the foreslope and toe of slope facies of the middle triassic latemar buildup dolomites northern italy abstract the latemar buildup was a circular carbonate buildup 4 km wide with a central platform core flat bedded interior platform and massive reef margin flanked on all sides by slope facies steeply dipping 30 35 foreslope breccias are present adjacent to the margin and flat lying graded grainstones at the toe of slope slope facies relate directly to depositional profile and slope angle the steeply dipping foreslopes consist of lobate breccia beds that are 25 m thick and a few tens of meters across and extend tens to hundreds of meters downslope some beds are conformably overlain by thinner 1 m thick beds of finer grained carbonate sediment the basal surfaces of the breccias are erosional and are anastamosing in both strike and dip views the breccia rains was derived principally from margin boundstones and deposited by rockfalls and avalanches planar clinoforms extend the entire height of the foreslope hundreds of meters and bracket depositional units clinothems tens of meters thick clinoforms appear to be shear surfaces formed during large slope failures avalanches graded grainstone beds less than 1 m thick are present at the nearly flat lying toe of slope these consist of redeposited shallow water platform interior and reef margin carbonate sands some with nodular limestone caps that are interpreted as proximal carbonate turbidites toe of slope breccias are the downdip extensions of foreslope breccias and pinch out abruptly basinward some slope depositional processes are related to high frequency fourth order and fifth order sea level changes toe of slope graded grainstones correspond to times of platform submergence in contrast foreslope breccia was deposited during both platform submergence and exposure the slope deposits do not record the high frequency cyclic rhythms identified in shallow water platform sections this is attributed to the nature of slope deposition downslope talus transport was episodic and localized graded grainstone beds reflect storm redeposition

the carbonate factory of middle triassic buildups in the dolomites italy a quantitative analysis middle triassic carbonate buildups of the dolomites were high in relief 500 1000m and small in size one to a few square kilometres in area a paradox results from the carbonate platform model that invokes the platform top including reef rims as the carbonate factory and flanking beds as talus deposits most buildups consist largely of clinoforms inclined at 10 50 whereas massive reef rocks and stratified buildup interiors are poorly developed or absent facies and modal analysis of 323 thin sections from buildups of the marmolada indicate that clinoforms are i predominantly composed of in situ boundstones 56 of all samples ii primarily made up of early cements 37 vol microbial crusts 17 vol micritic intraclasts 10 vol and tubiphytes 8 vol and iii contain diagnostic shallow water grains dasyclads coated grains that are less abundant by 1 2 orders of magnitude compared with buildup interior facies these data suggest that the clinoforms themselves were the main carbonate factory of the triassic buildups stratified buildup interior rocks and massive reef rocks were apparently not a prerequisite for buildup growth and clinoform progradation

do double ss precursors mean double discontinuities summary stacks of ss precursors have been widely used in the past two decades to investigate the existence and characteristics of upper mantle discontinuities on a global scale as well as in several regional cases here we present observations of ss precursors from an mb 6 7 earthquake recorded at the us transportable array in 2010 in this particular case the s660s precursors on the transverse component are strong enough to be identified on individual seismograms across the array without any stacking procedures two s660s precursors are observed seeming to suggest double discontinuities around 660 km depth in the bounce point region through careful analysis of 1 d and 3 d synthetic seismograms we however discover that although they have arrival times and slownesses that are very close to the theoretical values of ss precursors the apparent double precursors are artefacts because of mantle heterogeneity in the upper mantle near the receivers away from the bounce point region this suggests that caution must be taken about appropriate azimuthal coverage at the ss bounce point before interpreting double ss or pp precursors in terms of complex mineralogical transitions

multiparameter two dimensional inversion of scattered teleseismic body waves 3 application to the cascadia 1993 data set this is the third paper in a three part series that examines formal inversion of the teleseismic p wave coda for discontinuous two dimensional 2 d variations in elastic properties beneath dense arrays of three component broadband seismometers in this paper the method is applied to data from the incorporated research institutions for seismology program for array seismic studies of the continental lithosphere iris passcal cascadia 1993 experiment undertaken across central oregon two major features are imaged in the resulting model the continental moho becomes evident 150 km from the coast beneath the western cascades and extends through the eastern end of the profile at 35 40 km depth in the western portion of the model oceanic crust of the subducting juan de fuca plate dips shallowly 12 at the coast and more steeply 27 below the willamette valley and is evident to depths of 100 km beneath the high cascades the abrupt increase in plate dip at 40 km depth coincides with an apparent thickening of the oceanic crust followed by a diminution in its signature building on previous work we argue that these results are consistent with the consequences of prograde metamorphic reactions occurring within the oceanic crust progressive dehydration at lower grade facies conditions culminates in the transformation to eclogite producing a pronounced increase in the seismic velocity density and dip of the subducting plate and structural complexity in the overlying wedge

reef fabrics biotic crusts and syndepositional cements of the latemar reef margin middle triassic northern italy the latemar reef buildup of the central dolomites northern italy provides a rare opportunity to examine an in place middle triassic upper anisian to lower ladinian platform margin that is not strongly deformed or dolomitized the margin lies between the flat lying platform interior and steeply dipping foreslope clinoforms across this transition the depositional profile relates directly to a consistent lateral facies pattern 1 restricted biota grainstone of the platform interior 2 tubiphytes rich boundstone and 3 diverse biota grainstone that grades into 4 foreslope breccia beds the boundstone and diverse biota grainstone facies comprise the platform margin the boundstone facies consists of a framework of small 10 cm skeletal remains 10 by volume with associated biotic crusts internal sediments and syndepositional cements crusts and cements constitute most of the rock volume and created the boundstone fabric biotic crusts exhibit gravity defying geometries and range from a light grey structure grumeleuse rind to dark grey micritic laminae both cements and biotic crusts occur as redeposited talus in the foreslope talus deposits indicating a syndepositional origin the diverse biota grainstone facies primarily consists of skeletal peloidal grainstone with a diverse open marine biotic assemblage in contrast to the restricted biota grainstones of the platform interior that have a low diversity restricted marine biota metre scale hexacoral boundstone and centimetre scale sponge boundstone and microbial boundstone occur as isolated patches tens to hundreds of metres apart within the diverse biota grainstone facies the depositional profile facies zonation and biotic constituents all indicate that the latemar buildup had a shallow water reef margin in contrast to previous interpretations that these were upper slope reefs the syndepositional biotic crusts and inorganic cementation played key roles in stabilizing the boundstone fabric to form a wave resistant reef fabric

