a model for microbial phosphorus cycling in bioturbated marine sediments significance for phosphorus burial in the early paleozoic abstract a diagenetic model is used to simulate the diagenesis and burial of particulate organic carbon c org and phosphorus p in marine sediments underlying anoxic versus oxic bottom waters the latter are physically mixed by animals moving through the surface sediment bioturbation and ventilated by burrowing tube dwelling organisms bioirrigation the model is constrained using an empirical database including burial ratios of c org with respect to organic p c org p org and total reactive p c org p reac burial efficiencies of c org and p org and inorganic carbon to phosphorus regeneration ratios if p org is preferentially mineralized relative to c org during aerobic respiration as many previous studies suggest then the simulated p org pool is found to be completely depleted a modified model that incorporates the redox dependent microbial synthesis of polyphosphates and p org termed the microbial p pump allows preferential mineralization of the bulk p org pool relative to c org during both aerobic and anaerobic respiration and is consistent with the database results with this model show that p burial is strongly enhanced in sediments hosting fauna animals mix highly labile p org away from the aerobic sediment layers where mineralization rates are highest thereby mitigating diffusive po 4 3 fluxes to the bottom water they also expand the redox niche where microbial p uptake occurs the model was applied to a hypothetical shelf setting in the early paleozoic a time of the first radiation of benthic fauna results show that even shallow bioturbation at that time may have had a significant impact on p burial our model provides support for a recent study that proposed that faunal radiation in ocean sediments led to enhanced p burial and possibly a stabilization of atmospheric o 2 levels the results also help to explain c org p org ratios in the geological record and the persistence of p org in ancient marine sediments

a comparison of several methods for the determination of iron hydroxides and associated orthophosphates in estuarine particulate matter abstract five different methods commonly used for the extraction and the determination of iron hydroxides and or the associated phosphorus held in marine seston or in sediments have been tested on single phase minerals goethite and apatite on reference minerals so1 and so2 and on suspended matter samples from the st lawrence estuary and from the estuary of the eastmain river a major james bay affluent in northern quebec canada the citrate dithionite bicarbonate cdb procedure generally seemed to be more reproducible and more specific the validity of the other methods respectively using as extracting reagents ammonium oxalate oxalic acid hydroxylamine hydrochloride calcium nitrilotriacetic acid and acetate tartrate is discussed the cdb extraction is included in an analytical scheme which allows to distinguish between three fractions of phosphorus this chemical speciation is applied to the study of p retention on fe hydroxides and to its potential desorption

impact vaporization of planetesimal cores in the late stages of planet formation differentiated planetesimals may have delivered iron rich material to earth in giant impacts at the end of accretion impact experiments suggest that the planetesimals iron cores vaporized aiding dispersal and mixing into earth s mantle

tectonic framework of the northern junggar basin part i the eastern luliang uplift and its link with the east junggar terrane abstract the luliang uplift preserves relatively complete carboniferous strata and is an important region to study the spatio temporal framework and tectonic evolution of the junggar basin here we report new shrimp sims u pb ages whole rock sr nd data and in situ zircon hf isotopic compositions for carboniferous strata samples in the eastern luliang uplift the gravity and magnetic data suggest that the carboniferous volcanics are distributed as nw trending bands and also bring out n s oriented parallel amalgamation the sedimentary units and structural deformation of the eastern luliang uplift suggest that the basin evolution involved late carboniferous extensional graben stage and latest carboniferous early permian compressional stage the carboniferous batamayineishan formation is divided into the lower volcanic unit followed up sedimentary unit and an upper volcanic unit as inferred from the lithology and unconformities the lower volcanic unit from the drill cores mainly consists of andesite dacite rhyolite and tuff intercalated with minor basalt the middle sedimentary unit is made up of sandstone and mudstone with tuff and tuffaceous sandstone and the upper volcanic unit is composed of basalt rhyolite tuff and breccia with minor clastic sedimentary rocks zircon shrimp u pb age 337 2 ma for the tuff and sims u pb age 308 6 ma for basalt suggest that the lower and upper volcanic units belong to lower carboniferous and upper carboniferous respectively the basalts from upper volcanic unit in the eastern luliang uplift show typical calc alkaline affinity with low nb y ratios 0 17 0 28 and sio2 contents 47 54 and moderate th abundances 0 45 3 74 ppm enrichment in lree and liles and depletion in nb ta and ti they have low initial 87sr 86sr ratios 0 703571 0 705122 and positive end t values 5 5 8 6 and constant sm yb ratios 1 56 2 03 and variable trace element ratios e g ba th ba la and ba nb suggesting that the parental magmas were mainly derived from 2 to 8 partial melting of a spinel iherzolite mantle source metasomatized by hydrous fluids and melts of subducted sediments furthermore relatively high tio2 1 52 3 76 and zr contents 172 414 ppm indicate that they were formed in an extensional setting taking into account the occurrence of coeval island arc related volcanics we propose an intra arc rift basin model for the eastern luliang uplift the eastern luliang uplift and east junggar terrane display different tectonic features during the closure of the junggar ocean during the late carboniferous continued northward subduction prevailed and generated a fault controlled intra arc basin in the eastern luliang uplift intra arc basin contraction in permian is probably indicative of the closure of junggar ocean in the northern junggar basin our study confirms the important role of subduction accretion process associated with the carboniferous crustal growth in the junggar terrane

the phosphorus cycle in coastal marine sediments the concentration of dissolved phosphate in sediment box cores from the laurentian trough in the gulf of st lawrence increased sharply across the sediment water interface from 2 0 mol po4 1 in the bottom water to 6 3 mot po4 1 in the top cm remained almost constant at this value down to 5 15 cm depth and then increased rapidly with further depth in the region of constant concentration phosphate is buffered by sorption equilibria with the sediment the production rate of phosphate the sorption capacity of the sediment and the thickness of the diffusive boundary layer at the sediment water interface appear to control the shape of the pore water profile even though the buffering places an upper limit on the concentration gradient across the sediment water interface and hence on the flux the phosphate flux to the overlying water is controlled by the production rate of phosphate within the sediment a model is proposed to relate sediment chemistry to phosphorus fluxes

lunar impact history constrained by grail derived basin relaxation measurements abstract grail observations have been used to derive an updated catalog of lunar impact basins with diameters 450 km in this study we assess the age and relaxation state of these basins and find that the 13 15 stratigraphically younger basins are significantly less relaxed than the 8 16 identifiable older basins the change in relaxation state is most likely a signature of the cooling of the base of the lunar crust below 1300 1400 k which we infer happened between 4 21 4 45 ga based on geochronological measurements we compare the predicted number of basins before and after this reference point with several different modeled lunar cratering chronologies while these models are sensitive to the ratio of 1km 450 km craters we conclude that a model with a broad period of late heavy bombardment a sawtooth is more likely to fit both the number of relaxed and unrelaxed basins and the mass of material delivered as a late veneer

collisionless encounters and the origin of the lunar inclination the moon is generally thought to have formed from the debris ejected by the impact of a planet sized object with the proto earth towards the end of planetary accretion models of the impact process predict that the lunar material was disaggregated into a circumplanetary disk and that lunar accretion subsequently placed the moon in a near equatorial orbit forward integration of the lunar orbit from this initial state predicts a modern inclination at least an order of magnitude smaller than the lunar value a long standing discrepancy known as the lunar inclination problem here we show that the modern lunar orbit provides a sensitive record of gravitational interactions with earth crossing planetesimals that were not yet accreted at the time of the moon forming event the currently observed lunar orbit can naturally be reproduced via interaction with a small quantity of mass corresponding to 0 0075 0 015 earth masses eventually accreted to the earth carried by a few bodies consistent with the constraints and models of late accretion although the encounter process has a stochastic element the observed value of the lunar inclination is among the most likely outcomes for a wide range of parameters the excitation of the lunar orbit is most readily reproduced via collisionless encounters of planetesimals with the earth moon system with strong dissipation of tidal energy on the early earth this mechanism obviates the need for previously proposed but idealized excitation mechanisms places the moon forming event in the context of the formation of earth and constrains the pristineness of the dynamical state of the earth moon system

