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

shear wave splitting and subcontinental mantle deformation splitting observations are interpreted in terms of the strain induced lattice preferred orientation of mantle minerals especially olivine we consider three hypotheses concerning the origin of the continental anlsotropy 1 strain associated with absolute plate motion as in the oceanic upper mantle 2 crustal stress and 3 the past and present internal deformation of the subcontinental upper mantle by tectonic episodes it is found that the last hypothesis is the most successful namely that the most recent significant episode of internal deformation appears to be the best predictor of q for stable continental regions this is interpreted as fossil anisotropy whereas for presently active regions such as alaska the anisotropy reflects present day tectonic activity in the stable portion of north america there is a good correlation between delay time and lithospheric thickness this is consistent with the anisotropy being localized in the subcontinental lithosphere and suggests that intrinsic anisotropy is approximately constant the acceptance of this hypothesis has several implications for subcontinental mantle deformation first it argues for coherent deformation of the continental lithosphere crust and mantle during orogenies this implies that the anisotropic portion of the lithosphere was present since the deformational episode and rules out the addition of undeformed material to this layer by subsequent underplating or conductive growth of the thermal boundary layer one of the most important issues in the study of orogenies is the need to reconcile the formation of thickened lithosphere with the paradoxically high mantle temperatures often associated with orogenic episodes most efforts to date have focussed on modes of deformation whereby the cold lithospheric mantle is removed by convective instability or delamination and replaced by warm asthenosphere these models however are incompatible with the evidence for preserved coherent lithospheric deformation rather the deformed mantle appears to have been heated in place we suggest that the elevated mantle temperatures may be due to the strain heating accompanying the deformation

seismic anisotropy from the variscan core of iberia to the western african craton new constrains on upper mantle flow at regional scales abstract the regional mantle flow beneath the westernmost mediterranean basin and its transition to the atlantic domain is addressed by inspecting the anisotropic properties of the mantle more than 100 new sites from the variscan core of iberia to the northern rim of the western african craton are now investigated using the data provided by different temporary and permanent broad band seismic arrays our main objective is to provide a larger regional framework to the results recently presented along the gibraltar arc in order to check the validity of the different geodynamic interpretations proposed so far the significant variations in the retrieved anisotropic parameters suggest that different processes must be invoked to explain the origin of the observed anisotropy beneath the variscan units of the central iberian massif the new results show a moderate amount of anisotropy with fast polarization directions fpd oriented close to e w those results can only be explained in terms of global mantle flow if models accounting for contributions from surface plate motion net lithosphere rotation and density variations are taken into consideration one of the major results presented is the significant number of good quality data without evidence of anisotropy nulls observed beneath permanent stations in southern portugal those nulls can be explained by the presence of a predominantly vertical mantle flow associated to large variations in the lithospheric thickness beneath the gibraltar arc the fpd show a spectacular rotation evidenced by the results presented by diaz et al 2010 and miller et al 2013 those results are reviewed here taking also into consideration the geodynamic modeling presented recently by alpert et al 2013 and other geophysical and geodetic results further south the analysis of new broad band stations installed in the moroccan meseta and the high atlas show a small degree on anisotropy and a large number of null events pointing again to the presence of vertical flow in the mantle the results favor an asthenospheric origin related to present day mantle flow for the anisotropy observed from the variscan core of iberia to the northern rim of the west african craton this flow is deflected around the high velocity slab beneath the gibraltar arc and seems affected locally by vertical flow associated to edge driven convective cells the presence of significant backazimuthal variations in the anisotropic parameters retrieved from single events suggests that a second order contribution from an anisotropic layer within the lithosphere may also exist

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

new york alabama lineament a buried right slip fault bordering the appalachians and mid continent north america the new york alabama ny al lineament recognized in 1978 is a magnetic anomaly that delineates a fundamental though historically enigmatic crustal boundary in eastern north america that is deeply buried beneath the appalachian basin data not in the original aeromagnetic data set particularly the lack of any information available at the time to constrain the southern continuation of the anomaly southwest of tennessee left the source of the lineament open to conjecture we use modern digital aeromagnetic maps to fill in these data gaps and for the first time constrain the southern termination of the ny al lineament our analysis indicates that the lineament reflects a crustal scale right lateral strike slip fault that has displaced anomalies attributed to grenville orogenesis by 220 km palinspastic restoration of this displacement rearranges the trace of the grenville belt in southern rodinia and implies only passive influence on later formed appalachian structures the precise timing of dextral movement on the ny al structure is not resolvable from the existing data set but it must have occurred during one of or combinations of the following events 1 a late postcontractional post ottawan stage of the grenville orogeny 2 late neoproterozoic to cambrian rifting of laurentia or 3 right slip reactivation during the late neoproterozoic cambrian rifting of laurentia or during appalachian movements our palinspastic reconstruction also implies that the host rocks for modern earthquakes in the eastern tennessee seismic zone are metasedimentary gneisses and it provides an explanation for the spatial location and size of the seismic zone

grenville basement structure associated with the eastern tennessee seismic zone southeastern usa the eastern tennessee seismic zone extends more than 300 km from as far north as southeastern kentucky southward into alabama southeastern united states we propose that a large scale shear zone which originated as a continental transform fault during the grenville orogeny and assembly of supercontinent rodinia constitutes the framework for earthquake activity in the eastern tennessee seismic zone this new seismotectonic model is based on a diverse set of geophysical and geological observations including paleomagnetic and isotopic constraints on the growth of southeastern laurentia during the grenville orogeny

crustal evolution in the southern appalachian orogen evidence from hf isotopes in detrital zircons abstract paired u pb and lu hf isotopic compositions of individual detrital zircons reveal that mesoproterozoic lithosphere in the southernmost appalachian orogen evolved almost continuously from 1200 to 900 ma with a noticeable concentration only at 1050 ma the evolution of the lu hf system in this crust is characterized by a systematic linear evolution pattern of 176hf 177hf versus age over this interval which suggests a limited range of mixing ratios between juvenile and older crustal components to create a new mesoproterozoic lithospheric reservoir extrapolation of the lu hf systematics of this reservoir from the mesoproterozoic to the paleozoic using typical crustal values shows general coincidence with the lower part of the hf isotopic array defined by paleozoic detrital zircons because the paleozoic array extends to both much higher and much lower ehf values than are likely to develop from extrapolations of the mesoproterozoic array the paleozoic array is most compatible with an orogen fo

evidence for mechanically coupled lithosphere in central asia and resulting implications the recent dramatic increase in seismic anisotropy and surface global positioning system gps data for central asia permits a comprehensive examination of the mantle s role in mountain building a joint analysis of 178 shear wave splitting and 2000 gps observations using a new technique reveals that the crust and lithospheric mantle deform coherently arguing for crust mantle mechanical coupling during deformation the observed spatial variations in anisotropy refl ect the large scale pattern of lithospheric deformation as well as a change in deformational style from simple shear on the tibetan plateau transitioning to pure shear in surrounding regions

fe isotopes and the contrasting petrogenesis of a i and s type granite abstract we present new fe isotope data of 42 s i and a type ferroan granites from the cambrian delamerian orogen in south australia the palaeozoic lachlan fold belt and western usa interpretation of these data together with modelling suggests that magmatic processes do result in quite complex fe isotopic differentiation trends and can lead to granites with isotopically heavy iron with 57 fe 0 35 by comparison mid ocean ridge basalts morbs have 57 fe 0 15 teng et al 2013 these variations are similar to those previously reported poitrasson and freydier 2005 heimann et al 2008 telus et al 2012 but contrary to some interpretations beard and johnson 2006 heimann et al 2008 heavy values are not necessarily the product of late stage hydrothermal fluid loss though this process is undoubtedly also an important factor in some circumstances a type ferroan granites reach very heavy 57 fe values 0 4 0 5 whereas i types are systematically lighter 57 fe 0 2 s type granites show a range of intermediate values but also tend to be isotopically heavy 57 fe 0 2 0 4 our results show that the iron isotopic values and trends are signatures that reflect granite generation processes a modelling using the rhyolite melts software suggests that contrasting trajectories and end points in fe isotope evolution towards granite depend on oxidation state of the evolving magma and whether or not the system is oxygen buffered iron isotopic evolution supports an origin of ferroan a type granite from protracted closed magma chamber fractionation of moderately reduced mafic magmas in these systems magnetite saturation is delayed and the ferric iron budget is finite i type systems originate with the supply of relatively oxidised hydrous subduction related magmas from the mantle wedge to the upper plate crust these then experience oxygen buffered open system afc processes in lower crustal hot zones s type magmas are crustal melts that crystallise under reduced conditions initially imposed at source by sulphidic or graphitic sedimentary protoliths the composition of the resulting melts reflects the domination of partial melting where conditions are hence buffered open system followed by subsequent late stage closed system fractionation of these extracted reduced magmas

seismic anisotropy beneath the mississippi embayment and the new madrid seismic zone a study of shear wave splitting shear wave splitting associated with the mississippi embayment me is determined using teleseismic sks phases recorded by the northern embayment lithosphere experiment nele the usarray transportable array ta and the new madrid seismic network for the period 2005 2016 our data set consists of 5900 individual splitting measurements from 257 earthquakes recorded at 151 stations within and outside the me stations outside of the me exhibit significant shear wave splitting with average delay times between 0 4 s and 1 8 s to the northeast and east of the me nearly all observed fast orientations are approximately oriented northeast southwest in agreement with absolute plate motion apm predicted by hs3 nuvel 1a the homogeneity of the fast orientations in this region suggests that the splitting is due to active flow in the asthenosphere a counterclockwise rotation in the splitting orientation is observed moving northeast to northwest across the study area inside the me some stations show large and systematic deviations of the measured fast orientations from the apm the delay times within the entire me range from 0 9 s to 2 1 s splitting complexity is attributed to relic lithospheric fabrics formed during past tectonic events including passage of a hot spot in mid cretaceous time the anisotropy may also be linked to the presence of a southwest dipping region of low p and s wave velocities below the me or to deeper flow in the asthenosphere

