the tilt of mean sea level along the east coast of north america the tilt of mean sea level along the north american east coast has been a subject of debate for many decades improvements in geoid and ocean circulation models and gps positioning of tide gauge benchmarks provide an opportunity to produce new tilt estimates tilts estimated using tide gauge measurements referenced to high resolution geoid models the geodetic approach and ocean circulation models the ocean approach are compared the geodetic estimates are broadly similar with tilts downward to the north through the florida straits and at cape hatteras estimates from the ocean approach show good agreement with the geodetic estimates indicating a convergence of the two approaches and resolving the long standing debate as to the sign of the tilt these tilts differ from those used by yin and goddard 2013 to support a link between changing ocean circulation and coastal sea level rise

trace and minor elements in galena a reconnaissance la icp ms study minor and trace elements can substitute into the crystal lattice of galena at various concentrations in situ la icp ms analysis and trace element mapping of a range of galena specimens from different deposit types are used to obtain minor trace element data aimed at achieving insight into factors that control minor trace element partitioning the previously recognized coupled substitution ag bi sb 3 2pb2 is confirmed however the poorer correlation between ag and bi sb when the latter elements are present at high concentrations 2000 ppm suggests that site vacancies may come into play 2 bi sb 3 3pb2 galena is the primary host of tl in all mapped mineral assemblages along with cu tl is likely incorporated into galena via the coupled substitution ag cu tl bi sb 3 2pb2 tin can reach significant concentrations in galena 500 ppm cd and minor hg can be incorporated into galena the simple isovalent substitution cd hg 2 pb2 is inferred this paper shows for the first time oscillatory and sector compositional zoning of minor trace elements ag sb bi se te tl in galena from two epithermal ores zoning is attributed to slow crystal growth into open spaces within the vein at relatively low temperatures the present data show that galena can host a broader range of elements than previously recognized for many measured elements the data sets generated display predictable partitioning patterns between galena and coexisting minerals which may be dependent on temperature or other factors trace element concentrations in galena and their grain scale distributions may also have potential in the identification of spatial and or temporal trends within individual metallogenic belts and as markers of ore formation processes in deposits that have undergone superimposed metamorphism and deformation galena trace element geochemistry may also display potential to be used as a trace minor element vector approach in mineral exploration notably for recognition of proximal to distal trends within a given ore system

s velocity variations beneath north america 1 we investigate s velocity variation in the upper mantle beneath north american to better understand the effects of data heterogeneity model parameterization and regularization to this end we analyzed and fit regional s and rayleigh wave trains generated by earthquakes around north america that occurred between the years 2000 through 2006 including waveforms from the transportable array stations of earthscope s usarray these new data were combined with constraints used for the 3 d s velocity model na04 in order to create a new model na07 another model was created from a suite of good fit models to provide a useful guide for model velocities and uncertainties by estimating ranges of probable velocity variations throughout the upper mantle we find that the southern and eastern edges of the north american craton appear to be defined by paleozoic orogens rather than proterozoic ones on average the archean portion of the craton is 200 km thick while the paleozoic part averages 175 km thick with an 80 m s lower s velocity the horizontal gradients in velocity are over 1 0 100 km at the western margin of the craton 0 5 100 km in the south and 1 100 km at the eastern margin

seismic anisotropy in the continental crust of northwestern canada s u m m a r y most studies of the seismic structure of continental crust assume that the wave speeds are isotropic at seismic wavelengths the ability to measure surface wave propagation speed from the cross correlation of ambient seismic noise provides new opportunities to image the crust and uppermost mantle we investigate radial anisotropy in the continental crust of northwestern canada from group velocity curves of love and rayleigh waves obtained from ambient noise cross correlation we test the null hypothesis that the love and rayleigh group speed curves can be simultaneously fit by an earth model containing isotropic seismic velocities throughout the crust group velocity is predicted for 200 000 one dimensional earth models which are generated by randomly varying the crustal shear velocity and radial anisotropy within a prescribed range the goodness of fit of the predictions is assessed by comparison with two sets of observed dispersion curves that correspond to two tectonically distinct terranes the archean early proterozoic craton and the transition from craton to cordillera the majority of best fitting models contain vsh vsv 4 5 per cent in the middle crust the finding that the middle lower crust is seismically anisotropic across a large swath of northwestern canada combined with recent observations of anisotropic crust in much of the western united states suggests that anisotropy may be ubiquitous in the continental crust

s wave velocity structure of the canadian upper mantle abstract we investigate mantle structure beneath the canadian landmass using 500 surface wave waveforms recorded at stations of the canadian national seismic network and global seismic network the data are processed using the method of partitioned waveform inversion and afford a comprehensive sampling of s velocity structure beneath the north american craton and adjacent orogenic belts our study thereby extends results from previous regional s wave studies north of the coterminous us and provides a characterization of mantle structure beneath canada which is complementary to the body wave model of grand j geophys res 99 1994 11591 the resulting 3d velocity model is well resolved to a depth of 400 km over most of the region and displays two prominent large scale anomalies a high velocity structure beneath the canadian shield and platform associated with the cratonic keel and pronounced low velocities beneath the cordillera the contrast between these features is strong up to 10 and at more southerly latitudes is sharp with the transition occurring over distances of 600 km or less laterally coherent high velocities persist to depths of ca 250 km beneath the north american craton which we interpret to represent the base of the continental keel smaller scale variations are observed within the cratonic mantle but in general show little correlation with surface geological provinces moderately low velocities beneath the st lawrence valley region and labrador may be related to intracontinental volcanism and rifting respectively

shear velocity structure radial anisotropy and dynamics of the tibetan crust geophysical and geological data suggest that tibetan middle crust is a partially molten mechanically weak layer but it is debated whether this low viscosity layer is present beneath the entire plateau what its properties are how it deforms and what role it has played in the plateau s evolution broad band seismic surface waves yield resolution in the entire depth range of the tibetan crust and can be used to constrain its shear wave velocity structure indicative of crustal composition temperature and partial melting and radial anisotropy indicative of the patterns of deformation we measured love and rayleigh wave phase velocity curves in broad period ranges up to 7 200 s for a few tens of pairs and groups of stations across tibet combining in each case hundreds of interstation measurements made with cross correlation and waveform inversion methods shear velocity profiles were then determined by extensive series of non linear inversions of the data designed to constrain the depth dependent ranges of isotropic average shear speeds and radial anisotropy shear wave speeds within the tibetan middle crust are anomalously low and also show strong lateral variations across the plateau the lowest mid crustal shear speeds are found in the north and west of the plateau 3 1 3 2 km s 1 within a pronounced low velocity zone in southeastern tibet crustal shear wave speeds increase gradually towards southeast whereas in the north the change across the kunlun fault is relatively sharp the lateral variations of shear speeds within the crust are indicative of those in temperature a mid crustal temperature of 800 c reported previously can account for the low shear velocities across lhasa in the north the temperature is higher and exceeds the solidus resulting in partial melting that we estimate at 3 6 per cent strong radial anisotropy is required by the data in western central tibet 5 per cent but not in northeastern tibet the amplitude of radial anisotropy in the crust does not correlate with isotropic average shear speed and by inference with crustal rock viscosity or with surface elevation instead radial anisotropy is related to the deformation pattern and is the strongest in regions experiencing extension crustal flattening as noted previously the growth of tibet by the addition of indian crustal rocks into its crust from the south is reflected in the higher crustal seismic velocities and thus lower temperatures in the southern compared to northern parts of the plateau more recently added rocks having had less time to undergo radioactive heating within the thickened tibetan crust gravity driven flattening the basic cause of extension and normal faulting in the southern western and central tibet is evidenced by pervasive radial anisotropy in the middle crust beneath the regions undergoing extension the overall eastward flow of the crust is directed by the boundaries and motions of the lithospheric blocks that surround tibet

significant sink of ocean eddy energy near western boundaries ocean eddies generated through instability of the mean flow are a vital component of the energy budget of the global ocean modelling combined with satellite altimetry data suggests that the energy from westward propagating eddies is scattered and eventually dispersed when they reach the western boundary of an ocean basin

basinwide integrated volume transports in an eddy filled ocean the temporal evolution of the strength of the atlantic meridional overturning circulation amoc in the subtropical north atlantic is affected by both remotely forced basin scale meridionally coherent climate relevant transport anomalies such as changes in high latitude deep water formation rates and locally forced transport anomalies such as eddies or rossby waves possibly associated with small meridional coherence scales which can be considered as noise the focus of this paper is on the extent to which local eddies and rossby waves when impinging on the western boundary of the atlantic affect the temporal variability of the amoc at 26 5 degrees n continuous estimates of the amoc at this latitude have been made since april 2004 by combining the florida current ekman and midocean transports with the latter obtained from continuous density measurements between the coasts of the bahamas and morocco representing respectively the western and eastern boundaries of the atlantic at this latitude within 100 km of the western boundary there is a threefold decrease in sea surface height variability toward the boundary observed in both dynamic heights from in situ density measurements and altimetric heights as a consequence the basinwide zonally integrated upper midocean transport shallower than 1000 m as observed continuously between april 2004 and october 2006 varies by only 3 0 sv 1 sv 10 6 m 3 s 1 rms instead upper midocean transports integrated from western boundary stations 16 40 and 500 km offshore to the eastern boundary vary by 3 6 6 0 and 10 7 sv rms respectively the reduction in eddy energy toward the western boundary is reproduced in a nonlinear reduced gravity model suggesting that boundary trapped waves may account for the observed decline in variability in the coastal zone because they provide a mechanism for the fast equatorward export of transport anomalies associated with eddies impinging on the western boundary an analytical model of linear rossby waves suggests a simple scaling for the reduction in thermocline thickness variability toward the boundary physically the reduction in amplitude is understood as along boundary pressure gradients accelerating the fluid and rapidly propagating pressure anomalies along the boundary the results suggest that the local eddy field does not dominate upper midocean transport or amoc variability at 26 5 degrees n on interannual to decadal time scales

