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

natural deformation fabrics of plagioclase implications for slip systems and seismic anisotropy abstract the optical and tem microstructures and fabrics of twelve naturally deformed plagioclase containing rocks of compositions from an0 an80 have been studied with a view to determining the deformation mechanisms the optical indicatrix fabrics have been recorded in all samples with respect to the foliation and lineation in general and form a girdle in the foliation plane with a high concentration of normal to the foliation in some cases the orientation of 010 and 001 cleavages or albite and pericline twins has allowed the construction of pole figures in all cases 010 has been shown to be the dominant slip plane with either 001 or 100 the dominant slip direction tem shows that the dominant slip system is 010 001 with secondary 010 100 the seismic p wave anisotropy has been calculated for the first time from the lpo data of plagioclase the anisotropy coefficient is high at around 15 the minimum p velocity is normal to the lineation in the foliation plane and the maximum is sub parallel to the foliation normal the combined information on deformation kinematics and seismic anisotropy is valuable for interpretations of deep crustal seismic sections

continental crust composition constrained by measurements of crustal poisson s ratio deciphering the geological evolution of the earth s continental crust requires knowledge of its bulk composition and global variability the main uncertainties are associated with the composition of the lower crust seismic measurements probe the elastic properties of the crust at depth from which composition can be inferred of particular note is poisson s ratio this elastic parameter can be determined uniquely from the ratio of p to s wave seismic velocity and provides a better diagnostic of crustal composition than either p or s wave velocity alone1 previous attempts to measure have been limited by difficulties in obtaining coincident p and s wave data sampling the entire crust2 here we report 76 new estimates of crustal spanning all of the continents except antarctica we find that on average increases with the age of the crust our results strongly support the presence of a mafic lower crust beneath cratons and suggest either a uniformitarian craton formation process involving delamination of the lower crust during continental collisions followed by magmatic underplating or a model in which crust formation processes have changed since the precambrian era

seismic structure in the southeastern china using teleseismic receiver functions abstract the southeastern margin of china is an ideal area to study the modern plate interactions the previous models however are poorly constrained with respect to the geometry due to the sparse coverage here we present new observations from a temporary array with 20 stations in southeastern china we isolated converted seismic phases in the p and s wave coda to generate receiver function from the structure of the crust and upper mantle by using h k stacking and common conversion point stacking the geometry of discontinuities above was imaged along the southeastern chinese coastline the ccp section shows moho dips gently northeastward with a mean depth of 30 km the 410 and 660 km discontinuities are at the depth close to iasp91 model this means that we have not seen any significant anomaly from moho and mantle transition zone that corresponded with the geodynamics of plate subducting instead we found that the crust was ruptured by min river fault to depth of the moho we provide a 2d map of moho topography by combining our crustal thickness to that from permanent stations active seismic and obs offshore profiles the map is consistent with previous studies and shows a crust that thins coastward and southwestward in the rate of 1 5 km per 100 km we image the lithosphere asthenosphere boundary at a depth of 60 to 70 km by using s wave to combine with the p wave our crustal structure suggests that min river fault certainly plays an important role in adjusting regional stress field induced by plate interactions in the study area our lithospheric thickness is more consistent with a very strongly attenuated continental lithosphere given the close proximity to the coast this might suggest that the lithospheric mantle transitions to oceanic before the crust does alternatively we may infer that the continental lithosphere has been thermally eroded in this region

composition and tectonic evolution of the chinese continental crust constrained by poisson s ratio article i nfo we have measured both p and s wave velocities vp and vs and poisson s ratios of 60 typical ultrahigh pressure uhp metamorphic rock samples from the chinese continental scientific drilling ccsd main and pre pilot holes and surface outcrops in the sulu dabie orogenic belt at hydrostatic confining pressures up to 850 mpa the experimental results together with those compiled in handbook of seismic properties of minerals rocks and ores ji s c wang q xia b 2002 handbook of seismic properties of minerals rocks and ores polytechnic international press montreal 630 pp reveal that except for monomineralic rocks such as quartzite serpentinite anorthosite limestone and marble the rest of the rock types have poisson s ratios falling along an upward convex curve determined from the correlations between elastic moduli and density poisson s ratios increase with density as the lithology changes from granite felsic gneiss and schist through diorite syenite intermediate gneiss and metasediment to gabbro diabase amphibolite and mafic gneiss and then decrease as the rocks become ultramafic in composition eclogite has a higher density but a lower poisson s ratio than peridotite the results were applied to constrain the crustal composition and tectonic evolution of the chinese continental crust based on crustal thickness h and poisson s ratio from 248 broadband seismic stations measured using teleseismic receiver function techniques the north china yangtze south china and northeast china blocks and songpan ganzi terrane are dominated by low b0 26 and moderate 0 26 b0 28 values n70 suggesting the dominance of felsic composition in the crust the lhasa terrane qiangtang terrane and indochina block are characterized by high proportions 33 42 of measurements with very high values 0 30 and h is found for the south china block northeast block lhasa block qiangtang terrane and indochina block indicating either tectonic thickening of the felsic upper and middle crust by folding and thrusting or the removal of mafic layers from the lower crust into the upper mantle by delamination

structure of the crust beneath the southeastern tibetan plateau from teleseismic receiver functions abstract southeastern tibet marks the site of presumed clockwise rotation of the crust due to the india eurasian collision and abutment against the stable sichuan basin and south china block knowing the structure of the crust is a key to better understanding of crustal deformation and seismicity in this region here we analyze recordings of teleseismic earthquakes from 25 temporary broadband seismic stations and one permanent station using the receiver function method we find that the crustal thickness decreases gradually from the tibetan plateau proper to the sichuan basin and yangtze platform but that significant intra crustal heterogeneity exists on shorter lateral scales 0 30 are detected beneath the southeastern margin of tibet but in the sichuan basin and southeastern yangtze platform the values are close to the global average combined with high regional heat flow and independent evidence for mid crustal layers of high electric conductivity the large intra crustal s wave velocity reduction 12 19 and the intermediate to high average crustal poisson s ratios are consistent with partial melt in the crust beneath parts of southeastern tibet these results could be used in support of deformation models involving intra crustal flow with the caveat that significant lateral variation in location and strength of this flow may occur

elasticity of plagioclase feldspars elastic properties are reported for eight plagioclase feldspars that span compositions from albite nasi3alo8 to anorthite casi2al2o8 surface acoustic wave velocities measured using impulsive stimulated light scattering and compliance sums from high pressure x ray compression studies accurately determine all 21 components of the elasticity tensor for these triclinic minerals the overall pattern of elasticity and the changes in individual elastic components with composition can be rationalized on the basis of the evolution of crystal structures and chemistry across this solid solution join all plagioclase feldspars have high elastic anisotropy a the direction perpendicular to the b and c axes is the softest direction by a factor of 3 in albite from albite to anorthite the stiffness of this direction undergoes the greatest change increasing twofold small discontinuities in the elastic components inferred to occur between the three plagioclase phases with distinct symmetry c1 i1 and p1 appear consistent with the nature of the underlying conformation of the framework linked tetrahedra and the associated structural changes measured body wave velocities of plagioclase rich rocks reported over the last five decades are consistent with calculated hill averaged velocities using the current moduli this confirms long standing speculation that previously reported elastic moduli for plagioclase feldspars are systematically in error the current results provide greater assurance that the seismic structure of the middle and lower crusts can be accurately estimated on the basis of specified mineral modes chemistry and fabric

normal mode instabilities of a time dependent coastal upwelling jet the linear stability of a nearly time periodic nonlinear coastal upwelling downwelling circulation over alongshore uniform topography driven by a time periodic wind stress is investigated using numerical methods the near periodic alongshore uniform basic flow is obtained by forcing a primitive equation numerical model of coastal ocean circulation with periodic wind stress disturbance growth on this nearperiodic flow is explored in linear and nonlinear model simulations numerous growing normal modes are found in the linear analyses at alongshore scales between 4 and 24 km these modes vary in cross shore structure and timing of maximum disturbance growth rate one group of modes in the 6 5 8 5 km alongshore scale range bears strong resemblance to the ensemble average disturbance structures observed in perturbed nonlinear model simulations these modes are of a mixed type exhibiting both strong baroclinic and barotropic energy exchange mechanisms with maximum disturbance growth occurring during the transition from upwelling favorable to downwelling favorable winds nonlinear disturbance growth is characterized by similar structures at these same scales but with significant exchange of energy between disturbances at different alongshore scales such that overall disturbance energy accumulates at the longest domain scales and gradually propagates offshore mainly in the pycnocline over numerous forcing cycles

