the terrestrial alteration of saharan shergottites dar al gani 476 and 489 a case study of weathering in a hot desert environment abstract rare earth element ree and other selected trace and minor element concentrations were determined in various phases of dar al gani 476 and 489 two basaltic shergottites recently found in the libyan sahara whereas merrillite and feldspathic glass compositions do not seem to have been altered since the fall of these meteorites olivine and pyroxenes commonly show light ree enrichments sometimes accompanied by ce anomalies that are attributed to terrestrial alteration sr and ba enrichments are also observed the calcium carbonate that resides in most cracks is essentially devoid of ree but a fine grained amorphous silicate material that fills some veins and pockets has striking light ree enrichments and elevated p sr and ba it is argued that this material likely to be impact melt as well as the notoriously light ree poor olivine and pyroxenes were preferentially affected by a crustal light ree rich contaminant caution is urged when using whole rock or even mineral separate compositional and isotopic data for hot desert meteorites

ancient meteorite finds and the earth s surface environment abstract the flux of meteorites to the earth over the last 50 000 yr has remained approximately constant most meteorites that fall in temperate or tropical areas are destroyed on a time scale which is short compared to the rate of infall however in arid regions both hot deserts and the cold desert of antarctica weathering is slower and accumulations of meteorites may occur the initial composition for many meteorite groups is well known from modern falls and terrestrial ages may be established from analyses of the abundance of cosmogenic radionuclides providing an absolute chronology for recording terrestrial processes as samples are falling constantly and are distributed approximately evenly over the earth meteorites may thus be thought of as an appropriate standard sample for studying aspects of the terrestrial surface environment studies involving 14 c and 36 cl terrestrial ages of meteorites 57 fe mossbauer spectroscopy to quantify the degree of oxidation in samples stable isotopes and determination of halogen abundances are yielding information on the terrestrial history of meteorites i terrestrial age and oxidation frequency distributions for populations of samples allow the ages of surfaces to be estimated ii differences in the weathering rate of samples between sites allows constraints to be imposed on the effect of climate on rock weathering rates iii carbon isotopic compositions of generations of carbonate growth within meteorites allows in some cases temperatures of formation of carbonates to be estimated iv structure in the oxidation terrestrial age distribution for meteorites from some arid accumulation sites specifically the nullarbor of australia appears to be linked to previous humid arid cycles v meteorite accumulations in antarctica have been used to constrain aspects of the quaternary evolution of the ice sheet and terrestrial age and oxidation data have been used to constrain ice flow

the 2010 maule chile earthquake downdip rupture limit revealed by space geodesy radar interferometry from the alos satellite captured the coseismic ground deformation associated with the 2010 mw 8 8 maule chile earthquake the alos interferograms reveal a sharp transition in fringe pattern at 150 km from the trench axis that is diagnostic of the downdip rupture limit of the maule earthquake an elastic dislocation model based on ascending and descending alos interferograms and 13 near field 3 component gps measurements reveals that the coseismic slip decreases more or less linearly from a maximum of 17 m along strike average of 6 5 m at 18 km depth to near zero at 43 48 km depth quantitatively indicating the downdip limit of the seismogenic zone the depth at which slip drops to near zero appears to be at the intersection of the subducting plate with the continental moho our model also suggests that the depth where coseismic slip vanishes is nearly uniform along the strike direction for a rupture length of 600 km the average coseismic slip vector and the interseismic velocity vector are not parallel which can be interpreted as a deficit in strike slip moment release

axtell and allende a mossbauer spectroscopic study abstract mossbauer spectra showed the cv3 oxidized subgroup meteorites allende and axtell to be similar in olivine content and in a surprising lack of pronounced magnetic components but different in fe3 phases one atypical allende sample showed an 8 area under the curve for magnetite which is still less than a reported value for a cv3 reduced subgroup member allende s unusual fe3 spectral region distinguishes it from most other stony meteorites and is difficult to fit to known mineral parameters introduction axtell cv3 carbonaceous chondrite strongly resembles the well characterized 1969 fall allende however axtell s thermo luminescence suggests a terrestrial age of 100 years and its 6oco abundance and details of its refractory inclusions also differ from those of allende simon et al 1995 we present the fe mossbauer spectrum of axtell which resembles that of allende but with distinct differences especially obvious during attempts at curve fitting we report such attempts for allende which draw attention to its unusual ferric phases both meteorites are conventionally placed in the oxidized subgroup of the cv3 chondrites

