understanding how volume affects the mobility of dry debris flows 1 the prediction of the runout length l of large dry debris flows has long been the subject of a considerable research effort primarily due to the obvious concern caused by their destructive power one seemingly well established feature is the increase of the mobility of a rock avalanche defined as the ratio of the runout distance to the fall height with its volume v the physical nature of this lubrication mechanism remains however controversial in this paper we analyse field data and discrete numerical simulations of granular flows and demonstrate the geometrical origin of the apparent enhancement of the mobility with the volume we evidence the intertwined role of volume and topography and show the existence of two contributions in the runout defining two flow regimes one dominated by sliding in which the runout is independent of v and another dominated by spreading in which the runout is strongly dependent on v in the light of these results the search of a volume dependent lubrication mechanism appears to be an ill posed problem

form facies and depositional history of the north long john rock avalanche owens valley california the prehistoric but geomorphically pristine north long john rock avalanche of the inyo mountains piedmont california formed by the catastrophic collapse and disintegration of a 500 1000 m range front bedrock slab this failure rapidly produced and transferred 25 million cubic metres of new sediment to the piedmont where it was deposited in a trough between two coalesced alluvial fans the avalanche consists of nearly monolithologic aplitic unstratified very angular muddy cobble pebble gravel with boulders concentrated at the top and outer margins the deposits are clast supported except in the lower central zone coarse clasts exhibit crackle breccia fabric and the voluminous equant pebbles are the disaggregated products of these clasts the avalanche deposits are distributed in a u shaped body with paired lateral levees 10 60 m high that extend 1560 m from the range front to a 108 m high distal snout each levee contains three segments that along with the snout overlap and extend progress

gulf of mexico circulation within a high resolution numerical simulation of the north atlantic ocean 1 the gulf of mexico circulation is examined from the results of a high resolution 1 12 north atlantic simulation using the miami isopycnic coordinate ocean model the motivation for this paper is twofold first we validate the model s performance in the gulf of mexico by comparing the model fields to past and recent observations and second given the good agreement with the observed gulf of mexico surface circulation and loop current variability we expand the discussion and analysis of the model circulation to areas that have not been extensively observed analyzed such as the vertical structure of the loop current and associated eddies especially the deep circulation below 1500 m the interval between successive model eddy sheddings is 3 to 15 months the eddy diameters range between 140 and 500 km the life span is about 1 year and the translational speeds are 2 3 km d 1 in good agreement with observations areas of high cyclonic eddy occurrence in the model are southwest of florida the loop current boundary and the western campeche bay area the cyclonic eddy diameters range between 50 and 375 km the orbital speeds range between 1 and 55 cm s 1 the translational speeds range between 0 5 and 14 km d 1 and the eddy life spans range between 1 and 3 months the vertical structure of the temperature and salinity of each modeled eddy from the moment it is shed until it disintegrates in the western gulf of mexico is in agreement with the few available observations below 1500 m deep cyclonic eddies are associated with the surface loop current anticyclones the eddy variability is consistent with rossby waves propagating westward and there is bottom intensification of the flow close to steep topography overall we show that this very high horizontal resolution isopycnic coordinate ocean model which is able to produce a quite realistic surface circulation for the north and equatorial atlantic is also able to reproduce well the smaller scale basin wide intricate dynamics such as the gulf of mexico variability

oxygen isotopes in asteroidal materials measurement of the variation of the 17o 16o and 18o 16o ratios of extraterrestrial materials has proven to be a key tool in understanding the formation and evolution of the solar system this chapter attempts to collate the huge data set of oxygen isotopic measurements of asteroidal material as sampled by meteorites in order to understand some of the processes involved in the formation of these primitive bodies and how such events have affected the oxygen isotopic ratios ultimately offering a window back to the very origin of solar system and its primordialoxygen isotopic heterogeneity oxygen is generally a major element in the gas liquid and solid phases that have interacted throughout the evolution of the solar system its chemical properties ensuring that there is abundant opportunity for reactions and exchange the details of which can be recorded in the isotopic ratios of the products such processes can be crudely subdivided into the following six categories early solar nebular isotopic heterogeneity high temperature modifi cation of nebular components metamorphism and melting in asteroids aqueous alteration in asteroids mixing of components brecciation terrestrial weathering it is clear from the isotopic variation in the earliest formed nebular components such as refractory inclusions and chondrules that there was considerable oxygen isotopic heterogeneity in the early solar nebula spanning over 50 and perhaps much greater in both 17o and 18o the origin of this variation is discussed elsewhere in this volume however isotopic exchange between the 16o rich solids and 17o and 18o rich gas phase s resulted in a wide range of isotopic variation in these early formed components offering insight into the conditions of these processes and the evolution of the reservoirs with time and or space once accreted onto the early planetisemals much of the primitive nebular components experienced considerable modification the metamorphism and melting experienced by some of these bodies most probably the result of heating from the decay of short lived radionuclides e g 26al resulted in progressive homogenization within individual bodies of any original isotopic heterogeneity complete homogenization appears to have been achieved in the hed parent body indicating very high levels of melting and the development of a large magma ocean the carbonaceous and ordinary chondrite parent bodies experienced more modest heating sufficient to mobilize water ice that accreted along with the more refractory materials the subsequent reactions between the liquid and solid phases at low temperature imparted large isotopic fractionations which record some of the conditions of this alteration such as water rock ratio temperature and isotopic signature and thus potentially the origin of the water ice the evolution of the asteroidal bodies has been far from simple and an important use of oxygen isotope measurements has been in the identifi cation of the components present in some meteorites the result of breakup reassembly and mixing of different bodies during impact processing the final oxygen isotopic signatures imparted into meteorite samples are those associated with terrestrial weathering the isotopic compositions of the weathering products depend on location primarily latitude while the magnitude of the weathering is dependent on many factors with some meteorites e g highly reduced enstatite chondrites and the matrix rich co3s particularly susceptible to such effects

application of the sphalerite cosmobarometer to the enstatite chondrites sphalerite is a minor constituent of a number of enstatite chondrites the assemblage sphalerite troilite kamacite buffers the iron content of sphalerite so that it is a function of temperature and pressure only high iron contents in sphalerite in enstatite chondrites are consistent with equilibration at low pressures if nebular conditions are assumed and pressure is taken as zero it is then possible to calculate blocking temperatures for diffusion of iron t b and cooling rates for the meteorites studied the variable degree of equilibration of eh3 chondrites is correlated with calculated pressures assuming that the least equilibrated y69001 formed at zero pressure parent body radii calculated from these pressures are probably too large however inhomogeneities and minor elements in sphalerite as well as the assumptions made in the calculation may have had an adverse effect on the calculations the eh4 chondrite indarch appears to have cooled at an extremely rapid rate and has an unreasonably high t b inhomogeneities and minor element content may again have affected results the data for the el6 chondrites are consistent with relatively slow cooling ca 773 k whereupon rapid cooling occurred cooling rates at 773 k are too fast by a factor of 102 to 103 in comparison with metallographically determined rates

origin of a unique impact melt rock the l chondrite ramsdorf we have studied a unique impact melt rock the ramsdorf l chondrite using optical and scanning microscopy and electron microprobe analysis ramsdorf contains not only clast poor impact melt begemann and wlotzka 1969 but also a chondritic portion 60 g with what appears at low magnification to be a normal well defined chondritic texture however detailed studies at high magnification show that 90 vol of the crystals in the chondritic portion were largely melted by the impact the chondrules lack normal microtextures and are ghosts of the original features the only relics from the precursor chondrules are olivine crystals which have the highest melting temperature 1620 c pyroxene rich chondrules were so extensively melted that no phenocrysts were preserved and the melt crystallized in situ before significant mixing with exterior olivine rich melts fine grained pyroxene chondrule ghosts have sharper boundaries with the matrix than porphyritic olivine and pyroxene chondrule ghosts probably because pyroxene rich melts are significantly more viscous complex textures that formed by injection of melt along cracks and fractures in relic olivines suggest that the chondritic portion of ramsdorf formed directly from petrologic type 3 4 material by strong shock we infer that ramsdorf was largely melted by shock pressures of 75 90 gpa and that chondrule ghosts and relic olivine phenocrysts were locally preserved by rapid cooling quenching was not due to the addition of cold clasts into the melt but to heterogeneous shock heating that only caused internal melting of large olivines and pyroxenes ramsdorf appears to be one of the most heavily shocked meteorites that has retained some trace of its original texture

noble gases and mineralogy of meteorites from china and the grove mountains antarctica a 0 05 ma cosmic ray exposure age of grv 98004 we determined the mineralogical and chemical characteristics and the he ne and ar isotopic abundances of 2 meteorites that fell in china and of 2 meteorites that were recovered by the 15th chinese antarctic research expedition guangmingshan h5 zhuanghe h5 and grove mountain grv 98002 l5 yield cosmic ray exposure cre ages of 68 7 10 0 ma 3 8 0 6 ma and 17 0 2 5 ma respectively these ages are within the range typically observed for the respective meteorite types grv 98004 h5 had an extremely short parent body earth transfer time of 0 052 0 008 ma its petrography and mineral chemistry are indistinguishable from other typical h5 chondrites only 3 other meteorites exist with similarly low cre ages farmington l5 galim ll6 and alh 82100 cm2 we show that several asteroids in earth crossing orbits or in the main asteroid belt with orbits close to an ejection resonance are spectrally matching candidates and may represent immediate precursor bodies of meteorites with cre ages 0 1 ma

post shock annealing of miller range 99301 ll6 implications for impact heating of ordinary chondrites mil 99301 is an ll chondrite that has experienced successive episodes of thermal metamorphism shock metamorphism and annealing the first recognizable petrogenetic episode resulted in thermal metamorphism of the rock to petrologic type 6 as indicated by homogeneous olivine compositions significant textural recrystallization and the presence of coarse grains of plagioclase metallic fe ni and troilite the source of heat for this thermal episode is not identified the rock also experienced shock metamorphism to shock stage s4 as indicated by extensive silicate darkening caused by the dispersion within silicate grains of thin chromite melt veins and trails of metallic fe ni and troilite blebs polycrystalline troilite myrmekitic plessite a relatively high occurrence abundance oa of metallic cu 3 6 the presence of numerous chromite plagioclase assemblages and coarse grains of low ca clinopyroxene with polysynthetic twinning the shock event responsible for these effects must have occurred after the epoch of thermal metamorphism to type 6 levels otherwise the polycrystallinity of the troilite would have disappeared and the low ca clinopyroxene would have transformed into orthopyroxene despite abundant evidence of strong shock olivine and plagioclase in mil 99301 exhibit sharp optical extinction consistent with shock stage s1 and characteristic of an unshocked rock this implies that an episode of post shock annealing healed the damaged olivine and plagioclase crystal lattices and thereby changed undulose extinction into sharp extinction the rock was probably annealed to metamorphic levels approximating petrologic type 4 more significant heating would have transformed the low ca clinopyroxene into orthopyroxene it is not plausible that an episode of annealing occurring after the epoch of thermal metamorphism could have been caused by the decay of 26al because this isotope would have decayed away by that time impact heating is a more plausible source of post metamorphic annealing of rocks in the vicinity of impact craters on low density high porosity asteroids with rubble pile structures