strong sh to love wave scattering off the southern california continental borderland seismic scattering is commonly observed and results from wave propagation in heterogeneous medium yet deterministic characterization of scatterers associated with lateral heterogeneities remains challenging in this study we analyze broadband waveforms recorded by the southern california seismic network and observe strongly scattered love waves following the arrival of teleseismic sh wave these scattered love waves travel approximately in the same azimuthal direction as the incident sh wave at a dominant period of 10 s but at an apparent velocity of 3 6 km s as compared to the 11 km s for the sh wave back projection suggests that this strong scattering is associated with pronounced bathymetric relief in the southern california continental borderland in particular the patton escarpment finite difference simulations using a simplified 2 d bathymetric and crustal model are able to predict the arrival times and amplitudes of major scatterers the modeling suggests a relatively low shear wave velocity in the continental borderland

reverse time migration based reflection tomography using teleseismic free surface multiples converted and multiply reflected phases from teleseismic events are routinely used to create structural images of the crust mantle boundary moho and the elasticity contrasts within the crust and upper mantle the accuracy of these images is to a large extent determined by the background velocity model used to propagate these phases to depth in order to improve estimates of 3 d velocity variations and hence improve imaging we develop a method of reverse time migration based reflection tomography for use with wavefields from teleseismic earthquakes recorded at broad band seismograph arrays reflection tomography makes use of data redundancy that is the ability to generate numerous structural images of the subsurface with different parts of the wavefield in exploration seismology where it is known as migration velocity analysis reflection tomography typically involves the generation of an extended image e g offsetor angle gathers and the fitness of the background model is evaluated through the application of image domain annihilators in regional scale passive source seismology however annihilation based methods are inadequate because the sparse and irregular distribution of teleseismic sources is not likely to produce illumination over a sufficient range of angles to overcome this problem we turn towards a source indexed moveout scheme instead of extended image annihilation we determine the success of the tomographic velocity model by cross correlating images produced with multiply scattered waves from different teleseismic sources the optimal velocity model is the one that minimizes correlation power between windowed images away from zero depth shift we base our inversion scheme on the seismic adjoint method and a conjugate gradient solver for each image pair the update direction is determined by correlations between downgoing wavefields with upgoing adjoint wavefields for both images the sensitivity kernels used in this method is similar to those found in other forms of adjoint tomography but their shapes are controlled by the spatial distribution of the error function we present the method and a proof of concept with 2 d synthetic data

evolutionary aspects of lithosphere discontinuity structure in the western u s 1 we have produced common conversion point ccp stacked ps and sp receiver function image volumes of the moho and lithosphere asthenosphere boundary lab beneath the western united states using transportable array data the large image volumes and the diversity of tectonic environments they encompass allow us to investigate evolution of these structural discontinuities the moho is a nearly continuous topographic surface whereas the lab is not and the seismic images show a more complex expression the first order change in lab depth in the western u s occurs along the cordilleran hingeline the former laurasian passive margin along the southwestern precambrian north american terranes the lab is about 50 deeper to the east of the hingeline than to the west with most of the increase in lab thickness being in the mantle lithosphere we infer that the moho and the lab are late mesozoic or cenozoic everywhere west of the hingeline modified during farallon subduction and its aftermath between the hingeline and the rocky mountain front the lab and to a lesser extent the moho have been partially reset during the cenozoic by processes that continue today seismicity and recent volcanism in the interior of the western u s are concentrated along gradients in crustal and or lithospheric thickness for example the hingeline and the eastern edge of the coastal volcanic magmatic terranes to us this suggests that lateral gradients in integrated lithospheric strength focus deformation similarly areas conjectured to be the sites of convective downwellings and associated volcanism are located along gradients in regional lithosphere thickness

unraveling the geometry of the farallon plate synthesis of three dimensional imaging results from usarray abstract we compare 12 recent three dimensional 3d seismic imaging results that made extensive use of data from the earthscope transportable array ta our goal is to sort out what can be said about the geometry of the farallon plate our main approach is 3d visualization using a kinematic plate motion model as a framework comparison of results from all 12 image volumes indicates that the results are most consistent with a single coherent farallon slab overridden by north american the farallon can be tracked from the trench in the pacific northwest to its remnants in the lower mantle under eastern north america from the trench the lithosphere has a low dip to the volcanic arc immediately east of the arc the slab steepens sharply before undergoing a decrease in dip above the 410 km discontinuity the gently dipping section varies along strike under washington the deflection is minor but to the south the slab flattens to become nearly horizontal beneath southern idaho there is a strong agreement that the high velocity anomaly associated with the slab vanishes under eastern oregon scattered wave imaging results however suggest the top of the anomaly is continuous these can be reconciled if one assumes the wavespeed anomaly has been neutralized by processes linked to the yellowstone system we find that all results are consistent with a 4d kinematic model of the mendocino slab window under nevada and utah in the eastern us the larger scale models all show a lower mantle anomaly related to the older history of farallon subduction the link between the lower mantle and new results in the u s cordillera lies under the high plains where the required usarray coverage is not yet complete image volumes in a unified format are supplied in an electronic supplement

teleseismic shot profile migration the shot profile migration approach of wave equation migration generates subsurface images using the interferometric principle of crosscorrelating two passive wavefields these wavefields are typically a source wavefield containing energy from an excited source and a receiver wavefield comprised of scattered source wavefield energy by the discontinuous earth structure shot profile migration can be recast as a novel way of imaging the earth s lithosphere using teleseismic wavefield data where the source wavefield is the directly arriving wavefront and the receiver wavefield is the following wavefield coda we demonstrate that the shot profile technique can be tailored to suit teleseismic acquisition geometry and wavefields assuming an acoustic framework and 2 5d experimental geometry we develop procedures that enable kinematic and structural imaging migration using both transmission and free surface reflected passive wavefields experiments with synthetic data demonstrate the method s applicability a

