can mesoscale models reproduce meandering motions the influence of meandering flow on dispersion of pollutants is frequently underrepresented in dispersion models in terms of measurements meandering is primarily associated with time scales between the turbulence and the applied averaging time which is usually 1 h the related spatial scales thus range roughly from 10 2 to 10 4 m referred to here as submesoscales as the state of the art mesoscale models should be capable of reproducing flow features on scales larger than the turbulence and as the meandering generating mechanisms are not fully understood yet it is useful to examine if the mesoscale models can reproduce meandering for that purpose the wrf chem model at 1 3 km horizontal resolution is used to simulate a weak wind night during the cases99 experiment the measurements are used for detailed model verification the model with its typical set up fails to reproduce the variability at submesoscales and the locus of the under representation is traced to too strong horizontal diffusion reducing or removing the model diffusion allows the appearance of the submeso variability whose spectral properties and the resulting plume behaviour agree well with the measurements the linear correlation between the simulations with reproduced variability and the measurements is low as is the case between two simulations with only slightly different set up the conclusion is that mesoscale models are able to reproduce the strength of variability and the effects of meandering but only with reduced or removed horizontal diffusion the question arises whether it is possible to obtain a linear correlation i e to correctly reproduce individual modes at these scales at all copyright c 2010 royal meteorological society

holocene climatic and environmental changes inferred from midge records diptera chironomidae chaoboridae ceratopogonidae at lake berkut southern kola peninsula russia a radiocarbon dated sediment sequence from lake berkut in the southern part of the kola peninsula northwest russia was investigated by means of midge analysis in order to reconstruct the holocene climatic and environmental history of the region past mean july air temperatures at the study site and hypolimnetic oxygen contents of the lake water were inferred from chironomid based transfer functions the early holocene c 10 100 8400 cal yr bp is characterized by summer temperatures and hypolimnetic oxygen concentrations broadly similar to present day conditions the midge records give evidence of a lake level fall at c 7000 cal yr bp resulting in weakened thermal stratification of the lake water and improvement of the hypolimnetic oxygen conditions after c 4000 cal yr bp midge assemblages suggest a lake level rise related to increased effective moisture a secondary mid holocene climatic optimum with inferred mean july air temperatures of c 12 1 degrees c was recorded between 6000 and 4400 cal yr bp followed by minimum values c 11 3 degrees c between 3500 and 1500 cal yr bp accompanied by the onset of natural acidification of the lake the late holocene midge assemblages suggest weakly acidic conditions low hypolimnetic oxygen contents and a general warming trend during the last c 1500 years although paludification and natural acidification may have influenced the temperature reconstruction at this stage however the modern chironomid inferred mean july air temperature 12 5 degrees c is consistent with meteorological data from a nearby station in general the midge records reflect relatively warm and moist conditions at lake berkut before c 7000 cal yr bp a relatively warm and dry climate at c 7000 4000 cal yr bp and a shift to cooler and wetter climatic conditions in the region after c 4000 cal yr bp less

microstructures petrofabrics and seismic properties of ultra high pressure eclogites from sulu region china implications for rheology of subducted continental crust and origin of mantle reflections ultra high pressure uhp eclogites from sulu region china represent mafic components of the continental crust which were first subducted to mantle depths greater than 100 km and then exhumed to the earth s surface detailed investigation of microstructures chemical compositions petrofabrics and seismic properties of the uhp eclogites can provide important information on the operating deformation mechanisms and rheology of subducted continental crust and on the origin of seismic reflections within the upper mantle we present here results from field optical and tem observations electron back scattered diffraction ebsd measurements and numerical computations of the seismic properties of uhp eclogites collected from fresh surface outcrops at the drill site maobei donghai county jiangsu province of the chinese continental scientific drilling program ccsd two types of eclogites have been distinguished type 1 coarse grained eclogites deformed by recovery accommodated dislocation creep at the peak metamorphic conditions and type 2 fine grained eclogites which are composed of reworked type 1 materials during recrystallizationaccommodated dislocation creep in shear zones which were active during the exhumation of the uhp metamorphic rocks both garnet and omphacite in these eclogites deformed plastically and the flow strength contrast between these two constituent minerals is apparently much less than an order of magnitude under the uhp metamorphic conditions plasticity of eclogites under uhp conditions can effectively facilitate channeled flow along the interplate shear zone the

crystallographic fabrics of omphacite rutile and quartz in vendee eclogites armorican massif france consequences for deformation mechanisms and regimes abstract this study aims at further understanding of the mechanisms how lattice preferred orientations lpo develop during deformation in the main eclogite minerals microstructures and textures of deformed eclogites from the les essarts complex western france were investigated using optical microscopy and electron backscatter diffraction ebsd in the scanning electron microscope microfabric analyses of eclogite facies minerals are used to identify their deformation mechanisms which define the rheology at high pressure metamorphic conditions mechanisms of intracrystalline deformation by dislocation movement dislocation creep result usually in a non linear flow law typically power law while diffusive processes diffusion creep correspond to linear flow laws general microstructural observations may suggest intracrystalline deformation dislocation creep of omphacite the omphacite lpo vary between s and l type and correlate with oblate or prolate grain shape fabrics respectively until now these lpo types have not been understood by plasticity models based on dislocation glide on the known slip systems in clinopyroxene an alternative interpretation is given in terms of anisotropic growth and dissolution with grain boundary diffusion as the rate controlling process there are further indications suggesting diffusion creep with concomitant anisotropic growth and dissolution as a main deformation mechanism in omphacite in omphacite around a hollow garnet crystallographic and shape fabrics align with the c 001 axes parallel to the grain elongations defining the mineral lineation which rotates locally with the inferred flow direction in this part the grain sizes of omphacite and rutile are larger than in the surrounding matrix the geometry of both the shape and crystallographic fabrics is interpreted to represent the local stress regime directions and ratios of the principal stresses the lpo of rutile duplicate the lpo of omphacite and a similar distinction between s and l type was used rutile deformation mechanisms probably involve dislocation creep as well as diffusion creep quartz mainly occurs as an interstitial phase with weak lpo patterns interpreted as random no representative obliquity of the lpo in omphacite nor rutile with respect to foliation and lineation was observed to be used as potential shear sense criteria however the rutile lpo was slightly rotated relative to the omphacite lpo consistently in most samples the results suggest that diffusion processes are strongly involved in the deformation of eclogites a linear flow law should be taken into account in tectonic models where eclogites are incorporated

polyphase deformation in a fore arc back arc basin salin subbasin myanmar burma the salin subbasin of myanmar part of the larger central basin is a fore arc back arc basin couplet situated between an oblique subduction zone to the west and a major right lateral strike slip fault to the east surface and subsurface expressions of folds and faults suggest that the basin experienced north northwest directed extensional deformation in the miocene followed by east northeast directed pliocene pleistocene transpressional deformation resulting in a variety of structural styles including thrust faults oblique reverse faults strike slip faults and normal faults fault propagation folds cored by west dipping thrust faults in the basin center are located above steps in the top of basement surface most likely fault controlled unconformities at the base of and within the pliocene pleistocene synorogenic section indicate that the thrust faults were active during the pliocene pleistocene the southeastern region contains broad north northwest trending uplifts and east northeast striking normal faults associated with thickened miocene synorogenic deposits pliocene pleistocene sedimentary rocks lie unconformably above the miocene section and are folded above the uplifts reflecting pliocene pleistocene compression in the southern part of the basin miocene sedimentary rocks thicken dramatically over the 20 n uplift and the yedwet uplift suggesting that the north northwest striking faults that bound them represent pliocene pleistocene inversion of miocene normal faults during the miocene the burma plate acted as a fore arc sliver coupled with the india plate subducting obliquely underneath it and moved northward relative to asia along the sagaing fault normal faulting and local basin formation took place at this time when the northern part of the burma plate collided with eastern asia in the pliocene transpressional deformation predominated creating thrust and reverse faults positive flower structures and inverted basins

resurfacing of deeply buried oceanic crust in naga hills ophiolite north east india petrofabric microstructure and seismic properties abstract we have studied the microstructure texture and seismic anisotropy of a foliated blueschist eclogite rock in the naga hills ophiolite nho complex north east india the rock is composed essentially of omphacite sodic amphibole glaucophane sodic calcic amphibole barroisite phengite and garnet and represents oceanic crust that experienced neo tethyan subduction and metamorphism before it resurfaced and accreted in the ophiolite omphacite and glaucophane show weak shape preferred orientation spo while phengite displays a strong spo the crystallographic preferred orientation cpo of omphacite is characterized by the 001 axes gridle within the foliation and the 010 poles concentrated sub perpendicular to the foliation for glaucophane the 001 axis aligns parallel to lineation and the 100 axis and 110 pole plunge perpendicular to foliation these cpos correspond to sl type fabrics related to plane strain deformation geometry based on our analysis we propose that the observed texture had developed from plastic deformation through dislocation creep employing the textural data we have presented the seismic anisotropies of the individual minerals blueschist eclogite domains and discussed their contributions in the bulk rock anisotropy the calculated bulk rock seismic anisotropies avp and avs of the rock are 12 8 and 8 1 respectively which correlate with the observed seismic anisotropy of the subducting oceanic crust

seismic properties of lawsonite eclogites from the southern motagua fault zone guatemala abstract we present new data on the crystal preferred orientation cpo and seismic properties of omphacite and lawsonite in extremely fresh eclogite from the southern motagua fault zone guatemala to discuss the seismic anisotropy of subducting oceanic crust the cpo of omphacite is characterized by 010 001 and it shows p wave seismic anisotropies avp of 1 4 3 2 and s wave seismic anisotropies avs of 1 4 2 7 lawsonite exhibits 001 planes parallel to the foliation and 010 axes parallel to the lineation and seismic anisotropies of 1 7 6 6 avp and 3 4 14 7 avs the seismic anisotropy of a rock mass consisting solely of omphacite and lawsonite is 1 2 4 1 avp and 1 8 6 8 avs for events that propagate more or less parallel to the maximum extension direction x the fast s wave velocity vs polarization is parallel to the z in the y z section rotated from the x z section causing trench normal seismic anisotropy for orthogonal subduction based on the high modal abundance and strong fabric of lawsonite the avs of eclogites is estimated as 11 7 in the case that lawsonite makes up 75 of the rock mass on this basis we suggest that lawsonite in both blueschist and eclogite may play important roles in the formation of complex pattern of seismic anisotropy observed in ne japan weak trench parallel anisotropy in the forearc basin domains and trench normal anisotropy in the backarc region