initiation movement and run out of the giant tsaoling landslide what can we learn from a simple rigid block model and a velocity displacement dependent friction law abstract tsaoling landslide is the largest and best documented landslide among several large landslides induced by the 1999 taiwan chi chi earthquake pliocene sedimentary rocks of about 125 mm 3 in volume slid along very flat bedding planes dipping by 14 with an average speed of 35 40 m s for about 1650 m before hitting the bank of the chinshui river during the landslide detailed analysis of dtms before and after the earthquake using a gis software leads to an accurate determination of the locations of the centroids of landslide mass revealing the horizontal and vertical displacements of the 2524 m and 524 m respectively those displacements and landslide mass give an apparent friction coefficient of 0 21 and the release of the potential energy of 1 6 10 15 j we conducted rotary shear high velocity friction experiments on fault gouge from bedding parallel faults under semi wet conditions and at 3 mpa normal stress corresponding to the overburden pressure of the landslide mass we also compiled reported data on the frictional properties on shale powders and fault gouge from the landslide site under both dry and wet conditions and proposed a velocity displacement dependent friction law that can describe most experimental data newmark analysis of landslide motion with six scenarios for different landslide materials and conditions assuming a simple rigid block sliding and using measured frictional parameters revealed that the landslide did not occur with dry frictional properties and that the landslide occurred at 38 39 s with accumulated displacements of 0 62 m 1 09 m and reached at the river bank at 82 87 s after the generation of chi chi earthquake at its epicenter those timings are consistent with high frequency signals at 32 40 s and at 76 s recorded at a nearby seismic station and with a survivor s witness that the landslide initiated 10 s after he felt strong ground motion possible s wave arrival at 25 2 s slip weakening is essential in initiating the landslide and low friction coefficient 0 08 0 1 allowed high speed of the landslide possible the landslide was caused by a few peaks of northeast oriented strong accelerations of the ground motion frictional work during the sliding of the landslide mass was estimated to be of about 23 of potential energy and the rest of the released energy is likely to have been consumed during the stopping phase of the landslide after hitting the river bank in complex processes such as fragmentation heat dissipation and spreading of the landslide deposits

application of the material point method to simulate the post failure runout processes of the wangjiayan landslide abstract the first part of the paper presents a brief description of the material point method mpm including the governing equations solution scheme and a benchmark problem of soil collapse simulated using the method in the second and third part of the paper the post failure runout process of the wangjiayan landslide is simulated and analyzed the landslide s final topography and information from post failure in situ survey and laboratory tests are used to constrain the accuracy of computational results the kinematic behaviors of the failure mass are investigated in terms of displacement velocity effective plastic strain fields and topography changes during the movement comparisons are made between conditions with and without buildings on the deposition area numerical computations demonstrate that the presence of buildings on the sliding path strongly governs the flow regime run out distance velocity strain field and final deposition topography of the landslide so it is very essential to incorporate the effects of buildings in the modelling and analyses numerical results considering buildings show that the slide lasts about 30 s with the most rapid phase occurring between 6 and 12 s and that the maximum simulated velocity among the sliding particles in the landslide is 43 5 m s indicates that the moving of the landslide mass was very fast the run out distance simulated with mpm matches the measured post earthquake topography well whereas the shape of the simulated deposition zone is a little differs the buildings influence the sliding by shortening the overall run out distance decelerating the movement of the bottom layer and increasing the internal deformation and mixing among deposition layers

abee and related eh chondrite impact melt breccias abstract the abee eh chondrite is an impact melt breccia about 80 90 of the chondrules were melted many of those that remain have been partly resorbed euhedral enstatite phenocrysts are abundant many have nucleated on the surfaces of relict chondrules and now protrude into kamacite globules euhedral laths of graphite essentially identical to those produced magmatically on earth occur throughout the rock abee experienced two episodes of impact melting with an intervening period of brecciation the first impact melting event produced a relatively homogeneous rock with abundant melt upon cooling the rock was shattered by bombarding meteoroids igneous oldhamite rich dark inclusions were introduced at this time a second impact event produced melt which engulfed the abee fragments and dark inclusions primarily digesting the small ones heat lost to the surrounding clastic debris caused the groundmass melt to quench previously described diamonds in abee containing typical solar system isotopic compositions of n and xe were probably produced from graphite by shock several other eh chondrites may also be impact melt breccias the most extensively melted of these is adhi kot which contains shocked but largely unmelted chondrule rich clasts as well as chondrule free sulfide and silica rich clasts that also appear to be impact products

the chimborazo sector collapse and debris avalanche deposit characteristics as evidence of emplacement mechanisms abstract chimborazo is a late pleistocene to holocene stratovolcano located at the southwest end of the main ecuadorian volcanic arc it experienced a large sector collapse and debris avalanche da of the initial edifice ch i this left a 4 km wide scar removing 8 0 0 5 km 3 of the edifice the debris avalanche deposit dad is abundantly exposed throughout the riobamba basin to the rio chambo more than 35 km southeast of the volcano the dad averages a thickness of 40 m covers about 280 km 2 and has a volume of 11 km 3 two main dad facies are recognized block and mixed facies the block facies is derived predominantly from edifice lava and forms 80 vol of the dad with a probable volume increase of 15 25 vol the mixed facies was essentially created by mixing brecciated edifice rock with substratum and is found mainly in distal and marginal areas the dad has clear surface ridges and hummocks and internal structures such as jigsaw cracks injections and shear zone features are widespread structures such as stretched blocks along the base contact indicate high basal shear substratum incorporation is directly observed at the base and is inferred from the presence of substratum derived material in the dad body based on the facies and structural interpretation we propose an emplacement model of a lava rich avalanche strongly cataclased before and or during failure initiation the flow mobilises and incorporates significant substrata 10 14 vol while developing a fine lubricating basal layer the substrata dominated mixed facies is transported to the dad interior and top in dykes invading previously formed fractures

complex brecciation and shock effects in the buck mountain wash h3 5 chondrite buck mountain wash bmw is a new genomict breccia h35 found in the franconia h5 strewn field in arizona that shows complex brecciation and shock effects it contains three distinct chondritic lithologies in sharp contact a a main lithology that consists primarily of petrographic type 5 material but which has finely intermixed type 3 and 4 material b a shockblackened shock stage s5 type 3 lithology lithology a and c a shock blackened type 3 4 lithology lithology b buck mountain wash was lithified after impact mixing and impact melting of weakly and strongly metamorphosed materials possibly at depth in the regolith of the parent body shock effects included brecciation on a fine scale localized impact melting of silicates partial melting and mobilization of metal sulfide and chemical fractionations that produced non h group composition kamacite by two disequilibrium mechanisms shock heating did not cause significant thermal metamorphism in the shock blackened lithologies of bmw except possibly in areas adjacent to whole rock shock melt during lithification cooling must have been rapid at high temperatures to preserve glass and inhomogeneous silicate compositions but not so fast at lower temperatures as to produce dendritic metal sulfide globules or martensite

kinetic characteristics of debris flows as exemplified by field investigations and discrete element simulation of the catastrophic jiweishan rockslide china abstract the jiweishan rockslide of june 5 2009 in china provides an important opportunity to elucidate the kinetic characteristics of high speed long runout debris flows a 2d discrete element model whose mechanical parameters were calibrated using basic field data was used to simulate the kinetic behavior of this catastrophic landslide the model output shows that the jiweishan debris flow lasted about 3 min released a gravitational potential energy of about 6 10 13 j with collisions and friction dissipating approximately equal amounts of energy and had a maximum fragment velocity of 60 70 m s almost twice the highest velocity of the overall slide mass 35 m s notable simulated characteristics include the high velocity and energy of the slide material the preservation of the original positional order of the slide blocks the inverse vertical grading of blocks and the downslope sorting of the slide deposits field observations that verify these features include uprooted trees in the frontal collision area of the air blast wave downslope reduction of average clast size and undamaged plants atop huge blocks that prove their lack of downslope tumbling the secondary acceleration effect and force chains derived from the numerical model help explain these deposit features and the long distance transport our back analyzed frictions of the motion path in the pfc model provide a reference for analyzing and predicting the motion of similar geological hazards

brecciation among 2280 ordinary chondrites constraints on the evolution of their parent bodies abstract after accretion of meteorite parent bodies larger and smaller collisions have led to significant modifications of these bodies involved processes include excavation of material thermal metamorphism melting mixing of different materials re accretion and re lithification all these processes can be repeated several times in this study polished thin sections pts of 2280 chondrites 1193 h 947 l and 140 ll chondrites were investigated in order to obtain the abundance of brecciated rocks among the ordinary chondrites in addition we have determined the abundance and characteristics of shock vein bearing h l and ll chondrites and of impact melt rock clasts we also recognized xenolithic components based on o isotope studies noble gas data were considered in order to detect regolith breccias and to discuss late impact histories the investigation of 2280 samples shows that 23 276 of 1193 of the h chondrites 23 220 of 947 of the l chondrites and 79 110 of 140 of the ll chondrites are brecciated considering the heavily brecciated ll chondrites in 63 of the 140 chondrites 45 shock veins were clearly detected 57 of these 63 chondrites are brecciated rocks the investigation of the h and l chondrites has shown that about 26 310 of 1193 of the h chondrites and 40 379 of 947 of the l chondrites contain shock veins in our data set 20 of the h chondrites and 8 3 of the ll chondrites but only 3 0 of the l chondrites contain solar noble gases remarkably about 62 of all brecciated h chondrites with noble gases analyzed contain solar noble gases compared to only around 11 and 10 of the brecciated l and ll chondrites respectively the identification of xenolithic clasts e g ci cm and ureilite like lithologies in primitive type 3 chondrites indicates simultaneous accretion of clasts and chondrules these clasts must have been formed early within the first 2 ma on subsequently destroyed precursor first generation parent bodies the formation of complex breccias witnesses the collisions between asteroids of very different lithologies and heritage although the onion shell configuration of primordial parent bodies is necessary in order to form the chondrites with different degrees of metamorphic overprint petrologic types 3 6 subsequent catastrophic fragmentation and reassembly to form asteroids with a rubble pile structure are required to explain certain features discussed in this work however distinct peaks in the cosmic ray exposure age distributions indicate that not too many impacts in the last 100 ma were responsible to deliver the majority of the ordinary chondritic meteoroids to earth yet this certainly does not tell anything about the number of last generation parent bodies that exist in the asteroid belt since s type asteroids are the most abundant type of asteroid in the inner main belt and thought to be the parent bodies of ordinary chondrites

petrogenesis of mesosiderites i origin of mafic lithologies and comparison with basaltic achondrites abstract new petrologic and trace element data on basaltic and gabbroic clasts in mesosiderites and basaltic achondrites combined with existing petrologic and trace element data have served as a basis for interpretation of the petrogenesis of mesosiderite clasts compared with the basaltic achondrites the mesosiderite basaltic and gabbroic clasts contain more abundant modal tridymite and merrillite and more commonly contain augite as a late magmatic phase their pyroxenes tend to be more mgo rich and have lower fe mn ratios which are positively correlated with the fe mg ratio some of the mesosiderite basaltic and gabbroic clasts contain xenocrystic plagioclase the basaltic clasts commonly show super chondritic eu sm ratios and slight lree depletions the cumulate gabbro clasts are extremely depleted in lil have very high eu sm ratios and high lu sm ratios all of these features can be explained by a model in which the mafic lithologies of mesosiderites were formed by remelting of a mixed basalt cumulate gabbro metal source region near the parent body surface reducing agents p c s from the metallic fraction reduce feo out of the silicate melt and result in the positive correlation of fe mn with fe mg observed in pyroxene analyses and the modal abundances of tridymite merrillite and augite xenocrystic plagioclase is a natural consequence of remelting a cumulate gabbro rich source as are the unique ree patterns observed