shear wave splitting and the pattern of mantle flow beneath eastern oregon a r t i c l e i n f o article history the tectonic and geologic setting of eastern oregon includes the volcanically active high lava plains hlp province and the accreted terrains of the blue and wallowa mountains and is bounded by the columbia river ood basalts to the north basin and range extension to the south the cascade arc to the west and stable north america to the east several models have been proposed to explain the tectonic evolution of eastern oregon and in particular the voluminous volcanic activity in the hlp but a consensus on which model fully describes the complex range of processes remains elusive measurements of the seismic anisotropy that results from active mantle ow beneath the region can provide a crucial test of such models to constrain this anisotropy here we present new sks splitting results obtained at approximately 200 broadband seismic stations in eastern oregon and the surrounding region data come from the usarray transportable array ta and two temporary experiments carried out in the hlp and in the wallowa mountains our splitting data set includes 2900 individual splitting measurements from sks phases recorded between 2006 and 2008 stations in eastern oregon exhibit signi cant shear wave splitting with average delay times at individual stations between 0 8 s and 2 7 s in the hlp nearly all observed fast directions are approximately e w while to the north in the blue and wallowa mountains there is more variability in the splitting patterns the average delay time observed at stations located in the heart of the hlp province is 2 s well above the global average of 1 s for continental regions we infer from the large split times and homogeneous fast directions that there must be signi cant active ow in a roughly e w direction in the asthenosphere beneath the hlp this inferred ow eld places a strong constraint on models that seek to explain the young tectonomagmatic activity in the region in the wallowa region the anisotropic signature is more complicated and there may be a signi cant contribution from fossil fabrics in the crust or mantle lithosphere

a comparative analysis of pre silurian crustal building blocks of the northern and the southern appalachian orogen the new york promontory serves as the divide between the northern and southern segments of the appalachian orogen antiquated subdivisions distinct for each segment implied that they had lithotectonic histories that were independent of each other using new lithotectonic subdivisions we compare first order features of the pre silurian orogenic building blocks in order to test the validity of the implication of independent lithotectonic histories for the two segments three lithotectonic divisions termed here the laurentian iapetan and the peri gondwanan realms characterize the entire orogen the laurentian realm composed of native north american rocks is remarkably uniform for the length of the orogen it records the multistage neoproterozoic early paleozoic rift drift history of the appalachian passive margin formation of a taconic seaway and the ultimate demise of both in the middle ordovician the iapetan realm encompasses mainly oceanic and magmatic arc tracts that once lay within the iapetus ocean between laurentia and gondwana in the northern segment the realm is divisible on the basis of stratigraphy and faunal provinciality into peri laurentian and peri gondwanan tracts that were amalgamated in the late ordovician south of new york stratigraphic and faunal controls decrease markedly rock associations are not inconsistent with those of the northern appalachians although second order differences exist exposed exotic crustal blocks of the peri gondwanan realm include ganderia avalonia and meguma in the north and carolinia in the south carolinia most closely resembles ganderia both in early evolution and late ordovician silurian docking to laurentia our comparison indicates that to a first order the pre silurian appalachian orogen developed uniformly starting with complex rifting and a subsequent drift phase to form the appalachian margin followed by the consolidation of iapetan components and ending with accretion of the peri gonwanan ganderia and carolinia this deduction implies that any first order differences between northern and southern segments post date late ordovician consolidation of a large portion of the orogen

iron isotope fractionation during oceanic crust alteration abstract the purpose of this work is to study the mobility and budget of fe isotopes in the oceanic crust and in particular during low temperature interaction of seawater with oceanic basalt we carried out this investigation using samples from ocean drilling program odp site 801c drilled during leg 129 and leg 185 in jurassic pacific oceanic crust seaward of the mariana trench the site comprises approximately 450 m of sediment overlying a section of 500 m of basalt which includes intercalated pelagic and chemical sediments in the upper basaltic units and two low temperature 10 30 c ocherous si fe hydrothermal deposits fe was chemically separated from 70 selected samples and 57fe 54fe ratios were measured by mc icp ms isoprobe the isotopic ratios were measured relative to an internal standard solution and are reported relative to the international fe standard irmm 14 based on duplicate measurements of natural samples an external precision of 0 2 2 has been obtained the results indicate that the deep sea sediment section has a restricted range of 57fe which is close to the igneous rock value in contrast large variations are observed in the basaltic section with positive 57fe values up to 2 05 for highly altered basalts and negative values down to 2 49 for the associated alteration products and hydrothermal deposits secondary fe minerals such as fe oxyhydroxides or fe bearing clays celadonite and saponite have highly variable 57fe values that have been interpreted as resulting from the partial oxidation of fe2 leached during basalt alteration and precipitated as fe3 rich minerals in contrast altered basalts at site 801c which are depleted in fe up to 80 display an increase in 57fe values relative to fresh values which suggest a preferential leaching of light iron during alteration the apparent fractionation factor between dissolved fe2 and fe remaining in the mineral is from 0 5 to 1 3 and may be consistent with a kinetic isotope fractionation where light fe is stripped from the minerals alternatively the formation of secondary clays minerals such as celadonite during basalt alteration may incorporate preferentially the heavy fe isotopes resulting in the loss of light fe isotopes in the fluids because microbial processes within the oceanic crust are of potential importance in controlling rates of chemical reactions fe redox state and fe isotope fractionation we evaluated the possible effect of this deep biosphere on fe isotope signatures the fe isotope systematics presented in this study suggest that even though iron behavior during seafloor weathering may be mediated by microbes such as iron oxidizers 57fe variations of more than 4 may also be explained by abiotic processes further laboratory experiments are now required to distinguish between various processes of fe isotope fractionation during seafloor weathering

sks splitting beneath transportable array stations in eastern north america and the signature of past lithospheric deformation seismic anisotropy in the upper mantle beneath continental interiors is generally complicated with contributions from both the lithosphere and the asthenosphere previous studies of sks splitting beneath the eastern united states have yielded evidence for complex and laterally variable anisotropy but until the recent arrival of the usarray transportable array ta the station coverage has been sparse here we present sks splitting measurements at ta stations in eastern north america and compare the measured fast directions with indicators such as absolute plate motion surface geology and magnetic lineations we find few correlations between fast directions and absolute plate motion except in the northeastern u s and southern canada where some stations exhibit variations in apparent splitting with backazimuth that would suggest multiple layers of anisotropy a region of the southeastern u s is dominated by null sks arrivals over a range of backazimuths consistent with previous work we document a pattern of fast directions parallel to the appalachian mountain chain suggesting a contribution from lithospheric deformation associated with appalachian orogenesis overall our measurements suggest that upper mantle anisotropy beneath the eastern united states is complex with likely contributions from both asthenospheric and lithospheric anisotropy in many regions

lithospheric sources of north florida usa tholeiites and implications for the origin of the suwannee terrane abstract sr nd and pb isotopic data for mesozoic tholeiites from six drillholes in northern florida suwannee terrane indicate derivation of the magmas from a source that was slightly incompatible element enriched with respect to bulk earth probably continental lithospheric mantle variably contaminated by more enriched crust initial isotopic compositions of the florida tholeiites show a considerable range 87 sr 86 sr 0 7059 to 0 7097 end 4 6 to 0 1 206 pb 204 pb 18 30 to 18 65 207 pb 204 pb 15 57 to 15 66 and 208 pb 204 pb 38 22 to 38 35 these compositions are distinctly different from those of mesozoic alkali basalts from the subsurface of southwestern florida heatherington a l mueller p a 1991 geochemical evidence for triassic rifting in southwestern florida tectonophysics 188 291 302 it is suggested that the north florida tholeiites were derived from within the continental lithosphere in contrast with mesozoic volcanic rocks from southwestern florida which have been previously suggested to be related to a mantle plume sm nd isotope systematics suggest derivation of the tholeiites from a 1 ga source a similar age to that proposed by pegram pegram w j 1990 development of continental lithospheric mantle as reflected in the chemistry of the mesozoic appalachian tholeiites usa earth and planetary science letters 97 316 331 for the source of tholeiitic basalts within the carolina terrane this supports proterozoic tectonic models which suggest that both the suwannee and carolina terranes had affinities with south american portions of gondwana containing 1 ga crust specifically the sunsas rondonian province nance murphy 1996 mueller p a kozuch m heatherington a l wooden j l offield t w koeppen r p klein t l nutman a p 1996 evidence for mesoproterozoic basement in the carolina terrane and speculations on its origin in nance r d thompson m d eds avalonian and related peri gondwanan terranes of the circum north atlantic gsa special paper 304 pp 207 218

geoid anomalies and the structure of continental and oceanic lithospheres geoid anomalies in the wavelength range corresponding to spherical harmonies 6 to 30 are used to bring new constraints on the deep structure of the continental lithosphere on the nature of upper mantle seismic anomalies and on the thermal evolution of the oceanic lithosphere for the shallow lithospheric density anomalies considered here the geoid anomaly is shown to follow approximately the moment law derived from isostasy by a procedure of least squares inversion the geoid over old cratons is found to be equal to that over relatively young 50 myr oceanic lithosphere the oceanic geoid as a function of age follows the expected linear trend with flattening at old ages these results are independent of the degree at which the spherical harmonics are truncated if the tectosphere consisted only of a thick thermal boundary layer marked geoid lows with an amplitude larger than 20 m should be present over cratons in disagreement with the present observation the predicted geoid agrees with the observations if the negative density anomalies associated with a depleted peridotitic layer are present to the bottom of the lithosphere this analysis of the geoid confirms the petrological inferences that the deep roots observed seismically in the top upper mantle form a chemically differentiate reservoir the density of these cold roots is similar to that of mantle material elsewhere because the increase in density resulting from their lower temperature is largely balanced by the decrease in density caused by their depletion analysis in wavelength range corresponding to harmonics 6 to 30 in the oceans confirms that the geoid flattens at old ages and thus supports the view that an important amount of heat is transferred at the base of the lithosphere by small scale convection

