deep seismic structure of the kaapvaal craton the kaapvaal craton is remarkable for the intensive jurassic cretaceous kimberlite magmatism there are indications that the hot spot heating of the upper mantle in southern africa continued in the cenozoic however surface wave data in spite of their sensitivity to temperature failed to provide any evidence of thermal agitation at depths less than 350 km beneath the kaapvaal craton bloch et al 1969 we investigated the s velocity structure in the depth range of the mantle transition zone with the aid of teleseismic p to s converted phases our analysis suggests that a layer of anomalously low s velocity is present in the 370 470 km depth interval beneath the kaapvaal craton the anomalous layer is most likely of thermal origin its upper boundary may separate the deep mantle root of the craton from the underlying mantle the anomaly could arise beneath the craton already in the mesozoic and melting within this layer could contribute to the kimberlite magmatism

the mid cretaceous earth paleogeography ocean circulation and temperature atmospheric circulation a reconstruction of the global paleogeography of the mid cretaceous 100 m y ago including adjustment of continental outlines to account for microplate movements cmstal shortening and accretion in mid cretaceous and later orogenic regions is described and a map presented on the modified continents coastlines and significant mountain ranges are added this paleogeography is used as a framework for a reconstruction of ocean surface circulation and temperature distribution then the main features of the atmospheric circulation are deduced using the paleogeography and ocean temperatures as boundary conditions relative to the present these features are a much weaker westerly wind belt and greater seasonality of wind patterns leading to more extreme surface climates over the continents slightly equatorward positions of the subtropical anticyclones and monsoonal regimes over the continental margins bordering tethys and the central atlantic a comparison of the results with climatic evidence from t

differential compaction faults and their implications for fluid expulsion in the northern bozhong subbasin bohai bay basin china abstract a series of differential compaction faults was identified in the northern bozhong subbasin bohai bay basin china by using 3d seismic well log and lithology data the differential compaction faults display two obvious characteristics first they develop along a lithologic boundary which separates thick sandstone from underlying mudstones facies and thickness change such as an abrupt lithologic change between sandstone and mudstone a lateral thickness change of overlying sandstone are the basic controlling factors of these differential compaction faults second they have a definite strike direction according to the fault strike the differential compaction faults can be divided into three groups group a have an approximate orthogonal strike with the tectonic faults group b display a similar strike with the slope and group c show radial strikes on the circular basement uplift tectonic faults influence the planform patterns of differential compaction faults in their near vicinity and induce these faults displaying an approximate orthogonal intersection with the late period through going faults group a basin slope promote the formation of differential compaction faults by downslope gravity sliding and cause faults parallel to the strike of slope group b circular basement topography generates isotropic stress and leads the differential compaction faults above the basement dominated by radial strikes group c production and geochemistry data is an evidence of differential compaction faults developed in a late period when the strata reach a certain burial depth that the source rocks enter the oil generating window the presence of thermogenic fluid within shallow reservoirs represents as evidence of hydrocarbon drained and migrated through the differential compaction faults the differential compaction faults could serve as significant conduits for fluid expulsion and hydrocarbon accumulation in the bohai bay basin china

deep upper mantle melting beneath the tasman and coral seas detected with multiple scs reverberations abstract multiple scs reverberations are used to search for mantle reflectors beneath the tasman and coral seas with a hierarchical waveform inversion migration method in addition to the major transition zone discontinuities a low velocity layer above the 410 km discontinuity is detected the top of the low velocity layer lies at an average depth of 352 km indicating that the layer could be more than 70 km thick if it persists to the 410 km discontinuity which occurs at an average depth of 420 km along paths containing the low velocity layer we attribute the low velocities to partial melt resulting from volatile induced melting the considerable thickness of the partial melt layer may require thin films of a hydrous melt with a zero degree dihedral angle surrounding grains or the combined effect on melting of the addition of both water and carbon to the deep upper mantle via subduction although the depths of the transition zone discontinuities do not indicate that the transition zone itself is rich in water the impedance contrasts do contain a subtle signature that could be related to transition zone water namely a decrease in the impedance contrast across the 410 km discontinuity and a relatively strong 520 km discontinuity

cessation reactivation of polygonal faulting and effects on fluid flow in the voring basin norwegian margin polygonal faults mainly oriented n50 n110 and n170 are abundant in the upper part of the mud dominated kai formation upper miocene lower pliocene of the voring basin a second less developed tier of polygonal faults oriented n20 n80 and n140 exists at the base of the overlying naust formation upper pliocene present the faults abruptly terminate upward below a thick interval of debris flows we propose a dynamic model in which 1 the development of polygonal faults discontinues temporarily as a result of a change in regional sedimentation leading to inactive polygonal faults 2 rapid emplacement of debris flows in the late pleistocene creates a new interval of polygonal faults in the lower part of the naust formation immediately beneath the debris flow and some faults penetrate into the underlying kai formation 3 some polygonal faults within the kai formation are reactivated and propagated upward into the base of the naust formation the high interconnectivity between faulted layers allows the fluids to reach shallower depths forming well expressed pipes and pockmarks on the sea floor the model of cessation reactivation of polygonal faults constrains the sealing capacity of sedimentary cover over the reservoirs and helps to reconstruct the fluid migration history through the sedimentary column

did the rifting of the atlantic ocean cause the cretaceous thermal maximum the cretaceous thermal maximum was a major turning point in the history of earth s climate this interval of peak warmth in the turonian has been attributed to very high atmospheric pco2 resulting from rapid outgassing rates although crustal cycling rates peaked in the aptian albian interval on the basis of coupled ocean atmosphere model simulations of the middle cretaceous we hypothesize that the formation of an atlantic gateway could have contributed to the cretaceous thermal maximum differences between prerifting and postrifting climate experiments demonstrate substantial regional oceanographic changes in the north and south atlantic basins that are consistent with oxygen isotopic evidence used to infer a cretaceous thermal maximum the model results help reconcile the paleoclimate record inferred from foraminiferal d 18 o with our understanding of climate dynamics and cretaceous tectonism

upper mantle seismic shear discontinuities of the pacific 1 shear wave impedance discontinuities are inventoried for eight paths connecting circum pacific earthquakes with seismic stations on hawaii and oahu in addition to the transition zone discontinuities we observe a consistent impedance decrease at a depth of 80 km that marks the transition from the fast seismic lid to the low velocity zone the interval over which this transition occurs is less than 30 km the requisite impedance decrease ascribed almost entirely to diminished velocities in the low velocity zone exceeds predictions for peridotite chemistries of appropriate lithospheric age in all cases the transition is better matched by lithosphere of roughly half of the true age four paths show clear evidence of the x discontinuity an impedance increase of 3 8 near 300 km depth the only viable explanations would require extensive eclogite or basalt depleted mantle in the upper mantle of the western pacific the impedance contrast of the 410 km discontinuity which depends on the modal fraction of mantle olivine does not signal the presence of either although a mixture of the two remains a possibility we find no evidence of a low velocity layer atop of the 410 km discontinuity if present it is either consistently thin 15 km highly variable in thickness topography in excess of 60 km or has little impedance contrast 2 3 with overlying mantle the apparent absence of melt atop the 410 km discontinuity an intermittent and weak 520 km discontinuity and a thinned transition zone are consistent with relatively dry conditions in the deep upper mantle of the central pacific

convective patterns under the indo atlantic box using fluid mechanics we reinterpret the mantle images obtained from global and regional tomography together with geochemical geological and paleomagnetic observations and attempt to unravel the pattern of convection in the indo atlantic box and its temporal evolution over the last 260 myr the box presently contains a a broad slow seismic anomaly at the cmb which has a shape similar to pangea 250 myr ago and which divides into several branches higher in the lower mantle b a superswell centered on the western edge of south africa c at least 6 primary hotspots with long tracks related to traps and d numerous smaller hotspots in the last 260 myr this mantle box has undergone 10 trap events 7 of them related to continental breakup several of these past events are spatially correlated with present day seismic anomalies and or upwellings laboratory experiments show that superswells long lived hotspot tracks and traps may represent three evolutionary stages of the same phenomenon i e episodic destabilization of a hot chemically heterogeneous thermal boundary layer close to the bottom of the mantle when scaled to the earth s mantle its recurrence time is on the order of 100 200 myr at any given time the indo atlantic box should contain 3 to 9 of these instabilities at different stages of their development in agreement with observations the return flow of the downwelling slabs although confined to two main boxes indo atlantic and pacific by subduction zone geometry may therefore not be passive but rather take the form of active thermochemical instabilities