mechanical controls on the deformation of continents at convergent margins abstract spatial variations in the rigidity of continental plates expressed in terms of an effective elastic thickness t e can have a profound influence on the style of deformation of ocean continent convergent margins depending on the spatial distribution of t e strains related to plate boundary forces can become concentrated where t e is small we calculate t e and t e anisotropy in western canada by using and comparing the wavelet and multitaper coherence methods in addition to a nearly stepwise change in t e from the cordillera to the craton we show that weak axes of t e anisotropy are parallel with most compressive directions of horizontal stress components and fast axes of upper mantle seismic anisotropy maxima in the magnitude of t e anisotropy are spatially correlated with the locations of most earthquakes and the locations and directions of maxima in electrical anisotropy and conductivity the pattern of brittle failure and seismicity is explained as a response to plate boundary forces acting on a plate of variable rigidity and is expected to induce the observed mechanical anisotropy and enhance the flow of crustal fluids resulting in locally high electrical conductivities our combined results thus suggest for the first time that the elastic properties of continental lithosphere have a leading order influence on the deformation and evolution of convergent plate boundaries

the lithospheric root beneath hudson bay canada from rayleigh wave dispersion no clear seismological distinction between archean and proterozoic mantle abstract we characterise the nature and thickness of the seismological lithosphere beneath hudson bay using dispersion analysis of fundamental mode rayleigh waves along two station paths crossing the region hudson bay is largely underlain by the paleoproterozoic trans hudson orogen and is surrounded by archean cratons this study region thus provides an opportunity to investigate whether fundamental differences exist in the nature of the subcontinental lithosphere between archean and proterozoic terranes dispersion measurements for hudson bay carried out in the 15 220 s period range show seismic phase velocities consistently higher than those derived from global reference models in addition the phase velocities are higher than those of the canadian shield average and of many other cratonic regions worldwide monte carlo modelling is used to estimate 1d shear wave velocity profiles for each of the dispersion curves the models are characterised by a high velocity lid interpreted as the seismological expression of the subcontinental lithosphere beneath which velocities decrease gradually toward global reference values we find lithospheric thicknesses in the range 185 260 km beneath the hudson bay region with maximum lithospheric shear wave velocity perturbations of 4 5 7 3 above global reference values by treating the geotherm as a free parameter the average dispersion curve for hudson bay can be fit using laboratory based mineral physics relations with simple compositional models including constant composition and layered mantle models low mantle temperatures corresponding to surface heat flow values between 37 and 40 mw m 2 are required to match the observed data a layered model based on the archean slave craton is favoured as it provides a lithospheric root that is close to the isopycnic state i e neutrally buoyant for all depths in common with studies of other continental shields particularly fennoscandia and central australia the velocity structure modelled for the hudson bay region suggests that there is no systematic difference between the velocity structure and thickness of archean and proterozoic seismological lithosphere this result may have important implications for models of lithospheric stabilisation and evolution between 2 8 and 1 8 ga

adjustment of the ocean under buoyancy forces part i the role of kelvin waves abstract the early stages of the adjustment of an ocean toward equilibrium is examined using an ocean general circulation model the initial state is one with uniform meridional potential temperature gradients yielding density gradients representative of those observed in the north atlantic the main adjustment in the time examined here the first few months is by coastal kelvin waves the first baroclinic mode dominates so the behavior proves to be very similar to that in a shallow water model also the dynamics is locally close to that for an f plane but account must be taken of the way f varies with latitude the essential result of the coastal adjustment is to reduce the temperature gradients around the perimeter of the basin especially at the level where the first mode has the maximum effect this study also examines the way this adjustment process is distorted in models due to the constraints imposed by computer limitations namely in a model with too coarse a horizontal resolution and an artif

genesis of the stratiform zhenzigou pb zn deposit in the north china craton rb sr and c o s pb isotope constraints abstract isotopes rb sr c o s and pb were investigated from the zhenzigou pb zn deposit in the qingchengzi mineral field qmf of the north china craton as an aid to determine the genesis of stratiform pb zn deposits in the liao ji rift a step dissolution rb sr age of 1798 8 ma with 206pb 204pb ratios of 17 7477 17 8527 were obtained from sphalerite sulfur isotopic ratios for pyrite 5 14 4 sphalerite 2 4 8 6 and galena 0 3 8 6 from zhenzigou have a narrower range than those from the host paleoproterozoic dashiqiao formation and granite in the area calcite and limestone from ore and wallrocks at the deposit have similar c and o isotope compositions with 13cpdb ranging from 6 0 to 2 3 and 18osmow from 9 8 to 13 7 which are similar to those of carbonatite and the mantle comprehensive analysis of the pb isotopic composition of the sulfide from the zhenzigou deposit and pb zn deposits in adjacent area show that the pb originated from the upper crust and mixed with pb from the mantle sulfur isotopes from zhenzigou deposit indicate that the mineralization has a volcanic eruption source the 13cpdb and 18osmow values indicate that the co2 originated from a mixed mantle marine carbonate and organic source combined with the study of regional metallogenic background this paper proposes that deposition of stratiform pb zn mineralization in the qmf began ca 2052 ma during development of the liaoji rift the mineralization extended to ca 1798 ma prior to deformation associated with the lvliang movement which dismembered the stratiform pb zn mineralization the veined mineralization in the region cross cuts the stratiform deposits and represents remobilized and redeposited deposits associated with the emplacement of triassic plutons such as the xinling and shuangdinggou granites

seismicity in the vicinity of the snorcle corridors of the northern canadian cordillera the slave northern cordillera lithospheric evolution snorcle corridors of the northern cordillera sample some of the most and least seismically active regions of canada the earthquake history of this region is short precise determination of earthquake locations and depths is not possible even today nonetheless significant gains in our knowledge of the seismicity of this region have been made in recent years from studies of historic earth quakes microseismicity studies and advances in waveform modelling techniques combined with broadband data that allow for determination of focal mechanisms and depths for moderate earthquakes this article summarizes our current knowledge of the seismicity and seismic hazards across the region these detailed analyses have shown that i the largest historical earthquakes have occurred in regions of ongoing microseismicity ii the largest earthquakes have occurred in pairs or in swarms suggesting that stress triggering is important in this region iii the active faults are concentrated in the offshore region iv there is a concentration of seismicity in the fold and thrust belt several hun dred kilometres from the active plate margin and v there is no seismicity associated with the quaternary volcanic zone in northern british columbia potentially damaging magnitude m 5 earthquakes can be expected every few years in the vicinity of the northern cordillera the mw 7 9 denali alaska earthquake where mw is the moment magnitude was a good reminder that the effects of a large earthquake can be substantial even hundreds of kilometres from the epicentre detailed studies of seismicity earth structure and tectonics with the latter made possible in large part by the snorcle transect will allow for informed decision making for resource development and the design of safe structures and infrastructure in the northern canadian cordillera resume les corridors du projet snorcle de la cordillere septentrionale permettent d echantillonner quelques unes des regions sismiques les plus et les moins actives du canada l histoire des seismes de cette region est breve meme

boundary wave communication of bottom pressure and overturning changes for the north atlantic 1 the relationship between changes in sea surface height bottom pressure and overturning is explored using isopycnal model experiments for the north atlantic changes in high latitude forcing are communicated rapidly over the basin through boundary wave propagation along the continental slope involving a hybrid mixture of kelvin and topographic rossby waves as well as spreading more slowly through advection along the western boundary this wave communication leads to coherent signals in sea surface height and bottom pressure variability extending for several thousand kilometers along the continental slope the model results are in broad agreement with altimetric diagnostics and the patterns only alter in detail with the realism of the topography the adjustment in bottom pressure is directly linked to a change in overturning since west east contrasts in bottom pressure are associated with a zonal integral in the meridional geostrophic flow correlation patterns reveal that temporal changes in overturning are primarily connected to the vertical contrast in bottom pressure across the shelf and continental slope along the western boundary

architecture of the crust and uppermost mantle in the northern canadian cordillera from receiver functions the northern canadian cordillera ncc is an active orogenic belt in northwestern canada characterized by deformed autochtonous and allochtonous structures that were emplaced in successive episodes of convergence since the late cretaceous seismicity and crustal deformation are concentrated along corridors located far 200 to 800 km from the convergent plate margin proposed geodynamic models require information on crust and mantle structure and strain history which are poorly constrained we calculate receiver functions using 66 broadband seismic stations within and around the ncc and process them to estimate moho depth and p to s velocity ratio vp vs of the cordilleran crust we also perform a harmonic decomposition to determine the anisotropy of the subsurface layers from these results we construct simple seismic velocity models at selected stations and simulate receiver function data to constrain crust and uppermost mantle structure and anisotropy our results indicate a relatively flat and sharp moho at 32 2 km depth and crustal vp vs of 1 75 0 05 seismic anisotropy is pervasive in the upper crust and within a thin 10 15 km thick sub moho layer the modeled plunging slow axis of hexagonal symmetry of the upper crustal anisotropic layer may reflect the presence of fractures or mica rich mylonites the subhorizontal fast axis of hexagonal anisotropy within the sub moho layer is generally consistent with the se nw orientation of large scale tectonic structures these results allow us to revise the geodynamic models proposed to explain active deformation within the ncc

