new global marine gravity model from cryosat 2 and jason 1 reveals buried tectonic structure gravity models are powerful tools for mapping tectonic structures especially in the deep ocean basins where the topography remains unmapped by ships or is buried by thick sediment we combined new radar altimeter measurements from satellites cryosat 2 and jason 1 with existing data to construct a global marine gravity model that is two times more accurate than previous models we found an extinct spreading ridge in the gulf of mexico a major propagating rift in the south atlantic ocean abyssal hill fabric on slow spreading ridges and thousands of previously uncharted seamounts these discoveries allow us to understand regional tectonic processes and highlight the importance of satellite derived gravity models as one of the primary tools for the investigation of remote ocean basins

joint inversions of seismic and geodynamic data for models of three dimensional mantle heterogeneity the seismic models of three dimensional 3 d mantle heterogeneity may be interpreted in terms of the density perturbations which drive mantle flow and thus provide important predictions of flow related observables such as the nonhydrostatic geoid the current models of global scale shear velocity heterogeneity provide reasonably good fits to the long wavelength nonhydrostatic geoid data 60 70 variance reductions but rather poor fits to the corresponding free air gravity anomalies 30 40 variance reductions this major difference is due to two factors 1 the very different amplitude spectrum of the gravity anomalies which is nearly flat for degrees l 3 the largest mismatch between the pattern of predicted and observed gravity anomalies is in the southern hemisphere this observation suggests that one reason for the poor overall match between the two fields may be that the global seismic data are not resolving sufficiently well the heterogeneity in the southern hemisphere portion of the deep mantle in contrast the gravity data provide accurate and geographically uniform constraints on the vertically integrated heterogeneity in the mantle we therefore perform a series of experiments in which we simultaneously invert a large set of seismic data which includes long period waveforms ss s and scs s differential travel times and normal mode structure coefficients and the long wavelength gravity anomaly data we thus determine whether it is possible to derive new 3 d heterogeneity models which satisfy both data sets the gravity anomaly data are interpreted in the context of spherically symmetric viscous flow models of the mantle in these inversion experiments we test several radial viscosity and ln ln profiles and thereby assess their plausibility the joint seismic geodynamic inversions reveal that it is indeed possible to greatly improve the fit to the free air gravity anomalies with variance reductions of 80 90 readily accessible while preserving the fit to the seismic data this improvement is achieved with some adjustment to the heterogeneity in the depth range 1500 2500 km where the seismic data constraints appear to be weakest the joint inversions also reveal new structures in the southern hemisphere portion of the lower mantle which apparently are not resolved by the seismic data alone

the relationships between large scale variations in shear velocity density and compressional velocity in the earth s mantle a large data set of surface wave phase anomalies body wave travel times normal mode splitting functions and long period waveforms is used to investigate the scaling between shear velocity density and compressional velocity in the earth s mantle we introduce a methodology that allows construction of joint models with various levels of scaling complexity d ln d lnvs d lnvs d lnvp in order to detect seismological signatures of chemical heterogeneity we demonstrate that the data sets considered cannot be fit concurrently with a uniform or a positive and uniform throughout the mantle the variance reductions to p wave travel times and vp sensitive modes are up to 40 higher with our preferred model of anisotropic shear and compressional velocity than the recent anisotropic shear velocity model s362ani m which was constructed assuming a uniform throughout the mantle several features reported in earlier tomographic studies persist after the inclusion of new and larger data sets anticorrelation between bulk sound and shear velocities in the lowermost mantle as well as an increase in with depth in the lower mantle are largely independent of the regularization scheme when correlations between density and shear velocity variations are imposed in the lowermost mantle variance reductions of several spheroidal and toroidal modes deteriorate by as much as 40 recent measurements of the splitting of 0s2 in particular are largely incompatible with perfectly correlated shear velocity and density heterogeneity throughout the mantle a way to significantly improve the fits to various data sets is by allowing independent density perturbations in the lowermost mantle our preferred joint model consists of denser than average anomalies 1 peak to peak at the base of the mantle roughly coincident with the low velocity superplumes the relative variation of shear velocity density and compressional velocity in our study disfavors a purely thermal contribution to heterogeneity in the lowermost mantle with implications for the long term stability and evolution of superplumes

effect of upper mantle density structure on moho geometry a constant value of the moho density contrast is often assumed in the gravimetric methods used for determination of moho geometry this assumption might be sufficient in regional studies with a relatively homogenous lithospheric structure and consequently small lateral variations in moho density contrast in global studies however this assumption is not reasonable because not only the moho depth but also the moho density contrast vary substantially and are thus likely to result in systematic errors in moho geometry determined globally from gravity data in this study we address this issue by investigating the effect of variable moho density contrast on moho geometry we demonstrate that assumption of variable moho density contrast instead of a uniform model substantially improves agreement between the global gravimetric and seismic moho models by approximately 30

foreword to special section on remote sensing of the low and middle latitude thermosphere and ionosphere from the ground and from space the low and midlatitude thermosphere and ionosphere constitute a tightly coupled dynamic region of the near earth environment this region exhibits strong and complex coupling between charged and neutral species between different altitudes and between equatorial and nonequatorial latitudes the ion and neutral composition and temperature are affected by dynamics electric and magnetic fields photochemistry and geomagnetic and solar forcing this special section focuses on this region and the remote sensing techniques that are providing the measurements needed to better understand this complex region of the near earth space environment

using seismic waves to image earth s internal structure seismic waves generated in earth s interior provide images that help us to better understand the pattern of mantle convection that drives plate motions