horizontal meandering as a distinctive feature of the stable boundary layer abstractoscillations in the horizontal components of the wind velocity associated with oscillations in air temperature during low wind speed episodes are ubiquitous in the stable boundary layer and

deformation and recrystallization mechanisms in naturally deformed omphacites from the sesia lanzo zone geophysical consequences buatier m van r rmund h l m drury m r and lardeaux j m 1991 deformation and recrystallization mechanisms in naturally deformed omphacites from the sesia lanzo zone geophysical consequences teetonophysrc c 195 11 27 naturally deformed omphacites clinopyroxenes from the sesia lanzo zone western italian alps have been studied using light and transmission electron microscopy techniques deformation and recrystallization of omphacite took place at 5 50 600 c and minimum pressures of 14 16 kbar tem reveals isolated free dislocations loops nodal points tiltwalls complex dislocation networks minor twins stacking faults and antiphase domain boundaries the activated slip systems are l z llo llo l llo and al assisted by climb in nodal points and complex dislocation networks dislocations with burgers vector l 2 112 are present in low strain domains most of the subgrain transitional and new grain boundaries subparallel to wl develop from 110 tiltwalls which accommodate lattice bending produced by the l 2 110 110 slip system a component of the misorientation across such newly formed sub grain boundaries is however also formed by sub rain boundary migration grain rotations in the intermediate and high strain domains are more complex but can be explained by the activated slip systems the omphacite microstructures indicate that initial strain induct rec stallisation occurred by a rotation mechanism where single crystals become polycrystals by the development of numerous high angle grain boundaries at a subsequent more advanced stage migration recrystallization is also activated and a different kind of recrystallization mechanism occurs which involves the discontinuous development of new strain free grains these grains are derived from the extremum of the orientations produced by heterogeneous strain and slip system activity the evident ductility of omphacite during low to intermediate eclogite metamorphism is inferred to be facilitated by hydrolitic weakening effects as such the plastic behaviour of omphacite should be incorporated in geophysical flow models dealing with subducted oceanic and or lithosperic plate margins

insights into the dynamics of an orogenic wedge from lubrication theory implications for the himalayan tectonics abstract using lubrication theory we develop a mechanical model to evaluate the dynamic relation between an orogenic wedge and the overriding plate the model suggests that the subducting plate motion produces a dynamic pressure in the wedge which supports the gravity load of the overriding plate lying above it stable condition a drop in the dynamic pressure results in a rotational collapse of the overriding plate unstable condition we present an analytical solution to provide an estimate of the dynamic pressures in orogenic wedges the lubrication model is also implemented in computational fluid dynamics cfd simulations to perform real scale numerical experiments considering mainly three variables 1 plate convergence angle 2 subduction rate us and 3 viscosity ratio r between the overriding plate and wedge the overriding plates attain mechanical stability when us exceeds a threshold value us otherwise they become unstable as us

high temperature and pressure seismic properties of a lower crustal prograde shear zone from the kohistan arc pakistan anastomosing shear zones exposed in the lower crust of the kohistan palaeoisland arc in pakistan have parageneses indicating increasing pressure during deformation therefore they represent a rare example of strain localization during crustal thickening we investigated the seismic properties of a sheared gabbro with constant bulk chemistry across one of these shear zones the compressional wave velocity was measured at confining pressures of up to 0 5 gpa and temperatures of up to 600 8c the density the average vp compressional p wave velocity and the acoustic impedance at room temperature increase from the undeformed protolith through the strain gradient to the intensely sheared mylonite the seismic anisotropy is largest for the strain gradient the vp dependence of the velocities on temperature is much higher in the mylonite than in the protolith the acoustic impedance contrast between protolith and mylonite is high enough to generate seismic reflections at low temperatures but not at high temperatures this suggests that the seismic reflectivity may also depend on the temperature consequently ductile shear zones can be detected in reflection profiles of crusts with low geothermal gradients and may be transparent in crusts with high geothermal gradients

dynamic recrystallization and chemical evolution of clinoamphibole from senja norway clinoamphibole from a mylonitic amphibolite exhibits microstructures characteristic of dynamic recrystallization including porphyroclasts in a finer grained matrix of needle shaped amphibole the matrix amphibole defines an ls fabric and porphyroclasts have core and mantle structures with a core containing undulose to patchy extinction and 100 deformation twinning surrounded by a mantle of recrystallized grains in addition intragranular grains also occur within the cores tem analyses of the porphyroclasts reveal that they contain a wide variety of lattice defects including high densities 5 108cm 2 of free dislocations and dislocation arrays dissociated dislocations stacking faults and 100 micro twins tem also shows that matrix grains and intragranular grains have relatively low defect densities and that the intragranular new grains occur at localities in the porphyroclasts characterized by high densities of dislocations these observations along with the chemical and orientation relationships between the recrystallized grains and porphyroclasts indicate that the new grains may have formed by heterogeneous nucleation and that further growth probably occurred by both strain assisted and chemically induced grain boundary migration or liquid film migration this recrystallization event is interpreted to be synkinematic based on the fact that no recrystallization textures are present in the matrix grains and that the matrix grains define an ls fabric however the low defect densities in the matrix grains and the lack of intracrystalline strain in other phases indicate that post kinematic recovery processes were active

omphacite textures in eclogites of the tauern window implications for the exhumation of the eclogite zone eastern alps abstract we discuss the relationship of omphacite lattice preferred orientation lpo patterns in eclogite and kinematic indicators in the matrix surrounding the eclogite during the very rapid exhumation of the deeply buried eclogite zone in the tauern window of the eastern alps lpo patterns are presented from profiles parallel to the eclogite stretching lineation across the eclogite zone the omphacite textures show symmetric patterns across the entire eclogite zone only in few cases slight asymmetries are observed the patterns are characterized by an alignment of 110 with the foliation and a maximum of 001 close to the lineation and are indicative of deformation by intracrystalline glide on the 010 001 and 110 001 slip systems the patterns have close resemblance to s type lpo patterns and probably developed during the burial and accretion of the eclogites we argue that the lpo patterns are not related to deformation associated with the very rapid exhumation of the eclogite zone we conclude that exhumation related deformation was concentrated in the metasedimentary rocks that surround the eclogites allowing the eclogites to preserve their burial lpo signature during the exhumation process kinematic indicators show top n thrusting at the base of the eclogite zone and sinistral strike slip faulting at the top most of the kinematic indicators record blueschist and greenschist facies metamorphic conditions however because of the very rapid exhumation of the eclogite zone with rates exceeding 36 km myr 1 the kinematic indicators are interpreted to reflect the entire exhumation process from eclogite facies conditions we discuss a model according to which the eclogite zone was exhumed in an oblique extrusion wedge

rheology of omphacite at high temperature and pressure and significance of its lattice preferred orientations abstract we have investigated the rheology of hot pressed polycrystalline omphacite di 58 jd 42 space group c2 c at strain rates of 10 4 10 5 s temperatures of 1300 1500 k and a pressure of 3 gpa using a 5 gpa griggs type deformation apparatus the rheological constitutive equation of omphacite is determined with a stress exponent of 3 5 0 2 and an activation energy of 310 50 kj mol our study shows that 1 the creep strength of omphacite falls between those of diopside and jadeite 2 experimental omphacite microfabrics are indistinguishable from natural ones s type fabric and its mesoscopic foliation develop under conditions of axially symmetric shortening whereas l type fabric and its mesoscopic lineation develop under conditions of general strain with l parallel to the greatest elongation 3 as in naturally deformed omphacite the deformation substructure is characterized by the dominant slip systems 110 1 2 110 110 001 and 100 001 we conclude that both s and l type omphacite fabrics are produced by these slip systems fabric differences arise solely from variation of the geometry and orientation of the finite strain ellipsoid we also confirm the previous suggestion that na bearing pyroxenes are significantly weaker than na free pyroxenes

relationships between eclogite facies mineral assemblages deformation microstructures and seismic properties in the yuka terrane north qaidam ultrahigh pressure metamorphic belt nw china to understand the relationships between eclogite facies mineral assemblages deformation microstructures and the seismic properties of subducting oceanic crust eclogites from the yuka terrane no

eclogite facies shear zones deep crustal reflectors strongly foliated eclogite facies rocks in 30 150 m thick shear zones of caledonian age occur within a grenvillian garnet granulite facies gabbro anorthosite terrain in the bergen arcs of norway the predominant eclogite facies mineral assemblages in the shear zones are omphacite garnet zoisite kyanite in gabbroic anorthosite and omphacite garnet in gabbro eclogite facies rocks in shear zones are generally fine grained alternating omphacite garnet and kyanite clinozoisite rich layers define gneissic layering a strong shape preferred orientation of omphacite kyanite and white mica phengitic muscovite and or paragonite define the foliation the anorthositic eclogites show omphacite b axis maxima approximately normal to the foliation and c axis girdles within the foliation plane p wave velocities v determined at confining pressures to 600 mpa for samples from eciogite facies shear zones range from 8 3 to 8 5 km s l and anisotropy ranges from 1 to 7 the few samples with more pronounced anisotropy tend to be approximately transversely isotropic with minimum velocities for propagation directions normal to foliation and maximum velocities for propagation directions parallel to foliation the fast propagation direction lies within the c axis girdles parallel to foliation and the slow propagation direction is parallel to the b axis concentration normal to foliation in samples for which omphacite crystallographic preferred orientation was determined v for the granulite facies protoliths average about 7 5 km s high calculated reflection coefficients for these shear zones 0 04 0 14 indicate that they are excellent candidates for deep crustal reflectors in portions of crust that experienced high pressure conditions but escaped thermal reactivation

