multiple source downwellings beneath eastern north china revealed by 3 d ccp migration of receiver function data abstract we collected and processed a total of 97 700 teleseismic receiver functions recorded by 580 broadband seismic stations from 686 earthquakes to study the mantle transition zone beneath eastern north china we employed a recently developed 3 d p and s wave velocity model the east asia radially anisotropic model eara2014 to compute pds moveouts to migrate receiver function data amplitudes of the stacked p660s and p410s using the 3 d pds moveout table are approximately 30 higher than those calculated from the 1 d iasp91 model the 3 d volume of ccp common conversion point stacked images that covers the area of 110 125 e and 36 43 n revealed two remarkable mantle transition zone anomalies with significant depression of the 660 km discontinuity together with other seismic observations we speculated that these two anomalies are resulted from two different dynamic processes beneath eastern north china

global distribution of large lunar craters implications for resurfacing and impactor populations by using high resolution altimetric measurements of the moon we produced a catalog of all impact craters 20 kilometers in diameter on the lunar surface and analyzed their distribution and population characteristics the most densely cratered portion of the highlands reached a state of saturation equilibrium large impact events such as orientale basin locally modified the prebasin crater population to 2 basin radii from the basin center basins such as imbrium orientale and nectaris which are important stratigraphic markers in lunar history are temporally distinguishable on the basis of crater statistics the characteristics of pre and postmare crater populations support the hypothesis that there were two populations of impactors in early solar system history and that the transition occurred near the time of the orientale basin event

the importance of secondary cratering to age constraints on planetary surfaces small craters less than one kilometer diameter can be primary craters produced by impact of interplanetary debris or they can be secondary craters produced by fallback of high velocity ejecta blocks from much larger but infrequent primary impacts the prevalent assumption over recent decades has been that primaries are most abundant so most small craters are independent random events and can be used for dating however recent results from europa and mars support the early theory that distant secondaries globally dominate the number of small lunar craters this would invalidate part of production functions that have been widely used for age dating crater excavation results in higher mean ejection velocities for smaller fragments resulting in a steeper size frequency distribution for secondary craters than is produced by the same size frequency distribution of interplanetary debris this review also discusses how small craters can sometimes be used to derive meaningful age constraints

summary of the results from the lunar orbiter laser altimeter after seven years in lunar orbit in june 2009 the lunar reconnaissance orbiter lro spacecraft was launched to the moon the payload consists of 7 science instruments selected to characterize sites for future robotic and human missions among them the lunar orbiter laser altimeter lola was designed to obtain altimetry surface roughness and reflectance measurements the primary phase of lunar exploration lasted one year following a 3 month commissioning phase on completion of its exploration objectives the lro mission transitioned to a science mission after 7 years in lunar orbit the lola instrument continues to map the lunar surface the lola dataset is one of the foundational datasets acquired by the various lro instruments lola provided a high accuracy global geodetic reference frame to which past present and future lunar observations can be referenced it also obtained high resolution and accurate global topography that were used to determine regions in permanent shadow at the lunar poles lola further contributed to the study of polar volatiles through its unique measurement of surface brightness at zero phase which revealed anomalies in several polar craters that may indicate the presence of water ice in this paper we describe the many lola accomplishments to date and its contribution to lunar and planetary science

lithospheric thermal structure and rheology of the eastern china abstract temperature distributions of the lithosphere beneath the eastern china were estimated by local isostasy equilibrium constrained geothermal calculation in this study maps of the lateral temperature variation at depths of 50 and 100 km as well as moho boundary are presented for the eastern china continent and the 600 c and 1100 c isotherm depth maps are also given meanwhile the thermal thickness of lithosphere is calculated as the depth of 1350 c isotherm the rheological strength of lithosphere is calculated based on a four layer model which consists of the upper lower lowermost crust layers and a wet lithospheric mantle layer the results show that the lithosphere of 160 180 km thick exists under sichuan basin in the western part of yangtze craton but keel is absent beneath the entire north china craton it is notable that the lithospheric thickness is only 130 140 km beneath ordos basin in the western part of north china craton accordingly there is no lithospheric keel beneath ordos basin these geothermal modeling results are in good agreement with those of seismic tomography and other geothermal studies the temperatures in the lower crust of the north china craton estimated are in range of 500 600 c consequently the composition of lower crust of the north china craton should be more mafic than that of previous estimation based on much cooler geotherms the spatial variation of lithospheric rheology in the eastern china is influenced by local geotherms and crustal compositions the creme brulee model which is represent by a strong crust portion but a weak lithospheric mantle portion in vertical strength profile approximates the lithospheric rheological layering for the regions of the western half of north china craton and the northern part of ne china which has thicker crust or moderate to high geotherm on the other hand the jelly sandwich model demonstrates the rheological layering of the western part of the yangtze craton and the eastern half of the north china craton which has low to moderate geotherm and or thinner crust in general thermal age of the tectonic province controls the present day thermal structure and rheology of the lithosphere of the eastern china

lithosphere structure and thickness beneath the north china craton from joint inversion of ambient noise and surface wave tomography 1 we imaged detailed 3 d crustal and uppermost mantle seismic structures in the north china craton from inversion of rayleigh wave phase velocity at periods of 6 to 143 s the phase velocities were obtained from a combination of ambient noise and teleseismic surface wave tomography and then the phase velocities were inverted to s wave velocities the results show that both the huabei basin and ordos block have markedly rapid variations in both crustal velocities and the moho depth huabei basin has a thin 31 34 km crust with low velocities while ordos block has a thick 40 km crust with high velocities we also estimated the lithospheric thickness from the inverted s wave velocities using a simple s wave velocity temperature relationship huabei basin was imaged as a low s wave velocity anomaly in the uppermost mantle with very thin lithosphere 65 km while ordos block was revealed as a high s wave velocity anomaly with rather thick lithosphere 120 km these results indicated that huabei basin and ordos block have different thermal and or chemical properties and had experienced different mantle processes and evolution histories since the cenozoic furthermore slow s wave velocities and very thin lithosphere 65 km were also found beneath hetao and weihe rifts bounding ordos block at north and south respectively however shanxi rift the boundary between huabei basin and ordos block had a much thicker and higher velocity lithosphere than hetao and weihe rifts

upper mantle anisotropy beneath north china from shear wave splitting measurements abstract polarization analysis of teleseismic data was used to determine the sks fast polarization directions and the delay times between the fast and slow shear waves for each of the 52 seismic stations from both temporary and permanent broadband seismograph networks deployed in the north china craton ncc the analysis employed both the silver and chan 1991 and stacking analysis methods in this way an image of upper mantle anisotropy in the ncc was acquired the fast polarization directions are oriented along a wnw ese azimuth in the eastern and central blocks and rotate to a nnw sse azimuth in the western block the average fast polarization directions in the eastern and central blocks and the western block are 107 9 and 153 12 respectively the average delay time in eastern and central blocks is 0 98 0 19 s whereas it is 0 75 0 17 s in the western block in the eastern and central blocks the fast polarization direction is consistent with the absolute plate motion apm direction implying that the wnw trending asthenospheric mantle flow driven by the apm plays a major role in observed upper mantle anisotropy beneath the eastern and central blocks and makes the alignment of upper mantle peridotite lattice parallel to the deformation direction and thus generates consistently the wnw trending fast polarization direction however in the stable western block the weak anisotropy observed is possibly attributed to the fossil anisotropy frozen in the thick lithosphere of ancient cratonic ncc

impact of human activities on quality and geochemistry of groundwater in the merdja area tebessa algeria chemical data are used to clarify the hydrogeological regime in the merdja area in tebessa as well as to determine the status of water quality in this area groundwater from the aquifer in the merdja area can be divided into two major groups according to geographical locations and chemical compositions water in the center part of the area of study is characterized by the dominance of chloride sulfate sodium and potassium whereas waters in the limestone aquifers in the west are dominated by the same cations but have higher concentrations of bicarbonate stable isotopes show that the tebessa aquifers contain a single water type which originated in a distinct climatic regime this water type deviates from the global meteoric water line mwl as well as from the mediterranean meteoric water line the water is poor in tritium and thus can be considered generally older than 50 years piezometric map suggests that water is moving from the west towards the center of the studied area and from east towards center degradation of water quality can be attributed to agricultural fertilizers in most cases although the wadi el kebir river is a contributor to pollution in the middle part of the studied area

seismic evidence for the stratified lithosphere in the south of the north china craton 1 the north china craton ncc formed in the paleoproterozoic and suffered cratonic destruction in the mesozoic it consists of the western ncc wncc the trans north china orogen tnco and the eastern ncc encc we investigated the upper mantle structures in the southern ncc by using receiver functions analysis polarization analysis was applied to increase the quality of receiver functions the seismic images show significant stratified structures in the upper mantle in the south of the ncc in the south of the wncc the lithosphere is 280 km thick and contains a low velocity zone at 110 220 km depth this low velocity zone is interpreted as an intracratonic partial melting zone in the south of the tnco and encc there is a low velocity zone at 60 200 km depth which results from the partial melting during the mesozoic cratonic destruction its upper boundary is interpreted as new lithosphere asthenosphere boundary at 60 100 km depth below this low velocity zone there are the remains of archean lithosphere ral blocks of ral stagnate in the asthenosphere and reach depths over 300 km a high velocity slab extends from the uppermost mantle of the wncc into the ral with a dip angle of 20 this slab is interpreted as the paleoproterozoic slab which indicates an eastward subduction between the wncc and the encc the wncc is stable the lithosphere in the south of the tnco and encc suffered the mesozoic cratonic destruction while the destruction is relatively weaker than that in the north of the encc

