identifying global seismic anisotropy patterns by correlating shear wave splitting and surface wave data we compare a global compilation of shear wave splitting measurements with azimuthal seismic anisotropy parameters inferred from surface wave tomography the currently available splitting dataset is taken from a novel comprehensive collection of available publications that is updated interactively online the comparison between the two types of data is made by calculating predicted splitting parameters from the anisotropic tomography model comparing these predicted splitting parameters with the observed ones we find a considerable correlation between the two datasets at global scale this result is noteworthy since such correlation did not seem to exist in previous studies the spatial resolution associated with the two types of methods is rather different while surface waves have good vertical resolution and poor lateral resolution of several hundreds of kilometers sks splitting measurements have good lateral but poor vertical resolution the correlation can be understood in light of recent propositions that anisotropy seen by sks splitting constrains mostly the upper mantle and therefore a similar depth region as surface waves the correlation also confirms the generally good quality of the shear wave measurements as well as that of the anisotropic tomography model

evidence for ancient lithospheric deformation in the east european craton based on mantle seismic anisotropy and crustal magnetics abstract we present new shear wave splitting measurements performed at 16 stations on the east european craton and discuss their implications in terms of upper mantle anisotropy for this geophysically poorly known region previous investigations of mantle anisotropy in central europe have shown fast directions aligning smoothly with the craton s margin and various suggestions have been proposed to explain their origin such as asthenospheric flow or lithospheric frozen in deformation here we aim at investigating the continuation of this shear wave splitting pattern further to the east into the east european craton for the craton the interpretation appears to be less ambiguous than for central europe since several arguments support lithospheric anisotropy in this region 1 the large scale coherence within either of the four constituting blocks and the significant variations between the blocks on a small scale 2 the weak correlation with absolute plate motion vectors and 3 the good correlation between anisotropy and crustal features for which we use magnetic field alignments as a proxy rather good correlation of these magnetic features with seismic fast orientations strongly supports the idea of vertically coherent deformation throughout upper mantle and crust the observed splitting orientations thus reflect the last tectonic events of each block frozen in into the lithosphere for hundreds of millions of years

magnetic properties in an ash flow tuff with continuous grain size variation a natural reference for magnetic particle granulometry the tiva canyon tuff contains dispersed nanoscale fe ti oxide grains with a narrow magnetic grain size distribution making it an ideal material in which to identify and study grain size sensitive magnetic behavior in rocks a detailed magnetic characterization was performed on samples from the basal 5 m of the tuff the magnetic materials in this basal section consist primarily of low impurity magnetite in the form of elongated submicron grains exsolved from volcanic glass magnetic properties studied include bulk magnetic susceptibility frequency dependent and temperature dependent magnetic susceptibility anhysteretic remanence acquisition and hysteresis properties the combined data constitute a distinct magnetic signature at each stratigraphic level in the section corresponding to different grain size distributions the inferred magnetic domain state changes progressively upward from superparamagnetic grains near the base to particles with pseudo single domain or metastable single domain characteristics near the top of the sampled section direct observations of magnetic grain size confirm that distinct transitions in room temperature magnetic susceptibility and remanence probably denote the limits of stable single domain behavior in the section these results provide a unique example of grain size dependent magnetic properties in noninteracting particle assemblages over three decades of grain size including close approximations of ideal stoner wohlfarth assemblages and may be considered a useful reference for future rock magnetic studies involving grain size sensitive properties

magnetic properties of sedimentary greigite fe3s4 an update greigite fe3s4 is an authigenic ferrimagnetic mineral that grows as a precursor to pyrite during early diagenetic sedimentary sulfate reduction it can also grow at any time when dissolved iron and sulfide are available during diagenesis greigite is important in paleomagnetic environmental biological biogeochemical tectonic and industrial processes much recent progress has been made in understanding its magnetic properties greigite is an inverse spinel and a collinear ferrimagnet with antiferromagnetic coupling between iron in octahedral and tetrahedral sites the crystallographic c axis is the easy axis of magnetization with magnetic properties dominated by magnetocrystalline anisotropy robust empirical estimates of the saturation magnetization anisotropy constant and exchange constant for greigite have been obtained recently for the first time and the first robust estimate of the low field magnetic susceptibility is reported here the curie temperature of greigite remains unknown but must exceed 350 c greigite lacks a low temperature magnetic transition on the basis of preliminary micromagnetic modeling the size range for stable single domain behavior is 17 200 nm for cubic crystals and 17 500 nm for octahedral crystals gradual variation in magnetic properties is observed through the pseudo single domain size range we systematically document the known magnetic properties of greigite at high ambient and low temperatures and with alternating and direct fields and illustrate how grain size variations affect magnetic properties recognition of this range of magnetic properties will aid identification and constrain interpretation of magnetic signals carried by greigite which is increasingly proving to be environmentally important and responsible for complex paleomagnetic records including widespread remagnetizations

an extensive region of off ridge normal faulting earthquakes in the southern indian ocean an unusually large number of off ridge earthquakes have occurred within a broad region astride the southeast indian ridge the source mechanisms of nine of these earthquakes in lithosphere from 4 to 27 m y old have been determined with a formal inversion technique based on matching observed and synthetic p and sh waves all events occur in the oceanic mantle from 8 to 22 km below the seafloor the seismic moment and duration of faulting obtained from the inversion constrain the stress drop to lie between a few tens of bars and a few hundred bars for most of the events all of the off ridge earthquakes are characterized by normal faulting mechanisms with the t axes nearly parallel to the nearby ridge axis in sharp contrast to typical mid ocean ridge or intraplate earthquakes a variety of possible tectonic processes which might produce normal faulting in young oceanic lithosphere are considered as possible causes including bending stresses thermal stresses of various origins differential subsidence at a fracture zone off ridge volcanism latitudinal plate motions on a nonspherical earth basal shear stress from small scale convection and plate wide perturbations of the stress field due to the continental collision between india and asia no single mechanism is adequate to explain all the observed off ridge normal faulting earthquakes an apparent asymmetry in the observed seismicity with respect to the ridge suggests that the earthquakes on the antarctic and indian plates are caused by different processes the antarctic plate events can be satisfactorily attributed to the release of thermal and bending stresses associated with a residual depth anomaly between the kerguelen plateau and the southeast indian ridge a region which has been suggested as the site of a horizontal pipe for flow in the asthenosphere from the kerguelen hot spot to the vicinity of amsterdam and st paul islands on the southeast indian ridge the off ridge earthquakes in the indian plate are speculatively attributed to part of the plate wide response of the lithosphere to the ongoing continental collision

tracing dust sources and transport patterns using sr nd and pb isotopes continental dust transported through the atmosphere can be a tracer of atmospheric circulation and transport as well as being a source of information about climate in the dust s source area this information about the provenance of dust transported from desert areas and deposited elsewhere on the oceans and continents can be evaluated using several observational techniques satellite imagery has been used to this end in recent decades and air mass back trajectories have been calculated to trace dust deposits back to their source area another method consists of analysis of the concentration and composition of certain tracers in the dust itself and comparing them to soils and sediments from possible source areas this method has the advantage of being useable for paleo atmospheric circulation and paleo dust transport studies whereas satellite imagery and air mass back trajectories are restricted to relatively recent times we review here different kinds of isotopic tracers that have been used to trace dust provenance but special attention is focused on the use of sr nd and pb isotopes we evaluate their use in studies of both spatially as well as temporally varying continental dust source and transport

global anisotropy in the upper mantle inferred from the regionalization of phase velocities a data set of 2600 paths for rayleigh waves and 2170 paths for love waves was selected in order to resolve azimuthal anisotropy of surface waves in the period range 70 250 s the epicenters were chosen so that the paths provide uniform spatial and azimuthal coverage of earth a synthetic seismogram is computed for each path and compared to the observed seismogram in order to infer the phase velocity along each path to process such a large data set a new tomographic technique is designed a good correlation is found with surface tectonics in the whole period range for love waves and at shorter periods for rayleigh waves the directions of maximum velocities are also well correlated with plate tectonics motions for the 2 azimuthal term of rayleigh waves when the power spectrum of heterogeneities is computed it is found that for love waves the even orders are usually larger than the odd orders for rayleigh waves the degrees 2 and 6 dominate only at long periods suggesting a deep origin for these components

the upper mantle beneath ninetyeast ridge and broken ridge indian ocean from surface waves summary the rayleigh wave group velocities are used to determine the upper mantle structure of the aseismic ridges of the eastern indian ocean i e the ninetyeast ridge and the broken ridge naturaliste plateau for comparison profiles are studied across the bay of bengal and to the west of the ninetyeast ridge the group velocities are associated with the regions by the pure path method models are obtained down to 150 200 km for the profiles on and off ninetyeast ridge and down to 100km for broken ridge they reveal that except for a thick anomalous crust the structure beneath these ridges is quasi oceanic for the ninetyeast ridge however the uppermost 30 km of the mantle have lower velocities such low velocities are also obtained for the walvis ridge by chave for the paths off ridge no such low velocities are obtained indicating a small lateral extension of this anomaly a thermal origin is ruled out while a model with serpentinized peridotites as proposed by bowin which fits the gravimetric data is able to explain the low velocities of the uppermost mantle beneath the ninetyeast ridge

rock magnetic criteria for the detection of biogenic magnetite abstract we report results on the magnetic properties of magnetites produced by magnetotactic and dissimilatory iron reducing bacteria magnetotactic bacterial mtb strains ms1 mv1 and mv2 and dissimilatory iron reducing bacterium strain gs 15 grown in pure cultures were used in this study our results suggest that a combination of room temperature coercivity analysis and low temperature remanence measurements provides a characteristic magnetic signature for intact chains of single domain sd particles of magnetite from mtbs the most useful magnetic property measurements include 1 acquisition and demagnetization of isothermal remanent magnetization irm using static pulse and alternating fields 2 acquisition of anhysteretic remanent magnetization arm and 3 thermal dependence of low temperature 20 k saturation irm after cooling in zero field zfc or in a 2 5 t field fc from 300 k however potentially the most diagnostic magnetic parameter for magnetosome chain identification in bulk sediment samples is related to the difference between low temperature zero field and field cooled sirms on warming through the verwey transition t 100 k intact chains of unoxidized magnetite magnetosomes have ratios of fc zfc greater than 2 where the parameter is a measure of the amount of remanence lost by warming through the verwey transition disruption of the chain structure or conversion of the magnetosomes to maghemite reduces the fc zfc ratio to around 1 similar to values observed for some inorganic magnetite maghemite greigite and gs 15 particles numerical simulations of fc zfc ratios for simple binary mixtures of magnetosome chains and inorganic magnetic fractions suggest that the fc zfc parameter can be a sensitive indicator of biogenic magnetite in the form of intact chains of magnetite magnetosomes and can be a useful magnetic technique for identifying them in whole sediment samples the strength of our approach lies in the comparative ease and rapidity with which magnetic measurements can be made compared to techniques such as electron microscopy