zircon shrimp u pb ages and in situ hf isotopic analysis for the mesozoic intrusions in south taihang north china craton evidence for hybridization between mantle derived magmas and crustal components abstract the north china craton ncc was stabilized in paleo proterozoic times and the eastern part of it was remobilized in the mesozoic as is indicated by the presence of voluminous mesozoic magmas in eastern ncc in particular the lithospheric mantle beneath eastern ncc was significantly thinned during the intense mesozoic tectono magmatic activity which makes the ncc different from most other ancient cratons the mesozoic magmas may thus provide crucial evidence regarding the processes that transformed the ncc from craton to a tectonically active region the south taihang magmatic complex lies in the western part of the mesozoic magmatic zone in the ncc the complex falls into three main plutonic rocks the hongshan syenite the xishu gabbroic diorite monzonite and the wu an monzonitic rocks zircon u pb dating reveals that the three plutonic rocks were emplaced contemporaneously at 132 ma in situ hf isotopic analyses for the dated zircons indicate that the hongshan syenites show homogeneous hf t values 10 to 13 which are slightly lower than those 9 0 for the enriched subcontinental lithospheric mantle sclm as revealed by zircons from mafic rocks that originated from melting of sclm this suggests that the parental magma to the syenites was likely derived from melting of the enriched sclm and contaminated slightly by old lower continental crustal material during ascent the xishu and wu an gabbroic diorites to monzonitic rocks however show significantly varied hf isotopic compositions with hf t 9 2 to 16 and 15 5 to 24 respectively the wide range of hf t values for a single sample suggests that the xishu and wu an plutons formed through a process of hybridization between enriched mantle derived mafic magma and crustal components in variable proportions this is supported by the textural and compositional disequilibrium of plagioclase phenocrysts from the two plutons the wu an monzonitic rocks show lower hf t values than the xishu gabbroic diorite monzonite suggesting more incorporation of crustal components in the source the sudden surge of magmatic activity in the south taihang orogen took place as a result of lithospheric extension that caused partial fusion of the enriched portions of sclm generating voluminous mafic magmas underplating of the mafic magmas in the lower crust consequently caused partial melting of the old basement rocks to produce granitic melts which was followed by mixing between the mafic and granitic magmas

aspherical earth structure from fundamental spheroidal mode data free oscillation data reveal heterogeneity in the earth s mantle whose geographical pattern is dominated by spherical harmonics of angular degree two and correlates well with the hydrostatically referenced geoid the heterogeneity can be modelled as localized in the transition zone 420 670 km depth and may be related to a large scale component of mantle convection

a quantitative evaluation of the contribution of crustal rocks to the shear wave splitting of teleseismic sks waves abstract the seismic elastic properties of the crust have been modelled using hypothetical polycrystals with typical crustal compositions and commonly measured petrofabrics this modelling allows us to better evaluate and quantify the crustal contribution to splitting of teleseismic sks waves mafic rocks such as anorthosite or pyroxene bearing gabbros have complex s waves properties i e with small shear wave anisotropies

test of tectonic models by great circle rayleigh waves summary a large set of published great circle rayleigh wave phase velocities in the period range 125 350s is used to compare three recent tectonic models okal leveque jordan prior to any regionalization the symmetry property of the great circle integrals is used to obtain a lower limit of the signal noise ratio in the data it turns out that the signal is responsible for at least 30 per cent of the data variance in the period range 175 300s a standard regression method is applied for computing the pure path velocities and the model efficiency is derived from a variance analysis it is shown that even at great depth none of the three models explains more than 60 per cent of the energy due to the long wavelength lateral heterogeneities 6500 km the three models have nearly the same efficiency for explaining the short period data t 125s between 200 and 300s the higher performance of okal s model indicates that it is important to separate the subduction zones from the other orogenic zones by perturbing the lateral extension of the subduction zones it comes out that they constitute on both sides of the subducting slabs wider anomalies than often assumed suggesting large downgoing flows on the contrary the effect of surface features such as marginal seas are restricted to a close region in front of the trenches finally the anomalous ellipticity values deduced directly from great circle data are partly explained by a coupling between tectonics and ellipticity

palaeocontinental configurations and geoid anomalies reconstructions of past continental configurations help our understanding of the evolution of planetary surface morphology and impose valuable constraints on the models for planetary dynamics the problem is that although well established palaeogeographical maps now exist for mesozoic and later times1 2 thanks to excellent agreement between palaeomagnetic and marine magnetic deductions this is not true for earlier times mainly due to the lack of independent palaeogeophysical control over otherwise longitudinally ambiguous palaeomagnetic data the prospect of relating palaeocontinental configurations to geoid anomalies recently raised by anderson3 has thus given a fresh perspective to this problem here his continental insulation model is shown to be an inadequate explanation of the undulations of subduction compensated geoid instead the geoid highs and lows are shown to correlate well with the overall divergent and convergent plate tectonism since the middle palaeozoic and are thus ascribed respectively to the ascending and descending patterns of lower mantle convection

composition and evolution of ore fluids in a magmatic hydrothermal skarn deposit the chemistry of brine vapor and low salinity fluid inclusions measured by proton induced x ray emission from the bismark skarn deposit mexico is consistent with an evolving magmatic hydrothermal system with no evidence for external fluid inputs the results support a model that invokes early phase separation of magmatic fluids into brine and vapor two phase field at high temperature and lithostatic pressure followed by the entrapment of a low salinity magmatic fluid one phase field at lower temperature and hydrostatic pressure the early brine and vapor inclusions contain high pb and zn concentrations and low cu however the vapor contains significantly more cu than the brine and was likely transported as a sulfur complex the fluid phase changes observed and behavior of cu are comparable to those of porphyry cu systems the later low salinity fluid at bismark represents a distinct pulse of magmatic fluid with a high k ca ratio in which base metals including cu were transported by chloride complexes paragenetic relationships and variations in the relative concentrations of cu pb and zn suggest that this fluid was primarily responsible for ore deposition the relative cu pb and zn concentrations in fluid inclusions at bismark are consistent with those measured from base metal ores in high temperature carbonate replacement deposits throughout mexico and suggest that the bulk metal budget of these deposits is primarily controlled by magmatic hydrothermal fluids deficient in cu

seismic anisotropy in eastern tibet from shear wave splitting reveals changes in lithospheric deformation abstract knowledge about seismic anisotropy can provide important insight into the deformation of the crust and upper mantle beneath tectonically active regions here we focus on the southeastern part of the tibetan plateau in sichuan and yunnan provinces sw china we measured shear wave splitting of core refracted phases sks and skks at a temporary array of 25 iris passcal stations we calculated splitting parameters using a multi channel and a single record cross correlation method multiple layers of anisotropy cannot be ruled out but are not required by the data a fresnel zone analysis suggests that the shallow mantle between 60 and 160 km depth is the most likely source of anisotropy the polarization directions reveal a pronounced transition from primarily north south in the north sichuan to mostly east west orientations in the south yunnan in the southern part of the study region that is south of 26 n the fast polarization directions do not correlate well with known surface features and geodetic estimates of the crustal displacement fields whereas gps campaigns provide evidence suggesting north south crustal flow across the red river fault the pattern of anisotropy argues against such flow in the upper mantle these observations support models that allow differential movement of upper crust relative to lithospheric mantle in the northern part of the study region the relationships are more ambiguous and coherent deformation of the crust and mantle lithosphere cannot be excluded the interpretation of the shear wave splitting results is non unique but we suggest that the observed n s transition reflects a fundamental change in deformation regime across our study region it may be related to lateral variations in lithospheric rheology or may mark a transition from the direct impact of the continental collision to dominance of the far field strain field associated with regional subduction processes understanding the nature of the lateral change in deformation regime may prove critical for our understanding the geotectonic evolution of eastern tibet

the role of hydrous phases in the formation of trench parallel anisotropy evidence from rayleigh waves in cascadia 1 the cause of seismic anisotropy exhibiting trench parallel fast directions in subduction systems has been the subject of significant recent research we provide new constraints on the contributions of hydrous phases to seismic anisotropy from an unusually well localized region of trench parallel fast directions in rayleigh wave phase velocities near the cascade arc at 45 to 66 s periods we constrain the location of the anisotropic material to within or directly above the oceanic plate using the depth sensitivity of rayleigh waves as a function of frequency and the accurate slab imaging available for cascadia from scattered wave studies we infer that the likely source of trench parallel anisotropy is either a thin layer of sheared hydrous material directly above the slab or hydrated outer rise faults in the upper part of the subducting plate similar contributions to trench parallel anisotropy from hydrous phases are likely stronger in other subduction zones

new cocorp profiling in the southeastern united states part ii brunswick and east coast magnetic anomalies opening of the north central atlantic ocean new cocorp profiles on the coastal plain of georgia and northern florida support the hypothesis that the brunswick anomaly marks a late paleozoic suture they do not support the alternate view that this anomaly is caused by a mesozoic rift basin the trend of the brunswick anomaly relative to the appalachian gravity gradient indicates that in westernmost georgia and adjacent alabama african basement suwannee terrane is in proximity to autochthonous north american basement grenville farther east one or more paleozoic accreted terranes intervene between the north american and african sides of the orogen offshore the brunswick anomaly closely parallels the east coast magnetic anomaly this relationship implies that the east coast magnetic anomaly marks not only the present continental oceanic crustal transition but also the northward continuation of the late paleozoic suture between north america and africa transitional crust beneath the carolina trough baltimore canyon trough and correlative parts of the african atlantic margin is thus likely to have formed within a preexisting suture zone the dramatic change in character of the u s atlantic margin southward from the carolina trough to the blake plateau probably reflects the fact that two different types of prerift crust are juxtaposed in this region

shear wave splitting continental keels and patterns of mantle flow in this study we investigated the origin of seismic anisotropy in the mantle beneath north america in particular we evaluated whether shear wave splitting patterns in eastern north america are better explained by anisotropy caused by lithospheric deformation anisotropy due to mantle flow beneath the lithosphere or a combination of both we examined new measurements of shear wave splitting from the missouri to massachusetts broadband seismometer array moma the north american mantle anisotropy and discontinuity experiment nomad as well as splitting parameters from several previous studies we developed a simple finite difference model that approximates mantle flow around a complex three dimensional continental lithospheric keel to evaluate potential anisotropy from mantle flow beneath the lithosphere in eastern north america we compared shear wave splitting observations to predicted splitting parameters calculated using this mantle flow model our results indicate that a significant portion of observed shear wave splitting in eastern north america can be explained by mantle flow around the continental keel however shear wave splitting patterns in a few regions of eastern north america indicate that a component of lithospheric anisotropy must exist particularly in regions containing the largest keel thicknesses for eastern north america as well as for splitting observations in australia europe and south america we favor a model in which anisotropy is controlled by a combination of both lithospheric deformation and subcontinental mantle flow

