a strong wind event on the ross ice shelf antarctica a case study of scale interactions abstractin situ observations satellite imagery numerical weather prediction and reanalysis fields are used to investigate the synoptic and mesoscale environment of a strong wind event swe at mcmurdo station ross island region on the ross ice shelf antarctica on 10 october 2003 the swe occurred during the passage of a sequence of three mesoscale low pressure systems from the central ross ice shelf to the southwest ross sea a potential vorticity pv analysis showed that the lows drew air of continental origin down the glacial valleys of the transantarctic mountains and onto the ice shelf as a katabatic drainage flow however the analysis indicated that the air mass associated with the swe was of recurved maritime origin drawn in by the second mesoscale low l2 this air mass approached mcmurdo station from the south where interactions with the orography played a critical role in the early stages of the event when the wind speed was less than 10 m s 1 the air was deflected around the topograph

contrasting exhumation histories along a crustal scale strike slip fault zone the eocene to miocene ailao shan red river shear zone in southeastern tibet abstract four metamorphic massifs in southeastern tibet the xuelong shan xls diancang shan dcs ailao shan als and day nui con voi dncv have been suggested to constitute coherent parts of the ailao shan red river asrr shear zone this study details the cooling exhumation histories of the crustal scale shear zone by determining the cooling paths of the als massif and comparing these paths to those of the dcs massif we show that the different parts of the als massif have experienced two stages of diachronous cooling histories the two cooling stages of the als massif i e an early rapid cooling of ca 45 715 c myr and a late slow cooling of 10 17 c myr differ significantly from the cooling of the dcs massif along the same shear zone which featured an early slow cooling of 11 17 c myr and a late rapid cooling of 30 140 c myr this study confirms that differing cooling exhumation histories exist along the same crustal scale shear zone from the contrasting cooling exhumation histories we would argue that the als and dcs massifs are isolated units with different tectono thermal histories during the oligo miocene tectonic evolution of southeastern tibet

n body simulations of oligarchic growth of mars implications for hf w chronology dauphas and pourmand 2011 hf w th evidence for rapid growth of mars and its status as a planetary embryo nature 473 489 492 estimated the accretion timescale of mars to be 1 8 1 0 0 9myr from the w isotopes of martian meteorites this timescale was derived assuming perfect metal silicate equilibration between the impactor and the target s mantle however in the case of a small impactor most likely only a fraction of the target s mantle is involved in the equilibration while only a small part of the impactor s core equilibrates in the case of a giant impact we examined the effects of imperfect equilibration using results of high resolution n body simulations for the oligarchic growth stage these effects were found to be small as long as a planetary embryo has a deep liquid magma ocean during its accretion the effect due to partial involvement of the target s mantle in equilibration is small due to the low metal silicate partition coefficient for w suggested from the low hf w ratio of the martian mantle the effect due to partial involvement of the impactor s core is also small because a large fraction of the embryo mass is delivered from small planetesimals which are likely to fully equilibrate in the deep magma ocean on the embryo the accretion timescale of mars estimated by the hf w chronology is shorter than that expected for the minimum mass solar nebula model as long as more than 10 of each impactor s core re equilibrates with the martian mantle and the final stages of accretion are prolonged this probably indicates that accretion of mars rapidly proceeded due to solid and gas surface densities significantly larger than those for the minimum mass solar nebula or due to accretion of small fragments or pebbles

accurate measurement of silver isotopic compositions in geological materials including low pd ag meteorites very precise silver ag isotopic compositions have been determined for a number of terrestrial rocks and high and low pd ag meteorites by utilizing multicollector inductively coupled plasma mass spectrometry mc icpms the meteorites include primitive chondrites the group iab iron meteorites canyon diablo and toluca and the group iiiab iron meteorite grant silver isotopic measurements are primarily of interest because 107 ag was produced by decay of the short lived radionuclide 107 pd during the formation of the solar system and hence the pd ag chronometer has set constraints on the timing of early planetesimal formation a 2 precision of 0 05 can be obtained for analyses of standard solutions when ag isotopic ratios are normalized to pd to correct for instrumental mass discrimination and to bracketing standards caution must be exercised when making ag isotopic measurements because isotopic artifacts can be generated in the laboratory and during mass spectrometry the external reproducibility for geological samples based on replicate analyses of rocks is 0 2 2 all chondrites analyzed have similar ag isotopic compositions that do not differ significantly 0 3 from the terrestrial value of the nist srm 978a ag isotope standard hence they show no evidence of excess 107 ag derived from 107 pd decay or of stable ag isotope fractionation associated with volatile element depletion within the accretion disk or from parent body metamorphism the group iab iron meteorite samples analyzed show evidence of complex behavior and disturbance of ag isotope systematics therefore care must be taken when using this group of iron meteorites to obtain chronological information based on the pd ag decay scheme copyright 2005 elsevier ltd

centrifuge assisted percolation of fe s melts in partially molten peridotite time constraints for planetary core formation the mechanism which segregates molten fe s into metallic cores of planetary bodies is still not fully understood due to the high interfacial energy and wetting angle between fe s melts and silicate mantle minerals the continuous percolative flow of such melts cannot be efficient for the core segregation in planetary bodies a series of percolation experiments has been realized on a partially molten fertile garnet peridotite employing a centrifuging piston cylinder a high temperature garnet peridotite with mg 0 90 composed of 60 vol olivine 15 vol orthopyroxene 6 vol clinopyroxene and 19 vol garnet has been used as the silicate matrix peridotite powders with the 100 200 or 20 30 m grain size were mixed with 5 30 vol fe s of eutectic composition fe70s30 the aggregates were centrifuged at 500 700 g at temperatures below and above the melting point of the peridotite the centrifuge experiments revealed a negligible percolation of fe s melts through the unmolten peridotite matrix only at t 1260 c i e above the solidus of the peridotite and starting with 5 vol of fe70s30 the vertical melt gradient achieved 1 2 vol mm in samples with 15 vol fe70s30 the vertical separation achieved 2 2 5 vol mm after 10 h of centrifuging at 500 g an increase in the degree of partial silicate melting in the peridotite leads to an increase of the fe s separation rate from the peridotite matrix fe s contents 10 vol cause an increase of the fe s melt droplet size and of the effective percolation velocity of fe s melt a threshold dividing fast 10 cm per year and slow percolations 1 mm per year of fe s melt is found around 14 15 vol of fe70s30 the experimentally determined permeabilities of fe s melt in the unmolten peridotite with 7 10 vol of fe70s30 melt are 10 18 10 19 m2 which is 2 3 orders of magnitude lower than the values calculated previously from static experiments the presence of the silicate melt increases the segregation velocity of fe s melt in a partially molten peridotite by more than one order of magnitude with respect to the unmolten peridotite matrix this could provide an effective segregation of fe s melt in a planetary mantle down to 2 5 vol of residual fe s melt the extremely slow percolation of fe s melt in the absence of the partial silicate melting precludes a scenario of metallic core formation via percolation before temperatures allow a substantial partial melting of mantle silicates in planetary bodies

geomorphic constraints on surface uplift exhumation and plateau growth in the red river region yunnan province china field observations digital elevation model dem data and longitudinal profi le analysis reveal a perched low relief upland landscape in the red river region yunnan province china which correlates to an uplifted regional low relief landscape preserved over the eastern margin of the tibetan plateau as with other major rivers of the plateau margin the red river has deeply incised the lowrelief upland landscape which we interpret to be the remnants of a pre uplift or relict landscape we examine longitudinal river profi les for 97 tributaries of the red river most profi les consist of three segments separated by sharp knickpoints an upper lowgradient channel segment a steeper middle channel segment and a very steep lower channel segment upper channel segments correspond to the relict landscape and have not yet experienced river incision steeper middle and lower segments indicate onset of rapid two phase river incision on the basis of which changes in external forcings such as climate or uplift can be inferred in terms of two end member scenarios two phase incision could be the result of pulsed plateau growth in which relatively slow uplift during the fi rst phase is followed by rapid uplift during the second phase or it could refl ect adjustments of the main channel to changing climate conditions against the backdrop of steady plateau growth reconstruction of the paleo red river indicates 1400 m river incision 1400 1500 m surface uplift and a maximum of 750 m vertical displacement across the northern red river fault elevating the northern ailao shan range above the surrounding relict landscape on the basis of stratigraphic constraints incision along the red river likely began in pliocene time