constraints on the interpretation of s to p receiver functions summary we present results from forward modelling to study the feasibility of using s to p converted phases to image the seismic discontinuity structure of the crust and upper mantle we show that a significant level of p wave energy arriving before the direct s wave arrival can interfere with the s to p converted phases of interest and may result in sp receiver function phases that do not represent true earth structure the source of this p wave energy is attributable to a number of phases including those that have undergone multiple reflections off the earth s surface for deep focus earthquakes 300 600 km deep a significant amount of p wave energy is observed from pppp ppppp and spppp phases and arrives within the same time window as predicted for s to p converted phases from the direct s phase arrival furthermore for earthquakes at all depths interfering p wave energy arrives within the same time window as predicted for s to p converted phases from the sks phase arrival limiting the usefulness of sksp receiver functions for upper mantle imaging to isolate true sp receiver function phases from contamination due to other p wave phases we find it necessary to stack receiver functions from a range of epicentral distances and depths in order to aid the suppression of noise and other unwanted phases we provide constraints on the noise levels to be expected as a function of epicentral distance and earthquake depth we find that the lowest noise levels are achievable by restricting epicentral distance to less than 75 degrees and the depth of earthquakes used to less than 300 km

origin of water salinity in a lake and coastal aquifer system the studied area is in the algerian northeast a number of interacting factors at the site are able to modify salinity the main influences are 1 the lithology 2 fedzara lake 3 marine waters and 4 a prolonged drought 1 the lithology is very clearly delineated by the outcrop of metamorphic formations gneiss marbles micaschists and quartzites and sedimentary formations limestones clay sandstones and sands all these formations can influence the chemical composition of waters 2 fedzara lake evacuates its salted waters via the wadi meboudja which connects with the wadi seybouse and the phreatic surface these lake waters might induce changes in salinity 3 the marine waters represent the third source of salinity change over pumping of water from wells and drillings can cause an imbalance to the fresh salted water interface 4 the effects of a local prolonged drought of more than 10 years may increase water salinity over pumping to augment water supply generates a fall in water levels and the drier atmosphere increases evapotranspiration both may contribute to increased salinity results of water analysis were used to observe the evolution of these various factors

lithospheric structure of the northeastern north china craton imaged by s receiver functions lithosphere thickness variation is important for understanding the significant tectonic reactivation of the north china craton ncc in the mesozoic and cenozoic time here we determined the lithospheric structure in the northeastern ncc using s receiver functions from 305 teleseismic events recorded by 223 seismic stations the moho and lithosphere asthenosphere boundary lab are imaged clearly beneath the region the moho depth decreases from 45 km beneath the western ncc to 25 km beneath the eastern ncc we found that the lithospheric thickness varies from 60 to 80 km beneath the trans north china orogen tnco and eastern ncc with no significant change of the lab depth the lithosphere thickness beneath the northwestern ordos plateau is 100 130 km in addition there is a mid lithosphere discontinuity at a depth of 80 km beneath the plateau that is connected to the base of thinned lithosphere in tnco and eastern ncc we suggest that the mid lithosphere discontinuity represents a mechanically weak zone in the original cratonic lithosphere of the ncc the material in the lower lithosphere of the craton when warmed and hydrated by water released from the subducting slab of western pacific became weak due to decrease in viscosity and or partial melting and was subsequently removed through small scale mantle convections

nonuniform cratering of the moon and a revised crater chronology of the inner solar system abstract we model the cratering of the moon and terrestrial planets from the present knowledge of the orbital and size distribution of asteroids and comets in the inner solar system in order to refine the crater chronology method impact occurrences locations velocities and incidence angles are calculated semi analytically and scaling laws are used to convert impactor sizes into crater sizes our approach is generalizable to other moons or planets the lunar cratering rate varies with both latitude and longitude with respect to the global average it is about 25 lower at 65 n 90 e and larger by the same amount at the apex of motion 0 n 90 w for the present earth moon separation the measured size frequency distributions of lunar craters are reconciled with the observed population of near earth objects under the assumption that craters smaller than a few kilometers in diameter form in a porous megaregolith varying depths of this megaregolith between the mare and highlands is a plausible partial explanation for differences in previously reported measured size frequency distributions we give a revised analytical relationship between the number of craters and the age of a lunar surface for the inner planets expected size frequency crater distributions are calculated that account for differences in impact conditions and the age of a few key geologic units is given we estimate the orientale and caloris basins to be 3 73 ga old and the surface of venus to be 240 ma old the terrestrial cratering record is consistent with the revised chronology and a constant impact rate over the last 400 ma better knowledge of the orbital dynamics crater scaling laws and megaregolith properties are needed to confidently assess the net uncertainty of the model ages that result from the combination of numerous steps from the observation of asteroids to the formation of craters our model may be inaccurate for periods prior to 3 5 ga because of a different impactor population or for craters smaller than a few kilometers on mars and mercury due to the presence of subsurface ice and to the abundance of large secondaries respectively standard parameter values allow for the first time to naturally reproduce both the size distribution and absolute number of lunar craters up to 3 5 ga ago and give self consistent estimates of the planetary cratering rates relative to the moon

timing of destruction of the north china craton abstract the north china craton ncc is the typical example of destruction of an ancient craton however the destruction mechanism and geodynamic controlling factors still remain enigmatic due to controversy on the timing of destruction which is the key to understanding the destruction processes based on temporal and spatial distributions of the igneous rocks and their sources and tectonic settings it is recognized that six stages of tectono magmatism occurred in the ncc during the phanerozoic i e carboniferous to early permian late permian to middle triassic late triassic jurassic early cretaceous and cenozoic among them cenozoic magmatism mainly consists of alkali basalts and is found only occasionally in the eastern ncc the first four stages of magmatism and tectonism related to the southward subduction of the paleo asian plate and the assembly of sino korean and yangtze cratons are locally distributed in limited parts of the ncc reflecting a multiple stage modification of the ncc from the late carboniferous to jurassic however the intensive development of early cretaceous magmatism extensional deformation and associated gold mineralization with significant continental crustal growth indicate that the eastern ncc was destroyed during this time period this destruction was the result of paleo pacific subduction beneath the eastern asian continent with lithospheric removal and or replacement of an ancient cratonic lithosphere by a juvenile oceanic lithosphere

the lithospheric thinning of the north china craton inferred from rayleigh waves inversion summary joint inversion of interstation phase and group velocity dispersion data of rayleigh waves provides the regional shear wave velocity structure of the lithosphere across the central and eastern block of the north china craton ncc both the velocity dispersion curves and v s structure show strong lateral variation across the ncc which correlates well with the regional tectonic evolution at the lower crustal level the characteristics of v s structure reveal differences in composition of the two blocks in the upper mantle the lithospheric removal in the eastern ncc is more severe than in the central ncc the v s differences between the central ncc and the eastern ncc imply that multistage reactivation of the ncc occurred in the mesozoic and cenozoic time

estimation of long term diffuse groundwater discharge in the northern sahara using stable isotope profiles in soil water stable isotope profiles in soil water in the sahara have been interpreted in terms of the hydrologic processes taking place at one site where the water table is at about 10 m depth the isotope data are interpreted using the model of barnes and allison to show that the water loss by evaporation from the water table is about 2mm a 1 at another site nearby there is a net evaporative loss from the water table but the evaporation is interrupted by occasional infiltration events it is suggested that accumulation of chloride in soil water can give information about the onset of aridity in the sahara

determining the recharge mode of sahelian aquifers using water isotopes abstract it is proposed that the drainage network plays an important role in the recharge process of the fractured aquifers in the african precambrian shield and that the fractured aquifer system is likely to be hydraulically continuous this contrasts with most previous studies which suggested direct recharge by rainwater percolation two areas were selected in niger for the study of the aquifer recharge process using isotopic analyses of water 2 h 18 o 3 h the first area centred on the village of kobio is the 21 km 2 drainage basin of the lomona intermittent stream some 60 km southwest of niamey the capital city of niger the second area in the vicinity of niamey represents a portion of the niger basin draining a surface area many orders of magnitude larger than the lomona basin the mean 18 o composition of water from all wells in the kobio aquifer provides evidence for recharge by evaporated water this is confirmed by the concomitant increase of 18 o content with rising static water levels as recharge proceeded tritium data suggest progressive aging of the kobio aquifer water in the flow direction inferred from static water levels with a down gradient depletion of 18 o composition suggesting that enriched recharge water is progressively mixed with depleted aquifer water recharge by a reach of the lomona is proposed to explain these results in the niamey area wells the 18 o time series clearly define an injection of evaporated water from the surface into the fractured aquifer this recharging plume of evaporated water most likely originates from the niger river thus isotope data for two drainage basins of very different sizes indicate that aquifers are recharged by water from the rivers and that the flow regime of surface waters controls the recharge process