upper mantle heterogeneities in the indian ocean from waveform inversion a waveform inversion method is applied to 156 love and rayleigh wave seismograms to build up a 3 d model of the shear velocity in the upper mantle beneath the indian ocean the first step of the method consists in finding for each path a radially stratified upper mantle model compatible with the love and rayleigh wave seismograms relative to that path the fundamental mode and few higher modes are modelled in the waveform inversion in a second step the models related to the different paths are used in a tomographic inversion to map the 3 d upper mantle structure the 3 d velocity model has a lateral resolution of 1000 km no significant velocity anomalies are found below 300 km although the resolution is still good continental roots are confined to the upper 300 km and low velocities below mid oceanic ridges to the upper 250 km depending on their spreading rates at shallow depths 80 km we find a positive velocity anomaly beneath the west indian ridge near the rodriguez triple junction where gravimetric and bathymetric data indicate a reduced volcanic activity at greater depth around 200 km a low velocity signature is found beneath the hot spot of reunion mauritius islands and the central indian ridge it could reflect a real connection between the two structures

heat flow over reunion hot spot track additional evidence for thermal rejuvenation of oceanic lithosphere we present 99 new heat flow determinations obtained with a regular sampling 2 3 km along two seismic profiles across the mascarene ridge indian ocean this aseismic ridge is volcanic relief due to the activity of a hot spot now responsible of the active volcanism of reunion island our sampling technique allows us to identify short wavelength processes such as slope driven water flows that affect heat flow on the ridge with the exception of these perturbed sites heat flow appears to be very uniform across the ridge and significantly higher 6 8 mw m 2 than the reference heat flow predicted for the seafloor age although this anomaly is low it confirms other evidence for thermal rejuvenation of the lithosphere based on gravity and bathymetry the set of information now available for the mascarene ridge seems to indicate a mixed mode of compensation with dynamical support below the front of the swell track and thermal support behind for the older part of the swell

revealing soil erosion characteristics using deposited sediment sources in a complex small catchment in the wind water erosion crisscross region of the chinese loess plateau abstract sediment sources in catchments under the control of check dams in the wind water erosion crisscross region are more complicated compared to other regions on the chinese loess plateau this is due to their general complexity which mainly results from variation in soil landform vegetation and erosion agents accordingly we used the composite fingerprinting approach to trace sediment sources in a typical small catchment in this region the aim was to reveal the erosion characteristics of the catchment throughout the trapping history of the check dam sediment sources were classified into three source paleosol loess and sand and four source paleosol gully loess gully slope bare of sand and slope covered by sand groups on the basis of soil and landform types respectively sediment sources throughout the whole trapping history of the check dam 1978 2010 could be classified into three stages according to variation in sedimentation rate results showed that depositional sediment in the check dam was primarily from gullies averaging 80 1 especially the paleosol gully 54 1 the large contribution of gullies indicated that the main erosion agents were streamflow from rainstorm events and gravity coal mining also had a significant impact on contribution of sediment sources especially for slopes since 1987 mining began to change the structure of hills in this region leading to slope fissures collapse and landslides at junctions where gullies meet slopes which increased the risk of slope erosion this has caused an increase in sediment from slopes bare of sand distributed under condition of continues implementation of soil conservation measures which converted sloping cropland into grassland or forest further studies are necessary to gain better insight into sediment transport and deposition within such complex environments as well as to distinguish between the effects of multiple erosion agents

sem stem observations of magnetite in carbonates of eastern north america evidence for chemical remagnettzation during the alleghenian orogeny early to middle paleozoic carbonates of eastern north america have been pervasively remagnetized in order to determine the process of remagnetization scanning and scanning transmission electron microscopy have been used to characterize magnetite in thin sections and in concentrated separates samples included ordovician knox carbonates from east tennessee ordovician trenton limestone and devonian onondaga and helderberg limestones from new york and ordovician trenton carbonates from michigan inclusions of authigenic minerals within magnetite grains lack of cations other than iron and a variety of textural relations all imply that the magnetite is authigenic these data are consistent with estimates that paleotemperatures never exceeded values that would reset magnetic directions the remagnetization is thus a chemical remanent magnetization crm rather than viscous remanent magnetization vrm as the timing of remagnetization corresponds to the alleghenian orogeny the observed relations imply stress induced crystallization of magnetite that was mediated by fluids consistent with but not requiring fluid flow on a regional basis

magnetic hysteresis in young mid ocean ridge basalts dominant cubic anisotropy magnetic hysteresis data from young mid ocean ridge basalts include samples with saturation remanence to saturation magnetization mrs ms ratios greater than 0 5 the theoretical limit for an assemblage of single domain grains with uniaxial anisotropy under the usual assumption of dominant uniaxial anisotropy the narrow single domain grain size distribution implied by these high mrs ms values is difficult to reconcile with petrographic and remanence data that suggest the presence of larger multidomain grains dominant cubic anisotropy provides a plausible explanation for the high mrs ms ratios and if generally valid requires reinterpretation of granulometric and domain state inferences made from hysteresis data

new constraints on the tectonic evolution of the eastern indian ocean abstract from marine magnetic anomaly studies a fossil spreading ridge is identified beneath the nicobar fan in the northwestern wharton basin several north south trending transform faults offset this ridge left laterally east of the 86 e transform fault our findings show that this ridge which was part of the plate boundary between the indian and australian plates ceased its spreading shortly after formation of magnetic anomaly 20 45 6m y b p since the breakup of australia and antarctica probably occurred sometime between 110 and 90 m y b p we suggest that the indian australian and antarctic plates were moving relative to one another from about 90 to 45 m y b p a triple junction would have existed in the southeastern indian ocean during that period of time at anomaly 19 time 45m y b p the junction became inactive and australia and india became a single plate the northwest southeast trending southeast indian ridge was formed by connecting the india antarctica spreading center with the australia antarctica spreading center its activity has continued to the present time

fingerprinting sediment sources in the water wind erosion crisscross region on the chinese loess plateau abstract sand sheet sources in the wind water erosion crisscross region of the chinese loess plateau have not been specifically identified spatially we selected a transect that cuts across the eastern edge of the mu us sandy land sand sheets distributed loess hills sand loess hills loess hills and adjacent rocky mountains to collect surface sediment samples temporally we selected a site on a sampling sand loess hill to collected depth incremental samples in a 320 cm depth soil profile to analyze sediment sources using the multiple composite fingerprinting approach we screened out a group of optimal composite fingerprints that correctly classified sediment sources at 100 greater than half of all sediment on sand loess hills originated from the sandy land area on the sampling transect and roughly half from the sandy land in the soil profile while the remaining sediment all originated from the loess hills and rocky mountains had no contributing effect coarse particles 100 m on sand loess hills were mainly transported from the mu us sandy land while fine particles were mainly from loess hills indicating the importance of aeolian activity in the transport of sand from the mu us sandy land to loess hills environmental changes chronicled by sediment deposition at approximately 12 85 ka bp in the soil profile were primarily attributed to climate change this study confirms that the composite fingerprinting approach is a feasible method for future studies on sediment sources in areas influenced by complex erosion agencies landforms and soil types

synconvergent ductile flow in variable strength continental crust numerical models with application to the western grenville orogen 1 we present results from numerical models for a convergent orogen with laterally variable lower crustal strength representing a simplified orogenic system in which a strong craton flanked by progressively weaker terranes collides with another continent with progressive convergence crustal thickening and thermal relaxation lower crust becomes decoupled from upper and middle crust forming a ductile orogenic infrastructure beneath a stronger superstructure collision with strong external crust results in uplift and expulsion of ductile nappes from the orogenic core creating allochthonous terranes overlying a lower crustal indentor the extent of transport and exhumation of lower crustal nappes over the indentor reflects the amount of convergence and the erosion rate the western grenville orogen displays across strike variations in age tectonic history and protolith association suggesting a systematic variation in precollision crustal strength the laurentian craton margin and accreted terranes were variably reworked at synorogenic depths of 25 35 km during the ottawan orogeny deformation propagated from younger monocyclic rocks in the southeast into older polycyclic rocks flanking the craton on the northwest a comparison between numerical model results and crustal scale cross sections from the georgian bay and montreal val d or transects shows close correspondence between crustal structure and model geometry this indicates that the models produce geologically realistic results and provides a context for interpreting the tectonic evolution of the western grenville orogen contrasts between the results of homogeneous channel flow models and the present ductile nappe models suggest that the effects of different styles of ductile flow can be distinguished in the geologic record

low velocity crustal flow and crust mantle coupling mechanism in yunnan se tibet revealed by 3d s wave velocity and azimuthal anisotropy abstract we used teleseismic data recorded by a permanent seismic network in yunnan se tibet and measured the interstation rayleigh wave phase velocity between 10 and 60 s a two step inversion scheme was used to invert for the 3d s wave velocity and azimuthal anisotropy structure of 10 110 km the results show that there are two low velocity channels between depths of 20 30 km in yunnan and that the fast axes are sub parallel to the strikes of the low velocity channels which supports the crustal flow model the azimuthal anisotropy pattern is quite complicated and reveals a complex crust mantle coupling mechanism in yunnan the n s trending luzhijiang fault separates the dianzhong block into two parts in the western dianzhong block the fast axis of the s wave changes with depth which indicates that the crust and the lithospheric mantle are decoupled in the eastern dianzhong block and the western yangtze craton the crust and the lithospheric mantle may be decoupled because of crustal flow despite a coherent s wave fast axis at depths of 10 110 km in addition the difference between the s wave fast axis in the lithosphere and the sks splitting measurement suggests that the lithosphere and the upper mantle are decoupled there in the baoshan block the stratified anisotropic pattern suggests that the crust and the upper mantle are decoupled