deformation history of the paleoproterozoic liaohe assemblage in the eastern block of the north china craton the paleoproterozoic liaohe assemblage and associated liaoji granitoids represent the youngest basement in the eastern block of the north china craton various structural elements and metamorphic reaction relations indicate that the liaohe assemblage has experienced three distinct deformational events d1 to d3 and four episodes of metamorphism m1 to m4 the earliest greenschist facies event m1 is recognized in undeformed or weakly deformed domains wrapped by the s1 schistosity suggesting that m1 occurred before d1 the d1 deformation produced small mostly meter scale isoclinal and recumbent folds f1 an associated penetrative axial planar schistosity s1 a mineral stretching lineation l1 and regional scale ductile shear zones concurrent with d1 was m2 metamorphism which occurred before d2 and produced low to medium pressure amphibolite facies assemblages regionally divergent motion senses reflected by the asymmetric f1 folds and other sense of shear indicators together with the radial distribution of the l1 lineation surrounding the liaoji granitoids imply that d1 represents an extensional event the d2 deformation produced open to tight f2 folds of varying scales s2 axial crenulation cleavages and ene ne striking thrust faults involving broadly nw se compression following d2 was m3 metamorphism that led to the formation of sillimanite and cordierite in low pressure type rocks and kyanite in medium pressure rocks the last deformational event d3 formed nw wnw trending folds f3 axial planar kink bands spaced cleavages s3 and strike slip and thrust faults which deflect the earlier d1 and d2 structures d3 occurred at a shallow crustal level and was associated with or followed by a greenschist facies retrograde metamorphic event m4 the liaohe assemblage and associated liaoji granitoids are considered to have formed in a paleoproterozoic rift the late spreading of which led to the occurrence of the early extensional deformation d1 and the m1 and m2 metamorphism and the final closing of which was associated with the d2 and d3 phases of deformation and m3 and m4 metamorphism

heat flow heat generation and crustal temperatures in the northern canadian cordillera thermal control of tectonics 1 the heat flow in the northern canadian cordillera between 59 and 64 n is very high 105 22 mw m2 the average upper crust heat generation is 4 6 2 4 microw m3 giving a reduced deep heat flow of 59 mw m2 similar to the southern canadian cordillera 49 53 n estimated moho temperatures of 800 1000 c and lithosphere only 50 60 km thick are substantiated by slow upper mantle seismic velocities and by high elevations associated with crust only 32 35 km thick the new data support the conclusion that all of the north and south america cordilleras are hot the paleoproterozoic wopmay orogen to the east has a remarkably high heat flow of 90 15 mw m2 for such an old and stable region however basement samples indicate high heat generation and estimated deep temperatures are intermediate between the cordillera and the slave craton further to the east heat flow from the yellowknife area of the slave craton 53 mw m2 implies low lithosphere temperatures in agreement with kimberlite xenolith p t data the high temperatures in the cordillera result in a very thin and weak lithosphere and may allow a lower crust detachment the north and central cordillera have been inland of the coastal queen charlotte transform fault since subduction stopped in the eocene thus some process has maintained high temperatures in the former back arc for more than 40 ma

mantle flow through the northern cordilleran slab window revealed by volcanic geochemistry the northern cordilleran slab window formed beneath western canada concurrently with the opening of the californian slab window beneath the southwestern united states beginning in late oligocene miocene time a database of 3530 analyses from miocene holocene volcanoes along a 3500 km long transect from the northern cascade arc to the aleutian arc was used to investigate mantle conditions in the northern cordilleran slab window using geochemical ratios sensitive to tectonic affi nity such as nb zr we show that typical volcanic arc compositions in the cascade and aleutian systems derived from subduction hydrated mantle are separated by an extensive volcanic fi eld with intraplate compositions derived from relatively anhydrous mantle this chemically defi ned region of intraplate volcanism is spatially coincident with a geophysical model of the northern cordilleran slab window we suggest that opening of the slab window triggered upwelling of anhydrous mantle and displacement of the hydrous mantle wedge which had developed during extensive early cenozoic arc and backarc volcanism in western canada high heat fl ow throughout the western canadian cordillera is broadly coincident with the fi eld of intraplate volcanism and is linked to slab window induced mantle upwelling

observations inferences and mechanisms of the atlantic meridional overturning circulation a review this is a review about the atlantic meridional overturning circulation amoc its mean structure temporal variability controlling mechanisms and role in the coupled climate system the amoc plays a central role in climate through its heat and freshwater transports northward ocean heat transport achieved by the amoc is responsible for the relative warmth of the northern hemisphere compared to the southern hemisphere and is thought to play a role in setting the mean position of the intertropical convergence zone north of the equator the amoc is a key means by which heat anomalies are sequestered into the ocean s interior and thus modulates the trajectory of climate change fluctuations in the amoc have been linked to low frequency variability of atlantic sea surface temperatures with a host of implications for climate variability over surrounding landmasses on intra annual timescales variability in amoc is large and primarily reflects the response to local wind forcing meridional coherence of anomalies is limited to that of the wind field on interannual to decadal timescales amoc changes are primarily geostrophic and related to buoyancy anomalies on the western boundary a pacemaker region for decadal amoc changes is located in a western transition zone along the boundary between the subtropical and subpolar gyres decadal amoc anomalies are communicated meridionally from this region amoc observations as well as the expanded ocean observational network provided by the argo array and satellite altimetry are inspiring efforts to develop decadal predictability systems using coupled atmosphere ocean models initialized by ocean data

ocean to shelf signal transmission a parameter study 1 oceanic signal transmission onto and across the continental shelf to the coast is investigated focusing on pressure and surface elevation the model used represents a uniform cross slope section on an f plane with stratification along shelf wave number and oscillatory frequency inclusion of beta and probably a fully three dimensional numerical model would be necessary to treat all forms of oceanic signal at the model s oceanic boundary care is needed for the prescription of the oceanic signal to be physically realistic then substantial transmission across the slope and shelf is limited to 1 large response near a dispersion relation for a coastal trapped wave and 2 large along shelf scale relative to a frictional decay distance for coastal trapped mode 1 that is friction aids signal transmission as a consequence coastal gauges are likely to be effective monitors of only the largest scale oceanic motion typically thousands of kilometers

bathymetric influence on the coastal sea level response to ocean gyres at western boundaries abstractit is our aim with this paper to investigate how the presence of a continental shelf and slope alters the relationship between interior ocean dynamics and western boundary coastal sea lev

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

leaky slope waves and sea level unusual consequences of the beta effect along western boundaries with bottom topography and dissipation abstractcoastal trapped waves ctws carry the ocean s response to changes in forcing along boundaries and are important mechanisms in the context of coastal sea level and the meridional overturnin

surface wave images of western canada lithospheric variations across the cordillera craton boundary two station surface wave analysis was used to measure rayleigh wave phase velocities between 105 station pairs in western canada straddling the boundary between the tectonically active cordillera

crustal vs structure in northwestern canada imaging the cordillera craton transition with ambient noise tomography 1 crustal seismic velocity structure in northwest canada is imaged using group velocity measurements derived from ambient noise cross correlations the focus area surrounds the canadian northwest experiment canoe array a 16 month deployment of 59 broadband seismic stations the canoe array extended from the northern cordillera on the west into the archean slave province to the east crossing crustal terranes that span 4 gyr of earth history forty broadband stations from the canadian national seismograph network and the polaris network are also included the green s function for each pair of stations is estimated by cross correlating 24 h long time series of ambient noise for each day in the time period july 2004 to june 2005 fundamental mode rayleigh waves are observed on cross correlated vertical component records and love waves on the transverse components the group velocity measurements are inverted for 3 d shear wave velocity within the crust local sensitivity kernels are used to account for the effects of a laterally variable sedimentary layer at shallow depths and receiver function p s differential times at the canoe stations constrain total crustal thickness known sedimentary basins dominate lateral variations in wave speed in the shallow crust in the middle crust the model contains a strong low velocity region that correlates spatially with the location of proterozoic metasedimentary rocks that have been inferred from active source reflection profiles to occupy much of the crust beneath the cordilleran terranes velocity variations in the lower crust which are weakly resolved due to the limited period range of our data set 5 20 s suggest a west to east transition from lower to higher wave speeds that aligns with the cordilleran deformation front in parts of the study area the results presented here are consistent with but do not confirm the notion of proterozoic strata throughout much of the cordilleran crust these metasedimentary rocks if present must have experienced some deformation and metamorphism in order to also be consistent with upper mantle seismic models that contain a sharp transition from low to high velocity across the deformation front

temperature control of continental lithosphere elastic thickness te vs vs article i nfo the elastic thickness of the continental lithosphere is closely related to its total strength and therefore to its susceptibility to tectonic deformation and earthquakes recently it has been questioned whether the lithosphere thickness and strength are dependent on crustal and upper mantle temperatures and compositions as predicted by laboratory data we test this dependence regionally by comparison in northwestern north america of the effective elastic thickness te from topography gravity coherence with upper mantle temperatures mapped by shear wave tomography velocities vs and other temperature indicators the te values are strongly bimodal as found globally less than 20 km for the hot cordillera backarc and over 60 km for the cold stable craton these te correspond to low vs beneath the cordillera and high vs beneath the craton model temperature depth profiles are used to estimate model te for comparison with those observed only limited areas of intermediate thermal regimes i e thermotectonic ages of 300 ma have intermediate te that suggest a weak lower crust over a stronger upper mantle there are large uncertainties in model te associated with composition water content strain rate and decoupling stress threshold however with reasonable parameters model yield stress envelopes correspond to observed te for thermal regimes with 800 900 c at the cordillera moho and 400 500 c for the shield in agreement with temperatures from vs and other estimators our study supports the conclusion that lithosphere elastic thickness and strength are controlled primarily by temperature and that laboratory based rheology generally provides a good estimate of the deformation behaviour of the crust and upper mantle on geological time scales