reconstructing multiple arc basin systems in the altai junggar area nw china implications for the architecture and evolution of the western central asian orogenic belt abstract the altai junggar area in northwestern china is a critical region to gain insights on the tectonic framework and geological evolution of the western central asian orogenic belt caob in this study we report results from integrated geological geochemical and geophysical investigations on the wulungu depression of the junggar basin to determine the basement nature of the basin and understand its amalgamation history with the chinese altai within the broad tectonic evolution of the altai junggar area based on borehole and seismic data the wulungu depression is subdivided into two nw trending tectonic units suosuoquan sag and hongyan high by southward vergent thrust faults the suosuoquan sag consists of the middle late devonian basaltic andesite andesite dacite tuff tuffaceous sandstone and tuffite and the overlying early carboniferous volcano sedimentary sequence with lava flows and shallow marine sediments from a proximal juvenile provenance zircon e hf t 6 0 14 9 compared to the late carboniferous andesite and rhyolite in the hongyan high zircon sims u pb ages for dacites and andesites indicate that these volcanics in the suosuoquan sag and hongyan high erupted at 376 3 ma and 313 4 ma respectively the middle late devonian basaltic andesites from well lc1 are calc alkaline and exhibit primitive magma like mgo contents 7 9 8 6 and mg values 66 68 with low initial 87 sr 86 sr 0 703269 0 704808 and positive e nd t values 6 6 7 6 and relatively high zr abundance 98 2 116 0 ppm and zr y ratios 5 1 5 4 enrichment in lrees and liles e g th and u and depletion in nb ta and ti suggesting that they were probably derived from a metasomatized depleted mantle in a retro arc extensional setting the well lc1 andesitic tuffs well l8 dacites well wl1 dacitic tuffs and well l5 andesites belong to calc alkaline and metaluminous to peraluminous a cnk 0 8 1 7 series and display low mg values 35 46 and variably positive e nd t 4 5 8 5 and e hf t 10 2 16 8 values as well as young isotopic model ages these devonian carboniferous intermediate felsic volcanics are interpreted as the products of partial melting of a juvenile lower crust with some contributions from mantle components in an evolved island arc setting from immature to mature island arc the basin filling pattern and the distribution of arc volcanics and their zircon hf model ages with the eruptive time suggest that the wulungu depression represents an island arc basin system with the development of a carboniferous retro arc basin in combination with previous work we propose that the northern junggar area comprises three arc basin belts from south to north the darbut luliang karamaili wulungu yemaquan and saur fuhai dulate such tectonic subdivisions are consistent with the regional gravity and magnetic anomaly data the recognition of the wulungu arc basin system demonstrates that the junggar basin is likely underlain by juvenile continental crust rather than ancient precambrian basement and also implies that the caob was built by amalgamation of multiple linear arcs and accretionary complexes

the marine phosphorus cycle phosphorus introduced to the ocean must ultimately be removed if a steady state is to be maintained over geologic time aeolian input is insignificant and there is evidently no hydrothermal contribution rivers dominate p input to the ocean the fluvial p flux is poorly quantified due to the interactions of two factors 1 man s influence on river nutrient fluxes and 2 inherent complexities in understanding the biological and inorganic associations of p in estuarine and coastal waters our best estimate of the natural or pre man p input flux is about 10 x 10 sup 9 moles p cm sup 2 ocean surface year of the identified flux of phosphorus to the sediments about 90 percent is in the form of biogenic debris or its regeneration products the burial of phosphatic fish debris is negligible p removal by direct reaction of phosphate in seawater with sea floor basalts during mid ocean ridge hydrothermal circulation is insignificant p removal by processes such as sorption on clay surfaces or formation of authigenic fe and al phosphate phases is presently unquantified and remains a serious uncertainty in the phosphorus cycle the identified sources and sinks approximately balance yielding a residence time for p in the oceans of about 10 sup 5 yrs

turbulent mixing of metal and silicate during planet accretion and interpretation of the hf w chronometer in the current view of planet formation the final assembly of the earth involved giant collisions between proto planets 1000 km radius with the moon formed as a result of one such impact at this stage the colliding bodies had likely differentiated into a metallic core surrounded by a silicate mantle during the moon forming impact nearly all metal sank into the earth s core we investigate to what extent large self gravitating iron cores can mix with surrounding silicate and how this influences the short lived chronometer hf w used to infer the age of the moon we present fluid dynamical models of turbulent mixing in fully liquid systems attempting to place constraints on the degree of mixing erosion of sinking cores driven by rayleigh taylor instability does lead to intimate mixing and equilibration but large blobs 10 km diameter do not emulsify entirely emulsification is enhanced if most of the accreting metal cores deform into thin structures during descent through the earth s mantle yet only 1 20 of earth s core would equilibrate with silicate during earth s accretion the initial speed of the impactor is of little importance we proceed to evaluate the mixing potential for shear instabilities where silicate entrainment across vertical walls causes mixing the turbulent structure indicates that vortices remain at the largest scale and do not mix to centimeter length scale where diffusion operates and isotopes can equilibrate thus incomplete emulsification and equilibration of accreting iron cores is likely to occur the extent of metal silicate equilibration provides key information for interpretation of siderophile budgets and the timing of core formation using the hf w chronometer the time scale of core formation derived from the hf w chronometer is usually tied to the last major metal silicate re equilibration believed to coincide with time of the moon forming impact however we show that large cores have limited ability to reset the hf w system in the silicate earth excess 182 w in bulk silicate earth is more sensitive to early core formation processes than to radiogenic ingrowth after the last giant impact

turbulent metal silicate mixing fragmentation and equilibration in magma oceans abstract much of the earth was built by high energy impacts of planetesimals and embryos many of these impactors already differentiated with metallic cores of their own geochemical data provide critical information on the timing of accretion and the prevailing physical conditions but their interpretation depends critically on the degree of metal silicate chemical equilibration during core mantle differentiation which is poorly constrained efficient equilibration requires that the large volumes of iron derived from impactor cores mix with molten silicates down to scales small enough to allow fast metal silicate mass transfer here we use fluid dynamics experiments to show that large metal blobs falling in a magma ocean mix with the molten silicate through turbulent entrainment with fragmentation into droplets eventually resulting from the entrainment process in our experiments fragmentation of the dense fluid occurs after falling a distance equal to 3 4 times its initial diameter at which point a sizable volume of ambient fluid has already been entrained and mixed with the dense falling fluid contrary to previous assumptions we demonstrate that fragmentation of the metallic phase into droplets may not be required for efficient equilibration turbulent mixing by drastically increasing the metal silicate interfacial area may result in fast equilibration even before fragmentation efficient re equilibration is predicted for impactors of size small compared to the magma ocean depth in contrast much less re equilibration is predicted for large impacts in situations where the impactor core diameter approaches the magma ocean thickness

structural evolution of the irtysh shear zone northwestern china and implications for the amalgamation of arc systems in the central asian orogenic belt the nw se irtysh shear zone is a major tectonic boundary in the central asian orogenic belt caob which supposedly records the amalgamation history between the pen siberian orogenic system and the kazakhstan south mongolia orogenic system however the tectonic evolution of the irtysh shear zone is not fully understood here we present new structural and geochronological data which together with other constraints on the timing of deformation suggests that the irtysh shear zone was subjected to three phases of deformation in the late paleozoic d 1 is locally recognized as folded foliations in low strain areas and as an internal fabric within garnet porphyroblasts d 2 is represented by a shallowly dipping fabric and related similar to nw se stretching lineations oriented sub parallel to the strike of the orogen d2 foliations are folded by similar to nw se folds f 3 that are bounded by a series of mylonite zones with evidence for sinistral reverse kinematics these fold and shear structures are kinematically compatible and thus interpreted to result from a transpressional deformation phase d 3 two samples of mica schists yielded youngest detrital zircon peaks at similar to 322 ma placing a maximum constraint on the timing of d 1 d 3 deformation a similar to ne sw granitic dyke swarm similar to 252 ma crosscuts d 3 fold structures and mylonitic fabrics in the central part of the shear zone but is displaced by a mylonite zone that represents the southern boundary of the irtysh shear zone this observation indicates that the major phase of d 3 transpressional deformation took place prior to similar to 252 ma although later phases of reactivation in the mesozoic and cenozoic are likely the late paleozoic deformation d 1 d 3 at similar to 322 252 ma overlaps in time with the collision between the chinese altai and the intra oceanic arc system of the east junggar we therefore interpret that three episodes of late paleozoic deformation represent orogenic thickening d 1 collapse d 2 and transpressional deformation d3 during the convergence between the chinese altai and the east junggar on a larger scale late paleozoic sinistral shearing d3 together with dextral shearing farther south accommodated the eastward migration of internal segments of the western caob possibly associated with the amalgamation of multiple arc systems and continental blocks during the late paleozoic c 2015 elsevier ltd all rights reserved