s wave velocities and anisotropy of typical rocks from yunkai metamorphic complex and constraints on the composition of the crust beneath southern china abstract in order to constrain the interpretation of seismic data from receiver functions and deep profiles of the crust beneath southern china cathaysia and yangtze blocks we have measured s wave velocities v s and splitting as a function of hydrostatic confining pressure up to 650 mpa for 22 representative samples i e granite diorite felsic gneiss and mylonite amphibolite schist and marble from the yunkai metamorphic complex china that represent the crystalline basement beneath the region the experimental data were combined with electron backscattering diffraction ebsd analysis of rock forming minerals to constrain variations of v p v s ratios and understand the origin of seismic anisotropy the crusts beneath the yangtze and cathaysia blocks have different average thicknesses h 35 4 6 3 km and 29 8 1 8 km respectively but display almost the same v p v s values 1 73 0 08 and 1 74 0 04 respectively these ratios correspond to an average of bimodally distributed granitic and gabbroic lithologies which are dominant respectively in the upper and lower crusts instead a homogeneous andesitic composition of the overall crust positive and negative correlations between h and v p v s occur in west and east parts of southern china respectively the negative correlation indicates basaltic underplating from a partially molten mantle wedge above the subducting pacific plate into the southern china crust whereas the positive correlation implies that much larger thinning strain has taken place in the high temperature mafic lower crust high temperature than in the low temperature felsic upper crust during mesozoic cenozoic tectonic extension

shear wave velocities anisotropy and splitting in high grade mylonites shear wave velocities have been measured for 10 high grade granulite and upper amphibolite facies mylonites from the snowbird tectonic zone canada at various pressures up to 600 mpa in order to explore the kinematic significance of shear wave splitting in the lower crust at 600 mpa vs anisotropy ranges from 11 in amphibolitic mylonites to 2 in granulite facies pyroxene bearing and tonalitic mylonites hornblende bearing granitic mylonites display intermediate vs anisotropy 6 7 vs anisotropy is lower than vp anisotropy in hornblende rich mylonites whereas vs anisotropy is higher than vp anisotropy in feldspar rich mafic tonalitic granitic and diatexitic mylonites shear wave splitting is pronounced in rocks displaying strong s wave anisotropy in most of the high grade mylonites studied the polarization direction of the first arrival vs1 corresponds to the extension lineation x when propagation is parallel to y perpendicular to lineation and parallel to foliation or to the y direction when propagation is parallel to x for all other propagation directions the polarization direction of vs1 is oblique to the x y and z directions therefore it may be difficult to infer the structural implications of shear wave splitting in lower continental crustal shear zones if one does not know 1 the orientation of the propagation and fast vibration directions with respect to in situ lineation and foliation and 2 the lattice preferred orientation of in situ rock forming minerals

the structural setting of the song ma region vietnam and the indochina south china plate boundary problem abstract the song ma song da region of northern vietnam contains the song ma anticlinorium a polydeformed polymetamorphosed early palaeozoic island arc forearc terrane accreted to the south china plate in siluro devonian times the song ma anticlinorium is not an indosinian subduction zone and nor is the post triassic post cretaceous song ma fault the song ma fault is one of many northwest trending post cretaceous high angle reverse oblique slip faults and thrusts responsible for shortening and strike slip transposition of northern vietnam folds penecontemporaneous with this faulting include the song ma anticlinorium which is formed probably of thrust ramp folds the faulting and penecontemporaneous folding developed during oligocene sinistral strike slip on the song hong fault and was reactivated during pliocene quaternary times we conclude that the present plate boundary is a broad deformation zone between da nang and the song hong and that parts of the south china plate extend well to the south of the song hong fault

seismic velocities poisson s ratios and potential auxetic behavior of volcanic rocks abstract the present compilation of p and s wave velocities vp and vs for 395 dry and 664 wet basalt 231 dry and 63 wet rhyolite samples provide a new database for evaluating the porosity dependence of vp vs and poisson s ratio and the potential auxetic behavior i e negative poisson s ratio of volcanic rocks the correlation is always positive for the water saturated rocks but can be either positive rhyolite or negative basalt for dry rocks depending on the poisson s ratio of the non porous solid matrix 0 auxetic behavior cannot occur in wet volcanic rocks but may appear in dry basalts with extremely high porosity 70 for basalt such that a re entrant foam structure forms the auxeticity of highly porous volcanic rocks such as pumice and reticulite will be suppressed by infiltration of water into the rocks hence volcanic rocks cannot be auxetic in nature if their vesicles are filled with water under the laboratory conditions however a transition from conventional to auxetic behaviors in pumice and reticulite is expected to occur by changing the degree of water saturation these results provide a set of basic parameters for the modeling of ground deformation and temporal and spatial variations in vp vs vp vs ratio as precursors of volcanic eruption or volcanic edifice collapse

temperature trends over the past five centuries reconstructed from borehole temperatures for an accurate assessment of the relative roles of natural variability and anthropogenic influence in the earth s climate reconstructions of past temperatures from the pre industrial as well as the industrial period are essential but instrumental records are typically available for no more than the past 150 years therefore reconstructions of pre industrial climate rely principally on traditional climate proxy records each with particular strengths and limitations in representing climatic variability subsurface temperatures comprise an independent archive of past surface temperature changes that is complementary to both the instrumental record and the climate proxies here we use present day temperatures in 616 boreholes from all continents except antarctica to reconstruct century long trends in temperatures over the past 500 years at global hemispheric and continental scales the results confirm the unusual warming of the twentieth century revealed by the instrumental record but suggest that the cumulative change over the past five centuries amounts to about 1 k exceeding recent estimates from conventional climate proxies the strength of temperature reconstructions from boreholes lies in the detection of long term trends complementary to conventional climate proxies but to obtain a complete picture of past warming the differences between the approaches need to be investigated in detail

rheological contrast between garnet and clinopyroxene in the mantle wedge an example from higashi akaishi peridotite mass sw japan abstract garnet clinopyroxenites occur within foliated dunite in the higashi akaishi peridotite mass located within the subduction type high pressure low temperature sanbagawa metamorphic belt the garnet clinopyroxenites contain 3 80 garnet and garnet and clinopyroxene are homogeneously distributed garnet crystals contain extensive regular dislocation arrays and dislocation networks suggesting that dislocation creep was the dominant deformation mechanism analyses of crystallographic orientation maps indicate similar grain sizes and aspect ratios for garnet and clinopyroxene regardless of modal composition indicating that these minerals deformed with similar degree of plasticity moreover indexes of crystallographic fabric intensity i e j index and m index for both garnet and clinopyroxene tend to increase with increasing modal composition of garnet fourier transform infrared spectroscopy analysis revealed that water content in garnet is 60 ppm whereas that in clinopyroxene is 70 ppm olivine crystal preferred orientations in the higashi akaishi peridotite mass characterized by 0 0 1 0 1 0 are thought to have developed during deformation under wet conditions consequently we argue that the presence of water could act to enhance garnet plasticity during deformation the results reveal contrasting influences of water on the deformation of garnet and diopside under wet conditions compared with dry the strain rate increases by two orders of magnitude for garnet but by an order of magnitude for diopside given the influence of water on the creep strength of garnet garnet within the higashi akaishi mass may have become significantly as weak as clinopyroxene during deformation

tidal dynamics of the water table in beaches tidal motions of the water table height inside a sloping beach are investigated via field measurements and theoretical considerations only the movements forced by the tide are considered so a beach with negligible wave activity was chosen for the field measurements the data show that even in the absence of precipitation the time averaged inland water table stands considerably above the mean sea level also the water table at a fixed point inside the beach is far from sinusoidal even though its variation is forced by an essentially sinusoidal tide this latter effect is due to the boundary condition along the sloping beach face which acts as a highly nonlinear filter the observed behavior of the water table is explained in terms of perturbation extensions to the classical deep aquifer solution one extension deals with the nonlinearity in the interior the other with the boundary condition at the sloping beach face

geophysical profiling across the sulu ultra high pressure metamorphic belt eastern china abstract the largest ultra high pressure metamorphic uhpm belt in the world is located along the dabie sulu region which tectonically belongs to the east part of the central orogenic belt of china integrated geophysical investigations of using deep seismic reflection mt and geothermal observations have been carried out in the sulu area since 1997 the results of integrated interpretation suggest the existence of three features 1 a rift beneath the lianshui basin by the jiashan xionshui fault 2 a special crustal pattern called the magmatic multi arch structure occurs beneath the northern sulu uhpm zone and 3 a northwest dipping regional thrust crosses the sulu crust representing the intracontinental subduction of the yangtze craton beneath the sulu metamorphic belts after collision between the yangtze and sino korean cratons a magmatic multi arch structure consists of some arched reflectors that occur in both the lower and the upper crust where arched reflectors coincide with granitoid plutons the multi arch structures are common in eastern china where many mesozoic granitoid plutons of different scales occur the crustal structures in the sulu metamorphic belts resulted from intensive dynamic processes following the triassic collision between the yangtze and sino korean cratons the formation and exhumation of uhpm rocks followed the collision and then intracontinental subduction of the yangtze craton beneath the dabie sulu terranes took place in the early and middle jurassic in the late jurassic the sulu lithosphere turned to an extensional regime large scale granitic intrusions occurred in eastern china these likely resulted from lithospheric thinning and asthenospheric uplifting the granitic intrusions came to a climax during the cretaceous and were followed by rifting along existing faults in the early eogene resulting in many petroleum basins the granitoid emplacement that generated the magmatic multi arch structure and the rift were consequences of the lithospheric thinning process and deep intracontinental subduction of the yangtze craton beneath the sulu metamorphic belt might partially contribute to the lithospheric thinning

