gradients in thermal ion distributions and energetic and dynamic processes stimulated by the interaction between the solar wind interplanetary magnetic field imf and the thermal ionosphere a close correlation is identified between ion trough events and prominent published examples of 100 hz plasma waves detected by the orbiter electric field detector oefd which have been interpreted by scarf and russell 1983 and by ksanfomaliti et al 1983 as whistler mode propagation stimulated by lightning in the lower atmosphere and frequently occurring over mountains while the occasional coincidence between the detection of whistler waves and the overflight of venus mountain ranges is also observed for the ion troughs neither phenomenon is seen to exhibit convincing evidence of an association with the mountains overall these findings lead us to believe that many of the 100 hz noise bursts previously attributed to lightning are like the ion troughs actually the result of the interaction between the ionosphere and the combined effects of the solar wind and the draped imf if this interpretation is correct there may be little evidence for lightning from the pvo measurements similarly a supporting argument for active volcanism as a possible source for the deduced lightning events would also be discounted

reply to comment on venus nightside ionospheric troughs implications for evidence of lightning and volcanism by h a taylor jr j m grebowsky and p a cloutier

anisotropy of the asthenosphere the higher mode data of the pacific revisited surface wave data previously used by the authors to constrain upper mantle anisotropy in the pacific ocean are re examined after an error was found in the calculations of the love wave phase velocities sub lithospheric anisotropy is still required by the corrected data but it extends to shallower depth than we originally proposed using different parameterizations of the upper mantle we present strong evidence that the bottom of the anisotropic layer has been reached around 250 km in the pacific beneath north america no revision of our data is required and anisotropy could extend to around 400 km depth our results are in agreement with an upper mantle anisotropy due to preferred orientation of olivine crystals in an overall horizontal shear strain parallel to the present day plate motion we suggest that this preferred orientation of the crystals mainly occurs within the upper mantle low velocity layer

rayleigh wave phase velocities in the pacific with implications for azimuthal anisotropy and lateral heterogeneities summary the lateral distribution of fundamental mode rayleigh wave phase velocities in the pacific has been calculated in order to determine the variation in velocity as a function of the age of the oceanic plate the importance of azimuthal anisotropy and the presence of secondary lateral heterogeneities the data set used in this study consists of phase velocity measurements in the period range 20 125 s for 178 paths traversing the pacific both the pure path and spherical harmonic inversion techniques are used in this investigation with an emphasis placed on determining the effectiveness and resolving power of these methods in calculating the velocity distribution in an oceanic regime the first order velocity age relation which dominantly characterizes surface wave dispersion in an oceanic environment can be adequately modelled by either the pure path or spherical harmonic techniques azimuthal anisotropy is the dominant second order effect and is best developed in regions less than 80 myr in age in this age zone the faster direction of wave propagation is either in the direction of fossil seafloor spreading or in the direction of present day absolute plate motion in the western pacific there is a correlation with paleo relative motion fossil seafloor spreading for periods less than 50 s lateral velocity heterogeneities which are not related to the age of the oceanic plate are found by pure path inversions and are correlated with regions associated with shallow residual depth anomalies this effect slow velocities with respect to the velocity age model monotonically decreases as a function of period and is indicative of a shallow origin age independent anomalies were also modelled by the application of the pure path and spherical harmonic methods in a sequential inversion

fractal analysis of experimentally dynamically recrystallized quartz grains and its possible application as a strain rate meter abstract fractal analysis of experimentally recrystallized quartz grain shapes has been employed to study the relationship between the microstructures of dynamically recrystallized quartz grains and the deformation conditions such as temperature and strain rate samples used are quartz aggregates deformed under high temperature 800 c 900 c and 1000 c and high confining pressure 400 mpa the fractal dimension is useful to quantify the shapes of the recrystallized quartz grain boundaries at each set of conditions the fractal dimension is determined as the slope of a log log plot of the length of the grain boundaries perimeters against the grain size calculated as diameters of circles having the same areas as the actual grains the results show that the shapes of grains are self similar and the fractal dimensions d change systematically being dependent on both temperature and strain rate the skew of the grain boundary defined as d 1 and showing the degree of the serration may be proportional to the logarithm of the zener hollomon parameter that includes a component of the arrhenius term this relation indicates that strain rate can be calculated from the fractal dimension and the temperature it may therefore provide a new paleo strain rate meter for plastically deformed natural rocks

mountain building strike parallel motion and mantle anisotropy abstract geophysical and geological evidence indicates that tectonic movements parallel to the strike of orogenic belts and suture zones are the most important mode of displacement during continental collision and oblique subduction several hundred to a few thousand kilometers of displacement may have occurred this way resulting in a pervasive ductile deformation of the lithosphere consequently both crustal and mantle fabrics may reflect these movements and their study using both geological and geophysical methods could supply important clues to lithosphere behavior during mountain building on the basis of kinematic analysis of ductilely deformed crustal rocks in zones of movement a variety of tectonic models have been proposed which differ in 1 1 the timing of strike parallel motions early before or during continental accretion or late after accretion was completed 2 2 the geometric pattern of strike parallel displacement zones low angle or high angle and 3 3 the location of orogen parallel movement zones in outboard terranes on the subducting plate along the suture zone or within the continental hangingwall large scale displacements parallel to mountain belts also suggest that they occurred along lithospheric faults rooted in the upper mantle although few studies have been carried out from this view point thermal structural and petrological data support the conclusion that lithospheric faults involving the upper mantle may be discriminated from crustal faults rooted in some crustal decoupling zone where available data on mantle flow beneath orogenic belts are in agreement with mountain parallel displacements inferred from crustal studies this has an important bearing on the seismic anisotropy pattern which can be predicted in the lithospheric mantle below mountain belts the fast velocity direction which is parallel to the flow direction should therefore be recorded parallel to the strike of the belt