laboratory experiments on the breakup of liquid metal diapirs the validity of the iron rain scenario i e the widely accepted model for the dynamics of iron sedimentation through a magma ocean during the latest stage of the earth s accretion is explored via a suite of laboratory experiments liquid gallium and mixtures of water and glycerol are used as analogs of the iron and the molten silicate respectively this allows us to investigate the effects of the viscosity ratio between iron and silicate and to reproduce the relevant effects of surface tension on the fragmentation dynamics while the classical iron rain scenario considers a population of purely spherical drops with a single characteristic radius that fall towards the bottom of the magma ocean at a unique velocity without any further change our experiments exhibit a variety of stable shapes for liquid metal drops a large distribution of sizes and velocities and an intense internal dynamics within the cloud with the superimposition of further fragmentations and merging events our results demonstrate that rich and complex dynamics occur in models of molten metal diapir physics further we hypothesize that the inclusion of such flows into state of the art thermochemical equilibration models will generate a similarly broad array of complex and likely novel behaviors

constraints on terrestrial planet formation timescales and equilibration processes in the grand tack scenario from hf w isotopic evolution abstract we examine 141 n body simulations of terrestrial planet late stage accretion that use the grand tack scenario coupling the collisional results with a hafnium tungsten hf w isotopic evolution model accretion in the grand tack scenario results in faster planet formation than classical accretion models because of higher planetesimal surface density induced by a migrating jupiter planetary embryos that grow rapidly experience radiogenic ingrowth of mantle 182w that is inconsistent with the measured terrestrial composition unless much of the tungsten is removed by an impactor core that mixes thoroughly with the target mantle for physically earth like surviving planets we find that the fraction of equilibrating impactor core k core 0 6 is required to produce results agreeing with observed terrestrial tungsten anomalies assuming equilibration with relatively large volumes of target mantle material smaller equilibrating mantle volumes would require even larger k core this requirement of substantial core re equilibration may be difficult to reconcile with fluid dynamical predictions and hydrocode simulations of mixing during large impacts and hence this result does not favor the rapid planet building that results from grand tack accretion

the tungsten isotopic composition of the earth s mantle before the terminal bombardment it has long been speculated that a late heavy bombardment of earth by meteoritic material replenished the mantle s budget of siderophile iron loving elements such as tungsten that were largely lost to the core during its segregation however evidence for this late veneer remains indirect and its influence has been much debated matthias willbold and colleagues present high precision tungsten isotope analyses of ancient greenland rocks and show that they have significantly higher 182w 184w ratios than modern terrestrial samples this finding is in good agreement with the expected influence of a meteoritic late heavy bombardment they speculate that both the tungsten isotope data and the observed decrease in 142nd 144nd neodymium ratios can be explained if late meteorite bombardment triggered the onset of the current style of mantle convection many precious iron loving metals such as gold are surprisingly abundant in the accessible parts of the earth given the efficiency with which core formation should have removed them to the planet s deep interior1 one explanation of their over abundance is a late veneer a flux of meteorites added to the earth after core formation as a terminal bombardment that culminated in the cratering of the moon2 some 3 8 billion year old rocks from isua greenland are derived from sources that retain an isotopic memory of events pre dating this cataclysmic meteorite shower3 4 these isua samples thus provide a window on the composition of the earth before such a late veneer and allow a direct test of its importance in modifying the composition of the planet using high precision less than 6 parts per million 2 standard deviations tungsten isotope analyses of these rocks here we show that they have a isotopic tungsten ratio 182w 184w that is significantly higher about 13 parts per million than modern terrestrial samples this finding is in good agreement with the expected influence of a late veneer we also show that alternative interpretations such as partial remixing of a deep mantle reservoir formed in the hadean eon5 6 more than four billion years ago or core mantle interaction7 do not explain the w isotope data well the decrease in mantle 182w 184w occurs during the archean eon about four to three billion years ago potentially on the same timescale as a notable decrease in 142nd 144nd refs 3 and 6 we speculate that both observations can be explained if late meteorite bombardment triggered the onset of the current style of mantle convection

tectonostratigraphic evolution of the carboniferous arc related basin in the east junggar basin northwest china insights into its link with the subduction process abstract the junggar basin in northwest china is located in the southern part of central asian orogenic belt caob the tectonic mechanisms controlling sedimentary fill through space and geologic time within dynamic subduction environments remains poorly understood in the junggar basin this paper presents an integrated tectonostratigraphic and tectonic evolution of carboniferous volcanic arcs and associated basin in the east junggar basin using multichannel seismic reflection data well line data geochronological and geochemical data we propose a new tectonic sedimentary model for the east junggar basin during the carboniferous time based on geochemistry of volcanic rocks and four seismic tectonostratigraphic sequences the carboniferous succession of volcanogenic sediments represents progradational sequences mainly supplied from the northeast the negative ta nb and ti anomalies low rb ba ratios 0 01 0 15 and high incompatible trace element such as th u abundances of the basalts suggest that metasomatism may have occurred during the late carboniferous subduction the northeastward increase of the ba la ration k ca and decrease of na ti and fe indicate the northeast dipping subduction polarity in the east junggar basin during the early carboniferous tectonism in the east junggar basin took place in two stages deep marine sediments widely covered the junggar region and then the depocenter slightly shifted towards southwest which probably resulted from the northeast dipping subduction that led to the southwestward tilting of the dinan area during the early stage of the late carboniferous mixed marine and nonmarine deposits initially onlapped the volcanic arc towards the northeast and then gradually downlapped to the southwest at the end of the late carboniferous subduction of the junggar ocean continued towards northeast and depositional environment became nonmarine the main axis of the depocenter rapidly migrated towards southwest that resulted from the southwestward tilting of the luliang region

mars in the aftermath of a colossal impact abstract the abundance of highly siderophile elements hses inferred for mars mantle from martian meteorites implies a late veneer lv mass addition of 0 8 wt with broadly chondritic composition late accretion to mars by a differentiated ceres sized 1000 km diameter object can account for part of the requisite lv mass and geochronological constraints suggests that this must have occurred no later than ca 4480 ma here we analyze the outcome of the hypothetical lv giant impact to mars with smoothed particle hydrodynamics simulations together with analytical theory results show that in general about 50 of the impactor s metallic core shatters into 10 m fragments that subsequently fragment into sub mm metallic hail at re accretion this returns a promising delivery of hses into martian mantle compared to either a head on and hit and run collision in both cases 10 myr a dense pre noachian co2 atmosphere should lower the escape efficiency of hydrogen by ir emission a more detailed hydrodynamic atmospheric model of this early hydrogen atmosphere is warranted to examine its effect on pre noachian mars

geochemical criteria for a refined tectonic discrimination of orogenic andesites abstract minor trace element and sr isotope data are compiled for tertiary recent orogenic andesites of three tectonic settings 1 oceanic island arcs divided into low k and other andesites 2 continental island arcs and thin continental margins and 3 thick continental margins andean from 1 to 3 there is a steady overlapping increase in la ce ree la yb la y th th u zr y hf yb and ni co and a decrease in k la p la sc cr and sc ni optimum discriminationis achieved with a plots of la yb vs th and la yb vs sc ni and b cluster analysis using the critical parameters listed above shoshonitic andesites and high mg andesites boninites are considered separately orogenic andesites are distinguished from non orogenic andesites by high contents of al low contents of ti zr ree y nb ta and ga and the absence of pronounced negative eu anomalies