anisotropy and shear velocity heterogeneities in the upper mantle long period surface waves are used to map lateral heterogeneities of velocity and anisotropy in the upper mantle the dispersion curves are expanded in spherical harmonics up to degree 6 and inverted to find the depth structure the data are corrected for the effect of surface layers and both love and rayleigh waves are used shear wave velocity and shear polarization anisotropy can be resolved down to a depth of about 450 km the shear wave velocity distribution to 200 km depth correlates with surface tectonics except in a few anomalous regions below that depth the correlation vanishes cold subducted material shows up weakly at 350 km as fast s wave anomalies in the transition region a large scale pattern appears with fast mantle in the south atlantic s anisotropy at 200 km can resolve uprising or downwelling currents under some ridges and subduction zones the pacific shows a nw se fabric

impacts of grain size sorting and chemical weathering on the geochemistry of jingyuan loess in the northwestern chinese loess plateau abstract major and trace elemental compositions of loess samples collected from the jingyuan section in the northwestern chinese loess plateau clp were analyzed to investigate the potential impacts of grain size sorting and chemical weathering on the loess geochemistry and to extract appropriate geochemical indices for better evaluating the east asian monsoon variability based on variations of major and trace elements in different grain size fractions seventeen elements were classified into three types 1 si and na display higher contents with the increased particle sizes 2 al fe mg k mn zn rb cr v are mainly enriched in fine size fractions 3 ti ba zr p ca and sr show irregular variations among different size fractions comparison of al normalized elemental ratios with zr rb and rb sr ratios two commonly employed indicators for grain size sorting and pedogenic weathering indicates that si al zr al ti al variations match well with zr rb and grain size results whilst ca al sr al p al ratios display similar variability as that of rb sr ratio comparison of loess based proxies e g elemental ratios magnetic susceptibility grain size of jingyuan section with speleothem and ice core records confirms that elemental ratios of high resolution loess sequences developed in the northwestern clp can be employed to address fluctuations of the winter monsoon induced grain size sorting and summer monsoon related weathering and pedogenesis at glacial interglacial and millennial timescales

anisotropic tomography around la reunion island from rayleigh waves in the western indian ocean the reunion hot spot is one of the most active volcanoes on earth temporal interactions between ridges and plumes have shaped the structure of the zone this study investigates the mantle structure using data from the reunion hotspot and upper mantle reunions unterer mantel rhum rum project which significantly increased the seismic coverage of the western part of the indian ocean for more than 1 year 57 ocean bottom seismometer stations and 23 temporary land stations were deployed over this area for each earthquake station path the rayleigh wave fundamental mode phase velocities were measured for the periods from 30 s to 300 s and group velocities for the period from 16 s to 250 s a three dimensional model of the shear velocity in the upper mantle was built in two steps first the path mean phase and group velocities were inverted to obtain regionalized velocity maps for each separate period then all of the phase and group velocity maps were combined and inverted at each grid point to obtain the local s wave velocity as a function of depth using a transdimensional inversion scheme the three dimensional anisotropic s wave velocity model has resolution down to 300 km in depth the tomographic model and surface tectonics are correlated down to 100 km in depth starting at 50 km in depth a slow velocity anomaly beneath rodrigues ridge and the east west orientation of the azimuthal anisotropy show a connection between reunion upwelling and the central indian ridge the slow velocity signature beneath la reunion is connected at greater depths 150 300 km with a large slow velocity zone beneath the entire mascarene basin this develops along a northeast direction following the general motion direction of the african plate these observations indicate nonisotropic spreading of hot plume material and dominant horizontal flow in the upper mantle beneath this area

approach to saturation analysis of hysteresis measurements in rock magnetism and evidence for stress dominated magnetic anisotropy in young mid ocean ridge basalt abstract young mid ocean ridge basalts contain titanomagnetite crystals of varying size and composition many studies of their hysteresis properties have found m rs m s ratios considerably above the theoretical limit of 0 5 for uniaxial single domain particles since titanomagnetite is a cubic mineral high m rs m s could occur due to cubic anisotropy which allows for m rs m s values up to 0 866 on the other hand titanomagnetites with high ti content possess extremely large magnetostriction constants already slight internal stress easily outweighs cubic anisotropy and enforces uniaxial behavior are high m rs m s ratios now a proof for very low internal stress no on the contrary previous studies on synthetic titanomagnetite with high m rs m s show that after annealing this ratio decreases a possible explanation is that insufficient saturation of the hysteresis loop used to infer m rs m s leads to underestimation of m s here a systematic experimental study on a young mid ocean ridge basalt using fields of up to 7 t demonstrates that indeed the m rs m s ratio of the single domain fraction does not significantly deviate from the theoretical value of 0 5 for uniaxial anisotropy it is further estimated that internal stress above 200 mpa is necessary to explain the observed hysteresis behavior a value which is consistent with recent independent approximations on the other hand theoretical loops for cubic minerals do not fit the observed data in order to assess the validity of m s determinations from hysteresis measurements an improved method to evaluate the approach to saturation behavior of hysteresis loops is developed it allows to recognize insufficiently saturated loops and thereby helps to avoid misinterpretation of standard m rs m s measurements when high fields are not accessible

3 dimensional structure of the indian ocean inferred from long period surface waves to improve the lateral resolution of the first global 3 dimensional models of seismic wave velocities regional studies have to be undertaken the dispersion of rayleigh waves along 86 paths across the indian ocean and surrounding regions is investigated in the period range 40 300 s the regionalization of group velocity according to the age of the sea floor shows an increase of velocity with age up to 150 s only similar to the results in the pacific ocean but here this relationship vanishes more quickly at long period therefore the correlation of the deep structure with surface tectonics seems to be shallower in the indian ocean than in the pacific ocean a tomographic method is applied to compute the geographical distributions of group velocity and azimuthal anisotropy and then the 3 d structure of s wave velocity horizontal wavelengths of 2000 km for velocity and 3000 km for azimuthal anisotropy distribution can be resolved except for the central part of the south east indian ridge which displays high velocities at all depths the inversion corroborates a good correlation between lithospheric structure down to 120 km and surface tectonics low velocities along the central and southeast indian ridges velocity increasing with the age of the sea floor high velocities under african indian and australian shields at greater depths the low velocity zones under the gulf of aden and the western part of the southeast indian ridges hold but the low velocity anomaly of the central indian ridge is offset eastward the low velocity anomalies suggest uprising material and complex plate boundary

seafloor age dependence of rayleigh wave phase velocities in the indian ocean variations in the phase velocity of fundamental mode rayleigh waves across the indian ocean are determined using two inversion approaches first variations in phase velocity as a function of seafloor age are estimated using a pure path age dependent inversion method second a two dimensional parameterization is used to solve for phase velocity within 1 25 1 25 grid cells rayleigh wave travel time delays have been measured between periods of 38 and 200 s the number of measurements in the study area ranges between 4139 paths at a period of 200 s and 22 272 paths at a period of 40 s at periods 100 s the phase velocity variations are strongly controlled by seafloor age and shown to be consistent with temperature variations predicted by the half space cooling model for a mantle potential temperature of 1400 c the inferred thermal structure beneath the indian ocean is most similar to the structure of the pacific upper mantle where phase velocities can also be explained by a half space cooling model the thermal structure is not consistent with that of the atlantic upper mantle which is best fit by a plate cooling model and requires a thin plate removing age dependent phase velocity from the 2 d maps of the indian ocean highlights anomalously high velocities at the rodriguez triple junction and the australian antarctic discordance and anomalously low velocities immediately to the west of the central indian ridge

mapping convection in the mantle long period 100 250 sec love and rayleigh waves are used to map heterogeneity and azimuthal anisotropy in the upper mantle spherical harmonic descriptions of anisotropy up to l m 3 and 2 are derived azimuthal anisotropy obtains values as high as 1 there is good correlation of fast rayleigh wave directions with upper mantle return flow directions derived from kinematic considerations this is consistent with the a axis of olivine being aligned in the flow direction the main differences between the flow models and the rayleigh wave azimuthal variation maps occur in the vicinity of hotspots hawaii for example appears to perturb the return flow there is strong correlation of the geoid and surface wave velocity at l 4 and 5 slow regions at this scale are associated with geoid highs and high heat flow consistent with upwelling convective flow or with isostatically compensated regions of low density the correlation of azimuthal anisotropy with upper mantle return flow directions rather than with plate directions suggests that part of the return flow is in the upper mantle and this in turn implies a low viscosity channel

whole mantle p wave travel time tomography abstract a method of tomographic inversion to obtain three dimensional velocity perturbations in the earth s whole mantle has been developed and applied to more than two million p wave arrival time data reported by international seismology center isc the model is parameterized with 32 768 blocks the divisions in latitude longitude and radius are 32 64 and 16 respectively horizontal cell size is 5 6 5 6 the layer thicknesses vary with depth 29 km just below the surface and 334 km just above the core mantle boundary starting from a spherically symmetric earth model we obtained a three dimensional model using the following iterative procedures first we relocated all the events second we backprojected the residual into the whole mantle third we refined the spherically symmetric earth model the solutions have been converged in five iterations we adopted the following techniques in the backprojection procedure the first order smoothness was introduced as a damping which makes the solution independent of the starting model and its apparent fluctuation minimal the basic equations for delay times and smoothness are solved using the conjugate gradient method an iterative method which guarantees the convergence of solution into the exact least squares solution the weight on the smoothness i e the damping factor was objectively determined by a simplified cross validation technique the final solution was obtained as an average of the ten solutions each of which was derived from one tenth of the total data set the reliability of the solution is examined in two ways 1 mapping the resolution given by the reconstruction of checkerboard patterns and 2 mapping the variance given from the gaussian noise input this is the first result which delineates the whole mantle structure with its reliability mapping the longest wavelength anomalies of the lower mantle are similar to those of previous studies by dziewonski 1984 and hager and clayton 1989 however the shorter wavelength patterns have many discrepancies the fast anomalies of the uppermost mantle beneath the shield and the slow anomalies beneath the active tectonic regions are clearly seen we also revealed the l 2 pattern at the transition zone reported by the previous surface wave and free oscillation studies the most striking feature is that of the fast anomalies lying along the extension of the large subducting plate up to depths of about 1000 km or more the resolving powers in these regions are generally good