depth and age in the north pacific the concept of the oceanic lithosphere as a cooling thermal boundary layer on top of a viscous upper mantle accounts for the increase in depth with age of the ocean floor analyses of the exact nature of this relation provide constraints on the rheology and structure of this layer in past studies problems with uncertainties of age and in sediment thickness have limited the value of this relation on older ocean floor in this study we evaluate different tectonic histories for the quiet zones and construct a revised isochron chart for the north pacific we check and modify the current sediment thickness charts using new deep sea drilling data and revised ideas concerning reflectors in the southwestern north pacific averaging the synbaps digital data base into half by half degree elements and correcting for sediment load we plot basement depth versus age for the entire north pacific because of the skewness in the data associated with seamounts we present the data as contours about the mode and find that two thirds of the observations lie within 300 m of this value on crust between 0 and 80 ma the ocean floor subsides with the square root of age on ocean floor older than 100 ma the depths in general flatten with age with areally correlateable swells and valleys the hawaiian and line island swells correlate positively and the mariana basin valley negatively with geoid height the flattening in the depths indicates that the thermal boundary layer has reached equilibrium conditions under older ocean floor further the correlation of the swells and valleys with geoid height presents evidence for organized convection in the upper mantle beneath older lithosphere in the north pacific

the rheological structure of the lithosphere in the eastern marmara region turkey abstract the aim of this work is to propose the geometries of the crustal lithospheric mantle boundary moho and lithosphere asthenosphere boundary lab and the 1d thermal structure of the lithosphere in order to establish a rheological model of the eastern marmara region the average depths of moho and lab are respectively 35 km and 51 km from radially averaged amplitude spectra of egm08 bouguer anomalies the geometries of moho and lab interfaces are estimated from the parker oldenburg gravity inversion algorithm our results show the moho depth varies from 31 km at the northern part of north anatolian fault zone nafz to 39 km below the mountain belt in the southern part of the nafz the depth to the lab beneath the same parts of the region ranges from 45 km to 55 km having lithospheric strength and thermal boundary layer structure we analyzed the conditions of development of lithosphere thinning a two dimensional strength profile has been estimated for rheology model of the study area thus we suggest that the rheological structure consists of a strong upper crust a weak lower crust and a partly molten upper lithospheric mantle

total tectonic subsidence a parameter for distinguishing crust type at the u s atlantic continental margin total tectonic subsidence tts is the difference between the prerifting continental crust elevation and the present sediment unloaded basement depth in a sedimentary basin tts is calculated using observations of bathymetry and basement depth and assumptions about sediment density and the loading response of the lithosphere i use the extensional model for sedimentary basin formation to interpret the tts of a passive continental margin that model predicts that the tts on an old margin should define the major crust type boundaries and indicate the lateral distribution of extension within the extended continental crust tts analysis of the u s atlantic continental margin indicates that the boundary between extended continental and oceanic crusts lies along the east coast magnetic anomaly ecma to the north of the blake spur fracture zone bsfz and along the blake escarpment to the south there is no tts anomaly associated with the blake spur magnetic anomaly which seems to be underlain by normal oceanic crust the ecma appears to be associated with a tts minimum but i attribute that to artificially shallow estimates of depth to magnetic basement under the ecma tts estimates of extended continental crust thickness agree well with gravity models except where the problem with magnetic basement depth estimates interferes the amount of crust extension prior to seafloor spreading varies along the strike of the margin the most abrupt change is at the bsfz across the bsfz the amount of extension varies by 160 km but the volume of continental material does not vary the extension variation may be caused by lateral changes in the gross rheology of the continental lithosphere in the case of the bsfz it would be the suture of more ductile pre late paleozoic african craton with more brittle north american craton that could cause the abrupt change

regional variations in subsidence rate of oceanic plates a global analysis a global analysis of the dependence of seafloor depth on crustal age has been performed for each large oceanic plate independently each plate has been divided into regions bounded by major tectonic features a total of 32 regions have been considered bathymetry corrected for sediment loading has been plotted as a function of crustal age for each region except for three regions western pacific between 10 s and 40 n north american plate between 24 n and 38 n and african plate between 10 n and 24 n where ocean floor older than 80 100 ma flattens with age in other regions depth increases linearly with age1 2 subsidence rate over each region has been computed by linear regression large variations up to a factor 2 are reported from one region to another asymmetrical subsidence is also observed in a number of areas however the largest asymmetries are less than the regional variations in subsidence rate occurring on individual plates regional variations in subsidence rate appear linearly related to regional variations in ridge crest topography shallow ridge subsiding quickly and deep ridge subsiding slowly hence seafloor depth subsides at a rate modulated by the value of the initial axial depth this observation suggests that regional variations in subsidence rate reflect the thermal regime of the mantle beneath mid ocean ridges rather than lateral temperature variations inside the asthenosphere involving small scale convection

full fit reconstruction of the south china sea conjugate margins although the south china sea margins have been well studied there are no full fit reconstructions that document the complex rifting history in a regional geodynamic context we restored conjugate margins to their original late cretaceous unstretched geometries and generated the first full fit reconstructions of the south china sea conjugate margins the impact of magmatic underplating on restoration and full fit reconstruction was estimated quantitatively the full fit reconstruction model includes restoration uncertainties and results in minimum gaps and overlaps between the restored conjugate margin geometries based on our restoration the full fit reconstruction and the continental basement thickness distribution we estimate that there was more extension of continental basement on the western part of the conjugate margins compared with the eastern margin prior to the initiation of seafloor spreading therefore the mid ocean ridge initially formed in the east and propagated westward to open the south china sea seafloor spreading propagated along the xisha trough during nw sub basin formation but continental breakup occurred along the southern side of the zhongsha xisha islands where the lithosphere was probably weaker than along the xisha trough consistent with the geometry and evolution of the nw sub basin and the southward jump of the mid oceanic ridge c 2015 elsevier b v all rights reserved