tracing mineralization history from the compositional textures of sulfide association a case study of the zhenzigou stratiform zn pb deposit ne china abstract the qingchengzi orefield located in northeastern china hosts more than ten pb zn deposits and several au ag deposits among those the zhenzigou zn pb deposit displays a typical stratiform morphology comprising ore bodies in layers and lenses the ore minerals are simply composed of sphalerite galena pyrite and pyrrhotite together with minor arsenopyrite marcasite and argentite a sulfide association of sphalerite galena pyrite arsenopyrite was selected for this study the interior compositional texture of the sulfide association was investigated by means of la icpms spot and mapping analysis with the aim of constraining the ore genesis fluid evolution history and element partitioning behavior the results show that three distinct fluids were involved in the mineralization namely an episode of sedimentary fluids at 2052 ma which is responsible for the precipitation of pyrite core py0 an episode of metamorphic fluids at 1800 ma which formed an overgrowth of pyrite py 1 and new crystallization of sphalerite sph1 and arsenopyrite aspy1 and a final episode of hydrothermal fluids related to the triassic magmatism forming another overgrowth of pyrite py2 sphalerite sph2 and arsenopyrite aspy2 together with minor precipitation of galena ga the sedimentary fluids are relatively low in temperature 300 c and have remobilized as co and ni but only at mineral grain scale the late metamorphic and magmatic fluids are enriched in in cd au as ag cu pb sb sn co and ni and depleted in bi w mo te and se the partitioning of most of the metals from the fluids into the sulfide minerals was controlled by the metals availability in the fluids and by the compatibility with crystal structure through direct or coupled substitutions pyrite acts as the main host of co ni pb and as arsenopyrite hosts a major amount of sb and pb and a minor amount of au sphalerite is the primary host of cd in cu and the secondary host of ag and sn galena is the primary host of ag sb sn and subordinately hosts cd in and as in particular a remarkable amount of in and cd was carried by the hydrothermal fluids associated with the triassic magmatism indicating that the contribution of magmatic hydrothermal fluids to the mineralization is significant in conclusion our in situ geochemical evidence of sulfide minerals reinforces a sedimentation metamorphism magmatic hydrothermal reworking model for the zhenzigou stratiform zn pb mineralization this case study underlines the significance of compositional textures of coexisting sulfide minerals when assessing the ore genesis overall our study demonstrates that by integrating trace element mapping and spot analysis on coexisting sulfide minerals it is possible to re construct the fluid evolution history resolve the metal behaviors associated with fluids evolution and review the contribution of individual fluids to mineralization

mapping the moho with seismic surface waves a review resolution analysis and recommended inversion strategies abstract the strong sensitivity of seismic surface waves to the moho is evident from a mere visual inspection of their dispersion curves or waveforms rayleigh and love waves have been used to study the earth s crust since the early days of modern seismology yet strong trade offs between the moho depth and crustal and mantle structure in surface wave inversions prompted doubts regarding their capacity to resolve the moho here we review surface wave studies of the moho with a focus on early work and then use model space mapping to establish the waves sensitivity to the moho depth and the resolution of their inversion for it if seismic wavespeeds within the crust and upper mantle are known then moho depth variations of a few kilometres produce large 1 perturbations in phase velocities however in inversions of surface wave data with no a priori information wavespeeds not known strong moho depth shear speed trade offs will mask 90 of the moho depth signal with remaining phase velocity perturbations 0 1 only in order to resolve the moho with surface waves alone errors in the data must thus be small up to 0 2 for resolving continental moho with larger errors moho depth resolution is not warranted and depends on error distribution with period an effective strategy for the inversion of surface wave data alone for the moho depth is to first constrain the crustal and upper mantle structure by inversion in a broad period range and then determine the moho depth in inversion in a narrow period range most sensitive to it with the first step results used as reference prior information on crustal and mantle structure reduces the trade offs and thus enables resolving the moho depth with noisier data such information should be used whenever available joint analysis or inversion of surface wave and other data receiver functions topography gravity can reduce uncertainties further and facilitate moho mapping

plateau uplift in western canada caused by lithospheric delamination along a craton edge mantle convection helps create continental plateaux seismic imaging of the mantle beneath the canadian cordillera an ancient plateau suggests the plateau formed when upwelling mantle caused a block of lithosphere to detach

why is the north america cordillera high hot backarcs thermal isostasy and mountain belts global mountain belts are commonly concluded to be a consequence of crustal thickening resulting from continental collision with high elevations supported by crustal roots however accumulating seismic structure data indicate that many mountain belts have no crustal root most of the north american cordillera has a 30 35 km crust in contrast to 40 45 km for the lower elevation craton and other stable areas it has been shown previously that most such mountain belts are in present or recent backarcs that are uniformly hot from thermal constraints we predict a uniform 1600 m elevation support of the cordillera by thermal expansion compared to stable areas over most of the cordillera relative to stable areas the elevations after correction for variable crustal thickness and density are in excellent agreement when subduction and shallow backarc convection stop the lithosphere may cool and the elevations of mountain belts subside over 300 m y

layered crustal anisotropy around the san andreas fault near parkfield california the rheology of the earth s crust controls the long term and short term strength and stability of plate boundary faults and depends on the architecture and physical properties of crustal materials in this paper we examine the seismic structure and anisotropy of the crust around the san andreas fault saf near parkfield california using teleseismic receiver functions these data indicate that the crust is characterized by spatially variable and strongly anisotropic upper and middle crustal layers with a moho at 35 km depth the upper layer is 5 10 km thick and is characterized by strong 30 anisotropy with a slow axis of hexagonal symmetry where the plane of fast velocity has a strike parallel to that of the saf and a dip of 40 we interpret this layer as pervasive fluid filled microcracks within the brittle deformation regime the 10 15 km thick midcrustal layer is also characterized by a weak axis of hexagonal symmetry with 20 anisotropy but the dip direction of the plane of fast velocity is reversed the midcrustal anisotropic layer is more prominent to the northeast of the san andreas fault we interpret the mid crustal anisotropic layer as fossilized fabric within fluid rich foliated mica schists when combined with various other geophysical observations our results suggest that fault creep behavior around parkfield is favored by intrinsically weak and overpressured crustal fabric

the apparent british sea slope is caused by systematic errors in the levelling based vertical datum the spirit levelling based british vertical datum ordnance datum newlyn implies a south north apparent slope in mean sea level of up to 53 mm deg 1 latitude due to the datum falling on heading northwards although this apparent slope has been investigated since the 1960s explanations of its origin have remained inconclusive it has also been suggested that rather than a slope the british vertical datum includes a step of about 240 mm affecting all sites north of about 53 n in either case the british vertical datum may be of limited use for any study requiring accurate heights or changes in heights such as testing geoid models groundwater and hydrocarbon extraction the calibration and validation of satellite based digital terrain models and the unification of vertical datums internationally within the last decade however based on an apparent reduction in the slope to only 12 mm deg 1 latitude with respect to recent geoid models it has been claimed that the british vertical datum does provide a physically meaningful surface for use in scientific applications in this paper we reinvestigate the presence of apparent south north sea slopes around britain and reported slopes in the vertical datum using the egm2008 global gravitational model together with mean sea level and gps data from british tide gauges gps ellipsoidal heights of 178 fundamental benchmarks across mainland britain and vertical deflection observations at 192 stations we demonstrate a south north slope in the british vertical datum of 20 25 mm deg 1 latitude with respect to both mean sea level corrected for the ocean s mean dynamic topography and the inverse barometer response to atmospheric pressure loading and the egm2008 quasigeoid model while egm2008 is shown to exhibit a negligible slope of 2 4 mm deg 1 with respect to mean sea level it is clear therefore that the slope can only arise from systematic errors in the levelling although we are unable to isolate their exact origin using an offset detection method based on a penalized likelihood maximization using the schwarz information criterion we do not detect a step in the vertical datum affecting all sites north of 53 n but do identify regional distortions that we attribute to the inhomogeneity in both the levelling data used and the least squares adjustment procedures used to realize the datum we conclude that the british vertical datum remains unsuitable for scientific purposes

western boundary sea level a theory rule of thumb and application to climate models abstractto better understand coastal sea level variability and changes a theory that predicts sea levels along a curved western boundary using interior ocean sea level information is proposed the western boundary sea level at a particular latitude is expressed by the sum of contributions from interior sea levels propagating onto the western boundary by long rossby waves between that latitude and a higher latitude and from the western boundary sea level at the higher latitude this theory is examined by using a linear reduced gravity model a comparison between the theory and the model shows good agreement a simple scaling law or rule of thumb derived from the theory provides a measure of the higher latitude sea level and ocean interior sea level contributions the theory is then tested using data from 34 climate models in phase 5 of the coupled model intercomparison project cmip5 for dynamic sea level changes between the end of the twentieth and twenty first centuries the theory captures the nea

mean dynamic topography in the southern ocean evaluating antarctic circumpolar current transport 1 mean dynamic ocean topography mdt is the difference between the time averaged sea surface height and the geoid combining sea level and geoid measurements which are both attained primarily by satellite is complicated by ocean variability and differences in resolved spatial scales accurate knowledge of the mdt is particularly difficult in the southern ocean as this region is characterized by high temporal variability relatively short spatial scales and a lack of in situ gravity observations in this study four recent southern ocean mdt products are evaluated along with an mdt diagnosed from a southern ocean state estimate mdt products differ in some locations by more than the nominal error bars attempts to decrease this discrepancy by accounting for temporal differences in the time period each product represents were unsuccessful likely due to issues regarding resolved spatial scales the mean mass transport of the antarctic circumpolar current acc system can be determined by combining the mdt products with climatological ocean density fields on average mdt products predict higher acc transports than inferred from observations more importantly the mdt products imply an unrealistic lack of mass conservation that cannot be explained by the a priori uncertainties mdt estimates can possibly be improved by accounting for an ocean mass balance constraint