climatic implications of the natural variations of d h ratios in tree ring cellulose abstract natural variations in the deuterium composition of carbon bound hydrogen of cellulose nitrate from tree rings have been measured trees from edmonton have been analysed in detail and the d values of 5 year groups of rings show a strong temporal correlation with mean annual temperature at the growth site this is shown to result from the cellulose isotopic composition being related to the isotopic composition of soil water used during photosynthesis the soil water is in turn related to meteoric water which at this growth site appears to correlate temporally with mean annual temperature similar measurements from trees which grew in various areas of north america show a strong spatial correlation between d of cellulose and mean annual temperature the spatial functional relationship between d values and mean annual temperature at the growth site t is found to be d 5 5t 130 swhich compares with the spatial relationship between d of meteoric water and mean annual air temperature which is d 5 6t 100

jurassic to miocene magmatism and metamorphism in the mogok metamorphic belt and the india eurasia collision in myanmar situated south of the eastern himalayan syntaxis at the western margin of the shan thai terrane the highgrade mogok metamorphic belt mmb in myanmar occupies a key position in the tectonic evolution of southeast asia the first sensitive high resolution ion microprobe u pb in zircon geochronology for the mmb shows that strongly deformed granitic orthogneisses near mandalay contain jurassic 170 ma zircons that have partly recrystallized during 43 ma high grade metamorphism a hornblende syenite from mandalay hill also contains jurassic zircons with evidence of eocene metamorphic recrystallization rimmed by thin zones of 30 9 plus or minus 0 7 ma magmatic zircon the relative abundance of jurassic zircons in these rocks is consistent with suggestions that southern eurasia had an andean type margin at that time mid cretaceous to earliest eocene 120 to 50 ma i type granitoids in the mmb myeik archipelago and western myanmar confirm that prior to the collision of india an up to 200 km wide magmatic belt extended along the eurasian margin from pakistan to sumatra metamorphic overgrowths to zircons in the orthogneiss near mandalay date a period of eocene 43 ma high grade metamorphism possibly during crustal thickening related to the initial collision between india and eurasia at 65 to 55 ma this was followed by emplacement of syntectonic hornblende syenites and leucogranites between 35 and 23 ma similar syntectonic syenites and leucogranites intruded the ailao shan red river shear belt in southern china and vietnam during the eocene oligocene to miocene and the wang chao and three pagodas faults in northern thailand that most likely link with the mmb were also active at this time the complex history of eocene to early miocene metamorphism deformation and magmatism in the mmb provides evidence that it may have played a key role in the network of deformation zones that accommodated strain during the northwards movement of india and resulting extrusion or rotation of indochina

elasticity of glaucophane seismic velocities and anisotropy of the subducted oceanic crust abstract upon subduction the oceanic crust transforms to blueschists and eclogites with seismic properties that gradually become similar to those of the surrounding mantle in order to evaluate the anisotropy of blueschists and glaucophane bearing eclogites the elastic constants of glaucophane single crystal plates from the sesia lanzo zone aosta valley western alps were measured using brillouin spectroscopy at ambient conditions the mean p and s wave velocities are 7 8 and 4 6 km s 1 respectively and the anisotropy is high 38 1 av p and 27 3 av s glaucophane develops strong lpo characterized by the 001 axes concentrated sub parallel to the lineation and the 110 poles concentrated sub perpendicular to the foliation in both blueschist and eclogite rocks the measured lpo is in good agreement with viscoplastic self consistent numerical models seismic properties of glaucophane bearing blueschist and eclogite are calculated by combining measured lpo and the single crystal elastic moduli of glaucophane with the other main mineral constituents of the rock mostly epidote for blueschist and omphacite and garnet for eclogite blueschists present stronger anisotropies av p 16 1 and av s 10 3 than eclogites av p 2 9 and av s 1 7 the shear wave splitting and resulting delay times for a 7 km thick layer of eclogite or blueschist are low for the eclogite

seismic properties of subducting oceanic crust constraints from natural lawsonite bearing blueschist and eclogite in sivrihisar massif turkey abstract investigating the seismic properties of natural lawsonite lws bearing blueschist and eclogite is particularly important for constraining the seismic interpretation of subducting oceanic crust based on seismological observations to achieve this end we analyzed in detail the mineral fabrics and seismic properties of foliated lws blueschist and lws eclogites from sivrihisar massif in turkey in both blueschists and eclogites the lawsonite fabric is characterized by three different patterns 0 0 1 axes aligning sub normal to foliation and 0 1 0 axes aligning sub parallel to lineation normal type 0 0 1 axes aligning sub parallel to lineation and 1 0 0 axes aligning sub normal to foliation with a girdle sub normal to lineation abnormal type and 0 0 1 axes aligning both sub normal to foliation and sub parallel to lineation 0 1 0 axes aligning sub parallel to lineation and 1 0 0 axes aligning sub normal to foliation transitional pattern in contrast glaucophane and omphacite mostly present consistent axial fabrics with the 0 0 1 axes aligning to lineation these mineral fabrics produce whole rock seismic anisotropies with similar patterns however the variations in seismic anisotropies are mainly controlled by the rock type to a lesser extent are determined by the lawsonite fabric type and to only a small extent are affected by mineral fabric strength despite the constructive abnormal type lawsonite fabric on whole rock seismic anisotropies because of their weaker mineral fabric strength or deformation degree the abnormal type lws blueschist still exhibit comparatively lower seismic anisotropies than those normal type lws blueschist from other localities based on the calculated seismic anisotropies and velocities we estimated that when oceanic crust transforms from lws blueschist to lws eclogite with increasing subduction depth 1 p wave and max s wave polarization anisotropies reduce about 70 and 40 respectively and 2 variations of vp and vs contrasts relative to mantle peridotites are about 7 to 3 and 8 to 6 respectively these results corroborate the important roles of lws bearing blueschist and eclogite in interpreting the existence and gradual weakening of low velocity layers in subducting oceanic crust during the subduction process

medieval climate warming and aridity as indicated by multiproxy evidence from the kola peninsula russia data obtained from the low elevation khibiny mountains ca 67 68jn 33 34je on the kola peninsula northwest russia indicate a period of exceptionally warm and dry conditions commenced at ca ad 600 and was most pronounced between ca ad 1000 and 1200 warmer summer temperatures during this period coeval with the medieval warm period observed in other parts of europe are evident in a 100 140 m upward shift in the pine pinus sylvestris l limit in the khibiny mountains on average the cellulose of pine trees that grew between ca ad 1000 and 1300 is enriched by y 13 c values of around 1xcompared to the modern trees from the region further suggesting warmer summer climate than at present the medieval warm period was also accompanied by a steady decline in avalanche activity and the resulting formation of soils on the current avalanche cones in the khibiny mountains suggesting lower winter precipitation and thinner snow cover lower precipitation is also evident by currently submerged tree stumps dating to the medieval period that indicate lower lake levels on the kola peninsula in the middle of the peninsula at about ad 1000 the level of small closed basin lakes was f1 m lower than the modern time at some sites drier conditions may be attributable to decreased cyclonic activity the medieval warm and dry episode was followed at ca ad 1300 by the development of a colder climate with increased precipitation resulting in a decline in the alpine pine limits increased avalanche activity and higher lake levels that phase corresponds to the modern aeolian episode reconstructed in subarctic finland our results indicate that the medieval warm period on the kola peninsula

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

development of lattice preferred orientation in clinoamphiboles deformed under low pressure metamorphic conditions a sem ebsd study of metabasites from the aracena metamorphic belt sw spain the mechanical properties of the lower continental crust are intimately related to the rheology of calcic clinoamphibole naturally deformed clinoamphibole typically shows brittle behaviour under a wide range of deformation conditions whereas crystal plasticity is rarely observed in this study the microfabric of clinoamphiboles from metabasites deformed under low pressure medium to high temperature metamorphic conditions is presented amphiboles from all samples have developed lpo that can be attributed to different deformation mechanisms depending on deformation temperature fluid content structure and phase strength contrasts rigid body rotation of amphibole prisms within a weaker plagioclase matrix corresponds to metabasites deformed under medium deformation temperatures that show a weak layer structure and a high phase strength contrast between plagioclase and clinoamphibole lower temperatures and the presence of fluids mean that one of the studied rocks was affected also by dissolution precipitation creep and cataclastic flow in the final sample dislocation creep was accommodated by recovery and subgrain rotation dynamic recrystallization in monominerallic hornblende layers at higher temperatures which could be representative of the rheology of amphiboles in a lower continental crust at high temperature conditions

microstructures and petro fabrics of lawsonite blueschist in the north qilian suture zone nw china implications for seismic anisotropy of subducting oceanic crust abstract we conducted a detailed study on the microstructures and petro fabrics of massive and foliated lawsonite blueschist lbs in north qilian suture zone nw china the lattice preferred orientation lpo of glaucophane and lawsonite in foliated lawsonite blueschist lbs is considered to be dominantly formed by the deformation mechanism of dislocation creep and rigid body rotation respectively the lpo of glaucophane is mainly characterized by the 001 axis aligning parallel to lineation and the 100 axis and 110 pole plunging perpendicular to foliation in contrast the lpo of lawsonite features the maximum 010 axis concentrated close to lineation and the 001 axis strongly clustered normal to foliation the preferred orientation of 010 axis of lawsonite parallel to lineation is supported by a two dimensional numerical modeling using the finite volume method fvm the mineral lpos are much stronger in foliated lbs than in massive lbs in addition a kinematic vorticity analysis suggests that both pure shear dominant wm 0 18 0 26 and simple shear dominant wm 0 86 0 93 deformation regimes are present in foliated lbs the 001 axis and 010 pole of glaucophane and the 100 and 010 axes of lawsonite tend to distribute in a foliation parallel girdle in the pure shear dominant samples but simple shear dominant samples display more lineation parallel concentrations of a 001 axis of glaucophane and a 010 axis of lawsonite because the whole rock seismic anisotropies in foliated lbs are significantly higher than those in massive lbs and a counteracting effect on seismic anisotropies occurs between glaucophane and lawsonite the delay time of fast s wave polarization anisotropy induced by an actual subducting oceanic crust with a high subducting angle 45 60 is expected to range from 0 03 to 0 09 s lower bound for massive lbs and from 0 1 to 0 3 s upper bound for foliated epidote blueschist