iron isotope fractionation during skarn type alteration implications for metal source in the han xing iron skarn deposit abstract the han xing iron mineralization in the central north china craton is a typical fe skarn deposit associated with altered diorites here we report the fe isotopic compositions of whole rocks and mineral separates from this deposit with a view to evaluate the fe isotope fractionation during the formation of fe skarn deposit and to constrain the metal source the fe isotopes show a large variation both in whole rocks and mineral separates altered diorites show a wide range in 56 fe values 0 07 to 0 21 relative to the fe isotope standard irmm 014 which positively correlate with their tfe 2 o 3 tio 2 ratios fe 2 o 3 and feo calculated as tfe 2 o 3 the positive correlation indicates that heavy fe isotopes were preferentially leached from diorites during the skarn type alteration among the metallic minerals pyrite and pyrrhotite are isotopically heavier 0 12 to 0 48 than the magnetite 0 07 to 0 21 fe isotope fractionation between mineral pairs demonstrates that magnetite did not attain fe isotopic equilibrium with pyrite and pyrrhotite whereas pyrite and pyrrhotite might have attained isotopic equilibrium petrological observations and major element data also suggest that iron was leached from the diorites during the skarn type alteration if the leached iron provides the main fe budget of the han xing fe skarn deposit magnetite in ores would be isotopically heavier than the unaltered diorite however our results are in contrast with the magnetite being isotopically lighter than the unaltered diorite this suggests that the major fe source of the han xing fe skarn deposit is not from the leaching of diorites and might be from magmatic fluid which is isotopically lighter than the silicate melt our data demonstrate that fe isotopes can be used as important tracers in deciphering the metal source of fe skarn deposits

necessary conditions for intraplate seismic zones in north america the cause of intraplate seismic zones persists as an important scientific and societal question most intraplate earthquakes are concentrated in specific seismic zones along or adjacent to large scale basement structures e g rifts or sutures at ancient plate boundaries within continental crust the major intraplate seismic zones are limited to specific segments and are not distributed along the lengths of the ancient structures we present a new hypothesis that major intraplate seismic zones are restricted to places where concentrated crustal deformation ccd is overprinted on large scale basement structures examples where ccd affects the stability of specific parts of large scale structures in response to present day stress conditions include the most active seismic zones in central and eastern north america charlevoix eastern tennessee and new madrid our hypothesis has important implications for the assessment of seismic hazards

mapping p wave azimuthal anisotropy in the crust and upper mantle beneath the united states abstract much progress has been made on revealing seismic structure and mantle dynamics beneath the united states us with the earthscope usarray project seismic anisotropy revealed by shear wave splitting studies provides important constraints on constructing geodynamic models with regard to the seismic images but the shear wave splitting observations have poor vertical resolution and so their interpretations are often not unique in this work we used a large number of arrival time data from local and distant earthquakes recorded by the usarray to determine the first p wave azimuthal anisotropy tomography of the crust and upper mantle beneath the us our results show that fast velocity directions fvds in the lithosphere under the tectonically active areas correlate well with the surface tectonic features suggesting that the p wave anisotropy mainly reflects the present deformation a circular pattern of the fvds centered in the great basin is revealed which is well consistent with the specific circular shear wave splitting observations there suggesting that the anisotropy occurs in the crust and uppermost mantle in contrast beneath the stable cratonic region the fvds revealed by this study differ from the shear wave splitting observations but consistent with the features of gravity and magnetic anomalies indicating that the p wave fvds mainly reflect the fossil anisotropy in the lithosphere whereas the s wave splitting observations mainly reflect the significant anisotropy in the asthenosphere the present results shed new light on the seismic anisotropy in the crust and upper mantle and provide new constraints on constructing geodynamic models beneath the us

variability and origin of seismic anisotropy across eastern canada evidence from shear wave splitting measurements measurements of seismic anisotropy in continental regions are frequently interpreted with respect to past tectonic processes preserved in the lithosphere as fossil fabrics models of the present day sublithospheric flow often using absolute plate motion as a proxy are also used to explain the observations discriminating between these different sources of seismic anisotropy is particularly challenging beneath shields whose thick 200 km lithospheric roots may record a protracted history of deformation and strongly influence underlying mantle flow eastern canada where the geological record spans 3 ga of earth history is an ideal region to address this issue we use shear wave splitting measurements of core phases such as sks to define upper mantle anisotropy using the orientation of the fast polarization direction and delay time t between fast and slow shear wave arrivals comparison with structural trends in surface geology and aeromagnetic data helps to determine the contribution of fossil lithospheric fabrics to the anisotropy we also assess the influence of sublithospheric mantle flow via flow directions derived from global geodynamic models fast polarization orientations are generally ene wsw to ese wnw across the region but significant lateral variability in splitting parameters on a 100 km scale implies a lithospheric contribution to the results correlations with structural geologic and magnetic trends are not ubiquitous however nor are correlations with geodynamically predicted mantle flow directions we therefore consider that the splitting parameters likely record a combination of the present day mantle flow and older lithospheric fabrics consideration of both sources of anisotropy is critical in shield regions when interpreting splitting observations

reevaluation of the chandler wobble seismic excitation from recent data abstract since 1977 seismic moment tensors of major earthquakes have been systematically determined while high accuracy polar motion data have been made available from space techniques the seismic excitation of the chandler wobble during the period 1977 1983 has been obtained using the centroid moment tensor solutions of 1287 strong and moderate earthquakes occurring during that period changes in the earth inertia tensor induced by earthquakes which are derived from the elastic theory of dislocation are assumed to be step functions of time from a comparison between the derived synthetic chandler wobble and the observed one it turns out that seismic excitation is far too small by about two orders of magnitude to explain the chandler wobble amplitude variations during 1977 1983 in particular the increase in the wobble amplitude between 1980 and 1983 during the last two decades seismic moments of major earthquakes remained on the level of 10 27 to 10 28 dyne cm whereas in the past events of high magnitudes corresponding to seismic moments on the order of 10 30 to 10 31 dyne cm have been frequently reported as the later values are those needed to explain the amplitude variations of the chandler wobble the problem of the validity of magnitude estimations in the past and frequency of occurrence of great earthquakes is raised as well as the question of validity of previous positive conclusions on the influence of earthquakes on the chandler wobble excitation

iron isotope fractionation during supergene weathering process and its application to constrain ore genesis in gaosong deposit gejiu district sw china abstract fe isotope compositions of bulk samples from gaosong ore deposit in gejiu district sw china were investigated and an overall variation in 56 fe values from 0 33 to 0 20 has been observed in this study the 56 fe values of primary sulfide ores are lower than the oxidized ores while the iron isotope compositions of gossan samples which represent highest oxidation degree are heavier than the oxidized ore samples these data indicate that iron isotopes experienced fractionation during supergene weathering process furthermore heavier iron isotopes enriched in more oxidized products another highlight is the fe isotope compositions that are affected by mineralogy which is considered as the primary mechanism of the large fe isotopic variations in the primary ores enrichment of light iron isotopes in primary sulfide ores suggests that iron isotopes fractionated during fluid exsolution from its parental magma and the fe source of skarn ores is mainly the magmatic source this observation that significant fe isotope fractionation occurs in supergene weathering process and fluid exsolution process provides an example in using fe isotopes to trace supergene geochemical cycling and ore deposit formation evolution processes

whole rock pb and sm nd isotopic constraints on the growth of southeastern laurentia during grenvillian orogenesis the conventional view that the basement of the southern and central appalachians represents juvenile mesoproterozoic crust the final stage of growth of laurentia prior to grenville collision has recently been challenged new whole rock pb and sm nd isotopic data are presented from mesoproterozoic basement in the southern and central appalachians and the granite rhyolite province as well as one new u pb zircon age from the granite rhyolite province these data combined with existing data from mesoproterozoic terranes throughout southeastern laurentia further substantiate recent suggestions that the southern and central appalachian basement is exotic with respect to laurentia sm nd isotopic compositions of most rocks from the southern and central appalachian basement are consistent with progressive growth through reworking of the adjacent granite rhyolite province however pb isotopic data including new analyses from important regions not sampled in previous studies do not correspond with pb isotopic compositions of any adjacent crust the most distinct ages and isotopic compositions in the southern and central appalachian basement come from the roan mountain area eastern tennessee western north carolina the data set indicates u pb zircon ages up to 1 8 ga for igneous rocks inherited and detrital zircon ages 2 0 ga sm nd depleted mantle model t dm ages 2 0 ga and the most elevated 207 pb 204 pb observed in southeastern laurentia the combined u pb geochronologic and sm nd and pb isotopic data preclude derivation of southern and central appalachian basement from any nearby crustal material and demonstrate that grenville age crust in southeastern laurentia is exotic and probably was transferred during collision and assembly of rodinia these new data better define the boundary between the exotic southern and central appalachian basement and adjacent laurentian granite rhyolite province

depth dependent azimuthal anisotropy in the western us upper mantle abstract we present the results of a joint inversion of long period seismic waveforms and sks splitting measurements for 3d lateral variations of anisotropy in the upper mantle beneath the western us incorporating recent datasets generated by the usarray deployment as well as other permanent and temporary stations in the region we find that shallow azimuthal anisotropy closely reflects plate motion generated shear in the asthenosphere in the shallow upper mantle 70 150 km depth whereas at depths greater than 150 km it is dominated by northward and upward flow associated with the extension of the east pacific rise under the continent constrained to the east by the western edge of the north american craton and to the north by the presence of the east west trending subduction zone in particular the depth integrated effects of this anisotropy explain the apparent circular pattern of sks splitting measurements observed in nevada without the need to invoke any local anomalous structures

some comparisons of the structure and evolution of the southern appalachian ouachita orogen and portions of the trans european suture zone region abstract many aspects of the tectonic history of the appalachian ouachita orogen and the trans european suture region are similar in a tectonic sense they are geographically linked because at the end of the paleozoic one could travel from texas to poland following a continuous orogenic belt much of each of these orogenic belts is however buried by younger strata and thus geophysical studies are a key element of efforts to better understand them many more geophysical data are needed to provide a comprehensive picture of the deep structure but in several areas new models of the lithospheric structure are emerging in this paper we review some of these models and introduce two new ones for the southern appalachians in addition we explore the implications of these models for the evolution of these orogenic belts drawing attention to similarities and differences in their structure and evolution the appalachian and caledonian orogens represent temporally parallel development along irregular late proterozoic continental margins but the crustal structure is different because of different accretionary elements and complications in the geometry of the original margins lateral transport via thrusting can confuse efforts to tie geologic structures identified on the surface with deep structures for example in the appalachian ouachita orogen the thrust related transport distance for major features such as the blue ridge piedmont sheet and the benton uplift is at least 200 km on a crustal scale deformation in the appalachian ouachita orogen varies greatly in style and intensity in the ouachita orogen the late proterozoic continental margin seems to be preserved while in the northern appalachians crustal scale deformation is intense along the us appalachians the major crustal structure variation is the thin dense crust of avalonia abutting the relatively thick crust of laurentia along the ouachita orogen several large crustal blocks can be identified that are unlike anything seen along the appalachians