the red river fault system in the tonkin gulf vietnam abstract the red river fault system in the tonkin gulf offshore haiphong was studied using seismic profiles calibrated by deep wells well characterised left lateral strike slip occurred continuously within a narrow 30 km wide zone southwest of the vinh minh fault between 30 ma and 5 5 ma however the corresponding amount of offset probably does not exceed a few tens of kilometres no sign of post 5 5 ma right lateral motion can be detected prior to 30 ma there is a widespread extension in a wider 100 km wide zone which could be related to a significant amount of left lateral motion the motion of the fault splays to the northeast of the vinh minh fault prior to 30 ma was absorbed in the rifting of the gulf of beibu a 15 5 ma unconformity separates the transtensional regime from a later transpresional regime this 15 5 ma date coincides with the cessation of sea floor spreading in the south china sea

connectivity of molten fe alloy in peridotite based on in situ electrical conductivity measurements implications for core formation in terrestrial planets abstract the connectivity of molten fe s in peridotite has been experimentally investigated by means of in situ electrical conductivity measurements at high temperatures and 1 gpa starting materials were powdered mixtures of peridotite klb 1 with various amounts 0 3 6 13 19 24 vol of the 1 gpa eutectic composition in the fe fes binary system at temperatures above the eutectic point in the fe fes system 980 c and below the solidus of klb1 1200 c molten fe s in a solid silicate matrix interconnects when the volume fraction is over 5 conductivity temperature paths indicate that in the presence of partial silicate melting the connectivity of molten fe s in a peridotite matrix is inhibited based on observations of retrieved samples the percolation threshold of fe s melts in the presence of low to moderate degrees of silicate melt is estimated at 13 2 vol these results indicate that if the volume fraction of fe alloy in a planetesimal was initially greater than 5 and if early heating by decay of radionuclides raised the temperature of the interior above the fe alloy melting point initial metal segregation was controlled by permeable flow of molten iron alloy in a solid silicate matrix these conditions were likely met by many terrestrial objects in the early solar nebula efficient removal of residual fe alloy 5 vol from silicate requires high degree melting of silicate so that metal can segregate as droplets giant impacts during the final stage of accretion of large planetary objects could supply the energy required for high degrees of melting alternatively if initial metal segregation were delayed until a planetary object grew to large size 1000 km in diameter release of gravitational potential energy due to metal segregation could contribute enough heat to form a magma ocean

structural petrological and thermal evolution of a tertiary ductile strike slip shear zone diancang shan yunnan the diancang shan a horst massif within the red river fault zone in yunnan people s republic of china preserves a structural petrological and thermal record of two distinct phases of tectonic activity a left lateral ductile shear that terminated between 20 and 17 ma and a ductile to brittle phase of normal faulting which began at 4 7 ma and remains active mylonitic rocks in the core of the range display an early steep high temperature ht schistosity and a horizontal stretching lineation that are both parallel to the trend of the belt kinematic indicators indicate that shear was left lateral the complex shape of the ht schistosity at the southern termination of the massif likely results from a large scale oblique left lateral c shear plane that dismembered the shear zone and separated the ailao shan and the diancang shan as left lateral deformation terminated thermochronological and thermobarometric results suggest that the gneisses were partially unroofed during this event along the eastern edge of the diancang shan the ht fabrics were overprinted by low temperature structures during activation of east dipping normal faults cooling associated with this normal right lateral faulting along the diancang shan and perhaps activation of the right lateral normal movement on the range front fault farther south along the ailao shan began at 4 7 0 1 ma these results tend to support the view that extrusion of indochina occurred along the left lateral red river shear zone between 35 and 19 17 ma initiation of right lateral normal slip during the late miocene may relate to eastward extensional collapse of the thickened tibetan crust or more probably to initiation of the second phase of extrusion

magma ocean formation due to giant impacts current understanding of the last stages of planetary accretion suggests that mass and energy accumulation are dominated by a few large impacts an important thermal consequence of such impacts is melting and formation of a large melt pond if the planet s isostatic adjustment time scale is short compared to the magma pond s cooling time scale the melt may be extruded onto the surface and form a magma ocean of approximately uniform depth although a giant impact striking at 10 15 km s 1 deposits enough energy to melt the entire planet the distribution of that energy is important in determining the thermal outcome of the collision we examine the thermal effects of giant impacts by estimating the melt volume generated by the initial shock wave and corresponding magma ocean depths additionally we examine the effects of the planet s initial temperature on the generated melt volume the hugoniot curve plotted in pressure entropy space is used to determine the shock pressure required to completely melt the material for room temperature dunite this pressure is about 150 gpa and the partial melt region is narrow for dunite initially at the solidus temperature this pressure is about 115 gpa the partial melt region extends throughout the planet once the melting pressure is known an impact melting model based on the second hugoniot equation the linear shock particle velocity relationship and the empirical particle velocity distance relationship is used to estimate the radial distance melting occurred from the impact site once the distance is found the melt region s geometry determines the associated melt volume partial melt volume is also estimated the melt fraction that is not excavated during crater formation is estimated and magma ocean depths resulting from both excavated and retained melt are calculated the model is also used to estimate the fraction of a planet melted by the initial shock wave nominal conditions of the moon forming giant impact projectile planet mass 0 14 impact speed 15 km s 1 generate melting of 30 65 of the planet depending on its initial temperature whole planet melting requires projectile planet mass ratios of 0 4 for a 15 km s 1 impact if the planet was near its solidus before the impact isostatic relaxation may generate a significant volume of additional melting

the martian hemispheric dichotomy may be due to a giant impact mars is divided into two fundamentally different geological provinces of approximately hemispherical extent1 3 the more southerly province is heavily cratered contains relatively old geological units and superficially resembles the lunar and mercurian highlands the northern province is relatively lightly cratered and contains younger geological units including extensive plains volcanic edifices and volcanic calderas except for the tharsis and elysium regions and other large volcanoes most of the younger northern province consists of lowlands which lie an average of 3 km below the highlands lowlands occupy about one third of mars they are separated from the highlands by a distinct scarp or by a sloping transitional zone as much as 700km wide in which highland materials have been disrupted and partly replaced by lowland deposits fig 1 the transition is characterized by a variety of landforms unknown on other planets the highlands and lowlands are in isostatic equilibrium across the transitional zone4 no generally accepted explanation for the cause of the highland lowland dichotomy has been proposed although thinning of the lithosph re in the northern hemisphere by internal processes has been suggested5 large impacts which were a feature of early solar system history have also been suggested as an important cause of such early planetary surface heterogeneities3 6 7 subcircular lowlands such as argyre chryse hellas and isidis planitia and the plains south of tharsis occupy previously recognized impact basins8 10 we propose here that the largest expanse of lowlands also results from formation of a large impact basin early in mars history that has profoundly shaped the planet s surface

winter observations of the atmosphere over antarctic sea ice during the winter weddell sea project 1986 wwsp 86 meteorological data were gathered above antarctic sea ice in winter and spring this paper discusses near surface data from 1986 and 1987 which were provided by weather stations deployed on drifting sea ice in october 1986 the drift tracks of these buoys for the subsequent 18 months document the sea ice motion of a larger fraction of the complete weddell gyre than historical vessel drifts and previous buoy programs the wind roses calculated from the buoys wind measurements show the large scale rotational wind field over the weddell sea the northward components of near surface horizontal temperature gradients in winter vary between 1 3 and 2 6 k 100 km horizontal temperature gradients have a component toward the center of the gyre which varies between 1 and 1 6 k 100 km in the central weddell sea the marginal ice zone advances in autumn and retreats in spring with a speed significantly larger than the actual ice speed enhanced meridional temperature contrasts in the troposphere were found each time polarstern passed the marginal ice zone significant mean horizontal temperature gradients of 1 to 5 k 100 km in the troposphere have also been detected in the continental marginal zone frommore polarstern data and related aerological data of the georg von neumayer antarctic station less