coal as a source rock for oil a review the geological debate about whether and to what extent humic coals have sourced oil is likely to continue for some time despite some important advances in our knowledge of the processes involved it is clear that not only liptinites but also perhydrous vitrinites have the potential to generate hydrocarbon liquids in the course of natural coalification some liptinites especially alginite cutinite and suberinite contain a higher proportion of aliphatic moieties in their structure than other liptinites such as sporinite and resinite and are therefore more oil prone it is of potential value to be able to predict the several environments of deposition in which coals with high liptinite contents or containing perhydrous vitrinites may have been formed review of the distribution of oil prone coals in time and space reveals that most are jurassic tertiary with key examples from australia new zealand and indonesia methods based both on experimental simulations and the examination of naturally matured samples have been used to determine the order of generation of hydrocarbons from different macerals results are not entirely consistent among the different approaches and there is much overlap in the ranges of degradation but it seems probable that in the natural environment vitrinites begin to generate early followed by labile liptinites such as suberinite then cutinite sporinite and finally alginite petroleum potential may be determined by experimental simulation of natural coalification or inferred through various micro techniques especially fluorescence and infrared ir spectroscopy or bulk techniques such as elemental analysis and 13c nmr spectroscopy the latter three techniques enable a measure of the polymethylene component of the coal which now appears to be one of the best available approaches for determining petroleum potential no method of experimental simulation of petroleum generation from coals is without criticism and comparative results are highly variable however hydrous pyrolysis confined pyrolysis and forms of open system hydrous pyrolysis approach acceptable simulations whether and to what degree generated liquid hydrocarbons are expelled has long been the central problem in oil from coal studies the structure of vitrinite was believed until recently to contain an interconnected microporous network in which generated oil would be contained until an expulsion threshold was attained recent studies show the pores are not interconnected combined with a dynamic model of pore generation it now seems that expulsion of hydrocarbons is best explained by activated diffusion of molecules to maceral boundaries and ultimately by cleats and fractures to coal seam boundaries the main reason for poor expulsion is the adsorption of oil on the organic macromolecule which may be overcome 1 if coals are thin and interbedded with clastic sediments or 2 if the coals are very hydrogen rich and generate large quantities of oil the existence of oil in vitrinite is attested to by solvent extractions fluorescence properties and by microscopic observations of oil and bitumen experimental simulation of expulsion of oil from coals has only recently been attempted the relative timing of release of generated co2 and ch4 could have considerable importance in promoting the expulsion of liquid hydrocarbons but the mechanism is unclear as it is universally agreed that dispersed organic matter dom in some shales readily generates and expels petroleum it is curious that few consistent geochemical differences have been found between coal macerals and dom in interbedded shales unambiguous evidence of expulsion from coals is limited and in particular only a few commercial oil discoveries can be confidently correlated to coals these include upper cretaceous fruitland formation coals in the usa from which oil is produced new zealand tertiary coals and middle jurassic coals from the danish north sea it is likely that coals have at least contributed to significant oil discoveries in the gippsland basin australia in the turpan basin china and in the kutei and ardjuna basins in indonesia but this remains unproven early reports that early jurassic coals in mid norway were a major source of the reservoired oils have been shown to be inaccurate none of the proposed rules of thumb for generation or expulsion of petroleum from coals seem particularly robust decisions on whether a particular coal is likely to have been an active source for oil should consider all available geological and geochemical information the assumptions made in computational models should be well understood as it is likely with new understandings of processes involved that some of these assumptions will be difficult to sustain

palaeoclimatic evolution during eocene and its influence on oil shale mineralisation fushun basin china the fushun basin is a small explored coal and oil shale bearing cenozoic fault basin in the liaoning province northeast china the basin mainly consists of eocene swamp to lacustrine deposits of the guchengzi to xilutian formation and contains the biggest opencast oil shale mine in asia this mine has provided an ideal opportunity to undertake palaeoclimate reconstruction in this basin based on a single geological profile and the analyses of 93 samples using various approaches namely field geological observation clay mineralogical and geochemical sr ba sr cu stable c and o isotope analyses all of which were compared with palaeobotanical data the eocene climate of fushun basin evolved from warm temperate to north subtropical and generally changed from warm humid to subhumid semiarid paleoclimatic and geochemical parameters shows that the very warm and humid climate during jijuntun formation increased the initial productivity of lake water and caused a steady stratification of the lake water then caused oxygen lack in the bottom of water productivity of the lake provides the mean origin of organic matters for oil shale formation and steady anoxic environment is beneficial for the conservation of organic matters

crustal thickness anomalies in the north atlantic ocean basin from gravity analysis gravity derived crustal thickness models were calculated for the north atlantic ocean between 76 n and the chain fracture zone and calibrated using seismically determined crustal thickness about 7 of the ocean crust is 7 km thick and is interpreted to have been affected by excess magmatism thin crust probably reflects reduced melt production from relatively cold or refractory mantle at scales of up to hundreds of kilometers along the spreading axis by far the most prominent thick crust anomaly is associated with iceland and adjacent areas which accounts for 57 of total crustal volume in excess of 7 km much smaller anomalies include the azores 8 cape verde islands 6 canary islands 5 madeira 4 and new england great meteor seamount chain 2 all of which appear to be associated with hot spots hot spot related crustal thickening is largely intermittent suggesting that melt production is episodic on time scales of tens of millions of years thickened crust shows both symmetrical and asymmetrical patterns about the mid atlantic ridge mar axis reflecting whether melt anomalies were or were not centered on the mar axis respectively thickened crust at the bermuda and cape verde rises appears to have been formed by isolated melt anomalies over periods of only 20 25 myr crustal thickness anomalies on the african plate generally are larger than those on the north american plate this most likely results from slower absolute plate speed of the african plate over relatively fixed hot spots