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

neogene rejuvenation of central appalachian topography evidence for differential rock uplift from stream profiles and erosion rates abstract the persistence of topography within ancient orogens remains one of the outstanding questions in landscape evolution in the eastern north american appalachians this question is manifest in the outstanding problem of whether topographic relief is in a quasi equilibrium state decaying slowly over many millennia or whether relief has increased during the late cenozoic here we present quantitative geomorphic data from the nonglaciated portion of the susquehanna river drainage basin that provide insight into these end member models analysis of channel profiles draining upland catchments in the northern valley and ridge appalachian plateau blue ridge and piedmont provinces reveals that a large number of streams have well defined knickpoints clustered at 300 600 m elevation but not systematically associated with transitions from weak to resistant substrate cosmogenic 10 be inventories of modern stream sediment indicate that erosion rates are spatially variable ranging from 5 30 m myr above knickpoints to 50 100 m myr below knickpoints overall channel gradients normalized for drainage area scale linearly with catchment averaged erosion rates collectively regionally consistent spatial relationships among erosion rate channel steepness and knickpoints reveal an ongoing wave of transient channel adjustment to a change in relative base level reconstructions of relict channel profiles above knickpoints suggest that higher rates of incision are associated with 100 150 m of relative base level fall that accompanied epierogenic rock uplift rather than a change to a more erosive climate or drainage reorganization channel response timescales imply that the onset of relative base level change predates 3 5 ma and may have begun as early as 15 ma we suggest that adjustment of the channel network was likely driven by changes in mantle dynamics along the eastern seaboard of north america during the neogene

shear wave splitting across the mid atlantic region of north america a fossil anisotropy interpretation new shear wave splitting measurements n 76 from the mid atlantic section of north america when combined with previously reported measurements provide improved clarity to patterns of seismic anisotropy across the region including a rotation of fast polarization directions from east west to northeast southwest in pennsylvania usa we attribute the patterns in to frozen in i e fossil anisotropy in the lithospheric mantle most directions parallel the strike of the appalachian orogen except in parts of new england where directions are oriented perpendicular to both the strike of the orogen and continental margin the directions parallel to the strike of the appalachian orogen including those that rotate from east west to northeast southwest in pennsylvania are consistent with the expected orientation for fossil anisotropy developed during the appalachian orogenic cycle the directions in new england perpendicular to the continental margin are consistent with the expected orientation for fossil anisotropy developed during the breakup of pangea and directions at locations west of the appalachian mountains in areas not affected by the appalachian orogeny can be explained by fossil anisotropy developed during the proterozoic suturing of the granite rhyolite province and elzevir block to the eastern margin of laurentia

towards sub lithospheric stress determination from seismic moho topographic heights and goce data abstract sub lithospheric stresses can be estimated by analysis of gravity field measurements depending on the measured gravimetric quantity different methods can be employed to estimate those sub lithospheric stresses here we further develop the runcorn s theory for estimation of mantle stresses 1967 such that a moho model and full topographic information are used to recover the function from which the stress can be computed by taking derivatives northwards and eastwards we develop new integral equations for such a purpose and recover this function by solving those integral equations locally over the indo pak india pakistan region from 1 a gravimetric moho model computed from the srtm shuttle radar topography mission and the earth gravity model egm2008 2 srtm and the seismic moho model of crust1 0 and 3 data and measurements of the goce gravity field and steady state ocean circulation explorer mission finally we perform a joint inversion of seismic and goce data for the same purpose the numerical results show that the use of a seismic moho model recovers information about the stress field which is not seen in the results derived from a gravimetric moho model a combination of the seismic moho model srtm and goce yields a better stress field than that of either the seismic and or gravimetric data alone the magnitudes of the sub lithospheric stress are computed from the shear stress components over the area and good agreement is seen between the recovered combined stress field the regional tectonic boundaries and the seismicity of the world stress map 2008 database

global relationship between oceanic geoid and topography in order to compare model predictions of upper mantle convection with surface observations we have computed global residual depth and geoid anomalies on a 5 5 grid over all oceans after removal of lithospheric cooling effects and long wavelength geoid components 4000 km related to lower mantle sources we have derived the transfer function admittance of geoid over topography as a function of wavelength in the range 1000 4000 km the observed admittance is positive at all and presents a maximum of 2 5 3 5 m km at 2750 km comparing this result with the theoretical admittance computed for the lithospheric cooling plate model we ascribe most of the admittance peak at 2750 km to errors in the depth age and geoid age correction this suggests that a standard age correction applied to all seafloor is not valid at shorter wavelengths the admittance remains roughly constant on the order of 1 5 m km and can be explained in terms of sediment loading and crustal thickening effects comparing spatially the residual geoid and depth anomaly maps we note a positive correlation over a few areas coinciding with hot spot swells volcanic plateaus or seafloor deeps the geoid versus depth ratio amounts then to 6 8 m km in agreement with the values predicted above upwellings and downwellings by models of constant viscosity convection however the global admittance analysis leads to much lower values at all wavelengths suggesting that these areas are too limited in number and in extent to produce any significant signal

shear wave splitting around the northern atlantic frozen pangaean lithospheric anisotropy abstract although the number of teleseismic shear wave splitting measurements has considerably increased world wide during the last decade there is no consensus on a unique and universal interpretation of these data splitting might primarily originate in the lithospheric and or asthenospheric mantle but the technique has no vertical resolution and therefore leaves this question of anisotropy location unresolved generally the consequences of the two possibilities are used to infer which is more likely if splitting occurs in the lithosphere the splitting parameters the orientation of the fast split shear wave o and the delay time t should be related to frozen or active deformation on the other hand if the splitting occurs in the asthenosphere the observed splitting parameters should be related to the present day flow induced by the differential motion between the tectonic plates and the underlying mantle the aim of this paper is to test these hypotheses against shear wave splitting observations from western europe and the eastern u s indeed except in a few places splitting on either side of the atlantic on hercynian caledonian or grenvillian structures do not appear to have been deeply and pervasively affected by the opening of this ocean this provides us the opportunity to place these results in the pangaean reference frame of the hercynian caledonian belt before the opening of the atlantic in many places the close parallelism between lithospheric structure and the absolute plate motion apm impedes a reliable identification of the origin of the anisotropy especially an asthenospheric flow channelled around the deeply rooted north american craton may be compatible with the large scale anisotropy pattern in the eastern u s despite this ambiguity fast polarization directions o observed on or near some major lithospheric structures correlate better with the trend of the local tectonic structures than with the expected asthenospheric flow therefore we suggest that these lithospheric structures developed before the opening of the atlantic remain frozen since hercynian caledonian or grenvillian times and are responsible for the observed splitting at these places

seismic anisotropy beneath stable continental interiors a robust knowledge of seismic anisotropy beneath the continents is essential to our understanding of plate tectonic theory as anisotropy provides a unique constraint on the character of past and present deformation in the lithosphere and sublithospheric mantle this review paper summarizes the range of techniques currently available to image seismic anisotropy with passive source seismic data and addresses current issues surrounding the observation and interpretation of continental seismic anisotropy to this end we present case studies for four regions where seismic anisotropy has been extensively investigated in recent years eastern north america the canadian shield australia and southern africa based on this full suite of results we infer that stable continental regions generally contain seismic anisotropy that is clearly located within both the lithosphere and the sublithospheric mantle usually to depths of at least 200 km and perhaps more an implication of these results is that tectonic plates are at most only partially coupled to the underlying mantle the results from these case studies also demonstrate that while remarkable progress in seismic anisotropy imaging has been achieved in recent years it is clear that much more work will be required to adequately understand the origin of continental seismic anisotropy we suggest that a more robust characterization of anisotropic parameters can only be achieved by integrating complementary seismic datasets and by incorporating constraints from key related datasets from mineral physics magnetotellurics gravity and geodesy

no regional anisotropic domains in the northeastern u s appalachians a fabric frozen within the continental lithosphere should lead to regional anisotropic domains with close correlation between tectonics seismic anisotropy and shear wave travel time delays alternatively seismic anisotropy could be maintained by active deformation in the sub lithospheric mantle this scenario would predict broad spatial consistency in shear wave splitting and weak correlation between the splitting surface tectonics and travel time delays a coherent pattern of shear wave splitting is observed in the northeastern united states covering large parts of new york and new england spanning the appalachian orogen and areas underlain by the grenvillian basement the direction of fast shear wave propagation as measured from core refracted sks skks and pks phases varies systematically with event back azimuth at all sites examined and is fit well by two layers of anisotropy with subhorizontal symmetry axes relative travel time delays of shear waves that sample the region vary over 100 km length scale and correlate with surface geology tomographic images suggest lateral shear velocity variations 3 including a slow anomaly beneath the grenvillian basement exposed in the adirondack mountains there is little correlation between this horizontally rough seismic velocity and the horizontally smooth anisotropic model consistent with shear wave splitting we therefore conclude that in the northeastern us the concept of regional anisotropic domains i e distinct regions within the lithosphere characterized by coherent anisotropic properties reflective of present or past deformation does not apply