seismic anisotropy and shear wave splitting in lower crustal and upper mantle rocks from the ivrea zone experimental and calculated data to quantify the relationships between anisotropy s wave splitting and tectonics we determined the seismic properties of lower crustal and upper mantle rocks outcropping in the ivrea zone northern italy we obtained p and s wave seismic velocities by laboratory direct velocity measurements and or by calculations based on the modal compositions of the rocks the lattice preferred orientations lpos and the single crystal stiffness coefficients measured p and s wave velocities 6 0 7 5 km s 1 and 3 6 4 2 km s 1 are typical of the lower crust the p wave anisotropy is in the range 0 10 shear wave birefringence is in the range 0 0 0 6 km s 1 with typical values between 0 0 and 0 2 km s 1 in many cases the birefringence is clearly related to fabric elements foliation lineation mafic rocks such as anorthosite or pyroxene bearing gabbros exhibit low p wave anisotropies 5 and low shear wave birefringences less than 0 1 km s 1 in contrast the seismic properties of felsic rocks such as biotite bearing gneisses and mafic rocks such as amphibolites display high vp anisotropy 10 and strong birefringence 0 3 km s 1 biotite and amphibole preferred orientations clearly control seismic anisotropy and particularly shear wave splitting in these rocks maximum splitting is observed in directions parallel to the foliation with the fast split shear wave polarized parallel to the foliation plane to have an overview of the seismic properties of this lower crustal section at a broader scale we calculated from our data the anisotropic seismic properties of several hypothetical samples that are perhaps more representative of the regional anisotropy than each sample individually for instance the average lower crustal sample displays an anisotropy of 5 5 for p waves and a birefringence around 0 14 km s 1 for s waves propagating parallel to the foliation we observe little splitting for waves propagating at high angle to the foliation

ensemble based estimates of the predictability of wind driven coastal ocean flow over topography abstract the predictability of coastal ocean circulation over the central oregon shelf a region of strong wind driven currents and variable topography is studied using ensembles of 50 day primitive equation ocean model simulations with realistic topography simplified lateral boundary conditions and forcing from both idealized and observed wind time series representative of the summer upwelling season the main focus is on the balance relevant to practical predictability between deterministic response to known or well predicted forcing uncertainty in initial conditions and sensitivity to instabilities and topographic interactions large ensemble and single simulation variances are found downstream of topographic features associated with transitions between along isobath and cross isobath flow which are in turn related both to the time integrated amplitude of upwelling favorable wind forcing and to the formation of small scale eddies simulated predictability experiments are conducted and model fo

magmatism along the southeast margin of the yangtze block precambrian collision of the yangtze and cathysia blocks of china the time and the environment of formation of igneous rocks along the southern margin of the yangtze continental block in southern anhui province and northeastern jiangxi province china are discussed sm nd dating for samples from two ophiolite suites give ages of about 1 ga late proterozoic granodiorites in the study area have ages of about 0 9 ga and have normal intrusive relations against banxi group metamorphic country rocks trace element abundances and initial nd isotope ratios for ophiolite and proterozoic granodiorites are consistent with formation in an island arc environment in contrast sr and nd isotopes for mesozoic granitoids of the region suggest that they are products of remelting of crustal sources similar to the basement of the yangtze block these relations do not support a recently proposed mesozoic overthrust tectonic model for southeast china but rather favor a late precambrian collision history for the yangtze and cathysia blocks

crustal evolution of the hercynian belt of western europe evidence from lower crustal granulitic xenoliths french massif central abstract granulite facies lower crustal xenoliths scavenged by the tertiary basaltic pipes of bournac and roche pointue massif central france have been analysed for major and trace elements and radiogenic sr nd isotope ratios they display wide variations in major elements rare earth elements and isotopes 87 sr 86 sr 0 7041 0 7216 nd 11 9 to 1 5 which tend to correlate with the three different rock types encountered basic and acidic meta igneous and metasediments the basic liquids are of calc alkaline affinity and cumulates are abundant there is a gap in silica content between the basic and acid meta igneous xenoliths the isotopic compositions suggest mixing of old pre existing continental crust represented by the metasediments and mantle derived basic melts which represent juvenile addition to the crust during the hercynian orogeny the basic meta igneous rocks have been contaminated during their emplacement into the crust whereas the surrounding metasediments have suffered partial fusion and contamination by the same liquid producing the hercynian granitoids which have nd and sr initial ratios identical to those of the lower crustal xenoliths the residue from melting may be represented by the acid meta igneous rocks some of which have positive eu anomalies these results indicate that an important basaltic underplating event occurred during the evolution of hercynian orogenic belt although the exact timing of the underplating requires further constraint

petrofabric p wave anisotropy and seismic reflectivity of high grade tectonites abstract ji s salisbury m h and hanmer s 1993 petrofabric p wave anisotropy and seismic reflectivity of high grade tectonites tectonophysics 222 195 226 in order to understand seismic anisotropy and its influence on the reflectivity of lower crustal fault zones we have undertaken experimental measurements of p wave velocities up to 600 mpa for 20 granulite and upper amphibolite facies mylonites from the snowbird tectonic zone canada the rocks whose composition ranges from ultramafic to felsic have experienced extremely large ductile strain it is found that the amphibolitic mylonites exhibit significant vp anisotropy 6 13 at 600 mpa whereas the pyroxene bearing granulite facies mylonites and the quartz or feldspathic tonalitic granitic and diatexitic mylonites are quasi isotropic in order to constrain interpretation of the measured vp properties microstructural analyses have been systematically performed in the samples studied it is shown that the interaction between feldspar and quartz or pyroxene and the absence of amphibole cause anisotropy in the granulite facies mylonites to be low the amphibolitic mylonites are strongly anisotropic because of a large volume fraction of hornblende with strong lpo 001 lineation and 100 foliation the anisotropy pattern in the amphibolitic mylonites is consistently orthorhombic vp x vp y vp z where x is parallel to stretching lineation y is normal to the lineation in the foliation plane and z is normal to the foliation plane but the anisotropy pattern in the mica rich mylonites is transversely isotropic vp x vp y vp z if sufficiently large volumes of the crust display such patterns this difference may be an important indicator for kinematic analysis in the middle to lower crust using modern seismic techniques the study demonstrates that while seismic reflectivity is strongly lithology controlled fabric induced anisotropy can both enhance and decrease seismic reflectivity hence the discontinuity of seismic reflections along ductile shear zones in the lower crust is not necessarily indicative of the discontinuity of the shear zones but may indicate changes in composition or metamorphic grade

effects of hydrogeological and climate change on the subsurface thermal regime in the sendai plain abstract we estimated the effects of hydrogeological and surface temperature warming on subsurface thermal regime from the temperature depth profiles and hydrological data of groundwater quality both in the quaternary and tertiary systems in the sendai plain as a preliminary step toward reconstruction of climate changes annual mean air temperature in the plain has increased about 1 5 c in the last 70 years and this surface warming resulted in low or negative thermal gradient however anomaly of thermal gradient was recognized in not all temperature depth profiles groundwater chemical compositions and stable isotope data d and 18 o show that the groundwater flow system has marked difference between those of tertiary and quaternary systems calculated results of three dimensional groundwater flow and heat transport model ensure the above hypothesis and shows that thermal gradient changes at close to basement of the quaternary system the differences in groundwater flow systems are expressed as subsurface thermal gradient anomalies in the temperature depth profiles in the sendai plain furthermore one dimensional numerical analyze including the effect of surface warming indicates that calculated profile has departure from steady state line at depths in 60 80 m agree well with observed one

magnitude and symmetry of seismic anisotropy in mica and amphibole bearing metamorphic rocks and implications for tectonic interpretation of seismic data from the southeast tibetan plateau we calibrated the magnitude and symmetry of seismic anisotropy for 132 mica or amphibole bearing metamorphic rocks to constrain their departures from transverse isotropy ti which is usually assumed in the interpretation of seismic data the average bulk vp anisotropy at 600 mpa for the chlorite schists mica schists phyllites sillimanite mica schists and amphibole schists examined is 12 0 12 8 12 8 17 0 and 12 9 respectively most of the schists show vp anisotropy in the foliation plane which averages 2 4 for phyllites 3 3 for mica schists 4 1 for chlorite schists 6 8 for sillimanite mica schists and 5 2 for amphibole schists this departure from ti is due to the presence of amphibole sillimanite and quartz amphibole and sillimanite develop strong crystallographic preferred orientations with the fast c axes parallel to the lineation forming orthorhombic anisotropy with vp x vp y vp z effects of quartz are complicated depending on its volume fraction and prevailing slip system most of the mica or amphibole bearing schists and mylonites are approximately transversely isotropic in terms of s wave velocities and splitting although their p wave properties may display orthorhombic symmetry the results provide insight for the interpretation of seismic data from the southeast tibetan plateau the n s to nw se polarized crustal anisotropy in the sibumasu and indochina blocks is caused by subvertically foliated mica and amphibole bearing rocks deformed by predominantly compressional folding and subordinate strike slip shear these blocks have been rotated clockwise 70 90 around the east himalayan syntaxis without finite eastward or southeastward extrusion in responding to progressive indentation of india into asia