petrology and hydrocarbon potential of microalgal and macroalgal dominated oil shales from the eocene huadian formation ne china abstract a series of oil shales of middle to late eocene age occur in the huadian area of jinlin province northeast china analytical results from 22 rock samples collected from an underground mine in the guanglangtou district in the huadian basin show that the total organic carbon toc contents of the oil shale layers are very high 10 6 wt to 39 6 wt with vitrinite reflectance ro values of 0 41 0 02 and rock eval hydrogen index hi values up to 887 biomarker analyses show a high proportion of hopenes and hopanes with stereochemistry indicative of low maturity detailed organic petrologic analysis demonstrates that the organic matter is dominated by lamalginite and telalginite the presence of botryococcus in the telalginite indicates that the depositional environment of the oil shale is lacustrine this is consistent with low si and s contents and high c s ratios fragments from a newly identified benthic macroalgal rhodophyte were found in some thin layers raising the possibility that the depositional environment of some oil shale layers may have been influenced by marine flooding since rhodophyta are uncommon in freshwater systems two oil shale samples with different algal compositions were selected for assessment of hydrocarbon generation potential sample hd 21 is dominated by phytoplanktic lamalginite with a high hi value of 869 mg hc g toc while sample hd 20 has a lower hi value 490 mg hc g toc and contains high contents of the benthic rhodophyte as well as some phytoplanktic lamalginite hi values and thermal simulation experiments showed that the phytoplankton dominated shale hd 21 has a much higher hydrocarbon generation potential than the rhodophyte dominated oil shale hd 20 even though the toc content of hd 20 was much higher indicating that the benthic macroalgal macerals have a much lower capacity to generate oil when thermally mature

petrology palynology and organic geochemistry of eocene lignite of matanomadh kutch basin western india implications to depositional environment and hydrocarbon source potential abstract petrological palynological and organic geochemical investigations were undertaken to determine the source vegetation depositional conditions and hydrocarbon source potential of eocene matanomadh lignites from kutch basin western india the maceral study reveals that studied lignites are rich in huminite av 63 with sub ordinate amount of liptinite av 19 and low inertinite av 3 along with low to moderately high associated mineral matters av 15 the overall petrographic composition points to a lagoonal condition for the formation of these lignites the mean huminite reflectance values r r 0 28 0 34 av 0 31 as well as low rock eval t max av 417 c values for the seams suggest brown coal or lignitic stage rank for the studied lignites the palynological assemblages dominated by tropical angiospermic pollen suggest prevalence of warm humid tropical climate during the deposition of these lignites the total organic carbon toc content of lignites ranges between 26 and 58 wt whereas the toc content of the associated carbonaceous shales is around 4 wt the hydrogen index hi ranging from 23 to 452 mg hc g toc indicates that the lignite sequence has the potential to produce mixed oil and gaseous hydrocarbons on maturation the major pyrolysis products of lignites derived from curie point pyrolysis gc ms are straight chain aliphatics phenols and cadalene based c 15 bicyclic sesquiterpenoids the exclusive occurrence of c 15 bicyclic sesquiterpenoids suggests that these compounds are derived from dammar resin of angiosperm plants belonging to family dipterocarpaceae

gypsum a joint tomographic model of mantle density and seismic wave speeds 1 gypsum is a 3 d model of mantle shear wave s speeds compressional wave p speeds and density the model is developed through simultaneous inversion of seismic body wave travel times p and s and geodynamic observations while using realistic mineral physics parameters linking wave speeds and density geodynamic observations include the global free air gravity field divergence of the tectonic plates dynamic topography of the free surface and the flow induced excess ellipticity of the core mantle boundary gypsum is built with the philosophy that heterogeneity that most closely resembles thermal variations is the simplest possible solution models of the density field from earth s free oscillations have provided great insight into the density configuration of the mantle but are limited to very long wavelength solutions alternatively scaling higher resolution seismic images to obtain density anomalies generates density fields that do not satisfy geodynamic observations the current study provides a 3 d density model for the mantle that directly satisfies geodynamic and seismic observations through a joint seismic geodynamic inversion process notable density field observations include high density piles at the base of superplume structures supporting the general results of past normal mode studies however we find that these features are more localized and have lower amplitude than past studies would suggest when we consider both fast and slow seismic anomalies in gypsum we find that p and s wave speeds are strongly correlated throughout the mantle however we find a low correlation of fast s wave zones in the deep mantle 1500 km depth with the corresponding p wave anomalies suggesting a systematic divergence from simplified thermal effects in ancient subducted slab anomalies the cratonic lithosphere and d regions are shown to have strong compositional signatures however we argue that temperature variations are the primary cause of p wave speed s wave speed and density anomalies throughout most of the mantle

aleutian island arc magma production rates and primary controlling factors abstract island arc magmatism is considered a major mechanism of continental crustal growth hence the variation in island arc magma production rates and its influencing factors are of great importance the along arc strike variation in the island arc magma production rate is important for elucidating whether the subduction zone temperature is a controlling factor on arc magmatism no back arc spreading or ridge subduction is occurring in the intraoceanic subduction region of the aleutian subduction zone and the along arc temperatures vary due to differences in the subducting plate age convergence rate and slab dip therefore this is an ideal region to study the correlation between magma production rates and subduction zone temperatures however previous studies estimated the magma production rates at only a few locations due to the insufficient coverage of seismic data here we employ the gravity inversion method based on density modelling and seismic data constraints to calculate the present day arc crustal thickness and then obtain the magmatic thickness by removing the pre existing crustal thickness from the present day arc crustal thickness finally the magma production rates along the main intraoceanic subduction region of the aleutian arc are mapped by estimating the island arc magmatic thickness and the most recent subduction inception dating result in addition the subduction zone temperatures and mantle melt amounts along five profiles across the aleutian arc are calculated the magma production rate variation is highly correlated with the mantle melt amount the slab temperature controls the extent of the slab dehydration which is essential for mantle wedge melting and the mantle wedge temperature controls the size of the hydrated mantle melting region and the melting fraction therein therefore as the subduction zone temperature controls the mantle melt amount we suggest that the subduction zone temperature is the first order controlling factor on the magma production rate