perturbation of polygonal fault propagation by buried pockmarks and the implications for the development of polygonal fault systems abstract evidence is presented that constrains the earliest part of the growth history of a polygonal fault tier using high resolution 3d seismic data from the west african margin we document the interaction between a shallow buried wedge shaped polygonal fault tier and pockmarks located at the base of the fault tier strongly curved patterns of perturbed polygonal faults are mapped in the shallowest portions of a tier overlying a series of pockmark craters these perturbed patterns differ markedly from the background polygonal pattern developed away from areas of pockmark influence perturbation is attributed to local stress effects relating to residual topography of the underlying pockmarks by analysing the thickness variations of mapped layers within the polygonally faulted tier we demonstrate that any residual topography was most likely healed after approximately one third of the total tier thickness was deposited hence the nucleation of the polygonal faults into their perturbed propagation trajectories must have been established within the first 100 150 m of burial from these observations of early nucleation in the basal third of a tier we propose a new model of polygonal fault growth in which individual faults nucleate near the base of a tier at an early stage of burial and then propagate preferentially upwards with basal tips restricted by an underlying mechanically competent unit the base of the tier continued growth then shifts the locus of displacement such that final displacement distributions are more axio symmetrically disposed with respect to the base and top of the tier

frozen and active seismic anisotropy beneath southern africa 1 p receiver functions from 23 stations of the sase experiment in southern africa are inverted simultaneously with sks waveforms for azimuthal anisotropy in the upper mantle our analysis resolves the long standing issue of depth dependence and origins of anisotropy beneath southern africa in the uppermost mantle we observe anisotropy with a nearly e w fast direction parallel to the trend of the limpopo belt this anisotropy may be frozen since the archean at a depth of 160 km the fast direction of anisotropy changes to 40 and becomes close to the recent plate motion direction this transition is nearly coincident in depth with activation of dominant glide systems in olivine and with a pronounced change in other properties of the upper mantle another large change in the fast direction of anisotropy corresponds to the previously found low s velocity layer atop the 410 km discontinuity

the assessment of ree patterns and 143nd 144nd ratios in fish remains abstract the ree content and isotopic composition of sr and nd have been determined in fish teeth ranging in age from the trias to the present and from various localities mostly around the atlantic these measurements have been carried out on selachian and teleost remains from the same locality in togo and show no appreciable difference which suggests with the help of a mass balance calculation of the ce anomaly that diagenetic effects are not responsible for the ree enrichment of biogenic phosphates one group of fossil teeth has about 3 times the ree abundances of shale and a shale normalized pattern with a minimum at sm it is thought to reflect deposition in the open sea environment a second group has ree concentration about 10 times higher than the first group with either a regular light ree enrichment or more frequently a maximum in the middle ree both being probably indicative of deposition in estuarine or near shore conditions the shape of the ree spectra and the size of the ce anomaly can be used semi quantitatively to determine the depth of deposition the results presented here on late cretaceous eocene fish teeth samples from morocco reflect an increasing influx of deep waters with a lowla yb ratio and strong negative ce anomaly which agrees well with the evolution of sediment chemistry and microfauna associations in contrast nd is typical of the water mass in which the fish debris decayed examples of nearly isolated basins identified with nd isotopes include the south atlantic prior to the lutetian nd 13 5 the miocene persian gulf nd 3 1 and bolivia during the late cretaceous nd 12 8 togo and guinea bissau results suggest that in the south atlantic the meridional oceanic circulation had not started before 45 ma ago combination of ree and nd data suggests that the assignment of jurassic cretaceous samples measured so far to open sea water masses is still ambiguous

biostratigraphy and paleoceanography of the cretaceous seaway between norway and greenland abstract the narrow seaway between greenland and norway in cretaceous time was over 1500 km long and 300 km wide and partly of bathyal water depth during aptian through campanian it received a large volume of fine grained siliciclastic sediments with intercalated gravity flow sandstone wedges as a conduit for heat transport between the low latitudes and polar region atlantic watermasses particularly affected the eastern norwegian margin of this seaway despite its high latitude setting calcareous and few siliceous planktonic microfossils thus play an important role in regional stratigraphy and facies analysis and a majority of fossil events correlate to nw european basins the eastern margin sedimentary succession may be subdivided in several broad lithologic units 1 thin multicolored marly sediments of hauterivian barremian age with a shallow marine falsogaudryina nodosariid ostracod assemblage 2 dark mudstones and minor sands aptian early cenomanian in age with an upper bathyal agglutinated assemblage and monotypic hedbergella floods 3 thick mudstone facies with thin slope apron turbidite sands and an impoverished benthic planktonic assemblage of late cenomanian coniacian age deposited in an upper bathyal oxic dysaerobic environment where turonian sedimentation rates are low a planktonic foraminiferal assemblage with whiteinella hedbergella dicarinella and marginotruncana occurs 4 grayish laminated mudstones santonian campanian in age with local sands in the north a low diversity middle to upper bathyal benthic planktonic foraminiferal assemblage and an inoceramus prisms and radiolarian diatom flood a campanian agglutinated foraminiferal bloom also is known from the atlantic oceanic realm 5 more marly sediments of maastrichtian age with a low diversity planktonic benthic foraminiferal assemblage using the distribution of 1755 foraminiferal and dinoflagellate microfossil events in over 30 exploration wells a rasc ranking and scaling probabilistic zonation served as a template to build a cretaceous zonal model with 19 assemblage and interval zones including over 100 events variance analysis ranks 72 events according to reliability in correlation three new index taxa include uvigerinammina una and ammoanita globorotaliaeformis albian and fenestrella bellii campanian widespread planktonic flood events occur in late albian through early cenomanian early mid turonian late santonian earliest campanian and mid maastrichtian the result of northwards shifts of warmer water masses and disruptions in water stratification in the dysaerobic basins an earliest cretaceous hiatus separates jurassic from cretaceous strata ongoing block faulting coupled to thermal subsidence and global sealevel rise increased water depth in aptian albian time from neritic to bathyal and created sand accommodation space in dysaerobic restricted settings in cenomanian coniacian time sedimentation rates in the central basin increased 10 fold whereas paleo waterdepth did not deepen this relatively brief less than 10 m y tectonic episode resulting in deposition of deep water sands is tentatively linked to stress re orientation in the rockall area a widespread upper maastrichtian danian hiatus the result of shoulder uplift reflects break up prior to the onset of paleogene seafloor spreading in the norwegian sea

seismic evidence for a fossil mantle plume beneath south america and implications for plate driving forces a teleseismic travel time study reveals the presence of a fossil plume in the deep upper mantle beneath brazil which has apparently remained geographically fixed with respect to the overly ing continent despite thousands of kilometres of plate motion this result implies that the upper mantle and lithosphere beneath south america have remained coupled since the breakup of gondwanaland and may provide an answer to the long standing question of what forces drive continental plates

neodymium isotope evolution of nw tethyan upper ocean waters throughout the cretaceous neodymium isotope compositions of twenty four fish teeth nineteen from the nw tethys and five from different locations within the tethys are interpreted to reflect the evolution of tethyan upper ocean water composition during the cretaceous and used to track changes in erosional inputs to the nw tethys and in oceanic circulation throughout the cretaceous the rather high end up to 7 6 of the nw tethyan upper ocean waters recorded from the late berriasian to the early aptian and the absence of negative excursions during this interval support the presence of a permanent westward flowing tethys circumglobal current tcc this implies that temperature variations during this time period inferred from the oxygen isotope analysis of fish tooth enamel were not driven by changes in surface oceanic currents but rather by global climatic changes the results presented here represent a significant advance over previously published cretaceous seawater nd isotope records our newly acquired data now allow the identification of two stages of low end values in the nw tethys during the early albian middle albian interval down to 10 and the santonian early campanian down to 11 4 which alternate with two stages of higher end values up to 9 during the late albian turonian interval and the maastrichtian used in conjunction with the oxygen isotope record the fluctuations of end values can be related to major climatic oceanographic and tectonic events that appeared in the western tethyan domain d 2005 elsevier b v all rights reserved

a low velocity zone atop the transition zone in northwestern canada 1 seismic studies over the past decade have identified an s wave low velocity zone lvz above the transition zone at various locations around the globe this layer is hypothesized to be a lens of dense hydrous silicate melt ponding atop the 410 km discontinuity beneath the silicate melt density crossover predicted to exist within the upper mantle we have assembled a p and s receiver function data set to quantify the physical properties and geographical extent of the layer in northwestern canada geographic profiles formed from 1 d migration of receiver functions computed for the canadian northwest experiment canoe and portable observatories for lithospheric analysis and research investigating seismicity polaris slave arrays reveal an lvz beneath many stations at a nominal depth of 340 km to constrain layer thickness and poisson s ratio we performed a grid search over a suite of 1 d velocity profiles to model the relative delay times of direct conversions and reverberations from the top of the lvz and 410 km discontinuity as recorded at the yellowknife array in addition we performed linearized inversion of transmission coefficient amplitudes to estimate s velocity contrasts at the bounding interfaces the lvz is characterized by a thickness of 36 km with an s velocity contrast of 7 8 and poisson s ratio of 0 42 taken at face value the two latter results require an increase in p velocity into the lvz the poisson s ratio lies well above the iasp91 average of 0 29 0 3 for this depth range and favors the presence of high melt or fluid fractions