teleconnections between tropical pacific sst anomalies and extratropical southern hemisphere climate abstractteleconnections from tropical pacific sea surface temperature sst anomalies to the high latitude southern hemisphere sh are examined using observations and reanalysis analysis of tropical pacific sst anomalies is conducted separately for the central pacific cp and eastern pacific ep regions during the austral cold season extratropical sh atmospheric rossby wave train patterns are observed in association with both ep and cp sst variability the primary difference between the patterns is the westward displacement of the cp related atmospheric anomalies consistent with the westward elongation of cp related convective sst required for upper level divergence and rossby wave generation consequently cp related patterns of sh sst antarctic sea ice and temperature anomalies also exhibit a westward displacement but otherwise the cold season extratropical sh teleconnections are largely similar during the warm season however extratropical sh teleconnections associated with tropical cp and

identifying the characteristics of strong southerly wind events at casey station in east antarctica using a numerical weather prediction system abstract casey station in east antarctica is not often subject to strong southerly flow off the antarctic continent but when such events occur operations at the station are often adversely impacted not only are the dynamics of such events poorly understood but the forecasting of such occurrences is difficult the following study uses model output from a 12 month experiment using the antarctic limited area prediction system alaps to advance the understanding of the dynamics of such events and postulates that what are often described as katabatic wind events are more likely to be synoptic in scale with mid and upper level tropospheric dynamics forcing the surface layer flow strong surface layer flows that have a katabatic signature commonly develop on the steep antarctic escarpment but rarely extend out over the coast in the casey area most probably as a result of cold air damming however the development of a strong south southwesterly jet over casey provides a mechanism whereby the katabatic can

a case study of a ross ice shelf airstream event a new perspective abstract a case study illustrating cloud processes and other features associated with the ross ice shelf airstream ras in antarctica is presented the ras is a semipermanent low level wind regime primarily over the western ross ice shelf linked to the midlatitude circulation and formed from terrain induced and large scale forcing effects an integrated approach utilizes moderate resolution imaging spectroradiometer modis satellite imagery automatic weather station aws data and antarctic mesoscale prediction system amps forecast output to study the synoptic scale and mesoscale phenomena involved in cloud formation over the ross ice shelf during a ras event a synoptic scale cyclone offshore of marie byrd land draws moisture across west antarctica to the southern base of the ross ice shelf vertical lifting associated with flow around the queen maud mountains leads to cloud formation that extends across the ross ice shelf to the north the low level cloud has a warm signature in thermal infrare

the hf w isotopic system and the origin of the earth and moon abstract the earth has a radiogenic w isotopic composition compared to chondrites demonstrating that it formed while 182hf half life 9 myr was extant in earth and decaying to 182w this implies that earth underwent early and rapid accretion and core formation with most of the accumulation occurring in 10 myr and concluding approximately 30 myr after the origin of the solar system the hf w data for lunar samples can be reconciled with a major moon forming impact that terminated the terrestrial accretion process 30 myr after the origin of the solar system the suggestion that the proto earth to impactor mass ratio was 7 3 and occurred during accretion is inconsistent with the w isotope data the w isotope data is satisfactorily modeled with a mars sized impactor on proto earth proto earth to impactor ratio of 9 1 to form the moon at 30 myr

factors controlling the near surface wind field in antarctica abstract using data from the regional atmospheric climate model racmo ant1 the momentum budget of the antarctic atmospheric surface layer sl taken as the lowest model layer located at 6 7 m above the surface is presented in july winter the katabatic pressure gradient force pgf dominates the sl momentum budget over the steep coastal slopes which results in strong 10 15 m s 1 and directionally constant katabatic winds farther inland where surface slopes are more gentle the large scale pgf may become equally important with the circumpolar pressure trough north of the antarctic coastline the large scale pgf acts along with the katabatic pgf in the downslope direction in wilkes land dronning maud land and on the western ross ice shelf the large scale pgf causes equivalent geostrophic winds in excess of 10 m s 1 thermal wind effects that oppose the downslope acceleration are especially strong in areas where large scale forcing is weak which allows cold air to pile up over the flat ice she

exhumation of the diancang shan metamorphic complex along the ailao shan red river belt southwestern yunnan china evidence from 40ar 39ar thermochronology abstract exhumation of the high grade metamorphic rocks from deep to shallow crustal levels in the diancang shan dcs massif is evident by the temporal transition from shearing and mylonitization at the amphibolite facies in the lower to middle crust through retrograde ductile brittle faulting at greenschist facies in the middle crust and brittle faulting near the surface new 40ar 39ar ages of amphibole muscovite biotite and k feldspar mostly from mylonitic rocks help constrain the thermal evolution of the massif during its exhumation the thermochronologic studies have shown at least three stages of exhumation and cooling from late oligocene to pliocene e g 28 13 ma 13 4 ma and 4 0 ma respectively the initiation of the unroofing history of the dcs massif resulted from ductile left lateral shearing along the ailao shan red river shear zone asrr since the late oligocene diachronous onset and subsequent parallel cooling and exhumation characterize the early thermal history of the massif the first stage of exhumation might have stopped due to the cessation of the left lateral shearing at ca 21 ma although cooling continued until 13 ma ago to relatively low temperature conditions the second and third stages of cooling started from 13 ma and lasted until the recent active faulting the diversity of cooling rates during the second stage from 13 to 4 ma suggests differences in exhumation rates at various localities ductile to brittle shearing along the eastern flank retrograde normal shear zone is the best explanation for the exhumation during this stage the inhomogeneous cooling and exhumation of the lower plate of the normal fault zone possibly resulted from the tilting of the lower plate or differential exhumation of slabs in the lower plate during the third stage cooling and exhumation of the dcs massif since 4 ma ago is recognized when higher temperature cooling paths are extended and plotted at a lower temperature of about 16 c the present day average surface temperature therefore the diachronous cooling and exhumation continuously spanned to the surface the tectonic exhumation of the dcs massif constitutes a part of the tectono thermal evolution and diachronous exhumation of the metamorphic complexes in the fan shaped area bounded broadly in se asia by the red river fault zone and sagaing fault zone since 36 ma extrusion induced strike slip shearing and rotation associated normal faulting played important roles in the diachronous cooling and exhumation of the dcs massif and other metamorphic complexes in se asia

diachronous cooling along the mogok metamorphic belt shan scarp myanmar the trace of the northward migration of the indian syntaxis abstract we present new observations and new mineral ages eight by the 40 ar 39 ar and nine by the 40 k 40 ar methods from high grade metamorphic and foliated intrusive rocks collected along the mogok metamorphic belt of central myanmar that complete preliminary results we previously published all 30 ages presented here confirm the oligocene to middle miocene age of the mogok metamorphism moreover the ages are young from the gulf of martaban in the south to the china myanmar border in the north showing a clear diachronism these results confirm a northward migration of the tectonic event responsible for the cooling of our samples at a velocity similar to the india relative to indochina velocity at the same period in addition intensive field work along a 800 km long section of the mogok metamorphic belt has revealed the numerous ductile structures that resulted from a strong nnw sse trending extension from the analogy between the present day local extrusion around the eastern indian syntaxis and the extension observed along the mogok metamorphic belt and from the diachronism we document we suggest that the central part of myanmar has recorded the northward passage of the eastern indian syntaxis with respect to indochina from oligocene to middle miocene