quartz fabric transition in a cooling syntectonic granite hermitage massif france abstract the hermitage granite situated in the northwest massif central france is a syntectonic hercynian leucogranite emplaced along an active transcurrent shear zone during emplacement and cooling the progressive deformation is marked by the development of a primary homogeneous foliation gradually affected by ductile shear bands c s mylonites increase in strain heterogeneity during cooling corresponds to a change of dominant deformation mechanism of the quartz phase from grain growth and migration recrystallization to intracrystalline a slip and rotation recrystallization migration recrystallization is characterized by preferred orientations of c axes close to the principal extension direction we discuss relevant deformation mechanisms and rheological implications for syntectonic plutons in particular we argue that the transitions between homogeneous and heterogeneous accumulation of strain cannot generally be correlated with transition between magmatic and solid state flow

high resolution surface wave tomography beneath the aegean anatolia region constraints on upper mantle structure summary this study provides new constraints on the upper mantle structure from western greece to central anatolia using seismic data of permanent broad band networks recently installed in greece and turkey and from a two year temporary array simbaad experiment we used 200 seismic events recorded at 146 broad band stations with a typical interstation distance of 60 100 km across the study area the high resolution 3 d shear wave velocity model of the mantle is obtained by inversion of fundamental mode rayleigh wave phase velocity maps for periods between 20 and 195 s the tomography is based on ray tracing in heterogeneous media taking into account external propagation effects the horizontal resolution is approximately 100 km however small heterogeneities may suffer from some horizontal smearing and damping the vertical resolution is approximately 100 km the vertical smoothing is necessary to avoid unresolved spurious shear wave velocity oscillations in the upper mantle the errors on shear wave velocities in our 3 d model 0 02 0 1 km s 1 are significantly smaller than the amplitude of vs variations 0 3 0 5 km s 1 in spite of the vertical and horizontal smoothing our model shows details in the upper mantle structure never reached at regional scale in the area the overall structure is characterized by a low velocity zone 80 200 km depth reflecting a slow and warm asthenosphere underlying a thin lithosphere the southwesternmost termination of the low velocity anomaly corresponds to the northward dipping hellenic slab the detailed shear velocity structure of the upper mantle beneath anatolia appears to be far more geometrically complex than revealed in previous tomographic studies of the area at depths larger than or equal to 160 km velocities are overall high beneath anatolia partly due to the presence of dipping high velocity anomalies which we tentatively interpret as remnant slabs the southernmost high velocity anomaly beneath anatolia is separated from the eastern edge of the hellenic slab by a major low velocity anomaly which we interpret as the trace of asthenospheric mantle material rising inside a vertical slab tear beneath southwestern anatolia

upper mantle structure in southern norway from beamforming of rayleigh wave data presenting multipathing summary a model for the upper mantle sv wave velocity under southern norway is obtained by depth inversion of the average phase velocity of the rayleigh wave fundamental mode in the area the average dispersion curve is obtained in the period range 22 200 s by beamforming of 190 rayleigh waves recorded by the magnus network a temporary regional network of 41 broad band stations resolution of the beamforming procedure is increased by deconvolving the original beams from the array response function using the lucy richardson algorithm in addition to an average phase velocity beamforming gives us some information concerning the nature of the incoming wavefield we detect deviations of the wave propagation direction from the great circle paths which commonly reach 10 at a period of 25 s for the teleseismic events the amplitude of the deviations decreases with increasing period and with decreasing epicentral distance as expected the phase velocity measured by beamforming does not show any correlation with the deviation from great circle path suggesting that deviation does not bias phase velocity measurements we detect also significant multipathing with characteristics that vary rapidly with frequency the obtained sv wave velocity profile clearly shows that southern norway is underlain by a low velocity zone in the upper mantle and does not have shield like characteristics despite its location in the baltic shield these findings support the hypothesis that the high topography of southern norway is sustained by anomalous upper mantle material

anisotropy beneath 9 stations of the geoscope broadband network as deduced from shear wave splitting polarization of sks scs and s waves has been analyzed on digital 3 components seismograms recorded at 9 stations of the recently installed geoscope broadband network splitting was observed for about 15 records and is interpreted as being due to seismic anisotropy beneath the stations from every record it is possible to retrieve the fast direction at the station and the time difference between the fast and slow polarization directions some 30 observations of quasi linear s pulses also help constrain the direction of fast velocity synthetic seismograms were built to test the validity of the method used to retrieve the parameters of anisotropy typical time differences are about 1 sec corresponding for example to a 80 km thick zone of perfectly oriented pyrolite the fast directions obtained at 3 continental stations in america westford santa cruz heredia could be related to plate tectonic processes on the other hand the fast directions found in 3 oceanic islands kipapa papete la reunion differ strongly from the oceanic plate velocity direction there