stability of climate signal in carbon and oxygen isotope records and ring width from scots pine pinus sylvestris l in finland four hundred year long records of carbon and oxygen stable isotope ratios and ring width were measured from scots pine pinus sylvestris l from sites in northern and eastern finland responses of isotope ratios to temperature and precipitation were analysed for the 20th century carbon isotope ratios responded strongly to summer temperature at both sites whereas an influence of precipitation on the record was observed only at the site in eastern finland oxygen isotope ratios were less responsive to climatic variation than carbon at the high frequency level to shed light on the role of the possible divergence problem during last decades the climate responses were studied separately in the first and in the second half of the 20th century the responses to temperature were stable in the north but in eastern finland the significant period of summer occurred earlier during the later half of the century relationships between records were studied during the 400 a period all proxies correlated positively with each other although temporal changes occurred common forcing discovered in northern finland between carbon isotope and ring width records was weaker in the earlier period studied three climate reconstructions were created temperature reconstruction for northern finland and temperature and precipitation reconstructions for eastern finland copyright 2009 john wiley sons ltd

analysis of gravity waves generated at the top of a drainage flow abstract drainage or katabatic flows are common mesoscale circulations established as a result of differential radiative cooling of near surface air masses in sloping terrain the initial irruption of these flows with sudden shifts in wind speed and direction may result in vertical displacements of air parcels from their equilibrium position which prove to be a common source of internal gravity waves this paper illustrates this mechanism and describes the main features of the oscillations following the study of observational data gathered throughout one night during the stable atmospheric boundary layer experiment in spain 2006 sables2006 field campaign pressure differences measured by microbarometers set at different levels of a tower help to interpret the evolution of other atmospheric variables provide a detailed picture of the irruption of a drainage current and reveal the formation of gravity waves at its top the main parameters of the waves are derived from wavelet cross correlation of p

cataclastic deformation mechanism for the development of core mantle structures in amphibole core mantle structures in mineral grains have typically been interpreted as having formed during crystal plastic deformation optical scanning electron and transmission electron microscope investigations of what appear to be core mantle structures in amphibole from the cheyenne belt southeastern wyoming indicate that subgrainlike structures herein subgrains formed as a result of cataclastic rather than crystal plastic deformation optical and scanning electron microscope evidence to support a cataclastic origin include 1 the angular shape of subgrains with boundaries commonly parallel to 110 cleavage 2 the wide variety of subgrain sizes 3 the compositional zonation of the amphibole subgrains with actinolitic hornblende interiors overgrown by magnesio hornblende and 4 the observation that some of the undulatory extinction in porphyroclast cores is due to slip along cleavage planes whether dislocations observed in the amphibole grains were formed prior to cataclastic deformation work hardening or formed in response to crack propagation is unknown the implication of these observations is that core mantle structures in other minerals may at least in some cases have also formed during cataclastic deformation rather than during recovery and or recrystallization therefore optical identification of core mantle structures is not a priori evidence for a crystal plastic deformation mechanism

mediaeval climatic warming recorded by radiocarbon dated alpine tree line shift on the kola peninsula russia studies of the tree line history in northern fennoscandia provide useful evidence about the holocene environment and the region s climatic history here we report on late holocene alpine tree line movement in the khibiny low mountains on the kola peninsula northwestern russia a highly representative collection of subfossil woods above the modern tree line was obtained and 49 pine samples were radiocarbon dated their radiocarbon ages range from c 1400 to 3000 yr bp with a distinct maximum between c 800 and 1000 yr bp about cal ad 1000 to 1300 we conclude that especially during the mediaeval climatic optimum pine forests grew at least 100 140 m above the modern pine tree line in the khibiny mountains

high latitude eurasian paleoenvironments introduction and synthesis abstract this special issue developed partly from the open pages conference held in moscow in may 2002 the dominant theme of the present collection of articles is the late pleistocene and holocene paleoenvironmental history of northern eurasia from the white to the black sea and from the estonia to the kurile islands here we briefly summarize the available paleorecords from the fsu territory covering the last 1500 years a number of records allow one to distinguish the climatic pattern of the 9th 13th centuries from earlier and later colder conditions in the kola peninsula urals taymir russian plain caucasus and east siberia the 10th 12th centuries were also slightly warmer in the far east kurile islands the warming of the 14th century in several regions including the russian plain altai and central asia was at least as intense as the earlier one at ca 1 kyr before present or even warmer the available data for this time period remain controversial in the arid area of central asia records from the caspian sea area suggest moderate temperature and relatively high humidity in the first half of the millenium whereas in the tien shan mountains the beginning of the millenium seems to have been warm and dry various line of evidence suggest a climatic deterioration in the second half of the last millenium throughout the fsu including the european part siberia the caucasus the mountains of the central asia the far east and the arctic archipelagoes

holocene aeolian development in central spain chronology regional correlations and causal processes abstract extensive areas in the southern part of the duero tertiary basin central spain are covered by aeolian sands presently the aeolian system is relict but in its origin and development it can be described as a wet aeolian system climatic and environmental changes during the holocene are typified by alternating humid and arid periods these are recorded in the sedimentary record as either organic rich sandy palaeosols or clean aeolian sand respectively palaeosol dating 12 radiocarbon dated samples and stratigraphical and sedimentological analysis of several dunefields in quarries and boreholes allow the distinction of four periods of palaeosol development since the allerod aeolian sediments commonly rest on fluvial deposits which were themselves the major source area for aeolian sands these fluvial deposits have an age of about 14 000 cal yr bp the first phase of aeolian activity postdates these fluvial sediments and has an upper age of about 12 000 11 700 cal yr bp probably corresponding to the last cold oscillation of the lateglacial younger dryas the second phase ranges from about 11 500 to 9500 cal yr bp during which period the majority of dunes in the tierra de pinares area formed this is also a major phase of aeolian activity in other areas of the iberian peninsula a third and probably discontinuous phase of aeolian activity took place between 6800 and about 3000 cal yr bp the age for this phase is supported by the presence of visigothic burial sites covered by aeolian sands the presence of charred material and degraded slipfaces clearly indicate stabilisation by vegetation and the final degradation of the aeolian system at the end of the fourth aeolian phase 990 540 cal yr bp minor aeolian activity has also occurred subsequently in this area since aeolian sand movement was even reported in the 20th century the aeolian phases can be tentatively correlated with aeolian phases in europe aeolian activity tends to occur regionally during specific time intervals especially in dunefields with little human disturbance this argues for a broad climatic forcing in holocene aeolian accumulation such has been previously suggested for the little ice age the precise timing of these phases however is not strictly coincident probably due to the delayed responses of aeolian environments to climatic and subsequent vegetation change

rheological evolution of a mediterranean subduction complex abstract we use field and microstructural observations coupled to previously published p t time histories to track the rheological evolution of an intracontinental subduction complex exposed in the betic cordillera in the western mediterranean region the body of rock we focus on known as the nevado filabride complex nfc was originally part of the upper crust of the iberian margin it was subducted into hot asthenospheric mantle then exhumed back toward the surface in two stages an early stage of fast exhumation along the top of the subducting slab in a subduction channel and a late stage of slower exhumation resulting from capture by a low angle detachment fault rooted at the brittle ductile transition each stage of deformation in the nfc was punctuated by changes in the dominant deformation mechanism deformation during initial subduction of the complex was accommodated by pressure solution creep in the presence of a fluid phase the grain sizes stress magnitudes and estimated strain rates for this stage are most consistent with a thin film model for pressure solution in which the diffusion length scale is controlled by the grain size during the early stages of exhumation within the subduction channel deformation transitioned from pressure solution to dislocation creep due to increases in temperature which resulted in increases in both water fugacity and grain size each of which favor the dislocation creep mechanism differential stress magnitudes for this stage were 10 mpa and are consistent with simple models of buoyancy driven channel flow with continuing subduction channel exhumation deformation remained within the dislocation creep field because sequestration of free water into hydrous retrogressive minerals suppressed the pressure solution mechanism differential stresses progressively increased to 100 mpa near the mouth of the channel during cooling as the rocks moved into mid crustal levels during the final core complex stage of exhumation deformation was progressively concentrated into a narrow zone of highly localized strain beneath a mid crustal detachment fault localization was promoted by a transition from dislocation creep to dislocation creep accommodated grain boundary sliding at temperatures of 350 380 c grain sizes of 4 m and differential stress magnitudes of 200 mpa peak differential stress magnitudes of 200 mpa recorded just below the brittle ductile transition are consistent with byerlee s law in the upper crust assuming a vertical maximum principal stress and near hydrostatic pore fluid pressures overall the distribution of stress with temperature coupled to independent constraints on strain rate from field observations and geochronology indicate that the naturally calibrated hirth et al 2001 flow law for wet quartzite accurately predicts the rheological behavior of mid crustal rocks deforming by dislocation creep

the holocene vegetation history of the khibiny mountains implications for the post glacial expansion of spruce and alder on the kola peninsula northwestern russia

continental plate collision p t t z conditions and unstable vs stable plate dynamics insights from thermo mechanical modelling there was much debate recently on the mechanisms of continental convergence and related pressure temperature p t conditions both in modeling and petrologic community depending on the mechanisms of convergence subduction collision folding or rt instability one can argue about the possibility of large scale deviations of pressure and temperature in the accretion prism and below it from reference i e lithostatic conditions commonly used for petrologic reconstructions of evolution of exhumed metamorphic rocks these deviations can be caused for example by tectonic overpressure that as suggested in some studies may be responsible for formation of uhp ultra high pressure rocks however overpressure in exhumation zones can be built only in specific collision scenarios associated with plate coupling pure shear folding in this study we analyze conditions that define various mechanisms of convergence and consequently of exhumation these mechanisms can be represented as a superposition of 1 simple shear subduction 2 pure shear collision 3 folding and 4 rayleigh taylor instability we study these scenarios using a thermo mechanical model that accounts for brittle elastic ductile rheology surface processes and metamorphic changes it appears that stable oceanic type subduction may occur in the case of cold lithospheres tmohob550 c and relatively high convergence rates n3 5 cm yr depending on the lower crustal rheology strong or weak either the whole upper and lower crust or only the lower crust can be involved in subduction in case of weak metamorphic rheologies phase changes improve chances for stable subduction pure shear becomes a dominant mechanism when tmohon550 c or convergence rates are lower than 3 cm yr large scale folding is favored in case of tmoho 500 650 c and is more effective in the case of mechanical coupling between crust and mantle e g strong lower crust gravitational rayleigh taylor instabilities overcome other mechanisms for very high values of tmoho n800 c and may lead to development of subvertical cold spots however it is reasonable to assume that in most cases continental collision is initiated at oceanic subduction rate which is rarely slower than 5 cm yr this rate is sufficient to drive continental subduction during the first several myr of collision in this case the subduction channel is characterized by nearly lithostatic pressure conditions large scale zones of tectonic overpressure may be built outside the channel but do not affect the exhumed rocks overpressure may be built inside the channel in the short moment of its closure we suggest that most continental orogenic belts could have started their formation from continental subduction this evokes small tectonic overpressures and thus deep origin of the uhp rocks that may be brought to the surface via the suggested multi level mechanism of exhumation