a sporadic low velocity layer atop the western u s mantle transition zone and short wavelength variations in transition zone discontinuities teleseismic receiver function analysis of data from six dense arrays in the western u s is used to investigate mantle transition zone mtz discontinuities and the prevalence of a low velocity layer atop the 410 km discontinuity 410 lvl negative polarity ps arrivals indicative of a low velocity layer with a top 25 60 km above the 410 are identified in 8 11 out of 18 stacks of receiver functions from highly sampled back azimuth corridors the 410 lvl is interpreted as partial melt resulting from upwelling of hydrated mantle across a water solubility contrast at the 410 the 669 km mean depth of the 660 km discontinuity 660 and the magnitude of 660 topography suggest variable hydration locally approaching saturation in addition to 150 k lateral temperature variations beneath five arrays mean amplitudes of p410s and p660s increase monotonically with period from 2 to 10 s however greater variations are observed in the frequency dependence of p410s compared to p660s implying 410 thickness is more heterogeneous variable 410 thickness is attributed to changes in hydration modulating the width of the olivine to wadsleyite transition interval frequency dependence of p660s amplitudes suggests a broad velocity gradient consistent with multivariate phase changes in the olivine and garnet systems sporadic detection of the 410 lvl the magnitude and length scales of mtz discontinuity topography and inferred variations in hydration support the occurrence of vigorous small scale convection in the western u s mantle comparison of receiver functions with body wave tomography suggests small scale convection driven by sinking slab segments and lithospheric instabilities contributes to the intermittent nature of the 410 lvl

post critical sspmp and its applications to virtual deep seismic sounding vdss 3 back projection imaging of the crust mantle boundary in a heterogeneous lithosphere theory and application

simultaneous inversion for mantle shear velocity and topography of transition zone discontinuities summary until now modelling of three dimensional 3 d velocity variations in the mantle and topography of the transition zone discontinuities have been considered separately velocity models were obtained assuming that the radii of the discontinuities are constant then the travel time data sensitive to the topography such as the ss precursors were corrected for the effect of 3 d seismic structure and inverted for depth variations of a discontinuity such a procedure is unsatisfactory as it may introduce artefacts that could significantly affect the topographic results the opposite trade off is less likely to introduce conceptually important changes in the velocity distribution but should also be considered in this study we bring together the same set of s velocity sensitive data as used by gu et al and combine it with a large set of differential travel times of ss s400s s s670s and direct measurements of s400s s670s we formulate the inverse problem in terms of the volumetric 3 d and topographic 2 d perturbations for both the 400 and 670 km discontinuities the best fitting model of the joint inversion significantly improves the variance reduction of ss s400s and ss s670s residuals the velocity distribution in the resulting model topos362d1 is very similar to that in model s362d1 with correlation coefficients 0 9 throughout the mantle which indicates that lateral variations of discontinuity depths have only minor influence on global modelling of velocity important changes however have been made to the topography of the 400 and 670 km discontinuities with respect to those obtained earlier assuming an existing velocity model the overall undulation of the 400 km discontinuity is considerably less than that reported by earlier global studies in topos362d1 its maximum variation does not exceed 12 km the strong degree 1 component before the joint inversion has decreased such that the correlation between the velocities above the discontinuity and the shape of the discontinuity itself has substantially diminished spatially this result means a significant diminution in the strength of the earlier reported depression of the 400 km discontinuity under the pacific the power spectrum of the topography of the 670 km discontinuity has been enriched in long wavelength component especially in degree 2 the range of depth variations is 18 km and its shape correlates well with the radially averaged velocity perturbations in the transition zone at wavelengths greater than 1000 km there is little correlation between the depth perturbations of the 400 and 670 km discontinuities the topography of the 400 km discontinuity does not appear to be strongly influenced by thermal structures potentially associated with subduction processes and plumes this implies that thermal influence on the olivine to phase transformation may not fully account for the observed depth variations dynamical effects and potential variations in composition may be important near the top of the transition zone

determination and analysis of long wavelength transition zone structure using ss precursors summary global mapping of 410 and 660 km discontinuity topography and transition zone thickness has proven to be a powerful tool for constraining mantle chemistry dynamics and mineralogy numerous seismic and mineral physics studies suggest that the 410 km discontinuity results from the phase change of olivine to wadsleyite and the 660 km discontinuity results from the phase change of ringwoodite to perovskite and magnesiowustite underside reflections of the 410 and 660 km discontinuities arrive as precursors to ss with the recent development of a semi automated method of determining ss arrivals we have more than tripled the flanagan and shearer 1998a data set of handpicked ss waveforms we are able to increase resolution by stacking waveforms in 5 rather than 10 radius bins as well as increasing data coverage significantly in the southern hemisphere the resulting ss s410s and ss s660s times are heavily influenced by upper mantle velocity structure we perform a joint inversion for discontinuity topography and velocity heterogeneity as well as performing a simple velocity correction to the precursor differential times and find little difference between the two methods the 660 km discontinuity topography and transition zone thickness are correlated with velocities in the transition zone whereas the 410 km discontinuity topography is not in addition the 410 km discontinuity topography is not correlated with the 660 km discontinuity topography rather anticorrelated as expected due to the opposite signs of the clapeyron slopes of their respective phase changes these results suggest that whereas the topography of 660 km discontinuity could be dominated by thermal effects the topography of the 410 km discontinuity is likely dominated by compositional effects in addition unlike previous studies which find less topography on the 410 km discontinuity than on the 660 km discontinuity our 410 and 660 km topography have similar amplitudes

a sharp cratonic lithosphere asthenosphere boundary beneath the american midwest and its relation to mantle flow abstract beneath the american midwest s to p sp converted wave imaging and multi mode surface wave tomography identify a north trending transition in seismic structure at 150 250 km depth to the east of this american midwest transition amt the lithosphere asthenosphere boundary lab is imaged as a 1 2 sp sv amplitude arrival at 200 240 km depth consistent with the depth of negative shear velocity and azimuthal anisotropy gradients imaged by surface wave tomography to the west of the amt sp conversions are much shallower at 150 190 km depth and are much weaker 0 7 or absent azimuthal anisotropy constrained by surface wave tomography also changes across the amt with stronger anisotropy to the east of the transition beneath the thicker lithospheric root we suggest that the seismic changes across the amt can be explained by considering the effects of asthenospheric flow beneath the leading edge of the thick lithospheric root the mantle flow is dominantly driven by the drift of the north america plate locally higher flow velocities are expected where the asthenosphere is forced to flow beneath the thicker root this mantle underflow could create a sharper seismic lab east of the amt via two effects first the local increase in flow velocities could steepen the thermal gradient at the base of the lithosphere and hence the isotropic velocity contrast second the increased strain rate along edge of the lithosphere could enhance the magnitude of azimuthal anisotropy our results suggest that seismically detectable lab sharpness variations could be used to constrain geographic variations in coupling between plates and mantle convection a secondary result is the image of a mid lithospheric discontinuity arrival at 80 110 km depth that is found primarily to the east of the amt this arrival is interpreted as produced by a layer of low velocity metasomatic minerals that have accumulated since the 1 8 ga creation of the lithosphere