dynamics of agulhas retroflection and ring formation in a numerical model part ii energetics and ring formation abstract an energetics analysis of several numerical experiments on an idealized south atlantic indian ocean basin is presented the model used in the experiments is the quasi isopycnic coordinate model of bleck and boundra forced by wind and configured with two or three layers the region of focus is the most dynamically active one the agulhas current retroflection south of africa and the dynamical mechanisms associated with formation of agulhas rings are given special attention whether rings form in the model and their frequency depend on two primary factors the shape of africa and southward inertia baroclinicity in the overshooting agulhas the boundary condition on africa no slip free slip and horizontal resolution are also important experiments in which rings form exhibit considerably larger values of km to ke transfer than those in which no rings form in three of the experiments ring formation is studied in detail with the help of instantaneous top and bottom layer flow patterns and time se

nature of the h chondrite parent body regolith evidence from the dimmitt breccia the dimmitt h chondrite regolith breccia consists of in vol 40 h4 and h5 chondrite clasts 3 impact melt rock clasts 0 5 shocked h chondrite clasts 1 5 exotic clasts including carbonaceous and ll5 chondrites and 55 gas rich matrix the ll5 clast is the best documented example of an ordinary chondrite in a host of a different compositional group the matrix contains unequilibrated material which differs from typical h3 material in having little 0 2 vol fine grained opaque silicate matrix and having 20 of the olivines with compositions in the range fa21 24 about 10 15 of this unequilibrated material is probably derived from graphite magnetite rich chondrites and 2 from h3 0 3 5 chondrites the absence of h3 clasts suggests that most of the unequilibrated material was derived from unconsolidated type 3 components many exotic clasts may have been derived from planetesimals that accreted to the h chondrite parent body prior to regolith development one slowly cooled melt rock clast formed beneath a 500 m thick melt breccia pile on the floor of a large impact crater and was later excavated by additional impacts incorporated into the regolith and consolidated with other components to form the dimmitt breccia

the antarctic achondrite grove mountains 021663 an olivine rich winonaite abstract the grove mountains grv 021663 meteorite was collected from the grovemountains region of antarctica the meteorite is composed primarily of olivine fa 5 4 orthopyroxene fs 4 7 wo 3 0 chromian diopside en 53 6 fs 2 4 wo 44 troilite kamacite andplagioclase ab 74 5 or 4 an 21 5 minor phases include schreibersite and k feldspar themeteorite is highly weathered w3 and weakly shocked s2 we determine a whole rockoxygen isotopic composition of d 18 o 7 50 d 17 o 3 52 comparisons of these datawith other primitive achondrites have resulted in the reclassi cation of this meteorite as amember of the winonaite group the occurrences of troilite metal and schreibersite in grv021663 indicate that these minerals were once completely molten euhedral inclusions ofpyroxene within plagioclase further suggest that these may have crystallized from a silicatemelt while the depletion of plagioclase metal and troilite indicates that grv 021663 couldrepresent a residuum following partial melting on its parent asteroid trace elementdistributions in silicate minerals do not however con rm this scenario as with otherwinonaite meteorites the formation of grv 021663 probably relates to brecciation andmixing of heterogeneous lithologies followed by varying degrees of thermal metamorphismon the parent body asteroid peak metamorphic conditions may have resulted in localizedpartial melting of metal and silicate mineralogies but our data are not conclusive introductionthe primitive achondrite meteorites winonaites arecharacterized by having chondritic mineralogies andchemical compositions but achondritic recrystallized textures for the most part they are ne to mediumgrained equigranular rocks some samples however contain what appear to be relic chondrules e g pontlyfni mt morris wisconsin and northwest africa nwa 1463 benedix et al 1998 2003 their oxidationstates are intermediate between those of enstatite and hchondrites and feni fes veins that constitute the rstpartial melts of a chondritic precursor material arecommon see figs 1a and 2a meteorites of this groupare primarily composed of orthopyroxene olivine diopside plagioclase troilite fe ni alloy and minoramounts of chromite and phosphate in addition theymay contain characteristic accessory minerals such asalabandite daubree lite schreibersite benedix et al 1998 amphibole is reported in at least one sample hammadah al hamra hah 193 floss et al 2007 there are several attributes that collectivelydistinguish the winonaites from other achondritemeteorite groups such as 1 highly reduced mineralassemblage s 2 distinct oxygen isotopic compositions 3 the abundance and distribution of metal s andtroilite and 4 characteristic accessory mineralogies benedix et al 1998 winonaites may derive from a1329

can dispersive pressure cause inverse grading in grain flows grain flows in the collisional regime are self regulated in such a way that dispersive pressure at every level tends to balance static pressure and so cannot promote the upward segregation of large particles in a steady flow le roux adds new insights to this analysis by pointing out that dispersive and static pressures would not balance in unsteady flows when shear strain rate increases in a grain flow dispersive pressure which is positively correlated to shear strain rate increases too and the gradient of dispersive pressure becomes higher than the gradient of static pressure as a consequence the grain flow expands thus lowering the dispersive pressure until the two gradients reequilibrate during the

the reduction of friction in long runout landslides as an emergent phenomenon campbell et al 1995 modeled long runout landslides as granular flow using a soft particle code their model essentially simulates landslides from first principles and although no fluid or obvious mechanism for reduction of friction is included the model successfully reproduced many field observations of landslides e g the preservation of source stratigraphy in the final slide mass and a decreasing effective friction with increasing slide volume we extend the work of campbell et al 1995 with a focus on the mechanism that reduces friction in these slides we find sliding preferentially occurs when the overburden is relieved by pressure variations in the slide further analysis shows that our results are very similar to the predictions of the acoustic fluidization hypothesis moreover we determine that for long runout landslides the wavelength of vibrations associated with acoustic fluidization is determined by the size of the rock fragments in the slide

drop height and volume control the mobility of long runout landslides on the earth and mars long runout landslides are landslides with volumes of 105 m3 or more which move much farther from their source than expected the observation that martian landslides are generally less mobile than terrestrial landslides offers important evidence regarding the mechanism responsible for the high mobility of long runout landslides here we simulate landslides as granular flow using a soft particle discrete element model we show that while surface gravity plays a negligible role observed differences in fall height naturally reproduce the observed differences in mobility of martian and terrestrial landslides we also demonstrate that landslides on iapetus may fit this trend our simulations do not include any fluid and indicate that a mechanism similar to acoustic fluidization can explain the high mobility of long runout landslides this implies that long runout landslides on mars should not be considered as evidence for ice saturated clays or liquid water

is there a continuous subtropical front south of africa a 14 3 year series of weekly absolute sea surface height ssh and associated geostrophic velocities is used for a study of the subtropical to subantarctic frontal system in the region south of africa detecting the fronts from surface velocity maxima confirms a two stepped transition in both the southeastern atlantic ocean the northern and southern subtropical fronts nstf sstf and southwestern indian ocean the agulhas front and sstf as proposed previously from hydrographic data an additional front associated with westward flow north of the nstf is indicative of a partial eastern closure of the south atlantic subtropical gyre between 11 e and 17 5 e the role of northwestward propagating agulhas rings in connecting the two fronts explains the varying location the sstf which marks the southern limit of subtropical waters is found continuous from the atlantic to the indian ocean in the time averaged ssh field in the weekly fields however the velocity maximum criterion defining the front is often met at the southern flanks of agulhas rings or agulhas eddies at 12 e 23 e indicating front disruptions such discontinuities suggest that no south atlantic central water is directly advected into the indian ocean instead the eastward limb of the indo atlantic super gyre encompassing the subtropical gyres of both oceans would rest at these longitudes on diffusive processes at the upper levels and possibly be enhanced at depth a schematic diagram of the fronts and their relations to agulhas rings and eddies is proposed

petrologic evidence for collisional heating of chondritic asteroids abstract the identification of the mechanism s responsible for heating asteroids is among the major problems in planetary science because of difficulties with models of electromagnetic induction and the decay of short lived radionuclides it is worthwhile to evaluate the evidence for collisional heating localized impact heating is responsible for forming shock veins melt pockets metal sulfide mixtures vugs agglutinates and a wide variety of melt rock clasts new evidence for localized impact heating comes from the high proportion of relict type 6 material among impact melt bearing ordinary chondrites oc this relict material was probably metamorphosed by residual heat within large craters olivine aggregates composed of faceted crystals with 120 triple junctions occur within the melted regions of the chico and rose city oc melt rocks the olivine aggregates formed from shocked mosaicized olivine grains that underwent contact metamorphism large scale collisional heating is supported by the correlation in oc between petrologic type and shock stage no other heating mechanism can readily account for this correlation the occurrence of impact melt rock clasts in oc that have been metamorphosed along with their whole rocks indicates that some impact events preceded or accompanied thermal metamorphism such impact events occurring during or shortly after accretion are probably responsible for substantially melting 0 5 of oc these events most have heated a larger percentage of oc to subsolidus temperatures sufficient to have caused significant metamorphism if collisional heating is viable then oc parent asteroids must have been large large oc asteroids in the main belt may include those of the s iv spectral subtype collisional heating is inconsistent with layered onion shell structures in oc asteroids wherein the degree of metamorphism increases with depth but the evidence for such structures is weak it seems likely that collisional heating played an important role in metamorphosing chondritic asteroids

the lithophile trace elements in enstatite chondrites we report on the abundances of a selected set of lithophile trace elements namely rees y rb ba sr zr hf nb th u in a comprehensive suite of enstatite chondrites ec 13 eh and 11 el eh3 and el3 display only minor deviations from chondritic distributions for these elements in most metamorphosed ec a wide range of compositions is observed and suggests a mobility of many of the elements studied during the history of these rocks for example el6 chondrites exhibit light ree and nb depletions negative eu anomalies and positive y anomalies more important trace element fractionations are observed in metamorphosed eh like st marks rb depletion lap 02225 rb nb zr eu light ree depletions and galim b which displays large ba sr eu nb and light ree depletions leaching experiments were undertaken to investigate the contributions of sulfides in the whole rock budgets these phases control not only the ree budget but also important fractions of the other elements we studied these fractions strongly depend on the type of the rock eh or el and metamorphic grade for many elements the sulfide contributions increase with the metamorphic grades the trace element abundances of silicate residues are extremely variable negative sm and yb anomalies are observed in el3 and eh3 residues and are certainly the results of early nebular processes such anomalies are lacking in residues obtained with most metamorphosed ec underlining the importance of trace element redistributions during metamorphism in addition el6 residues display distinctive positive y anomalies that could be potentially ascribed to a less chalcophile behavior than ho in the conditions that prevailed during el metamorphism