annular modes in the extratropical circulation part i month to month variability the leading modes of variability of the extratropical circulation in both hemispheres are characterized by deep zonally symmetric or annular structures with geopotential height perturbations of opposing signs in the polar cap region and in the surrounding zonal ring centered near 458 latitude the structure and dynamics of the southern hemisphere sh annular mode have been extensively documented whereas the existence of a northern hemisphere nh mode herein referred to as the arctic oscillation ao has only recently been recognized like the sh mode the ao can be defined as the leading empirical orthogonal function of the sea level pressure field or of the zonally symmetric geopotential height or zonal wind fields in this paper the structure and seasonality of the nh and sh modes are compared based on data from the national centers for environmental prediction national center for atmospheric research reanalysis and supplementary datasets the structures of the nh and sh annular modes are shown to be remarkably similar not only in the zonally averaged geopotential height and zonal wind fields but in the mean meridional circulations as well both exist year round in the troposphere but they amplify with height upward into the stratosphere during those seasons in which the strength of the zonal flow is conducive to strong planetary wave mean flow interaction midwinter in the nh and late spring in the sh during these active seasons the annular modes modulate the strength of the lagrangian mean circulation in the lower stratosphere total column ozone and tropopause height over mid and high latitudes and the strength of the trade winds of their respective hemispheres the nh mode also contains an embedded planetary wave signature with expressions in surface air temperature precipitation total column ozone and tropopause height it is argued that the horizontal temperature advection by the perturbed zonal mean zonal wind field in the lower troposphere is instrumental in forcing this pattern a companion paper documents the striking resemblance between the structure of the annular modes and observed climate trends over the past few decades

cyclonically forced barrier winds along the transantarctic mountains near ross island abstract the effect of the transantarctic mountains on cyclonically forced boundary layer winds in the vicinity of ross island antarctica 77 5 s 167 e is discussed when cyclones are present over the western ross ice shelf and ross sea the low level easterly airflow is toward the mountains a barrier wind regime is set up as the flow is turned northward and becomes parallel to the mountain range it is found that cyclonically forced barrier winds occurred around 5 and 8 of the time during 1984 and 1985 respectively the case histories of two well defined barrier wind events lasting for 24 h are discussed in detail with regional analyses based on satellite photographs and automatic weather station data one case is for a katabatic wind forced mesoscale cyclone forming to the north of ross island and the other is for a synoptic scale cyclone moving through the western ross ice shelf ross sea region a numerical model for the vertically integrated boundary layer flow that calculates two horizontal

isotopic outcomes of n body accretion simulations constraints on equilibration processes during large impacts from hf w observations abstract most estimates of planetary core formation timescales using hafnium tungsten hf w isotopes employ analytical expressions assuming either continuous planetary growth or instantaneous core formation in contrast dynamical modelling of planetary accretion suggests that the final stage of terrestrial planet formation is punctuated by multiple large and stochastic impacts such giant impacts have significant thermal and isotopic consequences we present a framework for calculating the hf w isotope evolution of individual bodies based on the results of an n body accretion simulation and assuming constant partition coefficients the results show that smaller bodies exhibit a larger range in isotopic values than larger bodies because the latter have suffered more impacts the analytical core formation timescales calculated using these isotopic values can differ very significantly from the timing of the final giant impact each planet actually experiences simulations in which 1 even the largest impactors undergo re equilibration with the target s mantle rather than the cores merging directly and 2 the original planetary embryos possessed radially variable iron silicate ratios produce results which are consistent with the observed physical and isotopic characteristics of inner solar system bodies varying w partition coefficients due to changing mantle oxidation state or initial planetesimal hf w ratios might produce similar isotopic outcomes and potentially permit core mergers without violating the isotopic constraints the style of re equilibration required suggests that magma oceans were present on mars sized and larger bodies an alternative for bodies of mars size and smaller is that the bulk of the mass was delivered as impactors much smaller than the target for mars we conclude that a prolonged 10 myr accretion process is both dynamically and isotopically plausible we also predict likely pd ag isotopic anomalies for vesta mars and earth size bodies

an extreme wind event at casey station antarctica model output satellite data and in situ observations are used to investigate the conditions that gave rise to an extreme wind event at the australian casey station 66 27 s 110 53 e on the coast of east antarctica the event took place over the period march 20 22 1992 and resulted in casey station s highest ever wind gust for march 66 9 m s 1 130 knots and 10 m mean winds of near 50 m s 1 the event occurred when a deep low was located just north of the coast and there was high surface pressure inland the rapid deepening of the low took place within a strong baroclinic zone lying north south between a cold trough and a ridge bringing very warm air southward a conceptual model is proposed for the very strong winds experienced at casey station key elements of the model are 1 a synoptic scale high low pressure couplet providing a strengthening pressure gradient 2 entrainment of radiatively cooled air by the supercritical synoptic gradient leading to downslope flow 3 the acceleration of the wind down the lee slope of law dome occurring primarily in response to a topographically induced long period vertically propagating gravity wave and 4 sources of negative buoyancy including prestorm radiatively cooled air and later in the storm maritime air cooled by heat flux to the ice surface the topographically induced gravity wave increases the horizontal temperature difference thus increasing the negative buoyancy of the surface airflow

a dynamical investigation of the may 2004 mcmurdo antarctica severe wind event using amps on 15 16 may 2004 a severe windstorm struck mcmurdo antarctica the antarctic mesoscale prediction system amps is used along with available observations to analyze the storm a synoptic scale cyclone weakens as it propagates across the ross ice shelf toward mcmurdo flow associated with the cyclone initiates a barrier jet along the transantarctic mountains forcing terms from the horizontal equations of motion are computed in the barrier wind to show that the local time tendency and momentum advection terms are key components of the force balance the barrier jet interacts with a preexisting near surface radiation inversion over the ross ice shelf to set up conditions favorable for the development of large amplitude mountain waves leading to a downslope windstorm in the ross island area hydraulic theory can explain the structure of the downslope windstorms with amplification of the mountain waves possibly caused by wave breaking events the underestimation of amps wind speed at mcmurdo is caused by the misplacement of a hydraulic jump downstream of the downslope windstorms the dynamics associated with the cyclone barrier jet and downslope windstorms are analyzed to determine the role of each in development of the severe winds

summer drivers of atmospheric variability affecting ice shelf thinning in the amundsen sea embayment west antarctica satellite data and a 35 year hindcast of the amundsen sea embayment summer climate using the weather research and forecasting model are used to understand how regional and large scale atmospheric variability affects thinning of ice shelves in this sector of west antarctica by melting from above and below linked to intrusions of warm water caused by anomalous westerlies over the continental shelf edge el nino episodes are associated with an increase in surface melt but do not have a statistically significant impact on westerly winds over the continental shelf edge the location of the amundsen sea low and the polarity of the southern annular mode sam have negligible impact on surface melting although a positive sam and eastward shift of the amundsen sea low cause anomalous westerlies over the continental shelf edge the projected future increase in el nino episodes and positive sam could therefore increase the risk of disintegration of west antarctic ice shelves

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

182w and 187re 187os systematics of iron meteorites chronology for melting differentiation and crystallization in asteroids w isotopic compositions measured by n tims in five iron meteorite groups are used in conjunction with 187re 187os isotopic data to constrain the timing of metal segregation and crystallization respectively in the iron meteorite parent bodies fractionation of the parent isotope 182hf half life 9 2 ma from the daughter 182w likely occurred during segregation of metal from silicate in the iron meteorite parent bodies if w isotopic equilibrium was achieved between silicate and metal during metal segregation then the w isotopic compositions in the irons should record the timing of this event samples were taken from the five largest iron meteorite groups including the four magmatic groups iiab iiiab iva and ivb and the nonmagmatic iab iiicd group together these groups comprise approximately 90 by weight of iron meteorites classified so far with the exception of the iva group the groups have well defined 187re 187os isochron ages which are interpreted as the time of crystallization of the metal of their parent bodies within each magmatic group samples that crystallized both early and late in the sequence of each core were analyzed to evaluate possible evolution of the w isotopic composition during crystallization all the samples examined display very similar w values within a narrow range of compositions between 5 1 and 3 1 witzation began less than a few percent of additional metal was segregated to the cores moreover the average w values for the five groups have no resolvable difference ranging from 4 08 0 69 iva to 3 30 0 15 iab iiicd these data indicate that all of the iron meteorite parent bodies underwent metal segregation within 5 ma of each other apparently independent of their composition size and time of crystallization of the metal in all groups except the iiiab group there is a resolvable time interval between the timing of metal segregation as constrained by the w isotopic data and the initiation of core crystallization as given by the re os isotopic systematics