enstatite jadeite join and its role in the earth s mantle phase relations on the enstatite jadeite join were experimentally determined at solidus temperatures and 90 152 kb and at 1400 2050 c 175 219 kb with a split sphere anvil apparatus ussa 2000 new findings include immiscibility in garnet and determination of the stability of naalsio4 calcium ferrite structure with stishovite a thermodynamic model for the enstatite jadeite join was developed to calculate a complete phase diagram for the join at 500 2500 c and 0 270 kb the results indicate that the two major discontinuities in the earth s mantle at 400 and 670 km depths could correspond respectively to the formation and the breakdown of garnet with a pyroxene composition a model for a chondritic upper mantle is proposed in which large scale chemical and mineral layering was produced by fractionation of liquidus phases in a magma ocean solidification was completed at 400 km depth by crystallization of sodium enriched residual melts which produced a pyroxene layer at 300 400 km depths

development of polygonal fault systems a test of hypotheses polygonal networks of normal faults in layer bound sequences of fine grained mudstones have formed without regional tectonic extension the two leading hypotheses concerning the generic mechanism responsible for their development are 1 horizontal stresses are reduced by syneresis 2 coefficients of residual friction are very low to discriminate between these hypotheses the ratios between the minimum horizontal and the vertical effective stresses have been estimated in four north sea wells penetrating oligocene and miocene sequences that contain polygonal fault networks the effective stress ratios are c 0 8 consistent with very low coefficients of friction but not with syneresis

late cretaceous upwelling system along the southern tethys margin israel interrelationship between productivity bottom water environments and organic matter preservation organic rich upper cretaceous sequences in israel were deposited in an extensive highly productive upwelling linked system which prevailed along the southern tethys margin and lasted for 19 m y santonian to late maastrichtian an understanding of the spatial and temporal characteristics of this system was gained through detailed paleontological and geochemical analyses of subsurface sequences in two basins in israel representing an outer shefela and an inner zin facies belt the nature of the upwelling system and its effect on the sedimentary record is related to two basic environmental parameters namely paleoproductivity intensity and oxygen levels at the bottom the assessment of these parameters and their interrelationship has been performed through the development of paleontological foraminiferal criteria which are independent of the organic matter content following the establishment of these criteria it is concluded that the productivity reached its maximum intensity during the late campanian which was also the time of most notable differentiation between the center of the upwelling system in the inner belt and the less intense conditions in the outer basin this distribution is expressed in varied lithology organic rich carbonates phosphorites and siliceous rocks at the core of upwelling and a uniform lithology organic rich carbonates at the margin of this system the uniform lithology of the maastrichtian in both basins composed of organic rich carbonates is ascribed to a gradual weakening of productivity the bottom conditions in the inner belt during the late campanian the time of maximum surface productivity were near anoxic changing to more aerated dysaerobic conditions during the early maastrichtian in the outer belt a more aerated bottom dysaerobic prevailed throughout the late campanian to late maastrichtian the elevated organic matter content in both basins reflects the overall environment of high productivity its actual variations however seem to be unrelated to changes in surface productivity and bottom oxygen levels

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

neodymium isotopes as tracers in marine sediments and aerosols north atlantic nd and sm concentrations and nd isotopic compositions were measured on the detrital fraction of deep sea surface sediments and on aerosols sampled over the north atlantic and mediterranean sea the data expressed asend 0 and as model ages ranged from 14 5 end 0 4 9 and from 0 01 to 2 21 ga respectively two areas where the sediments contain relatively less radiogenic nd are to the west off north africa and eastward of the canadian shield this distribution is consistent with other tracers in suggesting that a significant fraction of the sediments are derived from aeolian material transported by major wind systems saharan dust transported in the equatorial trade winds belt and north american soil material transported in the latitudes of the westerlies between these aeolian dominated belts along an axis from the azores to gibraltar and the mediterranean lies a zone of more radiogenicend 0 values in sediments and aerosols influenced by the recent volcanism of this region previously reported distributions of nd isotopes in bottom formed iron manganese crusts and coatings are similar to distributions of nd isotope values in detrital sediments and aerosols this suggests that the detrital fraction has undergone partial dissolution and desorption in the water column and or in the pore waters of near surface sediments and that a significant proportion of nd in the authigenic ferromanganese phases is derived from this source and may therefore not represent strictly dissolved seawater nd isotope ratios useful as watermass tracers

understanding cratonic flood basalts the origin of continental flood basalts has been debated for decades these eruptions often produce millions of cubic kilometers of basalt on timescales of only a million years although flood basalts are found in a variety of settings no locale is more puzzling than cratonic areas such as southern africa or the siberian craton where strong thick lithosphere is breached by these large basaltic outpourings conventionally flood basalts have been interpreted as melting events produced by one of two processes 1 elevated temperatures associated with mantle plumes and or 2 adiabatic decompression melting associated with lithospheric thinning in southern africa however there are severe problems with both of these mechanisms first the rifting circumstances of several wellknown basaltic outpourings clearly reflect lithospheric control rather than the influence of a deep seated plume specifically rift timing and magmatism are correlated with stress perturbations to the lithosphere associated with the formation of collisional rifts second the substantial lithospheric thinning required for adiabatic decompression melting is inconsistent with xenolith evidence for the continued survival of thick lithosphere beneath flood basalt domains as an alternative to these models we propose a new two stage model that interprets cratonic flood basalts not as melting events but as short duration drainage events that tap previously created sublithospheric reservoirs of molten basalt formed over a longer time scale reservoir creation existence stage i requires long term e g 1 ma supersolidus conditions in the sublithospheric mantle that could be maintained by an elevated equilibrium geotherm appropriate for the archean a slow thermal perturbation e g thermal blanketing or large scale mantle upwelling or a subduction related increase in volatile content the drainage event stage ii occurs in response to an abrupt stress change in the lithosphere which leads to the initiation and propagation of lithospheric dikes such a model accounts for the short eruption time of flood basalts the evidence for lithospheric control of the eruptions and the continued survival of cratonic lithosphere following these magmatic events the most notable consequence of this model is that it implies the existence of large reservoirs of magma comparable to the eruption volume of flood basalts that have been and are still likely present beneath stable continental lithopshere

k o ocr relationships in soil the relationships between k o and ocr are investigated for primary loading unloading reloading conditions the study reviews laboratory data from over 170 different soils and presents an approach common to clays silts and sands simple empirical methods for predicting k o for normally consolidated and overconsolidated soils are evaluated the validity of the methods is supported by statistical analyses on the basis of the findings only the effective stress friction angle o and prior stress history ocr and ocrmax are needed to predict approximate values of k o

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

scattered wave imaging of the lithosphere asthenosphere boundary several recent studies have imaged discontinuities interpreted as the lithosphere asthenosphere boundary using receiver function methods these are exciting results since this boundary is fundamental and yet relatively elusive its location is not well imaged nor are its properties well understood the receiver function method provides high depth resolution and the multitude of studies using this method have increased lateral resolution a better global understanding of the location and nature of the boundary is developing which ultimately will have implications for mantle dynamics and planetary evolution however these new results do not all form a clear and consistent picture and in some cases introduce new complexities and questions some apparent contradictions may represent unmodeled earth structure overall interpretation and synthesis requires careful consideration of the approaches and sensitivities of individual studies

a review on the analysis of the crustal and upper mantle structure using receiver functions abstract the discontinuities in the earth such as moho lithosphere asthenosphere boundary lab 410 and 660 km discontinuities are characterized with an abrupt jump in velocities of p and s waves the depths of these discontinuities are an important parameter to investigate tectonic evolution in the lithosphere receiver functions technique with teleseismic events is very suitable for studying the crust and upper mantle structure beneath stations thus becoming one of the standard tools for such study the principle of receiver functions is to separate the converted ps or sp phases generated at the discontinuities beneath stations in the case that the direct p or s is a delta function in this paper the methods of receiver function analysis are collected from literatures we introduce the coordinate transform technique for the separation of ps or sp waves the deconvolution algorithm to extract p and s receiver functions the waveform fitting method to invert for s wave velocity structure the stacking technique to improve signals and the migration from time series to depth domain with some illustrative examples the care that should be taken in study of the crustal and upper mantle structure using receiver functions are summarized