paleoproterozoic arc magmatism in the north china craton no siderian global plate tectonic shutdown abstract arc magmatism in convergent plate margins has been a major contributor to continental growth following arc arc and arc continent collisions in the archean leading to the amalgamation of micro blocks the north china craton ncc witnessed major pulses of continental arc magmatism during the paleoproterozoic in this study we present geochemistry zircon u pb geochronology and lu hf isotope data from a suite of magmatic rocks sampled from the region of confluence of two major paleoproterozoic suture zones in the ncc the inner mongolia suture zone imsz and the trans north china orogen tnco our zircon u pb geochronological data indicate new zircon growth during multiple tectonothermal events as displayed in the 207pb 206pb weighted mean ages of 2410 41 ma for metagranite 2480 12 ma 2125 18 ma 1946 8 ma 1900 15 ma and 1879 12 ma from metagabbros 2446 11 ma from charnockite and 1904 6 ma and 1901 9 ma from metatuffs the 207pb 206pb upper intercept age of zircons in the khondalite shows 2102 76 ma which is identical to the age obtained from the magmatic zircons in one of the metagabbros the khondalites also carry a group of concordant metamorphic zircons with 207pb 206pb mean age of 1881 20 ma metamorphic zircons in the gabbros and charnockites also yield similar ages of 1890 14 ma and 1852 19 ma respectively the age data suggest prolonged arc magmatism in a convergent margin setting during ca 2 48 to 1 9 ga followed by metamorphism at ca 1 89 1 85 ga associated with the final collision lu hf analyses reveal that the dominant populations of zircons from all the rock types are characterized by positive ehf values 1 9 to 6 8 mean 1 8 the ehf and tdmc data suggest that the magmas were mostly derived from neoarchean and paleoproterozoic juvenile components the salient geochemical features of these rocks attest to magma generation from heterogeneous sources involving subduction derived arc components with minor input from continental crust the results presented in this study together with those from previous investigations in different domains of the imsz and tnco suggest major paleoproterozoic arc magmatic events in the ncc lasting for nearly 600 million years associated with the final assembly of the crustal blocks into a coherent craton construction of the final cratonic architecture of the ncc thus witnessed not only the arc continent amalgamations at 2 7 2 5 ga but also major crust building events in the paleoproterozoic through melts generated from juvenile and recycled components in continental magmatic arc systems along an active convergent margin followed by intense deformation and metamorphism during the final collision at 1 85 1 80 ga the prominent paleoproterozoic magmatic records in the ncc do not support the proposal of global plate tectonic shutdown in the siderian and confirm vigorous convergent margin magmatism and crust building processes throughout the paleoproterozoic

imprints of diverse mantle deformational episodes in the cauvery suture zone south india abstract this study attempts to understand the upper mantle deformation pattern beneath the northern part of southern granulite terrain sgt located to the south of archean dharwar craton in south india the study region comprises the tectonic blocks nilgiri biligiri rangan shevaroy and madras blocks separated from the northern part of madurai block by the cauvery suture zone csz associated with subduction accretion collision tectonics shear wave splitting observed on high quality xk k s sks skks pks waveforms from 119 teleseismic events recorded by 19 broadband seismic stations mostly within the csz and the northern part of madurai block is utilized in this study the 122 splitting measurements obtained show an average delay time of 0 8 s between the fast and slow waves strong lateral variations in the fast polarization azimuths fpa are observed with the splitting parameters at the majority of stations showing a dependence on back azimuth importantly excluding the madras block a poor correlation between the fpa and the present day absolute plate motion apm direction is observed this dominance of non apm strain reflects complex anisotropy preserved in the lithosphere by plotting the fast polarization trends based on the ray piercing points at a depth of 150 km three distinct splitting patterns associated with the i biligiri rangan block and the eastern part of the nilgiri block ii eastern part of the csz and the northern madurai block nmb and iii madras block and its vicinity within the csz are observed the strong lateral heterogeneity in the deformation of the continental lithosphere might be either related with the shear zones that are associated with frozen magmatic intrusions two episodes of ocean closure and the collision that followed plate motion related strain or a combination of these similar deformation patterns in the northern part of madurai block might be related to remnants of subducted oceanic lithosphere

global tectonics and the geoid abstract a digitised tectonic model initially built up for regionalization of rayleigh waves is applied to the geoid in order to define the mean geoid heights of the following regions 3 oceanic regions namely young oceans 0 30 ma middle aged oceans 30 80 ma and old oceans 80 ma trenches and subduction zones mountains and shields the relative importance of the deep sources is damped or enhanced by progressively removing or adding the lower or higher degrees of the geoid a statistical approach allows us to quantify the success of the correlation between tectonics and these filtered geoids significant variations are observed in these correlations for oceanic regions including subduction zones with a cut off between degree 2 and higher degrees for degrees 3 a well known trend is observed high values correspond to young oceans ridges and low values to old oceans high values are also obtained for subduction zones on the contrary and unexpectedly for the degree 2 alone a trend reversal is observed geoid lows are observed over ridges and geoid highs over old oceans trenches give the same geoid amplitude than old oceans clearly this denotes a degree 2 convection pattern connected to plate tectonics in addition it is shown that the minimum and maximum inertia axes of the surface distribution of young oceans and independently of old oceans and trenches coincide with the earth s equatorial inertia axes 74 e and 164 e i e with the equatorial extremes of the degree 2 geoid plate tectonics is uncorrelated with the polar anomaly of the degree 2 geoid namely the flattening which is not accounted for by earth rotation a north south axisymmetric convection with a degree 2 pattern is proposed to explain this extra flattening this model is supported by the latitude dependence of the depth of oceanic ridges

iron isotope fractionation during microbial reduction of iron the importance of adsorption in experiments investigating the causes of fe isotope fractionation the d 56 54 fe value of fe ii remaining in solution fe ii aq after reduction of fe iii goethite by shewanella putrefaciens is 21 2 relative to the goethite in agreement with previous research the addition of an electron shuttle did not affect fractionation suggesting that fe isotope fractionation may not be related to the kinetics of the electron transfer furthermore in abiotic anaerobic fecl2 aq experiments in which approximately one third of fe ii aq is lost from solution due to adsorption of fe ii onto goethite the d 56 54 fe value of fe ii aq remaining in solution is shifted by 20 8 relative to fecl 2 this finding demonstrates that anaerobic nonbiological interaction between fe ii and goethite can generate signif icant fe isotope fractionation acid extraction of sorbed fe ii from goethite in experi ments reveals that heavy fe preferentially sorbs to goethite simple mass balance modeling indicates that the isotopic composition of the sorbed fe ii pool is 11 5 to 12 5 heavier than fe in the goethite 2 7 3 7 heavier than aqueous fe ii mass balance is also consistent with a pool of heavy fe that is not released to solution during acid extraction

emag2 a 2 arc min resolution earth magnetic anomaly grid compiled from satellite airborne and marine magnetic measurements 1 a global earth magnetic anomaly grid emag2 has been compiled from satellite ship and airborne magnetic measurements emag2 is a significant update of our previous candidate grid for the world digital magnetic anomaly map the resolution has been improved from 3 arc min to 2 arc min and the altitude has been reduced from 5 km to 4 km above the geoid additional grid and track line data have been included both over land and the oceans wherever available the original shipborne and airborne data were used instead of precompiled oceanic magnetic grids interpolation between sparse track lines in the oceans was improved by directional gridding and extrapolation based on an oceanic crustal age model the longest wavelengths 330 km were replaced with the latest champ satellite magnetic field model mf6 emag2 is available at http geomag org models emag2 and for permanent archive at http earthref org cgi bin er cgi s erda cgi n 970

seismic azimuthal anisotropy beneath the eastern united states and its geodynamic implications systematic spatial variations of anisotropic characteristics are revealed beneath the eastern u s using seismic data recorded between 1988 2016 by 785 stations the resulting fast polarization orientations of the 5613 measurements are generally subparallel to the absolute plate motion apm and are inconsistent with the strike of major tectonic features this inconsistency together with the results of depth estimation using the spatial coherency of the splitting parameters suggests a mostly asthenospheric origin of the observed azimuthal anisotropy the observations can be explained by a combined effect of apm induced mantle fabric and a flow system deflected horizontally around the edges of the keel of the north american continent beneath the southern and northeastern portions of the study area the e w keel deflected flow enhances apm induced fabric and produces mostly e w fast orientations with large splitting times while beneath the southeastern u s anisotropy from the n s oriented flow is weakened by the apm

local recovery of lithospheric stress tensor from goce gravitational tensor the sub lithospheric stress due to mantle convection can be computed from gravity data and propagated through the lithosphere by solving the boundary value problem of elasticity for the earth s lit

determination of the fe ii aq magnetite equilibrium iron isotope fractionation factor using the three isotope method and a multi direction approach to equilibrium abstract magnetite is ubiquitous in the earth s crust and its presence in modern marine sediments has been taken as an indicator of biogeochemical fe cycling magnetite is also the most abundant fe oxide in banded iron formations bifs that have not been subjected to ore forming alteration magnetite is therefore an important target of stable fe isotope studies and yet interpretations are currently difficult because of large uncertainties in the equilibrium stable fe isotope fractionation factors for magnetite relative to fluids and other minerals in this study we utilized the three isotope method 57fe 56fe 54fe to explore isotopic exchange via an enriched 57fe tracer and natural mass dependent fractionation using 56fe 54fe variations during reaction of aqueous fe ii fe ii aq with magnetite importantly we employed a multi direction approach to equilibrium by reacting four 57fe enriched fe ii solutions that had distinct 56fe 54fe ratios which identifies changes in the instantaneous fe isotope fractionation factor and hence identifies kinetic isotope effects we find that isotopic exchange can be described by two 56fe 54fe fractionations where an initial rapid exchange 66 isotopic mixing within 1 day involved a relatively small fe ii aq magnetite 56fe 54fe fractionation followed by slower exchange 25 isotopic mixing over 50 days that was associated with a larger fe ii aq magnetite 56fe 54fe fractionation this later fractionation is interpreted to approach isotopic equilibrium between fe ii aq and the total magnetite all four fe ii solutions extrapolate to the same final equilibrium 56fe 54fe fractionation for fe ii aq magnetite of 1 56 0 20 2 at 22 c additional experiments that synthesized magnetite via conversion of ferrihydrite by reaction with aqueous fe ii yield final 56fe 54fe fractionations that are identical to those of the exchange experiments our experimental results agree well with calculated fractionation factors using the reduced partition function ratios for fe h 2 o 6 2 from rustad et al 2010 and stoichiometric magnetite from mineev et al 2007 and these relations may be combined with the experimental constraints to determine the temperature dependence of the fe ii aq magnetite fractionation factor 10 3 ln f e i i aq magnetite 0 145 0 002 10 6 t 2 0 10 0 02 where t is in k part of the reason for large discrepancies in calculated fe isotope fractionation factors for magnetite likely lies in the stoichiometry of the mineral in specific studies given the significant effect of octahedral versus tetrahedral fe isotope fractionation that has been calculated when our results are applied to bif genesis our experimentally determined fe ii aq magnetite fractionation factor indicates that magnetite siderite mineral pairs in 2 5 ga bifs did not form in fe isotope equilibrium with each other or with ancient seawater iron oxides in such bifs are therefore more likely to have formed through processes that were isolated from equilibrium with the oceans indicating that such bif minerals may not be suitable proxies for ancient paleoenvironments