implications of crustal property variations for models of tibetan plateau evolution shear coupled teleseismic p waves sampling the interior of the tibetan plateau provide evidence of systematic variations in crustal structure the crust thins by up to 20 km from south to north with a concomitant increase in poisson s ratio from normal values in the south to unusually high values in the north this suggests that the crust of the northern plateau is partially melted due to high temperatures these changes imply spatial and perhaps temporal variations in the way the elevation of the high plateau is created and maintained

detailed moho geometry beneath southeastern china and its implications on thinning of continental crust abstract we used teleseismic p wave receiver functions and the h stacking method to obtain crustal thicknesses beneath 121 permanent stations in the middle lower yangtze craton and its adjacent areas using nearly 700 teleseismic events in 2009 and 2010 we then combined them with results of previous work to map detailed moho geometry in the region the results show that in addition to overall thin crust of 30 km in thickness throughout southeastern china there are two ns oriented narrow zones of extensive crustal thinning in the region the western zone passes through the xiangzhong basin the jianghan basin and the nanxiang basin while the eastern zone follows the tanlu fault the two merge in the south forming a v shaped thin crust area in southeastern china we suggest different geodynamic mechanisms of crustal thinning north and south of the 29 n parallel crustal thinning in the northern part was caused by the westward subduction of the pacific plate and its eastward migration of the trench crustal thinning in the southern part is mainly controlled by the interaction between the philippine and the eurasia plates the change of subduction polarity from the northward subduction of the philippine plate under eurasia to the eastward high angle subduction of the eurasian plate under the philippine plate in taiwan is responsible for diverse extensional stress regime in south china the v shape crustal thinning zone was formed due to a mantle corner flow in the rear of subducting eurasia plate in a form of hot fingers growing from the mantle corner flow to cause the moho uplift in the southern part of the region

ne sw trending hepu hetai dextral shear zone in southern china penetration of the yunkai promontory of south china into indochina abstract the ne sw trending hepu hetai shear zone extends for about 480 km along the boundary between guangdong and guangxi provinces in the southern part of south china field mapping and kinematic analyses indicate that the zone is characterized by dextral ductile strike slip deformation with an estimated displacement along the fault zone in excess of 500 km studies of synkinematic phengite and gas liquid inclusions in quartz within mylonite suggest that the ductile shear deformation occurred under medium temperature pressure conditions of the greenschist facies and 40ar 39ar analyses of muscovite yield ages of 213 195 ma based on these data and late paleozoic mesozoic paleogeographic data for southern china we propose that the hepu hetai shear zone originated via the penetration of the yunkai promontory of south china into indochina during the triassic

seismic imaging of the transitional crust across the northeastern margin of the south china sea abstract crustal structure across the passive continental margin of the northeastern south china sea scs is presented based on a deep seismic survey cooperated between taiwan and china in august 2001 reflection data collected from a 48 hydrophone streamer and the vertical component of refraction reflection data recorded at 11 ocean bottom seismometers along a nw se profile are integrated to image the upper 1 6 2 4 km s lower 2 5 2 9 km s and compacted 3 4 5 km s sediment the upper 4 5 5 5 km s middle 5 5 6 5 km s and lower 6 5 7 5 km s crystalline crust successively the velocity model shows that the thickness 0 5 3 km and the basement of the compacted sediment are strongly varied due to intrusion of the magma and igneous rocks after seafloor spreading of the scs furthermore several volcanoes and igneous rocks in the upper middle crust 7 10 km thick and a high velocity layer 0 5 km thick in the lower crust of the model are identified as the ocean continent transition oct below the lower slope in the northeastern margin of the scs a thin continent nw of the oct and a thick oceanic crust se of the oct in the continental margin of the northeastern scs are also imaged but these transitional crusts cannot be classified as the oct due to their crustal thickness and the limited amount of the volcano the magma and the high velocity layer the extended continent next to the gravity low and a sag zone extended from the sw taiwan basin may have resulted from subduction of the eurasian plate beneath the manila trench whereas the thick oceanic crust may have been due to the excess volcanism and the late magmatic underplating in the oceanic crust after seafloor spreading of the scs

rayleigh wave phase velocity maps of tibet and the surrounding regions from ambient seismic noise tomography ambient noise tomography is applied to the significant data resources now available across tibet and surrounding regions to produce rayleigh wave phase speed maps at periods between 6 and 50 s data resources include the permanent federation of digital seismographic networks five temporary u s program for array seismic studies of the continental lithosphere passcal experiments in and around tibet and chinese provincial networks surrounding tibet from 2003 to 2009 totaling 600 stations and 150 000 interstation paths with such a heterogeneous data set data quality control is of utmost importance we apply conservative data quality control criteria to accept between 5000 and 45 000 measurements as a function of period which produce a lateral resolution between 100 and 200 km across most of the tibetan plateau and adjacent regions to the east misfits to the accepted measurements among passcal stations and among chinese stations are similar with a standard deviation of 1 7 s which indicates that the final dispersion measurements from chinese and passcal stations are of similar quality phase velocities across the tibetan plateau are lower on average than those in the surrounding nonbasin regions phase velocities in northern tibet are lower than those in southern tibet perhaps implying different spatial and temporal variations in the way the high elevations of the plateau are created and maintained at short periods 20 s very high velocities are imaged in the tarim basin the ordos block and the sichuan basin these phase velocity dispersion maps provide information needed to construct a 3 d shear velocity model of the crust across the tibetan plateau and surrounding regions

tidal effects on variations of fresh saltwater interface and groundwater flow in a multilayered coastal aquifer on a volcanic island jeju island korea summary we conducted various field studies at the seawater intrusion monitoring wells located in the eastern part of jeju island korea to observe the tidal effect on groundwater seawater flow in the coastal aquifer studies included monitoring the fluctuations of groundwater and tide levels electrical and temperature logging and 2 d heat pulse flowmeter tests according to time series analysis tidal effects on groundwater level reached up to 3 km inland from the coastline water level variation was more sensitive to tidal fluctuations near the coast and more related to rainfall toward inland areas temporal and spatial variations in the shape and location of the freshwater saltwater interface were analyzed using data from nine monitoring wells the results indicated that the interface toe is located at a distance of 6 8 km from the coastline and its location was related to geological layers present long term seasonal variations revealed no major changes in the interface minor variations were due to moving boundary conditions induced by tidal fluctuations using the two dimensional heat pulse flowmeter groundwater flow directions and velocities at four tidal stages were measured on three monitoring wells drilled into the multilayered aquifers this direct measurement enabled us to relate the differences of flow velocities and directions with geology and tidal fluctuations combining the results of ec logging and flowmeter tests we found a zone where freshwater and saltwater moved alternately in opposite directions as influenced by the tidal fluctuations integrating various physical logging and flowmeter data with water level fluctuations improved our understanding of the behavior of fresh and seawater flow in the coastal aquifers

formation and tectonic evolution of southeastern china and taiwan isotopic and geochemical constraints abstract the southern part of china consists of the proterozoic yangtze craton and the phanerozoic south china foldbelts including the himalayan foldbelt of taiwan models for continental growth have been many and controversial isotopic and geochemical data from mesozoic and younger granitoids and sediments are used here to place constraints on the tectonic evolution of southeastern china and to evaluate whether the young phanerozoic foldbelts are representative of old rejuvenated landmass whether they characterize crustal accretion through successive subduction processes hence suggesting a net growth of continental mass or whether they represent some intermediate situation available sm nd isotopic data for phanerozoic granitoids and metasediments from the south china foldbelts and taiwan invariably show proterozoic model ages t dm ranging from 1 to 2 5 ga with a mean of 1 54 0 30 1 ga all rocks have negative nd t values 2 to 15 suggesting variable but important contributions of old continental materials to the sources of the phanerozoic rocks obviously they do not represent wholesale growth of continental mass the granitoids of the south china foldbelts have multiple origins as viewed from their chemical and isotopic characteristics secular geochemical variation has been established for inland granitoids of proterozoic to mesozoic age their high i sr values 0 710 0 737 suggest that most granitoids are essentially anatectic products of ancient continental crust this is compatible with remelting via microcontinental collision or terrane accretion repeated intracrustal reprocessing by partial fusion and differentiation has undoutedly contributed to important mineralization mesozoic granitoids excluding a type alkaline granites in the coastal region and taiwan show relatively low i sr 0 705 0 710 and high nd values implying that greater amounts of mantle components have been added to ancient continental material in the generation of these rocks this means that mesozoic magmatism in the coastal region resulted from subduction of a paleo pacific plate kula beneath the asian continent the overall geochemical evidence seems to be consistent with a model of serial collisions between microcontinental blocks for the bulk of the south china foldbelts the latest arc continent collision began about 4 ma ago in eastern taiwan