wavelet analysis for geophysical applications wavelet transforms originated in geophysics in the early 1980s for the analysis of seismic signals since then significant mathematical advances in wavelet theory have enabled a suite of applications in diverse fields in geophysics the power of wavelets for analysis of nonstationary processes that contain multiscale features detection of singularities analysis of transient phenom ena fractal and multifractal processes and signal com pression is now being exploited for the study of several processes including space time precipitation remotely sensed hydrologic fluxes atmospheric turbulence can opy cover land surface topography seafloor bathymetry and ocean wind waves it is anticipated that in the near future significant further advances in understanding and modeling geophysical processes will result from the use of wavelet analysis in this paper we review the basic properties of wavelets that make them such an attractive and powerful tool for geophysical applications we dis cuss continuous discrete orthogonal wavelets and wavelet packets and present applications to geophysical processes

effect of water and stress on the lattice preferred orientation of olivine the influence of water and stress on the lattice preferred orientation lpo of olivine aggregates was investigated through large strain shear deformation experiments at high pressures and temperatures p 0 5 2 1 gpa t 1470 1570 k under both waterpoor and water rich conditions the specimens are hot pressed synthetic olivine aggregates or single crystals of olivine water was supplied to the sample by decomposition of a mixture of talc and brucite deformation experiments were conducted up to shear strain 6 using the griggs apparatus where water fugacity was up to 13 gpa at the pressure of 2 gpa the water content in olivine saturated with water increases with increasing pressure and the solubility of water in olivine at p 0 5 2 gpa was 400 1200 ppm h si several new types of lpo in olivine are found depending on water content and stress samples deformed in waterpoor conditions show a conventional lpo of olivine where the olivine 100 axis is subparallel to the shear direction the 010 plane subparallel to the shear plane type a however we identified three new types type b c and e of lpo of olivine depending on the water content and stress the type b lpo of olivine which was found at relatively high stress and or under moderate to high water content conditions is characterized by the olivine 001 axis subparallel to the shear direction the 010 plane subparallel to the shear plane the type c lpo which was found at low stress and under water rich conditions is characterized by the olivine 001 axis subparallel to the shear direction the 100 plane subparallel to the shear plane the type e lpo which was found under low stress and moderate water content is characterized by the olivine 100 axis subparallel to the shear direction the 001 plane subparallel to the shear plane observations by transmission electron microscopy tem and scanning electron microscopy sem show that the dislocations in water poor samples type a are curved and both b 100 and b 001 dislocations have a similar population numerous subgrains are seen in water poor samples in backscattered electron images in contrast water rich samples both type b and type c contain mostly b 001 dislocations and dislocations are straight and sub grain boundaries are rare compared to those in water poor samples these observations suggest that 1 dominant slip systems in olivine change with water fugacity and stress and 2 grain boundary migration is enhanced in the presence of water seismic anisotropy corresponding to the fabrics under water rich condition is significantly different from that under water poor condition consequently the relationship between seismic anisotropy and flow geometry in water rich regions is expected to be

calculating anisotropic physical properties from texture data using the mtex open source package this paper presents the background for the calculation of physical properties of an aggregate from constituent crystal properties and the texture of the aggregate in a coherent manner emphasis is placed on the important tensor properties of 2nd and 4th rank with applications in rock deformation structural geology geodynamics and geophysics we cover texture information that comes from pole figure diffraction and single orientation measurements electron backscattered diffraction or ebsd electron channelling pattern laue pattern optical microscope universal stage in particular we provide explicit formulae for the calculation of the averaged tensor from individual orientations or from an orientation distribution function odf for the latter we consider numerical integration and an approach based on the expansion into spherical harmonics this paper also serves as a reference paper for the mathematical tensor capabilities of the texture analysis software mtex which is a comprehensive freely available matlab toolbox that covers a wide range of problems in quantitative texture analysis for example odf modelling pole figure to odf inversion ebsd data analysis and grain detection mtex offers a programming interface which allows the processing of involved research problems as well as highly customizable visualization capabilities mtex is therefore ideal for presentations publications and teaching demonstrations

a complex pattern of mantle flow in the lau backarc shear wave splitting analysis of local events recorded on land and on the ocean floor in the tonga arc and lau backarc indicate a complex pattern of azimuthal anisotropy that cannot be explained by mantle flow coupled to the downgoing plate these observations suggest that the direction of mantle flow rotates from convergence parallel in the fiji plateau to north south beneath the lau basin and arc parallel beneath the tonga arc these results correlate with helium isotopes that map mantle flow of the samoan plume into the lau basin through an opening tear in the pacific plate

deformation fabrics of natural blueschists and implications for seismic anisotropy in subducting oceanic crust abstract investigations of microstructures are crucial if we are to understand the seismic anisotropy of subducting oceanic crust and here we report on our systematic fabric analyses of glaucophane lawsonite and epidote in naturally deformed blueschists from the diablo range and franciscan complex in california and the hida mountains in japan glaucophanes in the analyzed samples consist of very fine grains that are well aligned along the foliation and have high aspect ratios and strong crystal preferred orientations cpos characterized by a 1 0 0 0 0 1 pattern these characteristics together with a bimodal distribution of grain sizes from some samples possibly indicate the occurrence of dynamic recrystallization for glaucophane although lawsonite and epidote display high aspect ratios and a strong cpo of 0 0 1 0 1 0 the occurrence of straight grain boundaries and euhedral crystals indicates that rigid body rotation was the dominant deformation mechanism the p wave av p and s wave av s seismic anisotropies of glaucophane av p 20 4 av s 11 5 and epidote av p 9 0 av s 8 0 are typical of the crust consequently the fastest propagation of p waves is parallel to the 0 0 1 maxima and the polarization of s waves parallel to the foliation can form a trench parallel seismic anisotropy owing to the slowest v s polarization being normal to the subducting slab the seismic anisotropy of lawsonite av p 9 6 av s 19 9 is characterized by the fast propagation of p waves subnormal to the lawsonite 0 0 1 maxima and polarization of s waves perpendicular to the foliation and lineation which can generate a trench normal anisotropy the av s of lawsonite blueschist 5 6 9 2 is weak compared with that of epidote blueschist 8 4 11 1 calculations of the thickness of the anisotropic layer indicate that glaucophane and lawsonite contribute to the trench parallel and trench normal seismic anisotropy beneath ne japan but not to that beneath the ryukyu arc our results demonstrate therefore that lawsonite has a strong influence on seismic velocities in the oceanic crust and that lawsonite might be the cause of complex anisotropic patterns in subduction zones

the behavior of shape preferred orientations in metamorphic rocks amphiboles and jadeites from the monte mucrone area sesia lanzo zone italian western alps abstract in the eclogitic micaschists of the monte mucrone area sesia lanzo zone italian western alps we have measured in detail the eclogitic lineation at several outcrops we present observations at the markers scale this scale allowing the whole range of progressive deformations to be described populations of glaucophanes and jadeites show different statistical features which must be at least for a part produced by the distinct mechanical behavior for these markers during the alpine history the glaucophanes show a positive correlation between the intensity of preferred orientation and their aspect ratio due to a mainly rigid behavior the observed differences in shape and orientation of jadeites also show different behavior related to different retromorphic overprints we briefly discuss the implications of these observations on the significance of metamorphic lineations

omphacite fabric variation in the cabo ortegal eclogite nw spain relationships with strain symmetry during high pressure deformation petrostructural study of cabo ortegal eclogite tectonites provides an insight into the relationships between omphacite lattice preferred orientation and the fundamental deformation parameters in particular strain symmetry microstructural evidence is consistent with a tectonic origin of eclogite fabrics by coeval pyroxene plastic deformation and recrystallization under eclogite facies metamorphic conditions omphacite shape fabrics and garnet spatial distributions are anisotropic and representative of the fields of either apparent flattening or constriction omphacite lattice preferred orientations are dominated by 010 axis maxima normal to the foliation s type or flattening fabrics by 001 axis maxima parallel to the lineation l type or constriction or correspond to other fabric patterns described in the literature omphacite crystallographic fabrics are consistently asymmetric with respect to the structural framework defined by foliation and lineation this suggests that non coaxial deformation components either simple or general shear accompanied eclogite fabric development in addition to any flattening or constriction strain paths and permit shear sense determination these petrostructural features were acquired in the course of eo hercynian ductile deformation probably during deep subduction under 1 5 1 7 gpa confining pressure temperatures above 600 700 c low differential stress 15 20 mpa and slow strain rate 10 12 10 15s 1

seismic velocities from the kohistan volcanic arc northern pakistan the rocks bounded by the main mantle thrust and the northern suture in northern pakistan constitute an exhumed section through a cretaceous volcanic arc samples have been collected from all the principal lithological groups of the arc and p and s wave seismic velocities have been measured in the laboratory with the prime objective of comparing the velocities with those determined by seismic refraction experiments on modern volcanic arcs velocities were measured at up to 0 7 gpa and consideration has been given to the effect of confining pressure pore pressure and temperature and to the deformation and metamorphism involved in the himalayan collision the reconstructed velocity section through the arc shows a distinct upper crust comprising granitic dioritic intrusions metasediments and volcanics with a p wave velocity of 6 2 6 4 km s 1 depending on the parameters used beneath the lower crust of amphibolitcs and pyroxene granulite has a velocity mainly about 6 4 6 7 kms 1 though the garnet granulitcs extend to 7 8 km s 1 the more mature arc with a higher proportion of granitic rocks would show a slightly lower upper crustal velocity than the younger arc velocity inversions might be expected with a thermal gradient of as little as 10 15 c km 1 depending on the pore pressure in general the proposed velocity structure is comparable with that of volcanic arcs and with many other sections of the continental crust