the porosities of ordinary chondrites models and interpretation densities and porosities for 285 ordinary chondrites have been assembled and analyzed measured chondrite porosities are bimodal finds have an average porosity of 30 we conclude that mild degrees of weathering fill pore spaces lowering grain densities and porosities without significantly changing the bulk size or mass of the sample by assuming an original pristine grain density as a function of the meteorite s mineralogy determined by its class we can derive model pristine porosities these model porosities cluster around an average value of 10 for all classes of ordinary chondrites ordinary chondrites do not show any correlation of porosity model or measured with petrographic grade or sample size over a range from 0 2 g to 2 kg however we do see a correlation between shock state and porosity shock blackened meteorites are less porous than other meteorites furthermore less severely shocked meteorites show a much broader range of porosities with the maximum porosity seen among meteorites of a given shock class falling linearly as a function of that shock class this is consistent with the idea that shock compresses and closes pore space analysis of meteorite porosity provides a lower bound to the fine scale porosity of asteroids our densities even with 10 primordial porosity are significantly higher than inferred densities of possible asteroid parent bodies these asteroids are probably loose piles of rubble

geochemistry of meteorite rich marine limestone strata and fossil meteorites from the lower ordovician at kinnekulle sweden abstract thirteen fossil meteorites 1 5 9 cm have been found in lower ordovician orthoceratite limestone at kinnekulle sweden the meteorites were recovered from a 3 5 m thick quarried interval in the middle of a 30 m thick section of orthoceratite limestone the section formed in an epicontinental sea at very slow sedimentation rates 0 2 cm ka the limestones of the lower two thirds of the section are reddish brown except in the quarried interval where a conspicuous 1 m thick grey limestone bed occurs ten of the meteorites were found in a thin bed below the grey limestone one was found in the grey limestone and two in the red limestone above the meteorites are almost completely pseudomorphosed primarily by calcite and barite they were identified by their content of chromite grains and chondrule pseudomorphs the central part of one of the meteorites shows iridium 800 ppb gold 550 ppb and chromium 4400 ppm concentrations in typical chondritic abundances centimeter resolution profiles for iridium and eight other elements have been established through the quarried interval at a site at 4 km distant from the meteorite producing quarry in the reddish brown parts ir concentrations carbonate free basis lie typically in the range 300 400 ppt compared with 50 ppt ir in average shale in the grey limestone the ir concentrations are lower around 100 150 ppt iridium correlates with iron and appears to be related to sedimentation rate and or iron redox state rather than to any variations in the composition of the siliciclastic fraction with estimated sedimentation rates as above the excess ir flux to the sediment was 30 ng cm 2 ma which is a factor 2 3 higher than the present total ir flux and one order of magnitude higher than the extraterrestrial ir flux to the pacific sea floor our data cannot discriminate to what extent the ordovician ir enrichments are related to extraterrestrial matter or to precipitation of ir from seawater in recent deep sea sediments seawater derived ir enrichments are associated with mn oxides but no similar association occurs in the orthoceratite limestone the ten meteorites in the bed below the grey limestone reflect minimum meteorite accumulation rates of one meteorite per 150 m 2 and 175 ka probably the ten meteorites are related to a local strewn field rather than to background influx minimum accumulation rates calculated on three meteorite finds 20 g in the entire quarried interval give one meteorite per 570 m 2 and 1 17 ma which is one order of magnitude higher than present day large area averaged meteorite influx rates the probability is low that the small area 2 of the sea floor studied would happen to be one where an unusually high number of meteorites struck our results may reflect that meteorite and possibly also extraterrestrial ir influx rates were substantially higher than at the present during a period in the early ordovician enhanced influx rates could be related to an asteroid collision in space

new data on the stratigraphy and pedology of the clovis and plainview sites southern high plains abstract the well known clovis and plainview archaeological sites of new mexico and texas have yielded new data on regional late quaternary geologic paleoclimatic and pedologic histories eolian sedimentation at the clovis site from about 10 000 to less than 8500 yr b p was followed by the formation of a cumulic soil between 8500 and 5000 yr b p episodic eolian and slope wash deposition then culminated in massive eolian sedimentation about 5000 yr b p after which a haplustalf formed then was subsequently buried by part of a dune system within the last 1000 yr at the plainview site a basal stream gravel contains plainview cultural material ca 10 000 yr b p which is followed by a localized early holocene lacustrine deposit two eolian deposits the younger dating to about 5000 yr b p and a marsh deposit which slowly accreted as an argiustoll formed in the younger eolian unit the data indicate that on the southern high plains 1 between 12 000 and 8500 yr b p sedimentation varied from site to site 2 there was a regional climate change toward warming and drying in the early holocene 3 two episodes of severe drought apparently occurred in the middle holocene 6500 to 4500 yr b p 4 between 4500 yr b p and the present an essentially modern climate existed but with several shifts toward aridity within the last 1000 yr 5 argillic horizons have developed in late holocene soils 6 clay illuviation can occur in calcareous soils and 7 long distance correlation of holocene stratigraphy in the region is possible particularly with the aid of soil morphology