cumberland falls chondritic inclusions mineralogy petrology of a forsterite chondrite suite abstract as previously found for a chondritic inclusion of unknown affinity mineralogic and petrologic properties of 9 inclusions in the cumberland falls enstatitc achondrite are primitive members of the forsterite f chondrite group hitherto defined by 4 meteorites of similar redox state the inclusions define a primitive suite with properties indicating 8 as f3 and one of even lower petrologic type the abundant minerals include low ca pyroxene olivine plagioclase kamacite taenite schreibersite troilite ferroan alabandite and daubreelite diopside oldhamite and a ti rich sulfide are present in one or two inclusions petrologic textures and jadeitic pyroxene hitherto unidentified in meteorites indicate substantial degree of shock the inclusions acquired their chemical characteristics during nebular condensation and accretion over a broad redox range metal silicate trends in them verify prior s rules their parent body later impacted the enstatite meteorite parent body during impact the inclusions were shocked and incorporated with enstatite achondrite host as a breccia that would become cumberland falls

the gao guenie impact melt breccia sampling a rapidly cooled impact melt dike on an h chondrite asteroid the gao guenie h5 chondrite that fell on burkina faso march 1960 has portions that were impact melted on an h chondrite asteroid at 300 ma and through later impact events in space sent into an earth crossing orbit this article presents a petrographic and electron microprobe analysis of a representative sample of the gao guenie impact melt breccia consisting of a chondritic clast domain quenched melt in contact with chondritic clasts and an igneous textured impact melt domain olivine is predominantly fo80 82 the clast domain contains low ca pyroxene impact melt grown pyroxene is commonly zoned from low ca pyroxene in cores to pigeonite and augite in rims metal troilite orbs in the impact melt domain measure up to 2 mm across the cores of metal orbs in the impact melt domain contain 7 9 wt of ni and are typically surrounded by taenite and ni rich troilite the metallography of metal troilite droplets suggest a stage i cooling rate of order 10 c s 1 for the superheated impact melt the subsolidus stage ii cooling rate for the impact melt breccia could not be determined directly but was presumably fast an analogy between the ni rim gradients in metal of the gao guenie impact melt breccia and the impact melted h6 chondrite orvinio suggests similar cooling rates probably on the order of 5000 40 000 c yr 1 a simple model of conductive heat transfer shows that the gao guenie impact melt breccia may have formed in a melt injection dike 0 5 5 m in width generated during a sizeable impact event on the h chondrite parent asteroid

self lubrication for long runout landslides examination by computer simulation this paper describes the use of a discrete particle computer simulation to test whether the apparent low friction exhibited by long runout landslides could be explained in terms of simple granular mechanics the flow structure consists of an active basal shear zone supporting the majority of the landslide which travels as a relatively solid plug the observed runout appears to depend on the total energy dissipation which is a trade off between 1 the inelasticity of the particles which governs the energy dissipated in each event and 2 the size of the dissipating shear zone which governs the number of particles that are actively dissipating energy very inelastic particles quickly dissipate the work performed at boundaries and result in thin dissipative zones as a result these two factors balance and the runout is nearly independent of particle inelasticity along the same lines increasing the boundary roughness was found to increase the size of the dissipative shear zone and markedly decrease the runout also a distribution of particle sizes destroyed ordered structures within the body which once again increases the dissipation and decreases the runout unfortunately the simulations also indicate that the runout should be independent of the depth of the flow and thus cannot account for the observed volumetric effect on runout

evaluation of landslide mechanisms characterized by high speed mass ejection and long run out based on events following the wenchuan earthquake abstract in the 2008 wenchuan earthquake the mass ejection type of high speed and long run out landslide was an unusual hazard characterized by its dramatic phenomenon of a huge slope mass launching into the air and becoming airborne for a long distance quantitative and qualitative combined techniques were applied to reveal the formation mechanism of this type of landslide four prerequisites critical to form mass ejection are identified high position of the toe of the surface of rupture critical height and critical inclination of slope sufficient open space in the movement direction and adequate take off speed of ski jump like mass ejection these four area specific prerequisites provide a promising approach for screening and targeting the potential landslides subsequently a dynamic reliability analysis method that considers the feature of energy time distribution is proposed this site specific method provides a more credible evaluation by emphasizing the most significant period within the whole earthquake duration finally an aerodynamic inverse method combined with an energy conservation based method is applied in the quantitative evaluation to calculate take off speed of mass ejection this paper provides a viable solution for regional screening and site assessment for new potential targets of this type of landslide

diffusion in silicate minerals and glasses a data digest and guide to the literature the rates of diffusion of cations oxygen and hydrogen in silicates are of fundamental importance to a wide range of petrological and geochronological problems in order that the earth scientist may readily apply the available experimentally determined diffusion rates to such problems a compilation of data for diffusion in silicate minerals and glasses is presented along with a working guide for its use published data and experimental conditions are listed in tables and these are preceded by an outline of diffusion mechanisms terminology equations and units diffusion regimes factors controlling diffusion rates measurement techniques and diffusional behaviour

post impact thermal evolution of porous planetesimals abstract impacts between planetesimals have largely been ruled out as a heat source in the early solar system by calculations that show them to be an inefficient heat source and unlikely to cause global heating however the long term localized thermal effects of impacts on planetesimals have never been fully quantified here we simulate a range of impact scenarios between planetesimals to determine the post impact thermal histories of the parent bodies and hence the importance of impact heating in the thermal evolution of planetesimals we find on a local scale that heating material to petrologic type 6 is achievable for a range of impact velocities and initial porosities and impact melting is possible in porous material at a velocity of 4 km s burial of heated impactor material beneath the impact crater is common insulating that material and allowing the parent body to retain the heat for extended periods millions of years cooling rates at 773 k are typically 1 1000 k ma matching a wide range of measurements of metallographic cooling rates from chondritic materials while the heating presented here is localized to the impact site multiple impacts over the lifetime of a parent body are likely to have occurred moreover as most meteorite samples are on the centimeter to meter scale the localized effects of impact heating cannot be ignored

mineralogy and petrology of the abee enstatite chondrite breccia and its dark inclusions the abee e4 enstatite chondrite breccia consists of clasts many rimmed by metallic fe ni dark inclusions and matrix the clasts and matrix were well equilibrated by thermal metamorphism as evidenced by uniform mineral compositions recrystallized chondrules low mno content of enstatite and high abundance of orthoenstatite the clasts acquired their metal rich rims prior to this metamorphic episode the occurrence in abee of relatively unmetamorphosed dark inclusions clasts with nearly random magnetic orientations and a matrix with a uniform magnetic orientation 18 19 indicates that clast and matrix metamorphism occurred prior to the agglomeration of the breccia the dark inclusions are an unusual kind of enstatite chondritic material distinguished from the clasts and matrix by their relative enrichments in ree 21 23 low relative abundances of kamacite total metallic fe ni and silica lower niningerite total sulfide ratios high relative abundances of oldhamite and martensite smaller euhedral enstatite more heterogeneous enstatite and metallic fe ni more calcic enstatite and more nickeliferous schreibersite we propose the following model for the petrogenesis of the abee breccia the maximum metamorphic temperature of breccia parent material was 840 c the minimum temperature of formation of abee niningerite and perhaps near 950 1000 c the fe ni s eutectic temperature euhedral enstatite crystals in metallic fe ni and sulfide rich areas grew at these metamorphic temperatures into pliable metal and sulfide breccia parent material was impact excavated from depth admixed with dark inclusions and rapidly cooled 700 to 200 c in about 2 hours 15 during this cooling clast and matrix material acquired thermal remanent magnetization random conglomeration of clasts and unconsolidated matrix materials caused the clasts to have random magnetic orientations and the matrix areas to have net magnetic intensities of zero due to the cancellation of numerous randomly oriented magnetic vectors of equal intensity in the matrix a subsequent ambient magnetic field imparted a uniform net magnetic orientation to the matrix and caused the magnetic orientations of the clasts to be somewhat less random the abee breccia was later consolidated possibly by shock or by shallow burial and very long period low temperature 215 c metamorphism

conditions for pore water convection within carbonaceous chondrite parent bodies implications for planetesimal size and heat production abstract the critical rayleigh number for convective flow of pore water through a permeable spherical body is derived the result affords constraints on carbonaceous chondrite planetesimal sizes and rates of heat production if the chemical compositions of carbonaceous chondrites are taken as evidence against flow of pore water then the present calculations suggest that the parent bodies were less than 80 km in diameter the maximum diameter for absence of flow depends in part on the high permeabilities required by estimates of high water rock ratios in altered carbonaceous chondrites pore water would have flowed through parent bodies larger than 120 km in diameter with typical rock like permeabilities convective flow and isochemical alteration are not compatible and our calculations can be used to identify the combinations of parent body size and heat generation consistent with one or the other

agulhas ring formation as a barotropic instability of the retroflection 1 agulhas leakage is an important link in the global ocean circulation as it transfers a significant volume of relatively warm and salty water from the indian ocean to the atlantic ocean the main route of this transfer is through the shedding of large agulhas rings from the agulhas retroflection in this paper we study the dynamics of the ring formation process by analyzing the stability of the indian atlantic supergyre in a reduced gravity model we show that the ring shedding process results from a barotropic instability of the steady circulation in the agulhas retroflection region the destabilizing mode appears to be linked to a rossby basin mode of the combined south indian atlantic basin which is localized in the retroflection region by the background flow

a scaling distribution for grain composition of debris flow debris flow is composed of a wide range of grains this study proposes a general form of grain size distribution p d cd mu exp d d c which is satisfied well by various debris flows and by soils and sediments related to debris flows the parameters mu and d c are found to be related to debris flow density in power laws in particular represents some characteristic porosity of soil in a natural condition and controls the variation of soils in developing debris flows and d c defines a characteristic size governing the sediment concentration field observations indicate that debris flows fall into a certain range of parameters mu d c almost all debris flows have mu 0 10 and most debris flows of high density have mu 0 05 moreover experiments show that the exponent p increases during soil failures under rainfall providing an index varying in the course of debris flow initiation finally grain size distribution is used to evaluate the properties of debris flows in different regions the distribution provides a simple but quantitative method of predicting a potential flow through the source soils c 2013 elsevier b v all rights reserved

formation of mesosiderites by fragmentation and reaccretion of a large differentiated asteroid we propose that mesosiderites formed when a 200 400 km diameter asteroid with a molten core was disrupted by a 50 150 km diameter projectile to test whether impacts can excavate core iron and mix it with crustal material we used a low resolution smoothed particle hydrodynamics computer simulation for 50 300 km diameter differentiated targets we found that significant proportions of scrambled core material and hence potential mesosiderite metal material could be generated for near catastrophic impacts that reduce the target to 80 of its original diameter and about half of its original mass the proportion of scrambled core material would be about 5 vol equivalent to 10 vol of mesosiderite like material the paucity of olivine in mesosiderites and the lack of metal poor or troilite rich meteorites from the mesosiderite body probably reflect biased sampling mesosiderites may be olivine poor because mantle material was preferentially excluded from the metal rich regions of the reaccreted body molten metal globules probably crystallized around small cool fragments of crust hindering migration of metal to the core if mantle fragments were much hotter and larger than crustal fragments little metal would have crystallized around the mantle fragments allowing olivine and molten metal to separate gravitationally the rapid cooling rates of mesosiderites above 850 c can be attributed to local thermal equilibration between hot and cold ejecta very slow cooling below 400 c probably reflects the large size of the body and the excellent thermal insulation provided by the reaccreted debris we infer that our model is more plausible than an earlier model that invoked an impact at 1 km s to mix projectile metal with target silicates if large impacts cannot effectively strip mantles from asteroidal cores as we infer we should expect few large eroded asteroids to have surfaces composed purely of mantle or core material this may help to explain why relatively few olivine rich a type and metal rich asteroids m type are known some s type asteroids may be scrambled differentiated bodies