elemental and sr nd pb isotopic geochemistry of late paleozoic volcanic rocks beneath the junggar basin nw china implications for the formation and evolution of the basin basement the basement beneath the junggar basin has been interpreted either as a micro continent of precambrian age or as a fragment of paleozoic oceanic crust elemental and sr nd pb isotopic compositions and zircon pb pb ages of volcanic rocks from drill cores through the paleo weathered crust show that the basement is composed mainly of late paleozoic volcanic rock with minor shale and tuff the volcanic rocks are mostly subalkaline with some minor low k rocks in the western kexia area some alkaline lavas occur in the central luliang uplift and northeastern wulungu depression the lavas range in composition from basalts to rhyolites and fractional crystallization played an important role in magma evolution except for a few samples from kexia the basalts have low la nb 1 4 typical for oceanic crust derived from asthenospheric melts zircon pb pb ages indicate that the kexia andesite with a volcanic arc affinity formed in the early carboniferous 345 ma whereas the luliang rhyolite and the wucaiwan dacite with syn collisional to within plate affinities formed in the early devonian 395 and 405 ma respectively positive end t values up to 7 4 and low initial 87sr 86sr isotopic ratios of the intermediate silicic rocks suggest that the entire junggar terrain may be underlain by oceanic crust an interpretation consistent with the juvenile isotopic signatures of many granitoid plutons in other parts of the central asia orogenic belt variation in zircon ages for the silicic rocks different ba p ti nb or th anomalies in the mafic rocks and variable nb y and la nb ratios across the basin suggest that the basement is compositionally heterogeneous the heterogeneity is believed to reflect amalgamation of different oceanic blocks representing either different evolution stages within a single terrane or possibly derivation from different terranes

the onset of the lunar cataclysm as recorded in its ancient crater populations abstract the earliest bombardment history of the moon potentially provides powerful constraints for solar system evolution models a major uncertainty however is how much of this history is actually recorded in lunar craters for example some argue that most ancient lunar craters and basins were produced by a declining bombardment of leftover planetesimals produced by terrestrial planet formation processes others believe that most lunar craters and large basins were formed in a narrow time interval between 3 8 and 4 0 ga the so called lunar cataclysm in the light of recent improvements in our understanding of early solar system evolution it is possible that the contributions from both scenarios could be represented in the lunar crater record if so when did the declining bombardment end and the lunar cataclysm begin here we show using new counts of 15 150 km diameter craters on the most ancient lunar terrains that the craters found on or near nectaris basin appear to have been created by projectiles hitting twice as fast as those that made the oldest craters on various pre nectarian era terrains this dramatic velocity increase is consistent with the existence of a lunar cataclysm and potentially with a late reconfiguration of giant planet orbits which may have strongly modified the source of lunar impactors this work also suggests that the lunar cataclysm may have started near the formation time of nectaris basin this possibility implies that south pole aitken basin spa the largest lunar basin and one of the oldest by superposition was not created during the cataclysm this view is strengthened by our interpretation that a substantial fraction of ancient craters on spa were made by low velocity impactors finally we believe these results shed new light on the impact history of the primordial earth

182w and hse constraints from 2 7 ga komatiites on the heterogeneous nature of the archean mantle abstract while the isotopically heterogeneous nature of the terrestrial mantle has long been established the origin scale and longevity of the heterogeneities for different elements and isotopic systems are still debated here we report nd hf w and os isotopic and highly siderophile element hse abundance data for the boston creek komatiitic basalt lava flow bcf in the 2 7 ga abitibi greenstone belt canada this lava flow is characterized by strong depletions in al and heavy rare earth elements ree enrichments in light ree and initial e143nd 2 5 0 2 and intial e176hf 4 2 0 9 indicative of derivation from a deep mantle source with time integrated suprachondritic sm nd and lu hf ratios the data plot on the terrestrial nd hf array suggesting minimal involvement of early magma ocean processes in the fractionation of lithophile trace elements in the mantle source this conclusion is supported by a mean 142nd 3 8 2 8 that is unresolvable from terrestrial standards by contrast the bcf exhibits a positive 182w anomaly 182w 11 7 4 5 yet is characterized by chondritic initial 187os 0 1 0 3 and low inferred source hse abundances 35 5 of those estimated for the present day bulk silicate earth bse collectively these characteristics are unique among archean komatiite systems studied so far the deficit in the hse coupled with the chondritic os isotopic composition but a positive 182w anomaly are best explained by derivation of the parental bcf magma from a mantle domain characterized by a predominance of hse deficient differentiated late accreted material according to the model presented here the mantle domain that gave rise to the bcf received only 35 of the present day hse complement in the bse before becoming isolated from the rest of the convecting mantle until the time of komatiite emplacement at 2 72 ga these new data provide strong evidence for a highly heterogeneous archean mantle in terms of absolute hse abundances and w isotopic composition and also indicate slow mixing on a timescale of at least 1 8 billion years additionally the data are consistent with a stagnant lid plate tectonic regime in the hadean and archean prior to the onset of modern style plate tectonics

forming a moon with an earth like composition via a giant impact in the giant impact theory the moon formed from debris ejected into an earth orbiting disk by the collision of a large planet with the early earth prior impact simulations predict that much of the disk material originates from the colliding planet however earth and the moon have essentially identical oxygen isotope compositions this has been a challenge for the impact theory because the impactor s composition would have likely differed from that of earth we simulated impacts involving larger impactors than previously considered we show that these can produce a disk with the same composition as the planet s mantle consistent with earth moon compositional similarities such impacts require subsequent removal of angular momentum from the earth moon system through a resonance with the sun as recently proposed

the western central asian orogenic belt a window to accretionary orogenesis and continental growth abstract the architecture of accretionary orogens is a key to understand continental growth here we present an overview of the orogenic components and their amalgamation in the western central asian orogenic belt caob the caob records the convergence and interactions among various types of orogenic components including the japan type mariana type and alaska aleutian type arc systems as well as the active marginal sequences of the siberia craton which incorporated wide accretionary complexes and accreted arcs and terranes during construction of the caob the kazakhstan arc chain was characterized by multiple subduction whereas the northern fringe of the tarim craton remained mostly as a passive margin the multiple convergence and accretions among these various orogenic components generated huge orogenic collages in the late paleozoic and even in the early triassic involving parallel amalgamation circum microcontinent amalgamation and oroclinal bending the preservation of trapped basins played a significant role in orogenesis with some parts of the oceanic plate being subducted and others behaving as rigid units the orogenesis in the caob was long lived lasting for more than 800 m y involving multiple subduction and long continuous accretion and featuring the complexity of accretionary orogenesis and continent growth

magmagenesis in a subduction related post collisional volcanic arc segment the ukrainian carpathians abstract calc alkaline magmatism in the south west ukraine occurred between 13 8 and 9 1 ma and formed an integral part of the neogene subduction related post collisional carpathian volcanic arc eruptions occurred contemporaneously in two parallel arcs here termed outer arc and inner arc in the ukrainian part of the carpathians outer arc rocks mainly andesites are characterized by lile enrichment e g k and pb nb depletion low compatible trace element abundances high 87sr 86sr high 18o and low 143nd 144nd isotopic ratios 0 7085 0 7095 7 01 8 53 0 51230 0 51245 respectively inner arc rocks are mostly dacites and rhyolites with some basaltic and andesitic lavas they also show low compatible element abundances but have lower 87sr 86sr 18o and higher 143nd 144nd ratios 0 7060 0 7085 6 15 6 64 0 5125 0 5126 respectively than outer arc rocks both high nb and low nb lithologies are present in the inner arc based on the lile enrichment especially pb a higher fluid flux is suggested for the outer arc magmas compared with those of the inner arc combined trace element and sr nd o isotopic modelling suggests that the factors which controlled the generation and evolution of magmas were complex compositional differences between the inner and outer arcs were produced by introduction of variable proportions of slab derived sediments and fluids into a heterogeneous mantle wedge and by different extents of upper crustal contamination degrees of magmatic fractionation also differed between the two arcs the most primitive magmas belong to the inner arc isotopic modelling shows that they can be produced by adding 3 8 subducted terrigenous flysch sediments to the local mantle wedge source up to 5 upper crustal contamination has been modelled for fractionated products of the inner arc the geochemical features of outer arc rocks suggest that they were generated from mantle wedge melts similar to the inner arc primitive magmas but were strongly affected by both source enrichment and upper crustal contamination assimilation of 10 20 bulk upper crust is required in the afc modelling assuming an inner arc parental magma we suggest that magmagenesis is closely related to the complex geotectonic evolution of the carpathian area several tectonic and kinematic factors are significant 1 hydration of the asthenosphere during subduction and plate rollback directly related to collisional processes 2 thermal disturbance caused by ascent of hot asthenospheric mantle during the back arc opening of the pannonian basin 3 clockwise translational movements of the intracarpathian terranes which facilitated eruption of the magmas