oblique stepwise rise and growth of the tibet plateau two end member models of how the high elevations in tibet formed are i continuous thickening and widespread viscous flow of the crust and mantle of the entire plateau and ii time dependent localized shear between coherent lithospheric blocks recent studies of cenozoic deformation magmatism and seismic structure lend support to the latter since india collided with asia 55 million years ago the rise of the high tibetan plateau likely occurred in three main steps by successive growth and uplift of 300 to 500 kilometer wide crustal thrust wedges the crust thickened while the mantle decoupled beneath gently dipping shear zones did not sediment infilling bathtub like of dammed intermontane basins formed flat high plains at each step the existence of magmatic belts younging northward implies that slabs of asian mantle subducted one after another under ranges north of the himalayas subduction was oblique and accompanied by extrusion along the left lateral strike slip faults that slice tibet s east side these mechanisms akin to plate tectonics hidden by thickening crust with slip partitioning account for the dominant growth of the tibet plateau toward the east and northeast

the role of pre existing mechanical anisotropy on shear zone development within oceanic mantle lithosphere an example from the oman ophiolite structural and fabric analysis of the well exposed hilti mantle section oman ophiolite suggests that shear zone development which may have resulted from oceanic plate fragmentation was influenced by pre existing mantle fabric present at the paleoridge detailed structural mapping in the mantle section revealed a gently undulating structure with an east west flow direction a nw se strike slip shear zone cuts across this horizontal structure the crystal preferred orientation cpo of olivine within the foliation is dominated by 010 axial patterns rather than more commonly observed 010 100 patterns suggesting that the horizontal flow close to the moho involved non coaxial flow olivine cpo within the shear zone formed at low temperature is characterized by 001 100 patterns and a sinistral sense of shear the olivine cpo becomes weaker with progressive mylonitization and accompanying grain size reduction and ultimately develops into an ultra mylonite with a random cpo pattern the olivine 010 axis is consistently sub vertical even where the horizontal foliation has been rotated to a sub vertical orientation within the shear zone these observations suggest that the primary mechanical anisotropy mantle fabric has been readily transformed into a secondary structure shear zone with minimum modification this occurred as a result of a change of the olivine slip systems during oceanic detachment and related tectonics during cooling we propose that primary olivine cpo fabrics may play a significant role in the subsequent structural development of the mantle thus the structural behavior of oceanic mantle lithosphere during subduction and obduction may be strongly influenced by initial mechanical anisotropy developed at an oceanic spreading center

foundering of lower island arc crust as an explanation for the origin of the continental moho a long standing theory for the genesis of continental crust is that it is formed in subduction zones however the observed seismic properties of lower crust and upper mantle in oceanic island arcs differ significantly from those in the continental crust accordingly significant modifications of lower arc crust must occur if continental crust is indeed formed from island arcs here we investigate how the seismic characteristics of arc crust are transformed into those of the continental crust by calculating the density and seismic structure of two exposed sections of island arc kohistan and talkeetna the kohistan crustal section is negatively buoyant with respect to the underlying depleted upper mantle at depths exceeding 40 kilometres and is characterized by a steady increase in seismic velocity similar to that observed in active arcs in contrast the lower talkeetna crust is density sorted preserving only relicts about ten to a hundred metres thick of rock with density exceeding that of the underlying mantle specifically the foundering of the lower talkeetna crust resulted in the replacement of dense mafic and ultramafic cumulates by residual upper mantle producing a sharp seismic discontinuity at depths of around 38 to 42 kilometres characteristic of the continental mohorovicic discontinuity the moho dynamic calculations indicate that foundering is an episodic process that occurs in most arcs with a periodicity of half a million to five million years moreover because foundering will continue after arc magmatism ceases this process ultimately results in the formation of the continental moho

fabric related velocity anisotropy and shear wave splitting in rocks from the santa rosa mylonite zone california the directional dependence of p and s wave velocities have been measured at pressures up to 600 mpa and temperatures up to 700 c in rocks from the santa rosa mylonite zone southern california during tectonism these were progressively deformed from granodiorite protolith to mylonite and ultimately phyllonite the mineralogical and chemical composition of protolith and mylonite is nearly identical thus these rocks provide excellent material for documenting the effect of microstructural and textural changes on rock anisotropy velocity anisotropy increases significantly with the degree of deformation whereas average velocities and densities do not change at low pressure 50 mpa the velocity anisotropy ranges from 1 7 in granodiorite up to 19 in phyllonite and is due to both oriented microfractures and crystallographic preferred orientation at high pressure 600 mpa the residual anisotropy up to 12 is mainly due to preferred mineral orientation in particular of biotite significant shear wave splitting is measured parallel to the foliation plane and shows a good correlation with the biotite texture these observations confirm that oriented microcracks and preferred orientation of minerals should be taken into account in the interpretation of seismic reflection and refraction data in terranes with deformed rocks

crustal structure beneath china from receiver function analysis 1 we collected and processed a large amount of high quality broadband teleseismic waveform data recorded by the 48 chinese national digital seismic network stations to estimate large scale lateral variations of crustal thickness and vp vs ratio hence poisson s ratio beneath china a statistical method was used to select mutually coherent receiver functions at each station which yielded over 200 traces for most of the stations with the conventional h the crustal thickness and vp vs ratio approach there is a large trade off between h and consequently multiple maxima are frequently observed in the h domain we introduced a weight function that measures the coherence between the p to s conversion and the reverberation phases at each h grid to reduce the trade off a 4th root stacking method was further applied to reduce uncorrelated noise relative to the linear stack these modifications turned out to be very effective in reducing the h trade off and yielded reliable estimates of crustal thickness and vp vs ratio the crust beneath eastern china is as thin as 31 33 km and the underlying moho is relatively flat and sharp in the western part of china the crust is considerably thicker and shows large variations the moho is observed at about 51 km depth along the tian shan fold system and about 84 km deep beneath the central part of the tibetan plateau the transition occurs at the so called n s belt between about 100 and 110 e which is featured by unusually high seismicity and large gravity anomalies the average vp vs ratio over the mainland china crust is about 1 730 0 249 significantly lower than the global average 1 78 0 27 of the continental crust this lower vp vs ratio may suggest a general absence of mafic lowermost crustal layer beneath china

the early triassic indosinian orogeny in vietnam truong son belt and kontum massif implications for the geodynamic evolution of indochina new structural field data at various scale and 40ar 39ar geochronological results from the basement rocks in the truong son belt and kontum massif of vietnam confirm that ductile deformation and high temperature metamorphism were caused by the early triassic event of the indosinian orogeny in the range of 250 240 ma a compilation of isotopic data obtained in other countries along the sibumasu indochina boundary broadly indicates same interval of ages this tectonothermal event is interpreted as the result of a synchronous oblique collision of indochina with both sibumasu and south china inducing dextral and sinistral shearing along e w to nw se and n s fault zones respectively the collision along song ma follows the northwards subduction of indochina beneath south china and the subsequent development of the song da zone which in turn was affected by the late triassic indosinian phase of shortening within the indochina plate internal collisions occurred coevally in the early triassic as along the poko suture at the western border of the kontum massif

pressure dependence and anisotropy of p wave velocities in ultrahigh pressure metamorphic rocks from the dabie sulu orogenic belt china implications for seismic properties of subducted slabs and origin of mantle reflections the compressional wave velocities vp pressure derivatives vpv and anisotropy a of three types of eclogites and country rocks from the dabie sulu ultrahigh pressure uhp metamorphic belt china have been measured under confining pressures up to 800 mpa type 1 eclogites which are coarse grained and subjected to almost no retrograde metamorphism experienced recovery accommodated dislocation creep at peak metamorphic conditions in the diamond stability field type 2 eclogites are fine grained reworked type 1 materials that experienced recrystallizationaccommodated dislocation creep under quartz coesite boundary conditions during the early stage of exhumation type 3 eclogites are retrogressed samples that were overprinted by significant amphibolite facies metamorphism during a late stage of exhumation within the crust type 1 eclogites are richer in al2o3 and mgo but poorer in sio2 and na2o than type 2 and type 3 eclogites anisotropy of type 1 and type 2 eclogites is generally low b4 because volumetrically important garnet is elastically quasi isotropic while type 3 eclogites can exhibit high anisotropy n10 due to the presence of strongly anisotropic retrograde minerals such as amphibole plagioclase and mica the transition of the pressure dependence of velocity from the poroelastic to elastic regimes occurs at a critical pressure pc which depends mainly on the density and distribution of microcracks and in turn on the exhumation history of rocks the vp pressure relationship can be expressed by vp a lnp 2 blnp c pvpc and vp v0 dp pzpc where p is the confining