arsenopyrite pyrite association in an orogenic gold ore tracing mineralization history from textures and trace elements laser ablation inductively coupled plasma mass spectrometry la icp ms spot analysis and element mapping coupled with high resolution focused ion beam scanning electron microscopy fib sem imaging has been performed on au hosting sulfides from a proterozoic orogenic gold deposit tanami gold province north central australia gold distribution patterns in the arsenopyrite pyrite assemblage which probably crystallized toward the end of the au forming event suggest a process of initial scavenging of au into arsenopyrite and subsequent remobilization of that au following brittle fracture gold expelled from the sulfide lattice during the remobilization event is reconcentrated around the margins of the same arsenopyrite grains and within swarms of crosscutting microfractures the distribution of pb bi and ag closely mimic au indicating that these elements were also reconcentrated preservation of oscillatory zonation patterns for co ni sb se and te in arsenopyrite imply however that no significant degree of sulfide recrystallization took place residual concentrations of invisible gold in grain centers are 5 ppm in arsenopyrite and 1 ppm in coexisting pyrite the presence of submicron sized pores is suggestive of a fluid driven process rather than solid state diffusion micron scale 2 10 m remobilized gold is accompanied by fine particles 200 nm 2 m and nanoparticles 200 nm of gold the extensive variation of au concentrations within single arsenopyrite grains underlines the significance of textures when using trace element data to understand how gold ores evolved

an analysis of the 1985 nahanni earthquakes abstract two large magnitude earthquakes occurred in 1985 near the north nahanni river in the northeast cordillera northwest territories canada on 5 october m s 6 6 and 23 december m s 6 9 these events were unprecedented for this region of the cordillera and the december event is the largest earthquake ever known in the eastern part of the canadian cordillera this report presents detailed studies of the nahanni earthquakes their source parameters macroseismic effects aftershock sequences triggered rock avalanches their relationship to the geology of the epicentral area and their seismic hazard implications parameters calculated here for these two major events are parentheses indicate other studies the earthquakes occurred within a small relatively undeformed plateau the mackenzie plain in the foreland fold belt created along the northeastern cordillera during the columbian or laramide orogeny that fold belt is now subjected to northeast southwest horizontal compressive stresses possibly very similar to the original laramide stress regime and the fault plane implied by the seismic mechanisms is very similar to the laramide faults in the area however no surface fault break has been found and none of the mapped laramide faults in the epicentral area appears to be involved in the aftershock activity it is thus believed that the nahanni earthquakes occurred on a blind laramide thrust fault under the mackenzie plain the large magnitudes of the nahanni earthquakes show that the present seismic zoning for building code purposes in the eastern cordillera north of 60 n needs reassessment and suggest that the zoning in the eastern cordillera in british columbia and alberta may also need revision the felt areas of the earthquakes show that regional anelastic attenuation in the eastern canadian cordillera is significantly anisotropic and much lower along strike than across strike the felt areas also appear to scale with seismic moment rather than m b magnitude the thrust mechanisms regional stress regime shallow focal depth and high velocity sedimentary rocks in the focal region suggest that the nahanni earthquakes and particularly the near field strong ground motion recorded for the second event are ideal engineering design data for critical facilities in eastern north america

the north south tilt in the australian height datum is explained by the ocean s mean dynamic topography 1 using geodetic and oceanographic data we show that the apparent north south slope between the australian height datum ahd and the geoid is caused almost completely by the ocean s time mean dynamic topography mdt this is because the ahd was constrained to zero height at local mean sea level at multiple tide gauges around the australian continent using mdt models and corrected leveling data almost all of the apparent north south slope can be removed from the ahd an auxiliary observation is that a satellite only mdt model based on only around one year of goce data generates results commensurate with geodetic oceanographic and combined mdt models

coherent sea level fluctuations along the global continental slope signals in sea level or more properly sub surface pressure ssp sea level corrected for the inverse barometer effect are expected to propagate rapidly along the continental slope due to the effect of sloping topography on wave modes resulting in strongly correlated ssp over long distances observations of such correlations around the arctic and antarctic are briefly reviewed and then extended using satellite altimetry to the rest of the global continental slope it is shown that such long distance correlations are common especially in extra tropical regions simple correlations from altimetry cannot however establish the wave speed or whether waves are responsible for the correlations as opposed to large scale coherence in the forcing a case study around south america is used to highlight some of the complications and is found to strengthen the case for the importance of wave modes in such long distance ssp coherence although more detailed in situ data are required to resolve the cause of the correlations

critical frequencies at ocean boundaries past theoretical work has shown that for low frequency flow at a given ocean boundary location a critical frequency c exists such that for c unforced motion is trapped to the coast while for c energy leaves the coast alternatively for motion of a given frequency on the boundary there exists a critical latitude such that the motion is trapped to the coast poleward of that latitude but equatorward it is not this theory is discussed physically for both meridional and nonmeridional boundaries the simple formula for critical frequency along a nonmeridional boundary is used to document critical periods for the eastern and western atlantic pacific and indian ocean boundaries the theory occasionally breaks down when boundary curvature is too large

coherent sea level variability on the north atlantic western boundary interannual to decadal sea level variability on the north atlantic western boundary is surprisingly coherent over substantial distances stretching from the caribbean to nova scotia the physical mechanisms responsible for this basin scale low frequency coherence are explored in a diagnosis of simulated ocean fields from gecco which reproduces the observations to good approximation coastal sea level variability on the western boundary is known to be influenced by meridional divergence in the boundary current resulting in a geostrophic tilting of the sea surface this mechanism is found to be of leading order along some stretches of the boundary but it does not account for the coherence spanning the western north atlantic instead the coherence along the entire boundary is accounted for by vertical divergence resulting in the uniform rise and fall of the sea surface west of the 295 e meridian the vertical divergence is found to be due to net vertically integrated zonal transport across this meridian resulting from meridional variation in the sverdrup transport over the basin interior

ambient seismic noise tomography of canada and adjacent regions part i crustal structures this paper presents the first continental scale study of the crust and upper mantle shear velocity v s structure of canada and adjacent regions using ambient noise tomography continuous waveform data recorded between 2003 and 2009 with 788 broadband seismograph stations in canada and adjacent regions were used in the analysis the higher primary frequency band of the ambient noise provides better resolution of crustal structures than previous tomographic models based on earthquake waveforms prominent low velocity anomalies are observed at shallow depths 20 km beneath the gulf of st lawrence in east canada the sedimentary basins of west canada and the cordillera in contrast the canadian shield exhibits high crustal velocities we characterize the crust mantle transition in terms of not only its depth and velocity but also its sharpness defined by its thickness and the amount of velocity increase considerable variations in the physical properties of the crust mantle transition are observed across canada positive correlations between the crustal thickness moho velocity and the thickness of the transition are evident throughout most of the craton except near hudson bay where the uppermost mantle v s is relatively low prominent vertical v s gradients are observed in the midcrust beneath the cordillera and beneath most of the canadian shield the midcrust velocity contrast beneath the cordillera may correspond to a detachment zone associated with high temperatures immediately beneath whereas the large midcrust velocity gradient beneath the canadian shield probably represents an ancient rheological boundary between the upper and lower crust

control of lithospheric inheritance on neotectonic activity in northwestern canada lithospheric inheritance is thought to affect the location and reactivation of tectonic structures through successive cycles of supercontinent formation and dispersal however its relation to neotectonic activity remains unclear in northwestern canada abundant seismicity throughout the northern canadian cordillera ncc is geographically confined by several crustal scale boundaries yet its southern extent terminates abruptly along the inferred westward extension of a late cretaceous rifted margin boundary called the liard transfer zone ltz we use seismic data to show that the uppermost mantle beneath the cordillera exhibits a sharp north south contrast in fabric across the ltz south of the ltz fast axes of seismic wave propagation align closely with the lithospheric mantle fabric orientation of the adjacent canadian shield north of the ltz fast axes are reoriented subparallel to the motion of the pacific plate and follow the strike of the large dextral strike slip tintina and denali faults we attribute changes in anisotropic delay times across the tintina and denali faults to localized shear within the lithosphere this implies that the crust and lithospheric mantle remained mechanically coupled during shearing we propose that the contrast in uppermost mantle structure across the ltz reflects a change in the nature and origin of the lithospheric mantle from inherited rifted margin structures which affects the stability of the lithosphere and limits the extent of seismic activity within the ncc these results indicate that neotectonic activity in modern cordilleras is controlled in part by inherited upper mantle structures

partitioning of trace elements in co crystallized sphalerite galena chalcopyrite hydrothermal ores abstract there is an abundance of published trace element data for sphalerite galena and chalcopyrite in natural systems yet for a co crystallized assemblage comprising these base metal sulphides there is no detailed understanding of the preferred host of many trace elements laser ablation inductively coupled plasma mass spectrometry trace element maps and spot analyses were generated on 17 assemblages containing co crystallized sphalerite and or galena and or chalcopyrite from 9 different ore deposits these deposits are representative of different ore types geologic environments and physiochemical conditions of ore formation as well as superimposed syn metamorphic remobilisation and recrystallization the primary factors that control the preferred base metal sulphide host of mn fe co cu zn ga as se ag cd in sb te tl and bi are element oxidation state ionic radius of the substituting element element availability and the maximum trace element budget that a given sulphide mineral can accommodate temperature pressure redox conditions at time of crystallization and metal source do not generally appear to influence the preferred base metal sulphide host of all the trace elements exceptions are ga in and sn recrystallized at high metamorphic grades when the preferred host of ga and sn usually becomes chalcopyrite in more typical lower temperature ores the preferred host of ga is sphalerite indium concentrations also increase in chalcopyrite during recrystallization at lower temperatures the partitioning behaviour of sn remains poorly constrained and shows little predictable pattern among the data here the results obtained may be used as a tool to assess co crystallization if trace element distributions in a given base metal sulphide assemblage match those reported here and assuming those distributions have not been significantly altered post re crystallization then it may be suggestive of a co crystallized assemblage such information provides a foundation for novel attempts to develop trace element in sulphide geothermometers