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

mesozoic crust mantle interaction beneath the north china craton a consequence of the dispersal of gondwanaland and accretion of asia we present evidence from zircons entrained within lower crustal xenoliths in the cenozoic hannuoba basalt of multiple melting events beneath the north china craton in the late mesozoic peak activity was between 180 and 80 ma the upper crustal signature of which was the generation of voluminous granitoids and related volcanic rocks emplacement of dioritic and lamprophyric dikes and widespread gold mineralization the process involved partial loss of mantle lithosphere accompanied by wholesale rising of asthenospheric mantle beneath eastern china we correlate these events with lithospheric thinning resulting from the breakup and dispersal of gondwanaland accompanied by a major mantle overturn fueled by the destruction of oceanic lithosphere and triggered by its sinking into the lower mantle during the subsequent accretion of asia

automated crater shape retrieval using weakly supervised deep learning abstract crater ellipticity determination is a complex and time consuming task that so far has evaded successful automation we train a state of the art computer vision algorithm to identify craters in lunar digital elevation maps and retrieve their sizes and 2d shapes the computational backbone of the model is maskrcnn an instance segmentation general framework that detects craters in an image while simultaneously producing a mask for each crater that traces its outer rim our post processing pipeline then finds the closest fitting ellipse to these masks allowing us to retrieve the crater ellipticities our model is able to correctly identify 87 of known craters in the longitude range we hid from the network during training and validation test set while predicting thousands of additional craters not present in our training data manual validation of a subset of these new craters indicates that a majority of them are real which we take as an indicator of the strength of our model in learning to identify craters despite incomplete training data the crater size ellipticity and depth distributions predicted by our model are consistent with human generated results the model allows us to perform a large scale search for differences in crater diameter and shape distributions between the lunar highlands and maria and we exclude any such differences with a high statistical significance

characterization of the main karst aquifers of the tezbent plateau tebessa region northeast of algeria based on hydrogeochemical and isotopic data chemical properties and hydrogeological characterization of water resources were studied in the hammemt plain which is located in the northwest of the tezbent mountain range city of tebessa northeast of algeria which drains carbonate aquifers through various large karst springs the physical and chemical characteristics of spring and well water samples were studied for 2 years in order to assess the origin of groundwater and determine the factors driving its geochemical composition the ionic speciation and mineral dissolution precipitation were calculated where we found that water wells characterizing groundwater circulation at shallow depths are moderate to highly mineralized waters of the na hco3 type in contrast to the shallow environment the co2 rich deeper waters are of the ca hco3 type and undergo significant changes in their baseline chemistry along flow lines with increasing residence time the main factors controlling the groundwater composition and its seasonal variations are geology because of the presence of different carbonate formations additionally elevation and the rate of karst development supersaturation with respect to calcite indicates co2 degasing occurs either inside the aquifer in open conduits or at the outlet in reservoirs undersaturation with respect to calcite shows the existence of fast flow and short residence time conditions inside the aquifer the main springs and wells of the tazbent mountain have been studied by means of stable isotope measurement where the values are varied in 18o between 8 2 and 7 76 for spring samples and from 8 26 to 7 15 for well samples and in 2h between 52 92 and 49 11 for spring samples and from 55 47 to 47 44 for well samples showing that the groundwater recharge is of meteoric origin and suggests the absence of the evaporation effect on the isotopic composition

lithospheric structure beneath the central and western north china craton and the adjacent qilian orogenic belt from rayleigh wave dispersion analysis abstract we used surface wave tomography to image the lithospheric s wave velocity structure along a linear seismic array across the central and western north china craton ncc and the adjacent qilian orogenic belt qb using waveform data from 8 earthquakes collected at 60 broadband stations rayleigh wave phase velocities were measured at periods of 20 120 s and subsequently inverted for reliable s wave velocities from 60 to 200 km depth distinct lithospheric structures and marked lateral variations were revealed beneath the study region correlating well with regional geological and tectonic features the average s wave velocity from 60 to 200 km depth beneath the array is 4 45 km s 1 lower than that in model ak135 high velocities of 4 45 km s are most pronounced beneath the stable ordos block western ncc however the depth to which the observed high velocity body extends varies significantly laterally it is deepest 200 km under eastern ordos and becomes shallower on both sides along the array the maximum depth of the high velocity body gradually shallows westward and reaches 110 km near the western edge of ordos this depth variation suggests a coexistence of both preserved and modified lithosphere in ordos the depth of high velocities decreases rapidly eastward by 80 km over a lateral distance of

lithospheric thickness of the chinese continent abstract we invert for the upper mantle temperatures of the chinese continent in the depth range of 70 240 km from a recent s velocity model the depth where temperatures intersect a mantle adiabat with a potential temperature of 1300 c is in close correspondence with the top of the seismic low velocity zone for most regions this correspondence implies that seismic lithosphere estimated from short time scale seismic information may be equivalent to the long time scale geodynamical lithosphere defining the 1300 c adiabat as coinciding with the lithospheric base we estimate the seismic thermal lithosphere thickness the estimated thickness shows obvious dependence on the tectonic settings beneath eastern china which mainly belongs to the circum pacific tectonic domain it has a thickness of 100 km and beneath the qinghai tibet plateau and south to the tarim craton which belong to the tethyan tectonic domain it has a thickness of 160 220 km the lithospheric thicknesses of the three large para platforms cratons range from 170 km for the western yangtze 140 km for tarim and 100 km for sino korean the three cratons may have been reshaped by phanerozoic tectonic activities and are thinner than most cratons in other continents

an upper mantle s wave velocity model for east asia from rayleigh wave tomography abstract we present a new shear velocity model of the upper mantle beneath the east asia region derived by inverting rayleigh wave group velocity measurements between 10 and 145 s combined with previously published rayleigh wave phase velocity measurements between 150 and 250 s rayleigh wave group velocity dispersion curves along more than 9500 paths were measured and combined to produce 2d dispersion maps for 10 145 s periods the group velocity maps benefit from the inclusion of new data recorded by the china national seismic network and surrounding global stations the increase in available data has resulted in enhanced resolution compared with previously published group velocity maps the horizontal resolution across the region is about 3 for the periods used in this study the new shear wave velocity models indicate varying velocity structure beneath eastern china which yields estimates of a lithosphere asthenosphere boundary depth from around 160 km beneath the yangtze block to approximately 140 km beneath the western part of the north china craton ncc up to depths of 70 100 km beneath the eastern ncc northeast china and the cathaysia block the models reveal the subduction of two opposite facing continental plates under the southern and northern margin of tibet an obvious low velocity anomaly appears in the top 200 km of the upper mantle beneath northern tibet which is inconsistent with the presence of subducted asian or indian mantle lithosphere beneath northern tibet the cenozoic volcanism fields in the mongolian plateau are characterized by an obvious upper mantle negative anomaly but no signature of deep seated plume was observed

hydrogeochemical analysis of salinization processes in the coastal aquifer of oropesa castellon spain the coastal aquifer of oropesa is affected by salinization processes undoubtedly associated with intense groundwater exploitation for agriculture supply the aquifer corresponds geologically to a tectonic depression with plioquaternary fill hydrogeologically this aquifer is detrital with intergranular porosity which receives substantial recharge from adjacent mesozoic aquifers contact with the sea in addition to the presence of cultivated soil requiring extreme exploitation of groundwater frequently give rise to processes of seawater intrusion the present research is an attempt to understand the saltwater intrusion in this aquifer using hydrochemical analyses of the behavior of certain minor ions that could help in the characterization process in the case of the oropesa sector groundwater salinization does not appear to be attributable solely to the intrusion of seawater but there are also anomalies related largely to the geology of the sector and its surroundings the type of recharge the hydrodynamic conditions in the specific area etc

crater degradation on the lunar maria topographic diffusion and the rate of erosion on the moon landscape evolution on the moon is dominated by impact cratering in the post maria period in this study we mapped 800 m to 5 km diameter craters on 30 of the lunar maria and extracted their topographic profiles from digital terrain models created using the kaguya terrain camera we then characterized the degradation of these craters using a topographic diffusion model because craters have a well understood initial morphometry these data provide insight into erosion on the moon and the topographic diffusivity of the lunar surface as a function of time the average diffusivity we calculate over the past 3 ga is 5 5 m2 myr with this diffusivity after 3 ga a 1 km diameter crater is reduced to approximately 52 of its initial depth and a 300 m diameter crater is reduced to only 7 of its initial depth and craters smaller than 200 300 m are degraded beyond recognition our results also allow estimation of the age of individual craters on the basis of their degradation state provide a constraint on the age of mare units and enable modeling of how lunar terrain evolves as a function of its topography