crustal thickness over the nw pacific and its tectonic implications abstract igneous emplacement on the nw pacific oceanic crust via mantle activity such as hot spots and mantle plumes results in perturbations of crustal thickness therefore mapping crustal thickness variations is key for understanding these mantle structures and processes improvements in resolution and accuracy of marine gravity anomalies promote the use of moho gravity inversion effects especially for large scale applications for improving the moho gravity inversion accuracy density variations of the lithospheric mantle are modelled via lithospheric age temperature density relationship since age grid with a resolution of 2 arc minutes is available and density variations of the mantle beneath lithosphere are modelled via seismic wave velocity density relationship since velocity structure with penetration to 700 km is available comparisons between the moho geometries by gravity inversion and seismic interpretation demonstrate that the mantle density modelling improves the moho inversion accuracy our crustal map shows that 1 the crustal thickness of 26 of the nw pacific region is thicker than 7 km 2 the southern end of the emperor seamounts was emplaced on the western flank of the hess rise and a part of the central hawaiian seamounts was emplaced on the eastern end of the mid pacific mountains 3 the magma production of hawaiian seamounts is greater than that of the emperor seamounts 4 the leakiness of the fracture along which the line islands formed decreases in the order of the central southern and northern segments

flattening of the sea floor depth age curve as a response to asthenospheric flow the flattening of sea floor depths from the age dependence predicted by considering the cooling plate as a growing thermal boundary layer is a fundamental constraint on the evolution of oceanic lithosphere1 previous explanations for the flattening have included reheating from convective instabilities that form beneath lithosphere older than 80 myr ref 2 thermal rejuvenation of lithosphere that passes over stationary hotspots3 5 or a whole mantle flow forced by two converging plates6 we suggest here that the flattening of old ocean floors can perhaps best be explained as a dynamic phenomenon reflecting flow in asthenosphere underlying the oceanic lithosphere applying the model to the pacific plate we show that a solution for flow in an asthenosphere low viscosity channel which is consumed by plate accretion and the subduction of lithosphere at trenches and replenished by near ridge upwelling and near ridge hotspots generates the observed 1 km of sea floor flattening for asthenospheric viscosities of 2 1018 pa s and an absolute pacific plate motion of 100 mm yr 1 our model can also explain the asymmetric subsidence of the south american and african plates away from the mid atlantic ridge

upper mantle density modelling for large scale moho gravity inversion case study on the atlantic ocean moho geometry is an important parameter in geodynamic understanding seismic methods can provide accurate burial depths but the coverage is low the widely used crust1 0 model under oceans is greatly restricted by a low coverage of seismic data gravity inversion can provide high coverage of moho undulations but the accuracy is relatively low observed gravity anomalies integrate gravity effects induced by 3 d density perturbations in the earth for studies of the geometry of a specific density interface based on gravity all gravity effects caused by other interfaces should be removed from the total anomaly map based on 3 d density distributions we use temperature based and velocity based methods to model the lithospheric upper mantle density two temperature calculation parameter models psm and gdh1 three thermal expansion coefficients alpha and three scaling ratio models are tested for each method psm and gdh1 result in a similar mantle gravity anomaly mga pattern but different mga average values when the alpha model is the same different alpha and scaling ratio models result in different moho inversion results and the optimal result from the temperature based method has an rms of 3 2 km with the crust1 0 model a comparison between this inversion result and the crust1 0 model shows that the temperature based method performs well in reproducing moho geometry in the main part of the atlantic ocean especially in the central basin the optimal result from the velocity based method has an rms of 4 3 km with the crust1 0 model compared with the temperature based method the velocity based method performs worse in the central basin but better in regions with low velocity and low density mantle away from the mid ocean ridge

the relative density to shear velocity scaling in the uppermost mantle we perform inversions of gravity data geopotential model egm96 and seismic tomography model s16rlbm for the scaling factor which relates relative density anomalies to relative s wave velocity anomalies the gravity data and tomographic model are anti correlated below continents down to a depth of z 200 km this anti correlation is not present below oceans except for smoothness which is controlled by a damping factor no a priori information is added to the inversion data are filtered between degrees 11 and 16 of the spherical harmonic expansion this spectral window is well suited for the study of intermediate size 2000 4000 km anomalies in the uppermost mantle calculations are made separately for sub continental and sub oceanic mantle the sub continental and sub oceanic scaling factors are significantly different at depths shallower than 260 km in both cases the magnitude of is around 0 05 the sub continental scaling factor has a positive root down to z 220 km whereas the sub oceanic scaling factor yields positive values down to z 140 km only at depth shallower than 350 km models of do not depend on the damping factor or the viscosity model at depths greater than 350 km the resolution of z decreases significantly and low degrees 2 4 add information from large scale anomalies and from the lower mantle as a result the shape and values of for 2 16 and 11 16 are significantly different at depths greater than 350 km a possible explanation of the discrepancies between the sub continental and sub oceanic scaling factor is that intermediate scale anomalies are more important in the continental uppermost mantle than in the oceanic uppermost mantle 2001 elsevier science b v all rights reserved

black shale formation in the late paleocene early eocene arctic ocean and paleoenvironmental conditions new results from a detailed organic petrological study abstract the study of particulate organic matter om in arctic ocean sediments from the late cretaceous to the eocene iodp expedition 302 has revealed detailed information about the aquatic marine om fluxes biological sources preservation and export of terrestrial material here we present detailed data from maceral analysis vitrinite reflectance measurements and organic geochemistry during the campanian paleocene fluxes of land derived om are indicated by reworked and oxidized macerals vitrinite inertinite and terrigenous liptinite cutinite sporinite in the early eocene drastic environmental changes are indicated by peaks in aquatic om up to 40 45 lamalginite telalginite liptodetrinite dinoflagellate cysts and amorphous om up to 50 bituminite these events of increased aquatic om flux similar to conditions favoring black shale deposition correlate with the global 13c events paleocene eocene thermal maximum petm and elmo event freshwater discharge and proximity of the source area are documented by freshwater algae material pediastrum botryococcus and immature land plant material corphuminite textinite we consider that erosion of coal bearing sediments during transgression time lead to humic acids release as a source for bituminite deposited in the early eocene black shales