a revised chronology for aeolian activity in subarctic fennoscandia during the holocene detailed sedimentological studies and parallel sampling for 14c and infra red stimulated luminescence age assays were undertaken at six sites lying beyond and below the tree line with the objective of establishing the historical development of aeolian landforms in lapland the main issues were a the timing of dune activity and processes of stabilization b the specific processes responsible for the past and contemporary activity new data indicate that many of the primary dunes were active for several millennia after deglaciation diachronous stabilization at both local and regional scales appears likely initial stabilization occurred in local interdune areas and where regional dune fields were colonized by pine generally before 7 ka local large dunes and some regional dunefields only became stable around 4 3 ka when the regional groundwater table rose and late pine colonization was possible the latest episode of aeolian activity dates from ad 1100 1650 across the area a unique deflation trigg

holocene humidity changes in northern finnish lapland inferred from lake sediments and submerged scots pines dated by tree rings conclusive evidence for a rise in water levels has been found in connection with lake sediment studies undertaken partly in collaboration with the pine megafossil sampling and dendrochronological work in northern finnish lapland the change in lake level stands is shown by slow sedimentation rate in the early to mid holocene and an increase thereafter these data indicate a regional rise in water levels during the latter part of the holocene following a relatively dry period between 8000 and 4000 bp synchronous changes also indicating rising water levels have been observed in the diatom and cladoceran assemblages of the sediment cores subfossil scots pines pinus sylvestris l have been preserved in large quantities in small lakes in lapland because in many cases the rising water level has inundated the trunks after death the position of the subfossil trunks and stumps often indicates that the pines have been growing on dry land at the sides of the lakes in which they are now submerged traces of

crystallographic preferred orientations in eclogites a review abstract during the last decades processes taking place in subduction zones have been a topic of extensive debate there are many models on a tectonic scale but knowledge of deformation at microscopic levels is essential for an understanding of the processes involved crystallographic preferred orientation cpo investigations of minerals in eclogites yield the possibility to study deformation in the crustal part of subducted oceanic lithosphere as well as subducted continental units containing basic intrusions which are frequently exhumed during continental collision from cpo data of omphacite and garnet as well as other constituent minerals in eclogites conclusions on stress and strain at depth in currently active subduction zones can be drawn as the pressure temperature and strain path of the now exhumed rocks can be unraveled this contribution provides an overview of cpo studies of eclogites concerning slip systems deformation strain and other possible cpo forming mechanisms in all major constituent mineral phases in eclogites and the implications of these microstructural data on subduction zone processes are discussed nevertheless there are still many open questions and future research is essential

p wave velocity and anisotropy of lawsonite and epidote blueschists constraints on water transportation along subducting oceanic crust p wave velocity vp and the anisotropy of lawsonite and epidote blueschists were measured up to 1 0 gpa and 400 c using the ultrasonic pulse transmission technique the slowest vp in the direction normal to foliation is similar between lawsonite and epidote blueschists 7 0 7 2 km s at 1 0 gpa and room temperature while the fastest vp in the direction parallel to lineation markedly differs between lawsonite blueschists 7 4 7 6 km s at 1 0 gpa and room temperature and epidote blueschist 7 9 km s at 1 0 gpa and room temperature crystallographic orientation measurements for main constituent min erals revealed that both epidote 0 1 0 axes fastest vp direction in epidote single crystal and amphibole 0 0 1 axes fastest vp direction in amphibole single crystal are preferentially oriented parallel to lin eation to enhance vp anisotropy of the epidote blueschist in contrast lawsonite 0 0 1 axes fastest vp direction in lawsonite single crystal are oriented subnormal to foliation whereas amphibole 0 0 1 axes are oriented subparallel to lineation so that relatively weak vp anisotropy was observed in the lawsonite blueschist our experimental results in conjunction with recent seismological observations suggest that the vp of the subducting oceanic crust at 50 km has been observed in several subducting slabs however the high vp values at 50 km depth are difficult to be explained by blueschists this indicates that the blueschist would be at least partially transformed to hydrous mineral bearing eclogite at 50 km depth in subducting oceanic crusts

plastic deformation and development of clinopyroxene lattice preferred orientations in eclogites abstract we use an anisotropic viscoplastic self consistent vpsc model to simulate the development of omphacite lattice preferred orientations lpos in response to deformation by dislocation glide in these simulations we consider slip systems identified either in naturally deformed omphacite or in experimentally deformed diopside simulated lpos reproduce very well the characteristic omphacite lpo pattern in naturally deformed eclogites a strong concentration of 001 axes sub parallel to the lineation and of 010 poles sub perpendicular to the foliation these models reconcile the interpretation of omphacite lpos in eclogites and tem observations of naturally deformed omphacite since they show that omphacite lpos in naturally deformed eclogites may develop by dislocation glide on 1 2 110 110 001 110 and 001 100 we also investigate the effect of the strain regime on the omphacite lpo development the simulations show that changes in deformation regime lead to second order variations in omphacite lpo patterns similar to those observed in eclogites such as an asymmetry of the lpo relative to the structural frame a stronger concentration of the 001 axes relative to the 010 pole concentration or a dispersion of 001 axes in the foliation plane this suggests that omphacite lpo patterns may carry information on the deformation regime simple shear transtension active during the high pressure events

physical properties of ultrahigh pressure metamorphic rocks from the sulu terrain eastern central china implications for the seismic structure at the donghai ccsd drilling site about 30 samples representing major lithologies of sulu ultrahigh pressure uhp metamorphic rocks were collected from surface exposures and exploration wells and compressional vp and shear wave vs velocities and their directional dependence anisotropy were determined over a range of constant confining pressures up to 600 mpa and temperatures ranging from 20 to 600 degreesc samples range in composition from acidic to ultramafic p and s wave velocities measured at 600 mpa vary from 5 08 to 8 64 km s and 2 34 to 4 93 km s respectively densities are in the range from 2 60 to 3 68 g cm 3 to make a direct tie between seismic measurements refraction and reflection and subsurface lithologies the experimental velocity data corresponding to shallow depths were used to calculate velocity profiles for the different lithologies and profiles of reflection coefficients at possible lithologic interfaces across the projected 5000 m chinese continental scientific drilling program ccsd crustal segment comparison of calculated in situ velocities with respective intrinsic velocities suggests that the in situ velocities at shallow depths are lowered by an increased abundance of open microcracks the strongly reflective zone beneath the donghai drill site can be explained by the impedance contrasts between the different lithologies contacts between eclogite peridotite and felsic rocks gt gneiss granitic gneiss in particular may give rise to strong seismic reflections in addition shear induced lattice preferred orientation lpo related seismic anisotropy can increase reflectivity for the explanation of the high velocity bodies 6 4 km s around 1000 m and below 3200 m depth large proportions of eclogite peridotite about 40 and 30 vol respectively are needed c 2002 elsevier science b v all rights reserved

textures of eclogites and blueschists from syros island greece inferences for elastic anisotropy of subducted oceanic crust many blueschists and eclogites are inferred to have formed from oceanic basalts in subducted slabs knowledge of their elastic behaviour is essential for reconstructing the internal structure of subduction zones the cycladic blueschist unit exposed on syros island greece contains rocks belonging to an exhumed tertiary subduction complex they were possibly part of a subduction channel a shear zone above the subducting slab in which exhumation is possible during subduction intense plastic deformation forming crystallographic preferred orientations cpo accompanied blueschist and eclogite metamorphism cpo of the constituent minerals in the collected samples was determined by time of flight neutron diffraction two samples are foliated fine grained blueschists with strong cpo rich in glaucophane zoisite and phengite two coarser grained eclogite samples rich in omphacite and clinozoisite or glaucophane have weaker cpo vp and vs anisotropies were computed from the orientation distribution function and single crystal elastic constants all samples show velocity maxima parallel to the mineral lineation and minima normal to the foliation providing important constraints on orientations of seismic anisotropy in subduction channels vp anisotropies are up to three times higher 6 5 12 in the blueschists than in the eclogites 3 4 pointing to a potentially important lithological control of elastic anisotropy in subducted oceanic crust

microstructures and lattice preferred orientations in experimentally deformed clinopyroxene aggregates microstructures and lattice preferred orientations lpo were analysed on experimentally deformed natural and hot pressed clinopyroxene aggregates in order to understand the relationship between deformation processes and evolving microstructures the lpo was measured using electron backscatter diffraction techniques in the scanning electron microscope sem microstructures were observed by polarized light microscopy and by orientation contrast in the sem natural samples sleaford bay pyroxenite were deformed in axial compression stepping tests up to 16 shortening these samples deformed mainly by twinning and dislocation glide with very little recrystallization no clear lpo evolution apart from the initial lpo could be attributed to deformation synthetic clinopyroxenite samples were hot pressed from powders of the same material with three different grain size ranges and deformed in compression stepping experiments up to 28 shortening in the samples with coarse 30 m and intermediate 20 m grain sizes deformation was dominated by dislocation creep accommodated by subgrain rotation recrystallization the recrystallized grains have sizes up to 8 m and represent 15 25 of the sampled area the sample with the finest initial grain size 5 m deformed dominantly by diffusion creep accompanied by grain boundary migration all of the hot pressed samples deformed in compression have a similar texture consisting of a girdle of c 001 axes normal to compression and a point maximum of b 010 axes and a 100 poles parallel to the compression direction the lpo of recrystallized grains was separated on spatially resolved orientation maps and shows an s type fabric with b 010 parallel to the compression axis and a random a 100 distribution the bulk fabric was largely present in the hot pressed starting material and is interpreted as the result of compaction during cold pressing at moderate strains in axial compression the initial compaction fabric has been weakly overprinted by the recrystallization fabric one hot pressed sample coarse grain size was deformed in torsion to a shear strain of 0 1 the microstructure indicates dominant dislocation creep and contains about 20 recrystallized grains the texture evolved from the rotationally symmetric compaction lpo to an oblique fabric