the poisson ratio of the australian crust geological and geophysical implications the poisson ratio which depends on the vp vs ratio provides much tighter constraints on the crustal composition than either the compressional or the shear velocity alone the crustal poisson ratio can be determined from the joint analysis of the travel times of waves converted at the moho and of crustal multiples reflected at the top of the moho we have analyzed the records of the permanent stations installed on the australian continent complemented by the data of the skippy experiment the results reveal substantial variations in the poisson ratio in the different tectonic units for the proterozoic crust an increase of the poisson ratio with increasing crustal thickness is systematically observed while for the phanerozoic crust the poisson ratio tends to decrease for increasing crustal thicknesses these observations are in remarkable agreement with the results of the deep seismic soundings that were performed in the former soviet union the variations observed in the proterozoic provinces can perhaps be explained by underplating of mafic materials at the base of the crust fl 2000 elsevier science b v all rights reserved

saltwater intrusion in the unconfined coastal aquifer of ravenna italy a numerical model summary the ravenna pine forests represent an historical landmark in the po river plain they have great environmental historical and tourist value the san vitale pine forest is located 10 km north of the town it is surrounded by an urban area the city industrial infrastructure and the waterworks of the agricultural drainage system most land in this area is below mean sea level as a result no natural freshwater hydraulic gradient contrasts the density gradient of saltwater in the last century many events land subsidence land reclamation and drainage urban and industrial development and gas and deep groundwater extractions coastal dune destruction led to the intrusion of large volumes of brackish and saline groundwater today the freshwater in this coastal aquifer consists of low salinity water lenses floating on the saltwater wedge this study is aimed at understanding how past and present human activities have affected the saltwater intrusion process in the phreatic aquifer and how the predicted future sea level rise will affect the salinisation process we used a numerical model to quantify these effects on the density dependent groundwater flow hydraulic head and salinity distribution seepage and salt load fluxes to the surface water system the simulations show that over the last century artificial subsidence and heavy drainage started the salinisation process in the study area and a relative sea level rise will accelerate the increase in salt load in the coming decades affecting the entire aquifer climatic conditions in the area result in limited precipitations throughout the year and preclude efficient aquifer recharge especially in spring and summer when saltwater seepage is extensive the lack of a continuous coastal dune system favors salt wedge intrusion

a determination of the three dimensional seismic properties of anorthosite comparison between values calculated from the petrofabric and direct laboratory measurements bernard eront and david mainprice zaboratoire de tectonophysique i h iversit montpe lier ii montpe lier france nikolas i christensen department of earth and atmospheric sciences purdue unh ersity west lafayette btdiana we have undertaken a coinparative study of the seisnfic properties of an anorthosite the seisnfic properties have been calculated froin the lattice preferred orientation lpo of plagioclase 90 by volume and olivine 10 by voluine and the elastic constants of these minerals laboratory measurements of vp 24 directions and vs 6 directions have been made on the same sample at room temperature and pressures up to 1 0 gpa the twe techniques agree with 0 1 km s for all orientations studied when the voigt averaging method is used hill and reuss averaging methods give calculated velocities significantly lower than the experimental ones a study of the difference between the velocity values given by the two methods reveals a systematically larger departure in orientations normal to the foliation the orientation dependent difference between the two tedmiques can be explained if there are small errors in the elastic constants for single crystal plagioclase used in the initial calculations the axial lpo symmetry of the plagioclase with all the crystallographic b axes parallel to the specimen symmetry axis allowed us to calculate c22 norinal to 010 directly from the laboratory measurement of vp some constraints can be put on c22 c44 c66 c12 and c23 on average our data require 10 modification of the single crystal constants reported by ryzhova 1964

p wave velocities anisotropy and hysteresis in ultrahigh pressure metamorphic rocks as a function of confining pressure 1 the chinese continental drilling project ccsd has drilled to a depth of 5100 m at maobei n34 40 e118 67 donghai county jiangsu province in the eastern segment of the dabie sulu ultrahigh pressure uhp metamorphic terrane the borehole which penetrated through all of the high velocity layers and seismic reflectors observed within the uppermost crust on seismic refraction and reflection profiles reveals the main lithologies to be coesite bearing felsic gneisses metabasic rocks i e amphibolite retrogressed and non retrogressed eclogites and ultramafic rocks i e garnet peridotite and serpentinite p wave velocities anisotropy and hysteresis of 31 typical ccsd core samples and 35 representative surface samples collected from the sulu uhp belt were measured at hydrostatic confining pressures up to 800 mpa the velocity pressure curves can be well described by a four parameter exponential equation derived from theory v p v0 dp b0 exp kp where v0 is the projected velocity at zero pressure if pores cracks were absent d is the intrinsic pressure derivative of velocity in the linear elastic regime b0 is the initial velocity drop caused by the presence of pores cracks at zero pressure and k is the decay constant of the velocity drop in the nonlinear poro elastic regime the seismic hysteresis is caused by irreversible changes in grain contact increases in microcrack aspect ratios and reduction of void space during the pressurization depressurization cycle the statistical properties of p wave velocities in the uhp rocks provide an important set of basic information for the interpretation of field seismic data from the root zones of continental convergent orogenic belts and modern and ancient subduction zones

a new calibration of seismic velocities anisotropy fabrics and elastic moduli of amphibole rich rocks 1 a large portion of the middle to lower crust beneath the continents and oceanic island arcs consists of amphibolites dominated by hornblende and plagioclase we have measured p and s wave velocities vp and vs and anisotropy of 17 amphibole rich rock samples containing 34 80 vol amphibole at hydrostatic pressures p up to 650 mpa combined petrophysical and geochemical analyses provide a new calibration for mean density average major element contents mean vp p and vs p coefficients intrinsic vp and vs anisotropy poisson s ratios the logarithmic ratio rs p and elastic moduli of amphibole rich rocks the vp values decrease with increasing sio2 and na2o k2o contents but increase with increasing mgo and cao contents the maximum 0 38 0 40 km s and minimum s wave birefringence values occur generally in the propagation direction parallel to y and normal to foliation respectively amphibole plays a critical role in the formation of seismic anisotropy whereas the presence of plagioclase quartz pyroxene and garnet diminishes the anisotropy induced by amphibole crystallographic preferred orientations cpos the cpo variations cause different anisotropy patterns illustrated in the flinn diagram of vp x vp y vp y vp z plots the results make it possible to distinguish in terms of seismic properties the amphibolites from other categories of lithology such as granite granodiorite diorite gabbro diabase felsic gneiss mafic gneiss eclogite and peridotite within the earth s crust hence amphibole aligned by dislocation creep anisotropic growth or rigid body rotation is the most important contributor to the seismic anisotropy of the deep crust beneath the continents and oceanic island arcs which contains rather little phyllosilicates such as mica or chlorite

exposed cross sections through the continental crust implications for crustal structure petrology and evolution abstract the continental crust is exposed in cross section at numerous sites on the earth s surface these exposures which appear to have formed by obduction along great faults during continental collision may be recognized by exposures of deep crustal rocks exhibiting asymmetric patterns of metamorphic grade and age across the faults and by distinctive bouguer anomaly patterns reflecting dipping basement structure and an anomalously deep mantle from an examination of five complexes which meet these criteria it is concluded that the most prominent layering in the crust is not compositional but metamorphic the lower crust consists of granulite facies rocks of mafic to intermediate composition while the intermediate and shallow levels consist predominantly of amphibolite facies gneisses and greenschist facies supracrustal rocks respectively post metamorphic granitic intrusions are common at intermediate to shallow levels position of discontinuities in refraction velocity where present commonly correspond to changes in composition or metamorphic grade with depth the continental crust is characterized by lateral and vertical heterogeneities of varying scale which are the apparent cause of the complex seismic reflections recorded by cocorp field observations coupled with geochemical data indicate a complex evolution of the lower crust which can include anatexis multiple deformation polymetamorphism and reworking of older crustal material the complexity of the crust is thus the result of continuous evolution by recycling and metamorphism through time in a variety of tectonic environments

crustal thicknesses and poisson s ratios in china by joint analysis of teleseismic receiver functions and rayleigh wave dispersion 1 a new grid search scheme which extends the stacking h algorithm to multi layered crustal models and fits observed dispersion of surface wave group velocity simultaneously is proposed to estimate the thickness poisson s ratio and average p wave speed of the crust we first apply it to a synthetic data of a 2 layered crustal model then we show the results analyzing records from 45 permanent broadband seismic stations in china the estimates at six stations agree well with results from deep seismic sounding profiles the crustal thicknesses agree in general with the crust 2 0 model we find that the poisson s ratio in the yangtze platform is rather low compared with the other two platforms the stations along the southeast coast of china have higher poisson s ratios the poisson s ratio of the whole region tends to increase as the average p wave velocity

evolution of c axis pole figures and grain size during dynamic recrystallization results from experimentally sheared quartzite 1 quartzite samples experimentally sheared at conditions where subgrain rotation and grain boundary migration recrystallization are active show a striking change in the c axis crystallographic preferred orientation cpo with increasing shear strain up to 8 and degree of recrystallization up to 100 we used optical methods to determine the c axis cpo for the bulk samples and for porphyroclasts and recrystallized grains separately and to track the strengths of the cpos in five different orientation domains with increasing the c axis pole figure evolves from a broad peripheral maximum indicative of basal a slip to an inclined single girdle with two maxima indicative of rhomb a slip and finally an elongate single maximum at the girdle center indicative of prism a slip throughout this sequence the fabric skeleton rotates with the sense of shear the bulk preferred c axis orientation results from growth and shrinkage of differently oriented crystallographic domains grain boundary density analysis indicates that the size of prism a recrystallized grains is 1 5 times that of average and 2 times that of rhomb grains indicating that prism a slip is significantly easier at our experimental conditions this inference is supported by autocorrelation function analysis of the various orientation domains and how they evolve with strain similar progressive changes in c axis cpo are observed in quartzites naturally sheared at conditions where grain boundary migration recrystallization operates these results indicate that achievement of microstructural and mechanical steady state requires high strain and complete recrystallization