beyond receiver functions passive source reverse time migration and inverse scattering of converted waves 1 we present a wave equation prestack depth migration to image crust and mantle structures using multi component earthquake data recorded at dense seismograph arrays transmittedp and swaves recorded on the surface are back propagated using an elastic wave equation solver the wave modes are separated after the reverse time continuation of the wavefield from the surface and subjected to a cross correlation type imaging condition forming an inverse scattering transform reverse time migration rtm does not make assumptions about the presence or properties of interfaces notably it does not assume that interfaces are locally horizontal with synthetic experiments and different background models we show that passive source rtm can reconstruct dipping and vertically offset interfaces even in the presence of complex wave phenomena such as caustics and point diffraction and that its performance is superior to traditional receiver function analysis e g common conversion point ccp stacking in complex geological environments

mantle provinces under north america from multifrequency p wave tomography this is a survey of mantle provinces large scale seismic anomalies under north america from the surface down to 1500 1800 km depth the underlying p velocity model was obtained by multifrequency tomography a waveform based method that systematically measures and models the frequency dependence of teleseismic body waves a novel kind of three dimensional rendering technique is used to make the considerable structural complexities under north america accessible in the transition zone and below the north american mantle is dominated by seismically fast provinces which represent distinct subduction episodes of the farallon plate i attempt to date and interpret the various slab fragments by reconciling their present positions with paleotrench locations from plate tectonic reconstructions and with major geologic surface episodes differences in vertical sinking velocity have led to large vertical offsets across adjacent coeval slabs some of the mantle provinces have not been discussed much previously including 1 a seismically slow blanket overlying the oldest farallon subduction along the eastern continental margin 2 a transition zone slab coeval with the laramide orogeny ca 80 60 myr which i discuss in analogy to the stagnant slab subduction style commonly found in the western pacific today 3 the lower mantle root of present day cascadia subduction which may have started out as intraoceanic subduction 4 a lower mantle slab under arizona and new mexico the last material to subduct before strike slip motion developed along the san andreas boundary and 5 two narrow plate tears thousands of kilometers long one of which is the subducted conjugate of the mendocino fracture zone

tectonics of the dolomites southern alps northern italy abstract in post variscan times the dolomites underwent a number of tectonic events which may be summarized as follows permian and triassic rifting phases broke the area into n s trending basins with different degrees of subsidence a middle triassic transpressive event then deformed the region along a n70 e axis generating flower structures within the basement volcano tectonic domal uplift and subsequent caldera formation occurred at the same time as the late ladinian magmatism early jurassic rifting also controlled the subsidence which increased eastward this long period of deformation was followed by a pre neogene late cretaceous palaeogene e w ene wsw compression which generated a w vergent belt possibly equivalent to the folded foreland of the dinaric chain a 70 km e w section of the dolomites indicates shortening of at least 10 km during the neogene the dolomites as far north as the insubric lineament were the innermost part of a s vergent thrust belt the basement of the dolomites was thrust southwards along the valsugana line onto the sedimentary cover of the venetian prealps for at least 10 km this caused a regional uplift of 3 5 km the valsugana line and its backthrusts on the northern side of the central dolomites generated a 60 km wide pop up in the form of a synclinorium within which the sedimentary cover adapted itself mainly by flexural slip often forming triangle zones the shortening linked to this folding is about 5 km with neogene thrusts faulting and folding pre existing thrust planes on the north eastern side of the dolomites neogene deformation is apparently more strictly controlled by the transpressive effects of the insubric lineament and shortening of the sedimentary cover may be greater than in the central dolomites minor deformation linked to the giudicarie belt is present in the western dolomites the present structure of the dolomites is thus the result of a number of tectonic events of different significance and different strike only a 3 dimensional restoration can unravel the true structure of the dolomites

phosphorites hardgrounds and syndepositional solution subsidence a palaeoenvironmental model from the miocene of the maltese islands abstract two major phosphorite conglomerate horizons occur throughout the central mediterranean maltese islands within the lower middle miocene globigerina limestone formation the lower conglomerate lies directly upon a hardground and both conglomerates include lithoclasts of hardground material variation in clast size and bed thickness indicates a source area to the west and north of the present day islands of malta and gozo particularly thick phosphorite conglomerates occur in solution subsidence structures in western gozo being developed as a result of synsedimentary seafloor collapse these structures indicate that phosphorite clasts were deposited during several discrete pulses of turbulence punctuated by periods of non depositional hardground formation or normal marine pelagic sedimentation geochemical analysis of the contained phosphorite clasts within the conglomerates shows that p 2 o 5 generally is concentrated around the outer margins of the pebbles and contributes up to 17 by weight of some samples some 654 580 m 3 and 837 870 m 3 of phosphorite bearing strata are contained within the xlendi and qawra subsidence structures respectively the maltese islands represent part of a miocene carbonate shelf whose margin lay nearby to the west and which was subject to periodic erosion by strong currents transporting phosphorite pebbles eastwards to their present sites these currents further contributed phosphorus to semi autochthonous phosphorite developments located within the present maltese area the maltese phosphorites are related to other phosphorite areas in sicily a major province of miocene phosphogenesis is proposed to account for these occurrences it extends along the western margins of the malta ragusa rise

seismic imaging of upper mantle structure with new evidence for a 520 km discontinuity stacked images of long period seismic data reveal many phases some not previously observed which are caused by reflections and conversions at discontinuities in the earth s upper mantle these images support the existence of discontinuities at 410 520 and 660km depth but no evidence is found for a significant interface at 220 km