crustal stretching style variations in the northern margin of the south china sea linking deep seismic profiles with regional scale gravity inversion is a powerful tool to deduce the architecture of rifted margins and their structural evolution here we map upper and lower crustal thicknesses of the northern south china sea scs margin in order to investigate the occurrence of depth dependent crustal extension from the proximal to the distal margin by comparing upper and lower crustal stretching factors we find that the northern margin of the scs is segmented in three parts 1 sedimentary basins where upper crust is stretched more than lower crust 2 distal margin where lower crust is stretched more than upper crust 3 mostly proximal margin regions where the two layers have similar stretching factors our results suggest that sedimentary basins and distal margin prominently feature depth dependent extension however accommodated by different processes while differential thinning within sedimentary basins appears to be governed by lateral pressure variations inducing lower crustal flow we suggest the distal margin to be affected by a combination of mantle flow induced lower crustal shearing and sequential fault activity during crustal hyper extension

icp ms a powerful tool for high precision trace element analysis in earth sciences evidence from analysis of selected u s g s reference samples abstract inductively coupled plasma mass spectrometry icp ms is a powerful analytical technique with considerable application to geochemistry in this paper we demonstrate the power of icp ms as a tool in petrogenetic studies data for 28 elements in seven u s g s basalt and andesite reference samples agv 1 bcr 1 bhvo 1 bir 1 dnc 1 w 1 and w 2 are presented accuracy and precision standard deviation for 26 of these elements is either excellent a detailed description of the icp ms technique we have developed is given a simple hf hno 3 dissolution in screwtop teflon bombs was used for sample preparation icp ms instrumental sensitivity was measured by external solutions with surrogate calibration for 4 elements matrix correction was made by use of standard addition naturally occurring internal standards rb y ce and pb were used to correct for instrumental drift between sample and spiked sample measurements we report data for the elements li cs rb sr ba zr hf nb ta y sc u th pb and all 14 of the ree in addition the procedure acquired data for be mo w tl and bi many elements in this array are crucial for the evaluation of petrogenetic models and source tracing herein lies the real power of icp ms one technique one dissolution small sample size good limits of detection good to excellent accuracy and good precision for many geochemically important elements

hotspot volcanism in the southern south atlantic geophysical constraints on the evolution of the southern walvis ridge and the discovery seamounts abstract the southern atlantic hosts a variety of magmatic structures namely the walvis ridge the discovery seamounts and the shona ridge which are believed to be related to the evolution movement of hotspots although the basement of the walvis ridge has been sampled at different locations geophysical data are too sparse to provide sufficient information about its deeper structure to compare it with other hotspot tracks the discovery seamounts represent a completely different type feature in a way that it cannot be connected to any onshore volcanic feature however geological sampling of the volcanic basement indicates that the petrology of the discovery track is very similar to gough island and the southern branch of walvis ridge both structures erupted into already existing seafloor and so have been seismically investigated to document how if an associated thermal anomaly might have modified the underlying and surrounding oceanic crust seismic lines for both structures indicate rather normal seismic velocity distributions for oceanic crust both the walvis ridge and the largest volcano of the discovery seamounts have a maximum thickness in our research area of 13 km an interesting difference between these structures is a high velocity cone 6 km s at 2 4 km depth in the central part of discovery seamount this might indicate a primarily intrusional type of seamount such as has been reported for several similar structures in contrast the walvis ridge velocity structure does not show evidences for a shallow intrusional cone but seismic velocities typical for oceanic layer 3 at a more or less constant depth level along the entire profile this might indicate that the ridge s present day topography is built mainly by extrusive material

age spreading rates and spreading asymmetry of the world s ocean crust we present four companion digital models of the age age uncertainty spreading rates and spreading asymmetries of the world s ocean basins as geographic and mercator grids with 2 arc min resolution the grids include data from all the major ocean basins as well as detailed reconstructions of back arc basins the age spreading rate and asymmetry at each grid node are determined by linear interpolation between adjacent seafloor isochrons in the direction of spreading ages for ocean floor between the oldest identified magnetic anomalies and continental crust are interpolated by geological estimates of the ages of passive continental margin segments the age uncertainties for grid cells coinciding with marine magnetic anomaly identifications observed or rotated to their conjugate ridge flanks are based on the difference between gridded age and observed age the uncertainties are also a function of the distance of a given grid cell to the nearest age observation and the proximity to fracture zones or other age discontinuities asymmetries in crustal accretion appear to be frequently related to asthenospheric flow from mantle plumes to spreading ridges resulting in ridge jumps toward hot spots we also use the new age grid to compute global residual basement depth grids from the difference between observed oceanic basement depth and predicted depth using three alternative age depth relationships the new set of grids helps to investigate prominent negative depth anomalies which may be alternatively related to subducted slab material descending in the mantle or to asthenospheric flow a combination of our digital grids and the associated relative and absolute plate motion model with seismic tomography and mantle convection model outputs represents a valuable set of tools to investigate geodynamic problems