a 2000 year record of lake ontogeny and climate variability from the north eastern european russian arctic a lake sediment record from the north eastern european russian arctic was examined using palaeolimnological methods including subfossil chironomid and diatom analysis the objective of this study is to disentangle environmental history of the lake and climate variability during the past 2000 years the sediment profile was divided into two main sections following changes in the lithology separating the limno telmatic phase between 2000 and 1200 cal yr bp and the lacustrine phase between 1200 cal yr bp and the present owing to the large proportion of semi terrestrial chironomids and poor modern analogues a reliable chironomid based temperature reconstruction for the limno telmatic phase was not possible however the lacustrine phase showed gradually cooling climate conditions from 1200 cal yr bp until 700 cal yr bp the increase in stream chironomids within this sediment section indicates that this period may also have had increased precipitation that caused the adjacent river to overflow sub

ebsd measured lattice preferred orientations and seismic properties of eclogites we investigated the deformation mechanisms and the seismic properties of 10 eclogite samples from different localities alps norway mali and eastern china through the analysis of their microstructures and lattice preferred orientations lpo these samples are representative of various types and intensity of deformation under eclogitic metamorphic conditions omphacite and garnet lpo were determined from electron backscatter diffraction ebsd technique garnet appears to be almost randomly oriented whereas omphacite develops strong lpo characterized by the 001 axes concentrated sub parallel to the lineation and the 010 poles concentrated sub perpendicular to the foliation in order to analyze the deformation mechanisms that produced such omphacite lpo we compare our observations to lpo simulated by viscoplastic self consistent numerical models a good fit to the measured lpo is obtained for models in which the dominant slip systems are 1 2h110i 11 0 001 110 and 001 100 dominant activation of these slip systems is in agreement with tem studies of naturally deformed omphacite seismic properties of eclogite are calculated by combining the measured lpo and the single crystal elastic constants of omphacite and garnet although eclogite seismic anisotropies are very weak less than 3 for both p and s wave they are generally characterized by a maximum p wave velocity sub parallel to the lineation and by a minimum velocity approximately normal to foliation the mean p and s wave velocities are high respectively 8 6 and 4 9 km s the s wave anisotropy pattern displays complex relationships with the structural frame but the fast polarization plane generally tends to be parallel to the foliation calculated reflection coefficients show that an eclogite crust interface is generally a good reflector rc 0 1 whereas an eclogite body embedded in the upper mantle would be hardly detectable

cation ordering in omphacite and effect on deformation mechanism and lattice preferred orientation lpo we present microstructural data and lattice preferred orientations lpos of omphacites from a suite of eclogites from the adula cima lunga nappe central alps our work shows a surprisingly strong correlation between the measured lpo and the ordering state of cations in omphacite estimates of deformation temperature from metamorphic petrology together with measured omphacite compositions and lpos determine the field ordering state on the omphacite phase diagram into which each sample falls lpos dominated by l type and s type signatures are developed in samples that fall in the p2 n field ordered structure and c2 c field disordered structure respectively dislocations with b 1 2 110 or b 001 are observed in the transmission electron microscope tem in all samples the former change from a perfect dislocation in the c2 c structure to a partial in p2 n any movement of a partial dislocation requires the formation or growth of a stacking fault furthermore in order to pass an obstacle a partial dislocation has to constrict to a unit dislocation the energy to form a constriction is high in omphacite due to the large separation width thus the activity of the b 1 2 110 dislocation is hindered in the p2 n structure relative to the c2 c structure which change the balance between the two and might give rise to the different lpos

multicentennial megadrought in northern europe coincided with a global el nino southern oscillation drought pattern during the medieval climate anomaly the el nino southern oscillation enso is a pacemaker of global climate and the accu rate prediction of future climate change requires an understanding of the enso variability recently much debated aspects of the enso have included its long term past and future changes and its associations with the north atlantic and european sectors potentially in inter action with the north atlantic oscillation and the atlantic multidecadal oscillation here we present the fi rst european dendroclimatic precipitation reconstruction that extends through the alternating climate phases of the medieval climate anomaly and the little ice age we show that northern europe underwent a severe precipitation defi cit during the medieval climate anomaly which was synchronous with droughts in various enso sensitive regions worldwide while the subsequent centuries during the little ice age were markedly wetter we attribute this drought primarily to an interaction between the enso and the north atlantic oscillation and to a lesser or negligible degree to an interaction between the enso and the atlantic multidecadal oscillation

assessing meteoric water composition and relative humidity from18o and2h in wood cellulose paleoclimatic implications for southern ontario canada abstract an empirical model is presented that derives the initial isotopic composition of water used by terrestrial plants and the relative humidity that prevailed during photosynthesis from the isotopic composition of oxygen and carbon bound hydrogen in the plant cellulose the model uses fixed values for the fractionation factors that describe the evapotranspirative isotopic enrichment of leaf waters and the biochemical fractionations occurring during cellulose synthesis when applied to cellulose extracted from fossil plant matter the model can be used to generate quantitative estimates of the temperature and moisture regimes of the past the application of the model is demonstrated by consideration of 18o and 2h results on cellulose from fossil wood collected at brampton ontario the brampton data yield records of systematic changes in the temperature and moisture regimes of the eastern great lakes region over the past 11 500 a both mean annual temperature and photosynthetic humidity increased substantially from values much lower than the present at the end of the wisconsin stage to values higher than the present in the mid holocene the phase relation of the paleotemperature and paleohumidity curves engenders differentiation of the climatic history at brampton into four characteristic zones i a period of ameliorating climate predominantly much colder and drier than now lasting until about 7400 b p ii an early hypsithermal period of warm and dry conditions that transformed after 6000 a b p into iii the main hypsithermal time of warmth and pronounced moistness subsequent climatic detrioration led to establishment of iv cool moist conditions like the present sometime within the last few thousand years

tectonic evolution of the mogok metamorphic belt burma myanmar constrained by u th pb dating of metamorphic and magmatic rocks 1 the mogok metamorphic belt mmb extends for over 1500 km along the western margin of the shan thai block from the andaman sea north to the eastern himalayan syntaxis previous geochronology has suggested that a long lasting jurassic early cretaceous subduction related event resulted in emplacement of granodiorites and orthogneisses 171 120 ma and a poorly constrained tertiary metamorphic event on the basis of new u pb isotope dilution thermal ionization mass spectrometry and u th pb laser ablation multicollector inductively coupled plasma mass spectrometer geochronology presented here we propose two tertiary metamorphic events affected the mmb in burma the first was a paleocene event that ended with intrusion of crosscutting postkinematic biotite granite dikes at 59 ma a second metamorphic event spanned late eocene to oligocene at least from 37 possibly 47 to 29 ma this resulted in the growth of metamorphic monazite at sillimanite grade growth of zircon rims at 47 43 ma sillimanite muscovite replacing older andalusite and synmetamorphic melting producing garnet and tourmaline bearing leucogranites at 45 5 0 6 ma and 24 5 0 7 ma these data imply high temperature sillimanite muscovite metamorphism peaking at 680 c and 4 9 kbar between 45 and 33 ma to around 606 656 c and 4 4 4 8 kbar at 29 3 0 5 ma the later metamorphic event is older than 24 5 0 3 ma the age of leucogranites that crosscut all earlier fabrics our structural and geochronological data suggest that the mmb links north to the unexposed middle or lower crust rocks of the lhasa terrane south tibet and east to high grade metamorphic core complexes in northwest thailand

a wavelet analysis of low wind speed submeso motions in a nocturnal boundary layer in low wind regimes wind speed less than 1 5 m s 1 the nocturnal boundary layer is still inadequately understood in such conditions turbulence is weak and often intermittent whereas dynamics and total fluxes are often driven by submeso motions as a consequence the momentum mass and energy transfers are poorly represented by dispersion models in low wind conditions an important fraction of submeso motions is represented by meandering modes which can be detected through the eulerian autocorrelation functions of horizontal wind components and temperature such an approach has been proven to be reliable however a deeper insight could be useful for understanding the phenomenon especially when complex or multiple mesoscale motions simultaneously develop in this work eulerian autocorrelation functions and the morlet continuous wavelet transform were used to investigate an 8 h nocturnal period characterized by the coexistence of horizontal meandering and vertical oscillations rarely observed elsewhere this nice episode represents a good case study to compare the two used methodologies and to investigate the phenomenology of the two submeso phenomena simultaneously occurring in a low wind speed regime the two methodologies identified the same time scale for the detected meandering structures over the whole period moreover the wavelet analysis i was able to discriminate horizontal meandering and gravity waves which simultaneously developed in the second part of the analysed period ii showed that in the investigated case the horizontal meandering was not triggered by gravity waves which appeared later in the night iii highlighted how both gravity waves and meandering can contribute to an increase of the vertical turbulent energy and fluxes confirming the crucial role of submeso structures in the turbulence production during low wind regimes in stable conditions

radiocarbon dated pinus sylvestris l wood from beyond tree line on the kola peninsula russia radiocarbon dates were obtained from 24 samples of pinus sylvestris l scots pine wood recovered from sites beyond the modern conifer tree line on the kola peninsula of russia twenty one of the samples came from the shallow waters and eroding peats at the edges of two small lakes at 68 439n 35 109e located north of the modern conifer tree line three samples came from a small pond located above the modern elev ational limits of pinus sylvestris at 68 259n 35 199e the radiocarbon dates indicate that pine trees grew approximately 20 km north of the mapped modern limits of the species from 6680 bp to 3830 bp pine trees were also growing some 40 m above their modern elevational limits between 5890 bp and 3450 bp nineteen of the samples date from 6680 bp to 5070 bp suggesting that the density of trees north of the modern tree line was greatest between 7000 and 5000 bp the timing of tree line advance and greatest density on the kola peninsula are in agreement with the results of similar studies from northern fennoscandia which indicate that maximum northern and elevational extension of tree line occurred between 7000 bp and 4000 bp the general agreement between tree line reconstructions suggests that the climatic changes that promoted mid holocene tree line extension along the north atlantic margins in northern fennoscandia propagated eastward to the kola peninsula the late timing of initial pine expansion on the kola and in adjacent northern fennoscan dia remains problematic and may relate to lower winter insolation temperature regimes in the adjacent oceans or slow rates of migration