lithosphere asthenosphere interaction beneath the western united states from the joint inversion of body wave traveltimes and surface wave phase velocities summary the relation between the complex geological history of the western margin of the north american plate and the processes in the mantle is still not fully documented and understood several pre usarray local seismic studies showed how the characteristics of key geological features such as the colorado plateau and the yellowstone snake river plains are linked to their deep mantle structure recent body wave models based on the deployment of the high density large aperture usarray have provided far more details on the mantle structure while surface wave tomography ballistic waves and noise correlations informs us on the shallow structure here we combine constraints from these two data sets to image and study the link between the geology of the western united states the shallow structure of the earth and the convective processes in mantle our multiphase dna10 s model provides new constraints on the extent of the archean lithosphere imaged as a large deeply rooted fast body that encompasses the stable great plains and a large portion of the northern and central rocky mountains widespread slow anomalies are found in the lower crust and upper mantle suggesting that low density rocks isostatically sustain part of the high topography of the western united states the yellowstone anomaly is imaged as a large slow body rising from the lower mantle intruding the overlying lithosphere and controlling locally the seismicity and the topography the large e w extent of the usarray used in this study allows imaging the slab graveyard a sequence of farallon fragments aligned with the currently subducting juan de fuca slab north of the mendocino triple junction the lithospheric root of the colorado plateau has apparently been weakened and partly removed through dripping the distribution of the slower regions around the colorado plateau and other rigid blocks follows closely the trend of cenozoic volcanic fields and ancient lithospheric sutures suggesting that the later exert a control on the locus of magmato tectonic activity today the dna velocity models are available for download and slicing at http dna berkeley edu

the latemar a middle triassic polygonal fault block platform controlled by synsedimentary tectonics abstract detailed field mapping of a middle triassic carbonate buildup the latemar in the western dolomites northern italy has been carried out the latemar is an isolated carbonate buildup that nucleates on a fault bounded structural high horst cut into the underlying late anisian carbonate bank of the contrin fm this study demonstrates that extensional synsedimentary tectonics is the main factor controlling its geometry and provides an age for this tectonic phase in an early phase slopes were mostly composed of well bedded clinostratified grainstones and rudstones in a later stage the deposition of grainstones was accompanied by the emplacement of clinostratified megabreccias the upper portion of slopes is a microbial boundstone with abundant tubiphytes and patches or lenses of grainstone boundstones may occasionally expand into the platform interior and downward to the base of the slope the depositional profile was that of a mounded platform the buildup is dissected by a dense framework of high angle fractures and faults and by magmatic and sedimentary dikes exhibiting two principal directions trending nnw sse and ene wsw faults trending wnw ese were also observed magmatic dikes are related to the emplacement of the nearby predazzo intrusion and are thus upper ladinian kinematic indicators of strike slip activity were observed on fault planes trending nne ssw and nnw sse that can be attributed to cenozoic alpine tectonics faults magmatic dikes and sedimentary dikes show systematic cross cutting relationships with strike slip faults cutting magmatic dikes and magmatic dikes cutting sedimentary neptunian dikes ene wsw and wnw ese faults are cut by all other structures and record the oldest tectonic activity in the region structural analysis attributes this tectonic phase to an extensional stress field with a direction of maximum extension oriented ca n s several lines of evidence including sealed faults and growth wedge geometries allow us to recognize this old tectonic phase as syndepositional and to date it to the latest anisian avisianum and crassus ammonoid biochronozones the horse shoe shape of the platform and its margins rectilinear for long tracts are explained by the existence of a network of extensional faults whose activity lasted for part of the growth of the platform the latemar is thus a polygonal fault block platform controlled by synsedimentary tectonics the resulting sedimentary architecture is that of a growth wedge deposited probably on the uplifted side of a submerged half graben continuous reactivation of faults at platform margins locally determined anomalous facies transitions with well layered platform interior directly in contact with the clinostratified slopes

roughness of the mantle transition zone discontinuities revealed by high resolution wavefield imaging we processed two independent data sets 2 458 973 three component seismograms from all earthscope transportable array usarray stations and 141 080 pairs of high quality receiver functions from the earthscope automated receiver survey using the generalized iterative deconvolution method and shaped the output with a 0 1 hz ricker wavelet we used these data as input to our 3 d plane wave migration method to produce an image volume of p to s scattering surfaces under all of the lower 48 states model simulations show that compared to the widely used common conversion point stacking method our method is capable of resolving not only dipping discontinuities but also subtler details of amplitude and topography variations at scales near the diffraction limit maps of attributes derived from these discontinuities reveal several previously unobserved features of the 410 and 660 discontinuities d410 and d660 topography with many tens of kilometers is resolved at a range of scales additionally we observed large variations of amplitude on the radial component and in the radial to transverse amplitude ratio that correlate with inferred variations in discontinuity topography we argue that this combination of observations can be explained by roughness at a range of scales the structural fabric we imaged is preferentially aligned orthogonal to the farallon north american relative motion two regions we infer to have exceptional roughness show spatial correlation with locations where tomography models indicate that the subducted slab is passing through the transition zone we suggest that these rough regions are indicators of vertical mantle flows through the transition zone

constraints on upper mantle discontinuities from observations of long period reflected and converted phases stacked images combining over 5 years of long period global digital seismograph network data reveal many phases associated with reflections and conversions from upper mantle discontinuities these images show travel time and amplitude relative to a reference phase which is aligned and normalized on all seismograms prior to stacking results obtained for p s ss and pp reference arrivals resolve numerous phases from discontinuities near 410 and 660 km while some of the stacks also show evidence for a weaker discontinuity near 520 km phases of particular interest include p and sh multiples resulting from topside reflections precursors to ss from underside reflections and p to sv converted phases these phases can be clearly seen both in the waveform stacks and in cross correlation analysis of individual seismograms travel times for these arrivals are converted to discontinuity depths relative to velocities in the preliminary reference earth model and empirical corrections are applied for the effects of lateral velocity variations in the upper mantle average apparent depths to the discontinuities for the different phases agree to within 3 km for the 410 km discontinuity to within 4 km for the 520 km discontinuity and to within 8 km for the 660 km discontinuity the best global averages are obtained from the ss precursor data which indicate discontinuities at 415 519 and 659 km discontinuity depths obtained from the p to sv converted phases at over 35 individual seismic stations exhibit variations of less than 20 km apparent depths to the 660 km discontinuity consistently show greater variability than depths to the 410 km discontinuity supporting recent laboratory results which indicate that the clapeyron slope for the 660 km discontinuity is significantly larger in magnitude than the slope for the 410 km discontinuity precursors to ss seen between 110 and 180 are particularly useful for mapping possible lateral variations in discontinuity depths since each arrival can be associated with a single underside reflection point apparent discontinuity depths computed from ss precursors for different tectonic regions agree to within about 5 km the ss precursors have especially good coverage near the subducting slabs in the northwest pacific analysis of apparent discontinuity depths in this area suggests the presence of a broad 1000 to 1500 km wide region near the slab in which the 660 km discontinuity is depressed by about 20 km measuring absolute amplitudes for these phases is difficult due to the large corrections required to compensate for the effects of incoherent stacking relative amplitude analysis suggests that the p and s wave impedance changes at 410 km are about 0 8 1 1 times the size of the changes at 660 km and that the contrasts at 520 km are between 0 3 and 0 6 of the changes at 410 km