mapping crustal thickness using marine gravity data methods and uncertainties crustal thickness is a critical parameter for understanding the processes of continental rifting and breakup and the evolution of petroleum systems within passive margins however direct measurements of crustal thickness are sparse and expensive highlighting the need for methodologies using gravity anomaly data jointly with other geophysical data to estimate crustal thickness we evaluated alternative gravity inversion methodologies to map crustal thickness variations at rifted continental margins and adjacent oceanic basins and we tested our methodology in the south china sea scs different strategies were investigated to estimate and remove the gravity effect of density variations of sediments and the temperature and pressure variations of the lithospheric mantle from the observed free air gravity anomaly data sediment density was calculated using a relationship between sediment thickness porosity and density we found that this method is essential for crustal thickness inversion in the presence of a thick sedimentary cover by comparing the moho depths obtained from gravity inversion and seismic interpretation in the yinggehai basin where sediments are up to 13 km thick the inversion accuracy depended on the parameters of the exponential equation between porosity and the buried depth we modeled the lithospheric mantle temperature field based on oceanic crustal age continental crustal stretching factors and other boundary conditions we tested three different methods to calculate the thermal expansion coefficient which is either held constant or is a linear polynomial function of temperature for applying a thermal correction and found that the inversion results were relatively insensitive to alternative methods we compared inversion results with two recent deep seismic profiles that image the rifted continental edge at the northern margin of the scs and the continental liyue bank reed bank at the southern margin and we found that the inversion accuracy was improved considerably by removing sediment thermal and pressure gravity effects

topography of the ocean floor thermal evolution of the lithosphere and interaction of deep mantle heterogeneities with the lithosphere topography associated with large wave length geoid is derived by two methods first the bathymetry corrected for sediment loading is decomposed using a least squares method as a function of age plus terms proportional to the geoid the topography at old ages is flatter predicted by the law at degrees 2 and 3 very little topography is associated with the geoid the transfer function is not even certain in sign but is never smaller than 0 6 more topography seems associated with higher degree harmonics 6 and 7 second the function of age alone best fitting the topography is determined the correlation coefficients of the residual topography with the geoid are then computed a slight correlation appears for degree 6 but not for degrees 2 and 3 these results suggest a mechanical decoupling between the lower mantle mass heterogeneities and the lithosphere

joint seismic geodynamic and mineral physical constraints on three dimensional mantle heterogeneity implications for the relative importance of thermal versus compositional heterogeneity summary the joint interpretation of seismic and geodynamic data requires mineral physical parameters linking seismic velocity to density perturbations in the earth s mantle the most common approach is to link velocity and density through relative scaling or conversion factors r s dln dlnv s however the range of possible r s values remains large even when only considering thermal effects we directly test the validity of several proposed depthdependent conversion profiles developed from mineral physics studies for thermally varying properties of mantle materials the tests are conducted by simultaneously inverting shear wave traveltime data and a diverse suite of convection related constraints interpreted with viscous flow response functions of the mantle these geodynamic constraints are represented by surface spherical harmonic basis functions up to harmonic degree 16 and they consist of the global free air gravity field tectonic plate divergences dynamic surface topography and the excess ellipticity of the core mantle boundary cmb the tests yield an optimum 1 d thermal r s profile that is generally compatible with all considered data with the exception of the dynamic surface topography that is most sensitive to the shallow upper mantle this result is not surprising given that cratonic roots are known to be compositionally distinct from the surrounding ambient mantle moreover it is expected that the temperature dependence of the thermal r s in the upper mantle is significant due to the temperature dependence of seismic attenuation or q therefore a simple 1 d density velocity relationship is insufficient to address this problem we obtained independent estimates of the first order correction factors to the selected r s profile within the cratonic roots and in the ambient thermal upper mantle these correction factors defined as r s lnv s are highly negative within the cratons signifying considerable compositional buoyancy this result confirms that the negative buoyancy associated with the low temperatures in the cratons is significantly counteracted by the composition induced positive buoyancy resulting in near neutral buoyancy of the cratonic roots within the ambient upper mantle the correction factors are found to be positive which is consistent with the expected behaviour of the r s relationship in thermally varying upper mantle material we obtain a significantly greater reconciliation of the global gravity anomalies and dynamic surface topography when applying these laterally varying corrections compared to a simple 1 d r s relationship inversion for a fully 3 d r s relationship reveals secondary effects including additional compositional variation within the cratonic roots and the deep mantle superplume structures we estimate the relative magnitude of the thermal and compositional non thermal contributions to mantle density anomalies and conclude that thermal effects dominate shear wave and density heterogeneity throughout the non cratonic mantle we also demonstrate the potential pitfalls of scaling a purely seismically derived model to obtain density rather than performing a true joint inversion to obtain velocity and density simultaneously

paleogene temperature gradient seasonal variation and climate evolution of northeast china abstract continental paleogene climates have been well studied in europe and north america but very little is known from asia because paleoclimatic results have only been reported from particular geological intervals here based on 29 plant assemblages from 8 well age controlled fossiliferous sites we quantitatively reconstruct the climates through most of the paleogene of northeast china and discuss related seasonal variations our results demonstrate that the mean annual temperature mat gradient was fairly shallow 0 27 c 1 latitude during the paleocene throughout this region in the eocene seasonality was high in the region indicated by marked differences in both temperature and precipitation between winters and summers of the sites the paleo east asian monsoon must have had intensified at least in the late mid eocene shown by apparent differences in annual precipitation distribution at all the sites regarding the paleogene climatic evolution of northeast china our quantitative results suggest that mat overall declined from warm in the paleocene and eocene to moderate in the oligocene generally consistent with the trend of marine records but with some distinctions two significant cooling events are recognized in the early and mid eocene with mat 3 4 c and 3 8 c lower and winter temperature 5 8 c and 4 7 c lower respectively in similar magnitudes to corresponding variations in europe and north america furthermore the present results show that mat rebounded in the late mid eocene and then decreased until the oligocene a similar pattern demonstrated in europe during the mid eocene to oligocene interval