the namche barwa syntaxis evidence for exhumation related to compressional crustal folding abstract geological observation in the eastern end of the himalayas shows that the asia india suture is folded and continues southward into india and burma where the continuation of the transhimalayan plutonic complex can be identified metamorphic rocks derived from india occur structurally below the suture in the core of a regional antiform isotopic and fission track dating are consistent with the geological interpretation in addition they establish cooling exhumation of rocks from c 30 km depth within the last 4 ma rapid exhumation of deep crustal levels in mountain systems is generally related to extension subsequent to thermal softening of a thickened continental lithosphere however in the eastern himalayas we argue that exhumation is caused by c 10 mm yr 1 erosion coeval with crustal scale folding the general history of this syntaxis resembles the evolution of the western himalayas syntaxis in pakistan

nature of ophiolite occurrences along the eastern margin of the indian plate and their tectonic significance upper mesozoic to lower eocene ophiolitic rocks occur in two parallel belts along the eastern margin of the indian plate the eastern belt passes through central burma sumatra and java and coincides with a zone of gravity highs resulting from steeply dipping mafic rocks it denotes the locus of the subduction where these ophiolites were accreted just prior to middle eocene time in contrast the western belt which passes through nagaland manipur western burma and andaman is flanked to the east by a negative gravity anomaly zone in it the ophiolites occur as rootless subhorizontal bodies tectonically overlying eocene oligocene flysch sedimentary rocks they are inferred to be nappes that propagated westward from the eastern belt during late oligocene terminal collision of the indian and eurasian continental blocks ophiolite occurrences in andaman and mentawai islands belonging to the western belt are generally linked with active subduction west of the island arc this subduction began only in late miocene time and thus it could not have produced the ophiolites which had been emplaced on land much earlier

climate in southwestern ontario canada between ad 1610 and 1885 inferred from oxygen and hydrogen isotopic measurements of wood cellulose from trees in different hydrologic settings abstract oxygen and hydrogen isotopes were measured in wood cellulose and cellulose nitrate from trees that grew in different hydrologic settings in southwestern ontario canada an isotope model that accounts for isotopic fractionations associated with photosynthesis in plants was applied to the stable isotope data to infer past meteoric water isotopic composition and seasonal air moisture variations the model inferred climate data was rationalized in terms of the trees hydrologic environment and weather characteristics of the great lakes region the result is an account of summer and winter conditions in southwestern ontario for 275 years 1610 to 1885 prior to instrumental climate records conditions between 1610 and 1750 are inferred to have been cooler and drier than present this was followed by a warm moist climate interval between 1750 and 1885 during which there was an increase in winter precipitation cool dry conditions were recorded instrumentally in this region at the end of the nineteenth century

trench parallel anisotropy produced by serpentine deformation in the hydrated mantle wedge although seismic anisotropy in the upper mantle is generally attributed to the crystal preferred orientation of olivine the strong trench parallel anisotropy observed in several subduction systems is difficult to explain in terms of olivine anisotropy even if the entire mantle wedge were to act as an anisotropic source using high pressure deformation experiments ikuo katayama and colleagues show that the crystal preferred orientation of serpentine the main hydrous mineral in the upper mantle can produce the strong trench parallel seismic anisotropy observed in such subduction systems although seismic anisotropy in the upper mantle is generally attributed to the crystal preferred orientation of olivine the strong trench parallel anisotropy observed in several subduction systems is difficult to explain in terms of olivine anisotropy using high pressure deformation experiments it is now shown that the crystal preferred orientation of serpentine the main hydrous mineral in the upper mantle can produce the strong trench parallel seismic anisotropy observed in such subduction systems seismic anisotropy is a powerful tool for detecting the geometry and style of deformation in the earth s interior as it primarily reflects the deformation induced preferred orientation of anisotropic crystals1 2 although seismic anisotropy in the upper mantle is generally attributed to the crystal preferred orientation of olivine3 the strong trench parallel anisotropy delay time of one to two seconds observed in several subduction systems4 5 is difficult to explain in terms of olivine anisotropy even if the entire mantle wedge were to act as an anisotropic source here we show that the crystal preferred orientation of serpentine the main hydrous mineral in the upper mantle can produce the strong trench parallel seismic anisotropy observed in subduction systems high pressure deformation experiments reveal that the serpentine c axis tends to rotate to an orientation normal to the shear plane during deformation consequently seismic velocity propagating normal to the shear plane plate interface is much slower than that in other directions the seismic anisotropy estimated for deformed serpentine aggregates is an order of magnitude greater than that for olivine6 and therefore the alignment of serpentine in the hydrated mantle wedge results in a strong trench parallel seismic anisotropy in the case of a steeply subducting slab this hypothesis is also consistent with the presence of a hydrous phase in the mantle wedge as inferred from anomalously low seismic wave velocities7

deformation induced clinopyroxene fabrics from eclogites abstract clinopyroxene omphacite microfabric studies in eclogites are useful in characterizing the deformation that has affected deeper parts of subduction zones we present the microfabrics and tem structures of four samples representative of the various deformation types known in eclogites the 001 axis tends to be parallel to the lineation while the 010 plane is close to the foliation but these general features undergo strong variations in relation to the shape fabric in strongly lineated samples 010 tends to be spread out in a great circle normal to the lineation whereas 001 is dispersed in the foliation in the case of strongly foliated samples the slip systems identified by tem are 001 100 001 110 and 1 2 110 110 operation of dislocation creep is testified by the presence of dislocations and dislocation walls but this process alone cannot explain all the observed features particularly some aspects of the crystallographic preferred orientation hence other deformation mechanisms must be involved these may be dynamic migration recrystallization by grain boundary migration as well as mass transfer processes this study illustrates that not every crystallographic mineral preferred orientation can be explained by dislocation glide and or twinning processes alone in addition it also demonstrates that eclogite microfabrics can be used to unravel deformation parameters in subduction and or collision zones

stable carbon isotope ratios of pinus sylvestris from northern finland and the potential for extracting a climate signal from long fennoscandian chronologies stable carbon isotope ratios were measured on the latewood cellulose of 36 scots pine trees from four sites in northern finland 13c values were corrected for changes in the 13c of air and de trended to remove the effect of tree age simple linear and multivariate correlations were used to determine the nature and strength of any climate signal at three sites the dominant controls are in descending order summer sunshine temperature and antecedent precipitation at the fourth site the dominant controls are antecedent precipitation and air relative humidity while summer sunshine and temperature appear unimportant 13c values record changes in the concentration of co2 in the stomatal chambers which reflects the balance between stomatal conductance and photosynthetic rate photosynthetic rate is controlled primarily by photon flux sunshine and temperature suggesting that this dominates at three of the sites whereas stomatal conductance is controlled by air humidity and soil moisture status ant

deformation processes in eclogitic rocks evidence for the rheological delamination of the oceanic crust in deeper levels of subduction zones the deformation mechanisms and associated growth processes operating in omphacite during foliation development and veining have been studied in a km scale eclogitic ductile shear zone from the monviso meta ophiolitic complex italian western alps dislocation creep due to multiple slip and or climb is the dominant deformation mechanism whereas 100 and 001 twinning fracturing and intergranular fluid phase diffusional creep are subordinate active slip systems include 110 001 12 110 110 100 001 and 12 010 100 fracturing is interpreted in terms of brittle instabilities arising from strain and pore fluid pressure partitioning between adjacent omphacite domains the transition from plastic to brittle behaviour of rocks is cyclic in nature as the internally generated fluids can be released and trapped repetitively during progressive deformation the significance of the eclogitic shear zone is discussed in terms of a mechanically weak zone that developed during burial or at least prior to the peak of temperature at a minimum depth of 40 km in a subduction zone and which subsequently acted as a zone of detachment during a late stage of the alpine orogeny a rheological model for oceanic crust delamination in deeper levels of subduction zones is presented

a climatological study of internal gravity waves in the atmospheric boundary layer overlying the brunt ice shelf antarctica internal gravity waves are frequently observed in stably stratified regions of the atmospheric boundary layer in order to determine the statistical influence of such waves on the dynamics of the boundary layer it is necessary to compile information concerning properties of the waves such as frequency of occurrence propagation and spectral characteristics gravity wave climatologies have been compiled from relatively few locations in this paper a climatological study of gravity waves in the period range 1 20 min propagating in the stably stratified atmospheric boundary layer overlying an antarctic ice shelf is presented an extensive set of boundary layer measurements were compiled throughout 1991 surface pressure fluctuations were recorded from a spatial array of six sensitive microbarographs wind and temperature records from an instrumented mast were also available a beam steering technique has been used to determine wave parameters from the surface pressure data the microbarographs detected the presence of internal gravity waves throughout the observational campaign rootmean square pressure values were typically in the region 16 40 mb but a significant number of isolated events with amplitudes of up to 180 mb were also found wave properties have been studied in conjunction with the mean wind and temperature profiles in the boundary layer it was found that most of the wave activity did not originate locally but from shear layers aloft or more commonly from the katabatic flow regime where the ice shelf joins the antarctic continent

seismic anisotropy produced by serpentine in mantle wedge abstract trench parallel seismic anisotropy has been observed in many subduction zones in the upper mantle in this study the crystal preferred orientation cpo and seismic anisotropy of natural serpentine from val malenco in northern italy and punta bettolina in western italy are studied it is found that the 001 axes are aligned subnormal to the foliation but the 010 axes of the serpentine are aligned subparallel to the lineation which is significantly different from that produced in a recent high pressure experiment cpos of serpentine found herein can be used to explain the trench parallel seismic anisotropy in a cold mantle wedge for serpentine deformed not only at angles greater than 45 but also at low angles such as in horizontal shear from the surface indicating the broader implications of the cpo of serpentine for interpreting seismic anisotropy than previously thought it is also found that seismic anisotropy caused by the cpo of serpentine depends on the degree of serpentinization and flow geometry the seismic anisotropy increases with antigorite volume fraction the seismic anisotropy of shear waves is large i e 23 36 for samples with an antigorite volume fraction of 40 93 current data suggest that the trench parallel seismic anisotropy with a delay time of 1 2 s in the forearc mantle wedge can be attributed to the cpo of antigorite having 010 axes aligned subparallel to the flow direction and 001 axes subnormal to the flow plane