tidal effects on aquifer thermal regime an analytical solution for coastal ecosystem management summary an analytical model was developed to estimate the groundwater temperature change in the transition zone intermediate zone between seawater and fresh groundwater due to seawater and fresh groundwater temperature change in coastal aquifers a set of type curves was developed in such a way that the curves account for the advection effect of groundwater flow and can be applied under different aquifer and tidal conditions to estimate the resulting temperature distribution the proposed method will be important in evaluating the long term effects of urbanization and climate change on coastal ecosystems where limited observation wells are available the practical applicability of the composed methodology was tested in the sendai plain continuous 1 h water level from april 2005 to july 2007 and temperature from may 2007 to february 2008 observations were made at three aquifer depths in each observation well at four locations to examine the temporal and spatial variations time series analysis was performed to find the correlations of the tidal and groundwater level fluctuations results of the preliminary analysis and the time series analysis indicated that the groundwater level within 20 m depth from the ground surface is more sensitive to the recharge from precipitation while the depths below 20 m are greatly influenced by the tidal fluctuations reasonably high cross correlation 0 74 was found in tides with water level fluctuations and it was also noted that the tidal effect on groundwater level fluctuation and temperature distribution significantly decays as the distance from the coast increases the simulated temperature distribution from the proposed analytical solution shows good agreement with the observed temperature records among the hydrogeologic parameters hydraulic conductivity has a robust influence in determining the pattern of temperature distribution within the sea water and fresh groundwater boundaries verified results in the sendai plain indicated that the individual effect of seawater temperature change has a more profound effect on temperature change near to the coast than a fresh groundwater temperature change combined effects of temperature change at two boundaries within the range of 1 c will lead to a 0 4 1 c temperature change at a distance 500 m away from the coast where in general the coastal wetlands are located these figures may be significant for maintaining or achieving the ecological balance of coastal ecosystems and the findings of this research will assist planners and decision makers in coastal environment management programs

components and episodic growth of precambrian crust in the cathaysia block south china evidence from u pb ages and hf isotopes of zircons in neoproterozoic sediments abstract detailed lam icpms u pb dating and lam mc icpms lu hf isotope analysis were carried out on zircons from nine samples of basement metamorphic rocks in the southern cathaysia block south china the chemical compositions of these metamorphic rocks and zircon morphology indicate that their protoliths were sedimentary zircon u pb dating results show they mainly formed during the late neoproterozoic the precambrian crust of the cathaysia block can be divided into two distinct tectonic domains the wuyishan terrane to the northeast and the nanling yunkai terrane to the southwest the nearly e w boundary between these two terranes is also supported by geophysical petrological and geochemical evidence and the basement rocks of the two terranes are comprised of different components the wuyishan terrane is characterized by dominant paleoproterozoic 1 86 ga and lesser neoarchean magmatism and the southern central part of the terrane suffered strong neoproterozoic and early paleozoic tectonothermal reworking the zircon data suggest that there were five important episodes of juvenile crust generation 3 6 ga 2 8 ga 2 6 2 4 ga 1 85 ga and 0 8 0 7 ga in the wuyishan terrane strong paleoproterozoic 1 85 ga magmatism in northern wuyishan and neoproterozoic 0 8 0 7 ga magmatism in central and southern wuyishan both principally involved the remelting of old crust with minor input of juvenile material in contrast the nanling yunkai terrane contains abundant neoarchean and grenvillian zircons some evidence of mesoproterozoic activity and rare paleo to meso archean and neoproterozoic zircons u pb ages and hf isotopic compositions of the detrital zircons from the late neoproterozoic to early paleozoic meta sedimentary rocks in the nanling yunkai area suggest that the growth of juvenile crust mainly occurred at 3 6 ga 3 3 ga 2 5 2 6 ga 1 6 ga 1 0 ga and 0 8 0 7 ga neoarchaean 2 6 2 5 ga grenvillian 1 0 ga and neoproterozoic 0 8 0 7 ga magmatism mainly involved the recycling of old crust minor remnants of 4 1 ga crust may remain in the terrane this crustal history is distinct from that of the wuyishan terrane and analogous to those recorded for the eastern india east antarctic domain of northern gondwanaland suggesting that they probably were once linked

sst wind interaction in coastal upwelling oceanic simulation with empirical coupling observations primarilyfromsatellites haveshownastatisticalrelationshipbetweenthesurfacewindstress and underlying sea surface temperature sst on intermediate space and time scales in many regions inclusive of eastern boundary upwelling current systems in this paper this empirical sst wind stress relationship is utilized to provide a simple representation of mesoscale air sea coupling for an oceanic model forced by surface winds namely the regional oceanic modeling system roms this model formulation is applied to an idealized upwelling problem with prevailing equatorward winds to determine the coupling consequencesonflow sst stratification andwindevolutions theinitiallyuniformwindfieldadjuststhrough coupling to a cross shore profile with weaker nearshore winds similar to realistic ones the modified wind stress weakens the nearshore upwelling circulation and increases sst in the coastal zone the sst induced wind stress curl strengthens offshore upwelling through ekman suction the total curl driven upwelling exceeds the coastal upwelling the sst induced changes in the nearshore wind stress field also strengthen and broaden the poleward undercurrent the coupling also shows significant impact on the developing mesoscale eddies by damaging cyclonic eddies more than anticyclonic eddies which leads to dominance by the latter dynamically this is a consequence of cyclones with stronger sst gradients that induce stronger wind perturbations inthis particularupwellingproblemandthatarethereforegenerally moresusceptibletodisruption than anticyclones at finite rossby number the net effect is a weakening of eddy kinetic energy

shear velocity and vp vs ratio structure of the crust beneath the southern margin of south china continent abstract we here present the results of the inverse modeling of crustal s phases recorded from a 400 km long seismic profile with azimuth nearly n30w from lianxian near hunan province to gangkou island near guangzhou city guangdong province in the southern margin of south china continent the finding in this case is that many shot gathers provided by this wide angle seismic experiment show relatively strong reflected and refracted s phases in particular some crustal refractions sg waves and moho reflections sms waves or simply sm waves the p wave velocity structure of the crust and uppermost mantle was already obtained through the interpretation of vertical component shot gathers now with constraints introduced by the p wave velocity architecture and after picking up s wave traveltime data on the seismograms we have obtained the s velocity model of the crust by adjusting these traveltimes but keeping the geometry of the crustal reflectors our results demonstrate 1 the average crustal s velocity is about 3 64 km s to the northwest of the wuchuan sihui fault and 3 62 km s to the southeast of this fault 2 relatively constant s velocity of about 3 42 km s for the upper crust 3 55 km s for the middle crust and laterally varying shear velocity around 3 82 km s for the lower crust 3 correspondingly vp vs ratio is 1 73 for the upper crust 1 71 for the middle crust and 1 74 for the lower crust both shear velocities and vp vs ratio correlate well with the major active faults that break the study area and show significant changes especially in the upper crust high poisson s ratio 1 8 is observed at shallow depth beneath the minzhong depression to the southeast of the wuchuan sihui fault and the huiyuan depression in the southern margin of south china continent in contrast a very low vp vs ratio 1 68 is observed between 8 and 14 km depth beneath huiyuan at deeper depth a high vp vs ratio 1 76 is observed in the lower crust beneath the minzhong depression