misalignment of quartz c axis fabrics and lineations due to oblique final strain increments in the ruby mountains core complex nevada abstract to interpret c axis stereonet patterns of deformed quartz the patterns must be viewed in the xz strain plane which is usually assumed to contain the elongation lineation this study describes several c axis patterns from a region of complex amphibolite facies deformation in the northern ruby mountains where the late xz plane is oblique to most of the lineations without the lineation as a guide the proper orientation for interpretation of each pattern is determined by rotating the c axis data around the normal to the foliation until the c axes within the foliation plane lie at the center of the stereonet this new view is inferred to be the xz plane for the final increments of strain the rotation produces an internal symmetry in the patterns in addition the rotated views across the area show a more consistent geographic orientation than the lineations this geographic orientation is aligned with strain in a mylonitic shear zone which represents the latest macroscopic evidence for plastic strain along the edge of the study area the complete reorientation of the quartz textures during the final strain increments implies that they record very little of the finite strain history quartz is the only mineral recrystallized during the late strain thereby providing insight into the geometry of strain increments that cannot be determined from other minerals

s velocity structure and radial anisotropy in the aegean region from surface wave dispersion summary the lithospheric structure of the aegean region is investigated by analysis of rayleigh wave fundamental mode dispersion measurements isotropic 1 d models for almost 100 two station ray paths across the region display distinct variations in the moho depth and crustal s wave velocities the descending slab of the subducting african plate can be resolved down to 120 km depth beneath the volcanic arc three different regions are distinguished in terms of moho depth 1 the forearc with large crustal thicknesses between 38 and 48 km and an average of 43 km 2 the northern aegean with an average moho depth of 28 km and 3 the southern aegean central volcanic arc i e cyclades and sea of crete with an even thinner crust of around 25 km lateral variations in structure between 25 and 55 km depth indicate a marked difference between the western and eastern forearc collocated with pronounced changes in trench and slab geometry as well as published deformation rates s velocities between 25 and 55 km depth are low everywhere beneath the forearc but increase from the peleponnesus to crete an abrupt change occurs between western and central crete in terms of the visibility of the aegean moho and the seismic structure of the lithospheric mantle wedge an aegean mantle wedge with s velocities above 4 4 km s 1 is only observed to the east of central crete whereas to the west velocities of less than 4 0 km s 1 occur down to the plate contact these low velocities above the slab may indicate the presence of a melange of metamorphic rocks at the depths a low velocity asthenospheric layer is observed beneath the sea of crete and the cyclades below 40 km depth between the thinned lithosphere above and the slab below the observed radial anisotropy in the northern part of the aegean is likely to be due to preferred orientation of anisotropic minerals within the lower crust possibly caused by lateral ductile flow associated with recent lithospheric extension

fluid inclusion petrography abstract a procedure of fluid inclusion studies is proposed with emphasis on the criteria of selecting fluid inclusions for detailed microthermometry and spectroscopic analysis an overview of descriptive and genetic classifications of fluid inclusions in single crystals and in massive rocks is given with the intention of further differentiating the commonly used terms primary and secondary fluid inclusions some principles of fluid inclusion modification are explained cathodoluminescence cl studies of quartz with the optical high power cl microscope and the electron microprobe provided with a cl detector are an important help in fluid petrography cl textures are subdivided in primary growth textures and a wide variety of secondary microtextures which are in part induced by fluid inclusions the latter is grouped in textures indicative of local lower crystal order increasing defect structures and microtextures indicative of local quartz healing reduction of the defect structures microtextures showing the genetic relationship between fluid inclusions and the host mineral provide information about the possible post entrapment changes of fluid inclusions and therewith testify their geological relevance

new insights into the lithosphere beneath the superior province from rayleigh wave dispersion and receiver function analysis we study the azimuthally anisotropic upper mantle structure of the superior craton and grenville province in ontario canada using rayleigh wave phase velocity data in the period range 40 160 s 152 two station dispersion measurements are combined in a tomographic inversion that solves simultaneously for isotropic and anisotropic terms using a least squares technique we perform a series of tests to derive optimal regularization smoothing and damping and to assess the resolution of and trade offs between isotropic and anisotropic anomalies the tomographic inversion is able to resolve isotropic phase velocity anomalies on a scale of 200 300 km and to distinguish between different anisotropic regimes on a 500 km scale across the study region isotropic phase velocity anomalies in the tomographic model span a range of up to 2 per cent around a regional average which is similar to the canadian shield dispersion curve of brune dorman 1963 with phase velocities up to 3 per cent above global reference models the amplitude of azimuthal phase velocity anisotropy reaches a maximum of 1 2 per cent a clear east west division of the study area based on both isotropic phase velocity anomalies and azimuthal anisotropy is apparent in the western superior isotropic phase velocities are generally higher than the regional average anisotropy is observed at all periods with ene wsw to ne sw fast propagation directions at periods 120 s the anisotropy likely results from frozen lithospheric fabric aligned with tectonic boundaries whereas the anisotropy at longer periods is interpreted to arise from present day sublithospheric flow the fast directions from published sks measurements are close to the fast rayleigh wave propagation directions throughout the period range sampled and the large sks splitting times may be accounted for by this near coincidence of fast propagation directions across most of eastern ontario phase velocities are lower than the regional average fast propagation directions rotate from nw se at 40 130 s period to wnw ese at periods 140 160 s the results suggest a difference in fast propagation directions between the anisotropic fabric frozen into the lithosphere and the fabric due to current and recent sublithospheric flow the superior craton and grenville province are characterized by large scale structural variations that reflect the complex tectonic history of the region this study highlights differences between the characteristics of eastern and western ontario and indicates the occurrence of multiple layers of anisotropy in the subcratonic upper mantle