aeolian sediment fingerprinting using a bayesian mixing model identifying sand provenance in depositional aeolian environments e g dunefields can elucidate sediment pathways and fluxes and inform potential land management strategies where windblown sand and dust is a hazard to health and infrastructure however the complexity of these pathways typically makes this a challenging proposition and uncertainties on the composition of mixed source sediments are often not reported this study demonstrates that a quantitative fingerprinting method within the bayesian markov chain monte carlo mcmc framework offers great potential for exploring the provenance and uncertainties associated with aeolian sands eight samples were taken from dunes of the small 58 km2 ashkzar erg central iran and forty nine from three distinct potential sediment sources from the surrounding area these were analyzed for 61 tracers including 53 geochemical elements trace major and rare earth elements ree and 8 ree ratios kruskal wallis h tests and stepwise discriminant function analysis dfa allowed the identification of an optimum composite fingerprint based on six tracers rb sr 87sr la yb n ga and ce and a bayesian mixing model was applied to derive the source apportionment estimates within an uncertainty framework there is substantial variation in the uncertainties in the fingerprinting results with some samples yielding clear discrimination of components and some with less clear fingerprints quaternary terraces and fans contribute the largest component to the dunes but they are also the most extensive surrounding unit clay flats and marls however contribute out of proportion to their small outcrop extent the successful application of these methods to aeolian sediment deposits demonstrates their potential for providing quantitative estimates of aeolian sediment provenances in other mixed source arid settings and may prove especially beneficial where sediment is derived from multiple sources or where other methods of provenance e g detrital zircon u pb dating are not possible due to mineralogical constraints

rayleigh wave group velocity studies beneath the indian ocean the fundamental mode rayleigh wave generated by 16 earthquakes which occurred in the indian ocean and were recorded at 14 seismic stations of asia africa and australia are analyzed to estimate the rayleigh wave group velocity at periods of 10 to 60 sec by using the multiple filter analysis technique in addition to this rayleigh wave group velocity data available in the literature across different propagation paths of the indian ocean forming a dense distribution of seismic wave traverses have been considered for tomographic studies the group velocity distribution maps have been obtained at periods of 10 20 30 40 50 and 60 sec for the rayleigh wave the minimum value of the group velocity of 2 0 km sec is centered near the rodriguez triple junction 25 s 70 e at 10 sec and higher value 3 4 4 0 km sec at 20 sec and greater period as we move in the north northwest direction from the rodriguez triple junction the rayleigh wave group velocity isolines at 10 and 20 sec are also increasing in the northern direction in both the east and west sides of the ridge axis another minimum value of group velocity isolines 1 9 km sec is centered near 25 s 90 e at 10 sec and there is a gradual increase in the northern direction across the ninetyeast ridge these observations are in accordance with the increase in the age of the ocean floor and there is a gradual increase in the group velocity isolines this can be interpreted as due to the hot uprising convection current the material shows low shear wave velocity along the ridge axis and farther away from the ridge axis the material has become cooler with higher shear wave velocity the inversion of rayleigh wave group velocity across the ninetyeast ridge shows 120 km thick lvz low velocity zone of shear wave velocity of 4 38 4 78 km sec at a depth of 40 km from the water surface whereas other parts of the indian ocean show 44 km thick lvz with shear wave velocity of 4 12 4 17 km sec at a depth of 40 km from the water surface the high shear wave velocity below moho 4 19 4 75 km sec beneath the ninetyeast ridge indicates the presence of a cold and dense lithosphere beneath it

partitioned waveform inversion and two dimensional structure under the network of autonomously recording seismographs nonlinear optimization methods are very effective in finding models that predict optimal waveform fits to observed seismograms provided the number of model parameters is small to reduce the size of the large scale two or three dimensional seismic modelling problem path integrals over seismic velocities may be defined as model parameters instead of the seismic velocities themselves this partitions the large scale optimization problem into a number of independent small scale problems and reduces the computational effort by several orders of magnitude the path integral parameters are transformed such that their correlation matrix becomes diagonal a linear inversion performs the mapping from the space of path integral parameters into the model space of seismic velocities and makes backus gilbert resolution analysis possible the method has been applied to body wave and surface wave data from the broadband portable network of autonomously recording seismographs nars in western europe using a surface wave ray approximation to generate synthetics by mode summation waveforms were fitted for frequencies as high as 50 mhz variations in s velocity as large as 6 1 have been established with a vertical resolution of 100 150 km and a horizontal resolution as small as 400 km in parts of the model although a low velocity layer is present under the southern part of the nars array such layer is very weak or absent north of the paris basin horizontal velocity gradients are well resolved down to 400 km depth

fingerprinting suspended sediment sources in the catchment of the river ouse yorkshire uk statistically verified composite fingerprints and a multivariate mixing model have been employed to establish the main sources of the suspended sediment transported through the lower non tidal reaches of the river ouse and one of its main tributaries the river wharfe during the period 1994 1997 in the case of the suspended sediment samples collected from the river ouse the load weighted mean contributions from uncultivated topsoil cultivated topsoil and channel bank sources were estimated to be c 25 38 and 37 respectively while for the river wharfe these sources contributed c 70 4 and 23 respectively c 4 was derived from woodland topsoil suspended sediment samples collected during higher flows evidenced a greater contribution from channel banks than samples collected during lower flows source materials were also differentiated according to the three main geological source areas carboniferous permian and triassic and jurassic and their load weighted mean contributions were estimated to be c 24 41 and 35 for the river ouse and c 91 9 and 0 there are no jurassic rocks in this catchment for the river wharfe respectively when suspended sediment samples from tributary streams were used to characterize each geological source area the equivalent results for the river ouse were c 30 46 and 24 considering the three main tributaries that contribute to the river ouse the load weighted mean contributions from the rivers swale ure and nidd were estimated to be 82 15 and 3 respectively these values have been compared with estimates of the relative magnitude of the annual suspended sediment loads of these three rivers for the years 1995 and 1996 derived from continuous monitoring of discharge and turbidity differences between the two sets of results are ascribed to the different periods of record involved and to the timing of suspended sediment sampling relative to the overall storm hydrograph and thus the degree to which the available samples are representative of the overall suspended sediment flux although a number of limitations must be recognized the fingerprinting approach to source ascription is seen as providing valuable information regarding suspended sediment sources in the study catchments copyright 1999 john wiley sons ltd

mapping the upper mantle three dimensional modeling of earth structure by inversion of seismic waveforms a method is presented for the inversion of waveform data for the three dimensional distribution of seismic wave velocities the method is applied to data from the global digital networks international deployment of accelerometers global digital seismograph network the selected data set consists of some 2000 seismograms corresponding to 53 events and 870 paths the moment tensors of the earthquakes are determined through an iterative procedure which minimizes the corrupting influence of lateral heterogeneity a global model is constructed for shear wave velocity expanded up to degree and order 8 in spherical harmonics and described by a cubic polynomial in depth for the upper 670 km of the earth s mantle although no a priori information is incorporated the model predictions reproduce much of what is known about the dispersion of mantle waves for example high phase velocities for shields low velocities at ridges and a strong degree 2 pattern for rayleigh waves since the method makes use of complete waveforms overtone data are also included it is shown that the model is reproducible in that substantially the same model can be constructed from each half of the total data set considered independently the model shows that shields and ridges are major features in the depth interval 25 250 km the ridges of the southern pacific and the larger shields persist to 350 km but the southeast indian rise is underlain by a high velocity anomaly at this depth as is much of the mid atlantic ridge at 450 650 km the major features are a broad region of high velocities incorporating south america much of the south atlantic and parts of west africa a broad region of low velocities in the central and eastern pacific high velocities in the western pacific and a low velocity anomaly beneath the red sea and the gulf of aden in the absence of a crustal correction degrees 2 and 3 show a high positive correlation with the geoid paradoxically this is largely destroyed when the distribution in crustal thickness is taken into account spherical harmonic degrees 4 7 show a significant negative correlation

comparing crustal and mantle fabric from the north american craton using magnetics and seismic anisotropy a central target in earth sciences is the study of deformation at various depth levels within the earth seismology has offered a remarkable tool for doing this via seismic anisotropy it is however not always clear how to interpret those observations a question of interest is to understand the relation between the deformation of the mantle and the crust and in studying the relation between the two mantle deformation is expressed in seismic anisotropy in this paper we seek an objective way of extracting information about crustal fabric as well to be able to compare with seismic anisotropy the magnetization of crustal rocks offers an attractive possibility for doing this we thus explore the use of magnetic data and we compare magnetic crustal fabric orientation with mantle fabric observations from seismic anisotropy we apply our technique to the north american craton for which we have an excellent magnetic dataset and we show that there is a clear relation between crustal and mantle fabric for the cratonic region this has important implications for crustal formation and for interpreting seismic anisotropy observations

provenance of aeolian sediment in the taklamakan desert of western china inferred from ree and major elemental data abstract to identify the provenance of aeolian deposits in the extensive dune field in the taklamakan desert is of great importance for understanding the formation of this the largest sand sea in china the opinions from earlier studies are quite dipolar and are as follows a local origin of the dune sands in different parts of the desert on the basis of various heavy mineral assemblages and b strong homogenization of the sands in the entire taklamakan on the basis of geochemical data from whole rock samples by separately examining the ree characteristics and major elemental composition in coarse and fine fractions of the samples from aeolian deposits this paper provides new data for interpreting sources of aeolian deposits in the taklamakan the sampling sites are distributed in four different fluvial systems i e the areas of the keriya river niya river and cele river in the southern part and the northern margin near the tarim river fig 1 our results show that there are some significant differences in concentrations of trace elements and in ree features between the coarse and the fine fractions of the aeolian sediment the major elemental and ree data suggest that the coarser sand is different from area to area in the desert rather than a homogenization of the entire basin the fine fractions mainly silts are more homogenized the regional difference of coarse fractions in the study areas is consistent with the fluvial and wind systems in the basin this confirms that the sands are often mixed between the northern and southern parts but there is much less mixing along the east west direction it should be emphasized that not only glacial and aeolian processes but also fluvial and lacustrine processes have jointly contributed to the formation of the huge sand sea in addition little variation is found between old and young sands in two sediment sequences in the central part of the desert indicating consistency of sand sources in a given site during the last 40 ka