3 d seismic velocities calculated from lattice preferred orientation and reflectivity of a lower crustal section examples of the val sesia section ivrea zone northern italy summary to quantify the seismic properties of lower crustal rocks and to better constrain the origin of the lower crustal seismic reflectivity we determined the complete 3 d seismic properties of a lower crustal section eight representative samples of the main lithologic and structural units outcropping in the val sesia ivrea zone were studied in detail the seismic velocities were calculated using the single crystal stiffness coefficients and the lattice preferred orientation lpo of each mineral in all samples the 21 stiffness coefficients characterizing the elastic behaviour of each rock are determined mafic and ultramafic rocks such as pyroxenite and pyroxenebearing gabbros display complex shear wave properties these rocks are weakly birefringent maximum 0 1 km s and it is difficult to find consistent relationships between the seismic properties and the rock structure on the other hand seismic properties of deformed felsic rocks are essentially controlled by mica they display strong s wave birefringence 0 3 km s and relatively high vp anisotropy 7 6 per cent amphibole also strongly influences the rock birefringence patterns for both kind of rocks the foliation is highly birefringent and the fast polarized shear wave is systematically oriented parallel to the foliation we show that the number of mineral phases in the rock strongly controls the anisotropy the seismic anisotropy has a complex role in the p wave reflectivity compared to the isotropic case anisotropy enhances the reflection coefficient for about 60 per cent of the possible lithological interfaces for 40 per cent of the interfaces the reflection coefficient is much lower when one considers the medium as anisotropic

timing of formation and exhumation of the montagne noire double dome french massif central new u pb monazite zircon and xenotime ages date the late carboniferous crystallization of the anatectic vialais granite in the montagne noire axial zone and the high temperature deformation and metamorphism of the augen gneiss ordovician granite protolith from which the granite was likely derived the u pb monazite ages obtained from the augen gneiss 308 3 ma late kinematic vialais granite 303 4 ma and post kinematic leucogranite 298 2 ma bracket the high temperature deformation and metamorphism at 310 300 ma clearly postdating regional contraction and nappe emplacement 320 ma the planar linear and locally linear fabrics in the augen gneiss outline a regional scale double dome structure caroux and espinouse sub domes containing smaller km scale upright folds compared to the caroux sub dome the larger migmatitic espinouse sub dome contains abundant leucosome leucogranite bodies and late kinematic intrusions vialais granite the vialais granite displays a weak magmatic foliation that defines the main layering of the espinouse migmatite ellipsoidal quartz sillimanite nodules concentrated above the roof of the granite recorded an increment of strain vertical shortening e ne elongation during granite emplacement and crystallization consistent with the extension event that exhumed the domes these new geochronological and structural data suggest that the montagne noire double dome formed in a pull apart structure within a dextral strike slip system upright folding in the sub domes has been traditionally assigned to a regional contraction event alternatively we propose that local contraction is associated with the convergence of low viscosity crust beneath the upper crust pull apart dynamic models of extension of hot crust indicate that contraction at depth is generated by flow of low viscosity orogenic crust converging and rising to fill the gap created by upper crust extension this interpretation solves the long standing problem of apparent coeval contraction and extension in the montagne noire double dome and establishes migmatite dome emplacement in strike slip corridors as a style of late variscan tectonics

finite amplitude evolution of instabilities associated with the coastal upwelling front abstract a primitive equation model is used to study the finite amplitude evolution of instabilities associated with the coastal upwelling front simulations of increasing complexity are examined that represent idealizations of summer conditions off the oregon coast including cases with steady and with time variable wind in a domain with alongshore uniform bathymetry and with time variable wind in a domain with realistic oregon coast bathymetry the numerical results indicate that the fastest growing mode in this system has approximately an 8 10 km alongshore wavelength but that once the disturbances grow to finite amplitude the predominant alongfront scale increases rapidly because of nonlinear effects separation of the total kinetic energy into contributions from the alongshore average flow and perturbation about that average shows that the initial growth of the perturbation kinetic energy is due to potential energy conversion but transfer of energy from the kinetic energy of the alongshore average

seismic structure in the northeastern south china sea s wave velocity and vp vs ratios derived from three component obs data a nearly 500 km long seismic profile with reflective and refractive wide angle ocean bottom seismometer obs data and multi channel seismic mcs data was acquired across the northeastern continental margin of the south china sea scs the s wave crustal structure and vp vs ratios have been obtained based on a previously published p wave model using the software raylnvr modeling of vertical and horizontal component obs data yields information on the seismic crustal velocities lithology and geophysical properties along the obs 2001 seismic profile s wave velocities in the model increase generally with depth but exhibit high spatial variability particularly from the shelf to the upper slope of the northeastern scs margin vp vs ratios also reveal significant lithological heterogeneity dongsha penghu uplift dpu is a tectonic zone with a thicker crust than adjacent areas and a high magnetic anomaly with a vp vs of 1 74 and a p wave velocity of 5 0 5 5 km s the dpu primarily consists of felsic volcanic rocks in the upper crust and is similar to the petrology of zhejiang fujian volcanic provinces which perhaps is associated with a mesozoic volcanic arc the ocean continent transition oct in the northeastern scs is characterized by a thinning continental crust volcanoes in the upper crust and a high velocity layer hvl in the lower crust the s wave velocity and vp vs ratio suggest that the hvl has a mafic composition that may originate from underplating of the igneous rocks beneath the passive rifted crust after the cessation of seafloor spreading c 2009 elsevier b v all rights reserved

continental shelf baroclinic instability part i relaxation from upwelling or downwelling abstractthere exists a good deal of indirect evidence from several locations around the world that there is a substantial eddy field over continental shelves these eddies appear to have typical swirl velocities of a few centimeters per second and have horizontal scales of perhaps 5 10 km these eddies are weak compared to typical wind driven alongshore flows but often seem to dominate middepth cross shelf flows the idea that motivates the present contribution is that the alongshore wind stress ultimately energizes these eddies by means of baroclinic instabilities even in cases where obvious intense fronts do not exist the proposed sequence is that alongshore winds over a stratified ocean cause upwelling or downwelling and the resulting horizontal density gradients are strong enough to fuel baroclinic instabilities of the requisite energy levels this idea is explored here by means of a sequence of idealized primitive equation numerical model studies each driven by a modest nearly steady alongs

reprint of p wave velocities and anisotropy of typical rocks from the yunkai mts guangdong and guangxi china and constraints on the composition of the crust beneath the south china sea abstract in order to provide constraints on the interpretation of seismic data of the crust beneath the south china sea scs and its continental margins we have measured p wave velocities and anisotropy as a function of hydrostatic confining pressure up to 650 mpa for 31 representative samples i e granite diorite felsic gneiss mylonite and ultramylonite amphibolite schist and marble from the yunkai mts guangdong and guangxi provinces china that represent the crystalline basement beneath the continental margins of the scs the intrinsic velocity of each crack free rock increases with increasing density which is linearly dependent on the chemical composition increases with increasing mgo cao feo fe 2 o 3 and al 2 o 3 contents but decreases with increasing contents of sio 2 and na 2 o k 2 o most of the rocks have small m f of 41 43 and the ratio shows a general increase from the continental margin to the central basin the high velocity 7 0 7 6 km s materials in the lower crust could be either the former lower crustal mafic rocks that were present before rifting which have experienced less extensional thinning than the felsic upper crust or the materials crystallized from mafic magma which underplated the lower crust from the partially molten upper mantle during rifting

dislocation creep regimes in quartz aggregates abstract using optical and tem microscopy we have determined that three regimes of dislocation creep occur in experimentally deformed quartz aggregates depending on the relative rates of grain boundary migration dislocation climb and dislocation production within each regime a distinctive microstructure is produced due primarily to the operation of different mechanisms of dynamic recrystallization at lower temperatures and faster strain rates the rate of dislocation production is too great for diffusion controlled dislocation climb to be an effective recovery mechanism in this regime recovery is accommodated by strain induced grain boundary migration recrystallization with an increase in temperature or decrease in strain rate the rate of dislocation climb becomes sufficiently rapid to accommodate recovery in this regime dynamic recrystallization occurs by progressive subgrain rotation with a further increase in temperature or decrease in strain rate dislocation climb remains sufficiently rapid to accommodate recovery however in this regime grain boundary migration is rapid thus recrystallization occurs by both grain boundary migration and progressive subgrain rotation the identification of the three regimes of dislocation creep may have important implications for the determination of flow law parameters and the calibration of recrystallized grain size piezometers in addition the identification of a particular dislocation creep regime could be useful in helping to constrain the conditions at which a given natural deformation has occurred

scale evolution of finite amplitude instabilities on a coastal upwelling front nonlinear model simulations of a coastal upwelling system show frontal instabilities that initiate at short alongshore scales but rapidly evolve to longer wavelengths several factors associated with the nonstationarity of this basic state contribute to the progression in scale a portion of the system evolution is associated with the external forcing another portion is associated with the alteration of the alongshore mean flow resulting from wave growth direct interactions between the finite amplitude disturbances also promote emergence of new scales the relative role of each of these mechanisms is isolated through tangent linear simulations about basic states that approximate the nonlinear system to differing degrees the basic states include an alongshore uniform time evolving upwelling solution the alongshore average of a three dimensionally evolving upwelling solution and the full three dimensional nonlinear solution disturbance growth about a frozen field upwelling state is also examined perturbation experiments are performed for persistent and relaxed wind forcing although the frontal disturbances in the nonlinear model exhibit a progression to larger scale over the full range of forcing scenarios considered the mechanisms most responsible for the process differ between wind forced and unforced cases under relaxed wind conditions the perturbation growth experiments indicate that the scale evolution over the first four days is reflected in the way linear disturbances respond to the adjustment of an alongshore uniform upwelling front to wind cessation the continued increase in scale between days 4 and 7 is related to the linear disturbance evolution on the alongshore average of a flow state that has been altered by wave mean flow interaction past day 7 the observed scale change is not captured in the linear growth experiments and evidently results largely from nonlinear wave wave interaction processes under sustained upwelling winds the linear growth experiments fail to describe even the earliest scale change in the nonlinear solutions indicating that nonlinear wave wave effects are significant from very near the start of the simulations