tungsten isotope composition of the acasta gneiss complex high precision tungsten 182w 184w isotope measurements on well characterised mafic and felsic samples of the ca 3960 ma acasta gneiss complex agc northwest territories canada show radiogenic e182w values between 0 06 to 0 15 two ca 3600 ma felsic samples from this terrane have e182w 0 and are the oldest samples so far documented to have a w isotopic composition indistinguishable from that of the modern mantle the e182w data are correlated with e142nd roth et al 2014 and we attribute this variability to incomplete metamorphic homogenisation of the 3960 ma protolith with more recent material in a 3370 ma tectono thermal event notably the value of the positive e182w anomalies seen in the 3960 ma agc samples that are least affected by metamorphic homogenisation is comparable to that observed in other early archean rocks isua supracrustal belt greenland nuvvuagittuq supracrustal belt canada and the late archean kostomuksha komatiites karelia this demonstrates a globally constant signature we infer that the presence of a pre late veneer mantle represents the most straightforward interpretation of a uniform distribution of ew182 0 15 value in archean rocks of different ages we show that such a notion is compatible with independent constraints from highly siderophile element abundances in mafic and ultra mafic archean mantle derived rocks the absence of anomalous e182w and e142nd so far measured in samples younger than ca 2800 ma suggests progressive convective homogenisation of silicate reservoirs the downward mixing of an upper mantle rich in late delivered meteoritic material might account for these combined observations

origin of the ganymede callisto dichotomy by impacts during the late heavy bombardment jupiter s large moons ganymede and callisto are similar in size and composition but different in surface and interior characteristics simulations with geophysical models of core formation indicate that the difference in impact energy received by the two satellites during the period of late heavy bombardment can explain the dichotomy jupiter s large moons ganymede1 2 and callisto2 3 are similar in size and composition however ganymede has a tectonically evolved surface1 and a large rock metal core2 whereas callisto s surface shows no sign of resurfacing3 and the separation of ice and rock in its interior seems incomplete2 these differences have been difficult to explain4 5 6 7 8 9 10 11 here we present geophysical models of impact induced core formation to show that the ganymede callisto dichotomy can be explained through differences in the energy received during a brief period of frequent planetary impacts about 700 million years after planet formation termed the late heavy bombardment12 13 14 15 we propose that during the late heavy bombardment impacts would have been sufficiently energetic on ganymede to lead to a complete separation of rock and ice but not on callisto in our model a dichotomy between ganymede and callisto that is consistent with observations is created if the planetesimal disk that supplied the cometary impactors during the late heavy bombardment is about 5 30 times the mass of the earth our findings are consistent with estimates of a disk about 20 times the mass of the earth as used in dynamical models that recreate the present day architecture of the outer solar system and the lunar late heavy bombardment15 16

differentiated planetesimal impacts into a terrestrial magma ocean fate of the iron core abstract the abundance of moderately siderophile elements iron loving e g co ni in the earth s mantle is 10 to 100 times larger than predicted by chemical equilibrium between silicate melt and iron at low pressure but it does match expectation for equilibrium at high pressure and temperature recent studies of differentiated planetesimal impacts assume that planetesimal cores survive the impact intact as concentrated masses that passively settle from a zero initial velocity and undergo turbulent entrainment in a global magma ocean under these conditions cores greater than 10 km in diameter do not fully mix without a sufficiently deep magma ocean we have performed hydrocode simulations that revise this assumption and yield a clearer picture of the impact process for differentiated planetesimals possessing iron cores with radius 100 km that impact into magma oceans the impact process strips away the silicate mantle of the planetesimal and then stretches the iron core dispersing the liquid iron into a much larger volume of the underlying liquid silicate mantle lagrangian tracer particles track the initially intact iron core as the impact stretches and disperses the core the final displacement distance of initially closest tracer pairs gives a metric of core stretching the statistics of stretching imply mixing that separates the iron core into sheets ligaments and smaller fragments on a scale of 10 km or less the impact dispersed core fragments undergo further mixing through turbulent entrainment as the molten iron fragments rain through the magma ocean and settle deeper into the planet our results thus support the idea that iron in the cores of even large differentiated planetesimals can chemically equilibrate deep in a terrestrial magma ocean

heterogeneous delivery of silicate and metal to the earth by large planetesimals after the moon s formation earth experienced a protracted bombardment by leftover planetesimals the mass delivered during this stage of late accretion has been estimated to be approximately 0 5 of earth s present mass based on highly siderophile element concentrations in the earth s mantle and the assumption that all highly siderophile elements delivered by impacts were retained in the mantle however late accretion may have involved mostly large 1 500 km in diameter and therefore differentiated projectiles in which highly siderophile elements were sequestered primarily in metallic cores here we present smoothed particle hydrodynamics impact simulations that show that substantial portions of a large planetesimal s core may descend to the earth s core or escape accretion entirely both outcomes reduce the delivery of highly siderophile elements to the earth s mantle and imply a late accretion mass that may be two to five times greater than previously thought further we demonstrate that projectile material can be concentrated within localized domains of earth s mantle producing both positive and negative 182w isotopic anomalies of the order of 10 to 100 ppm in this scenario some isotopic anomalies observed in terrestrial rocks can be explained as products of collisions after moon formation

heat partitioning in metal silicate plumes during earth differentiation abstract we present an analytical model for core formation that includes both metal diapirs and liquid conduits and produces a superheated core we start from the standard model of earth formation consisting of accretion by planetesimal or planetary embryo impacts large enough to create global or local magma oceans our model consists of two main fluid dynamical structures 1 large liquid metal diapirs and 2 narrow conduits with liquid silicate and small liquid metal droplets we assume that transport of metal from a near surface magma ocean to the growing core occurs within these structures the release of gravitational potential energy from the descent of the metal is converted to heat through viscous dissipation which is broadly distributed around the large liquid metal diapirs but localized in the conduit around the smaller metal droplets this model gives an average core temperature during accretion and a post accretion average core temperature for a broad range of impact histories and chemical quilibration assumptions we consider three types of earth accretion histories with impacts that are evenly spaced over 30 ma these include 1 equal sized impacts 2 equal sized impacts with a final mars sized impact and 3 exponentially decreasing impact sizes with a final mars sized impact our preferred model is based on core mantle chemical equilibrium estimates that correspond to a fractionation f the ratio of metal in the diapir to the total metal content in each impact of f 0 64 and accretion history type 3 this model produces a post accretion average core temperature that ranges from 5930 k to 5700 k for 8 to 90 impacts respectively the efficiency of the metal silicate conduits defined as the ratio of the heating of the core by the conduits to their potential energy released has an approximate value of 0 59 for our preferred model the residual post accretion structures include a basal magma ocean and a network of mantle conduits that may dictate the style of hadean tectonics

telltale tungsten and the moon advances in high precision isotopic analysis have provided key constraints on the origin and early evolution of the earth and moon measurements of the isotopes of tungsten provide the most stringent constraints on this history

a sawtooth like timeline for the first billion years of lunar bombardment abstract we revisit the early evolution of the moon s bombardment our work combines modeling based on plausible projectile sources and their dynamical decay rates with constraints from the lunar crater record radiometric ages of the youngest lunar basins and the abundance of highly siderophile elements in the lunar crust and mantle we deduce that the evolution of the impact flux did not decline exponentially over the first billion years of lunar history but also there was no prominent and narrow impact spike 3 9 gy ago unlike that typically envisioned in the lunar cataclysm scenario instead we show the timeline of the lunar bombardment has a sawtooth like profile with an uptick in the impact flux near 4 1 gy ago the impact flux at the beginning of this weaker cataclysm was 5 10 times higher than the immediately preceding period the nectaris basin should have been one of the first basins formed at the sawtooth we predict the bombardment rate since 4 1 gy ago declined slowly and adhered relatively close to classic crater chronology models neukum and ivanov 1994 overall we expect that the sawtooth event accounted for about one fourth of the total bombardment suffered by the moon since its formation consequently considering that 12 14 basins formed during the sawtooth event we expect that the net number of basins formed on the moon was 45 50 from our expected bombardment timeline we derived a new and improved lunar chronology suitable for use on pre nectarian surface units according to this chronology a significant portion of the oldest lunar cratered terrains has an age of 4 38 4 42 gyr moreover the largest lunar basin south pole aitken is older than 4 3 gy and therefore was not produced during the lunar cataclysm