an analysis of strong wind events simulated in a gcm near casey in the antarctic abstract strong wind events occurring near casey antarctica in a long july gcm simulation have been studied to determine the relative roles played by the synoptic situation and the katabatic flow in producing these episodes it has been found that the events are associated with strong katabatic and strong gradient flow operating together both components are found to increase threefold on average for these strong winds and although the geostrophic flow is the stronger it rarely produces strong winds without katabatic flow becoming stronger than it is in the mean the two wind components do not flow in the same direction indeed there is some cancellation between them since katabatic flow acts in a predominant downslope direction while the geostrophic wind acts across slope the stronger geostrophic flow is associated with higher than average pressures over the continent and the approach of a strong cyclonic system toward the mast and a blocking system downstream the anomalous synoptic patterns lea

strong wind speed events over antarctica and its surrounding oceans abstractstrong wind events swes over antarctica and its surrounding oceans are investigated using gridded surface wind data from the era interim for the 1979 2017 period throughout the year swe

core formation in earth s moon mars and vesta stimulated by new experimental results on metal silicate partitioning of elements at elevated temperatures and pressures we have revisited the question of core formation in earth s moon mars and vesta the probable source of the eucritic meteorites earlier studies suggested metal silicate equilibrium in mars but led to the paradox that mars accreted homogeneously while the earth accreted heterogeneously using new elevated pressure and temperature metal silicate partition coefficients we show that abundances of the moderately siderophile elements in the mantles of the moon mars and vesta are consistent with early magma oceans on these bodies the most successful model for explaining the lunar mantle siderophile element abundances requires a core of 5 of the mass of the moon 500 km radius siderophile element abundances in mars are consistent with intermediate pressure metal silicate equilibrium as has also been recently suggested for the earth the most successful model for explaining the martian siderophile element abundances requires a bulk planetary composition that has greater than ci chondritic abundances of the moderately siderophile elements and a core of 30 of the mass of mars siderophile element abundances in the mantle of vesta are consistent with low pressure liquid metal liquid silicate equilibrium as expected for an asteroid sized body and a core of 10 of the mass of vesta comparison of our best fit oxygen fugacities for vesta with thermodynamic calculations of oxygen fugacity for silicate bearing iron meteorites indicates that parts of the inner solar system were homogeneous with respect to redox state at 4 5 ga approximately 2 log fo2units below the fe feo buffer much higher than estimates for the solar nebula similar comparisons for mars and the earth indicate that these bodies have undergone oxidation since 4 5 ga because the oxygen fugacities associated with metal silicate equilibrium in both mars and the earth moon system are much lower than those recorded in martian and terrestrial basaltic and periodotitic samples the oxidation on mars is most likely due to atmospheric effects whereas earth s much wider range of oxygen fugacities must be due to both atmospheric and plate tectonic effects

an early miocene transition in deformation regime within the red river fault zone yunnan and its significance for indo asian tectonics recent work has tended to support the view that lateral extrusion of indochina along the red river fault zone was a significant factor in accommodating the convergence of india with asia to better understand the nature and timing of this feature 40ar 39 ar age spectrum analyses were undertaken on minerals from the ailao shan red river metamorphic belt in southern yunnan china interpreted using diffusion domain theory these results yield thermal histories in the temperature range 550 150 c discontinuities in cooling rates observed from these results suggest a transition in deformation style in the shear zone during the early miocene at least in the vicinity of our samples left lateral strike slip ductile deformation appears to have ceased by about 20 ma the mylonitic gneisses in the shear zone were subsequently obliquely unroofed probably due to a component of normal faulting along the eastern edge of the shear zone causing a brief locally 100 c m y cooling episode this transition may have resulted from a component of northeast southwest extension attributable to greater clockwise rotation of indochina relative to south china after 20 ma than that consistent with pure strike slip along the fault k ar ages on clay minerals from gouge within the normal faults bounding the ailao shan and diancang shan yield a range of ages between 20 and 185 ma but show a significant clustering at 20 25 ma these results suggest that early miocene movement on a precursor to the range front normal fault in the ailao shan caused oblique unroofing of the shear zone this early miocene event corresponds in time with a transition from low to very high denudation rates throughout the himalaya and southern tibet this coincidence may reflect that once left lateral strike slip motion on the red river fault zone slowed or was terminated accommodation of much of the continued northward convergence of india occurred on the main central thrust resulting in rapid uplift in the tethyan himalaya and gangdese belt

60fe 60ni chronology of core formation in mars abstract the timescales of accretion core formation and magmatic differentiation in planetary bodies can be constrained using extinct radionuclide systems experiments have shown that ni becomes more siderophile with decreasing pressure which is reflected in the progressively higher fe ni ratios in the mantles of earth mars and vesta mars formed rapidly and its mantle has a high fe ni ratio so the 60fe 60ni decay system t 1 2 2 62 myr is well suited to establish the timescale of core formation in this object we report new measurements of 60ni 58ni ratios in bulk snc martian shergotty nakhla chassigny meteorites and chondrites the difference in e ni 60 values between snc meteorites and the building blocks of mars assumed to be chondritic 55 ordinary chondrites 45 enstatite chondrites is 0 028 0 023 95 confidence interval using a model of growth of planetary embryo this translates into a time for mars to have reached 44 of its present size of 1 9 0 8 1 7 myr with a strict lower limit of 1 2 myr after solar system formation which agrees with a previous estimate based on 182hf 182w systematics the presence of mars when planetesimals were still being formed may have influenced the formation of chondrules through bow shocks or by inducing collisions between dynamically excited planetesimals

magnetostratigraphy of the dali basin in yunnan and implications for late neogene rotation of the southeast margin of the tibetan plateau 1 the rotation pattern and fault activity in the southeast margin of the tibetan plateau semtp provide meaningful constraints on the geodynamic evolution of the plateau however the lack of cenozoic paleomagnetic studies and accurate age constraints on neogene sediments prevents a better understanding of the late cenozoic tectonic activity in this area to clarify the tectonic rotation pattern and deformation history of the semtp we report new magnetostratigraphic data from a late neogene sedimentary sequence in the dali basin northwestern yunnan province china rock magnetic analyses indicate that both magnetite and hematite are the main carriers of the characteristic remanent magnetizations chrms magnetostratigraphic results show that the sedimentary profile spans from chron c4n 1r to chron c2n the age of the sedimentary sequence in the dali basin can thus be paleomagnetically constrained to an interval from late miocene to early pleistocene the basal age of the sediments is 7 6 ma which indicates that the unroofing of diancang shan and activation of the dali fault system were initiated at this time the appearance of conglomerates and syntectonic sediments suggests the reactivation of the dali fault system at 2 5 ma moreover the overall mean chrm direction suggests that the dali basin experienced significant 4 4 2 5 but minor post late miocene rotation this indicates that most of the clockwise rotation demonstrated by previous paleomagnetic studies in the semtp occurred prior to late miocene and may be concentrated between eocene and miocene which is contemporaneous with the sinistral slip of the ailao shan red river fault

experiments on turbulent metal silicate mixing in a magma ocean we compare the results of laboratory fluid dynamics experiments with theoretical models of turbulent entrainment in two phase buoyant plumes and thermals to estimate the amount of mixing between the iron core of a planetesimal or planetary embryo and the molten silicates in a magma pool formed by its impact with a growing planet during accretion we demonstrate experimentally that turbulent plumes in immiscible fluids fragment into droplets and that the envelope of the droplet distribution is indistinguishable from the envelope of a turbulent plume in a single phase fluid under the same dynamical conditions implying that turbulent entrainment concepts are applicable to immiscible fluids mixing a series of experiments are made on the time evolution of a two phase turbulent thermal representing a planetesimal core falling under its own negative buoyancy in a spherical fluid representing an impact produced magma pool two stages of mixing are observed in these experiments the first corresponding to turbulent entrainment during free fall of the thermal the second corresponding to entrainment in turbulent gravity currents that form after the thermal reaches the base of the magma pool we demonstrate that the amount of mixing between metals and silicate liquids in a magma pool depends on the rouse number of the metal fragments and increases rapidly with the radius of the proto planet we derive a similarity model for metal silicate mixing in a spherical magma pool assuming a constant entrainment coefficient for the turbulent liquid metal phase this model supports our experimental finding that a small metal core of an impactor will become diluted i e mix within a deep magma pool but a large impacting core will not fully dilute before reaching the base of the magma pool