high resolution mantle tomography of china and surrounding regions 1 a high resolution p wave tomographic model of the crust and mantle down to 1100 km depth under china and surrounding regions is determined by using about one million arrival times of p pp pp and pcp waves from 19 361 earthquakes recorded by 1012 seismic stations the subducting pacific slab is imaged clearly as a high velocity zone from the oceanic trenches down to about 600 km depth and intermediate depth and deep earthquakes are located within the slab the pacific slab becomes stagnant in the mantle transition zone under east china the western edge of the stagnant slab is roughly coincident with a surface topographic boundary in east china the active changbai and wudalianchi intraplate volcanoes in northeast china are underlain by significant slow anomalies in the upper mantle above the stagnant pacific slab these results suggest that the active intraplate volcanoes in ne china are not hot spots but a kind of back arc volcano associated with the deep subduction of the pacific slab and its stagnancy in the transition zone under the mariana arc however the pacific slab penetrates directly down to the lower mantle the active tengchong volcano in southwest china is related to the eastward subduction of the burma microplate the subducting indian and philippine sea plates are also imaged clearly the indian plate has subducted down to 200 300 km depth under the tibetan plateau with a horizontal moving distance of about 500 km high velocity anomalies are revealed in the upper mantle under the tarim basin ordos and sichuan basin which are three stable blocks in china

sources of recharge at abu delaig sudan abstract various components of the water cycle in and around abu delaig a small town in a semiarid region of sudan have been investigated with geochemical and isotopic techniques to determine the sources of groundwater recharge rain samples total deposition during storms contain significant concentrations of dissolved solids for a continental site mean 4 6 mgl 1 for 1982 1985 the heaviest rains important for recharge tend to have the lowest chlorinities and are also the most negative isotopically wadi floods generally have lower chlorinity than the rainfall indicating the proportionally lower amounts of dust in the more intense rainfall events shallow ground waters at abu delaig have relatively evolved compositions higher mg ca ratios compared with rainfall and wadi floods yet they also contain tritium and retain isotopic signatures similar to the local rainfall they also have a distinctive chemistry compared with the deeper ground waters in the region and recharge from the former to the latter is considered to be insignificant ground waters in the unsaturated zone are saline and have isotopic compositions highly enriched in heavy isotopes compared with rainfall indicating strong evaporation the chloride balance indicates that mean recharge rates are 0 2 1 3 mm year 1 through the interfluve areas it is concluded that the only significant replenishable resources at abu delaig are from wadi recharge during floods and that direct regional recharge is insignificant fluctuations in the water table however lead to solutes from the lower unsaturated zone contributing to the chemistry of the shallow ground waters elsewhere it is possible that wadi recharge may be a possible route for deeper replenishment but this needs to be demonstrated by dedicated experiments

high resolution body wave tomography models of the upper mantle beneath eastern china and the adjacent areas 1 we present new 3 d tomographic models of vp vs and vp vsratio anomalies in the upper mantle beneath ec and adjacent areas this data was collected and interpreted with the goal of clarifying geodynamic processes that caused spatially variable event histories throughout eastern china ec during mesozoic to cenozoic time the tomographic images were constructed by inverting body wave travel times recorded at 1300 stations within the upgraded china national seismic network and 9 temporary arrays resolution tests for different depths and the featured velocity anomalies verify that the tomographic images capture the velocity heterogeneities in the upper mantle to depths of 700 km the salient features of vp vs and vp vsratio anomalies can be clearly identified these include strong multiscale heterogeneities occupying the upper mantle beneath ec and differences in the spatial scale of anomalies found beneath northern and southern areas of ec these features demonstrate a degree of spatial variability in the geodynamic evolution of ec we propose two mechanisms to explain these patterns first the western front of the subducted slab may have imparted greater horizontal compressional stress in areas where it impinged further eastward into ec these areas would experience stronger convection and an altered stress regime in the upper mantle creating significant thermal anomalies beneath the south china block scb relative to the eastern north china craton ncc second differing thermal states and viscosities for the eastern ncc and the cathaysia block cab resulted in differing responses to regional deformation the archean hinterland of the eastern ncc specifically has a colder thermal state and higher viscosity and therefore exhibits only small scale heterogeneities due to the effect of shear localization the neoproterozoic cab has a relatively warm thermal state with lower viscosity and thus deformed more continuously

hydrochemical and isotopic investigation of a sandstone aquifer groundwater in a semi arid region el ma el abiod algeria this work present results of the hydrochemical and isotopic studies on groundwater samples from the study area chemical and environmental isotope data are presented and discussed in terms of the origin of dissolved species and of groundwater all of the investigated groundwater are categorized into two chemical types low and relatively high mineralized waters type interpretation of chemical data based on both thermodynamic calculations and stability diagrams suggests that the chemical evolution of groundwater is primarily controlled by water rock interactions interpretation of 18o and 2h suggests that the recharge of the investigated groundwater may result from differents mechanisms

a new global database of mars impact craters 1 km 1 database creation properties and parameters 1 impact craters have been used as a standard metric for a plethora of planetary applications for many decades including age dating geologic mapping and stratigraphic relationships as tracers for surface processes and as locations for sampling lower crust and upper mantle material utilizing craters for these and other investigations is significantly aided by a uniform catalog of craters across the surface of interest consequently catalogs of craters have been developed for decades for the moon and other planets we present a new global catalog of martian craters statistically complete to diameters d 1 km it contains 384 343 craters and for each crater it lists detailed positional interior morphologic ejecta morphologic and morphometric data and modification state information if it could be determined in this paper we detail how the database was created the different fields assigned and statistical uncertainties and checks in our companion paper robbins and hynek 2012 we discuss the first broad science applications and results of this work

a new lunar digital elevation model from the lunar orbiter laser altimeter and selene terrain camera abstract we present an improved lunar digital elevation model dem covering latitudes within 60 at a horizontal resolution of 512 pixels per degree 60 m at the equator and a typical vertical accuracy 3 to 4 m this dem is constructed from 4 5 10 9 geodetically accurate topographic heights from the lunar orbiter laser altimeter lola onboard the lunar reconnaissance orbiter to which we co registered 43 200 stereo derived dems each 1 1 from the selene terrain camera tc 1010 pixels total after co registration approximately 90 of the tc dems show root mean square vertical residuals with the lola data of

high resolution lithospheric structure beneath mainland china from ambient noise and earthquake surface wave tomography abstract we present a new high resolution shear velocity model of the lithosphere down to about 160 km beneath china using rayleigh wave tomography we combined ambient noise and earthquake data recorded at 1316 seismic stations the largest number used for the region to date more than 700 000 dispersion curves were measured to generate group and phase velocity maps at periods of 10 140 s the resolution of our model is significantly improved over previous models with about 1 2 in eastern china and 2 3 in western china we also derived models of the study region for crustal thickness and averaged s velocities for upper and mid lower crust and uppermost mantle these models reveal important lithospheric features beneath china and provide a fundamental data set for understanding continental dynamics and evolution different geological units show distinct features in the moho depth lithospheric thickness and shear velocity in particular the north china craton ncc lithosphere shows strong east west structural variations with thin and low velocity lithosphere in eastern ncc and thick and high velocity lithosphere beneath western ncc and the lithosphere of the ordos block seems to have undergone strong erosion the results support the progressive destruction of the ncc lithosphere from east to west at least partly caused by the thermal chemical erosion of the cratonic lithosphere from the asthenosphere another pronounced feature of our model is the strong lateral variations of the mantle lithosphere beneath the tibetan plateau tp the indian lithosphere beneath the tp shows variable northward advancement with nearly flat subduction in western and eastern tp and steep subduction in central tp with evidence for the tearing of indian lithosphere beneath central tp which may be important for the riftings at the surface in himalayas and southern tp the low velocity zone in northern tp shows strong correlation with the region of the mid miocene to quaternary potassic magmatism suggesting that delamination of lithosphere may have played an important role in the rise of the tp