lack of late accreted material as the origin of 182w excesses in the archean mantle evidence from the pilbara craton western australia abstract we report 182w and 142nd isotopic compositions 187re 187os systematics and abundances of highly siderophile elements hse re os ir ru rh pt pd and au for a suite of komatiites and basalts from the 3 3 ga ruth well formation and the 3 45 ga warrawoona group of the pilbara craton western australia the 182w compositions from all samples are indistinguishable from each other and more radiogenic than modern bulk silicate earth with a mean 182w value of 9 1 4 2 2sd by contrast the 142nd values for all samples are indistinguishable from each other and terrestrial standards with a mean 142nd value of 1 6 3 2 2sd the 146sm 142nd and 187re 187os systematics are consistent with chondritic sm nd and re os ratios in the mantle source during the lifetime of 182hf and the observed 182w excesses therefore cannot be accounted for by early hf w fractionation by magma ocean processes neither by silicate liquid crystal fractionation nor by high p t metal silicate equilibration the estimated abundances of hse in the mantle source however are significantly lower than modern bulk silicate earth with only 51 9 1sd of modern bulk silicate earth abundances these results are consistent with a partial lack of late accreted material within the pilbara source at 3 3 ga to account for the 182w excesses further widespread 182w excesses of similar magnitude in other archean mantle derived rocks worldwide strongly suggests that a common process most likely incomplete addition of late accreted material was responsible the apparent mismatch between late accreted 182w hse systematics for some other localities likely reflects either the inherent difficulties associated with estimating source hse abundances and or dissociation of w and hse by mantle processes finally the combined average 182w hse systematics of archean samples indicate that the pre late accretion bse likely had a 182w value similar to that of the lunar mantle which strongly suggests post giant impact earth moon equilibration and indicates that the moon formed after 182hf extinction

distribution of phosphorus in sediments from tomales bay california abstract the distribution of phosphorus among six sequentially extracted fractions was determined in suspended load and bottom sediments from lagunitas creek and tomales bay california the sequential extraction scheme was a modification of the sedex scheme of ruttenberg 1992 using the surfactant sodium dodecyl sulfate sds to extract organic phosphorus sds effectively removed organic phosphorus from sediments with little interference from inorganic phosphorus containing phases the distribution of phosphorus in the sequentially extracted fractions was similar in suspended load and bottom sediments collected from lagunitas creek and the bay the concentration of phosphorus in cdb extractable iron oxide phases was below detection in all samples most of the phosphorus 70 80 contained in these sediments was found in the organic and residual phases porewaters from sediment cores were analyzed for dissolved inorganic carbon ammonium phosphate sulfate iron calcium and fluoride within bay sediments porewaters were depleted in phosphate relative to dissolved inorganic carbon and ammonium suggesting that phosphate released from organic matter decomposition is being removed from the porewaters sequential extraction results suggest that approximately 15 of the phosphate released from organic matter decomposition could be removed from the porewaters by adsorption into the exchangeable phosphorus fraction and an additional 3 may be precipitated as authigenic phosphate minerals the remaining phosphate 82 released from organic matter decomposition must be either taken up within the sediment mixed layer 0 40 cm or escapes to the overlying water column

accretionary orogenesis of the chinese altai insights from paleozoic granitoids zircon u pb dating and whole rock major oxide trace element and nd sr isotope compositions have been determined for four representative granitic intrusions in the sw chinese altai in order to understand the orogenesis and history of crustal growth in the central asian orogenic belt caob the ashile and halatas bodiesare relatively small intrusions formed in the late carboniferous 318 6ma andpermian 267 4ma respectively thelargertarlang tb andkeketuohaibatholiths kb havemagmaticagesof 359 to 412 ma the granitoids consist chiefly of tonalite granodiorite and granite and are metaluminous to weakly peraluminous in composition asi 0 8 1 1 the ashile pluton is characterized by relatively high mgo 2 73 3 54 wt and sr 395 456 ppm contents with low k2o na2o ratios 0 31 0 42 and mantle like nd sr isotopic compositions endt 2 85 to 3 26 initial 87 sr 86 sr 0 7047 0 7051 it probably formed by fractional crystallization of a mantle derived magma with limited assimilation of oldcrustalmaterial theotherintrusionshavenear zeroornegative endtvalues 0 67to 4 41 andhighersrisotopiccompositions initial 87 sr 86 sr 0 7067 0 7092 indicating a mixture of juvenile and old components in their genesis these intrusions are characterized by relatively low k rb cs contents and low rb sr ratios mostly b0 6 and generally exhibit moderate to high heavy rare earth element hree concentrations ybn 8 26 and weak hree fractionation dy ybnb1 5 with or without negative europium anomalies eu eu 0 5 1 0 these characteristics are consistent with an origin by dehydration melting of a hornblendebearing mid crustal source above the garnet stability field dominated by mafic to intermediate rocks this suggests that the deep crust of the chinese altai may contain a considerable proportion of juvenile material mantle derived magmatism probably in an active extensional continental margin setting played an important role in the formation of the chinese altai acting not only as a heat sourceforcrustalmeltingbutasasourceofjuvenilecomponents therelativelysmallvolumesanddistinctgeochemicalcompositions of the ashile and halatas plutons may imply a substantial change in the geodynamic setting in the late paleozoic 2007 elsevier b v all rights reserved

origin and age of phosphorite from the last glacial maximum to holocene transgressive succession off the orange river south africa a major erosional unconformity between upper cretaceous sediments and the last glacial maximum lgm transgressive succession occurs on the inner continental shelf off the orange river vibracores from 122 m water depth consist of upper pleistocene shelly phosphatic sands deposited in a high energy shoreface environment during the lgm lowstand between 22 and 19 ka the gravel rich shoreface sand grades into condensed shell rich delta front sands as sea level rose between 19 and 14 3 ka an abrupt facies transition to prodelta muddy sands corresponds to the rapid rise in sea level associated with melt water pulse mwp 1a at 14 3 ka and the facies transition to clayey silt corresponds to mwp 1b at around 11 ka a large decrease in macro and microfossil diversity indicates low oxygen conditions as the sea level rose phosphorite recovered from throughout the succession includes large interior mollusc moulds sand size peloids and friable nodules sr derived ages of the phosphorite range from early miocene to quaternary x ray amorphous friable ca phosphate nodules occur in organic rich holocene mud deposits quaternary sediment on the shelf represents a complex condensed section in which reworked phosphorite pebbles show multiple episodes of phosphogenesis often separated by millions of years within individual pebbles the phosphorite indicates that organic rich mud deposition on the shelf was prevalent during the early to middle miocene marine transgressions and sea level highstands that were associated with increased upwelling as indicated by the extensive early to middle miocene eolianites of the tsondab sandstone formation most friable phosphorite that formed during quaternary marine transgressions and highstands was probably fragmented and transported off shelf during succeeding marine regressions