geochemical and geomorphological evidence for the provenance of aeolian deposits in the badain jaran desert northwestern china abstract identifying provenance of aeolian deposits in the mid latitude deserts of asia is essential for understanding formation and changes of earth surface processes due to palaeoclimatic fluctuations while some earlier studies focused on the interpretation of palaeoenvironments on the basis of aeolian deposits mainly in the desert margins and inter dune lacustrine sediments research on provenance of desert sands in the vast asian mid latitude deserts is still rare in this paper we present new geochemical data which provide insight to the provenance of dune sands in the badain jaran desert northwestern china an important part of this desert belt we sampled aeolian and lacustrine sediments in various parts of the badain jaran desert and examined their major trace and rare earth elements ree in bulk samples coarse and fine fractions respectively in addition we took and analyzed samples from a rarely known dune field with red sands northeast of the badain jaran our results show that the sands from the badain jaran desert are generally different from those in the red sand dune field in terms of ree pattern and geochemical characteristics suggesting different sediment origins geochemical composition of the aeolian sand samples indicates these sediments should be mainly derived from mixed source rocks of granite granitoids and granodiorite comparing the immobile trace elements and ree ratios of the samples from the badain jaran desert red sand dune field with rocks of granite granitoids in their potential source areas we conclude that 1 the aeolian deposits in the badain jaran desert are predominantly derived from the qilian mountains northeastern tibetan plateau initially via fluvial processes 2 the altay mountains and mongolian gobi are the ultimate source areas for the red sand dune field 3 the altai mountains and mongolian gobi in the northwest that could produce massive amounts of materials via intensive deflation and alluvial process are additional sand sources of the badain jaran desert although their contribution is of secondary significance as the badain jaran desert acts as sediment sinks of sediments from the qilian mountains of northeastern tibetan plateau via fluvial processes it is likely that zircon grains of loess on the chinese loess plateau with age distributions similar to those of the northern tibetan plateau could be derived from the badain jaran desert as the wind data suggest

s wave velocity basalt chemistry and bathymetry along the mid atlantic ridge major element chemistry of mid ocean ridge basalt s wave velocity and bathymetry along the mid atlantic ridge are correlated on an intermediate length scale and the large anomalies in these observations are associated with hotspot locations the best correlations are for at depths of 100 200 km and there is no correlation for depths of 300 km or deeper s wave velocities are low directly under the mid atlantic ridge above 100 km but the low velocity regions shift away from the ridge at greater depth and a sinuous strip of asthenospheric low velocity extends along the atlantic hotspots from the azores to tristan da cunha these features suggest that common physical processes in the upper mantle produce these anomalies an inspection of the history of the atlantic ocean suggests that the asthenospheric low velocity strip may record earlier ridge position or possible upwelling in the mantle possible interaction between hotspots and the ridge blurs the distinction between passive and active upwellings

remagnetizations as a tool to analyze the tectonic history of inverted sedimentary basins a case study from the basque cantabrian basin north spain 1 in this work we use syntectonic remagnetization data to determine the synrift geometry of inverted basins this methodology analyzes remagnetization directions in order to obtain the tilting of beds at the moment of the acquisition of the overprint filtering the subsequent compressional deformation we collected samples from jurassic and lower cretaceous limestones and red beds cabuerniga and pas groups in the cabuerniga basin one of the most important mesozoic basins developed near the iberia europe mesozoic plate boundary in northern spain that later inverted during the uplift of the pyrenees these deposits represent the synrift sequence linked to a widespread extensional stage in the iberian basins during the mesozoic all sampled rocks show a normal polarity remagnetization fold and conglomerate tests indicate that remagnetization postdates the main extensional stage of basin formation late jurassic barremian and was acquired before the subsequent compressional deformation the analysis of these overprinted directions allows the basin geometry of the studied area to be restored at the moment of acquisition of the remagnetization this approach represents a powerful tool to study basinal evolution and uplift of sedimentary basins to be tested in other inverted basins with syn extensional related secondary overprints

regional 3 d heterogeneities by waveform inversion application to the atlantic area the waveform inversion method described in woodhouse dziewonski 1984 was modified to retrieve regional scale 3 d heterogeneities by using the minor arc part of seismograms the lateral heterogeneities are expanded horizontally into blocks 10 10 and radially into legendre polynomials up to order 3 0 670 km and thus the results show much fine details of lateral variation than previous global scale studies we assumed that the heterogeneities produce the perturbation of eigenfrequencies which are the minor arc average of local eigenfrequency shift we applied the method to the upper mantle beneath the atlantic ocean and its environments care was taken about the weighting of the data set we found that the fit of each seismogram became better when the weighting of each seismogram is proportional to the inverse of initial data residuals resolution is good in the triangular region surrounded by south america europe and north america resolution is not good in the south atlantic because of the poor path coverage depth resolution is not clear because of the use of legendre polynomials though the results suggest a broad half width of the order of 200 km or more we found some similarities between previous global studies and our results for example low velocities beneath the east pacific rise chile rise and azores triple junction and a high velocity canadian shield are obtained however there are also differences the high velocity zone beneath the brazilian shield at shallow depth is not a prominent feature in this study instead we found a somewhat unexpected feature near the romanche and vema fracture zones where shallow positive anomalies exist smoothed results calculated by the spherical harmonic expansion are also shown for the purpose of comparison with global studies

interactions between fluvial and eolian geomorphic systems and processes examples from the sahara and australia abstract the remains of once integrated drainage systems are still discernible in many of the hot deserts of the world some of these date back to the mesozoic as in arid western australia where they now form chains of salt lakes others were active in miocene times such as the sahabi rivers that once flowed from chad to the mediterranean a few remained active during quaternary interglacials as in the sahara all contributed sediments that were reworked by wind during drier phases to form desert dunes the desert dunes of australia and of the 9500 km long chain of deserts extending from the sahara through arabia to the thar desert of india originated from sediments eroded from the uplands and deposited in closed interior basins formed during the course of late mesozoic and cenozoic faulting rifting and epeirogenic movements it was the unconsolidated neogene sediments laid down in large subsiding sedimentary basins such as the kufra sirte basin in libya and the chad basin which provided the source material for the late pliocene and quaternary desert dunes of the sahara one effect of the progressive build up of high latitude ice sheets during the neogene was to steepen the temperature and pressure gradients between the equator and the poles resulting in increased trade wind velocities stronger winds were better able to mobilize the alluvial sands of the increasingly dry sahara and adjacent deserts and to fashion them into desert dunes a more subtle form of interaction between eolian and fluvial processes concerns the interplay between desert dust loess accumulation on hill slopes in arid regions and the onset of fine grained valley fill accumulation by sluggish low energy streams in mountain valleys some of these late pleistocene wetlands served as refuge areas for plants reptiles and invertebrates at a time when the surrounding desert plains were very cold and dry as in the flinders ranges of south australia in the arid flinders ranges such valley fills were built up between 35 kyr and 15 kyr ago after which the return of the summer monsoon led to stream channel incision and the formation of a network of gullies often erroneously attributed to human activities understanding the causes of such accelerated erosion can prevent unnecessary and expensive attempts at restoration since the latter are based on the incorrect assumption that overgrazing and present day land use are responsible

geochemical elements characteristics and sources of the riverbed sediment in the yellow river s desert channel the yellow river flows through an extensive area of aeolian desert and extends from xiaheyan ningxia province to hekouzhen inner mongolia province for a total of 1 000 km in the desert channel of the yellow river the major chemical components are sio2 fe2o3 al2o3 ti cao mgo ba p mn ce co in which sio2 al2o3 fe2o3 and ti have significant value as indicators of the sources of the coarse sediment the spatial distribution of the elements weight percentages and the ratios of si ti si al between sediment sources and riverbed sediment of the gansu reach and the desert channel of the yellow river indicating that the coarse sediments deposited in the desert reach of the yellow river are mostly controlled by the local sediment sources and due to the higher mobility of the fine sediments they are primarily contributed by the local sediment sources and the tributaries that originate from the loess area of the upper reach of yellow river the results of r factor analysis illustrate that the first component score mainly shows negative values in the desert channel suggesting that the coarse sediments in this reach contain a higher content of si and a lower content of mg ca al fe which further proves that the ningxia hedong inner mongolian wulanbuhe and kubuqi deserts are the primary sources of the coarse sediment in the desert channel of the yellow river

phase velocity distribution in the indian ocean and indonesian region inferred from geoscope records to improve the lateral resolution of 3 dimensional models of seismic wave velocities in the indian ocean and surrounding regions we analyzed direct earthquake to station rayleigh waves observed on the vertical long period components of four geoscope stations tam algeria pcr la reunion paf kerguelen and agr djibouti the phase velocities along 51 well distributed paths are obtained in the period range 40 350 s after corrections for the phase pattern at the source and for the instrumental response a tomographic method is then applied montagner 1986a to compute the geographical distribution of phase velocities without any a priori regionalization the location of velocity anomalies is quite stable and well resolved the phase velocity distributions are compared with global results from nakanishi and anderson 1984b woodhouse and dziewonski 1984 tanimoto 1985 nataf et al 1986 and with regional studies using group velocities for the same region montagner 1986a b c

upper mantle lateral heterogeneities and magnetotelluric daily variation data we use telluric and magnetic data of the diurnal variation recorded in europe australia and north america to study the magnetotelluric tensor in the 6h 24h period range we use associate directions and we eliminate the effects of deviation of telluric currents we thus obtain for each observatory reliable phases and apparent resistivity values representative of the neighbouring stratified substratum it appears that the values obtained in the four european observatories saint maur france ebro spain toledo spain nagycenk hungary give similar results and that these results are different from those obtained either in tucson usa or in watheroo australia

low temperature magnetic behavior of titanomagnetites titanium substitution has a significant effect on the temperature dependence 5 300 k of low temperature saturation remanence and of initial susceptibility in synthetic and natural titanomagnetite fe3 xtixo4 0 x 0 4 and electronic and lattice relaxation phenomena over the entire titanomagnetite compositional range these features produce diagnostic magnetic behavior useful for titanomagnetite identification in natural samples moreover the apparent similarities between the thermal decay of low temperature remanence of titanomagnetite with pyrrhotite pure magnetite and superparamagnetic phases can lead to complications in interpreting low temperature remanence data when titanomagnetite is present