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

lithospheric discontinuities beneath the u s midcontinent signatures of proterozoic terrane accretion and failed rifting abstract seismic discontinuities between the moho and the inferred lithosphere asthenosphere boundary lab are known as mid lithospheric discontinuities mlds and have been ascribed to a variety of phenomena that are critical to understanding lithospheric growth and evolution in this study we used s to p converted waves recorded by the usarray transportable array and the oiink ozarks illinois indiana kentucky flexible array to investigate lithospheric structure beneath the central u s this region a portion of north america s cratonic platform provides an opportunity to explore how terrane accretion cratonization and subsequent rifting may have influenced lithospheric structure the 3d common conversion point ccp volume produced by stacking back projected sp receiver functions reveals a general absence of negative converted phases at the depths of the lab across much of the central u s this observation suggests a gradual velocity decrease between the lithosphere and asthenosphere within the lithosphere the ccp stacks display negative arrivals at depths between 65 km and 125 km we interpret these as mlds resulting from the top of a layer of crystallized melts sill like igneous intrusions or otherwise chemically modified lithosphere that is enriched in water and or hydrous minerals chemical modification in this manner would cause a weak layer in the lithosphere that marks the mlds the depth and amplitude of negative mld phases vary significantly both within and between the physiographic provinces of the midcontinent double or overlapping mlds can be seen along precambrian terrane boundaries and appear to result from stacked or imbricated lithospheric blocks a prominent negative sp phase can be clearly identified at 80 km depth within the reelfoot rift this arrival aligns with the top of a zone of low shear wave velocities which suggests that it marks an unusually shallow seismic lab for the midcontinent this boundary would correspond to the top of a region of mechanically and chemically rejuvenated mantle that was likely emplaced during late precambrian early cambrian rifting these observations suggest that the lithospheric structure beneath the reelfoot rift may be an example of a global phenomenon in which mlds act as weak zones that facilitate the removal of cratonic lithosphere that lies beneath

seismic evidence for significant lateral variations in lithospheric thickness beneath the central and western north china craton abstract we have migrated teleseismic s receiver functions to construct detailed lithospheric structure images that cover the three constituent parts of the north china craton ncc our images show that in contrast to the eastern ncc where significantly thinned lithosphere 60 100 km is widespread the central and western ncc are characterized by the coexistence of both preserved thick and dramatically thinned lithosphere the thick lithosphere 200 km is present beneath the stable ordos plateau and the thinned lithosphere up to 80 km is found in the late cenozoic yinchuan hetao and shaanxi shanxi rift areas with sharp changes occurring over a lateral distance of

cenozoic tectonic evolution of asia a preliminary synthesis abstract asia has been a major testing ground for various competing models of continental deformation due to its relatively well understood plate boundary conditions in the cenozoic exceptional exposure of active structures and strain distribution and widespread syn collisional igneous activity as a proxy for the thermal state of the mantle and crust two cenozoic orogens dominate the continent the himalayan tibetan orogen in the east induced by the india asia collision and the turkish iranian caucasus orogen in the west induced by the arabia asia collision the development of the two orogens was accomplished by shortening in the early stage followed by strike slip faulting and extension in the late stage in the himalayan tibetan orogen shortening across two discrete thrust belts at 55 30 ma in southern and northern tibet created a large intracontinental basin the paleo qaidam basin in between subsequent crustal thickening and a possible thermal event in the mantle e g convective removal of central tibetan mantle lithosphere may have raised the elevation of this early intra plateau basin up to 2 3 km to its current height collision between india and asia also caused lateral extrusion of southeast asia between 32 ma and 17 ma the latest stage of the india asia collision was expressed by north trending rifting and the development of trench facing v shaped conjugate strike slip faults in central mongolia central tibet eastern afghanistan and southeast asia in the turkish iranian caucasus orogen early crustal thickening in the orogenic interior began at or prior to 30 20 ma this style of deformation was replaced by strike slip faulting at 15 5 ma associated with further northward penetration of arabia into asia westward extrusion of the anatolia turkey block and rapid extension across the sea of crete and sea of aegean the late stage extension in both orogens was locally related to extensional core complex development the continental margin extension of east asia was developed in two stages initially in a widely distributed zone that has an east west width of 500 800 km during 65 35 ma which was followed by localized extension and opening of back arc basins associated with the development of spreading centers at 32 17 ma e g japan sea or east korea sea bohai bay and south china sea opening of the back arc basins could be induced by 1 rapid eastward migration of the western pacific trench system or 2 oblique subduction of pacific plate beneath asia that had produced a series of en echelon right slip primary shear zones linking with back arc spreading centers oriented obliquely to the strike of the nearby trench since 15 ma the eastern margin of asia became contractional in the east west direction as indicated by the collapse of back arc basins in the western pacific and the development of fold thrust belts along the eastern continental margin coeval with the contraction is widespread east west extension in siberia north china and the tibetan plateau the above observations can be explained by a change in boundary condition along the eastern margin of asia that allowed the thickened asian continent to spread eastward causing east west extension in its trailing edge and east west compression in its leading edge in west asia continental margin extension started at about 25 20 ma in the aegean and cretan regions which was associated with a rapid southward retreat of the hellenic arc the complex evolution of cenozoic deformation in asia may be explained by a combined effect of temporal changes in plate boundary conditions thermal evolution of the upper mantle perturbed by collisional tectonics and the built up of gravitational energy through crustal thickening and thermal heating although the past research in asia has treated the india asia and arabia asia convergence as separate collisional processes their interaction may have controlled the far field cenozoic deformation in asia the most pronounced result of this interaction is the creation of a northeast trending 300 400 km wide and 1500 km long zone of northwest striking right slip faults which extends from the zagros thrust belt in the south to western mongolia in the north and links with the active tian shan and altai shan intracontinental orogens cenozoic deformation and coeval igneous activity spatially overlap with one another in the himalayan tibetan and turkish iranian caucasus orogens a large cenozoic magmatic gap exists between tibet in the south and mongolia in the north where cenozoic deformation has not been associated with any coeval igneous activity finally cenozoic igneous activity is always associated with jurassic cretaceous magmatic arcs suggesting a causal relationship between the early arc magmatism and later syn collisional magmatism

a geologic model for lunar ice deposits at mining scales abstract water ice has been detected at the lunar poles but existing and near future orbital datasets do not have the capabilities to determine its horizontal and vertical distribution at meter to hundred meter scales relevant for mining operations additionally there has not yet been a coherent geologic model put forward for how ice deposits have formed and evolved that can be used to assist in planning prospecting campaigns or developing relevant hardware here we propose a system model for understanding these deposits at scales of meters to hectares the model considers sources of water ice capture at and below the surface and retention it focuses heavily on impact gardening as a modifying process that drives changes in how ice is distributed 3 dimensional stochastic impact simulations are then used to test the system model and explore how ice deposits might evolve over an area the size of a potential mining outpost the simulation results showed ice concentrations should eventually become fairly homogeneous at meter to hectare scales due to impact gardening and high concentrations are distributed randomly rather than clustered in earth like ore bodies we found the best ice deposits for extracting likely exist 10s of cm deep or more even in locations where ice is currently stable at the very surface terrestrial mining software was then used to create block models and grade tonnage curves that can inform future in situ resource utilization demonstration missions and future mining operations planning

geochemical calculations and observations on salt water intrusions i a combined geochemical minxing cell model abstract a combined geochemical mixing cell flow model has been developed the geochemical model is based on the computer program eq 3 6 wolery 1982 has been modified to include cation exchange reactions and is incorporated in a one dimensional mixing cell model for stationary one dimensional transport dispersion or diffusion is calculated by mixing the cell contents with neighbouring cells relationships between mixing factors and dispersivity and diffusion coefficients are derived the model is used to simulate concentration changes during salt water intrusions fundamental differences are shown to exist between diffusion of salt water from a stagnant water body and dispersive intrusions during marine transgressions or flooding events with dispersive flow characteristic water compositions develop in space and time as a result of cation exchange with diffusion these steep concentration gradients are smoothed out and mixed compositions occur the concept that characteristic concentrations occur during dispersive flow is used to obtain paleohydrological information in a dutch polder the depth of the fresh salt water interface before polder development is deduced from a simulation of observed exchange reactions in the polder groundwater

suitability assessment of deep groundwater for drinking and irrigation use in the djeffara aquifers northern gabes south eastern tunisia the multilayered djeffara aquifer system south eastern tunisia has been intensively used as a primary source to meet the growing needs of the various sectors drinking agricultural and industrial purposes the analysis of groundwater chemical characteristics provides much important information useful in water resources management detailed knowledge of the geochemical evolution of groundwater and assessing the water quality status for special use are the main objective of any water monitoring study an attempt has been made for the first time in this region to characterize aquifer behavior and appreciate the quality and or the suitability of groundwater for drinking and irrigation purposes in order to attend this objective a total of 54 groundwater samples were collected and analyzed during january 2008 for the major cations sodium calcium magnesium and potassium anions chloride sulfate bicarbonate trace elements boron strontium and fluoride and physicochemical parameters temperature ph total dissolved salts and electrical conductivity the evolution of chemical composition of groundwater from recharge areas to discharge areas is characterized by increasing sodium chloride and sulfate contents as a result of leaching of evaporite rock in this study three distinct chemical trends in groundwater were identified the major reactions responsible for the chemical evolution of groundwater in the investigated area fall into three categories 1 calcite precipitation 2 gypsum and halite dissolution and 3 ion exchange based on the physicochemical analyses irrigation quality parameters such as sodium absorption ratio sar percentage of sodium residual sodium carbonate residual sodium bicarbonate and permeability index pi were calculated in addition groundwater quality maps were elabortaed using the geographic information system to delineate spatial variation in physico chemical characteristics of the groundwater samples the integration of various dataset indicates that the groundwater of the djeffara aquifers of the northern gabes is generally very hard brackish and high to very high saline and alkaline in nature the water suitability for drinking and irrigation purposes was evaluated by comparing the values of different water quality parameters with world health organization who guideline values for drinking water piper trilinear diagram was constructed to identify groundwater groups where the relative major anionic and cationic concentrations are expressed in percentage of the milliequivalent per liter meq l and it was demonstrated that the majority of the samples belongs to so4 cl ca na cl so4 na ca and na cl hydrochemical facies as a whole all the analyzed waters from this groundwater have revealed that this water is unsuitable for drinking purposes when comparing to the drinking water standards salinity high electric conductivity sodium adsorption ratio and sodium percentages indicate that most of the groundwater samples are inappropriate for irrigation the sar vary from medium s2 to very high s4 sodicity therefore the water of the djeffara aquifers of the northern gabes is dominantly of the c4 s2 class representing 61 23 of the total wells followed by c4 s3 and c4 s4 classes at 27 27 and 11 5 of the wells respectively based on the us salinity classification most of the groundwater is unsuitable for irrigation due to its high salt content unless certain measures for salinity control are undertaken