body wave tomography of western canada abstract in this study we have produced p and s wave velocity models for western canada using 23 420 delay times measured on vertical component seismograms and 15 805 delay times measured on transverse component seismograms respectively from a range of permanent and temporary networks resolution is best in southwestern british columbia and along the canoe northwestern alberta southern yukon and northwest territories and batholiths northwestern bc arrays where the station density is the highest and fair elsewhere we focus our attention on two distinct features 1 the transition from phanerozoic to cratonic mantle in northwestern canada and 2 the complex tectonic environment at the northern terminus of the cascadia subduction zone where the plate boundary changes from convergent to transform we find that the main transition from phanerozoic to cratonic mantle in northwestern canada occurs at the cordilleran deformation front and represents a sharp jump in seismic velocity from 2 to 2 over a distance of 50 km in northern cascadia we have imaged and characterized the signature of the subducting juan de fuca plate and observed evidence of subduction beyond the northern edge of the slab we also demonstrate that the anahim hotspot track is underlain by a 2 low velocity zone possibly extending to 400 km beneath nazko cone that appears to be the source of volcanism in this area consequently we associate the source of magmatism in this area to a mantle scale rather than lithospheric scale process

trace and minor elements in sphalerite from base metal deposits in south china a la icpms study laser ablation icp mass spectroscopy has been used to investigate the geochemistry of sphalerite in a range of nine zn pb deposits in south china the deposits which are of different ages and belong to different metallogenic provinces have been assigned to the following genetic types skarn hetaoping luziyuan syngenetic massive sulphide dabaoshan laochang and bainiuchang and mississippi valley type huize mengxing niujiaotang based on the features of the ore even though their origin is heavily debated based on other criteria the giant jinding deposit is considered separately sphalerite from each genetic class of deposit shows a distinct chemical signature sphalerite from the skarn deposits is characterised by elevated lattice bound concentrations of co and mn the distal character of these skarn systems is reflected by the low in content of sphalerite the three syngenetic massive sulphide deposits feature sphalerite strongly enriched in in sn and ga whereas the deposits of mvt type are typically enriched in ge cd tl and as these divergent characters are reflected in absolute element abundances as well as in element ratios time resolved depth profiles for sphalerite from the chinese deposits confirm the presence of elements such as co in ge ga and cd in solid solution but the dataset expands the understanding of sphalerite mineral chemistry by also indicating that other elements whose ability to enter the crystal structure of sphalerite has been previously debated ag sn tl sb may also be in solid solution sphalerite is a refractory mineral and trace element analysis of sphalerite shows promise as a tracer of ore genesis even in overprinted ores systematic work on larger sample suites may help define the geochemical signature of different metallogenic epochs in regions as geologically complex as south china and help resolve the mechanism by which many of the debated ore deposits were formed

new ultrahigh resolution picture of earth s gravity field 9 10 abstract 11 we provide an unprecedented ultra high resolution picture of earth s gravity over all continents 12 and numerous islands within 60 degree latitude this is achieved through augmentation of new 13 satellite and terrestrial gravity with topography data and use of massive parallel computation 14 techniques delivering local detail at 200 m spatial resolution as such our work is the first of 15 its kind to model gravity at unprecedented fine scales yet with near global coverage the new 16 picture of earth s gravity encompasses a suite of gridded estimates of gravity accelerations 17 radial and horizontal field components and quasigeoid heights at over 3 billion points covering 18 80 of earth s land masses we identify new candidate locations of extreme gravity signals 19 suggesting that the codata standard for peak to peak variations in free fall gravity is too low 20 by about 40 the new models are beneficial for a wide range of scientific and engineering 21 applications and freely available to the public 22 23 keywords 24

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

la icp ms elemental mapping of pyrite an application to the palaeoproterozoic atmosphere a hydrothermal origin has been advocated for the genesis of rounded and subhedral euhedral pyrite in some neoarchaean palaeoproterozoic clastic sedimentary rocks thereby limiting their value as proxies for the composition of the early atmosphere we present laser ablation inductively coupled plasma mass spectrometry la icp ms element maps of rounded and euhedral subhedral pyrite grains from the basal conglomerates of the palaeoproterozoic mississagi formation huronian supergroup canada these maps reveal the common existence of rounded detrital cores and isolated grains variably modified by hydrothermal overgrowth the detrital origin of pyrite grains is demonstrated by the rounding of isolated grains and the presence of cores in subhedral euhedral grains rounding and breakage of grains is implied to have occurred via physical abrasion during sediment transport furthermore trace element maps expose truncated cores of originally rounded detrital fragments that also indicate abrasive rather than accretional or dissolutional rounding finally we document a complex core that consists of multiple grains suggestive of various source materials that were co deposited in the original placer textural and geochemical evidence further suggests the detrital porous pyrite had a diagenetic origin prior to fluvial transport grain size and shape analysis suggests that the large porous pyrite cores and grains may have had a shorter transport distance than the on average smaller compact rounded grains transport was prolonged from tributaries into the main valley and the high energy setting implies well aerated palaeoproterozoic river water since pyrite is unstable under oxidising conditions the frequent survival of detrital pyrite in the fluvial mississagi formation after sustained transport in the catchment basin and alluvial valley as well as aerated palaeoproterozoic river waters therefore implies that the contemporary atmosphere was oxygen deficient the depositional age of the mississagi formation is between 2 45 ga thessalon fm and 2 31 ga gordon lake fm and the presence of the detrital pyrite therefore suggests that the atmosphere was devoid of any significant amount of free oxygen at the time immediately preceding the great oxygenation event c 2017 elsevier b v all rights reserved

lithospheric structure in the southern canadian cordillera from a network of seismic refraction lines lithospheric velocity structure and its relationship to regional tectonics and development of the southern canadian cordillera are derived from a synthesis of interpretations from nine in line seismic refraction wide angle reflection profiles and broadside data recorded during the lithoprobe southern cordillera refraction experiment score and other refraction experiments across southern british columbia and one profile in northwestern washington consistency of the score two dimensional models at their intersection positions is achieved through application of a simultaneous inversion of all relevant traveltime data the cross sectional and map presentations demonstrate the strong degree of three dimensional heterogeneity within the crust and upper mantle a first order characteristic is the continuous increase in crustal velocities westward from the foreland belt to the insular belt the variations do not correlate with the morphogeological belts they do correspond with large scale geological and or

gulf stream s induced sea level rise and variability along the u s mid atlantic coast 1 recent studies indicate that the rates of sea level rise slr along the u s mid atlantic coast have accelerated in recent decades possibly due to a slowdown of the atlantic meridional overturning circulation amoc and its upper branch the gulf stream gs we analyzed the gs elevation gradient obtained from altimeter data the florida current transport obtained from cable measurements the north atlantic oscillation nao index and coastal sea level obtained from 10 tide gauge stations in the chesapeake bay and the mid atlantic coast an empirical mode decomposition hilbert huang transformation emd hht method was used to separate long term trends from oscillating modes the coastal sea level variations were found to be strongly influenced by variations in the gs on timescales ranging from a few months to decades it appears that the gs has shifted from a 6 8 year oscillation cycle to a continuous weakening trend since about 2004 and that this trend may be responsible for recent acceleration in local slr the correlation between long term changes in the coastal sea level and changes in the gs strength was extremely high r 0 85 with more than 99 99 confidence that the correlation is not zero the impact of the gs on slr rates over the past decade seems to be larger in the southern portion of the mid atlantic bight near cape hatteras and is reduced northward along the coast the study suggests that regional coastal sea level rise projections due to climate change must take into account the impact of spatial changes in ocean dynamics

sea level on the u s east coast decadal variability caused by open ocean wind curl forcing one of the puzzling features of sea level on the east coast of the united states is the decedal scale variability the fluctuations are 10 15 cm peak to peak at periods longer than a few years the authors find that this variability in the frequency band treated with the model is largely caused by a deep sea signal generated by the wind stress curl over the north atlantic a simple forced long rossby wave model of the response of the thermocline to wind forcing is used computing long wave speeds from observed hydrographic data the authors model the response of the ocean at periods longer than 3 years for the full width of the atlantic and for the north south extent of the main anticyclonic gyre 188 388n the model output in deep water shows remarkably good agreement with tide gauges both at bermuda 328n and puerto rico 188n as well as with dynamic height fluctuations of 20 cm peak to peak once these fluctuations reach the western side of the ocean the authors estimate coastal sea level by constructing a complementary coastal model the coastal model is geostrophic and conserves mass within a nearshore region that encompasses the gulf stream by extending this nearshore region as far south as 148 188n and using only the oceanic fluctuations to force the variability in the stream between 80 and 90 of the variance of sea level at coastal tide gauges can be explained sea level along the coast is used to test the model assumptions the basic results however seem important because they are constrained only by open ocean wind forcing and not by input boundary conditions

gold and trace element zonation in pyrite using a laser imaging technique implications for the timing of gold in orogenic and carlin style sediment hosted deposits laser ablation icp ms imaging of gold and other trace elements in pyrite from four different sedimenthosted gold arsenic deposits has revealed two distinct episodes of gold enrichment in each deposit an early synsedimentary stage where invisible gold is concentrated in arsenian diagenetic pyrite along with other trace elements in particular as ni pb zn ag mo te v and se and a later hydrothermal stage where gold forms as either free gold grains in cracks in overgrowth metamorphic and or hydrothermal pyrite or as narrow goldarsenic rims on the outermost parts of the overgrowth hydrothermal pyrite compared to the diagenetic pyrites the hydrothermal pyrites are commonly depleted in ni v zn pb and ag with cyclic zones of co ni and as concentration the outermost hydrothermal pyrite rims are either as au rich as in moderate to highgrade deposits such as carlin and bendigo or co ni rich and as au poor as in moderate to low grade deposits such as sukhoi log and spanish mountain the early enrichment of gold in arsenic bearing syngenetic to diagenetic pyrite within black shale facies of sedimentary basins is proposed as a critical requirement for the later development of carlin style and orogenic gold deposits in sedimentary environments the best grade sediment hosted deposits appear to have the gold climax event toward the final stages of deformation related hydrothermal pyrite growth and fluid flow