magnetism and magnetic mineralogy of ash flow tuffs from yucca mountain nevada the magnetic susceptibility and remanent magnetization of an ash flow sheet are profoundly influenced by cooling history after emplacement spatial variations in these properties therefore provide a potentially useful tool for geological studies maxima and minima in measured along profiles at yucca mountain nevada identify persistent magnetic marker horizons within vitric portions of the tiva canyon and underlying topopah spring members of the paintbrush tuff the correlatable variations of with vertical position in these units exist over the 8 km of strike examined the observed stratigraphic changes in magnetic properties reflect variations in amounts and mineralogy of fe ti oxide phenocrysts and the presence shape size and mineralogy of magnetic fe oxide microcrystals that precipitated at high temperature after emplacement of each sheet vitrophyre near the top of the topopah spring member has a distinctive maximum in due to titanomagnetite phenocrysts susceptibility in the lower portion of the overlying tiva canyon member reaches maximum values of about 1 3 10 2 si near the base of the member beneath the columnarly jointed vitrophyre due to the presence of abundant superparamagnetic cubic fe oxide these elongate microcrystals are several tens of nm long and are typically deformed and tapered up section in the tiva canyon member the susceptibility decreases going to a minimum within the columnar vitrophyre at this stratigraphic level the precipitated fe oxides are larger and carry intense nrm of up to 30 a m is only 3 10 3 the whisker like microcrystals of fe oxide which typically nucleated on what appears to be chain silicate grew as needles up to 25 m in length the size variations of the precipitated fe oxides which were established using transmission electron microscopy tem and petrographic observation are consistent both with variations in magnetic susceptibility measured at the outcrop and with variations in the intensity of remanent magnetization several interpretations of the shape anisotropy of the precipitated feoxide are possible including growth by a dislocation mechanism additionally the observed elongation of precipitated microcrystals is consistent with theoretical predictions for growth in a uniaxial stress field susceptibility variations as established at the outcrop as well as in the borehole offer a potentially useful tool for stratigraphic correlation of ash flow sheets

crust and upper mantle heterogeneities in the southwest pacific from surface wave phase velocity analysis abstract direct earthquake to station rayleigh and love wave data observed on high gain broadband records are analyzed in order to improve the lateral resolution of the uppermost mantle in the southwest pacific region we used data of nine permanent geoscope and iris stations located in the southern hemisphere and nine other stations as part of two temporary networks the first one installed in new caledonia and vanuatu hereafter named cavascope network by orstom and the eost from louis pasteur university in strasbourg france and the second one installed in the fiji tonga and niue islands hereafter named spase network by washington university in st louis usa in order to collect more significant details on the surficial structures we included the analysis of short period waves down to 8 s a multiple frequency filtering technique has been used to recover phase velocities of rayleigh and love waves for selected earthquakes with magnitude greater than 5 5 and with known centroid moment tensor cmt about 1100 well distributed seismograms have been processed in the period range 8 100 s and corrections for topography and water depth have been applied to the observed phase velocities the geographical distribution of phase velocity anomalies have then been computed using the tomographic method developed by montagner montagner j p 1986a regional three dimensional structures using long period surface waves ann geophys 4 b3 283 294 due to a poor knowledge of dense well distributed crustal thickness values and corresponding velocity models we did not perform or speculate on the construction of an s wave 3d velocity model therefore we limited this study to the interpretation of the phase velocity distribution the location of phase velocity anomalies are well determined and the deviations are discussed within the framework of the geological context and compared with other tomographic models at long periods from 40 s to 100 s our results agree well with most of previous studies the tomographic imaging shows a large contrast between low and high phase velocities along the solomon new hebrides and fiji tonga trenches the lowest phase velocity anomalies are distributed beneath northern and southern fiji basins and the lau basin corresponding to the volume situated just above the dipping slabs whereas the highest values are displayed beneath the pacific plate and the eastern part of indian plate downgoing under the north fiji basin at shorter periods our results show that the phase velocity distributions are well correlated with the large structural crustal domains the use of local temporary broadband stations in the central part of the studied area gives us the opportunity to observe surface waves showing well dispersed trains allowing extended velocity measurements down to 8 s although aliasing due to multipaths become important the continental regions eastern australia new guinea fiji islands and new zealand show low velocities which are likely due to thick continental crust whereas the tasmanian d entrecasteaux and the northern and southern fiji basins are characterized by higher velocities suggesting thinner oceanic crust additional analysis including the anisotropic case and s wave velocity inversion with depth is in progress

three dimensional structure of the upper mantle beneath the atlantic ocean inferred from long period rayleigh waves 1 group and phase velocity distributions group and phase velocity distributions of rayleigh wave fundamental modes are determined in the atlantic ocean using a method of regionalization without a priori constraints for a period range from 50 to 200 s eighty six direct source station paths are studied and 38 out of the best data from weidner s 1974 phase velocities are added to our data set for periods lower than 100 s the importance of shallow layer corrections is described in detail the general features of the distributions agree with global models and smaller scale heterogeneities are revealed a spatial resolution of 1500 km is needed to detect fine lateral heterogeneities in the atlantic the small lateral extent of young oceanic regions and strong lateral velocity gradients do not allow to quantify velocity versus age relationships using our data set on the other hand the regionalization without a priori constraints of phase velocities confirms the presence of a high velocity anomaly beneath the central part of the atlantic for periods greater than 100 s

seismic anisotropy and global geodynamics for many years seismic anisotropy was often neglected mostly because of the inherent heavy mathematical and computational tools needed to describe and model its effects on seismic waves the usual basic knowledge about propagation in isotropic media cannot easily apply to anisotropic media where new phenomena come up such as birefringence or shear wave splitting or difference between directions of propagation of phase velocity and of group velocity consequently geophysicists often claimed that it was a second order effect and considered the earth as isotropic this hypothesis was assumed to be a good approximation because of the random orientation of crystals in most parts of the earth and of the random sampling of anisotropic regions by seismic rays this assumption furthermore made easier the description of wave propagation as well as the parameterization of media in inverse problems an isotropic elastic medium can be described by two independent elastic parameters and lame parameters but the simplest anisotropic medium transverse isotropy with a vertical symmetry axis requires 5 independent parameters love 1927 anderson 1961 to date seismic observations have been explained in terms of isotropic and often thermal lateral heterogeneities ignoring manifestations of anisotropy however since the 1960s it was recognized that most parts of the earth are not only laterally heterogeneous but also anisotropic and that seismic anisotropy provides a simple explanation of different observational data seismic anisotropy contrary to isotropy is reflecting some inherent

runoff and soil loss characteristics on loess slopes covered with aeolian sand layers of different thicknesses under simulated rainfall abstract in the wind water erosion crisscross region of the northern loess plateau parts of loess slopes have been covered by layers of aeolian sand of different thicknesses knowledge of soil erosion processes and magnitudes on these slopes is essential to understanding the coupled water wind erosion processes and to address the resulting downstream coarse sediment problems in the yellow river simulated rainfall intensity 90 mm h 1 was performed to explore the effects of sand layer thickness on runoff and soil loss from loess slopes covered with different sand layer thicknesses 0 0 5 2 5 10 15 20 and 25 cm initial runoff time increased with increasing sand layer thickness with greater changes occurring for the increases in the thinner 0 5 cm than for the thicker layers 5 25 cm total runoff yield from the sand covered loess slopes was 18 55 lower than from the uncovered loess slope and decreased with increasing sand layer thickness in contrast total sediment yield was up to 14 times greater from the sand covered loess slopes than from the uncovered loess slope and rapidly increased with increasing sand layer thickness during the rainstorm runoff and soil loss rates exhibited unimodal distributions and they were related by a positive linear function both before and after the maximum soil loss rate that had a high determination coefficient r2 0 8 p

biomarkers in sedimentary sequences indicators to track sediment sources over decadal timescales abstract long term sedimentary sequence research can reveal how human activities and climate interact to affect catchment vegetation flooding soil erosion and sediment sources in this study a biomarker sediment fingerprinting technique based on n alkanes was used to identify long timescale decadal sediment sources in a small agricultural catchment however the highly saline carbonate environment and bacterial and algal activities elevated the levels of even chain n alkanes in the sediments leading to an obvious even over odd predominance of short and middle components c 15 c 26 therefore by analyzing three odd long chain n alkanes c 27 c 29 and c 31 in 27 source samples from cropland gully and steep slope areas and one sediment sequence one cultivated horizon and 47 flood couplets a composite fingerprinting method and genetic algorithm optimization were applied to find the optimal source contributions to sediments the biomarker fingerprinting results demonstrated that the primary sediment source is gullies followed by cropland and steep slope areas the average median source contributions associated with 47 flood couples collected from sediment core samples ranged from 0 0 1 to 91 9 0 4 with an average of 45 0 for gullies 0 0 4 to 95 6 1 6 with an average of 38 2 for cropland and 0 2 1 to 60 7 0 4 with an average of 16 8 for steep slopes however because farmers were highly motivated to manage the cropland after the 1980s over half the sediments were derived from cropland in the 1980s biomarkers have significant advantages in the identification of sediments derived from different landscape units e g gully and steep slope areas and n alkanes have considerable potential in high resolution research of environmental change based on soil erosion in the hilly loess plateau region

the identification and biogeochemical interpretation of fossil magnetotactic bacteria magnetotactic bacteria which most commonly live within the oxic anoxic transition zone oatz of aquatic environments produce intracellular crystals of magnetic minerals specifically magnetite or greigite the crystals cause the bacteria to orient themselves passively with respect to the geomagnetic field and thereby facilitate the bacteria s search for optimal conditions within the sharp chemical gradients of the oatz the bacteria may also gain energy from the redox cycling of their crystals because magnetotactic bacteria benefit from their magnetic moments natural selection has promoted the development of traits that increase the efficiency with which the intracellular crystals impart magnetic moments to cells these traits also allow crystals produced by magnetotactic bacteria called magnetofossils when preserved in sediments to be distinguished from abiogenic particles and particles produced as extracellular byproducts of bacterial metabolism magnetofossils are recognizable based on their narrow size and shape distributions distinctive morphologies with blunt crystal edges chain arrangement chemical purity and crystallographic perfection this article presents a scheme for rating magnetofossil robustness based on these traits the magnetofossil record extends robustly to the cretaceous and with lesser certainty to the late archean because magnetotactic bacteria predominantly live in the oatz the abundance and character of their fossils can reflect environmental changes that alter the chemical stratification of sediments and the water column the magnetofossil record therefore provides an underutilized archive of paleoenvironmental information several studies have demonstrated a relationship between magnetofossil abundance and glacial interglacial cycles likely mediated by changes in pore water oxygen levels more speculatively a better developed magnetofossil record might provide constraints on the long term evolution of marine redox stratification more work in modern and ancient settings is necessary to explicate the mechanisms linking the abundance and character of magnetofossils to ancient biogeochemistry