glacial interglacial variations in the neodymium isotope composition of seawater in the bay of bengal recorded by planktonic foraminifera this study presents neodymium isotope and elemental data for cleaned planktonic foraminifera from odp site 758 in the southernmost reaches of the bay of bengal in the north east indian ocean cleaning experiments using oxidative reductive techniques suggest that diagenetic fe mn oxyhydroxide coatings can be effectively removed and that the measured nd isotope composition reflects the composition of seawater from which the foraminiferal calcium carbonate was precipitated modern core top pulleniatina obliquiloculata and globorotalia menardii give end values of 10 12 0 16 and 10 28 0 16 respectively indistinguishable from recent direct measurements of surface seawater in this area a high resolution nd isotope record obtained from g menardii for the past 150 kyr shows systematic variations end 3 on glacial interglacial timescales the timing of those variations shows a remarkable correspondence with the global oxygen isotope record which suggests a process controlling the nd isotope composition that responds in phase with global climate cycles palaeoclimate reconstruction indicates that during the last glacial maximum changes in monsoon circulation resulted in a reduction in rainfall over the indian subcontinent and a decrease in the flux of river water delivered to the bay of bengal thus changes in the riverine input of nd a change in either flux or composition most likely caused the isotope variations although changes in dust source or local ocean circulation may have also played a role these results clearly establish a link between climate change and variations in radiogenic isotopes in the oceans and illustrate the potential of nd isotopes in foraminifera for high resolution palaeoceanographic reconstruction

measurement of diagenetic compaction strain from quantitative analysis of fault plane dip we developed a new technique for quantifying the amount of porosity loss during diagenetic transformation of opal a to opal ct the technique is based on 3d seismic data from offshore norway where the widely developed biosiliceous sediments of the brygge formation are deformed by a polygonal fault system evidence is shown from two study areas that the dip of the polygonal fault planes reduces abruptly across the opal a to opal ct diagenetic boundary suggesting that the fault planes were passively rotated into shallower dips due to diagenesis the reduction of fault plane dip was used to quantify the vertical compaction strain due to diagenesis using an independent assessment of the magnitude of the porosity loss we are able to validate the method based on fault plane dips and also to evaluate whether the porosity loss results in an exclusively vertical strain additionally the impact of silica diagenesis on the shear strength of the sediments and fault growth is investigated we present evidence suggesting that deviations from classical mohr coulomb behaviour may be expected during the combined processes of diagenesis and porosity collapse and may indeed be sufficient to promote continued fault growth

converted waves reveal a thick and layered tectosphere beneath the kalahari super craton abstract thick and high velocity roots are generally observed beneath the archean cratons inside these high velocity keels velocity contrasts are detected neither by surface nor by body waves tomographies we present here evidences based on the s to p and p to s converted waves for the existence of an irregularly stratified and thick keel beneath the kalahari super craton to satisfy surface wave data and s to p conversions the velocity model should have beneath the moho a 160 km thick anisotropic structure with vertical slow axis and decreasing anisotropic parameters with depth such a structure may stem from the preferred orientation of olivine 100 axis in the horizontal plane under shearing deformation this structure together with the 100 km thick layer underlying it forms a 300 km thick continental root beneath the cratons inside this root the p and s velocities should be higher on average respectively by an amount of 6 and 4 than the ak135 velocity model beneath 300 350 km depth a low velocity zone is clearly detected that may be either the remainder of large magma reservoirs related to cratonic flood basalts or a melted silicate layer created by the transformation just above the 410 km deep discontinuity of wadsleyite assembly to olivine assembly

global scale analysis of the mantle pds phases a global scale analysis of travel times of the mantle pds phases converted from p to s from the discontinuity at a depth d beneath the receiver is presented most of the data are related to p 410 s and p 660 s recorded by the broadband stations of geoscope incorporated research institutions for seismology iris and other networks in order to provide a good global scale coverage published measurements at 37 stations are complemented by our measurements at 45 stations lateral resolution of our data is many times higher than that of ss and its precursors previously used for similar purposes but we have fewer data in the oceans lateral variations of travel times of the major pds phases are strongly correlated with the lateral p and s velocity variations in the uppermost mantle as revealed by tomographic studies the scaling coefficient between the teleseismic s and p residuals as found from the variations of travel times of the major pds phases is around 3 7 for north america and around 3 3 for the rest of the world almost all the differential travel times t p 660 s t p 410 s are in the range of 1 s relative to the average value of 24 0 s if the lateral variations of the velocities within the mantle transition zone mtz can be neglected the corresponding variations of thickness of the mtz are in the range of 10 km relative to the standard depth of 250 km and do not show significant correlation with either velocities in the upper mantle above the mtz or with the variations of thickness of the mtz as found in some recent studies of precursors to ss there is a weak but marginally significant positive correlation between the variations of thickness of the mtz inferred from our data and the s velocity variations in the mtz as given by su et al 1994 this correlation suggests that both variables contain temperature dependent components lateral variability of the mtz is also manifested by extreme weakness of p 410 s at several locations this may indicate either anomalous topography on 410 km discontinuity or strong broadening of the otherwise sharp discontinuity at some stations there are arrivals that can be interpreted as p 520 s this interpretation implies that the strengh and or sharpness of 520 km discontinuity as well as its depth are laterally variable in a broad range

structure of the kaapvaal craton from surface waves phase delays of rayleigh and love waves from teleseismicearthquakesrecordedduringthesouthernafrica seismic experiment have been inverted for upper mantle seismic velocities along the propagation paths and beneath the station array successful models of subarray struc turedisplayedsignicantradialanisotropyintheuppermost mantle but no shear wave low velocity zone supporting the hypothesisthatthelithospherebeneaththekaapvaalcraton isthick theazimuthalvariationsofrayleigh waveslowness are not consistent with simple models based onskssplit tingobservationsandanisotropy measurementsofkaapvaal mantlexenoliths thisdiscrepancymayimplysomeamount of small scale heterogeneity in anisotropy

reactive infiltration of hydrous melt above the mantle transition zone 1 seismic studies repeatedly image a low velocity layer overlying the mantle transition zone in tectonic settings ranging from subduction zones to continental cratons this layer has been hypothesized to result from the presence of a dense partial melt formed by dehydration melting as relatively wet transition zone material is advected by convection currents into the low water solubility upper mantle here we examine this hypothesis by considering the dynamic infiltration of a low viscosity reactive hydrous melt into a high viscosity ambient solid the thickness of the melt layer is strongly controlled by return flow induced in the surrounding viscous solid and in steady state a dynamic equilibrium is achieved where the melt lens is restrained from collapse by the exterior mantle melt layers with thicknesses in excess of 10 km develop for a wide range of mantle parameters and develop on timescales equivalent to the lifespan of an ocean basin

multiresolution imaging of mantle reflectivity structure using ss and p p precursors summary knowledge of the mantle reflectivity structure is highly dependent on our ability to efficiently extract and properly interpret small seismic arrivals among the various data types and techniques long period ss pp precursors and high frequency receiver functions are routinely utilized to increase the confidence of the recovered mantle stratifications at distinct spatial scales however low resolution and a complex fresnel zone are glaring weaknesses of ss precursors while over reliance on receiver distribution is a formidable challenge for the analysis of converted waves from oceanic regions a promising high frequency alternative to receiver functions is ppprecursors which are capable of resolving mantle structures at verticalandlateralresolutionof 5and 200km respectively owingtotheirspectralcontent shallow angle of incidence and near symmetric fresnel zones this study presents a novel processing method for both ss or pp and ppprecursors based on deconvolution stacking radon transform and depth migration a suite of synthetic tests is performed to quantify the fidelity and stability of this method under different data conditions our multiresolution survey of the mantle at targeted areas near nazca south america subduction zone reveal both olivine and garnet related transitions at depths below 400km we attribute a depressed 660 to thermal variations whereas compositional variations atop the upper mantle transition zone are needed to explain the diminished or highly complex reflected scattered signals from the 410km discontinuity we also observe prominent ppreflections within the transition zone and the anomalous amplitudes near the plate boundary zone indicate a sharp 10km thick transition that likely resonates with the frequency content of ppprecursors the migration of ss precursors in this study shows no evidence of split 660 reflections but potential majorite ilmenite 590 640km and ilmenite perovskite transitions 740 750km areidentifiedbasedonsimilarlyprocessedhigh frequencyppprecursors additionalfindings of severely scattered energy in the lithosphere and distinct lower mantle reflections at 800km could be potentially important but require further verifications overall our improved imaging methods and the strong sensitivity of ppprecursors to the existence depth sharpness and strengthofreflective structuresoffersignificant futurepromisefortheunderstanding ofmantle mineralogy and dynamics

extensional layer parallel shear and normal faulting abstract an extensional fault system in bare mountain nevada u s a contains abundant evidence of layer parallel shear deformation contemporaneous with faulting layer parallel shear is manifest by deformation of pre faulting fabrics and cleavage at low angles to bedding that indicate shear in the down dip direction perpendicular to fault bedding intersections layer parallel shear along discrete bedding planes locally offsets normal faults and shear distributed within layers reorients block bounding normal faults in simple rigid block models of extension accommodated by normal faults above a low angle detachment or decollement extension causes faults to rotate to progressively shallower dips while originally horizontal beds rotate to steeper dips these rotations reorient faults out of originally optimum conditions for slip into orientations of a lower slip tendency whereas bedding rotates to steeper dips with progressively higher slip tendency the timing or amount of rotation before the initiation of layer parallel shear depends on the frictional resistance to sliding or resistance to shearing within layering in fault blocks offset or deflection of block bounding normal faults may cause faults to lock as extension increases alternatively bedding and faults may become simultaneously active progressively lowering dips of faults and bedding until neither is well oriented for slip at which point new faults are required to accommodate additional extension at bare mountain early extension within the fault system was accomplished by fault slip and associated block rotation continued extension took place by slip along bedding within fault blocks