structure and fabric of the crust and uppermost mantle in the northern canadian cordillera from rayleigh wave tomography abstract the seismic structure and fabric of the lithosphere and underlying mantle beneath the northern canadian cordillera provides important constraints on its evolution and current tectonics however it is poorly characterized due to historically sparse networks of seismic instruments we use data from past and recently deployed networks of broadband seismic stations in northwestern canada and measure rayleigh waves propagating between all available pairs of seismic stations using two complementary techniques ambient noise and teleseismic two station interferometry the rayleigh wave data are processed to obtain phase velocity dispersion curves that are inverted for phase velocity maps at periods between 8 and 80 s to first order these maps show high velocity anomalies within the canadian shield and low velocity anomalies within the cordillera at all periods at short periods 30 s mostly sensitive to uppermost mantle depths high velocity anomalies of the canadian shield extend west past the cordilleran deformation front and suggest the presence of cratonic lithosphere beneath the cordillera whereas the lowest velocities underlie the allochtonous terranes anisotropy within the crust and uppermost mantle exhibits fast axis orientations aligned with the major faults and fabric of the cordillera and show evidence for vertical changes in anisotropy these results provide new constraints on geodynamic models proposed to explain neotectonic deformation in this area

one dimensional models of shear wave velocity for the eastern mediterranean obtained from the inversion of rayleigh wave phase velocities and tectonic implications summary on a sw ne profile from the libyan coast towards central turkey phase velocity curves of the fundamental rayleigh mode were measured using a two station method the inversion of phase velocity curves yields 1 d models of shear wave velocity down to approximately 200 km depths that may be interpreted as estimates of average models between neighbouring stations on the profile strong lateral variations in the shear wave velocity structure are imaged along the profile the subducted oceanic african mantle lithosphere is indicated in 1 d models for the region around crete by significantly enlarged shear wave velocities it is also imaged by an average model of the structure between stations on crete and santorini on a path crossing the libyan sea south of crete the resulting model is slower than a model expected for 110 myr old oceanic lithosphere the passive african margin is thus assumed to extend northwards beneath the libyan sea anomalous low shear wave velocities are found for the uppermost mantle beneath central turkey down to a depth of approximately 130 km using two stations on crete the average depth of the oceanic moho within the subducting slab is estimated to be at approximately 50 km beneath crete for this arc parallel path an enlarged standard deviation of the measured phase velocities of approximately 0 2 km s 1 between 10 and 30 mhz is observed that is probably caused by strong lateral heterogeneity related to the subducting slab in addition in this frequency range an anomalous propagation of the fundamental rayleigh mode is detected that is indicated by measured phase velocities that are approximately one standard deviation faster than phase velocities expected from a great circle approximation an average shear wave velocity of approximately 3 5 km s 1 is observed above the oceanic moho in order to explain the recent lithospheric structure of the hellenic subduction zone a tectonic model is assumed for the ne sw striking profile considered it is based on the calculated 1 d models tectonic reconstructions and on a model derived from the metamorphic history of rocks exposed on crete the suggested model summarizes the tectonic development at a lithospheric scale starting in the late cretaceous accretion of crustal material of two microcontinents to eurasia is assumed while continuous subduction of the oceanic lithosphere of different ocean basins and possibly of the mantle lithosphere of the microcontinents resulted in a single slab the length of the oceanic lithosphere that was subducted south of crete is estimated to be not greater than approximately 550 km

signature of the atlantic meridional overturning circulation in sea level along the east coast of north america in this letter we examine the relationship between the north atlantic meridional overturning circulation moc and sea level sl along the east coast of north america in the eddy permitting ocean model occam we find a distinctive topography following pattern of sl variability in the western north atlantic that is closely linked with the changing strength of the moc with a 2 cm drop in sl along the us east coast corresponding to a 1sv increase in the moc we find a similar pattern of sl variability in the altimetry record and show that this meridionally coherent sl mode dominates interannual sl variability at tide gauges along the north american east coast between 40 50n hence we conclude that north american coastal sea level may indeed be a useful indicator of moc variability on interannual timescales allowing an observationally based estimate of the likely range of interannual moc fluctuations to be determined citation bingham r j and c w hughes 2009 signature of the atlantic meridional overturning circulation in sea level along the east coast of north america geophys res lett 36 l02603 doi 10 1029 2008gl036215

tibetan and indian lithospheres in the upper mantle beneath tibet evidence from broadband surface wave dispersion broadband seismic experiments over the last two decades have produced dense data coverage across tibet yet the mechanism of the india asia lithospheric convergence beneath it remains a puzzle with even its basic features debated and with very different end member models advocated today we measured highly accurate rayleigh and love wave phase velocity curves in broad period ranges up to 5 200 s for a few tens of pairs and groups of stations across tibet combining in each case hundreds to thousands of interstation measurements made with cross correlation and waveform inversion methods robust shear velocity profiles were then determined by extensive series of nonlinear inversions of the data designed to constrain the depth dependent ranges of isotropic average shear speeds and radial anisotropy temperature anomalies in the upper mantle were estimated from shear velocities using accurate petrophysical relationships our results reveal strong heterogeneity in the upper mantle beneath tibet very large high velocity anomalies in the upper mantle are consistent with the presence of underthrust beneath southwestern tibet and subducted beneath central and eastern tibet indian lithosphere the corresponding thermal anomalies match those estimated for subducted indian lithosphere in contrast to the indian lithosphere tibetan lithosphere and asthenosphere display low to normal shear speeds tibetan lithosphere is thus warm and thin radial anisotropy in the upper mantle is weak in central and strong in northeastern tibet possibly reflecting asthenospheric flow above the subducting indian lithospheric slab

seismic anisotropy associated with continental lithosphere accretion beneath the canoe array northwestern canada we examine upper mantle seismic anisotropy beneath the cordillera and craton of northwestern canada using the multi event station averages of shear wave splitting of sks skks and ssks phases recorded during the canadian northwest experiment canoe splitting times derived from multi event averaging at each station range from 0 to 1 4 s with an array average of 0 65 s over broad portions of the array fast directions are coherent and roughly consistent with the direction of absolute plate motion in a hotspot reference frame suggesting that coherent asthenospheric fabric underlies the plate in much of the region within this broad framework fast directions and splitting times show marked variability over length scales of 50 200km and are generally correlated with surface and or crustal tectonics anomalous splitting is observed across an ancient suture within the cratonic lithosphere apparently associated with complex dipping fabric produced during continental assembly the deformation front of the canadian rockies correlates with a significant change in splitting behavior consistent with the front range demarking the craton cordillera transition within the mantle splitting times are small across much of the cordillera indicating that lithospheric and or asthenospheric fabric is weaker or less coherent than beneath the craton in the western cordillera fast directions rotate abruptly to parallel the plate boundary implying that fabric associated with plate boundary deformation extends 200km into the north american continent

seismic velocity model of the crust in the northern canadian cordillera from rayleigh wave dispersion data models of the seismic velocity structure of the crust in the seismically active northern canadian cordillera remain poorly constrained despite their importance in the accurate location and characterization of regional earthquakes on 29 august 2014 a moderate earthquake with magnitude 5 0 which generated high quality rayleigh wave data occurred in the northwest territories canada 100 km to the east of the cordilleran deformation front we carefully selected 23 seismic stations that recorded the rayleigh waves and divided them into 13 groups according to the azimuth angle between the earthquake and the stations these groups mostly sample the cordillera in each group we measured rayleigh wave group velocity dispersion which we inverted for one dimensional shear wave velocity models of the crust we thus obtained 13 models that consistently show low seismic velocities with respect to reference models with a slow upper and lower crust surrounding a relatively fast mid crustal layer the average of

geochronology geochemistry and hf isotope of late triassic magmatic rocks of qingchengzi district in liaodong peninsula northeast china abstract the initiation timing and mechanism of lithospheric thinning of the north china craton ncc was still controversial late triassic igneous rocks especially mantle derived mafic rocks would provide constrains on early mesozoic lithospheric mantle geodynamics and initiation of lithospheric thinning this paper reports late triassic magmatic rocks including lamprophyre diorite dykes and biotite monzogranite cropped out in qingchengzi district of liaodong peninsula northeastern ncc la icpms zircon u pb dating yield ages of 210 227 ma and 224 ma for lamprophyres and biotite monzogranite respectively lamprophyre is ultrapotassic strongly enriched in ree and liles depleted in hfses and negative hf isotopes which are discriminating signatures of crustal source but distinguishingly high compatible element contents indicate the primary magma originated from mantle source a fertile one lamprophyre derived from partial melting of an enriched lithospheric mantle which was modified by slab derived hydrous fluids melts associated with deep subduction between the yangtze craton and the ncc the diorite displays distinct features with relatively enriched nb ta hree and depleted th u which suggest it derived from a relatively depleted source the depletion was caused by break off of the yangtze slab during deep subduction introducing asthenospheric mantle into the source the biotite monzogranite shows adakitic affinity and originated from partial melting of the thickened lower crust with addition of small proportion of mantle material the recognition of late triassic magmatism implies extensional tectonic settings in liaodong peninsula and suggests initiation of lithospheric thinning of north china craton in eastern segment might begin early in late triassic

oceanic control of sea level rise patterns along the east coast of the united states 1 along the eastern seaboard of the u s from florida to maine sea level rise slr shows notable patterns and significant deviation from the global mean which have been attributed to land subsidence consistent with several recent studies we analyze various observation and modeling data and find that ocean dynamics is also an important factor in explaining these coastal slr patterns despite a southward shift since the 1990s an overall northward shift of the gulf stream during the twentieth century contributed to the faster slr in the mid atlantic region north carolina to new jersey in response to the 21st century climatic forcing the rise fall of the dynamic sea level north south of cape hatteras is mainly induced by the significant decline of ocean density contrast across the gulf stream this baroclinic process is the likely cause of the recent switch of the coastal slr to a pattern with faster slower rates north south of cape hatteras citation yin j and p b goddard 2013 oceanic control of sea level rise patterns along the east coast of the united states geophys res lett 40 doi 10 1002 2013gl057992