quantitative models of sediment generation and provenance state of the art and future developments abstract an overview of quantitative approaches to analysis and modelling of sediment generation and provenance is presented with an emphasis on major framework components as determined by means of petrographic techniques conceptual models of sediment provenance are shown to be consistent with two classes of numerical statistical models i e linear mixing models and compositional linear models these cannot be placed within a common mathematical framework because the former requires that sediment composition is expressed in terms of proportions whereas the latter requires that sediment composition is expressed in terms of log ratios of proportions additivity of proportions a fundamental assumption in linear mixing models cannot be readily expressed in log ratio terms linear mixing models may be used to describe compositional variability in terms of physical and conceptual un mixing models of physical un mixing are appropriate for describing compositional variation within transport invariant subpopulations of grains as a result of varying rates of supply of detritus from multiple sources conceptual un mixing governs the relations among chemical mineralogical and petrographic characteristics of sediments which represent different descriptive levels within a compositional hierarchy compositional linear process models may be used to describe compositional and or textural evolution resulting from selective modifications induced by sediment transport as well as chemical and mechanical weathering current approaches to modelling of surface processes treat the coupled evolution of source areas and sedimentary basins in terms of bulk mass transfer only and do not take into account compositional and textural sediment properties moving from the inverse modelling approach embodied in provenance research to process based forward models of sediment generation which provide detailed predictions of sediment properties meets with considerable albeit not insurmountable problems strategies for developing more advanced parameterizations of sediment properties and for simulating their evolution are proposed and expansion of current data acquisition protocols is discussed in the light of data requirements for such advanced sediment generation models inclusion of sediment generation modules in models of landscape evolution and basin filling will mark a significant step towards full fledged source to sink simulations of earth surface processes

where can seismic anisotropy be detected in the earth s mantle in boundary layers during the last 30 years considerable evidence of seismic anisotropy has accumulated demonstrating that it is present at all scales but not in all depth ranges we detail which conditions are necessary to detect large scale seismic anisotropy firstly minerals must display a strong anisotropy at the microscopic scale and or the medium must be finely layered secondly the relative orientations of symmetry axes in the different crystals must not counteract in destroying the intrinsic anisotropy of each mineral and there must be efficient mechanisms of orientation of minerals and aggregates finally the strain field must be coherent at large scale in order to preserve long wavelength anisotropy part of shallow anisotropy can be related to the past strain field frozen in anisotropy however the deep anisotropy is due to the present strain field all these conditions are fulfilled only in boundary layers of convective mantle we review in this paper the seismic data sets which provide insight into the location at depth of large scale anisotropy from the d layer up to the lithosphere in addition to the well documented seismic anisotropy in the lithosphere and asthenosphere there is new evidence of seismic anisotropy in the upper 400 660 km and lower 660 900 km transition zones and in the d layer nonetheless the bulk of the lower mantle seems close to isotropy if we assume the hypothesis that seismic anisotropy is associated with boundary layers in convective systems these observations strongly suggest that the transition zone is a boundary layer which makes the pasage of matter between the upper and the lower mantle difficult however this general statement does not rule out flow circulation between the upper and lower mantles finally the geophysical mineral physics and geological applications are briefly reviewed an intercomparison between surface wave anisotropy and body wave anisotropy data sets is presented we discuss the scientific potential of seismic anisotropy and how it makes it possible to gain more insight into continental root deformation and geodynamics processes

rotational basement kinematics deduced from remagnetized cover rocks internal sierras southwestern pyrenees 1 paleomagnetic data from the internal sierras unravel the kinematic relationship between basement guarga gavarnie bielsa and cover thrusts larra monte perdido the new data come from an area of 100 km along strike and 5 15 km across strike of the southwestern pyrenees the area covers a variety of structural positions that range from cover to basement thrusts from 84 sites located in upper cretaceous two meaningful magnetic components are found 1 the higher temperature c component unblocks at 575 c presents two polarities is prefolding has a mean declination and inclination d i of 010 44 95 8 k 15 and is considered primary and 2 the intermediate b component unblocks between 250 c and 450 c has a mean d i of 198 43 95 4 k 18 and has always reverse polarity and postfolding the nine sites located in the eocene flysch south of the upper cretaceous show the same postfolding component b the acquisition of this intermediate component alludes to a widespread tectonic related remagnetization event affecting the internal sierras this event must be younger than the folding of the flysch deposits middle upper eocene the tilting induced by the basement thrust gavarnie bielsa in the axial zone does not alter the inclination of the b so that the sediments acquire the b component later than priabonian emplacement age of the gavarnie thrust the b component is rotated clockwise with respect to the tertiary reference this means that the rotation takes place after the remagnetization event the position of the c component before the rotation of the b component is negligibly rotated d i of 002 44 95 7 k 94 with respect to the cretaceous reference therefore the b component records the last and only rotational event in the region the rotation is related to the latest basement deformation guarga thrust during upper oligocene times and it reflects the regional shortening gradient in the southwestern pyrenees the emplacement of the larra monte perdido cover thrust system that took place prior to basement thrusts mentioned above did not undergo any significant rotation

anomalous unblocking temperatures viscosity and frequency dependent susceptibility in the chemically remagnetized trenton limestone abstract chemical remagnetization of many carbonate rock units occurred by diagenetic alteration of iron sulfide precursors and by authigenesis of fine grained magnetite which can commonly be recognized by a distinctive set of rock magnetic attributes these carbonates also typically exhibit anomalously high unblocking temperatures for recent thermoviscous components that have overprinted the characteristic chemical remanence recent work has shown that departures from neel theory as applied in the model of pullaiah et al can generally be attributed to vrm carried by multidomain particles to which the theory does not apply in the remagnetized carbonates however rock magnetic data all point to an overwhelming dominance of fine superparamagnetic and stable single domain particles therefore we explore possible alternative causes for the anomalous unblocking temperatures including maghemitization and magnetocrystalline rather than shape anisotropy new blocking unblocking models for these cases however fail to match the observed behavior leading to the conclusion that the anomalous unblocking temperatures are indeed probably attributable to multidomain carriers a possible alternative explanation is an increase in coercivity due to maghemitization of single domain particles after acquisition of the viscous overprint causing a significant increase in their unblocking temperatures new frequency dependent susceptibility measurements at low temperatures allow us to focus on the time temperature behavior of the particles at the superparamagnetic stable single domain threshold and we find that these do closely follow the predictions of neel theory as formulated in the models of pullaiah et al and walton middleton schmidt

orogenic remagnetizations in the front ranges and inner foothills of the southern canadian cordillera chemical harbinger and thermal handmaiden of cordilleran deformation abstract paleomagnetic studies of carbonate rocks in mountain belts have been helpful to the understanding of orogenic mational origin with only one exception the a component has normal polarity in the front ranges and reverse processes the timing of deformation and the nature of fluid flow in actively deforming foreland basins most studies on shallow water carbonates indicate that their remanence is not primary but rather they record remagnetization events contemporaneous with orogeny by considering the remanent directions fold test results and rock magnetic properties and tying these results to complementary structural geochronological and geochemical studies we are able to interpret deformation history hydrological environment and orogenic diagenesis we study the relationship between remagnetization and deformation of paleozoic carbonates of the front ranges and inner foothills of the southern canadian rockies the magnetic properties are remarkably constant along 500 km strike length as sampled at 124 sites through 4 transects primary paleozoic remanent directions which would have shallow inclination are never observed rather the paleomagnetic signal is dominated by geographically persistent remagnetizations characterized by steep inclination as well as a soft present field overprint we observed two distinctive secondary magnetizations named the a and b components carried by fine grained magnetite pervasive diagenesis induced the a component a total chemical remanent remagnetization poles for the a component are better concentrated after bedding correction indicating a pre or early syndefor polarity in the inner foothills pole positions polarity and geological and thermal constraints indicate that the a component was acquired diachronously in advance of the eastward migrating cordilleran tectonic wedge subsequently an intermediate temperature partial thermo remanent remagnetization the b component was superimposed on large regions of the front ranges and inner foothills b component directions are brought into optimal concentration by differential untilting of 0 to 50 indicating that the component was acquired after the rocks were incorporated into the orogenic wedge but before the end of contractional deformation the b component is strongest within a couple of kilometers of the frontal thrust of the front ranges the relative magnitude of the b to a components and the maximum unblocking temperature of the b component decrease away from the frontal thrust over about 30 km both to the west and to the east the b component thermal overprint was attained by 250 c heating in response to tectonic or possibly sedimentary loading it was preserved by a rapid cooling accompanying a differential uplift and erosion of up to 8 km in the vicinity of the frontal thrust late in or post dating its local tilting history the likely cause was uplift of the exposed structural panel by contraction of younger underlying thrust structures

the upper mantle degree 2 constraints and inferences from global mantle wave attenuation measurements we present the results of an analysis of global lateral variations in anelasticity of the upper mantle as measured from very long period rayleigh waves observed on the geoscope network four consecutive wave trains are used on each record to eliminate uncertainty on the amplitude at the source and to take into account in a linear manner focussing effects due to lateral variations in elastic parameters local estimates of attenuation are obtained using an inversion method based on the introduction of a correlation length as an alternative to spherical harmonics expansion comparison of phase velocity and attenuation maps obtained at various periods shows a strong correlation of high q and high velocity regions respectively low q and low velocity both for great circle and minor arc data at periods around 200 s the detailed analysis of the degree 2 pattern well resolved in the attenuation maps around this period shows that it originates in the depth range 250 500 km and indicates that of the upper mantle degree 2 pattern observed in shear velocity is likely to be of thermal origin possibly related to the topmost part of the large scale convective system corrections for dispersion due to anelastic attenuation in degree 2 lead to significant decrease of corresponding lateral variations in shear velocity and a better agreement in phase and amplitude of the upper mantle degree 2 pattern with that observed in the geoid this study shows that it is important to consider correcting presently available upper mantle tomographic models for the effects of intrinsic attenuation at long periods before performing any comparison with short period data or other geophysical parameters

a high resolution absolute dated late pleistocene monsoon record from hulu cave china oxygen isotope records of five stalagmites from hulu cave near nanjing bear a remarkable resemblance to oxygen isotope records from greenland ice cores suggesting that east asian monsoon intensity changed in concert with greenland temperature between 11 000 and 75 000 years before the present yr b p between 11 000 and 30 000 yr b p the timing of changes in the monsoon as established with 230th dates generally agrees with the timing of temperature changes from the greenland ice sheet project two gisp2 core which supports gisp2 s chronology in this interval our record links north atlantic climate with the meridional transport of heat and moisture from the warmest part of the ocean where the summer east asian monsoon originates