investigation of the h7 ordinary chondrite watson 012 implications for recognition and classification of type 7 meteorites abstract despite the fact that the number of officially classified meteorites is now over 45 000 we lack a clearly defined sequence of samples from a single parent body that records the entire range in metamorphic temperatures from pristine primitive meteorites up to the temperatures required for extensive silicate partial melting here we conduct a detailed analysis of watson 012 an h7 ordinary chondrite to generate some clarity on the textural and chemical changes associated with equilibrium based silicate partial melting in chondritic meteorites to do this we compare the textures in the meteorite with those preserved in metamorphic contact aureoles on earth the most distinctive texture generated by the partial melting that affected watson 012 is an extensively interconnected plagioclase network which is clearly observable with a petrographic microscope enlarged metal troilite grains are encapsulated at widenings in this plagioclase network and this is clearly visible in reflected light together with these features we define a series of other characteristics that can be used to more clearly classify chondritic meteorites as being of petrologic type 7 to provide comprehensive evidence of silicate partial melting and strengthen the case for using simple petrographic observations to classify similar meteorites we use high resolution x ray computed tomography to demonstrate that the plagioclase network has a high degree of interconnectedness and crystallised as large cm scale skeletal crystals within an olivine orthopyroxene clinopyroxene framework essentially pseudomorphing a melt network back scattered electron imaging and element mapping are used to show that some of the clino and orthopyroxene in watson 012 also crystallised from silicate melt and the order of crystallisation was orthopyroxene clinopyroxene plagioclase x ray diffraction data supported by bulk geochemistry are used to show that plagioclase and ortho and clinopyroxene were added to the watson 012 sample by through flowing basaltic melt along with the absence of glass and granophyre this interconnected network of coarse grained skeletal plagioclase indicates that the sample cooled slowly at depth within the parent body the evidence of melt flux indicates that watson 012 formed in the presence of a gravitational gradient and thus at significant distance from the centre of the h chondrite parent body the gravitational gradient at the centre would be zero our interpretation is that incipient silicate partial melting in watson 012 occurred when a region of radiogenically heated h6 material located at considerable depth possibly at 15 20 km from surface was heated by an additional ca 200 300 c in association with a large shock event due to insulation at depth within an already hot parent body the post shock temperature equilibrated and remained above the solidus long enough for widespread equilibrium based silicate partial melting and for melt to migrate although the observed melting may have been facilitated by additional heating from an impact event this is not an example of instantaneous shock melting which produces thermal disequilibrium at short length scales and distinctly different textures a small number of h l and ll chondrites have been previously classified as being of petrologic type 7 with our new criteria to support that classification these represent our best opportunity to explore the transition from high temperature sub solidus metamorphism through the onset of silicate partial melting in three different parent bodies

cat mountain a meteoritic sample of an impact melted asteroid regolith cat mountain is a new ordinary chondrite impact melt breccia that contains several shocked chondrule bearing clasts of l5 material these clasts are surrounded by a total impact melt of similar composition material which appears to have cooled over a period of a few thousand years probably within a melt breccia lens in the bottom of a large 1 km diameter crater on an l chondrite asteroid noble gas isotopes indicate that the sample was involved in at least two different impact events approximately 880 and 20 myr ago following the 4 55 ga accretion of primitive chondritic material the 880 ma event is responsible for the impact breccia texture of the sample and the 20 ma event reduced the sample to a meter sized object we also infer that another impact occurred between 880 and 20 ma possibly the 500 ma event recorded in many other l chondrites to jettison the material from the asteroid belt into an orbit that evolved into an earth crossing trajectory the shock metamorphic processes that occurred at 880 ma redistributed the opaque phases in the meteorite and altered the crystalline characteristics of silicate phases this reduced the reflectance of the l5 material and decreased the amplitude of its spectral absorption features these characteristics are consistent with the spectral characteristics of some c class asteroids and suggest that some dark asteroids that appear to belong to the c class could be covered with shocked ordinary chondrite material if one assumes that cat mountain came from the same asteroid as other l chondrites with the same cosmic ray exposure age then the juxtaposition of these different materials suggests asteroids are rubble piles which are heterogeneous on a scale less than 100 m furthermore the structural integrity of cat mountain and other l chondrites suggests the strengths of asteroid rubble piles are limited by fractures and contrasting material properties and are thus inherently weak in a ram pressure regime produced when they enter a planetary atmosphere however in a regime where the asteroid is the target of impact fragmentation rather than the projectile the added porosity of a rubble pile structure will compensate for the presence of fractures and absorb a large amount of the impact energy in this case the structural integrity of the asteroid may appear to be the same as a previously unshocked chondritic material

postshock annealing and postannealing shock in equilibrated ordinary chondrites implications for the thermal and shock histories of chondritic asteroids abstract in addition to shock effects in olivine plagioclase orthopyroxene and ca pyroxene petrographic shock indicators in equilibrated ordinary chondrites oc include chromite veinlets chromite plagioclase assemblages polycrystalline troilite metallic cu irregularly shaped troilite grains within metallic fe ni rapidly solidified metal sulfide intergrowths martensite and various types of plessite metal sulfide veins large metal and or sulfide nodules silicate melt veins silicate darkening low ca clinopyroxene silicate melt pockets and large regions of silicate melt the presence of some of these indicators in every petrologic type 4 to 6 ordinary chondrite demonstrates that collisional events caused all equilibrated oc to reach shock stages s3 s6 those type 4 to 6 oc that are classified as shock stage s1 on the basis of sharp optical extinction in olivine underwent postshock annealing due to burial beneath materials heated by the impact event those type 4 to 6 oc that are classified s2 on the basis of undulose extinction and lack of planar fractures in olivine were shocked to stage s3 s6 annealed to stage s1 and then shocked again to stage s2 some oc were probably shocked to stage s3 after annealing it seems likely that many oc experienced multiple episodes of shock and annealing because 40ar 39ar chronological data indicate that mil 99301 ll6 s1 was annealed 4 26 ga ago presumably as a consequence of a major impact it seems reasonable to suggest that other equilibrated s1 and s2 oc which contain relict shock features were also annealed by impacts because some type 6 s1 oc e g guarena kernouve portales valley all of which contain relict shock features were annealed 4 44 4 45 ga ago during a period when impacts were prevalent and most oc were thermally metamorphosed it follows that impact induced annealing could have contributed significantly to oc thermal metamorphism

origin of rapidly solidified metal troilite grains in chondrites and iron meteorites inclusions of troilite and metallic fe ni 0 2 4 mm in size with a dendritic or cellular texture were observed in 12 ordinary chondrites cooling rates in the interval 1400 950 c calculated from the spacing of secondary dendrite arms or cell widths and published experimental data range from 10 7 to 104 c sec in 8 of these chondrites which are breccias containing some normal slow cooled metal grains the inclusions solidified before they were incorporated into the breccias their cooling rates of 1 300 c sec indicate cooling by radiation or by conduction in contact with cold silicate or hot silicate volumes only 6 40 mm in size this is quantitative evidence that these inclusions and their associated clasts were melted on the surface of a parent body by impact and were not formed at depth from an internally derived melt in ramsdorf rose city and shaw which show extensive reheating to 1000 c fe fes textures in melted areas are coarser and indicate cooling rates of 10 1 to 10 4 c sec during solidification this metal may have solidified inside hot silicate volumes that were 10 300 cm in size as shaw and rose city are breccias of unmelted and melted material their melted metal did not necessarily cool through 1000 c within a few m of the surface shock melted fine grained irregular intergrowths of metal and troilite formed in situ in many irons and some chondrites by rapid solidification at cooling rates of 105 c sec their kamacite and taenite compositions may result from annealing at 250 c of metallic glass or exceedingly fine grained quench products

motion and evolution of oceanic rings in a numerical model and in observations observed properties of oceanic rings are compared to rings produced in a two gyre wind driven numerical ocean model and in a model of the south atlantic indian ocean their temporal evolution is discussed in terms of structure and translation rate they exhibit substantial similarity in terms of thermocline depth ring size swirl velocities and translations speeds in both observations and numerical model results the propagation speeds are 2 to 5 times faster than that of an equivalent isolated eddy which is of the order of the long rossby wave speed this is attributed to advection by the mean flows furthermore it is observed that the model rings have a coherent structure all the way to the bottom there is strong evidence that this is also the case in real oceanic rings one major difference between observed and modeled rings is in their decay rate the temporal decay of the rings in the models and observations is therefore discussed in relation to the decay mechanisms at work and the frictional parameterization of the model

thermal and impact history of the h chondrite parent asteroid during metamorphism constraints from metallic fe ni abstract we have studied cloudy taenite metallographic cooling rates and shock effects in 30 h3 6 chondrites to elucidate the thermal and early impact history of the h chondrite parent body we focused on h chondrites with old ar ar ages 4 4 gyr and unshocked and mildly shocked h chondrites as strongly shocked chondrites with such old ages are very rare cooling rates for most h chondrites at 500 c are 10 50 c myr and do not decrease systematically with increasing petrologic type as predicted by the onion shell model in which types 3 5 are arranged in concentric layers around a type 6 core some type 4 chondrites cooled slower than some type 6 chondrites and type 3 chondrites did not cool faster than other types contrary to the onion shell model cloudy taenite particle sizes which range from 40 to 120 nm are inversely correlated with metallographic cooling rates and show that the latter were not compromised by shock heating the three h4 chondrites that were used to develop the onion shell model ste marguerite beaver creek and forest vale cooled through 500 c at 5000 c myr our thermal modeling shows that these rates are 50 higher than could be achieved in a body that was heated by 26al and cooled without disturbance by impact published ar ar ages do not decrease systematically with increasing petrologic type but do correlate inversely with cloudy taenite particle size suggesting that impact mixing decreased during metamorphism metal and silicate compositions in regolith breccias show that impacts mixed material after metamorphism without causing significant heating impacts during metamorphism created portales valley and two other h6 chondrites with large metallic veins excavated the fast cooled h4 chondrites around 3 4 myr after accretion and mixed petrologic types metallographic data do not require catastrophic disruption by impact during cooling

chondrules in the qingzhen type 3 enstatite chondrite possible precursor components and comparison to ordinary chondrite chondrules abstract the qingzhen eh3 fall appears to be the least equilibrated enstatite chondrite mineral compositions vary widely from chondrule to chondrule and in some cases from grain to grain within individual chondrules as in ordinary chondrite oc chondrules most elements show appreciable ranges in concentration porphyritic olivine pyroxene pop chondrules are richer than porphyritic pyroxene pp and radial pyroxene rp chondrules in refractory lithophiles and siderophiles unlike oc chondrules qingzhen s rp and pp chondrules have similar bulk compositions elements in each of the following sets intercorrelate significantly probably because these elements were present in the same nebular components 1 1 fe co ni ir au 2 2 ca eu se 3 3 al sc hf 4 4 na ree 5 5 cl br several additional elements show no correlations set 1 elements were probably derived from a metal component as in oc chondrules set 3 elements which occur in higher concentrations in olivine bearing pop chondrules suggest the existence of a refractory lithophile rich olivine rich component similar to the one previously inferred for oc chondrules set 2 elements suggest a precursor component rich in oldhamite and set 4 elements suggest another refractory bearing component components 2 and 4 were not precursors of oc chondrules for some chondrules interelement ratios of refractory lithophiles such as ca al ti sc and ree are similar to ci ratios this indicates that these elements were probably derived from silicates we suggest that the earliest solid phases were refractory silicates that were sulfurized before chondrule formation some of these sulfurized components e g one rich in oldhamite were abundant in the region where the qingzhen chondrules formed