love rayleigh wave incompatibility and possible deep upper mantle anisotropy in the iberian peninsula love and rayleigh wave phase velocities are analyzed with the goal of retrieving information about the anisotropic structure of the iberian lithosphere the cross correlation method is used to measure the interstation phase velocities between diverse stations of the iliha network at periods between 20 and 120 s despite the 2 d structure of the network the love wave data are too few to enable an analysis of phase velocity azimuthal variations azimuthal averages of love and rayleigh wave phase velocities are calculated and inverted both in terms of isotropic and anisotropic structures realistic isotropic models explain the rayleigh wave and short period love wave phase velocities therefore no significant anisotropy needs to be introduced in the crust and down to 100 km depth in the upper mantle to explain our data a discrepancy is observed only at long periods where the data are less reliable love wave data at periods between 80 and 120 s remain 0 15 km s faster than predicted by isotropic models explaining the long period rayleigh wave data possibilities of biases in the measurements due to interferences with higher modes are examined but seem unlikely a transversely isotropic model with 8 of s wave velocity anisotropy in the upper mantle at depths larger than 100 km can explain the whole set of data in terms of a classical model of mantle anisotropy this corresponds to 100 of the crystals perfectly oriented in the horizontal plane in a pyrolitic mantle this is a rather extreme model which predicts at time delay between 0 and 2 seconds for split sks

the origin of tablet boudinage results from experiments using power law rock analogs abstract we used power law viscous plasticine n ca 7 as a rock analog to simulate boudinage of rocks undergoing dislocation creep and brittle fracture a competent plasticine layer oriented perpendicular to the main shortening direction z underwent bulk pure flattening inside a less competent plasticine matrix computer tomographic analyses of the deformed samples revealed that boudinage results from an initial phase of viscous necking followed by tensile failure along the previously formed necks the resulting boudins display a polygonal shape in plan view and are referred to as tablet boudins in contrast to the square to rectangular shaped chocolate tablet boudins the ratio between the plan view long and short axis r ranges from 1 2 to 2 6 the polygonal non isometric shape of the tablet boudins can be explained by the strong interaction of concentric and radial tensile fractures with increasing layer thickness h i the mean diameter of the boudin tablets w a increases while the number of boudins n decreases progressive finite strain results in a higher number of the boudins and a smaller mean diameter the thickness of the boudins h f is almost the same as the initial layer thickness h i while the aspect ratio w d w a h f decreases with layer thickness and finite strain the mean w d values obtained from all experiments span from ca 4 to ca 11 tablet boudins described in the present paper have yet not been described from natural outcrops the reasons might be that pure flattening strain is not common in nature and the characterization and evaluation of tablet boudins requires geometrical analysis in three dimensions which is a difficult task when such structures occur in nature

global azimuthal seismic anisotropy and the unique plate motion deformation of australia differences in the thickness of the high velocity lid underlying continents as imaged by seismic tomography have fuelled a long debate on the origin of the roots of continents1 2 3 4 5 some of these differences may be reconciled by observations of radial anisotropy between 250 and 300 km depth with horizontally polarized shear waves travelling faster than vertically polarized ones2 this azimuthally averaged anisotropy could arise from present day deformation at the base of the plate as has been found for shallower depths beneath ocean basins6 such deformation would also produce significant azimuthal variation owing to the preferred alignment of highly anisotropic minerals7 here we report global observations of surface wave azimuthal anisotropy which indicate that only the continental portion of the australian plate displays significant azimuthal anisotropy and strong correlation with present day plate motion in the depth range 175 300 km beneath other continents azimuthal anisotropy is only weakly correlated with plate motion and its depth location is similar to that found beneath oceans we infer that the fast moving australian plate contains the only continental region with a sufficiently large deformation at its base to be transformed into azimuthal anisotropy simple shear leading to anisotropy with a plunging axis of symmetry may explain the smaller azimuthal anisotropy beneath other continents