reactivation of an archean craton constraints from p and s wave tomography in north china 1 the unusual reactivation of the north china craton ncc challenges the classical views concerning the strength and stability of cratonic lithosphere by using teleseismic body waves recorded at 250 seismic stations this paper presents high resolution north china models of p and s wave velocity based on finite frequency kernel tomography both p and s wave velocity models reveal that 1 an obvious n s trending narrow low velocity region is located at the base of the lithosphere beneath the central block cb of the ncc which extends to more than 500 km depth 2 a region of high velocity extends to more than 250 300 km depth beneath the western block in contrast to the much shallower high velocity zones beneath the cb and shallower high velocities beneath the eastern block these features suggest that warm mantle material with a source at least as deep as the transition zone possibly a mantle plume may be responsible for the reactivation of the ncc the central block may have behaved as a sublithospheric corridor for the warm mantle material due to its pre existing weakness

spatio temporal characterization of the pliocene aquifer conditions in wadi el natrun area egypt wadi el natrun area has recently undergone extensive urban and agricultural expansion due to the absence of natural surface irrigation supplies the only source of water in the area is the pliocene groundwater aquifer as a result secondary salinization from increased abstractions is the major threat to the groundwater aquifer there is a dire need for efficient strategies to ensure long term sustainability of the area s productive agriculture these strategies should be based on scientific spatio temporal monitoring and analysis of the groundwater conditions that is also lacking to capture the spatio temporal variability in groundwater conditions field measurements of total dissolved solids electrical conductivity ph temperature and water level as well as lab based ionic composition were performed on 47 groundwater samples collected during 2006 and 2007 determinations of the hydrochemical characteristics water types salt assemblages and the sodium adsorption ratio were carried out on the samples reference data sets recorded in 1973 and 1997 were available for the area and were used to monitor the changes occurred in these periods geographic information system gis was appraised for mapping and for integrated analysis of the different layers remotely sensed change detection techniques were applied to the landsat tm and the etm imageries and used to highlight the extensive reclamation and urbanization and to find key trends for the alterations in the groundwater conditions and their spatial association with land covers results revealed a topographic depression induced flow pattern predominance of leaching and dissolution processes the presence of saline lakes over pumping from the pliocene aquifer and temporal changes in land uses are the main factors combined to control the spatio temporal variability in the groundwater results also clarified the presence of two northwestern and southeastern zones that varied distinctively in their hydrodynamic and hydrochemical characteristics the northwestern zone showed an average water level decline of 15 m the water of which is brackish av 2 037 mg l with dominant na cl and so42 ions the groundwater of this zone is characterized by high to very high salinity hazard and high to very high alkali hazard and is not recommended for irrigation on soils with poor drainage and without proper management for salinity control the southeastern zone showed water level decline less than 2 m the water of which is fresh av 424 mg l with major na hco3 cl and so42 ions and quality suitable for irrigation with medium to high salinity and low to medium alkali hazards the article represents the first step towards an integrated management of wadi el natrun groundwater resources within a gis framework

groundwater evolution in the continental intercalaire aquifer of southern algeria and tunisia trace element and isotopic indicators abstract the geochemical processes taking place along an 800 km flow line in the non carbonate continental intercalaire aquifer ci aquifer in north africa are described using chemical major and trace element and isotopic indicators the aquifer is hydraulically continuous from the atlas mountains in algeria to the chotts of tunisia and the geochemical evidence corroborates this the highest discharge temperature is 73 c but silica geothermometry indicates a maximum temperature of 94 c at depth chloride concentrations increase from 200 to 800 mg l 1 and the br cl ratios confirm the dissolution of non marine evaporites or interstitial waters as the main source of salinity fluoride concentrations are low and are likely to be derived from rainfall recording oscillations in source radiocarbon ages except near outcrop are at or near detection limits and the 18o and 2h values indicate a cooler recharge regime with rainfall having lower primary evaporation than today this is shown by the fact that mean isotope ratios of ci waters are around 3 lighter than the present day weighted mean value for rain major ion ratios and most trace elements indicate that despite the complex structure and stratigraphy uniform evolution with continuous water rock interaction takes place along the flow lines which are only disturbed near the tunisian chotts by groundwater converging from additional flow lines the ageing of the water can also be followed by the smooth increase in several indicator elements such as li k and mn which are least affected by solubility controls similarly the influence of marine facies in the tunisian sector may be recognised by the changing mg ca and higher br cl as well as trace element indicators the groundwaters are oxidising up to 300 km from outcrop dissolved o2 has persisted for at least 20 ka and within this zone the concentrations of several elements forming oxy anions such as u and cr increase and no3 remains conservative beyond 300 km from outcrop the groundwaters are reducing and contain high fe concentrations the basin contains huge reserves of fresh brackish waters but these need careful development due to the limiting high salinity and scaling tendency resulting from the high temperatures and mineral super saturation caused during abstraction as well as high concentrations of some harmful elements such as cr in the oxidising section

archean blocks and their boundaries in the north china craton lithological geochemical structural and p t path constraints and tectonic evolution an examination of lithological geochemical geochronological structural and metamorphic p t path data suggests that the basement of the north china craton can be divided into eastern and western blocks separated by major crustal boundaries that roughly correspond with the limits of a 300 km wide zone called the trans north china orogen the eastern block consists predominantly of late archean domiform tonalitic trondhjemitic granodioritic ttg batholiths surrounded by anastomosing networks and linear belts of open to tight synforms of minor volcanic and sedimentary rocks metamorphosed from greenschist to granulite facies at 2 5 ga with anticlockwise p t paths some early to middle archean rocks are locally present in the eastern block but their tectonic history is unclear due to reworking by the 2 5 ga tectonothermal event the western block has a late archean assemblage structural style and metamorphic history similar to that of the eastern block but it differs in the absence of early to middle archean assemblages and in being overlain by and interleaved with paleoproterozoic khondalites which were affected by a 1 8 ga metamorphic event involving clockwise p t paths a mantle plume model is proposed for the formation and evolution of late archean basement rocks in the eastern and western blocks based on a combination of extensive exposure of ttg gneisses affinities of mafic rocks to continental tholeiitic basalts presence of voluminous komatiitic rocks dominant diaprism related domiform structures anticlockwise p t paths and a short time span from the primary emplacement of ttg and ultramafic to mafic rocks until the onset of regional metamorphism between the two blocks is the trans north china orogen which is bounded by two major fault systems and is composed of late archean to paleoproterozoic ttg gneisses and granitoids interleaved with abundant sedimentary and volcanic rocks that are geochemically interpreted as having developed in magmatic arc and intra arc basin environments these rocks underwent multiple phases of compressional deformation and peak high pressure metamorphism followed by rapid exhumation during the late paleoproterozoic at 1 8 ga as a result of collision between the eastern and western blocks resulting in the amalgamation of the north china craton

geochemical and qualitative assessment of groundwater of the high mekerra watershed nw algeria groundwater constitutes the main source of water supply in the high mekerra watershed of northwestern algeria this resource is currently under heavy pressures to meet the growing needs of drinking water and irrigation this study assesses the geochemical characteristics of groundwater of the high mekerra watershed at 21 points distributed across the two main aquifers ras el ma and mouley slissen in the region hydrochemical facies of ras el ma groundwater are dominantly mgcl and cacl type while those of mouley slissen groundwater are of cahco3 type principal component analysis shows a strong correlation between groundwater mineralization and ca2 na cl and so4 2 ions stemming from the dissolution of carbonates gypsum and anhydrite groundwater mineralization evolves from south to north geochemical modeling shows that the high mekerra groundwater is saturated with respect to calcite and dolomite and undersaturated with respect to gypsum and anhydrite nitrate concentrations that exceed the who standard 50 mg l 1 at several points are linked to the agro pastoral activities in this region