concentrations of siderophile elements in nonmagnetic fractions of antarctic h and l chondrites a quantitative approach on weathering effects the nonmagnetic separates of antarctic h and l chondrite finds from the lewis cliff stranding area are enriched in fe and siderophile elements such as ni co cu as ir and au relative to those of non antarctic falls the siderophile enrichments are caused by the oxidation of metallic fe ni to nonmagnetic hydrous fe ni oxides the concentrations of fe ni and co in each sample were used to calculate the amount of oxidized metal which serves as a quantitative measure of the degree of weathering the amount of oxidized metal is generally between 1 10 wt and shows a rough correlation with the qualitative a b c weathering classification for increasing rustiness no clear correlation was found between weathering and terrestrial age although meteorites older than 0 2 ma contain on the average 50 more oxidized metal also no correlation was found between the degree of weathering and the natural thermoluminescence tl level which is dominated by the thermal history in space rather than by the thermal history in or on the antarctic ice the only significant parameter for the degree of weathering seems to be the location of find with the most weathered specimens being found in a part of the stranding area where melt water ponds are known to occur this observation confirms that the occasional presence of liquid water plays an important role in the antarctic weathering process and explains the poor correlation of the degree of weathering of antarctic meteorites with terrestrial age and surface exposure age

stones from mohave county arizona multiple falls in the franconia strewn field one of the most productive and well sampled dense collection areas for meteorites on earth is the franconia strewn field in mohave county arizona which since 2002 has yielded hundreds of meteorites in an ellipsoidal area approximately 5 16 km across based on petrographic mineral chemical and terrestrial age data we conclude that among 14 meteorites examined there are at least 6 and possibly 8 distinct meteorites represented which fell over a period of approximately 0 20 kyr ago these include equilibrated h chondrites such as franconia h5 and buck mountains bm 001 h6 h3 6 breccias such as buck mountains wash and bm 004 and l6 chondrites such as bm 002 and bm 003 which may be paired palo verde mine and bm 005 to confidently pair such meteorites often requires thorough petrographic examination mineral chemical analyses and terrestrial ages we estimate that 50 10 of the larger specimens in this area are paired yielding a relatively high value of approximately 2 3 2 9 distinct meteorites km 2 the meteorite flux estimated for franconia area is higher than the flux inferred from contemporary fireball data for larger masses we suggest that one large h3 6 meteoroid fell in the area most likely that of buck mountains wash approximately 4 kyr ago which produced an elliptical strewn field with masses generally increasing toward one end and which raised the meteorite productivity in the recovery area

weathering of meteorites from oman correlation of chemical and mineralogical weathering proxies with 14c terrestrial ages and the influence of soil chemistry fifty four fragments of ordinary chondrites from 50 finds representing all searched areas in central oman and all weathering stages were selected to compare the physical chemical and mineralogical effect of terrestrial weathering with 14c terrestrial ages 14c ages range from 2 0 to 49 kyr with a median value of 17 9 kyr the peak of the age range which is between 10 20 kyr falls in an arid climate period a comparison of the chemical composition of omani chondrites with literature data for unweathered h and l chondrites demonstrates a strong enrichment in sr and ba and depletion in s during weathering water contents in h chondrites increase with terrestrial age whereas l chondrites show a rapid initial increase followed by nearly constant water content correlating sr ba and h2o with age indicates two absorption trends i an initial alteration within the first 20 kyr dominated by h2o uptake mainly reflecting fe ni metal alteration and ii a second baand sr dominated stage correlated with slower and less systematic weathering of troilite that starts after h2o reaches 2 wt sulfur released from troilite partly combines with ba and sr to form sulfate minerals other parameters correlated with 14c age are degree of weathering color of powdered meteorites and the ni fe ratio chemical analyses of 145 soils show a high degree of homogeneity over the entire interior oman desert indicating large scale mixing by wind soil samples collected from beneath meteorite finds typically are enriched in ni and co confirming mobilization from the meteorites high cr and ni concentrations in reference soil samples which decrease from ne to sw are due to detrital material from ultramafic rocks of the oman mountains