rheological constraints on martian landslides we use a dynamic finite difference model to simulate martian landslides in the valles marineris canyon system and olympus mons aureole using three different modal rheologies frictional bingham and power law the frictional and bingham modes are applied individually fluidized rheology is treated as a combination of frictional and power law modes general fluidization can include pore pressure contributions whereas acoustic fluidization does not we find that general fluidization most often produces slides that best match landslide geometry in the valles marineris this implies that some amount of supporting liquid or gas was present in the material during failure the profile of the olympus mons aureole is not well matched by any landslide model suggesting an alternative genesis in contrast acoustic fluidization produces the best match for a lunar slide a result anticipated for dry crust with no overlying atmosphere the presence of pressurized fluid during valles marineris landsliding may be due to liquid water beneath a thin cryosphere 1 2 km or flash sublimation of co2

an oxygen isotope dichotomy in cm2 chondritic carbonates a sims approach abstract we present petrologic and secondary ion mass spectrometry sims oxygen isotope analyses of ca carbonate within a group of paired antarctic cm2 chondrites the carbonates can be grouped into two isotopically and morphologically distinct populations type 1 grains small matrix grains possess average 18 o of 33 7 2 3 1 and average 17 o of 0 81 0 90 1 type 2 grains calcite aggregates possess distinct oxygen isotopic compositions average 18 o of 19 4 1 5 1 and average 17 o of 1 98 0 9 1 these differences are interpreted to indicate that the two populations of calcite formed under different conditions at different times the carbonates have textural features that suggest an extraterrestrial origin the data presented here fall within error of a previously measured array for carbonates from cm falls benedix et al 2003 the presence of two generations of carbonate suggests carbonate formation in two discrete events on the parent body of these meteorites the oxygen isotopic data presented here deviate from prior bulk carbonate measurements undertaken for these meteorites most likely this deviation is because bulk carbonate analyses included vein carbonate which formed during terrestrial weathering

the oxygen isotopic record in enstatite meteorites oxygen isotopic compositions were determined for a suite of enstatite chondrites and aubrites in agreement with previous work clayton et al 1984 most samples have o isotopic compositions close to the terrestrial fractionation line tfl and there appear to be no significant differences in o isotopic compositions between individual eh and el chondrites and aubrites five enstatite meteorites have o isotopic compositions that are significantly different from the other samples and 0 2 away from the tfl two of these have petrographic evidence of brecciation and interaction between other meteorite types for the other three similar scenarios are suggested there appears to be a systematic increase in 18o from enstatite chondrites both eh and el of petrologic type 3 to those of type 6 there is also good evidence that the eh meteorites do not fall along a mass fractionation line but along a line slope 0 66 at the present time detailed understanding of the origin of these o isotopic systematics remain elusive but clearly point to a complex accretion history parent body evolution or both

asteroid 2008 tc 3 almahata sitta a spectacular breccia containing many different ureilitic and chondritic lithologies abstract asteroid 2008 tc3 impacted earth in northern sudan on october 7 2008 the meteorite named almahata sitta was classified as a polymict ureilite in this study 40 small pieces from different fragments collected in the almahata sitta strewn field were investigated and a large number of different lithologies were found some of these fragments are ureilitic in origin whereas others are clearly chondritic as all are relatively fresh w0 w0 1 and as short lived cosmogenic radioisotopes were detected within two of the chondritic fragments there is strong evidence that most if not all belong to the almahata sitta meteorite fall the fragments can roughly be subdivided into achondritic ureilitic 23 samples and chondritic lithologies 17 samples among the ureilitic rocks are at least 10 different lithologies a similar number of different chondritic lithologies also exist most chondritic fragments belong to at least seven different e chondrite rock types eh3 el3 4 el6 el breccias several different types of el and eh impact melt rocks and impact melt breccias some of the latter are shock darkened in addition two h group ordinary chondrite lithologies were identified and one sample of a chondrite type that is so far unique the latter has some affinities to r chondrites oxygen isotope compositions of 14 fragments provide further fundamental information on the lithological heterogeneity of the almahata sitta meteorite based on the findings presented in this study the reflectance spectrum of asteroid 2008 tc3 has to be evaluated in a new light

oxide bearing and feo rich clasts in aubrites we report the occurrence of an oxide bearing clast and an feo rich clast from aubrites the feo rich clast in pesyanoe is dominated by olivine and pyroxene phenocrysts with mineral compositions slightly less feo rich than is typical for h chondrites in allan hills alh 84008 the oxide bearing clast consists of a single forsterite grain rimmed by an array of sulfides oxides and phosphides we consider a number of possible origins we can exclude formation by melting of oxide bearing chondrules and cais formed in enstatite chondrites the pesyanoe clast may have formed in a more oxidized region of the aubrite parent body or more likely is a foreign clast from a more oxidized parent body the alh 84008 clast likely formed by reaction between sulfides and silicates as a result of cooling oxidation or de sulfidization this clast appears to be the first oxide bearing clast from an aubritic breccia that formed on the aubrite parent body identification of additional oxide bearing clasts in aubrites could shed light on whether this was a widespread phenomenon and the origin of these enigmatic objects

formation of large metal nodules in ordinary chondrites literature data show that many large 2 30 mm metallic fe ni nodules in ordinary chondrites are depleted in refractory siderophiles e g re os ir ru pt and rh and cu relative to fine grained metal but are not depleted in normally refractory w and mo common siderophiles e g ni and co and volatile siderophiles e g au as and sb it was recently proposed that metamorphic diffusion could form the metal nodules and that partitioning of siderophile elements between kamacite and taenite could account for the nodules unusual compositions however the nodules have the same compositional trends as metal nodules and veins in shocked meteorites that clearly formed by impact related processes if large metal nodules formed during metamorphism type 6 chondrites should contain abundant large nodules instead the mean metal grain size in h6 chondrites is 0 12 0 15 mm far smaller than any of the nodules it seems likely that the metal nodules formed by impact vaporization oxidation of w and mo to form volatile oxides concomitant partial oxidation of re and os rapid fractional condensation of refractory siderophiles transport of the residual vapor condensation of cu s and se into vugs and fractures to form sulfide and condensation of the remaining siderophiles to form metal nodules and veins during vapor cooling and condensation or during subsequent parent body annealing w mo re and os oxides were reduced

a kinematic model of the hsiaolin landslide calibrated to the morphology of the landslide deposit abstract this paper presents results of a case study on the hsiaolin catastrophic landslide including its kinematic process and the geometry of deposition based on geomorphologic analysis the landslide initiated in thick multi aged colluvium soils at the headwaters of a small stream upslope of hsiaolin village a 3d discrete element program pfc3d was used to model the kinematic process that led to the landslide and destruction of hsiaolin village the landslide advanced from debris slide to debris avalanche during the kinematic process assuming a friction coefficient of each particle of 0 1 the predicted maximum velocity was about 70 m s a velocity which permits the debris to cross qishanxi stream and deposit on the opposite bank based on simulation results hsiaolin village was inundated in 60 to 65 s after failure initiation and at 112 s after the event the debris avalanche came to rest forming a landslide dam

the ungrouped chondrite el medano 301 and its comparison with other reduced ordinary chondrites abstract el medano 301 em 301 is an ungrouped chondrite with overall texture and trace element distribution similar to those of ordinary chondrites ocs but with silicate olivine and low ca pyroxene compositions that are more reduced than those in ocs with average olivine and low ca pyroxene of fa3 9 0 3 and fs12 8 4 9 respectively these values are far lower than the values for ocs and even for chondrites designed as reduced chondrites low ca pyroxene is the dominant mineral phase and shows zoning with higher mgo contents along the crystal rims and cracks reverse zoning the co content of kamacite is also much lower than the concentrations observed in ocs below detection limit of 0 18 wt versus 0 44 37 wt oxygen isotopic composition is 17o 0 79 0 78 and slightly different from that of ocs the lower modal olivine pyroxene ratio different infrared ir spectra lower co content of kamacite lower mean feo contents of olivine and pyroxene different kamacite texture and different oxygen isotopic composition show that em 301 does not belong to a known oc group em 301 shows similarities with chondritic clasts in cumberland falls aubrite and with northwest africa 7135 nwa 7135 and acfer 370 ungrouped chondrites however dissimilar to nwa 7135 and the clasts it does not contain highly reduced mineral phases like daubreelite our observations suggest the formation of em 301 in a nebular region compositionally similar to ocs but with a different redox state with oxygen fugacity o2 in this region lower than that of ocs and higher than that of enstatite chondrites condensation region a second possibly nebular phase of reduction by the production of reducing gas phases e g c rich could be responsible for the subsequent reduction of the primary material and the occurrence of reverse zoning in the low ca pyroxene and lower average fa fs ratio based on the ir spectra of em 301 we suggest the possibility that the parent body of this chondrite was a v type asteroid

the galim ll eh polymict breccia evidence for impact induced exchange between reduced and oxidized meteoritic material galim is a polymict breccia consisting of a heavily shocked shock stage s6 ll6 chondrite galim a and an impact melted eh chondrite galim b relict chondrules in galim b served as nucleation sites for euhedral enstatite grains crystallizing from the impact melt many of the reduced phases typical of eh chondrites e g si bearing metallic fe ni ti bearing troilite are absent galim b was probably shock melted while in contact with a more oxidized source namely galim a during this event si was oxidized from the metal and ti was oxidized from troilite galim a contains shock veins and recrystallized unzoned olivine the absence of evidence for reduction in galim a may indicate that the amount of ll material greatly exceeded that of eh material shock metamorphism may have taken place on the ll parent body shock induced redox reactions such as those inferred for the galim breccia appear to be restricted mainly to asteroids because the low end tail of their relative velocity distribution permits mixing of intact disparate materials including accretion of projectiles of different oxidation states whereas the peak of the distribution leads to high equilibration shock pressures allowing impact induced exchange between previously accreted disequilibrated materials galim probably formed by a two stage process 1 accretion to the ll parent body of an intact eh projectile at low relative velocities and 2 shock metamorphism of the assemblage by the subsequent impact of another projectile at significantly higher relative velocities

on the origin of shocked and unshocked cm clasts in h chondrite regolith breccias cm chondrite clasts that have experienced different degrees of aqueous alteration occur in h chondrite and hed meteorite breccias many clasts are fragments of essentially unshocked cm projectiles that accreted at low relative velocities to the regoliths of these parent bodies a few clasts were heated and dehydrated upon impact these objects most likely accreted at higher relative velocities we examined three clasts and explored alternative scenarios for their formation in the first scenario we assumed that the h and hed parent bodies had diameters of a few hundred kilometers so that their high escape velocities would effectively prevent soft landings of small cm projectiles this would imply that weakly shocked cm clasts formed on asteroidal fragments family members associated with the h and hed parent bodies in the second scenario we assumed that weakly shocked cm clasts were spall products ejected at low velocities from larger cm projectiles when they slammed into the h and hed parent bodies in both cases if most cm clasts turn out to have ancient ages e g 3 4 4 1 ga a plausible source for their progenitors would be outer main belt objects some which may have been dynamically implanted 3 9 ga ago by the events described in the so called nice model on the other hand if most cm clasts have recent ages 200 ma a plausible source location for their parent body would be the inner main belt between 2 1 2 2 au in that case the possible source of the cm clasts progenitors parent fragments would be the breakup 160 ma ago of the parent body 170 km in diameter of the baptistina asteroid family baf