seismic anisotropy in the eastern united states deep structure of a complex continental plate we have analyzed shear wave splitting recorded by portable and permanent broadband and long period stations located in the eastern united states teleseismic shear waves sks skks and pks were used to retrieve the splitting parameters the orientation of the fast wave polarization plane and the delay time t in total 120 seismic events were processed allowing for more than 600 splitting measurements within the appalachians stations located in the western external part are characterized by t 1s and trending n50 70 e in the south and central regions and n30 40 e in the north closely following the trend of the orogenic belt in these areas the transition region between north and central is characterized by t 1 1 3 s and by e w trending that are at a high angle to the regional geologic trend measurements at two stations located in the eastern internal part of the belt indicate very weak anisotropy the large scale pattern of anisotropy is not consistent with that predicted for simple asthenospheric flow beneath the plate splitting along the southern and eastern margins of the continent is consistent with that expected for grenvillian deformation an alternative model of asthenospheric flow around the cratonic keel cannot be ruled out within the cratonic core the correlation between t and lithospheric thickness suggests a lithospheric anisotropy smaller length scale variations also argue for a significant contribution of lithospheric structures the fabric responsible for shear wave splitting may have formed during tectonic episodes that affected the eastern united states i e the grenville and appalachian orogenies and the subsequent rifting of the north atlantic ocean our observations in the western appalachians suggest that the anisotropy may be preserved since the grenvillian orogeny the absence of detectable splitting in the two stations in the eastern appalachians is attributed to the igneous intrusions related to the atlantic rifting the measurements in the transition between the northern and central southern appalachians constitute an intriguing anomaly whose e w have little obvious relation to the regional surface geology we suggest two possible causes 1 the local dominance of asthenospheric flow motivated by the proximity of a pervasive low velocity anomaly and 2 lithospheric deformation in a transcontinental strike slip fault zone active during the appalachian collision

seismic anisotropy in the lowermost mantle beneath north america from sks skks splitting intensity discrepancies abstract we examined sks skks splitting intensity discrepancies for phases that sample the lowermost mantle beneath north america which has previously been shown to exhibit seismic anisotropy using other analysis techniques we examined data from 25 long running seismic stations along with 244 stations of the temporary usarray transportable array located in the eastern southeastern and western u s we identified 279 high quality sks skks wave pairs that yielded well constrained splitting intensity measurements for both phases of the 279 pairs a relatively small number 15 exhibited discrepancies in splitting intensity of 0 4 s or greater suggesting a contribution to the splitting of one or both phases from anisotropy in the lowermost mantle because only a small minority of sk k s phases examined in this study show evidence of being affected by lowermost mantle anisotropy the traditional interpretation that splitting of these phases primarily reflects anisotropy in the upper mantle directly beneath the stations is appropriate the discrepant pairs exhibited a striking geographic trend sampling the lowermost mantle beneath the southern u s and northern mexico while other regions were dominated by non discrepant pairs we carried out ray theoretical modeling of simple anisotropy scenarios that have previously been suggested for the lowermost mantle beneath north america invoking the alignment of post perovskite due to flow induced by the impingement of the remnant farallon slab on the core mantle boundary we found that our measurements are generally consistent with this model and with the idea of slab driven flow but relatively small scale lateral variations in the strength and or geometry of lowermost mantle anisotropy beneath north america are also likely present

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

upper mantle anisotropy and transition zone thickness beneath southeastern north america and implications for mantle dynamics a variety of models for mantle flow beneath southeastern north america have been proposed including those that invoke westward driven return flow from the sinking farallon slab small scale convective downwelling at the edge of the continental root or the upward advective transport of volatiles from the deep slab through the upper mantle we use shear wave splitting observations and receiver function analysis at broadband seismic stations in the southeastern united states to test several of these proposed mantle flow geometries near the coast stations exhibit well resolved null no splitting behavior for sks phases over a range of back azimuths consistent with either isotropic upper mantle or with a vertical axis of anisotropic symmetry farther inland we identify splitting with mainly ne sw fast directions consistent with asthenospheric shear due to absolute plate motion apm lithospheric anisotropy aligned with appalachian tectonic structure or a combination of these phase weighted stacking of individual receiver functions allows us to place constraints on the timing of arrivals from the 410 and 660 km discontinuities and on average transition zone thickness beneath individual stations at most stations we find transition zone thicknesses that are consistent with the global average 240 km with two stations showing evidence for a slightly thickened transition zone 250 km our results are relevant for testing different models for mantle dynamics beneath the southeastern united states but due to the sparse station coverage we are unable to uniquely constrain the pattern of mantle flow beneath the region our sks splitting observations support a model in which mantle flow is primarily vertical either upwelling or downwelling beneath the southeastern edge of the north american continent in contrast to the likely horizontal apm driven flow beneath the continental interior however our receiver function analysis does not provide unequivocal support either for widespread hydration of the transition zone or for widespread thickening due to the downwelling of relatively cold mantle material we expect that the necessary data to constrain such models more tightly can be obtained from the operation of denser seismic networks including the transportable array and flexible array components of usarray

lithospheric and asthenospheric contributions to shear wave splitting observations in the southeastern united states we present observations of both null and non null sks splitting from temporary deployments across the southeastern united states in order to evaluate the relative contributions of lithospheric deformation and asthenospheric flow to regional anisotropy data for this study come from four temporary broadband seismic deployments the appalachian seismic transect ast the test experiment for eastern north america teena the south carolina earth physics project scepp and the florida to edmonton array fled in general we find fast directions aligned roughly parallel to absolute plate motion of the north american plate apm within and west of the southern appalachians whereas to the southeast we find a broad area dominated by complex splitting patterns consisting of well constrained null splitting measurements over a range of backazimuths along with a very small number of resolved non null measurements this change in splitting patterns is consistent with a transition from drag induced asthenospheric flow beneath the older sections of the north american continent to vertical or incoherent mantle flow likely in combination with complex lithospheric anisotropy beneath the younger accreted terranes to the southeast in addition to these general patterns we find a number of non null splitting measurements that are not aligned with apm but are instead aligned with prominent magnetic anomalies that may correspond to ancient continental suture zones or faults this would suggest that in these areas a strongly anisotropic but localized lithospheric fabric dominates over any ambient asthenospheric anisotropic signature in areas with generally strong apm parallel splitting this would imply a thick sheared mantle lithosphere whose deformation induced anisotropy is strong enough to overprint the anisotropy induced by apm and is aligned with the shallower crustal structures responsible for generating the observed magnetic anomalies in the southeastern areas dominated by null splitting measurements there may be no strong signature from asthenospheric anisotropy to override but a substantial lithospheric thickness is still required to generate the magnitude of the observed sks splitting 1 s more data are required to verify these results but future datasets including data from usarray may be able to exploit the correlations between null and non null sks splitting measurements and magnetic lineaments to better constrain the provenance of the regional anisotropic signature

iron isotope fractionation during magmatic differentiation in kilauea iki lava lake magmatic differentiation helps produce the chemical and petrographic diversity of terrestrial rocks the extent to which magmatic differentiation fractionates nonradiogenic isotopes is uncertain for some elements we report analyses of iron isotopes in basalts from kilauea iki lava lake hawaii the iron isotopic compositions 56fe 54fe of late stagemeltveins are 0 2 permil per thousand greater than values for olivine cumulates olivine phenocrysts are up to 1 2 per thousand lighter than those of whole rocks these results demonstrate that iron isotopes fractionate during magmatic differentiation at both whole rock and crystal scales this characteristic of iron relative to the characteristics of magnesium and lithium for which no fractionation has been found may be related to its complex redox chemistry in magmatic systems and makes iron a potential tool for studying planetary differentiation

integration of cocorp deep reflection and magnetic anomaly analysis in the southeastern united states implications for origin of the brunswick and east coast magnetic anomalies integration of magnetic anomaly analysis with cocorp deep reflection data from the southeastern united states provides three new constraints on the interpretation of the brunswick and east coast magnetic anomalies as well as on the reflection data these are as follows 1 the source of the brunswick anomaly lies within the deep crust this anomaly is not caused by a mesozoic rift basin as proposed by some workers 2 a simple seaward dipping high susceptibility slab model can explain both the brunswick and east coast magnetic anomalies the along strike change in character of the two anomalies results largely from a change in azimuth of the source body 3 beneath the southeastern united states this source body dips south lies immediately on the south flank of the prominent southward dipping reflective zone revealed on cocorp surveys and was previously associated with the alleghanian suture between north america and africa these results imply that a dipping highly magnetized zone in the upper plate of the alleghanian suture is responsible for both the brunswick and east coast magnetic anomalies the high susceptibility material responsible for these anomalies might be mafic lower continental or oceanic crust thrust upward during alleghanian continental collision or mafic igneous material intruded into the upper plate of the suture zone during subsequent mesozoic rifting or both the latter hypothesis implies that the alleghanian suture acted as a zone of weakness a repository which was reactivated to control the site of ultimate atlantic rifting and possibly initial sea floor spreading

multiple layers of seismic anisotropy and a low velocity region in the mantle wedge beneath japan evidence from teleseismic receiver functions 1 a complete characterization of seismic anisotropy can yield powerful constraints on mantle flow and deformation this is particularly important for the mantle wedge above subducting slabs where the geometry of mantle flow remains poorly understood we seek to better characterize the geometry and strength of anisotropy in the mantle wedge beneath northeast honshu and hokkaido both of which overlie the subducting pacific plate previous studies indicate that upper mantle anisotropy in the japan subduction zone is highly complex and exhibits dramatic spatial variations to provide complementary constraints on the along strike variations in anisotropy we analyze teleseismic receiver functions from stations of the broadband f net array using the multitaper correlation receiver function estimator backazimuthal variations in p to sh converted energy provide clear evidence for complicated anisotropic structure in the mantle wedge beneath northeast honshu and hokkaido in northeast honshu forward modeling of receiver functions using synthetic seismograms suggests the presence of an anisotropic layer in the forearc mantle wedge above the subducting slab and a second anisotropic layer beneath the crust of the overriding plate we also see evidence for a region of low isotropic velocity in the central part of the wedge beneath ne honshu comparisons between transverse component receiver functions at stations located in ne honshu and hokkaido reveal striking differences providing further evidence for along strike variation in anisotropic structure in the mantle wedge beneath japan