cosmogenic tungsten and the origin and earliest differentiation of the moon the decay of formerly live 182hf with a half life of 9 myr results in variations in the abundance of 182w in early solar system objects here we demonstrate that major excesses in 182w in some lunar samples are the results of cosmogenic additions apollo 17 high ti mare basalts yield high 182w 184w of up to w 11 1 even more extreme variations of up to w 22 1 are found for mineral separates although these lavas were erupted more than 500 myr after the start of the solar system the measured 182w excess in the separated minerals is correlated with their ta w confirming theoretical models that implicate the 181ta n 182ta 182w reaction from cosmic irradiation as the most likely cause in contrast olivine basalt 15555 which has a low cosmic ray exposure age displays no internal 182w variations and defines an w of 1 3 0 4 this is consistent with earlier conclusions that the moon formed about 50 myr after the start of the solar system the high ti mare basalt source with very high hf w has a w isotopic composition that is not grossly different from which a time limit of 70 myr after the start of the solar system can be inferred for the formation of ilmenite rich layers in the final stages of the lunar magma ocean

oxygen isotope constraints on the origin and differentiation of the moon we report new high precision laser fluorination three isotope oxygen data for lunar materials terrestrial silicates with a range of 18 o values 0 5 to 22 9 were analyzed to independently determine the slope of the terrestrial fractionation line tfl 0 5259 0 0008 95 confidence level this new tfl determination allows direct comparison of lunar oxygen isotope systematics with those of earth values of 17 o for apollo 12 15 and 17 basalts and luna 24 soil samples average 0 01 and are indistinguishable from the tfl the 18 o values of high and low ti lunar basalts are distinct average whole rock 18 o values for low ti lunar basalts from the apollo 12 5 72 0 06 and apollo 15 landing sites 5 65 0 12 are identical within error and are markedly higher than apollo 17 high ti basalts 5 46 0 11 evolved low ti lapaz mare basalt meteorite 18 o values 5 67 0 05 are in close agreement with more primitive low ti apollo 12 and 15 mare basalts modeling of lunar mare basalt source composition indicates that the high and low ti mare basalt mantle reservoirs were in oxygen isotope equilibrium and that variations in 18 o do not result from fractional crystallization instead these differences are consistent with mineralogically heterogeneous mantle sources for mare basalts and with lunar magma ocean differentiation models that result in a thick feldspathic crust an olivine pyroxene rich mantle and late stage ilmenite rich zones that were convectively mixed into deeper portions of the lunar mantle higher average 18 o wr values of low ti basalts compared to terrestrial mid ocean ridge basalts 0 18 suggest a possible oxygen isotopic difference between the terrestrial and lunar mantles however calculations of the 18 o of lunar mantle olivine in this study are only 0 05 higher than terrestrial mantle olivine these observations may have important implications for understanding the formation of the earth moon system 2006 elsevier b v all rights reserved

multiple metamorphic events revealed by zircons from the diancang shan ailao shan metamorphic complex southeastern tibetan plateau abstract analyses of mineral inclusions within complexly zoned zircons combined with sims u pb ages for various domains within the zircons provide evidence of the origin and multistage metamorphic evolution of the diancang shan ailao shan metamorphic complex southeastern tibetan plateau zircons separated from paragneisses amphibolites garnet pyroxenites and marbles were subdivided into inherited magmatic or detrital and metamorphic zircons based on cathodoluminescence cl and laser raman spectroscopy weakly zoned inherited detrital zircons from paragneisses yield ages of 700 540 ma 1000 800 ma 1800 ma and 2550 2450 ma and contain inclusion assemblages of qtz kfs pl ap recording widespread geological events throughout the ancient gondwana continent in contrast clearly zoned inherited magmatic zircons in amphibolites and garnet pyroxenites yield ages of 778 773 ma and contain cpx pl qtz ap inclusions representing the crystallization age of the mafic protolith metamorphic zircons also record discrete early middle triassic and the eocene oligocene thermal events homogeneous metamorphic zircons with low th u ratios these new data suggest a clockwise p t t path for the diancang shan ailao shan metamorphic complex belt typical of continent continent collision indicating collision subduction tectonism prior to the strong left lateral ductile deformation along the ailao shan red river asrr shear zone that started at 32 ma and lasted until 25 ma causing mid crustal 18 25 km depth high temperature metamorphic conditions continued uplift and a slowing of left lateral ductile shearing occurred at 25 14 ma at a depth of 10 15 km and under relatively low temperature conditions this temporal and kinematic link between left lateral shearing along the asrr and the opening of the south china sea supports the occurrence of the block extrusion of indochina from eurasia along lithospheric scale strike up faults

oblique stepwise rise and growth of the tibet plateau two end member models of how the high elevations in tibet formed are i continuous thickening and widespread viscous flow of the crust and mantle of the entire plateau and ii time dependent localized shear between coherent lithospheric blocks recent studies of cenozoic deformation magmatism and seismic structure lend support to the latter since india collided with asia 55 million years ago the rise of the high tibetan plateau likely occurred in three main steps by successive growth and uplift of 300 to 500 kilometer wide crustal thrust wedges the crust thickened while the mantle decoupled beneath gently dipping shear zones did not sediment infilling bathtub like of dammed intermontane basins formed flat high plains at each step the existence of magmatic belts younging northward implies that slabs of asian mantle subducted one after another under ranges north of the himalayas subduction was oblique and accompanied by extrusion along the left lateral strike slip faults that slice tibet s east side these mechanisms akin to plate tectonics hidden by thickening crust with slip partitioning account for the dominant growth of the tibet plateau toward the east and northeast

interpretation of recent southern hemisphere climate change climate variability in the high latitude southern hemisphere sh is dominated by the sh annular mode a large scale pattern of variability characterized by fluctuations in the strength of the circumpolar vortex we present evidence that recent trends in the sh tropospheric circulation can be interpreted as a bias toward the high index polarity of this pattern with stronger westerly flow encircling the polar cap it is argued that the largest and most significant tropospheric trends can be traced to recent trends in the lower stratospheric polar vortex which are due largely to photochemical ozone losses during the summer fall season the trend toward stronger circumpolar flow has contributed substantially to the observed warming over the antarctic peninsula and patagonia and to the cooling over eastern antarctica and the antarctic plateau

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

core merging and stratification following giant impact the earth s outermost core is thought to be stratified turbulent mixing experiments suggest that merging between the cores of projectile and planet following the moon forming giant impact could have produced the stratification

foehn winds in the mcmurdo dry valleys antarctica the origin of extreme warming events abstract foehn winds resulting from topographic modification of airflow in the lee of mountain barriers are frequently experienced in the mcmurdo dry valleys mdvs of antarctica strong foehn winds in the mdvs cause dramatic warming at onset and have significant effects on landscape forming processes however no detailed scientific investigation of foehn in the mdvs has been conducted as a result they are often misinterpreted as adiabatically warmed katabatic winds draining from the polar plateau herein observations from surface weather stations and numerical model output from the antarctic mesoscale prediction system amps during foehn events in the mdvs are presented results show that foehn winds in the mdvs are caused by topographic modification of south southwesterly airflow which is channeled into the valleys from higher levels modeling of a winter foehn event identifies mountain wave activity similar to that associated with midlatitude foehn winds these events are found to be caused by str

the red river fault zone in the yinggehai basin south china sea abstract the red river fault a major strike slip fault of onshore southeast asia is suggested to be closely related to the formation of the south china sea and uplift of the tibetan plateau yet published documentation of the offshore segment of the red river fault is sparse high resolution seismic reflection and borehole data obtained by the petroleum industry along the northwestern margin of the south china sea permit mapping of the offshore segment of the red river fault in the yinggehai basin as well as demonstration of the timing of its shear movement and slip reversal two boundary faults and two basin center faults are mapped three successive deformation phases for the offshore red river fault zone include sinistral movement from 30 to16 ma slip reversal between 16 and 5 5 ma and dextral movement with low rates after 5 5 ma although no robust piecing points were observed for the sinistral movement period the horizontal displacement of dextral movement is estimated to be tens of kilometers this study supports a two stage model for the evolution of the india asia collisional orogen before the middle miocene sinistral movement of the red river fault likely was linked to spreading of the south china sea consistent with the concept of continental extrusion after the middle miocene distributed shortening better explains a low rate of dextral accommodation of the red river fault in response to the continuing india asia collision