lithospheric structure of the ordos block and its boundary areas inferred from rayleigh wave dispersion abstract we have measured rayleigh wave phase velocities of the ordos block and its southern and western boundary areas and inverted these data to describe the upper mantle structure the ordos block was found to be characterized by distinctly high seismic velocities at depths commonly associated with a low velocity asthenosphere to the south abnormally slow velocity anomalies appeared in the weihe rift probably indicating subsolidus grain boundary weakening effect under high temperatures near solidus instead of partial melt in the asthenosphere an intermediate seismic velocity structure was observed beneath the northern qinling orogen nql to the south of the weihe rift a thin high velocity lid which was probably a cratonic relic was found under the haiyuan arcuate tectonic region hatr west of the ordos block a thick lithosphere was present beneath the ordos block 200 km and the nql 140 km while a thinner lithosphere 100 km was found beneath the hatr and the weihe rift the observed structural differences were likely associated with different lithospheric tectonics in the study region whereas the weihe rift and the hatr had been strongly affected by cenozoic lithospheric modification and thinning the ordos block and the nql appeared to have been much less influenced combined with previous studies our results suggested that the far field effect of the indo asia collision may have played an important role in the unique lithospheric process in the study region such as the extension of the weihe rift the preservation of a cratonic relic under the hatr and the localized intense lithospheric modification of these two regions the substantial variations of deep structure and thus contrasting rheological properties between the ordos block and the surrounding notable seismic belts the hatr and weihe rift may be a candidate mechanism for the contrasting seismicity of the region the lateral variations in the lithospheric structure estimated here generally agreed with changes in upper mantle deformation patterns previously derived from sks splitting measurements

regional variations in the chemical and helium carbon isotope composition of geothermal fluids across tunisia abstract tunisia has numerous thermo mineral springs previous studies have shown that their chemical composition and occurrence are strongly influenced by the regional geology however little work has been done so far to study the isotopic composition of volatiles associated with these geothermal manifestations here we report on the results of an extensive survey of both natural hot springs and production wells across tunisia aimed at investigating the spatial distribution of thermal fluids geochemical characteristics and he c isotopic composition the chemistry of the analyzed samples highlights the heterogeneity of the water mineralization processes in tunisia as a consequence of the complex geological and tectonic setting of the country in terms of chemical composition we are able to conclude however that dissolution of halite and gypsum plays a key control on groundwater chemistry helium and carbon isotope systematics confirm the prevalently crustal origin of the volatiles interacting with the aquifer systems consistent with the absence of any recent magmatism most samples are characterized by crustal type helium 3 he 4 he in the range 0 02 ra 0 4 ra associated with a co 2 predominantly metamorphic in origin with the exception of the saharan platform where the carbon content is low and mostly organically derived in eastern tunisia however a few samples have he c isotope compositions which suggest at least partial mantle derivation of the dissolved gas phase the 3 he 4 he ratio reaches 2 4 ra corresponding to 30 of mantle derived helium at the ain garci site a co 2 rich mineral spring located some 30 km south of the city of zaghouan this mantle signature is consistent with the fact that the pelagian block to which eastern tunisia belongs has been deeply affected by extensional and transtensional tectonics since the opening of the tethys a process which is still ongoing in the sicily channel pantelleria rift as a whole however our results show that the italian mantle gas anomaly only marginally extends to northwestern africa

the removal of free surface interactions from three component seismograms summary the effect of the free surface can be removed from three component seismic recordings to recover the incident upgoing wavefield if the slowness and azimuth of the current wavefront are known as a function of time for a single threecomponent station it is usually possible to estimate an azimuth for an event from the first arriving p waves but slowness estimates are less reliable when more than one wavetype is presented in the seismic wavetrain however the free surface correction operators are generally slowly varying functions of slowness and so some error in slowness can be tolerated effective approximations for the removal of the free surface effects can be made for hard rock sites to cover slowness bands for the main regional phases pn pg sn and lg by applying these operators in turn over group velocity windows appropriate to the particular phases the relative amplitude of the p sv and sh contributions to the wavefield can be estimated because the free surface amplification effects have been removed the amplitudes can be compared directly and provide useful constraints on the radiation characteristics of the source this procedure is therefore helpful for developing discrimination measures for different classes of sources

crustal structure across the san andreas fault southern california from teleseismic converted waves crustal structure along a 140 km long profile across the san andreas fault saf in southern california was imaged by stacking teleseismic p s converted phases recorded by a dense short period seismic array the crust mantle discontinuity moho is visible as a continuous feature at a depth around 30 km but is offset 6 to 8 km beneath the saf a small moho disruption can also be seen under the eastern california shear zone ecsz these results suggest that the saf and ecsz extend through the entire crust the moho upwarp under the san gabriel mountains indicates that the mountain ranges were lifted en masse as a result of crustal buckling under horizontal compression

crust and uppermost mantle beneath the north china craton northeastern china and the sea of japan from ambient noise tomography 1 a 3 d shear velocity model of the crust and uppermost mantle to a depth of 100 km is presented beneath the north china craton ncc northeastern china the korean peninsula and the sea of japan ambient noise rayleigh wave tomography is applied to data from more than 300 broadband seismic stations from chinese provincial networks cearray the japanese f net and the iris global seismic network continuous data from 2007 to 2009 are used to produce group and phase velocity maps from 8 s to 45 s periods the model is motivated to constrain the distributed intraplate volcanism crustal extension cratonic rejuvenation and lithospheric thinning that are hypothesized for the study region numerous robust features are observed that impose new constraints on the geometry of these processes but discussion concentrates only on four 1 the north south gravity lineament follows the 40 km contour in crustal thickness and crustal thickness is anticorrelated with water depth beneath the sea of japan consistent with crustal isostasy for a crust with laterally variable composition 2 the lithosphere is thin 70 km beneath the songliao bohai graben but seismically fast 3 even thinner more attenuated lithosphere bounds three sides of the eastern ncc in a horseshoe shape identifying a region of particularly intense tectonothermal modification where lithospheric rejuvenation may have reached nearly to the base of the crust 4 low velocity anomalies reach upward in a y shape in the mantle beneath the eastern and western borders of the sea of japan extending well into continental east asia in the west and are separated by a 60 km thick lithosphere beneath the central sea of japan this anomaly may reflect relatively shallow slab dehydration in the east and in the west may reflect deeper dehydration and convective circulation in the mantle wedge overlying the stagnant slab

distinct lateral variation of lithospheric thickness in the northeastern north china craton abstract a detailed knowledge of the thickness of the lithosphere in the northeastern north china craton ncc is important for understanding the significant tectonic reactivation of the craton in the mesozoic and cenozoic time we achieve this goal by applying the newly proposed wave equation based migration technique to the s receiver functions recently collected in the region distinct negative signals are identified below the moho in all the s receiver function migrated images and stacks which we interpret as representing the s to p conversions from the lithosphere asthenosphere boundary lab the imaged lab is as shallow as 60 70 km in the southeast basin and coastal areas and deepens to no more than 140 km in the northwest mountain ranges and continental interior these observations indicate widespread lithospheric thinning in the study region in comparison with the 180 km lithospheric thicknesses typical of most cratonic regions the revealed topography of the lab generally agrees with the lateral variation in upper mantle seismic anisotropy previously measured through sks splitting analysis in particular a sharp lab step of 40 km is detected at the triple junction of the basin and mountains at almost the same place where an abrupt change from nw se to ne sw in fast polarization direction of shear waves was found these findings suggest a close correlation between the seismic anisotropy and hence deformation of the upper mantle the lithospheric thickness and the surface tectonics of the northeastern ncc while the thinned lithosphere and the nw se fast shear wave polarizations in the east areas probably are related to the dominant nw se tectonic extension in the late mesozoic cenozoic time the thicker lithosphere and the ne sw fast polarization direction in the west mountain ranges may reflect earlier contractional deformations of the region synthetic tests indicate that the lab beneath the northeastern ncc is a well defined zone 10 20 km thick combined with seismic tomography results and geochemical and petrological data this suggests that complex modification of the lithosphere probably accompanied significant lithospheric thinning during the tectonic reactivation of the old craton

the status of isotope hydrology today abstract the present status of isotope hydrology is reviewed with the accent on techniques which are most frequently used or the potential of which is perhaps as yet not fully utilised applications are grouped under two headings 1 applications of intentionally introduced tracers and nucleonic instruments and 2 applications of environmental isotope techniques under the first classification are included the use of tracers in flow gauging sediment transport as bedload and in suspension measurement of flow and its direction in boreholes and the use of artificial tritium for the estimation of recharge the topics included within the group of environmental isotope techniques are recharge and dating of groundwater elevation of recharge area runoff studies arid zone hydrology interaction of surface water with groundwater leakage between aquifers mechanisms of salinization role of environmental isotope techniques in the assessment of geothermal resources and the hydrology of waste disposal sites with regard to the future the author points to the need for a more quantitative approach to the interpretation and presentation of results and broadening the range of dating capability

crust and upper mantle structure of the north china craton and the ne tibetan plateau and its tectonic implications abstract understanding the mesozoic cenozoic tectonic evolution of the north china craton ncc and the ne tibetan plateau tp requires detailed knowledge of the lithospheric structure using dense regional networks and temporary deployments as well as updated reference models we obtain the crust and upper mantle structure to 120 km depth our tomographic results show several major features which have particular implications for the weihe shanxi rift system wsrs deformation of the ne tp and lithospheric evolution of the ncc beneath the wsrs the crust gradually thickens from south to north the lithospheric mantle gradually becomes slower and the mid lower crustal velocities are lower in the weihe rift where rifting of the wsrs initiated we suggest that along strike variations of the lithospheric structures of the wsrs have played an important role in its multistage evolution a low velocity zone lvz in the mid crust beneath the qilian orogen is characterized by relatively higher velocities compared to lvzs in other parts of the tp thus coherent lithospheric deformation may occur due to the high viscosity of the lvz during early plateau growth causing strong anisotropy to develop the western ncc including the ordos block and part of the alashan block shows a high velocity cratonic root extending to the base of our model in contrast the lithosphere of the eastern ncc appears to have been completely modified during the mesozoic through cenozoic and presents a thin lithosphere of relatively low velocities underlain by hot asthenosphere we observed significant upper mantle heterogeneities in the ncc which may reflect its diachronous lithospheric modification