tungsten isotopic evidence for disproportional late accretion to the earth and moon examination of three lunar samples reveals that the moon s mantle has an excess of the tungsten isotope 182w of about 20 parts per million relative to the present day earth s mantle this suggests that the two bodies had identical compositions immediately following the formation of the moon and that the compositions then diverged as a result of disproportional late accretion of chondritic material to the earth and moon two papers published in this issue of nature present precise measurements of tungsten isotope composition in lunar rocks that are best explained by the earth and moon having had similar composition immediately following formation of the moon and then having diverged as a result of disproportional late accretion of material to the two bodies mathieu touboul et al found small 182w excess of about 21 parts per million relative to the present day earth s mantle in metals extracted from two kreep rich apollo 16 impact melt rocks while thomas kruijer et al measured tungsten isotopes in seven kreep rich whole rock samples that span a wide range of cosmic ray exposure ages and found a 182w excess of about 27 parts per million over the present day earth s mantle characterization of the hafnium tungsten systematics 182hf decaying to 182w and emitting two electrons with a half life of 8 9 million years of the lunar mantle will enable better constraints on the timescale and processes involved in the currently accepted giant impact theory for the formation and evolution of the moon and for testing the late accretion hypothesis uniform terrestrial mantle like w isotopic compositions have been reported1 2 among crystallization products of the lunar magma ocean these observations were interpreted to reflect formation of the moon and crystallization of the lunar magma ocean after 182hf was no longer extant that is more than about 60 million years after the solar system formed here we present w isotope data for three lunar samples that are more precise by a factor of 4 than those previously reported1 2 the new data reveal that the lunar mantle has a well resolved 182w excess of 20 6 5 1 parts per million 2 standard deviations relative to the modern terrestrial mantle the offset between the mantles of the moon and the modern earth is best explained by assuming that the w isotopic compositions of the two bodies were identical immediately following formation of the moon and that they then diverged as a result of disproportional late accretion to the earth and moon3 4 one implication of this model is that metal from the core of the moon forming impactor must have efficiently stripped the earth s mantle of highly siderophile elements on its way to merge with the terrestrial core requiring a substantial but still poorly defined level of metal silicate equilibration

dynamical and collisional constraints on a stochastic late veneer on the terrestrial planets abstract given their tendency to be incorporated into the core during differentiation the highly siderophile elements hses in earth s mantle are thought to have been accreted as a late veneer after the end of the giant impact phase bottke et al bottke w f walker r j day j m d nesvorny d elkins tanton l 2010 science 330 1527 proposed that the large earth to moon hse abundance ratio can be explained if the late veneer was characterized by large d 1000 4000 km impactors here we simulate the evolution of the terrestrial planets during a stochastic late veneer phase from the end of accretion until the start of the late heavy bombardment 500 myr later we show that a late veneer population of 0 05m dominated by large d 1000 km bodies naturally delivers a 0 01m veneer to earth consistent with geochemical constraints the eccentricities and inclinations of the terrestrial planets are excited by close encounters with the largest late veneer bodies we find the best agreement with their post veneer orbits if either a the terrestrial planets pre veneer angular momentum deficit amd0 was less than about half of the current one amdnow or b amd0 amdnow and the veneer was limited to smaller dmax 2000 km bodies veneer impacts on venus earth and mars were mostly accretionary but on mercury and the moon they were mostly erosive in 20 of simulations an energetic impact occurred that could have removed 25 of mercury s mass thereby increasing its iron mass fraction we show that due to the erosive nature of larger impacts the moon cannot accrete any material from objects larger than 500 1000 km the large earth to moon hse abundance ratio is naturally explained if the late veneer included large impactors d 500 1000 km regardless of their size distribution as long as most of earth s veneer came from large bodies the spin angular moment imparted by stochastic late veneer impacts was far in excess of the current ones for mercury and venus meaning that their post veneer spin rates were much faster the late veneer if it included large impactors was an accretionary phase for venus earth and mars but an erosive phase for mercury and the moon

forms of phosphorus and phosphorus iron relationships in the suspended matter of the st lawrence estuary the partition of phosphorus between the organic fraction porg and both the detrital apatite rich and non detrital adsorbed fractions pap and pcdb was studied in the particulate matter of the st lawrence estuary and two of its tributaries the adsorption of the pcdb fraction on particulate iron was examined porg makes up about one third of the total particulate p which ranges betweeen 44 and 64 g at g everywhere in the estuary and regardless of salinity the concentration of pap represents twice that of pcdb the hydroxide fraction fecdb is on the average 25 and 29 of the total particulate iron in may and september respectively but is much higher in the tributaries the atom ratio fe p cdb of hydroxide fe to adsorbed p fluctuates around 16 for may and 19 for september low values 13 16 are characteristic of the turbidity maximum whereas higher ones are found in the deeper more saline waters 16 26 and in the tributaries 17 26 although any iron precipitation in the low salinity

the timeline of the lunar bombardment revisited abstract the timeline of the lunar bombardment in the first gy of solar system history remains unclear basin forming impacts e g imbrium orientale occurred 3 9 3 7 gy ago i e 600 800 my after the formation of the moon itself many other basins formed before imbrium but their exact ages are not precisely known there is an intense debate between two possible interpretations of the data in the cataclysm scenario there was a surge in the impact rate approximately at the time of imbrium formation while in the accretion tail scenario the lunar bombardment declined since the era of planet formation and the latest basins formed in its tail end here we revisit the work of morbidelli et al 2012 that examined which scenario could be compatible with both the lunar crater record in the 3 4 gy period and the abundance of highly siderophile elements hse in the lunar mantle we use updated numerical simulations of the fluxes of asteroids comets and planetesimals leftover from the planet formation process under the traditional assumption that the hses track the total amount of material accreted by the moon since its formation we conclude that only the cataclysm scenario can explain the data the cataclysm should have started 3 95 gy ago however we also consider the possibility that hses are sequestered from the mantle of a planet during magma ocean crystallization due to iron sulfide exsolution o neil 1991 rubie et al 2016 we show that this is likely true also for the moon if mantle overturn is taken into account based on the hypothesis that the lunar magma ocean crystallized about 100 150 my after moon formation elkins tanton et al 2011 and therefore that hses accumulated in the lunar mantle only after this timespan we show that the bombardment in the 3 4 gy period can be explained in the accretion tail scenario this hypothesis would also explain why the moon appears so depleted in hses relative to the earth we also extend our analysis of the cataclysm and accretion tail scenarios to the case of mars the accretion tail scenario requires a global resurfacing event on mars 4 4 gy ago possibly associated with the formation of the borealis basin and it is consistent with the hse budget of the planet moreover it implies that the noachian and pre noachian terrains are 200 my older than usually considered

processes controlling phosphate adsorption by iron hydroxides in estuaries abstract phosphate adsorption by iron hydroxides is studied in the laboratory on p depleted and p saturated seston and on post glacial clays all samples from the saint lawrence estuary levels of adsorption and desorption are distinguished on the basis of significantly different ratios of the particulate iron hydroxides fecdb to inorganic non detrital phosphorus pcdb adsorption equilibrium is quickly reached for the desorbed and the sediment samples when agitated with po4 p enriched seawater this level is characterized by a mean fe p cdb value of 14 identical to the dominant one in the st lawrence p adsorption on p saturated particulate matter is found to be reversible under low reducing conditions because of the narrow ph range in the st lawrence estuary ph does not seem to influence the reaction rate the partial phosphate desorption corresponds to values of the fe p cdb ratio of 18 without any fe release these conditions are similar to those at the surface of estuarine marsh sediments the stirring experiments in the laboratory are adequately reproducing the natural behaviour of the particulate matter but the kinetics of the re adsorption reaction are much faster than in the estuary

genesis of post collisional granitoids and basement nature of the junggar terrane nw china nd sr isotope and trace element evidence the post collisional magmatism of the junggar terrane is characterized by intrusion of large amounts of granitoids and minor basic ultrabasic rocks the granitoids comprise two magmatic suites calc alkaline and alkaline which were emplaced contemporaneously at about 294 ma the calc alkaline rocks are typically sodium rich na2o k2o 1 1 3 5 and metaluminous a nk 1 0 a cnk 0 78 1 04 they show mildly fractionated ree patterns la yb n 15 and spidergrams with strong depletion of nb ti and to a lesser extent sr the alkaline granites have high contents of sio2 75 78 alkalis nb hree y sn f and high feo mgo ratios and huge sr and eu depletion in the spidergrams moreover they display characteristic tetrad ree patterns and non charac trace element behaviour the two rock suites have similar initial nd and sr isotopic compositions with end t in the range 5 2 to 7 1 and isr mostly in the range 0 7031 0 7041 this points to a predominance of juvenile components in their sources the calc alkaline rocks are most probably derived by dehydration melting of a basic lower crust leaving behind a granulite residue the process was probably triggered by underplating of mantle derived basic magmas in an extensional regime the alkaline granites are considered to have formed by differentiation of the calc alkaline granitoids our study argues for a juvenile continental crust for the basement of the junggar terrane which is likely dominated by early paleozoic oceanic crust and arc complex that were deeply buried during the late paleozoic subduction and accretion