shallow anisotropy in the mediterranean mantle from surface waves 1 we present new evidence for the existence of the love rayleigh discrepancy in the mediterranean region and constrain the average polarization anisotropic structure of the mediterranean mantle we analysed regional rayleigh and love waveforms recorded at 3 component broadband seismic stations none of the 3 component seismograms could be fit with a single 1d isotropic and smooth velocity model however satisfactory fits for individual rayleigh and love waveforms could often be obtained using realistic 1d velocity models we used these 1d path average velocity structures to derive 3d s velocity models for the mediterranean region our results show that love waves require higher velocities about 200 m s compared to rayleigh waves between 30 and 120 km depth we relate the observed anisotropy to lattice preferred orientation of crystallographic axes of elastically anisotropic minerals such as olivine

the role of dynamic recrystallization in the development of lattice preferred orientations in experimentally deformed quartz aggregates abstract experiments on coaxially deformed quartz aggregates show that when dynamic recrystallization involves grain size reduction the lattice preferred orientation lpo of the recrystallized grains depends on the recrystallization mechanism at low temperatures and fast strain rates strain induced grain boundary migration recrystallization favors growth of grains oriented poorly for slip on the basal and prism planes resulting in an lpo of c axes parallel to the 1 direction at higher temperatures or slower strain rates progressive subgrain rotation produces recrystallized grains which inherit the small circle girdle lpo of their deformed host grains and which continue to re orient by slip at even higher temperatures and slower strain rates progressive subgrain rotation is accompanied by rapid grain boundary migration which does not favor grains of any particular orientation thus the lpo is again similar to that of non recrystallized grains in contrast when dynamic recrystallization involves grain growth driven by surface energy reduction a strong lpo of c axes parallel to 1 develops during grain growth but then evolves with increasing strain toward a small circle girdle the correlation of lpos with recrystallization mechanisms has important implications for the assumption of homogeneous strain in theoretical models of lpos and for interpreting natural lpos in recrystallized rocks

global patterns of azimuthal anisotropy and deformations in the continental mantle summary we present a summary of measurements of azimuthal anisotropy in the continental mantle based on the sks technique and performed mostly with the active participation of the authors the directions of polarization of the fast quasi shear wave and the time delays between the quasi shear waves are obtained at nearly 70 locations in all continents except antarctica these data are interpreted in terms of lattice preferred orientation of olivine which is caused by deformations in the mantle the depth interval responsible for anisotropy is unknown but the data suggest that it may reach at least 300 km the fast directions in sks do not show clear correlation with the fast directions of the teleseismic p at the same seismograph stations in the regions of present day convergence the fast direction of anisotropy usually aligns with the plate boundary this correlation implies that the direction of shortening is the same in the crust and the upper mantle in the regions of rifting the inferred direction of mantle flow usually aligns with the direction of extension in the crust outside the regions of recent tectonic activity we most likely observe a combined effect of frozen anisotropy in the subcrustal lithosphere and of recently formed anisotropy in the asthenosphere on a global scale in these regions there is a positive correlation between the absolute plate velocity directions and the fast directions of anisotropy the correlation is especially strong in central and eastern parts of north america a clear absence of any evidence of large scale azimuthal anisotropy in the data of long range refraction profiling for the upper 100 km of the mantle of that region implies that the effect in sks is generated mainly at greater depths in the asthenosphere orientation of olivine at these depths reflects recent and present day flow in the mantle rather than processes of a distant geologic past

delineation of deformation grades of low strain granitoids using assemblages of elementary deformation textures abstract based on microscopic observations of the miocene tokuwa granodiorite central japan a method of delineating deformation grades of low strain granitoids has been derived which utilizes assemblages of elementary deformation textures edts such as subdomains in quartz bent twins in plagioclase and kink bands in biotite although the granodiorite is comprised of equant grains and shows no evidence of deformation to the naked eye except for brittle fractures it shows a variety of edts at the microscale in thin section assemblages of edts belonging to quartz plagioclase or biotite are used for deformation grading of the corresponding rock the deformation grading by edts based on quartz correlates with deformation grading based on plagioclase or biotite eigenvalues derived from a principal component analysis indicate that the first principal component explains approximately three quarters of the variance of deformation grading by edts based on quartz plagioclase and biotite the deformation grading by edts using quartz correlates well with the first principal component score these results indicate that the deformation grading by assemblages of edts based on quartz as well as on the first principal component score is useful for deformation grading of low strain granitoids

quartz c axis fabric development and large scale post nappe folding wandfluhhorn fold penninic nappes quartz c axis fabrics have been investigated within a suite of quartz veins and monomineralic layers around a major post nappe fold hinge the wandfluhhorn fold in the bosco area swiss italian border within the lower penninic nappes two kinematic domains which are separated by the axial plane trace of the wandfluhhorn fold are recognized on the lower limb the measured quartz c axis fabric asymmetry indicates a sense of shear in which the overlying layers move to the southwest i e top to sw whereas on the upper limb the shear sense is reversed with the top moving to northeast the shear direction n60 e n80 e however is constant in both areas and oblique to an older stretching lineation as well as to the d3 fold hinge such a distribution of asymmetric quartz c axis fabrics and the constant orientation of their interpreted shear direction which is apparent only from the fabric data and not from field evidence indicates fabric development pre or early syn wandfluhhorn folding with subsequent folding and modification of the existing textures and possibly rotation of the initial fold axis an overall westward directed shear has been suggested for the whole of the lepontine alps however this study demonstrates that this simple general pattern has been modified locally by later folding it also demonstrates that the dominant lineation may be a finite stretching lineation due to more than one phase of deformation and is not necessarily related to any particular transport direction