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

lithospheric structure variations between the eastern and central north china craton from s and p receiver function migration abstract i imaged the lithospheric structure beneath the bohai bay basin bbb in the eastern north china craton ncc and the taihang mountains tm and areas further to the west in the central ncc by applying the wave equation migration technique to both the s and p receiver functions rfs collected in this region the data images and synthetic modeling results indicate that s rf imaging is more appropriate than p rf imaging for mapping lithospheric discontinuities especially the lithosphere asthenosphere boundary lab in various types of regions even directly applicable to basin areas that are covered by thick sediments the constructed s rf images show that the lithospheric thickness of the study region is highly variable the imaged lab is on average 80 km beneath the bbb and displays obvious undulations from 120 km under the tm to 40 km under the mountain areas in the central ncc consistent with previous p rf imaging results the observed structural differences between the eastern and central ncc are likely associated with different lithospheric tectonics in these two regions while widespread lithosphere reactivation and extension in the eastern ncc during the late mesozoic time was plausibly responsible for both the thinned crust and lithosphere in the bbb lithospheric thinning in the central ncc may be equally heterogeneous but less significant and probably occurred mainly in cenozoic such a process may have given rise to the highly variable present day lithospheric thickness in this region however it probably did not noticeably affect the overlying crust that was reported to have thickened in response to the early magmatic underplating in the mesozoic time the different tectonic processes in the eastern and central ncc may have induced the formation of the nsgl which likely serves as a major tectonic boundary separating the two regions of contrasting lithospheric structures at present

presence of an intralithospheric discontinuity in the central and western north china craton implications for destruction of the craton detailed knowledge of lithospheric structure is essential for understanding the long term evolution and dynamics of continents we present an image of lithospheric structure across the central and western north china craton ncc derived using s and p receiver functions from a dense seismic array a negative velocity discontinuity is identified at 80 100 km depth within the thick lithosphere 160 200 km similar to that observed in many other cratonic regions and roughly at the same depth as the base of the lithosphere in the eastern ncc the intralithospheric discontinuity may indicate an ancient mechanically weak layer within the overall strong cratonic lithosphere and probably also existed beneath the eastern ncc before the mesozoic the presence of such a weak layer could have facilitated simultaneous lithospheric modification at the base and the middle of the lithosphere in the eastern ncc especially under the strong influence of the mesozoic pacific subduction leading to the severe lithospheric thinning and destruction recorded in this region the weak layer probably did not strongly affect the stability and evolution of the central and western ncc and other cratonic regions where effects from plate boundary processes were weak our seismic images integrated with geological data provide new insights into structural heterogeneities in the subcontinental lithospheric mantle and their roles in the dynamic evolution of continents

martian cratering vi crater count isochrons and evidence for recent volcanism from mars global surveyor this paper develops a methodology to establish absolute martian ages by deriving isochrons on a plot of martian impact crater density vs crater diameter calibrated by lunar crater age data the isochrons illustrated here are based on a mars moon cratering ratio of 1 6 at constant size but there is a factor of 2 to 4 uncertainty in this ratio and the consequent model ages martian crater diameter distributions are determined in several areas down to diameter d 16 45 m the shapes of the curves in young areas are found to be close to that of the predicted isochrons and close to the standard production function found by neukum the youngest areas studied here display the lunar like production function down to d 30 m where saturation equilibrium sets in model crater retention ages of several volcanic units are found to be a few hundred million years or less with estimated uncertainties ranging from a factor of 2 lower to a factor of 4 higher the results are consistent with martian meteorite ages volcanism on mars has probably persisted into the last 10 to 15 of the planet s history and is likely ongoing because surfaces as young as a few hundred million years have reached crater saturation equilibrium at d 60 to 100 m mars is likely to have widespread impact produced regoliths at least a few meters deep and this may contribute to the widespread mobile dust and boulder fields of mars

the hydrogeochemical characterization of morsott el aouinet aquifer northeastern algeria a study of the hydrogeochemical processes in the morsott el aouinet aquifer was carried out with the objective of identifying the geochemical processes and their relation with groundwater quality as well as to get an insight into the hydrochemical evaluation of groundwater the high salinity coupled with groundwater level decline pose serious problems for current irrigation and domestic water supplies as well as future exploitation a combined hydrogeologic and isotopic investigation have been carried out using chemical and isotopic data to deduce a hydrochemical evaluation of the aquifer system based on the ionic constituents water types hydrochemical facies and factors controlling groundwater quality the ionic speciation and mineral dissolution precipitation was calculated by wateqf package software the increase in salinity is related to the dissolution and or precipitation processes during the water rock interaction and to the cationic exchange reactions between groundwater and clay minerals the isotopic analysis of some groundwater samples shows a similarity with the meteoric waters reflect their short residence time and a lowest evaporation phenomenon of infiltrated groundwater

a catalogue of impact craters larger than 200 m and surface age analysis in the chang e 5 landing area abstract chang e 5 ce 5 is the first sample return mission of china s lunar exploration and will be launched in 2020 the planned landing area is near mons rumker in oceanus procellarum it is important to have a detailed geological analysis of the landing area prior to the lunar sample collection the crater size frequency distribution curve combined with radioisotope dating of components of the returned sample by ce 5 may allow a refinement of the lunar chronology function based on a digital orthophoto map with a pixel size of 1 5 m generated from more than 700 lunar reconnaissance orbiter camera narrow angle camera images of the ce 5 landing area all impact craters larger than 200 m in diameter were extracted using the resultant crater catalogue of 32 277 craters a systematic analysis of the landing area including the crater distribution morphology characteristics and geologic model ages is conducted the results show that craters smaller than 1 000 m are denser in the east and the west parts of the region while those larger than 1 000 m tend to be more concentrated in the central part particularly within the range of 61 5 w 64 5 w within nine geologic units divided using the spectral characteristics the geologic unit of em1 eratosthenian aged mare em near the mons rumker is the youngest with a model age of 2 02 0 16 0 16 ga the three rumker plateau ir units are the oldest parts of the landing area with the largest model age of 3 49 0 12 0 073 ga the crater catalogue and the surface model age analysis results can contribute to the ce 5 mission as well as further scientific research

hydrogeochemical assessment of groundwater quality along the coastal aquifers of southern tamil nadu india hydrogeochemical investigation of groundwater has been carried out in the coastal aquifers of southern tamil nadu india seventy nine dug well samples were collected and analyzed for various physicochemical parameters the result of the geochemical analysis indicates the groundwater in the study area is slightly alkaline with moderate saline water the cation and anion concentrations confirm most of the groundwater samples belong to the order of na mg2 ca2 k and cl so42 hco3 thereby three major hydrochemical facies ca cl mixed ca mg cl and na cl were identified based on the us salinity diagram majority of the samples fall under medium to very high salinity with low to high sodium hazard the cross plot of ca2 mg2 versus chloride shows 61 of the samples fall under saline water category higher ec tds and cl concentrations were observed from tiruchendur to koodankulam coastal zone it indicates that these regions are significantly affected by saltwater contamination due to seawater intrusion saltpan deposits and beach placer mining activities

the variability of crater identification among expert and community crater analysts abstract the identification of impact craters on planetary surfaces provides important information about their geological history most studies have relied on individual analysts who map and identify craters and interpret crater statistics however little work has been done to determine how the counts vary as a function of technique terrain or between researchers furthermore several novel internet based projects ask volunteers with little to no training to identify craters and it was unclear how their results compare against the typical professional researcher to better understand the variation among experts and to compare with volunteers eight professional researchers have identified impact features in two separate regions of the moon small craters diameters ranging from 10 m to 500 m were measured on a lunar mare region and larger craters 100s m to a few km in diameter were measured on both lunar highlands and maria volunteer data were collected for the small craters on the mare our comparison shows that the level of agreement among experts depends on crater diameter number of craters per diameter bin and terrain type with differences of up to 45 we also found artifacts near the minimum crater diameter that was studied these results indicate that caution must be used in most cases when interpreting small variations in crater size frequency distributions and for craters 10 pixels across because of the natural variability found projects that emphasize many people identifying craters on the same area and using a consensus result are likely to yield the most consistent and robust information