mid cretaceous ocean circulation results from model sensitivity studies a series of ocean general circulation model gcm experiments for mid cretaceous continental paleogeography with atmospheric forcing prescribed from atmospheric gcm experiments are utilized to investigate the nature of the mid cretaceous ocean circulation the experiments illustrate a tethys system of clockwise currents and predominant eastward flow in marked contrast with earlier reconstructions this result is apparently robust for changes in bathymetry and in the degree of planetary warmth changes in sea level have the largest potential to produce alternative circulation characteristics two major current systems outside of tethys dominate the model simulation the site of bottom water formation is the north pacific however in a sensitivity experiment for a warmer climate the eastern tethys became a site of deep water formation

deep structure of the afro arabian hotspot by s receiver functions 1 we investigated deep structure of the afro arabian hotspot by using recordings from geoscope seismograph station atd the records are processed with the s receiver function technique which allows a detection of sp converted phases from the upper mantle discontinuities the seismic data reveal two unusual discontinuities the discontinuity at a depth of 160 km beneath the gulf of aden corresponds to the onset of melting if the water content in olivine is around 800 h 106si melting at this depth requires a temperature close to 1550 c about 120 c higher than the average another remarkable discontinuity is found at a depth of 480 km where s velocity drops with depth by about 0 2 km s this can be the head of another plume which is trapped in the mantle transition zone

senonian basin inversion and rejuvenation of rifting in africa and arabia synthesis and implications to plate scale tectonics abstract the late paleozoic to tertiary stratigraphic record of much of the african plate reflects the effects of continental rifting and passive margin development several short lived but widespread and tectonically important compressional or wrench dominated events occurred however during the permian to recent evolution of africa we focus here on the best documented of these events which occurred during the late santonian at that time older sedimentary basins mostly ene wsw trending were folded and inverted including some basins along the tethyan margin from morocco to the syrian arc and the intraplate benue southern chad basins and the lugh mandera basin in oman ophiolites were obducted following the santonian tectonism an extensive phase of rifting occurred in central and north africa and northern arabia spanning from campanian to maastrichtian or paleocene times rejuvenation or acceleration of subsidence occurred in several basins located along the tethyan margin along the atlantic and indian ocean margins as well as within the intraplate domain rifting was sometimes accompanied by magmatic activity especially in offshore northern libya and along the indian ocean margin compressional deformations rejuvenated or developed by latest maastrichtian times along the tethyan margin and locally within the intraplate domain one of the most remarkable attributes of the santonian tectonic event which we consider representative of the major trans african stress field changes is the rapidity with which the change was reflected stratigraphically across north and central africa and its short duration the cause of the santonian compressional event is directly linked to the change in poles of rotation for the opening of the atlantic at 83 85 ma the end of the cretaceous normal magnetic quiet zone this was also synchronous with the obduction of ophiolites along the northeast margin of arabia oman the onset of separation between india and madagascar with formation of the mascarene oceanic basin and the development of the european alpine chain we interpret these phenomena as causally related aspects of a global tectonic event the santonian compressional event as well as the campanian maastrichtian rifting event and the end cretaceous compressional event illustrate the critical connection between intraplate tectonic histories and processes occurring at sometimes very distant plate boundaries

polygonal fault systems and channel boudinage 3d analysis of multidirectional extension in analogue sandbox experiments abstract a systematic set of analogue models has been carried out to study the structural evolution of a sedimentary pile consisting of superposed brittle and ductile lithologies in a regional context of passive margins the models are composed of silicone representing a ductile basal layer of evaporites or overpressured shales and sand progressively sedimented on top to simulate brittle overburden sediments channels with various shapes are embedded in the silicone deformation is triggered by gravitational instability of the growing sedimentary pile and basal slope angles ranging from 0 to 5 the main results follow a polygonal fault pattern developed due to the 3d boudinage of the overburden sand above the silicone layer during multidirectional extension if a sandy channel was embedded in the ductile base it was immediately cut by faults which were perpendicular to the channel boundaries no matter what the angle between channel and slope direction the boundaries of the channel preferentially localised faults which propagated through the sedimentary pile above ongoing deformation along these faults therefore strongly influenced further accumulation of sediments

mantle discontinuities beneath the deccan volcanic province abstract mantle discontinuities beneath the deccan volcanic province dvp are imaged using about 900 seismograms from a network of six broadband stations deployed in the dvp along a 350 km long north south profile paralleling the west coast of india teleseismic receiver function analysis of the data enabled distinct identification of the moho 410 and 660 km discontinuities presence of sub moho low velocity zones with velocity reductions in the range of 0 1 0 4 km s have been brought out through modeling of receiver function stacks at individual stations the arrival times of p410s and p660s are normal as predicted by the iasp91 model and the mantle transition zone thickness is 252 km which is close to the global average this study reveals that the upper mantle beneath dvp south of the narmada rift does not exhibit any anomalous signatures associated with a mantle plume a shield like lithosphere coupled with the presence of an upper mantle low velocity zone confined to shallow depths beneath dvp imposes constraints on the mechanisms feasible for deccan volcanism the present study does not favour the plume impact plume incubation models instead necessitates searching for clues offshore west coast of india and exploring alternate mechanisms

studying the 410 km and 660 km discontinuities beneath spain and morocco through detection of p to s conversions this is a contribution of the projects consolider ingenio 2010 topoiberia csd2006 00041 topomed cgl2008 03474 e bte rifsis cgl2009 09727 cgl2012 31472 and p09 rnm 5100 l bonatto benefits from a ph d jaepredoc csic grant

influence of stratigraphic setting and simple shear on layer bound compaction faults offshore mauritania abstract we have used three dimensional seismic data to examine the geometry of layer bound compaction faults on the mauritanian continental margin the faults deform a fine grained neogene unit which mantles buried canyons above the canyons most layer bound faults strike perpendicular to the canyon axes whereas adjacent to the canyons the faults are omni directional and intersect bedding planes in polygonal patterns on the flanks of a large structural high faults also strike perpendicular to the slope direction displaying a concentric pattern faults that show preferential alignment are located in areas with increased bedding dip and most aligned faults are antithetic to the bedding dip where the bedding dip is greater than 1 the synthetic faults dip more steeply than the antithetic faults this discovery was unexpected because the stress tensor due to the effect of gravity on a dipping margin would cause the antithetic faults to form with steeper dips which we show theoretically we hypothesise that the layer hosting the faults has been subjected to simple shear of 20 or more with the top of the layer displaced downdip by 100 m relative to its base a potential application of these and similar observations is to assess slope stability on continental margins

the s receiver functions synthetics and data example summary recently the s receiver function method has been successfully developed to identify upper mantle interfaces s receiver functions have the advantage of being free of s wave multiple reflections and can be more suitable than p receiver functions for studying mantle lithosphere however because of specific ray geometry and interference of diverse phases the s receiver function method has some technical difficulties and limitations we use synthetic seismograms to demonstrate the feasibility and limitations of s receiver functions for studying mantle structures full wavefield seismograms were calculated using the reflectivity method and processed to generate synthetic s receiver functions for s sks and scs waves results show that s receiver functions can be obtained from waveforms of s sks and scs waves the synthetic s receiver functions for these incident waves show s to p converted phases at all discontinuities in the crust and upper mantle useful ranges of epicentral distances for calculation of s receiver functions are 55 85 for s 85 for sks and 50 75 for scs waves we apply both the s and p receiver function methods to data recorded at broadband station ykw3 in northwest canada the study shows that there is significant agreement among different receiver function methods and demonstrates the usefulness of s receiver functions for imaging the mantle lithosphere

observations of s410p and s350p phases at seismograph stations in california 1 we analyze a new set of seismic data from seismograph stations in california this data set consists of nearly 5000 s receiver functions for 47 seismograph stations as a rule the stacked srfs display a distinct s410p seismic phase s wave converted to p at the 410 km discontinuity the wave paths of s410p sample the upper mantle beneath california and the neighboring region of the pacific in northernmost california the s410p travel times are close to those of the iasp91 global model further south s410p usually arrives about 2 s earlier than predicted by the iasp91 model this early arrival can be explained either by an anomalously high vp vs velocity ratio 1 9 in a 125 km thick layer of the upper mantle versus 1 8 in iasp91 by a depression of the 410 km discontinuity of 15 km or by a combination of both effects with smaller amplitudes we observe systematically s350p phase which is converted from a negative discontinuity with a lower s velocity at the lower side near a depth of 350 km the observations of s350p are indicative of a low s velocity layer a few tens of kilometers thick atop the 410 km discontinuity beneath southern california and the neighboring oceanic region some receiver functions also display s480p phase which is interpreted as evidence of an intermittent low velocity layer in the transition zone