igneous and metaigneous age constraints for the aishihik metamorphic suite southwest yukon the pericratonic aishihik metamorphic suite occurs outboard of accreted oceanic and oceanic arc terranes in southwest yukon it consists of a structurally lower unit of feldspathic quartz mica schi

a theory for the surface atlantic response to thermohaline variability abstract the response of the upper warm limb of the thermohaline circulation in the north atlantic to a rapid change in deep water formation at high latitudes is investigated using a reduced gravity ocean model changes in deep water formation rate initiate kelvin waves that propagate along the western boundary to the equator on a timescale of months the response in the north atlantic is therefore rapid the southern hemisphere response is much slower limited by a mechanism here termed the ldquo uatorial buffer since to leading order the flow is in geostrophic balance the pressure anomaly decreases in magnitude as the kelvin wave moves equatorward where the coriolis parameter is lower together with the lack of sustained pressure gradients along the eastern boundary this limits the size of the pressure field response in the southern hemisphere interior adjustment is by the westward propagation of rossby waves but only a small fraction of the change in thermohaline circulation strength is commun

geophysical investigation and reconstruction of lithospheric structure and its control on geology structure and mineralization in the cordillera of northern canada and eastern alaska a reconstruction of the tintina fault is applied to regional geophysical and topographic data facilitating the definition of west trending lineaments within the lower crust and or mantle lithosphere oblique to the nw trending structure of the cordilleran terranes the lineaments which exhibit a range of geophysical and geological signatures are interpreted to be related to the liard transfer zone continuous to the denali fault that divided lower and upper plates during late proterozoic cambrian rifting of the laurentian margin three dimensional gravity models show a density increase in the lower crust and mantle lithosphere to the north the transfer zone also divides bimodal mantle xenolith suites to the south from unimodal suites to the north these conclusions suggest that extended north american basement related to laurentian margin rifting that would have brought mantle lithosphere rocks to a shallow depth continuously underlies a thin carapace of accreted terranes in western yukon and eastern alaska the interpreted continuity of north american basement reaffirms that if oroclinal bending of the intermontane terranes occurred then it was prior to its emplacement upon the rifted basement examination of the spatial relationships between mineral occurrences and postaccretionary cretaceous lithospheric lineaments from their manifestation in geophysical geological and topographic data suggest that the late proterozoic lineaments influenced mesozoic mineralization through influence on the development of the shallow crustal structure intrusion and exhumation and erosion

on enso coastal currents and sea levels abstract sea level measurements along the western coast of the americas have shown that there is a strong signal at enso frequencies approximately 2 2 yr 1 to 2 5 yr 1 that propagates poleward at about 40 to 90 cm s 1 this enso sea level signal must be associated with enso coastal currents but because adequate interannual current time series are unavailable the structure and strength of these currents are not known coastal enso currents must be fundamentally affected by bottom topography and bottom friction but previous theory has not taken these effects into account a near boundary numerical model with realistic bottom friction stratification and shelf and slope topography was therefore constructed to study enso coastal flow i at enso frequencies previous results for models with no bottom topography and no bottom friction suggest that sea level should not propagate poleward with realistic bottom friction and bottom topography coastal sea level propagates poleward at speeds similar to tho

global shear speed structure of the upper mantle and transition zone s u m m a r y the rapid expansion of broad band seismic networks over the last decade has paved the way for a new generation of global tomographic models significantly improved resolution of global upper mantle and crustal structure can now be achieved provided that structural information is extracted effectively from both surface and body waves and that the effects of errors in the data are controlled and minimized here we present a new global vertically polarized shear speed model that yields considerable improvements in resolution compared to previous ones for a variety of features in the upper mantle and crust the model sl2013sv is constrained by an unprecedentedly large set of waveform fits 3 4 of a million broad band seismograms computed in seismogram dependent frequency bands up to a maximum period range of 11 450 s automated multimode inversion of surface and s wave forms was used to extract a set of linear equations with uncorrelated uncertainties from each seismogram the equations described perturbations in elastic structure within approximate sensitivity volumes between sources and receivers going beyond ray theory we calculated the phase of every mode at every frequency and its derivative with respect to sand p velocity perturbations by integration over a sensitivity area in a 3 d reference model the normally small perturbations of the 3 d model required to fit the waveforms were then linearized using these accurate derivatives the equations yielded by the waveform inversion of all the seismograms were simultaneously inverted for a 3 d model of shear and compressional speeds and azimuthal anisotropy within the crust and upper mantle elaborate outlier analysis was used to control the propagation of errors in the data source parameters timing at the stations etc the selection of only the most mutually consistent equations exploited the data redundancy provided by our data set and strongly reduced the effect of the errors increasing the resolution of the imaging our new shear speed model is parametrized on a triangular grid with a 280 km spacing in well sampled continental domains lateral resolution approaches or exceeds that of regionalscale studies the close match of known surface expressions of deep structure with the distribution of anomalies in the model provides a useful benchmark in oceanic regions spreading ridges are very well resolved with narrow anomalies in the shallow mantle closely confined near the ridge axis and those deeper down to 100 120 km showing variability in their width and location with respect to the ridge major subduction zones worldwide are well captured extending from shallow depths down to the transition zone the large size of our waveform fit data set also provides a strong statistical foundation to re examine the validity field of the jwkb approximation and surface wave ray theory our analysis shows that the approximations are likely to be valid within certain time frequency portions of most seismograms with high signal to noise ratios and these portions can be identified using a set of consistent criteria that we apply in the course of waveform fitting

crustal and upper mantle anisotropy related to fossilized transpression fabric along the denali fault northern canadian cordillera we analyze crustal and upper mantle structure near the denali fault northern canadian cordillera using 11 broadband seismic stations receiver functions at five stations within 5 30 km of the fault trace display a strong p to s conversion within the midcrust 10 25 km depth that systematically varies with back azimuth stacking and velocity inversion along complementary northwest southeast and northeast southwest back azimuth ranges yield a strong anisotropy 10 in the midcrust with complex crustal anisotropic behavior at least two layers close to the denali and duke river faults junction anisotropy occurs in a low velocity zone with the fast axis parallel to the denali fault trend three additional stations close to the denali fault 15 30 km as well as two stations further away 100 km show no significant crustal anisotropy shear wave sks splitting analysis indicates similar upper mantle anisotropy with a fast axis parallel to the trend of the denali fault for all stations except for station why located 125 km away we relate this crustal and upper mantle anisotropy to fossilized structural and mineral fabrics due to eocene transpression on the denali fault these results suggest the main transpression phase 400 km displacement was accommodated in a shear zone at least 50 60 km less than 125 km wide in the midcrust and upper mantle lack of clear anisotropy in the lowermost crust may relate to complex deformation within a detachment layer orogenic float model online material table of sks splitting information and figures of receiver function analysis

lith5 0 a revised crustal model for canada based on lithoprobe results summary during the last 15 yr numerous seismic refraction experiments have been conducted overthe canadian landmass most as part of the lithoprobe initiative the new results providethe basis for revising existing global models of crustal structure e g crust5 1 mooney et al 1998 which do not incorporate the new lithoprobe data the crustal model discussedhere lith5 0 combines the lithoprobe and crust5 1 data to provide better constraints oncrustal structure in canada the objectives of the study are to 1 compile available new datainto a single consistent database of crustal thickness and velocity including the uppermostmantle pn velocity and 2 to construct a revised 5 5 crustal model of the canadianlandmass in a format that is generally compatible with existing global models the lithoproberesults suggest a 5 5 km average root mean square rms crustal thickness difference betweenlith5 0andcrust5 1 evenwiththeincorporationofthenewdata thegeographiccoveragein north and central canada remains sparse the new model does not explicitly incorporategeological constraints but instead relies on spherical spline interpolation for extrapolatingvalues into regions that lack control to illustrate the implications of this new crustal model we use lith5 0 to correct for the isostatically compensated crustal heterogeneity in order toobtain improved estimates of the dynamic surface topography the latter provides importantconstraints on the density structure of the uppermost mantle

tectonics of the northern canadian cordillera imaged using modern magnetotelluric analysis abstract magnetotelluric data from lithoprobe snorcle corridor 2 in western canada crossing the rocky mountain trench tintina fault between 56 and 60 n have been analyzed using modern mt methods to provide new insights into the tectonics of the north american cordillera and ancestral north america resistivity images of the crust were obtained using two independent sets of unconstrained 2 d inversions and constrained 2 d inversions incorporating seismic constraints structure to the west of the tintina fault includes uniform moderate mid to lower crustal resistivity in a seismically defined westward tapering wedge of ancestral north american rocks to the east between the tintina fault and the liard line a transfer zone in asymmetric neoproterozoic rifting the wedge includes a major synformal conductor that parallels seismic reflections the large lateral changes in resistivity can be explained by transition between different blocks of asymmetric rifting the synformal conductor is attributed to graphitic rocks from the aida formation of the mesoproterozoic muskwa assemblage that were re distributed in a sag basin on the lower plate margin in the blackwater block spatially complex upper crustal resistivity in the cordillera can be interpreted in terms of lithological variations and alteration processes an east dipping conductor in stikinia is attributed to east dipping jurassic and relatively high conductivity beneath the eskay rift may be explained by crustal fertilization a conductor in the cache creek terrane is attributed to listwanite alteration of ultramafic bodies on the king salmon fault and high conductivity in the slide mountain terrane within the sylvester allochthon to localized carbonaceous alteration a series of conductors above north american basement is attributed to deformation and metamorphic processes associated with mesozoic thrust faulting to the west of the tintina fault the source material for these conductors is likely from the stikinia terrane and to the east it is likely from the muskwa assemblage