a gravitational spreading origin for the socompa debris avalanche abstract socompa volcano arguably provides the world s best exposed example of a sector collapse derived debris avalanche deposit new observations lead us to re interpret the origin of the sector collapse we show that it was triggered by failure of active thrust anticlines in sediments and ignimbrites underlying the volcano the thrust anticlines were a result of gravitational spreading of substrata under the volcano load about 80 of the resulting avalanche deposit is composed of substrata formerly residing under the volcano and in the anticlines the collapse scar can be traced up to 5 km from the edifice truncating two spreading related anticlines which collapsed in the event outcrops near the volcano preserve evidence of edifice material being carried along on top of mobilised substrata on the north side of the scar the avalanche motion was initially at right angles to the failure edge structural relations indicate that immediately prior to collapse the substrata disintegrated became effectively liquidised and were ejected from beneath the edifice catastrophic mobilisation of substrata probably resulted from breakdown of ignimbrite clasts and cement it may have occurred through progressive rock fracture by high shear strain during spreading material ejected from under socompa formed a layer on which volcanic edifice debris was transported this interpretation of events explains the puzzling observation that avalanche units with the lowest gravitational potential energy moved the furthest it can also account for avalanche motion normal to the collapse scar walls ignimbrites and other rock types probably capable of similar behaviour underlie many other volcanoes identification of spreading at other sites could therefore be a first step towards assessment of the potential for this style of catastrophic sector collapse

compositional and petrographic similarities of cv and ck chondrites a single group with variations in textures and volatile concentrations attributable to impact heating crushing and oxidation abstract greenwood et al 2010 gathered data on o isotopic and elemental compositions and reevaluated literature data for cv and ck chondrites they concluded that these two chondrite groups originated on the same parent asteroid with ck chondrites being metamorphosed cv chondrites which are otherwise missing types 4 through 6 to test this interpretation we have gathered new instrumental neutron activation analysis inaa data for cv and ck chondrites and reexamined their petrographic features the new inaa data like the older data show scatter attributable to weathering effects but we conclude that the refractory lithophile abundances are the same in cv and ck in agreement with the greenwood et al interpretation several volatile elements are significantly lower in ck than in cv chondrites among the elements we determine the greatest difference between cv and ck is found for br for which the cv ck ratio is 4 as and sb are about 20 lower in ck than cv and smaller differences are observed for zn ga and se it seems likely that volatiles were lost during impact heating events that also provided the heat responsible for metamorphic recrystallization within statistical uncertainty chondrules in cv and ck chondrites are the same size and have similar textural distributions a significant petrographic difference between ck and cv chondrites cited by kallemeyn et al 1991 was the much higher percentage of igneous rims around cv chondrules however we now recognize that many chondrules in ck3 8 nwa 1559 have igneous rims and in ck4 chondrites igneous rims are recognizable by their associated sulfide rich rings there are no quantifiable cv ck differences in igneous rim abundances we used ca and al maps to show that ck chondrites have cai abundances similar to those of cv chondrites it thus appears that there are no resolvable pre metamorphic petrographic differences between cv and ck chondrites we recommend that the ck designation be abandoned and that the cv group be acknowledged as spanning the range of petrologic types 3 6 we suggest that ck3 chondrites be designated cv3oxk most ck4 chondrites are highly fragmental collisional crushing appears to be much more common than in cv chondrites it seems likely that ck chondrites formed from reduced cv3 materials after the latter was impacted buried aqueously altered and annealed

particle fabric in a small type 2 ignimbrite flow unit laacher see germany and implications for emplacement dynamics ignimbrites of the 13 ka upper laacher see tephra were deposited from small highly concentrated moderately fluidized pyroclastic flows their unconsolidated nature and the prominence of accidental devonian slate fragments make these ignimbrites ideal for clast fabric studies the upper flow unit of ignimbrite m14 has characteristics typical of a type 2 ignimbrite layer 2a and the lower part of layer 2b of the flow unit have strong upstream inclined a p fabrics a p means long particle axes parallel to flow direction only clasts with a b axial ratios of 2 5 or greater preserve good a p fabrics whereas the a b planes of flat fragments dip upstream irrespective of axial ratio the a axis fabric becomes weaker flatter and more girdle like in the upper half of layer 2b at one locality the a axis fabric appears to rotate 40 up through the flow unit suggesting either shear decoupling of different levels in the moving flow or unsteadiness effects in a flow depositing progressively at its base the existence of similarly strong a p fabrics in layer 2a and the lower half of layer 2b appears inconsistent with the common interpretation that ignimbrite flow units are emplaced as a plug of essentially non shearing material layer 2b on a thin shear layer layer 2a and that the entire flow freezes en masse to form the deposit the data suggest that if the flow froze en masse it was shearing pervasively through at least half its thickness another possibility is that the flow unit aggraded progressively from the base up and that the fabrics record the integrated history of shear directions and intensities immediately above the bed throughout the duration of deposition

large scale landslide simulations global deformation velocities and basal friction the cause of the apparent small friction exhibited by long runout landslides has long been speculated upon in an attempt to provide some insight into the matter this paper describes results obtained from a discrete particle computer simulation of landslides composed of up to 1 000 000 two dimensional discs while simplified the results show many of the characteristics of field data the volumetric effect on runout preserved strata etc and with allowances made for the two dimensional nature of the simulation the runouts compare well with those of actual landslides the results challenge the current view that landslides travel as a nearly solid block riding atop a low friction basal layer instead they show that the mass is completely shearing and indicate that the apparent friction coefficient is an increasing function of shear rate the volumetric effect can then be understood with all other conditions being equal different size slides appear to travel with nearly the same average velocity however as the larger landslides are thicker they experience smaller shear rates and correspondingly smaller fractional resistance

rings in the ocean certain robust long lived eddy features in t he world s ocean have come to be k nown as rings the nomenclature stems from fuglister 1 1972 who c oined t he name based on the c ircle or ring of gulf stream waters t hat surrounded a class of eddies formed from t he g ulf stream through the pinch off of meanders here it s uffices to define rings as intense eddies or vortices that represent a wrapped up piece of a major ocean c urrent they t ranslate over space scales of hundreds to thousands of k ilometers and exist for periods lasting from months to years rings move t hrough the ocean carrying anomalies s imilar to the contrasts in physical biological and chemical properties observed across the major ocean c urrents while the term ring is t ied to fuglister t he existence ofthese features was evident at least as early as t he 1930s when iselin 2 1936 1940 encountered strong cold anomalies in the region south of the gulf stream that we would identify as c old corc cyclonic rings today iselin fully rec ognized these features as part of the highly time dependent eddy motion in the ocean later iselin fuglister 1948 were the first to survey what is now k nown as a warm core anticyc lonic ring there are tw o types of rings cold core rings are made up of w aters from the poleward s ide of c urrents like the gulf stream that are introduced to

the tsaoling landslide triggered by the chi chi earthquake taiwan insights from a discrete element simulation article i nfo in the village of tsaoling in yunlin county taiwan a major landslide was triggered by the chi chi earthquake in 1999 with more than 125 10 6 m 3 of rock displaced the kinematic behaviour of this landslide is simulated using a 2d discrete element model pfc2d code our numerical model is composed of discs bonded together the initial boundary conditions are applied along the ball wall contacts by using derived velocities integrated from the strong motion data with a duration of 160 s including the peak acceleration near tsaoling the constraints are mainly issued from the final geometry of the landslide including its capacity to cross the river valley and reach a significant elevation on the opposite mountain flank they also result from a variety of geological and hydrological observations including the local levels of material disruption and the location of survivors our modelling thus indicates that a low friction coefficient about 0 15 and a medium strength are required to account for the actual landslide characteristics a self lubrication mechanism probably accounts for the low residual friction our model also suggests that the maximum velocity of sliding reached 50 m s a result that cannot be checked in the absence of actual measurements in addition to friction the strength of sliding block is of special importance because it controlled the possibility for the upper layer fragments to roll and get buried and hence the probability of survival

noble gases in enstatite chondrites ii the trapped component the trapped noble gas record of 57 enstatite chondrites e chondrites has been investigated basically two different gas patterns have been identified dependent on the petrologic type all e chondrites of type 4 to 6 show a mixture of trapped common chondritic rare gases q and a subsolar component range of elemental ratios for e4 6 chondrites 36ar 132xe 582 270 and 36ar 84kr 242 88 e3 chondrites usually contain q gases but also a composition with lower 36ar 132xe and 36ar 84kr ratios which we call sub q 36ar 132xe 37 0 18 0 and 36ar 84kr 41 7 18 1 the presence of either the subsolar or the sub q signature in particular petrologic types cannot be readily explained by parent body metamorphism as postulated for ordinary chondrites we therefore present a different model that can explain the bimodal distribution and composition of trapped heavy noble gases in e chondrites trapped solar noble gases have been observed only in some e3 chondrites about 30 of each group eh3 and el3 chondrites amounting to 9 of all analyzed e chondrites show the solar signature notably only one of those meteorites has been explicitly described as a regolith breccia

new findings for the equilibrated enstatite chondrite grein 002 we report new petrographic and chemical data for the equilibrated el chondrite grein 002 including the occurrence of osbornite metallic copper abundant taenite and abundant diopside as inferred from low si concentrations in kamacite the presence of ferroan alabandite textural deformation chemical equilibration of mafic silicates and a subsolar noble gas component we concur with grein 002s previous classification as an el4 5 chondrite furthermore the existence of pockets consisting of relatively coarse euhedral enstatite crystals protruding large patches of fe ni alloys suggests to us that this el4 5 chondrite has been locally melted we suspect impact induced shock to have triggered the formation of the melt pockets mineralogical evidence indicates that the localized melting of metal and adjacent enstatite must have happened relatively late in the meteorites history the deformation of chondrules equilibration of mafic silicates and generation of normal zoning in fe zn sulfides took place during thermal alteration before the melting event following parent body metamorphism daubreelite was exsolved from troilite in response to a period of slow cooling at subsolidus temperatures exsolution of schreibersite from the coarse metal patches probably occurred during a similar period of slow cooling subsequent to the event that induced the formation of the melt pockets overall shock features other than localized melting correspond to stage s2 and were likely established by the final impact that excavated the grein 002 meteoroid

observations of mesoscale eddies in the south atlantic cape basin baroclinic and deep barotropic eddy variability 1 anticyclones and cyclones in the eastern south atlantic are characterized based on data collected during january 2003 to march 2005 along a jason 1 satellite altimeter ground track as part of the agulhas south atlantic thermohaline transport experiment large and small cyclones and anticyclones were ubiquitous in the deep ocean of the eastern south atlantic as well as in the upper ocean eddy structures jointly corotating in the upper and deep water column were common most of the time 94 these were not axially aligned as they copropagated the agulhas rings and cyclones that populate the region generally carry both a steric component baroclinic and a mass loading component deep barotropic structure average translation speeds were 7 5 cm s 1 for baroclinic eddies and twice as fast for barotropic eddies irrespective of polarity translation speeds were higher than advection by the mean background flow field in addition large mixed baroclinic barotropic rings crashed into the agulhas ridge and nearby seamounts and split into two or more parts some ring parts were also observed to fuse together deep cyclones as well as interactions with topography were observed to play a role in the fission process of agulhas rings these processes can increase the population of agulhas rings and their remnant eddies which took three pathways from the agulhas and into the cape basin 1 a deep pathway between the continental slope and erica seamount 2 a shallower pathway over or near the agulhas ridge and schmitt otto seamount and 3 a deep seaward pathway around the agulhas ridge