termination of carbonate slope progradation an example from the carnian of the dolomites northern italy abstract the demise of carbonate platforms during carnian time is a widespread phenomenon of the western tethys but the controlling factors are not well understood the dolomites of the southern alps northern italy are well known for their large scale ladinian and carnian prograding carbonate platforms platform growth stopped during the early carnian and both platforms and basinal areas were subsequently covered by mixed carbonate siliciclastic sediments raibl group we present a carbonate platform whose slope progradation came to a halt prior to draping by the siliciclastic sediments judging from the height of the clinoforms a platform to basin relief of at least 100 m existed during the final stage of progradation this paleo slope was colonized by coral patches draped by skeletal packstones to microbial bindstones forming typically lens shaped mounds on the steep slope the formation of mounds on the platform flank was only possible because the downslope transport of detritus from the platform and or upper slope was stopped the sedimentary evolution in the adjacent basin indicates a poorly oxygenated environment with abundant brackish water ostracods of low diversity based on the inherited platform to basin relief and the lithofacies of the basin fill a local sea level drop in the order of 60 80 m is postulated with rising sea level the accommodation space between former basin and platform became filled by shallow marine mixed carbonate siliciclastic sediments the abundance of epibenthic suspension feeders of the basin fill such as megalodonts suggests increased nutrient supply the termination of slope progradation was a multiphased process triggered by a stagnation of the regional subsidence a reduction of water circulation followed by a sea level drop the influx of freshwater and the input of siliciclastics fluctuating salinity caused intermittently a biotically stressed environment

inventory fluxes and residence times from the depth profiles of naturally occurring 210pb in marine sediments of mumbai harbor bay measurements of the vertical concentration profile of deposited 210pb and its parent 226ra in cores of recent marine sediment of mumbai harbor bay mhb were made to determine the various depth distribution parameters sedimentation rate age of sediment total inventory fluxes residence times scavenging rate linear attenuation coefficient and relaxation mass depth overall the profile distributions of 226ra and 210pb showed a decreasing trend with increasing the depth the mean of sedimentation rate in the studied area was obtained to be about 0 76 cm year 1 which corresponds to average age of sediment of about 56 years the average total deposited 210pb for the studied sediment profile was 9 68 k bq m 2 and correspondingly the average value of fluxes of total 210pb and excess 210pb atmospheric flux were 0 59 and 0 32 k bq m 2 year 1 respectively the residence time of 210pb was in the range of 26 226 years throughout the sediment profile and showed generally an increasing trend from top to bottom the mean relaxation mass depth h0 derived from the depth profile of 210pb at the studied area was about 190 kg m 2 the negative association between clay content of cores and the h0 of 210pb indicates that as the clay content increases the penetration depth of deposited 210pb in sediment profile decreases

multiple transition zone seismic discontinuities and low velocity layers below western united states with p to s converted waves recorded at seismic stations of the us transportable array we image the fine structure of upper mantle and transition zone tz beneath the western us we map the topographies of seismic discontinuities by stacking data by common conversion points along profiles systematic depth and amplitude measurements are performed not only for the well known 410 and 660 interfaces but also for minor seismic discontinuities identified around 350 590 and 630 km depths the amplitude of conversion suggests shear wave velocity vs increase by 4 at the 410 and the 660 the observed 660 velocity contrast is smaller than expected from the 6 in iasp91 but consistent with a pyrolitic model of mantle composition the gorda plate subducted under northern california is tracked to the tz where it seems to flatten and induce uplift of the 410 under northern nevada maps of 410 660 amplitude topography reveal that the tz is anomalous beneath the geographical borders of washington oregon and idaho with i a thickened tz ii a sharp change in depth of the 660 iii a reduced 410 conversion amplitude in the north and iv a positive 630 discontinuity such anomalous structure might be inherited from the past history of plate subduction accretion a thinned tz under the yellowstone suggests higher than average temperatures perhaps due to a deep thermal plume both the 350 and the 590 negative discontinuities extend over very large areas they might be related either to an increased water content in the tz a significant amount of oceanic material accumulated through the past 100 my or both

global de correlation of the topography of transition zone discontinuities analysis of long period shear wave underside reflections from upper mantle discontinuities shows the shape of the 410 km discontinuity to be neither globally nor locally correlated with that of the 660 km discontinuity the long wavelength pattern of 410 topography is dominated by degree 1 spherical harmonics and has a reasonable correlation with the seismic velocity perturbations in the mantle above it the global topography of 660 dominated by degree 2 spherical harmonics is strongly correlated with shear wave velocity variations in the transition zone the poor correlation between the observed topography of the 410 and 660 km discontinuities is inconsistent with a simple model of large scale whole mantle flow thus implying a more complex pattern which includes at least temporary accumulation of subducted material in the transition zone ringwood and irifune nature 331 1988 131 136 tackley et al nature 361 1993 699 704 the modest seismic discontinuity at 520 km is well observed when the reflections are under mid age oceans but is not observed when they are under continental shields interpretation of this observation in terms of olivine depletion in the deep continental mantle indicates the possible existence of continent ocean chemical heterogeneity at depths exceeding 500 km