receiver function tomography of the central tien shan abstract to obtain an image of the deep structure of the tien shan in central asia we invert p and s receiver functions jointly for almost 40 local broad band seismograph stations the inversion is performed using a simulated annealing technique the combined inversion is an improvement on earlier studies where p and s receiver functions were inverted separately using this approach we deal with structural imaging problems that are usually investigated with teleseismic body wave and surface wave tomography techniques we demonstrate that the uppermost mantle in the north of the central tien shan is composed of a high velocity lid a few tens of kilometers thick above a pronounced low velocity zone the crustal structure in this region provides evidence of magmatic underplating these features are likely related to a small plume that is manifested by basaltic eruptions of cretaceous paleogene age the low velocity layer is also found in a southeast trending corridor which may correspond to the bachu uplift in the tarim basin crustal thickness beneath the orogen varies from about 45 to about 70 km the smallest values most likely inherited from the pre orogenic era are found in a neighborhood of the talas fergana fault similar values are characteristic of the kazakh shield in the north and the tarim basin in the south the largest values are found beneath the bounding ranges we infer that uplift of the central tien shan is unlikely to be caused by crustal shortening alone

lithospheric and upper mantle structure of the northeastern tibetan plateau 1 we use receiver functions calculated for data collected by the indepth iv seismic array to image the three dimensional geometry of the crustal and upper mantle velocity discontinuities beneath northeastern tibet our results indicate an average crustal thickness of 65 to 70 km in northern tibet in addition we observe a 20 km moho offset beneath the northern margin of the kunlun mountains a 10 km moho offset across the jinsha river suture and gently northward dipping moho beneath the qaidam basin a region in the central qiangtang terrane with higher than normal crustal vp vs ratio of 1 83 can be the result of the eocene magmatic event in the qiangtang terrane we observe a significant lithospheric mantle discontinuity beneath the bangong nujiang suture at 80 km depth which dips 10 to the north reaching 120 km depth we interpret this feature as either a piece of lhasa terrane or remnant oceanic slab underthrust below northern tibet we detect a 20 km depression of the 660 km discontinuity in the mantle transition zone beneath the northern lhasa terrane in central tibet which suggests this phase transition has been influenced by a dense and or cold oceanic slab a modest 10 km depression of the 410 km discontinuity located beneath the northern qiangtang terrane may be the result of localized warm upwelling associated with small scale convection induced by the penetration of the sinking indian continental lithosphere into the transition zone beneath the central tibetan plateau

relationship between polarity of extensional fault arrays and presence of detachments abstract extensional fault arrays are often dominated by a single fault vergence forming domino fault blocks the polarity of faults can be defined as synthetic or antithetic in relation to the overall shear sense across the fault system observations of the geometry of a number of field examples of extensional fault arrays vs the lithologies as a proxy for strength profile show that synthetic extensional arrays from the north sea and bristol channel basin detach on salt layers whereas examples of antithetic arrays from the north sea are found to pin out downwards and no basal detachment is present in the sacramento mountains core complex of the basin and range the major low angle detachment fault post dates antithetic shears that evolved at mid crustal level and are preserved in the granitic footwall these antithetic shears were cut by the main low angle detachment whose hanging wall disintegrated into an array of synthetic faults the kinematics of synthetic vs antithetic arrays dictate that faults within synthetic arrays must branch onto a basal detachment whereas faults within antithetic arrays may die out downwards therefore the results emphasise that fault polarity in domino arrays may be related to the boundary conditions of the fault blocks and therefore may be diagnostic of the strength profile of the faulted stratigraphy

lehmann discontinuity beneath north america no role for seismic anisotropy 1 the lehmann discontinuity in the upper mantle is often interpreted as a boundary separating anisotropic and isotropic media we demonstrate however that seismic anisotropy plays if any a minor role in the origin of the lehmann discontinuity our data are obtained with s receiver function technique from recordings of the moma seismograph array in the eastern usa part of the data is processed with a new modification of this technique we observe sp phase converted from the lehmann discontinuity at a depth around 200 km with comparable amplitudes and similar polarities in two azimuths differing by about 90 contrary to the observations the polarity in the synthetic seismograms for models with azimuthal anisotropy is opposite for the azimuths differing by 90 radial anisotropy with a slow vertical direction results in the sp phase with the polarity opposite to the observed one

the melt content of the low velocity layer in the eastern south china implications for the subduction process of the western pacific plate abstract the low velocity layer lvl atop the mantle transition zone involves diapiric segregating melt upwelling mantle mixing magmatic eruption and the remnants the lateral variations of the lvl could record the process of the subducting plates the lvl beneath the eastern south china intensively affected by the subduction of western pacific plate since mesozoic is imaged with observed p wave triplications recorded by the dense chinese digital seismic network the thicknesses of the lvl are 57 km for sub region a 40 km for sub region b and 20 km for sub region c the melt fractions related to the different velocity structures of the lvl beneath three north to south adjacent sub regions a b and c of the eastern south china are estimated with the bulk solid compositions reference potential temperatures compositions and dihedral angles the spatial characteristics of the melt fractions and the lvl thicknesses are in accord with the recession directions of the subduction fronts of the western pacific plate this consistency provides a powerful information for understanding the plate subduction process

mantle anomalies beneath southern africa evidence from seismic s and p receiver functions summary to understand deep structure and processes beneath southern africa we apply the doublestacking version of the s receiver function srf technique to the recordings of the south african seismic experiment in this technique the wavefields of s and sks are separated by space time filtration and the receiver functions are constructed separately for the s and sks seismic phases the results are consistent with those obtained from the srfs of the permanent stations bosa and lbtb evidence for a reduced s velocity atop the 410 km discontinuity is present in both srfs and p receiver functions the s velocity contrast at the 410 km discontinuity is 40 per cent larger than the norm and there are observations of s350p and p350s seismic phases from the negative 350 km discontinuity beneath the kaapvaal craton the s350p and p350s phases display a dependence on the azimuth which can be caused by anisotropy in the layer atop the 350 km discontinuity this dependence is consistent with observations of shear wave splitting in sks there are observations of the s450p phase from the 450 km negative discontinuity in the transition zone the most anomalous transition zone is found close to the region where the kalahari craton was located in the mesozoic lateral variations of the s velocity are found beneath the 660 km discontinuity teleseismic s and p traveltime residuals with respect to iasp91 model are evaluated from the traveltimes of the p410s and pp410s seismic phases in the uppermost mantle these residuals as well as s410p traveltimes require a reduced vp vs ratio around 1 75 0 01 versus 1 8 in iasp91 an effect of the depletion of the mantle lithosphere in basaltic material in the models obtained by a joint inversion of the receiver functions and the teleseismic traveltime residuals the low velocity zone lvz with the onset of low velocity at a depth of 140 20 km is present at most locations the minimum s velocity in the lvz is 4 5 km s 1 the lvz in our models is consistent with the s velocity vp vs velocity ratio and depth range of high temperature lerzholites in the mantle xenoliths from southern africa our most intriguing finding is a very low quality factor qs on the order of a few tens in the upper mantle we interpret high attenuation the lvz and the low s velocity atop the 410 km discontinuity as the effects of plume like phenomena in the upper mantle

outer slope faulting associated with the western kuril and japan trenches summary elongated fault escarpments on the outer slopes of the western kuril and japan trenches have been investigated through detailed swath bathymetric mapping numerous horsts and grabens formed by these escarpments were identified distinct n70 e linear alignment of the escarpments parallel to the magnetic anomaly lineations was revealed on the outer slope of the western kuril trench in the japan trench north of 39 00aen most of the escarpments are parallel to the trench axis and oblique to the magnetic lineations a zig zag pattern of faulting exists south of 39 00aen each topographic profile was decomposed by computer analysis into two curves representing 1 the smoothed long wavelength slope of the subducting ocean crust surface and 2 the short wavelength 10 km roughness of plateaus and valleys edged by outwardand inward facing fault escarpments throughout the surveyed areas escarpment heights increase from the crest of the trench outer swell down to a depth of about 6000 m on the slope of the outer trench wall but with no distinct increase below that depth no significant diverence is recognized in fault throws towards and away from the trench it can be concluded that these elongated escarpments originate from normal faults on the upper layer of the oceanic crust under extensional stress in a direction perpendicular to the trench axis which is caused by downward bending of the subducting lithosphere the relationship of escarpment height to escarpment length is similar to that obtained from normal fault escarpments in the east pacific rise crest the maximum length and height of escarpments are small in the kuril trench compared with those in the japan trench implying a diverence in mechanical strength depending on the fault orientation the crust is weakest along the inherited spreading fabric second weakest probably along the non transform ovset direction and strongest in directions very oblique to these orientations seamounts appear to be more rigid than normal ocean crust with no particular weak orientations resulting in fewer but larger faults along the axis of plate bending as most clearly represented in the subducting daiichi kashima seamount