azimuthal anisotropy in the earth from observations of sks at geoscope and nars broadband stations abstract we have analyzed observations of low frequency sks waves recorded on horizontal components at several broadband stations of the geoscope and nars arrays splitting of sks is consistently observed and in good agreement with a hypothesis of azimuthal anisotropy due to transverse anisotropy with a horizontal axis in the upper mantle beneath the receivers we have designed an inversion method which takes advantage of observations made simultaneously at different azimuths and which permits us to obtain estimates of the direction of fast axis of anisotropy as well as the time delay between the orthogonal quasi shear waves in general the directions of fast velocity obtained both for stations around the atlantic and around the pacific appear to be related to directions of past and present plate motions

progressive evolution from uplift to orogen parallel transport in a late acadian upper amphibolite to granulite facies shear zone south central massachusetts fabrics within a 1 km wide shear zone along the eastern margin of the bronson hill anticlinorium in central massachusetts provide important information on the regional tectonic development during the devonian acadian orogeny two distinct mineral lineations observed within the zone are each defined by alignment of coarse sillimanite needles and elongated quartz and feldspar grains and aggregates both lineations are associated with shearing and development of mylonitic fabrics the character of the two lineations and related fabrics differs mainly in orientation and in the relationship of each lineation to the local orientation of quartz c axis fabrics the interpreted earlier lineation has a steep west plunge and the later lineation has a shallow plunge and north south to southwest trend parallel to the regional trend of the orogen extensive dynamic recrystallization of feldspar the possible activity of prism slip in quartz and the mineral assemblages in apparent equilibrium during deformation suggest that both lineations probably formed under upper amphibolite facies conditions just after the thermal peak of acadian metamorphism a progressive change between the two deformation fabrics is suggested by evidence of overlap between the two by their striking similarity in style and metamorphic conditions of formation and by the similarity in orientation of their bulk strain axes with a change only in the transport direction between them kinematic indicators associated with each phase of lineation development are consistent throughout the shear zone the earlier phase has a west side up sense of shear and the later phase indicates west side north movement these phases are correlated with the regional backfold and dome stages of acadian deformation the kinematics and relationships between them suggest a revised tectonic model for the later part of the acadian orogeny and for development of orogen parallel lineations in this region in this model uplift and thickening of basement gneisses in the bronson hill anticlinorium during the backfold stage was impeded by gravitational instability in a thermally weakened crust this led to a change from subvertical to subhorizontal extension east west acadian shortening was still in progress constraining this extension to a north south direction parallel to the trend of the orogen

lateral inhomogeneities of the hercynian crust in central spain abstract an azimuthal layout of deep seismic profiles has been partially completed in the central iberian massif data from two new profiles and a reinterpretation of previous profiles make possible two dimensional models for the hercynian crust in central spain from which some lateral crustal inhomogeneities can be established these inhomogeneities due to alpine intraplate tectonics coincide with the spanish central system and consist of a 5 km crustal thickening with respect to the surrounding areas

evaluating quartz crystallographic preferred orientations and the role of deformation partitioning using ebsd and fabric analyser techniques quartz crystallographic preferred orientations cpo from three distinct orthogneisses using both the electron back scatter diffraction ebsd and fabric analyser fa techniques reveal a clear trend from basal and rhomb slip for high p t conditions 670 20 degrees c 9 kbar rhomb and basal slip for medium p t 590 15 degrees c 6 kbar and a dominance of prism slip for lower p t conditions 570 degrees c 4 5 kbar the textural variations are interpreted in terms of a temperature field gradient and microscale strain partitioning controlled by a weak feldspar matrix that can locally invert the expected slip system sequences locally quartz cpus are different within one thin section and in comparison to bulk orientation measurements both ebsd and the fabric analyser techniques are ideal to determine such textural heterogeneities while the ebsd is a powerful technique to determine the full cpo measurements from similar locations inside several quartz grains from the orthogneisses and an annealed and undeformed quartzite show that the fa is an accurate tool to determine cpus of c axis orientations in uniaxial materials in a cpo focussed study the fa is a cheap alternative to ebsd as the analysis of whole thin section can be accomplished in a very short time with minimal sample preparation with the fa it is possible to evaluate the cpus of several samples quickly with an accuracy that allows identification of the main slip systems and their homogeneity

strong lateral variations of lithospheric mantle beneath cratons example from the baltic shield abstract understanding mechanisms for creation and evolution of precambrian continental lithosphere requires to go beyond the large scale seismic imaging in which shields often appear as laterally homogeneous with a thick and fast lithosphere we here present new results from a seismic experiment polenet lapnet in the northern part of the baltic shield where we identify very high seismic velocities vs 4 7 km s in the upper part of the mantle lithosphere and a velocity decrease of 0 2 km s at approximately 150 km depth we interpret this velocity decrease as refertilisation of the lower part of the lithosphere this result is in contrast to the lithospheric structure immediately south of the study area where the seismic velocities within the lithosphere are fast down to 250 km depth as well as to that of southern norway where there is no indication of very high velocities in the lithospheric mantle vs of 4 4 km s while the relatively low velocities beneath southern norway can tentatively be attributed to the opening of the atlantic ocean the velocity decrease beneath northern finland is not easily explained with present knowledge of surface tectonics our results show that shield areas may be laterally heterogeneous even over relatively short distances such variability may in many cases be related to lithosphere erosion and or refertilisation at the edge of cratons which may therefore be particularly interesting targets for seismic imaging