mobility of large rock avalanches evidence from valles marineris mars measurements of h l height of drop length of runout vs volume for landslides in valles marineris on mars show a trend of decreasing h l with increasing volume this trend which is linear on a log log plot is parallel to but lies above the trend for terrestrial dry rock avalanches this result and estimates of 10 4 to 10 5 pa yield strength suggest that the landslides were not water saturated as suggested by previous workers the offset between the h l vs volume trends shows that a typical martian avalanche must be nearly two orders of magnitude more voluminous than a typical terrestrial avalanche in order to achieve the same mobility this offset might be explained by the effects of gravity on flows with high yield strengths these results should prove useful to future efforts to resolve the controversy over the mechan ics of long runout avalanches

the hadley rille enstatite chondrite and its agglutinate like rim impact melting during accretion to the moon hadley rille is a millimeter size eh chondrite containing euhedral and acicular enstatite grains kamacite globules and preferentially aligned silicate aggregates separated by elongated kamacite rich patches the hadley rille chondrite was significantly impact melted when it accreted to the lunar regolith at relative velocities of 3 km s 1 65 75 of the chondrules present initially were melted during the impact portions of the local regolith were melted and an agglutinate like rim formed around the chondritic projectile the rim consists of flow banded vesicular glass blebs of troilite and low ni metallic fe rock fragments glass shards and mineral grains the mineral grains include enstatite which is otherwise absent from the moon and must have been derived from the projectile and poorly characterized micrometer size phases enriched in light rare earth elements lree which probably formed during the impact several of the rock fragments contain 33 mg g cl which was probably derived through impact induced volatilization of cl from chondrule mesostases in the eh projectile

on sverdrup discontinuities and vortices in the southwest indian ocean abstract the southwest indian ocean is distinguished by discontinuities in the wind driven sverdrup circulation these connect the northern and southern tips of madagascar with africa and the southern tip of africa with south america in an analytical barotropic model with a flat bottom the discontinuities produce intense westward jets those off the northern tip of madagascar and the southern tip of africa are always present while the strength of that off southern madagascar depends on the position of the zero curl line in the indian ocean the jet is strong if the line intersects madagascar but weak if the line is north of the island all three jets are barotropically unstable by the rayleigh kuo criterion the authors studied the development of the instability using a primitive equation model with a flat bottom and realistic coastlines the model produced westward jets at the three sites and these became unstable after several weeks generating 200 300 km scale eddies the eddies generated west of

on the dynamic fragmentation and lubrication of coseismic landslides national natural science foundation of china fundamental research funds for the central universities and rockhorizon advanced tools for rockfall hazard and risk zonation at the regional scale

unraveling driving factors for large rock ice avalanche mobility large rock ice avalanches have attracted attention from scientists for decades and some of these events have caused high numbers of fatalities a relation between rock slope instabilities in cold high mountain areas and climate change is currently becoming more evident and questions about possible consequences and hazard scenarios in densely populated high mountain regions leading beyond historical precedence are rising to improve hazard assessment of potential rock ice avalanches their mobility is a critical factor this contribution is an attempt to unravel driving factors for the mobility of large rock ice avalanches by synthesizing results from physical laboratory experiments and empirical data from 64 rock ice avalanches with volumes 1x106 m3 from glacierized high mountain regions around the world the influence of avalanche volume water and ice content low friction surfaces and topography on the apparent coefficient of friction as a measure of mobility is assessed in laboratory experiments granular ice in the moving mass was found to reduce bulk friction up to 20 while water led to a reduction around 50 for completely saturated material compared with dry flows evidence for the effects of water as a key driving factor to enhance mobility was also found in the empirical data while the influence of the ice content could not be confirmed to be of much relevance in nature besides liquefaction it was confirmed that mobility increases with volumes and that frictional surface characteristics such as flow paths over glaciers are also dominant variables determining mass movement mobility effects of the topography along the flow path as well as channeling are assumed to be other critical factors the results provide an empirical basis to roughly account for different path and flow characteristics of large rock ice avalanches and to find appropriate ranges for friction parameters for scenario modeling and hazard assessments copyright 2011 john wiley sons ltd

interannual eddy kinetic energy modulations in the agulhas return current interannual variability in the mesoscale eddy field in the agulhas return current arc of 32 42 degrees s and 15 35 degrees e is investigated based on satellite altimeter observations and state estimate from the estimating the circulation and climate of the ocean phase ii from 1993 to 2016 it is found that the interannual modulation of eddy kinetic energy in the arc region is externally mediated by the wind stress forcing that generates the westward propagating sea surface height anomalies across the south indian ocean subtropical gyre the wind forced sea surface height anomalies influence the upstream agulhas current volume transports by modulating the intensity of barotropic instability of the arc mean flow centered around the retroflection region the agulhas current inflow variability leads to the downstream interannual eddy kinetic energy fluctuations in the arc region

constraints on the role of impact heating and melting in asteroids received 1996 august 30 accepted in revised form 1997 january 30 abstract imaging of asteroids gaspra and ida and laboratory studies of asteroidal meteorites show that im pacts undoubtedly played an important role in the histories of asteroids and resulted in shock metamorphism and the formation of breccias and melt rocks however in recent years impact has also been called upon by numerous authors as the heat source for some of the major geological processes that took place on asteroids such as global thermal metamorphism of chondrite parent bodies and a variety of melting and igneous events the latter were proposed to explain the origin of ureilites aubrites mesosiderites the eagle station pallasites acapulcoites lodranites and the iab iiicd and iie irons we considered fundamental observations from terrestrial impact craters combined with results from laboratory shock experiments and theoretical consider ations to evaluate the efficiency of impact heating and melting of asteroids studies of terrestrial impact craters and relevant shock experiments suggest that impact heating of aster oids will produce two types of impact melts 1 large scale whole rock melts total melts not partial melts at high shock pressure and 2 localized melts formed at the scale of the mineral constituents mineral specific or grain boundary melting at intermediate shock pressures the localized melts form minuscule amounts of melt that quench and solidify in sifu thus preventing them from pooling into larger melt bodies partial melting as defined in petrology has not been observed in natural and experimental shock metamor phism and is thermodynamically impossible in a shock wave induced transient compression of rocks the total impact melts produced represent a minuscule portion of the displaced rock volume of the parent crater internal differentiation by fractional crystallization is absent in impact melt sheets of craters of sizes that can be tolerated by asteroids and impact melt rocks are usually clast laden thermal metamorphism of country rocks by impact is extremely minor experimental and theoretical considerations suggest that 1 single dis ruptive impacts cannot raise the average global temperature of strength or gravity dominated asteroids by more than a few degrees 2 cumulative global heating of asteroids by multiple impacts is ineffective for asteroids less than a few hundred kilometers in diameter 3 small crater size low gravity and low impact velocity suggest that impact melt volume in single asteroidal impacts is a very small 0 014 1 fraction of the total displaced crater volume 4 total impact melt volume formed during the typical lifetime of an asteroid is a small fraction 0 001 of the volume of impact generated debris and 5 much of the impact melt generated on asteroidal targets is ejected from craters with velocities greater than escape velocity and thus not retained on the asteroid the inescapable conclusion from these observations and calculations is that impacts cannot have been the heat source for the origin of the meteorite types listed above and we must turn to processes other than impact such as decay of short lived radionuclides or electromagnetic induction during an early t tauri phase of the sun to explain heating and melting of the parent bodies of these meteorites

asteroid 6 hebe the probable parent body of the h type ordinary chondrites and the iie iron meteorites the s iv type asteroid 6 hebe is identified as the probable parent body of the h type ordinary chondrites and of the iie iron meteorites the ordinary chondrites are the most common type of meteorites falling to earth but prior to the present study no large mainbelt source bodies have been confirmed hebe is located adjacent to both the v6 and 3 1 resonances and has been previously suggested as a major potential source of the terrestrial meteorite flux hebe exhibits subtle rotational spectral variations indicating the presence of some compositional variations across its surface the silicate portion of the surface assemblage of hebe is consistent both in overall average and in its range of variation with the silicate components in the suite of h type chondrites the high albedo of hebe rules out a lunar style space weathering process to produce the weakened absorption features and reddish spectral slope in the s type spectrum of hebe linear unmixing models show that a typical ni fe metal spectrum is consistent with the component that modifies an h chondrite spectrum to produce the s type spectrum of hebe on the basis of the association between the h chondrites and the he iron meteorites our model suggests that large impacts onto the relatively metal rich h chondrite target produced melt bodies sheets or pods that differentiated to form thin laterally extensive near surface layers of ni fe metal fragments of the upper silicate portions of these melt bodies are apparently represented by some of the igneous inclusions in h chondrite breccias alternately masses of metal could have been deposited on the surface of hebe by the impact of a core or core fragment from a differentiated parent body of h chondrite composition subsequent impacts preferentially eroded and depleted the overlying silicate and regolith components exposing and maintaining large masses of metal at the optical surface of hebe in this interpretation the nonmagmatic iie iron meteorites are samples of the ni fe metal masses on the surface of hebe whereas the h chondrites are samples from between and or beneath the metal masses

shock post shock annealing and post annealing shock in ureilites the thermal and shock histories of ureilites can be divided into four periods 1 formation 2 initial shock 3 post shock annealing and 4 post annealing shock period 1 occurred 4 55 ga ago when ureilites formed by melting chondritic material impact events during period 2 caused silicate darkening undulose to mosaic extinction in olivines and the formation of diamond lonsdaleite and chaoite from indigenous carbonaceous material alkali rich fine grained silicates may have been introduced by impact injection into ureilites during this period about 57 of the ureilites were unchanged after period 2 during period 3 events impact induced annealing caused previously mosaicized olivine grains to become aggregates of small unstrained crystals some ureilites experienced reduction as feo at the edges of olivine grains reacted with c from the matrix annealing may also be responsible for coarsening of graphite in a few ureilites forming euhedral appearing idioblastic crystals orthopyroxene in meteorite hills met 78008 may have formed from pigeonite by annealing during this period the rb sr internal isochron age of 4 0 ga for met 78008 probably dates the annealing event at this late date impacts are the only viable heat source about 36 of ureilites experienced period 3 events but remained unchanged afterwards during period 4 7 of the ureilites were shocked again as is evident in the polymict breccia elephant moraine eet 83309 this rock contains annealed mosaicized olivine aggregates composed of small individual olivine crystals that exhibit undulose extinction ureilites may have formed by impact melting chondritic material on a primitive body with heterogeneous o isotopes plagioclase was preferentially lost from the system due to its low impedance to shock compression brief melting and rapid burial minimized the escape of planetary type noble gases from the ureilitic melts incomplete separation of metal from silicates during impact melting left ureilites with relatively high concentrations of trace siderophile elements