the lithosphere asthenosphere boundary beneath the western united states summary s receiver functions from 67 broad band seismic stations in the western united states clearly reveal the existence of a mantle discontinuity with velocity reduction downward which we interpret as the lithosphere asthenosphere boundary lab the average depth of the lab is 70 km the boundary is relatively sharp with an overall sharpness of less than 20 km the boundary is more prominent south of the mendocino triple junction where the farallon plate has completely subducted this may indicate partial melts at the base of the lithosphere caused by the upwelling of the asthenospheric flow through the slab window a double low velocity zone is observed at base of the lithosphere beneath southern sierra nevada implying a second melting zone at a depth of 100 km well correlated with previous studies of lithospheric delamination in the area

seismic evidence for a global low velocity layer within the earth s upper mantle above the 410 km discontinuity in the upper mantle an intermittent layer characterized by low seismic wave velocities is thought to represent partial melting in areas of subduction or mantle plume activity seismic data now show that the low velocity layer extends globally with no affinity to a particular tectonic environment

implications of passive salt diapir kinematics for reservoir segmentation by radial and concentric faults abstract reservoirs associated with salt diapirs that are circular or elliptical in plan view can be segmented by radial faults concentric faults both or neither explanations for this variation are offered based on integration of fault kinematics published studies and seismic examples strata around diapirs can be divided into three structural domains with characteristic fault styles 1 roof zone between the present day depositional surface and crest of a buried inactive diapir this zone is characterised by doming radial faults and occasionally conic graben doming is usually caused by differential compaction and increases with depth 2 a steeply dipping sheath of strata surrounds the diapir out to a distance of less than one diapir radius recording near surface diapir growth in poorly lithified sediments these contain early gravity slumps and late concentric extensional faults regional layer bound polygonal fault systems form radial faults within approximately one diapir radius the only significant radial faulting mechanism below the roof zone 3 diapir root zone of strata whose structural architecture records the diapirs initiating mechanism typically rim synclines or graben that detach on the salt source layer concentric faults at radial distances of a kilometre or more have been found only in root zone rim synclines and sheared sheath strata these models and observations can assist seismic interpretation and structural model building in areas of poor geophysical imaging for instance below overhanging salt

a sporadic low velocity layer atop the 410 km discontinuity beneath the pacific ocean waveforms of ss precursors recorded by global stations are analyzed to investigate lateral heterogeneities of upper mantle discontinuities on a global scale a sporadic low velocity layer immediately above the 410 km discontinuity lvl 410 is observed worldwide including east asia western north america eastern south america the pacific ocean and possibly the indian ocean our best data coverage is for the pacific ocean where the lvl 410 covers 33 50 of the resolved region lateral variations of our lvl 410 observations show no geographical correlation with 410 km discontinuity topography or tomographic models of seismic velocity suggesting that the lvl 410 is not caused by regional thermal anomalies we interpret the lvl 410 as partial melting due to dehydration of ascending mantle across the 410 km discontinuity which is predicted by the transition zone water filter hypothesis given the low vertical resolution of ss precursors it is possible that the regions without a clear lvl 410 detection also have a thin layer therefore the strong lateral heterogeneity of the lvl 410 in our observations suggests partial melting with varying intensities across the pacific and further provides indirect evidence of a hydrous mantle transition zone with laterally varying water content

super deep low velocity layer beneath the arabian plate 1 s and p receiver functions reveal indications of a low s velocity layer at 350 410 km depths beneath the arabian plate a similar layer was previously found beneath the kaapvaal craton in southern africa and tunguska basin of the siberian platform we hypothesize that the boundary at 350 km depth may separate dry mantle root of the arabian plate from the underlying wet mantle layer this boundary is not found beneath the gulf of aden where the root is destroyed by sea floor spreading

subcratonic low velocity layer and flood basalts 1 teleseismic recordings of several seismograph stations are processed with the aid of the s receiver function technique farra and vinnik 2000 the data provide evidence of a strong reduction of s velocity at a depth around 360 km station bosa and 280 300 km station lbtb in the east of southern africa a similar feature is found in the tunguska basin of the siberian platform from the recordings of station nril in both regions large volumes of flood basalts have been erupted 190 180 ma and 250 ma ago respectively the coincidence suggests a causal relation between the two phenomena this relation implies that the low velocity anomalies migrate with the plates

high resolution 3d seismic data indicate focussed fluid migration pathways above polygonal fault systems of the mid norwegian margin seismic attribute analysis and interpretation of high resolution 3d and 2d seismic data reveal focussed fluid flow processes through the gas hydrate stability zone ghsz at the northern flank of the giant storegga slide diffusive fluid migration predominantly starts from a widespread polygonal fault system in fine grained sediments of the miocene kai formation the overlying 600 700 m thick plio pleistocene naust formation shows spatially related soft sediment deformation and overlying fluid conduits a low relief antiform structure connects to an overlying 250 m high 300 m wide and 3 km elongated columnar zone where seismic signatures suggest self enhanced permeability i e natural hydraulic fracturing push down effects create an elongated depression caused by increased gas accumulations where a cluster of vertical cylindrical acoustic pipe structures originates these pipe clusters pierce the ghsz and indicate focussed fluid flow pathways originating from potentially overpressured sediments high seismic reflection amplitudes at the seafloor above the pipe structures may indicate pockmarks with authigenic carbonates and or gas hydrates the observed objects and seismic features presented are not stand alone indicators for fluid flow but a joint perspective illustrates that they are vertically tied together providing new insights to the effects of focussed fluid flow

seismic shear wave reflectivity structure of the mantle beneath northeast china and the northwest pacific 1 using multiple scs reverberations we examine the mantle reflectivity structure beneath northeast china and the northwest pacific we find several upper mantle discontinuities including a melt layer with a mean thickness of 64 km atop the 410 km discontinuity present on both sides of the subducting slab near the nankai trench the transition zone contains a split 520 km discontinuity in several paths and tomographic images show stagnant slabs at this depth we believe that this may be slab related based on experimental work a negative reflector is found in one path beneath the northeast china craton at a depth of 598 km mid mantle reflectors are found in all of our paths and are present throughout a wide depth range 750 1600 km

velocity structure of the mantle transition zone beneath the southeastern margin of the tibetan plateau abstract p wave triplications related to the 410 km discontinuity the 410 were clearly observed from the vertical component seismograms of three intermediate depth earthquakes that occurred in the indo burma subduction zone ibsz and were recorded by the chinese digital seismic network cdsn by matching the observed p wave triplications with synthetics through a grid search we obtained the best fit models for four azimuthal profiles i iv from north to south to constrain the p wave velocity structure near the 410 beneath the southeastern margin of the tibetan plateau tp a ubiquitous low velocity layer lvl resides atop the mantle transition zone mtz the lvl is 25 to 40 km thick with a p wave velocity decrement ranging from approximately 5 3 to 3 6 related to the standard earth model iasp91 an abrupt transition in the velocity decrement of the lvl was observed between profiles ii and iii we postulate that the mantle structure beneath the southeastern margin of the tp is primarily controlled by the southeastern extrusion of the tp to the north combined with the eastward subduction of the indian plate to the south but not affected by the emeishan mantle plume we attribute the lvl to the partial melting induced by water and or other volatiles released from the subducted indian plate and the stagnant pacific plate but not from the upwelling or the remnants of the emeishan mantle plume a high velocity anomaly ranging from approximately 1 0 to 1 5 was also detected at a depth of 542 to 600 km providing additional evidence for the remnants of the subducted pacific plate within the mtz

preservation of seawater sr and nd isotopes in fossil fish teeth bad news and good news abstract we analyzed 87sr 86sr ratios in foraminifera pore fluids and fish teeth for samples ranging in age from eocene to pleistocene from four ocean drilling program sites distributed around the globe site 1090 in the cape basin of the southern ocean site 757 on the ninetyeast ridge in the indian ocean site 807 on the ontong java plateau in the western equatorial pacific and site 689 on the maud rise in the southern ocean sr isotopic ratios for dated foraminifera consistently plot on the global seawater sr isotope curve for sites 1090 757 and 807 sr isotopic values of the pore fluids are generally less radiogenic than contemporaneous seawater values as are values for fossil fish teeth in contrast pore fluid 87sr 86sr values at site 689 are more radiogenic than contemporaneous seawater and the corresponding fish teeth also record more radiogenic values thus sr isotopic values preserved in fossil fish teeth are consistently altered in the direction of the pore fluid values furthermore there is a correlation between the magnitude of the offset between the pore fluids and the seawater curve and the associated offset between the fish teeth and the seawater curve these data suggest that the hydroxyfluorapatite of the fossil fish teeth continues to recrystallize and exchange sr with its surroundings during burial and diagenesis therefore sr chemostratigraphy can be used to determine rough ages for fossil fish teeth in these cores but cannot be used to fine tune age models in contrast to the sr isotopic system our nd concentration data combined with published isotopic and rare earth element data suggest that fish teeth acquire nd during early diagenesis while they are still in direct contact with seawater the concentrations of nd acquired at this stage are extremely high relative to the concentrations in surrounding pore fluids as a result nd isotopes are not altered during burial and later diagenesis therefore fossil fish teeth from a variety of marine environments preserve a reliable and robust record of deep seawater nd isotopic compositions from the time of deposition