magma oceans in the inner solar system theory and observations point to the occurrence of magma ponds or oceans in the early evolution of terrestrial planets and in many early accreting planetesimals the apparent ubiquity of melting during giant accretionary impacts suggests that silicate and metallic material may be processed through multiple magma oceans before reaching solidity in a planet the processes of magma ocean formation and solidification therefore strongly influence the earliest compositional differentiation and volatile content of the terrestrial planets and they form the starting point for cooling to clement habitable conditions and for the onset of thermally driven mantle convection and plate tectonics this review focuses on evidence for magma oceans on planetesimals and planets and on research concerning the processes of compositional differentiation in the silicate magma ocean distribution and degassing of volatiles and cooling

late paleozoic strike slip shear zones in eastern central asia nw china new structural and geochronological data 1 new structural studies and 40ar 39ar dating in northwest china provide information about late paleozoic strike slip motions subsequent to accretional events which built eastern central asia during the paleozoic two principal areas were affected by these large transcurrent motions first in the tianshan range main east west ductile shear zones are dextral and coeval with an eastward decreasing greenschist retrograde metamorphism associated biotites give ages ranging from 290 ma to 245 ma the earlier n110 shearing occurred in western tianshan while the last one dextral in whole tianshan occurred 250 245 myr ago second in the chinese altay region several nw se shear zones structured the area the main motion is sinistral and occurred along the erqishi zone at 280 290 ma it is followed by a complex succession of dextral and sinistral shearing episodes leading to the northwestward structuring dated at 245 ma of a metamorphic zone that was folded during a compressive event

the tethered moon abstract we address the thermal history of the earth after the moon forming impact taking tidal heating and thermal blanketing by the atmosphere into account the atmosphere sets an upper bound of 100 w m2 on how quickly the earth can cool the liquid magma ocean cools over 2 10 myr with longer times corresponding to high angular momentum events tidal heating is focused mostly in mantle materials that are just beginning to freeze the atmosphere s control over cooling sets up a negative feedback between viscosity dependent tidal heating and temperature dependent viscosity of the magma ocean while the feedback holds evolution of the moon s orbit is limited by the modest radiative cooling rate of earth s atmosphere orbital evolution is orders of magnitude slower than in conventional constant q models which promotes capture by resonances the evection resonance is encountered early when the earth is molten capture by the evection resonance appears certain but unlikely to generate much eccentricity because it is encountered early when the earth is molten and q q tidal dissipation in the earth becomes more efficient q q later when the moon is between 20 r and 40 r if lunar eccentricity grew great this was when it did so perhaps setting the table for some other process to leave its mark on the inclination of the moon

highly siderophile element and 182w evidence for a partial late veneer in the source of 3 8 ga rocks from isua greenland abstract the higher than expected concentrations of highly siderophile elements hse in earth s mantle most likely indicate that earth received a small amount of late accreted mass after core formation had ceased known as the late veneer small 182w excesses in the moon and in some archaean rocks such as the source of 3 8 billion year old isua magmatics also appear consistent with the late veneer hypothesis with a lower proportion received however 182w anomalies can also relate to other processes including early mantle differentiation to better assess the origin of these w isotope anomalies and specifically whether they relate to the late veneer we have determined the hse abundances and 182w compositions of a suite of mafic to ultramafic rocks from isua from which we estimate hse abundances in the source mantle and ultimately constrain the 182w composition of the pre late veneer mantle our data suggest that the isua source mantle had hse abundances at around 50 65 of the present day mantle consistent with partial but not complete isolation from the late veneer these data also indicate that at least part of the late veneer had been added and mixed into the mantle at the time the isua source formed prior to 3 8 ga for the same isua samples we obtained a 13 4 ppm 182w excess compared to the modern terrestrial mantle in excellent agreement with previous data using combined 182w and hse data we show that the moon isua and the present day bulk silicate earth bse produce a well defined co variation between 182w composition and the mass fraction of late accreted mass as inferred from hse abundances this co variation is consistent with the calculated effects of various late accretion compositions on the hse and 182w signatures of earth s mantle the empirical relationship therefore implies that the moon isua source and bse received increasing proportions of late accreted mass supporting the idea of disproportional late accretion to the earth and moon and consistent with the interpretation that the lunar 182w value of 27 4 ppm represents the composition of earth s mantle before the late veneer was added in this case the isua source can represent ambient mantle after the giant moon forming impact into which only a part of earth s full late veneer was mixed rather than an isotopically distinct mantle domain produced by early differentiation which would probably require survival through the giant moon forming impact

the coupled 182w 142nd record of early terrestrial mantle differentiation new sm nd lu hf hf w and re os isotope data in combination with highly siderophile element hse including re os ir ru pt and pd and w abundances are reported for the 3 55 ga schapenburg komatiites south africa the schapenburg komatiites define a re os isochron with an age of 3550 87 ma and initial 187os 3 7 0 2 2sd the absolute hse abundances in the mantle source of the schapenburg komatiite system are estimated to be only 29 5 of those in the present day bulk silicate earth bse the komatiites were derived from mantle enriched in the decay products of the long lived 147sm and 176lu nuclides initial 143nd 2 4 0 1 176hf 5 7 0 3 2sd by contrast the komatiites are depleted relative to the modern mantle in 142nd and 182w 182w 8 4 4 5 142nd 4 9 2 8 2sd these results constitute the first observation in terrestrial rocks of coupled depletions in 142nd and 182w such isotopic depletions require derivation of the komatiites from a mantle domain that formed within the first 30 ma of solar system history and was initially geochemically enriched in highly incompatible trace elements as a result of crystal liquid fractionation in an early magma ocean this mantle domain further must have experienced subsequent melt depletion after 182hf had gone extinct to account for the observed initial excesses in 143nd and 176hf the survival of early formed 182w and 142nd anomalies in the mantle until at least 3 55 ga indicates that the products of early planetary differentiation survived both later planetary accretion and convective mantle mixing during the hadean this work moreover renders unlikely that variable late accretion by itself can account for all of the observed w isotope variations in archean rocks

paleozoic accretion and cenozoic redeformation of the chinese tien shan range central asia the tien shan range in central asia contains two late paleozoic sutures the older southern suture marks the collision of a passive margin at the north of the tarim block and an active continental margin subduction under the latter was to the north the younger northern suture separates a northern carboniferous island arc from an active continental margin developed over a south dipping subduction zone the subduction direction under the island arc is unknown mesozoic elastics were deposited over the doubly sutured orogen rate and energy of sedimentation waned until deposition of oligocene conglomerates above a regional unconformity interpreted as marking the onset of deformation induced by the india asia collision molasse deposition accelerated in pliocene and quaternary time and deposition continues today as active thrusts generate relief paleozoic structures control the gross divergence of cenozoic thrusts across the orogen

a re evaluation of metal diapir breakup and equilibration in terrestrial magma oceans abstract due to mechanisms such as impact heating early atmospheric thermal blanketing and radioactive heating the presence of at least one global magma ocean stage in the early histories of terrestrial planets seems unavoidable in such a context a key question to constrain the early thermo chemical evolution of the earth is how much iron diapirs provided by differentiated impactors emulsified during their sinking towards the bottom of an early magma ocean in the past years several workers have focused on this question using however various approaches and making different assumptions while most studies favor rapid breakup and equilibration of iron bodies during their sinking through the magma ocean recent work suggests that iron bodies of size comparable or greater than a few tens of kilometers may preserve most of their initial volume as they reach the bottom of a magma ocean therefore leading to metal silicate disequilibrium to clarify the discrepancies and the differences among studies i have conducted a series of numerical simulations and theoretical calculations to derive the conditions and the timing for the breakup of metal diapirs of any size sinking through a silicate magma ocean with a large range of plausible viscosity values the obtained breakup criterion is used to derive stable diapir sizes and their ability to equilibrate with the surrounding silicates i show that for plausible magma ocean viscosities diapirs with initial radii smaller than the thickness of a magma ocean rapidly break up into stable diapir sizes smaller than 0 2 m at which metal silicate equilibration is rapidly achieved