chemical characterization of atmospheric dust from a weekly time series in the north red sea between 2006 and 2010 abstract atmospheric dust loads and chemical compositions serve as a key link between global climate patterns and marine biogeochemical cycles the primary source of atmospheric dust in the world today is the sahara arabian desert belt although this source was also active during the quaternary the interpretation of paleo dust records and their effects on marine ecosystems is complicated by the scarcely reported atmospheric load patterns of bioavailable phases i e water and acid leachable phases and present day contamination of anthropogenic components this study reports a multi annual time series of atmospheric dust loads 2006 2016 and their chemical compositions 2006 2010 collected in the north gulf of aqaba north red sea at a weekly to bi weekly resolution major and trace element abundances in each sample are reported for three fractions water soluble salts carbonates and oxides weak acid leach and al silicates dust loads vary seasonally from low values in late summer 20 30 g m 3 to higher values in the fall and highest values in late winter and early spring 150 250 g m 3 major and trace element abundances allow to distinguish between the sources and chemical compositions that dominate high and low dust loads in each season the water leachable fraction l0 is relatively enriched in na ca k and mg the acid leachable fraction l1 is enriched in ca as well as na al mg zn cd and pb and the silicate residue l2 in al and fe high dust loads occurring mainly during winter and spring months are characterized by low mg ca l1 l2 low k al and na al l1 and high ca al l1 high mg al l2 and relatively un weathered l2 contents high dust load intervals during winter months are characterized by low passing air masses originating from the sahara while the ambient winter dust low dust load is associated with proximal source regions from the east sahara and arabian peninsula during late winter and spring months high dust loads originate from central and west sahara and to a lesser extent from north sahara low dust loads characterize the summer with limited compositional variability relative to winter spring months summer dust is generally characterized by high k al l1 ratios relative to late winter and spring it is also relatively high in anthropogenic trace elements in the l0 and l1 fractions e g zn al pb al cr al ni al and v al whereby back trajectories indicate the source of these components is primarily from south and east europe the total load ng m 3 of anthropogenic trace elements however remains higher during winter and spring stemming from the overall significantly higher dust loads characterizing this time window the temporal load patterns of important micronutrients such as fe cd zn cu ni and others in the bio available phases l0 l1 are not correlated with major nutrients or chlorophyll a sea surface concentrations suggesting that the atmospheric dust plays a limited role in driving primary productivity in the oligotrophic surface waters of the gulf of aqaba on a wider scale the results provide unique chemical fingerprinting of sahara arabian dust that can be applied to reconstruct past trends in dust loads recorded in deep sea cores and other geological archives from this and other regions

discriminating sediment archives and sedimentary processes in the arid endorheic ejina basin nw china using a robust geochemical approach abstract geochemical characteristics have been intensively used to assign sediment properties to paleoclimate and provenance nonetheless in particular concerning the arid context bulk geochemistry of different sediment archives and corresponding process interpretations are hitherto elusive the ejina basin with its suite of different sediment archives is known as one of the main sources for the loess accumulation on the chinese loess plateau in order to understand mechanisms along this supra regional sediment cascade it is crucial to decipher the archive characteristics and formation processes to address these issues five profiles in different geomorphological contexts were selected analyses of x ray fluorescence and diffraction grain size optically stimulated luminescence and radiocarbon dating were performed robust factor analysis was applied to reduce the attribute space to the process space of sedimentation history five sediment archives from three lithologic units exhibit geochemical characteristics as follows i aeolian sands have high contents of zr and hf whereas only hf can be regarded as a valuable indicator to discriminate the coarse sand proportion ii sandy loess has high ca and sr contents which both exhibit broad correlations with the medium to coarse silt proportions iii lacustrine clays have high contents of felsic ferromagnesian and mica source elements e g k fe ti v and ni iv fluvial sands have high contents of mg cl and na which may be enriched in evaporite minerals v alluvial gravels have high contents of cr which may originate from nearby cr rich bedrock temporal variations can be illustrated by four robust factors weathering intensity silicate bearing mineral abundance saline alkaline magnitude and quasi constant aeolian input in summary the bulk composition of the late quaternary sediments in this arid context is governed by the nature of the source terrain weak chemical weathering authigenic minerals aeolian sand input whereas pedogenesis and diagenesis exert only limited influences hence this study demonstrates a practical geochemical strategy supplemented by grain size and mineralogical data to discriminate sediment archives and thereafter enhance our ability to offer more intriguing information about the sedimentary processes in the arid central asia

variation with age of the deep structure of the pacific ocean inferred from very long period rayleigh wave dispersion the propagation of rayleigh waves along 44 direct paths across the pacific ocean is studied and a regionalization of the dispersion according to the age of the sea floor is performed the group velocity dispersion curves characteristic of each one of four age regions considered are obtained for periods up to 300 s these curves show an increase of group velocities with age over the whole period range considered the shear wave velocity models inferred yield a lithosphere thickening with age and show the presence below the lithosphere of two zones where negative velocity anomalies decrease with increasing age the low velocity zone and a zone at a depth of 350 km

investigation of upper mantle structure under young regions of the southeast pacific using long period rayleigh waves abstract long period rayleigh wave group velocity dispersion curves are presented for paths across the east pacific ocean the records are from the ipg site at pamatai tahiti and the ida station at nana for the first time direct path observations of group velocities up to 300 s have been obtained this study shows that for young oceanic regions group velocities are low even at long periods the observations are interpreted in terms of an s wave velocity model by a generalized inversion scheme in the models for young ages the low velocity zone under the asthenosphere lid is well developed with a strong velocity gradient at the bottom of this zone followed at larger depths by a plateau representing a lower velocity zone and a marked gradient at 400 km

authigenesis of magnetite in organic rich sediment next to a dike implications for thermoviscous and chemical remagnetizations rock magnetic results from organic rich sediment around a tertiary dike in scotland indicate changes in magnetic mineralogy and magnetite content as well as grain size in the contact zone sediment specimens within 85 cm of a 90 cm thick dike contain a tertiary magnetization that is equivalent in direction to the thermal remanent magnetization in the dike whereas the sediment at greater distances does not carry a stable remanence based on acquisition of isothermal remanent magnetization irm thermal decay of triaxial irms and s ratio determinations magnetite is the dominant magnetic phase in the sediment except near the dike 8 cm where hematite is abundant maximum laboratory unblocking temperatures tbmax for the magnetization are higher than predicted by a thermal cooling model at distances greater than 40 cm but the tbmax values are not corrected for gradual cooling of the dike and are therefore overestimates trends in rock magnetic parameters such as irm at 300 mt and anhysteretic remanence arm are consistent with an increasing contribution of single domain pseudosingle domain magnetite towards the dike an increase in saturation irm sirm along with a decrease in arm sirm values 25 cm from the dike also suggest an increase in multidomain magnetite low temperature experiments indicate the presence of abundant superparamagnetic magnetite changes in hysteresis parameters are consistent with changes in the relative amounts of the different magnetite size fractions towards the dike the onset of changes in the magnetite grain size budget starting at 85 cm or approximately one dike width suggests that chemical processes contributed to the remanence at temperatures as low as 220 c petrographic and geochemical studies suggest that the contact zone was not pervasively altered by hydrothermal fluids utilizing the dike as an analog for thermal processes that occur during burial the results of this study suggest that moderately elevated burial temperatures are sufficient to cause magneto chemical changes

thermal regime of the southeast indian ridge between 88 e and 140 e remarks on the subsidence of the ridge flanks 1 the flanks of the southeast indian ridge are characterized by anomalously low subsidence rates for the 0 25 ma period less than 300 m ma 1 2 between 101 e and 120 e and less than 260 m ma 1 2 within the australian antarctic discordance aad between 120 e and 128 e the expected along axis variation in mantle temperature 50 c is too small to explain this observation even when the temperature dependence of the mantle physical properties is accounted for we successively analyze the effect on subsidence of different factors such as variations in crustal thickness the dynamic contribution of an old detached slab supposedly present within the mantle below the aad and depletion in m a parameter here defined as the ubiquitously distributed melt fraction within the asthenosphere these effects may all contribute to the observed anomalously low subsidence rate of the ridge flanks with the most significant contribution being probably related to the depletion in m however these effects have a deep seated origin that cannot explain the abruptness of the transition across the fracture zones that delineate the boundaries of the aad near 120 e and near 128 e respectively

rock magnetism of remagnetized carbonate rocks another look authigenic formation of fine grained magnetite is responsible for widespread chemical remagnetization of many carbonate rocks authigenic magnetite grains dominantly in the super paramagnetic and stable single domain size range also give rise to distinctiverock magnetic prop erties now commonly used as a fingerprint of remagnetization we re examine the basis of this association in terms of magnetic mineralogy and particle size distribution in remagnetized carbon ates having these characteristic rock magnetic properties including wasp waisted hysteresis loops high ratios of anhysteretic remanence to saturation remanence and frequency dependent susceptibility new measurements on samples from the helderberg group allow us to quantify the proportions of superparamagnetic stable single domain and larger grains and to evaluate the mineralogical composition of the remanence carriers the dominant magnetic phase is magnetite like with sufficient impurity to completely suppress the verwey transition particle sizes are extremely fine approximately 75 of the total magnetite content is superparamagnetic at room temperature and almost all of the rest is stable single domain although it has been pro posed that the single domain magnetite in these remagnetized carbonates lacks shape anisotropy and is therefore controlled by cubic magnetocrystalline anisotropy we have found strong exper imental evidence that cubic anisotropy is not an important underlying factor in the rock magnetic signature of chemical remagnetization the usefulness of a palaeomagnetic remanence is directly related to the accuracy with which its age is known e g van der voo 1990 primary remanence acquiredduringorverysoonafterrockformation pro videsdirectinformationonpalaeofieldorientationand strengthatthattime thepossibilityofpartialorcom plete remagnetization at a later time complicates palaeomagneticinterpretation ashaslongbeenrecog nized e g graham 1949 every robust palaeomag netic study must therefore include some effort to constrain the ages of identified components of the natural remanent magnetization nrm relative dating with respect to sedimentary processes struc tural tilting or cross cutting relationships is the basis of the classical geometric palaeomagnetic tests fold test and conglomerate test graham 1949 baked contact test everitt clegg 1962 unconformity test kirschvink 1978 the special circumstances required for application of these tests are often not available however or positive test results may providerelativelylooseconstraintsallowingmagneti zation ages that significantly post date the age of the rock formation as a result other evidence although generally more indirect becomes essential in evaluating the age origin and significance of nrm components such evidence commonly includes petrographic observations isotopic andgeo chemical data and rock magnetic characterization by their very existence magnetic overprints provide evidence of some process or event of