from isolated buildups to buildup mosaics 3d seismic sheds new light on upper carboniferous permian fault controlled carbonate buildups norwegian barents sea abstract carbonate buildups are a common feature of many ancient carbonate platforms and were especially abundant during the palaeozoic our present understanding of buildup distribution and the ability to better predict their location is however hampered by the fact that maps of buildups rarely show evidence of widespread spatial organisation and indeed their distribution often appears chaotic a previously unrecognized pattern of buildup distribution has been revealed by three dimensional 3d seismic data recently acquired from the loppa high norwegian barents sea here syn rift carboniferous permian buildups are not isolated but are instead linked into a mosaic of laterally extensive ridges the buildups location is controlled by the intersection of three trends of syndepositional faults systematic organisation of buildup height width density and external form across the study area appears to have been controlled by changes in accommodation space driven by differential subsidence the buildups were remarkably long lived and developed over an interval of 35 ma despite this longevity buildup location remained relatively static and true to the underlying pattern of basement faults indicating that their progradation was likely restricted by a combination of factors including limited highstand production their depositional relief

thermal evolution of cretaceous tethyan marine waters inferred from oxygen isotope composition of fish tooth enamels 1 the evolution of subtropical 30 35 n upper ocean temperatures through the cretaceous is inferred from the oxygen isotope compositions of 64 fish teeth enamel coming from the western tethyan platform mean 18o values of 22 at the berriasian valanginian boundary decrease with oscillations to 18 5 around the cenomanian turonian boundary and progressively increase to 21 5 by the end of the cretaceous the similarity of this oxygen isotope curve for bioapatites from platform environments with those for foraminifera and bulk carbonates that were deposited in deeper waters and at other paleolatitudes indicates that they record global climatic signals major cooling events at the million year scale can be distinguished 1 at the berriasian valanginian boundary and 2 during the earliest late valanginian a third cooling event is detected during the earliest aptian these events already proposed as icehouse interludes during the lower cretaceous are also recorded at subtropical latitudes a progressive warming is identified from the aptian to the cenomanian turonian interval that corresponds to a thermal optimum and then upper ocean temperatures decreased to the maastrichtian minimum isotopic temperatures range from 15 c to 28 c assuming a 18oseawater of 1 for an ice free world taking more realistic 18oseawater values of 0 for tropical waters during glacial periods within the berriasian valanginian interval and earliest aptian or with above average salinities possibly the maastrichtian temperatures are increased by 4 5 c temperature differences between climatic extremes of the valanginian and cenomanian turonian are estimated to have been 10 c latitudinal thermal gradients for the albian cenomanian turonian and maastrichtian were 0 2 0 3 c latitude and thus weaker than modern oceanic values at about 0 4 c latitude

shock wave equation of state of serpentine to 150 gpa implications for the occurrence of water in the earth s lower mantle the shock equation of state of serpentine has been determined to 150 gpa four distinct regions occur along the hugoniot a low pressure phase a mixed phase region a high pressure phase and a very high pressure phase the low pressure phase lpp exists under shock pressures to about 40 gpa this material exhibits shock properties that are partially consistent with those of low pressure serpentine but steep release paths and a low value of k 2 77 suggest transformation to another possibly amorphous assemblage thermodynamic calculations indicate that under equilibrium conditions serpentine would decompose to oxides plus water at conditions below 10 gpa along the hugoniot a mixed phase region begins at 40 gpa with complete transition to a high pressure phase occurring by about 55 gpa the high pressure phase hpp occurs at shock pressures between 55 gpa and 125 gpa model hugoniots based on perovskite plus periclase plus water and brucite plus periclase plus stishovite reproduce the serpentine hpp hugoniot within experimental error so definitive identification of the hpp as a distinct hydrous mineral phase or as a free water containing mixture is not possible above 125 gpa a transition to a very compressible phase possibly a hydrous partial melt occurs the serpentine hpp hugoniot is about 15 20 less dense than the earth s lower mantle models of the lower mantle based on shock equations of state for olivine pyroxene and serpentine indicate that for an atomic mg mg fe ratio of 0 80 the presence of 2 wt h 2o is consistent with seismically determined lower mantle density estimates greater amounts of h 2o can be accommodated if accompanied by an increase in fe content calculated hugoniot sound speeds of the serpentine hpp although poorly constrained are broadly consistent with lower mantle sound speeds thus the high pressure density and sound speed of an h 2o rich magnesium silicate determined from shock equation of state experiments indicate that the observed seismic properties of the lower mantle allow the existence of several weight percent of water in the lower mantle

episodic basin wide fluid expulsion from geopressured shale sequences in the north sea basin a proposed general model for the episodic dewatering of thick shale successions is based on the recognition of a pervasive polygonal extensional fault network developed in the dominantly fine grained lower tertiary of the north sea basin seismic data show that the faults are arranged in stratigraphically bound structural units tiers that are delimited vertically by almost undeformed condensed sections and are restricted in distribution to the lowest permeability slope and basin floor facies i propose an episodic three stage mechanism to explain the fault genesis involving 1 the development of basin wide overpressured compartments 2 a density inversion between the overpres sured units and the overlying seal and 3 natural hydraulic fracturing pressure bleed off and resealing of the pressure compartment leading to a repeat of the cycle

upper mantle stratification by p and s receiver functions summary seismic stratification of the upper mantle is investigated by applying two complementary techniques to the records of the graefenberg array in southern germany the anisotropic p receiver function technique kosarev et al 1984 vinnik montagner 1996 is modified by using summary seismic events instead of individual events and different weighting functions instead of the same function for the harmonic angular analysis of the sv and t components of the pds phases the summary events provide better separation of the second azimuthal harmonic than the individual events the parameters of the second harmonics of sv and t thus evaluated should be similar if they reflect the effects of azimuthal anisotropy this can be used as a criterion to identify the anisotropy to detect the sdp phases and their azimuthal variations caused by azimuthal anisotropy we have developed a stacking technique which can be termed the s receiver function technique it includes axis rotation to separate interfering p and s arrivals determination of the principal m component of the s wave motion deconvolution of the p components of many recordings by their respective m components and stacking of the deconvolved p components with weights depending on the level of noise and the angle between the m direction and the backazimuth of the event both techniques yield consistent results for the graefenberg array as indicated by the p receiver functions the upper layer of the mantle between the moho and 80 km depth is anisotropic with dvs vs around 0 03 and the fast direction close to 20 clockwise from north the fast direction of anisotropy below this layer is around 110 the boundary between the upper and the lower anisotropic layers is manifested by the detectable pds and sdp converted phases shear wave splitting in sks is strongly dominated by azimuthal anisotropy in the lower layer asthenosphere

receiver function imaging of upper mantle complexity beneath the pacific northwest united states abstract small scale topographic variations on the upper mantle seismic discontinuities provide important constraints on the thermal influences of upwellings and downwellings in geodynamically complex regions subduction of the juan de fuca plate and other tectonic processes dominating the pacific northwest united states in the cenozoic involve massive thermal flux that likely result in an upper mantle that has strong 3 d temperature variations we address the interaction of such processes in the region using receiver functions to image the upper mantle seismic discontinuities at 410 and 660 km we utilized over 15 000 high quality receiver functions gathered from 294 teleseismic earthquakes recorded at 277 regional broadband seismic stations primarily those of the earthscope usarray transportable array we find the average depths of the discontinuities to be 412 km and 658 km respectively with no obvious 520 km discontinuity detected the peak to peak range is greater on the 410 than the 660 suggesting the possibility of more significant regional dynamic processes at upper mantle depths our results are not consistent with a mantle plume below central oregon in the high lava plains region our observation of a thinner transition zone beneath the western snake river plain region however is consistent with a regional increase in mantle temperatures perhaps due to either asthenospheric flow from beneath and around the southern edge of the juan de fuca plate or to vertical flow in the form of regional mantle upwelling related to the snake river plain yellowstone hotspot track further our results are not consistent with a simple subducting juan de fuca slab morphology but rather suggest similar levels of significant complexity in slab structure found by recent regional tomographic studies we find evidence for a thickened and therefore cooler mantle transition zone beneath the wallowa idaho batholith region consistent with tomographic models which suggest broad scale increased seismic velocities to transition zone depths we speculate that this region may be the location of mantle downwelling at larger scales than previously proposed