numerical modelling of asymmetric boudinage abstract asymmetric boudinage structures are commonly used as shear sense indicators but their development is incompletely understood this paper describes the influence of initial shape and kinematic parameters on the evolution of boudin trains using a numerical approach based on the finite difference code flac boudin trains are simulated as a series of competent objects embedded in a soft matrix subjected to general monoclinic ductile flow deformation of boudin trains includes heterogeneous stretching rotation of boudins and offset along the neck regions the sense of relative boudin offset is mainly influenced by the initial orientation of the interboudin plane in the boudinaging layer while kinematic vorticity number of the flow and the orientation of the boudin train with respect to the flow extensional eigenvector usually the shear zone boundary also play a role viscosity ratio and aspect ratio influence the magnitude of offset along the neck regions and the amount of rotation of boudins but not the sense of slip and rotation on the interboudin plane knowledge of the orientation of the interboudin plane itself is insufficient to use asymmetric boudins as independent shear sense indicators details of the boudin geometry such as the sense of deflection of marker horizons along the interboudin plane must be used for this purpose

dating of lithospheric buckling 40ar 39ar ages of syn orocline strike slip shear zones in northwestern iberia abstract orogenic curvature is a ubiquitous feature of mountain belts and the plate tectonic and geodynamic setting responsible for the development of curved orogens is a subject of debate in order to distinguish between different models of orocline formation it is necessary to tightly constrain the absolute timing of oroclinal development however determining the absolute isotopic timing of oroclinal bending is challenging the most direct method available to constrain the time interval during which an orocline formed is to obtain absolute age constraints on fabrics generated within syn orocline strike slip shear zones that accommodated rotations around a vertical axis during the development of crustal or lithospheric scale orogenic curvature here we present a data set of 40ar 39ar ages obtained from five shear zones some of which display curved traces parallel to the cantabrian orocline structural grain in nw iberia and are interpreted to have been generated coevally to it the 40ar 39ar ages were obtained by laser rastering induced step heating on single muscovite crystals that grew synkinematically during shearing all five samples yielded ages that cluster tightly at 308 3 ma providing direct evidence for the age of oroclinal bending this age is consistent with the age constraints obtained from paleomagnetic and structural data that place the onset of oroclinal bending in moscovian times our 40ar 39ar age determinations therefore provide a reliable absolute constraint on the age of buckling of the variscan orogen around a vertical axis and provide further evidence that oroclinal bending is unrelated to variscan convergence collision or the subsequent extensional collapse of the mountain belt

anisotropic grain growth in quartz aggregates under stress and its implication for foliation development fine grained quartz aggregates show significant grain growth during high temperature 700 1000 c and high pressure 400 mpa deformation experiments when water is present flattening of grains that exceeds the deformation induced flattening and a resultant clear foliation are found in the samples recrystallized at relatively low temperatures and high strain rates i e high deviatoric stresses the distribution of water as inferred from the distribution of pore space is also anisotropic in these samples in contrast the samples recrystallized at relatively high temperatures and low strain rates i e low deviatoric stresses show small grain flattening and almost isotropic water distribution the observed very large flattening under high stress indicates a significant contribution of anisotropic grain growth because the anisotropy of grain growth is correlated with the anisotropy of water distribution we suggest that the observed foliation under high stress is due to anisotropic grain growth caused by enhanced mass transport through water foliation caused by this mechanism will be related to the stress orientation

waveform inversion of surface wave data test of a new tool for systematic investigation of upper mantle structures summary in most tomographic inversion of surface wave data the long period seismograms are first interpreted in terms of dispersion and or attenuation curves before performing an inversion in terms of laterally and depth varying properties an alternative to this approach is to perform a direct waveform inversion or as in cara lev que 1987 to use another set of secondary observables built up from the seismograms in this paper we systematically test with actual rayleigh wave records this latter technique by considering laterally homogeneous models we use for this purpose a set of recent long period digital records from the geoscope station dumont d urville antarctica for surficial events in the south indian ocean and the southeast pacific ocean and for intermediate depth events in the vanuatu and kermadec trenches in addition to the obvious advantages of being able to deal with situations where overtones are present in the seismogram it is found that the waveform inversion procedure allows us to reach a better depth resolution than in classical inversion of dispersion curves even when only the fundamental mode is present in the seismogram quite good resolution is obtained to depth as large as 300km for s velocity when using surficial events located at a few thousand kilometres from the station while classical surface wave studies do not allow us to resolve s velocity at depth larger than 150 km for these events when intermediate depth events are used at distances of about 5000 km the presence of overtones in the signal allows us to get resolution to depth as large as 600 km for s velocity poorer resolution is obtained in both situations for the attenuation factor s velocity appears furthermore to be more robust than attenuation at depth where good resolution is achieved due to the great sensitivity of surface wave amplitude to departure from the assumption of lateral homogeneity more sophisticated direct modelling would be required to get more confidence in the inverted attenuation models