using probabilistic seismic tomography to test mantle velocity density relationships we use a neighborhood algorithm to explore the fit to long period seismic data of a wide variety of long wavelength mantle models this approach to the global tomographic inverse problem yields probability distributions for seismic velocities density and related properties as functions of depth such distributions can be robust even when individual models are not and allow us to test several assumptions about the earth that have long been enforced a priori in inversions in particular we are able to test the paradigm ofdeep mantle heterogeneity that is dominantly thermal in origin producing velocity and density perturbations that are well correlated and have relative amplitudes given by nlnb nlnvs 6 0 5 our distributions show that such relationships are unlikely and even though the results are consistent with recent best fitting models from damped seismic inversions they demonstrate that many specific properties ofsuch models are not robust the data clearly f density perturbations that are poorly or negatively correlated with velocity heterogeneity and have amplitudes several times larger yielding nlnb nlnvs s 1 0 than damped inversions allow these characteristics are most pronounced in the upper mantle transition zone and the base ofthe lower mantle suggesting layered convection the negative density velocity correlations f at these depths imply dominantly chemical heterogeneity while the likelihood ofrelatively high amplitude density variations suggests that variable iron content is an important component ofthis heterogeneity these results which we show to be consistent with independent gravity constraints represent a profound change in the interpretation of seismic constraints in addition the distributions show that even though best fitting density models from recent inversions or our sampling are consistent with the data most specific properties of such models are not robust this implies that it is more appropriate to use seismic model distributions rather than individual models to make geodynamic and geochemical inferences

classification of oil shales coals and other organic rich rocks abstract oil shales are a complex group of rocks which were deposited in a wide range of sedimentary environments and have a wide range of largely alginite dominated maceral assemblages a system of classifying oil shales and sapropelic coals is based on relative abundances of macerals classification of oil shales has applications to the commercial development of oil shale deposits and to the classification of petroleum source rocks

symmetry of the south china sea conjugate margins in a rifting drifting and collision context abstract the symmetry of conjugate rifted margins is a first order observable feature reflecting the geodynamic processes acting during and after continental rifting the symmetry of the south china sea scs rifted margins can be deduced from comprehensive geophysical datasets on a continental margin scale here we combine three key approaches 1 lateral fault distributions are delineated according to free air gravity anomalies 2 crustal stretching styles are mapped based on gravity inversion constrained by deep seismic profiles and 3 total extension of conjugate margins is estimated according to margin restorations and tectonic settings we infer a predominantly symmetric rifting style caused by pure shear extension with only narrow domains of asymmetric deformation in continent ocean transition cot regions that have undergone simple shear and where the lower crust of the highly thinned distal margin is embrittled before continental breakup however our analysis also suggests that this symmetry has been modified by post rift geodynamic processes southward lower crustal flow which occurred only on the southern margin due to the low viscosity of the lower crust and the slab pull induced by the subducting proto scs plate during seafloor spreading shifted the crustal stretching styles from symmetric to asymmetric the collision between the southern margin and borneo thickened the lower crust more than the upper crust at the southern end of the southern margin and shortened the southern margin this event had a large impact on the se margin but a small impact on the sw margin we conclude that 1 for the se and ne margins the crustal stretching styles shifted from asymmetric to approximately symmetric and the total extension shifted from symmetric to asymmetric 2 for the sw and nw margins the crustal stretching and total extension remained asymmetric and symmetric respectively

three dimensional gravity inversion for moho depth at rifted continental margins incorporating a lithosphere thermal gravity anomaly correction summary this paper describes a method for determining moho depth lithosphere thinning factor 1 1 and the location of the ocean continent transition at rifted continental margins using 3 d gravity inversion which includes a correction for the large negative lithosphere thermal gravity anomaly within continental margin lithosphere the lateral density changes caused by the elevated geotherm in thinned continental margin and adjacent ocean basin lithosphere produce a significant lithosphere thermal gravity anomaly which may be in excess of 100 mgal and for which a correction must be made in order to determine moho depth accurately from gravity inversion we describe a method of iteratively calculating the lithosphere thermal gravity anomaly using a lithosphere thermal model to give the present day temperature field from which we calculate the lithosphere thermal density and gravity anomalies for continental margin lithosphere the lithosphere thermal perturbation is calculated from the lithosphere thinning factor 1 1 obtained from crustal thinning determined by gravity inversion and breakup age for thermal re equilibration time for oceanic lithosphere the lithosphere thermal model used to predict the lithosphere thermal gravity anomaly may be conditioned using ocean isochrons from plate reconstruction models to provide the age and location of oceanic lithosphere a correction is made for crustal melt addition due to decompression melting during continental breakup and seafloor spreading we investigate the sensitivity of the lithosphere thermal gravity anomaly and the predicted moho depth from gravity inversion at continental rifted margins to the methods used to calculate and condition the lithosphere thermal model using both synthetic models and examples from the north atlantic

marine incursion events in the late cretaceous songliao basin constraints from sulfur geochemistry records abstract songliao basin in ne china developed the most productive oilfield in the world sourced from terrestrial rocks the main source rock of the basin includes member 1 of the qingshankou k2qn1 and members 1 and 2 of the nenjiang formation k2nj1 2 however the exact reasons for the formation of the source rock especially the k2qn1 are still controversial former paleontological and organic geochemical research suggested that organic matter was deposited during marine incursion events of k2qn1 but further geochemical evidence is needed this paper explores the distinct sulfate levels that distinguish marine from fresh waters of the songliao paleo lake we undertook a systematic investigation the sulfur geochemistry of the sediments from top of member 4 of the quantou formation k1q4 to top of member 1 of the qingshankou k2qn1 the ratio of organic carbon to the pyrite sulfur toc pys proved the previously suggested saline conditions during the deposition of k2qn1 and the pyrite sulfur isotope indicated that marine incursion may not only have occurred for k2qn1 but also for top of k1q4 the exact time for the beginning of marine incursion is to be determined the marine incursion within k2qn1 is not strong and partially controlled by the fluctuation of paleo lake level the present study will be helpful for understanding the contribution of marine incursion events to the burial of organic carbon in the songliao paleo lake although further studies are still needed

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