case study of a barrier wind corner jet off the coast of the prince olav mountains antarctica abstractthe ross ice shelf airstream ras is a barrier parallel flow along the base of the transantarctic mountains previous research has hypothesized that a combination of katabatic flow barrier winds and mesoscale and synoptic scale cyclones drive the ras within the ras an area of maximum wind speed is located to the northwest of the protruding prince olav mountains in this region the sabrina automatic weather station aws observed a september 2009 high wind event with wind speeds in excess of 20 m s 1 for nearly 35 h the following case study uses in situ aws observations and output from the antarctic mesoscale prediction system to demonstrate that the strong wind speeds during this event were caused by a combination of various forcing mechanisms including katabatic winds barrier winds a surface mesocyclone over the ross ice shelf an upper level ridge over the southern tip of the ross ice shelf and topographic influences from the prince olav mountains these forcing mechanisms induced a b

spatial and temporal pattern of erosion in the three rivers region southeastern tibet convergence and collision between india and eurasia have produced the tibetan plateau which stands 5 km high over a region of 3 million km2 its southeastern margin lies in the restraining bend between the sichuan basin and the eastern himalayan syntaxis in this region three parallel rivers the salween the mekong and the yangtze carve gorges up to 3 km deep along the longitudinal profiles large scale knickzones defined by very high steepness correspond to the gorges of the salween and mekong the yangtze instead has a nearly linear profile upstream from its first big bend new low temperature thermochronometric data reveal a complex pattern of erosion in the three rivers region from the salween in the west to the yangtze in the east the magnitude and rate of erosion decrease from south to north erosion rates exhibit variable gradients in space and time along the salween and the mekong a northward increase of erosion rate is followed by a decrease with additional distance to the north variations of erosion rate in time are characterized by a deceleration along the salween and a general deceleration with local acceleration along the mekong this pattern together with river profile analysis is best explained by active coupling between tectonics and river incision related to the indentation and northward migration of the corner of the indian continent

the role of katabatic winds on the antarctic surface wind regime abstract antarctica is known for its strong and persistent surface winds that are directed along topographic pathways surface winds are especially strong during the winter period the high directional constancy of the wind and the close relationship of the wind direction to the underlying terrain can be interpreted as evidence of katabatic wind activity observations show that the directional constancy of the antarctic surface wind displays little seasonal variation summertime winds cannot be expected to contain a significant katabatic component owing to enhanced solar heating of the ice slopes observations also show that the coastal environs are subjected to wide variation in atmospheric pressure associated with frequent cyclone activity the robust unidirectional nature of the antarctic surface wind throughout the year implies that significant topographic influences other than those from katabatic forcing must be acting idealized numerical simulations have been performed to illustrate the potential

antarctic summer sea ice trend in the context of high latitude atmospheric circulation changes abstractthe potential mechanisms underlying the observed increasing trend in antarctic summertime sea ice cover for the 1979 2017 period have been investigated using a relatively novel method called the self organizing map som among the nine nodes generated to explain the variability of antarctic sea ice cover two nodes 3 and 7 exhibit a statistically significant linear trend in the time series of the frequency of the som pattern occurrence that together explain 40 of the total trend in the sea ice cover these two nodes have completely opposite spatial patterns and directions of trend and are associated with different atmospheric circulation patterns node 3 which represents an increase in sea ice over the weddell sea and the eastern ross sea and a decrease over the other coastal seas of west antarctica appears to be related to the positive phase of the southern annular mode sam linked with the la nina pattern of sea surface temperature sst over the tropical pacific ocean the opposite spati

tungsten isotopic evolution during late stage accretion constraints on earth moon equilibration abstract we couple the results of n body simulations of late stage accretion o brien et al 2006 to a hafnium tungsten hf w isotopic evolution code to investigate the evolution of planetary bodies in the inner solar system simulations can simultaneously produce planets having earth and mars like masses and hf w systematics by assuming that the tungsten partition coefficient decreases with increasing semi major axis e g due to increasing oxidation simulations assuming that jupiter and saturn occupy circular orbits are more successful at reproducing the hf w systematics than those assuming present day jupiter and saturn orbits to generate earth like tungsten anomalies 30 80 of each impactor core is required to re equilibrate with the target mantle some model outcomes yield a target and final impactor having similar earth and moon like tungsten anomalies however in no case can the inferred lunar hf w ratio be simultaneously matched this result suggests that the moon isotopically equilibrated with the earth s mantle in the aftermath of the giant impact cf pahlevan and stevenson 2007 alternatively either the dynamical models which show the moon being derived primarily from the impactor mantle or the accretion timescales obtained by the n body simulations are incorrect

thermal evolution of a growing mars 1 we developed a new numerical model which can simulate the thermal history and metal silicate separation of a growing mars in this model the thermal disturbance caused by planetesimal impacts is calculated for each impact event by taking into account the effects of shock heating crater excavation and isostatic rebound a metallic blob is assumed to form at the base of a magma pond if an impact site is heated above the melting temperature sinking of the metal blobs is traced assuming stokes velocity their coalescence during sinking is treated by a monte carlo approach a series of simulations is carried out assuming that mars is formed by the runaway growth from a swarm of planetesimals as was suggested by recent numerical simulations of the planetary accretion process our numerical results show that 1 no global magma ocean is formed during accretion 2 metal silicate separation takes place without global scale melting and 3 instead of a metallic core a metal rich layer is formed at the late stage of accretion

the pacific south american modes and tropical convection during the southern hemisphere winter abstract atmospheric circulation features and convection patterns associated with two leading low frequency modes in the southern hemisphere sh are examined in multiyear global reanalyses produced by ncep ncar and nasa dao the two leading modes referred to as the pacific south american psa modes are represented by the first two eof patterns the two patterns are in quadrature with each other and are dominated by wavenumber 3 in midlatitudes with large amplitudes in the pacific south american sector in the pacific anomalies in the subtropics and in the midlatitudes are opposite in phase taken together the two psa modes represent the intraseasonal oscillation in the sh with periods of roughly 40 days the evolution of the psa modes shows a coherent eastward propagation a composite analysis was conducted to study the evolution of tropical convection and the corresponding circulation changes associated with the psa modes outgoing longwave radiation olr anomaly composites during the mature phase

the xuelongshan high strain zone cenozoic structural evolution and implications for fault linkages and deformation along the ailao shan red river shear zone abstract new structural geometric petrographic and u pb zircon data constrain the kinematics of the xuelongshan high strain zone northermost parts of the ailao shan red river shear zone in the xuelongshan range mylonitic foliation mainly trends nw se on steep foliation and flatted foliation mineral stretching lineation is various from gentle to steep and ductile shear senses indicate a left lateral top to the northwest shear movement on the eastern limb and a left lateral top to the southeast shear on the western limb of the range these dome related ductile geometries and kinematics namely d1 deformation represent regional high temperature metamorphism due to crustal thickening the superimposed sinistral strike slip shearing of d2 deformation occurred locally along the earlier domal fabrics metamorphism migmatization and the emplacement of leucogranitic veins associated with partial melting were syntectonic with the regional scale upright antiform la icp ms u pb dating of zircons reveals the late permian triassic and oligocene thermal events the latter event ca 33 26 ma or possibly earlier from the leucogranitic veins corresponds to the regional metamorphism during crustal thickening along the xuelongshan these data indicate that the jiali xuelongshan diancangshan ailao shan high strain zones can belong to a system around the eastern himalayan syntaxis ehs and that the xuelongshan zone played a role in linking other segments between the tibet to indochina in cenozoic