p t path development derived from shearband boudin microstructure abstract this work focuses on the development of a regional p t path from the malpica lamego ductile shear zone nw portugal based on the microstructures of shearband boudins evolved during progressive simple shear the combination of microstructural analysis fluid inclusion studies crystallographic preffered orientation and fractal geometry analyses allows to link several stages in the internal evolution of the boudin to regional p t conditions the boudinage process is initiated under differential stress after the original layer achieved sufficient viscosity contrast relative to the surrounding matrix two main transformations occur simultaneously i change in the external shape with continuous evolution from tabular rigid body to sigmoidal asymmetric morphology shearband boudin and ii localized dynamic recrystallization in the sharp tips of the structure acute edge of shearband boudin and along the boudin s margin and grain boundaries smaller recrystallized grains particularly in the sharp tip domains accommodate most of the external strain and larger relict grains are preserved in the centre dynamic recrystallization under constant strain rates and strain partitioning inside the boudins is indicated by fractal geometry based on grain boundary and grain area analysis progressive deformation leads to the generation of structural and textural heterogeneous domains inside the boudins and is recorded by quartz c axis orientation analysis and fluid inclusion studies the last deformation episode shows the final formation of the blunt tip domain and internal secondary shear planes the regional p t path begins with the crystallization of andalusite after an internal shearband boudin dilation event and ends with quartz dynamic recrystallization on boudin tips the main deformation stage 310 315 ma led to reactivation of internal secondary shear zones with sillimanite crystallization

boudinage and shearband boudins a meso to micro scale tool in structural analysis abstract a classification of boudinage and boudins is made presenting a simplified parametric description of boudin block geometry end members the most important shearband boudins parameters ratios microstructural domains and internal evolutions are described and interpreted shearband boudins are related to a large number of geological meso and microstructures e g pinch and swell drawn or torn boudins mica fish porphyroclasts foliation boudinage tectonic lozenges and c s c several factors can control the asymmetric boudinage process such as the obliquity of a competent layer the orientation of an initial fracture boudin axial ratio the viscosity ratio between matrix and layer flow type and shear strain this review highlights the correlation of shearband boudins with other asymmetrically deformed structures and shows their geological relevance finally this study presents a phenomenological framework for shearband boudins

structural analysis of flow related textures in lavas abstract the textures of coherent volcanic rocks including lavas and volcanic intrusives commonly contain features that are attributed to flowage previous applications of structural analysis to volcanic rocks are expanded here to provide a framework for analysis textures defined as the crystallinity granularity and shapes and arrangements of the components crystals glass and voids of a rock together with structures defined as individual features composed of the disposition attitude arrangement or relative positions of the components of a rock are first described second the spatial fabrics shapes and arrangements of the components of a rock and the orientation of textures and structures are identified third textures structures and fabrics are placed in the spatial and temporal geological context finally detailed interpretations of the kinematics and rheology of structures and fabrics is made leading to an integrated flow history of the rock illustrative case studies include rhyolite from the basal part of the tertiary minyon falls dome northeastern new south wales australia which has a texture comprising planar domains of differing crystal abundance flow bands multiple folds of these domains relatively homogeneous crystal alignment parallel to the fold axes and microfolding of these domains in the zone of interaction between phenocrysts and matrix including retrorotation of phenocrysts on short limbs of inequant folds trachyte dykes on fraser island queensland australia have a texture comprising crystal alignment planar concentration domains banding two planar domains of crystal alignment interpreted to be conjugate shear zones phenocrysts influence the spacing and distribution of the domains and interacted with shear zones by undergoing small amounts of rotation the shear zones overprinted a homogeneous crystal alignment during the last stage of flow before solidification as a result of dilatant granular interactions lava from miocene submarine banded silicic mafic domes on katsurajima on the coast of the shimane peninsula southwestern japan has a texture comprising crystal alignment irregular domains interpreted as the result of quenching local internal deformation of crystals including brittle boudinage and elongate vesicles and amygdales dacite from the late stages of the 1991 1995 eruption of mount unzen in western kyushu japan has a texture comprising crystal alignment deformation of phenocrysts and their surrounding matrix producing voids by mechanical means with the possible involvement of vapour phases the pervasive mechanical failure of the flowing magma may have triggered frontal collapse and the ensuing pyroclastic eruptions a spectrum of increasingly intense flow related textures can be recognised from simple planar alignments of crystals and vesicles to overprinting effects and domainal textures such as banding and shear zones and deformed domains pervasive ductile tearing and ultimately brittle fracture record flow during the transition from ductile magma to brittle rock the development of these flow related textures is controlled by the interplay of driving forces magma pressure gravity and resisting forces viscosity where driving forces are strong flow related textures are well developed when viscous resistance exceeds the driving forces flow and the development of flow related textures ceases