shear wave splitting in the appalachians and the pyrenees importance of the inherited tectonic fabric of the lithosphere splitting of teleseismic shear waves has been measured in the appalachians eastern usa and the pyrenees western europe using data recorded by permanent and portable stations from a comparison of the results it appears that an interpretation of the recorded seismic anisotropy in terms of geodynamics is not straightforward successive geodynamic events have generated structures that may have resulted in a similar pattern of mantle flow and that therefore may have contributed in the development of the recorded anisotropy combining geological and geophysical arguments it appears that the mantle anisotropy measured across the appalachians and the pyrenees may not be systematically appalachian or pyrenean in age but may be mainly due to a lithospheric structure formed during earlier major tectonic events i e the grenvillian and the hercynian orogenies respectively we suggest that during major episodes of continent assembly a pervasive tectonic fabric is developed in the lithospheric mantle in the subsequent evolution of the continent this fabric may induce a significant mechanical anisotropy that will drastically influence the mechanical behaviour of the iithosphere when submitted to new tectonic events

iron isotope fractionation during leaching of granite and basalt by hydrochloric and oxalic acids abstract transport of iron fe within hydrothermal and soil environments involves the transferral into aqueous solutions by leaching of complex polyminerallic rocks understanding the isotope fractionation mechanisms during this process is key for any application of the fe isotope system to biogeochemical studies here we reacted biotite granite and tholeiite basalt with 0 5 m hydrochloric acid and 5 mm oxalic acid solutions at ambient temperature solution aliquots were recovered over a seven day period and analysed for major and trace element concentrations and fe isotopic compositions in all experiments fe initially released into solution was isotopically lighter with 56fesolution rock as low as 1 80 in the granite hydrochloric acid system the oxalic acid experiments showed similar patterns but smaller fractionation in all experiments the 56fesolution rock reduced over time which would be in line with the formation of a leached layer as proposed before brantley s l liermann l j guynn r l anbar a icopini g a and barling j 2004 fe isotopic fractionation during mineral dissolution with and without bacteria geochim cosmochim acta 68 15 3189 3204 granite and basalts reacting with hydrochloric acid reached apparent steady state values of 0 60 0 15 and 0 40 0 20 respectively whilst experimental values with oxalic acid were 1 0 0 15 and 0 50 0 15 during the granite experiments alteration of biotite to chlorite followed by dissolution of chlorite were likely the dominant processes whilst in the basalt experiments dissolution of pigeonite was likely the principal source of fe variations in ph during the hydrochloric acid experiments were minimal remaining below 0 5 at all times in oxalic acid solutions the ph increased to over 4 leading likely to precipitation of secondary minerals and adsorption co precipitation of fe onto mineral surfaces these processes could contribute to the greater fractionation observed in the final stages of the oxalic acid experiments our results highlight the importance of mineralogy and fluid composition on the fe isotope systematics during weathering the fractionation processes identified for granites and basalts are in line with those inferred from field observations in soils sediments groundwater and hydrothermal deposits and from laboratory studies of single mineral leaching

mantle dynamics and seismic anisotropy abstract observations of seismic anisotropy yield some of the most direct constraints available on both past and present day deformation in the earth s mantle insight into the character of mantle flow can also be gained from the geodynamical modeling of mantle processes on both global and regional scales we highlight recent progress toward understanding mantle flow from both observations and modeling and discuss outstanding problems and avenues for progress particularly in the integration of seismological and geodynamical constraints to understand seismic anisotropy and the deformation that produces it to first order the predictions of upper mantle anisotropy made by global mantle circulation models match seismological observations well beneath the ocean basins but the fit is poorer in regions of greater tectonic complexity such as beneath continental interiors and within subduction systems in many regions of the upper mantle models of anisotropy derived from surface waves are seemingly inconsistent with shear wave splitting observations which suggests that our understanding of complex anisotropic regions remains incomplete observations of anisotropy in the d layer hold promise for improving our understanding of dynamic processes in the deep earth but much progress remains to be made in characterizing anisotropic structure and relating it to the geometry of flow geochemical heterogeneity or phase transitions major outstanding problems related to understanding mantle anisotropy remain particularly regarding the deformation and evolution of continents the nature of the asthenosphere subduction zone geodynamics and the thermo chemical state of the lowermost mantle however we expect that new seismological deployments and closer integration of observations with geodynamical models will yield rapid progress in these areas

microblock amalgamation in the north china craton evidence from neoarchaean magmatic suite in the western margin of the jiaoliao block abstract the archaean earth is considered to have been characterized by microcontinents that formed dominantly through the accretion of oceanic arcs and plateaus the north china craton ncc provides a typical case where at least seven ancient microcontinental nuclei with distinct lithological features and independent tectonic histories were amalgamated into the cratonic framework at the end of the archaean here we investigate a suite of magmatic rocks developed at the periphery of one of these microblocks the jiaoliao block that forms part of the composite eastern block of the ncc we present petrological geochemical and zircon u pb geochronological data from the taipingzhai charnockite suite and associated amphibolites metagabbros and orthogneisses from the qianxi complex geochemically the rocks show a wide range of sio 2 charnockite suite 52 57 75 50 wt metagabbro 43 71 wt amphibolite 50 24 wt garnet bearing biotite 63 73 wt and mgo charnockite suite 0 89 5 01 wt metagabbro 3 99 wt amphibolite 6 23 wt garnet bearing biotite 2 08 wt the composition of the felsic units straddle from diorite through syeno diorite to granite with both alkalic and subalkalic affinity with dominantly magnesian composition and arc related features their immobile trace element relationships suggest calc alkaline affinity they show positive pb ba la nd and gd and negative nb ta sr th and ti anomalies with slightly negative anomalies of ce and y attesting to arc related features in tectonic classification diagrams the rocks plot in the vag syn colg field or the vag area suggesting subduction related origin the dominant population of zircons in all these rocks displays magmatic crystallization features including high th u values with core rims textures indicating subsequent thermal events the zircon u pb data yield upper intercept ages of 2587 10 ma to 2543 17 ma and 207 pb 206 pb mean ages of 2578 7 3 ma to 2536 8 ma for the charnockite suite marking the timing of emplacement of the arc magmas the overgrowth rims as well as discrete neoformed grains are interpreted as dating subsequent metamorphism and yield 207 pb 206 pb ages between 2533 ma to 2490 ma zircons in the metagabbro preserve upper intercept ages of 2556 20 ma representing the crystallization age of this rock the younger ages of 2449 58 ma upper intercept age and 1845 25 ma 207 pb 206 pb spot age are interpreted to represent subsequent multiple thermal events in this area zircons in the amphibolite preserve the 207 pb 206 pb mean age of 2539 9 ma representing the crystallization age of this rock the garnet bearing biotite gneiss shows an upper intercept age of 2562 10 ma mswd 0 66 n 36 and the 207 pb 206 pb mean age of 2561 9 ma mswd 0 63 n 33 which is taken to represent the crystallization age of this rock some inherited zircons are also identified with 207 pb 206 pb ages of 2664 26 ma and 2628 26 ma zircon lu hf data show dominantly positive ehf t values and combined with crustal residence ages the results suggest mesoarchean to neoarchean juvenile crust formation in the ncc we interpret the data presented here to represent a phase of major late neoarchaean arc magmatism along the western margin of the jiaoliao block related to the birth of microcontinental nuclei within the ncc our data suggest that the western and eastern blocks might not have existed as discrete crustal blocks and that the construction of the ncc is a result of the assembly of several microblocks or terranes at the end of archaean similar archean cratonic nuclei in other regions of the world might have formed part of a primitive supercontinent in the early earth

crustal structure beneath the florida to edmonton broadband seismometer array 1 ps receiver functions were stacked to determine crustal thickness and vp vs ratios for the 28 stations of the florida to edmonton broadband seismometer array and 6 adjacent permanent stations roots of thickened crust exist beneath the paleozoic appalachian orogen and the proterozoic trans hudson orogen the ratios of surface elevation to root thickness are lower than observed in young active orogens as are average crustal root buoyancies determined from gravity data these results are consistent with global trends and may be explained by increased crustal root density due to metamorphism crustal thickening is also observed beneath the mid continent rift in iowa consistent with compressional inversion of the rift during the grenville orogeny

reprocessing and enhanced interpretation of the initial cocorp southern appalachians traverse abstract reprocessing of the 1978 1980 cocorp southern appalachian seismic reflection data has produced improved images of structures related to the emplacement of the blue ridge inner piedmont allochthon the results enhance and extend the interpretation presented previously that the blue ridge and inner piedmont are allochthonous above a shallow and shallow dipping detachment that can be followed from outcrop at the blue ridge valley and ridge transition to at least beneath the carolina terrane the continuity of reflections in the new images supports the interpretation that the southern appalachian detachment is not rooted on the east side of the inner piedmont but rather projects as a low angle detachment or zone of decoupling to beneath the coastal plain an implication of this geometry is that terranes such as the carolina terrane between autochthonous north america and the alleghanian suture beneath the coastal plain are detached thin flakes

na sws 1 1 a uniform database of teleseismic shear wave splitting measurements for north america 1 this version of shear wave splitting sws database db for north america na contains 6224 pairs of splitting parameters fast polarization directions and splitting times measured using all the available data recorded by digital broadband seismic stations over the period of 1980 2007 and archived at the incorporated research institutions for seismology data management center the measurements were produced using a set of robust procedures that involve automated batch processing and manual screening and were ranked quantitatively on the basis of a uniform criterion the result is a homogeneous database of individual rather than station averaged splitting parameters that can be used by a variety of geoscientists for the understanding of the structure and dynamics of the earth s deep interior beneath na this data brief describes the seismic data and techniques used to generate the sws results the spatial and azimuthal coverage and the limitations of the db the db will be periodically updated and enhanced by adding newly recorded data and by measuring splitting parameters using the pks and skks phases in addition to sks the database can be accessed at http www mst edu liukh sws