3 d shear wave radially and azimuthally anisotropic velocity model of the north american upper mantle summary using a combination of long period seismic waveforms and sks splitting measurements we have developed a 3 d upper mantle model sawum na2 of north america that includes isotropic shear velocity with a lateral resolution of 250 km as well as radial and azimuthal anisotropy with a lateral resolution of 500 km combining these results we infer several key features of lithosphere and asthenosphere structure a rapid change from thin 70 80 km lithosphere in the western united states wus to thick lithosphere 200 km in the central cratonic part of the continent closely follows the rocky mountain front rmf changes with depth of the fast axis direction of azimuthal anisotropy reveal the presence of two layers in the cratonic lithosphere corresponding to the fast to slow discontinuity found in receiver functions below the lithosphere azimuthal anisotropy manifests a maximum stronger in the wus than under the craton and the fast axis of anisotropy aligns with the absolute plate motion as described in the hotspot reference frame hs3 nuvel 1a in the wus this zone is confined between 70 and 150 km decreasing in strengthwithdepthfromthetop fromthermftothesanandreasfaultsystemandthejuande fuca gorda ridges this result suggests that shear associated with lithosphere asthenosphere couplingdominatesmantledeformationdowntothisdepthinthewesternpartofthecontinent the depth extent of the zone of increased azimuthal anisotropy below the cratonic lithosphere is not well resolved in our study although it is peaked around 270 km a robust result radial anisotropy is such that predominantly 1 where vsh vsv 2 under the continent and its borders down to 200 km with stronger in the bordering oceanic regions across the continent and below 200 km alternating zones of weaker and stronger radial anisotropy with predominantly 1 correlate with zones of small lateral changes in the fast axis direction of anisotropy and faster than average vs below the lab suggesting the presence of small scale convection with a wavelength of 2000 km finally in the western united states complex 3 d patterns of isotropic velocity and anisotropy reflect mantle dynamics associated with the rich tectonic history of the region

high resolution transition zone structures of the gorda slab beneath the western united states implication for deep water subduction 1 the current data set from usarray provides an unprecedented opportunity to investigate mantle transition zone structures beneath the western united states we have made transition zone images with the common converted point ccp stacking method more than 9600 high quality receiver functions were stacked with reference to two different three dimensional tomography models and a one dimensional velocity model where the gorda plate passes through the transition zone the 410 discontinuity has been elevated 25 km and the 660 discontinuity has been depressed 35 km we interpret the transition zone topography in terms of mineral physics results in several different ways noting in particular that recent measurements on the clapeyron slope for the ringwoodite to perovskite phase transition under dry conditions give a phase boundary slope of 1 3 to 0 4 mpa k the 35 km deflection of the 660 discontinuity observed in the receiver functions seems to be the evidence that the subducted slab can carry abundant water from the surface to the transition zone and in the transition zone the water in the slab may be fully saturated e g the water content is 2 0 wt analyses of the velocity perturbations in the tomography models and the transition zone thickness indicate that the deep water is likely well confined within the subducted slab we infer that the presence of water in the subducted gorda slab might have contributed 15 km and the thermal anomaly in the slab might have contributed 20 km to the depression of the 660 discontinuity

environmental factors influencing skeletal grain sediment associations a critical review of miocene examples from the western mediterranean the presence of foramol rhodalgal and bryomol skeletal grain associations in ancient shallow marine limestones is commonly interpreted as evidence for non tropical palaeoclimate despite temperature being only one of several factors influencing skeletal grain associations such interpretations neglect the multitude of factors other than temperature that influence carbonate producing biota these include nutrients water energy water transparency depth of the sea floor salinity oxygen ca2 and co2 concentrations mg ca ratio alkalinity substrate requirements competitive displacement as well as biological and evolutionary trends this uniformitarian approach also disregards the probability that conditions of present day biological systems may not be representative of past conditions of analogous systems here the importance of considering these other factors is illustrated through two examples of carbonate platforms in the western mediterranean these platforms are dominated by foramol rhodalgal and bryomol associations of miocene age in spite of having formed in tropical conditions the platforms discussed are 1 the lower tortonian ramp on menorca balearic islands and 2 the lower middle miocene ramps of the central apennines italy evidence for tropical conditions in the mediterranean during the period of growth of these platforms is provided by species of red algae and larger foraminifera by data from coeval continental basins and by global oxygen isotope data

nature and evolution of middle triassic carbonate buildups in the dolomites italy during the middle triassic an evolution from carbonate bank to buildup highly elevated in respect of the adjacent basins is observed in the alps the dolomites in the southern alps italy are here considered as an example during the anisian subtidal banks of the upper serla fm with rare peritidal cycles show only a limited biologic density and diversity with the late anisian contrin fm a gradual development of binding and framework building communities can be observed the sinking of wide areas of the contrin carbonate bank into anoxic conditions plattenkalke fm allowed the birth of isolated buildups their increased carbonate production due to a greater diversity and density of organisms was able to keep up with the rate of subsidence the latemar buildup with additional data for the slope taken from mt coldai civetta and sass da putia is used to illustrate the main character of a lower ladinian buildup the restricted platform sediments display peritidal cycles prevalent in the subtidal portion is dasycladacean packstone grainstone associated with gastropods ammonoids and blue green algae in the supratidal portion desiccation and tepee structures are present scleractinian and sphinctozoan frameworks are rare on the upper part of the slope which is bound predominantly by encrusting organisms mainly blue green algae porifers and tubiphytes the prevailing sediments on the upper part of the slope are bindstones whilst packstones and rudstones are in the lower part of the slope the latter carbonates were cemented early under submarine conditions mostly by isopachous palisade cement polyphasic internal sediments with phreatic vadose influence are present and can in the middle lower part of the slope replace most of the original sediment

meso cenozoic basin and carbonate platform development in the sw dolomites unraveled by basin modelling and apatite ft analysis rosengarten and latemar northern italy abstract the rosengarten and latemar middle triassic carbonate platforms indicate similar subsidence patterns during equivalent times of platform evolution as calculated by numerical basin reverse modelling in the case of rosengarten and latemar thermo tectonic subsidence is the most significant among all three subsidence components thermo tectonic s flexural s compaction induced s hence the influence of differential tectonics as recorded in the formation of structural highs and lows in the dolomites during the lower to middle anisian almost ceases in late anisian times basin modelling of rosengarten and latemar requires the correlation and integration of two sets of chronostratigraphic data from buchenstein fm basin and schlern dolomite fm 1 platform subsidence modelling argues for a microcycle i e a single shallowing upward cycle duration of less than 1 97 ka in the cyclic succession at latemar however previous time series analyses identify milankovitch cyclicities in larger order cycle stacking patterns and thus indicate a microcycle duration of 4 2 ka according to each model total subsidence reaches values of 650 700 m ma 4 2 ka model or 780 850 m ma 1 97 ka model during the first stage of platform evolution as both platforms successfully keep up with this subsidence peak it is evident that the carbonate factory despite its low diversity must have recovered from the p t faunal crisis after this regionally observed peak subsidence drops and triggers fast progradation at rosengarten subsidence in the study area is controlled by active strike slip tectonics and the subsequent formation of a magmatic chamber predazzo monzoni above the deep reaching truden stava line the area close to this tectonic line and to the volcanic centre of predazzo monzoni undergoes a higher heat flow pulse during the late ladinian and is possibly buried at shallower levels than the rosengarten area as shown by fission tracks in apatites the heat flow pulse almost disappears laterally underlining the localised thermal influence of the late ladinian volcano thermal event of predazzo monzoni