new w isotope evidence for rapid terrestrial accretion and very early core formation the short lived hf 182 w 182 isotope system is an ideal clock to trace core formation and accretion processes of planets planetary accretion and metal silicate fractionation chronologies are calculated relative to the chondritic hf 182 w 182 isotope evolution here we report new high precision w isotope data for the carbonaceous chondrite allende that are much less radiogenic than previously reported and are in good agreement with published internal hf w chronometry of enstatite chondrites if the w isotope composition of terrestrial rocks representing the bulk silicate earth is homogeneous and 2 24 epsilon 182w units more radiogenic than that of the bulk earth metal silicate differentiation of the earth occurred very early the new w isotope data constrain the mean time of terrestrial core formation to 34 million years after the start of solar system accretion early terrestrial core formation implies rapid terrestrial accretion thus permitting formation of the moon by giant impact while hf 182 was still alive this could explain why lunar w isotopes are more radiogenic than the terrestrial value copyright c 2002 elsevier science ltd

three dimensional simulations of the southern polar giant impact hypothesis for the origin of the martian dichotomy we demonstrate via numerical simulations that the impact of a lunar sized body with mars is capable of creating a hemispherical magma ocean that upon cooling and solidification resulted in the formation of the southern highlands and thus the martian dichotomy the giant impact may have contributed a significant amount of iron to the martian core and generated a deep thermal anomaly that led to the onset and development of the volcanism in the southern highlands our model predicts several mantle plumes converging to the south pole from the equatorial regions as well as new plumes forming in the equatorial region and also an absence of significant large scale volcanism in the northern lowlands the core heat flux evolution obtained from our numerical models is consistent with the decline of the magnetic field we argue that such a scenario is more consistent with a range of observations than a northern giant impact excavating the borealis basin for the formation of the martian dichotomy

a thermal model for the differentiation of asteroid 4 vesta based on radiogenic heating a finite element code has been developed to model the thermal history of asteroid 4 vesta this is the first attempt to model the thermal history of a differentiated asteroid through core and crust formation and subsequent cooling until geochemical closure is attained the results of the simulation are consistent with chronological measurements and other constraints provided by cumulate and noncumulate eucrites believed to have been derived from vesta the work solves two major problems with the hypothesis of heating by decay of26al an extinct radionuclide postulated to be a plausible heat source in the early solar system first the model demonstrates that it is possible to keep the mantle of vesta hot for 100 ma thereby explaining the observed difference in ages between cumulate and noncumulate eucrites second the simulation offers a possible explanation of why detectable excesses of26mg the decay product of26al are not observed in noncumulate eucrites the simulation draws a model chronology of vesta and predicts times relative to cai formation for accretion at 2 85 myr core formation at 4 58 myr crust formation at 6 58 myr and geochemical closure at 100 myr for a h chondrite asteroidal bulk composition decay of60fe is found to cause no perceptible difference in the thermal history of vesta even when sequestered into a central core although chondritic xenoliths have not been described in hed igneous lithologies the thermal model suggests the possibility that a veneer of unmelted near surface material should remain

high temperature metamorphism in a major strike slip shear zone the ailao shan red river people s republic of china abstract petrographic and thermobarometric analysis provides constraints on thept path of the mylonitic gneisses of the left lateral ailao shan red river shear zone which has accommodated the lateral extrusion of indochina during the tertiary two different paragenesis p1 and p2 are coeval with this deformation and correspond respectively to the amphibolite and greenschist facies microprobe analysis reveals that p1 garnets bear a chemical zonation from core to rim this zonation indicates a temperature increase during garnet growth conditions of formation of garnet rims p1b which are estimated using biotite garnet and plagioclase garnet thermobarometers are close to the granitic solidus 710 70 c and4 5 1 5 kbar p2 conditions are estimated to be approximately 500 c and

cenozoic exhumation of the ailaoshan red river shear zone new insights from low temperature thermochronology continental scale shear zones play an important role in accommodating block extrusion and rotation as shown by deformation on the ailaoshan red river shear zone asrrsz in the se tibetan plateau this study presents 13 apatite u th he 11 zircon u th he and three apatite fission track dates together with thermal modeling in the ailaoshan and xuelongshan segments alsz and xlsz of the shear zone to investigate its cenozoic exhumation history and mechanism which are critical for understanding its tectonic and landscape evolution our results combined with published chronologic data reveal that shear zone rocks along the alsz experienced prominent and rapid cooling from high temperature 500 c to 120 60 c at a rate of 75 100 c myr during 29 17 ma with northwestward younging onset a second lower magnitude accelerated cooling occurred at 14 10 ma along the alsz at a rate of 20 30 c myr with a later initiation on the xlsz at 5 ma and continuing to present with a cooling rate of 20 c myr thermal modeling reveals a single rapid cooling phase with a rate of 17 14 c myr in the eocene to early oligocene for samples outside the shear zones these three fast cooling episodes are directly related to deformation stages including crustal shortening across the se plateau sinistral ductile shearing along the asrrsz and dextral faulting with a dip slip component on the red river and weixi qiaohou faults along the shear zone flanks furthermore the northward migration of kinematic reversal and associated cooling along strike since the mid late miocene likely reflects the northward advance of the eastern himalayan syntaxis

met office unified model high resolution simulations of a strong wind event in antarctica during winter much of the antarctic coast is susceptible to severe and hazardous strong wind events swes associated with the enhancement of katabatic winds by synoptic weather systems in this study a swe that occurred at mawson east antarctica involving a hurricane force wind speed of 39 m s 1 is simulated by the met office unified model at high horizontal resolutions with grid lengths between 12 and 1 5 km it is shown that all the simulations capture the qualitative evolution of the swe but underestimate its peak wind speed the extent of the underestimate is dependent on horizontal resolution with the 4 and 1 5 km 12 km models underforecasting the peak wind speed by around 15 36 in addition to a strengthening of the katabatic flow the simulated low level cyclonic winds associated with the depression responsible for the swe caused the formation of a barrier type jet parallel to the coast resulting in strong wind convergence interaction at the coastline and suggesting a strong topographic influence on the dynamics responsible for swe formation moreover it suggests that mawson is influenced by small scale gravity waves that formed in response to the stronger winds and that representation of this was particularly sensitive to horizontal resolution additional experiments suggest that the met office unified model simulation of the swe is most sensitive to the representation of turbulent mixing under stable conditions this study is important to identify shortcomings in the performance of the met office unified model near antarctica s coastal regions as well as to improve understanding of the processes responsible for swes

heat partitioning in terrestrial planets during core formation by negative diapirism article i nfo we investigate the gravitational heat partitioning between silicate and metallic phases during core formation by negative diapirism in terrestrial planets we model the dynamic evolution of an iron diapir sinking through a solid silicate proto mantle our calculations include viscous heating and strong temperature and composition dependence of viscosity we show that the diapir mean temperature evolves towards an asymptotic value td which depends on the efficiency of viscous heating and heat transfer between the diapir and its surroundings and on the viscous rheology we derived a simple analytic model that captures the thermal evolution observed in our numerical experiments this model can be applied to determine the heat distribution within terrestrial planets with a large number of diapirs during their growth and early differentiation we show that the partitioning of core formation heating during negative diapirism depends strongly on the size distribution of the iron diapirs a large number of small sinking iron diapirs favors metal silicate heat exchange and leads to a relatively hot core which allows a sustainable dynamo as on earth a small number of large diapirs have the opposite effect and could correspond to a mars like planet with an early dynamo that is no longer active in all cases negative diapirism tends to leave the lowermost mantle significantly hotter than its upper part which could trigger large amounts of melting in the early deep mantle

survival of impact induced thermal anomalies in the martian mantle 1 a number of geophysical arguments point out the possibility that global mantle convection could have been extremely sluggish or even absent during a large part of martian history this implies that early mantle thermal anomalies produced during planetary formation might not have been quickly erased by vigorous convection one likely mechanism of early thermal inhomogeneity is large impacts at the end of heavy bombardment we suggest that tharsis province might be related to such an impact induced thermal anomaly rather than a convective plume the shape of the present day geoid for our preferred model is in good agreement with the geoid measured by mars global surveyor mgs