multi mode conversion imaging of the subducted gorda and juan de fuca plates below the north american continent abstract receiver function analysis and seismic tomography show tectonic structures dipping eastward in the mantle below the cascadia volcanic arc western us that have been related to the subduction of the gorda and juan de fuca oceanic micro plates inconsistencies in the dip angle and depth extent of the slab between the two methods undermine the interpretation of the structure and processes at work receiver function imaging is biased by multiple reflection phases that interfere with converted phases and produce spurious discontinuities in images here we correct the interference using a multiple mode conversion imaging technique that efficiently removes artifacts under dipping structures the method has the advantage of being applicable to large aperture arrays and can image large scale structures down to the transition zone with this approach the interfaces between the subducting and overriding plates and the oceanic moho are imaged at shallow depths

p and s wave tomography of the mantle beneath the united states mantle seismic structure beneath the united states spanning from the active western plate margin to the passive eastern margin was imaged with teleseismic p and s wave traveltime tomography including usarray data up to may 2014 to mitigate artifacts from crustal structure 5 40 s rayleigh wave phase velocities were used to create a 3 d starting model major features of the final p and s models include two distinct low velocity anomalies at depths of 60 300 km beneath the central and northern appalachians and passive margin the central appalachian low velocity anomaly coincides with eocene basaltic magmatism and the northern anomaly is located along the cretaceous track of the great meteor hot spot at depths of 300 700 km beneath the central and eastern u s large high velocity anomalies are inferred to be remnants of the farallon slab that subducted prior to 40 ma during the laramide orogeny

cascadia subduction slab heterogeneity revealed by three dimensional receiver function kirchhoff migration we present a 3 d model of upper mantle seismic discontinuity structure below cascadia using a receiver function kirchhoff migration method a careful analysis of the primary and multiple reverberated phases allows imaging of the juan de fuca plate dipping below the north american continent the subducting slab is observed as an eastward dipping signal at all latitudes we associate this signal with a thermal gradient between the slab and surrounding mantle rather than a sharp chemical discontinuity our model also shows along strike variations in the dipping angle and strength of this signal to the southern and northern ends of the subduction system the signal is clearly observed down to 300 km however beneath central oregon this structure is missing below 150 km depth we propose that this gap is due to weakening of the slab beneath central oregon possibly caused by deformation and hydration combined with plume slab interaction processes after subduction

evidence for strong shear velocity reductions and velocity gradients in the lower mantle beneath africa we present data which indicate that the broad low shear velocity anomaly beneath southern africa is stronger and more extensive than previously thought recordings of earthquakes in the southwestern atlantic ocean at an array of broadband seismic stations in eastern africa show anomalously large propagation time delays of the shear phases s scs and sks which vary rapidly with epicentral distance by forward modeling we estimate that the low velocity anomaly extends from the core mantle boundary about 1500 km up into the mantle and that the average shear velocity within this structure is 3 lower than in standard models such as prem strong velocity contrasts exist at its margins 2 over about 300 km these seismic characteristic are consistent with recent numerical simulations of lower mantle mega plume formation

seismic receiver functions and the lithosphere asthenosphere boundary abstract the lower boundary of the lithospheric plates has remained as an enigmatic boundary for seismologists since it is relatively poorly observed by seismic means there is traditionally a broad consensus that the asthenosphere is observable as a low velocity zone by seismic surface waves seismic techniques which use shorter period p to s or s to p converted body waves are now far enough developed to be successful in observing such a low velocity zone with a higher resolution the principle of this technique the so called receiver function technique is that a strong teleseismic mother phase e g p s pp or sks incident from below on any seismic discontinuity beneath a station produces a converted phase ps or sp which indicates its depth and properties we discuss details of this technique a sufficient number of such observations exist already to indicate that the top of the low velocity zone is a globally observable discontinuity and it is sharper than previously thought an intriguing observation is that in some cratons the new seismic data indicate that the low velocity zone exists already at shallower depths than obtained from surface waves this confirms earlier results from controlled source observations thybo and perchuc 1997 we discuss possible interpretations of this shallow low velocity zone in cratonic regions

contrasting lithospheric signatures across the western united states revealed by sp receiver functions abstract to explore how lithospheric structure varies between tectonic and magmatic terranes of the western united states we use observations of shear to compressional wave conversions across lithospheric velocity interfaces with a newly developed automatic method designed to take advantage of the earthscope transportable array and other broadband seismic arrays deployed across the region and an optimized deconvolution technique based on the extended time multi taper method we map variations in the depth to the seismic moho lithosphere asthenosphere boundary lab and mid lithospheric discontinuities mlds beneath areas that have undergone substantial extension in the neogene including the eastern great basin the southern basin and range and the southern rio grande rift we detect strong sp conversions across a relatively shallow 60 80 km seismically defined lab we detect sp conversions across an 80 90 km depth discontinuity beneath the high rockies which we interpret as the seismically defined lab beneath areas that have remained relatively undeformed including the wyoming craton and the great plains craton we detect sp conversions in the 90 140 km depth range that are substantially weaker and more distributed in depth than those beneath less stable regions beneath the colorado plateau sp ccp stacks show that lithospheric thinning has accompanied magmatic encroachment and the lab beneath the margins of the plateau is indistinguishable from the lab of the surrounding extensional provinces in contrast beneath central and northern colorado plateau weaker sp conversions are observed in the 90 140 km depth range the observed variations in lithospheric structure across structural blocks with different magmatic and deformational histories imply that 1 both mechanical thinning and magmatic and thermal erosion have likely contributed to the thin lithosphere observed in the basin and range and southern rio grande rift 2 at the margins of the colorado plateau and beneath the high rockies where extension has been relatively minor strong and shallow seismic labs indicate magmatic alteration of the lithosphere 3 mlds seen in comparatively thick stable lithosphere produce weaker sp conversions and are often more distributed in depth than seismically observed labs in regions of thin lithosphere 4 mlds and weak deep phases consistent with a seismic lab are sometimes observed together