terrestrial ages of ordinary chondrites from the lewis cliff stranding area east antarctica abstract we determined terrestrial ages of ordinary chondrites from the lewis cliff stranding area east antarctica on the basis of the concentrations of cosmogenic 10be t 1 51 ma 26al t 0 705 ma and 36cl t 0 301 ma after an initial 26al ray survey of 91 meteorites suggested that many have terrestrial ages 0 1 ma we selected 62 meteorites for 10be and 26al measurements by accelerator mass spectrometry ams and measured 36cl in twelve of those low terrestrial ages 2 ma welten et al 1997 our major conclusions are 1 the lewis cliff h chondrites show similar ages to those from the allan hills icefields but the l chondrites are about a factor of 2 younger than those from allan hills which indicates that lewis cliff is a younger stranding area 2 the terrestrial age distributions at different parts of the lewis cliff stranding area generally agree with simple meteorite concentration models although differences in weathering rate may also play a role 3 we confirm that meteorites with natural thermoluminescence tl levels 80 krad are associated with low terrestrial ages benoit et al 1992 but conclude that natural tl levels 80 krad can not be used to calculate the terrestrial age of a meteorite natural tl levels do seem useful to estimate relative terrestrial ages of large groups of meteorites and to determine differences in the surface exposure age of paired meteorite fragments 4 of the 62 meteorites measured with ams 31 were assigned to 11 different pairing groups mainly on the basis of their cosmogenic nuclide record the meteorites are estimated to represent between 42 and 52 distinct falls

terrestrial ages of meteorites from the nullarbor region australia based on 14c and 14c 10be measurements we have investigated the terrestrial ages or residence times of 78 meteorites representing 73 discrete falls recovered in western australia and one from south australia using both 14c measurements and also 14c 10be the samples studied included two ureilites one ck and one el chondrite we have included 10be measurements from 30 meteorites including some meteorites for which the 14c terrestrial age was previously determined we find that the 14c 10be terrestrial ages are more precise than 14c alone as we can correct for shielding effects in general the two different age determinations age by 14c 10be are precise to 0 5 1 ka and 14c alone within 1 2 ka however measurement of the 14c age alone gives good agreement with the 14c 10be for most samples the study of the terrestrial ages of meteorites gives us useful information concerning the storage and weathering of meteorites and the study of fall times and terrestrial age we have compared the terrestrial ages to weathering degree of oxidation estimated from mossbauer studies and d17o in this study we found that weathering is not well correlated with terrestrial age for nullarbor meteorites however there is a good correlation between degree of oxidation and d17o the implications for the study of terrestrial ages and weathering from other desert environments will be discussed

terrestrial weathering of antarctic stone meteorites formation of mg carbonates on ordinary chondrites abstract white efflorescences of weathering origin occur superposed on fusion crusts or along fractures in the interiors of approximately 5 of all meteorites in the us antarctic collection efflorescences from equilibrated ordinary chondrites consist of the hydrous mg carbonates nesquehonite hydromagnesite x ray diffraction and scanning electron microscope studies of efflorescences from lew 85320 h5 show abundant elongate prismatic crystals of nesquehonite idiomorphic not pseudomorphous after lansfordite with minor local encrustations of hydromagnesite abundances of na k ca and rb in efflorescences from lew 85320 suggest that the observed contents of these elements would require only modest fractionation of chondritic composition whereas extensive fractionation would be required to derive the observed cation ratios from terrestrial sea salts therefore cations in evaporite minerals on antarctic meteorites are most likely not products of contamination by terrestrial marine salts the mg in the efflorescences probably originated from weathering of meteoritic olivine other cations in the efflorescences are also of meteoritic provenance thermodynamic analysis of the reaction forsterite water carbon dioxide nesquehonite silica at antarctic temperatures and pco 2 indicates spontaneity for all water activities greater than 0 65 compatible with the presence of liquid water as brines and or thin films

meteorites found on misfits flat dry lake nevada meteorites have been found on the small misfits flat dry lakebed near stagecoach nevada 119 382w 39 348n since the first find on sept 22 2013 a total of 58 stones of weathering stage w2 3 with a combined mass of 339 g have been collected in 19 visits to the area this small 3 3 3 6 km lakebed is now a newly designated dense collection area dca most meteorites were found in a small 350 180 m area along the north shore and most are fragments of several broken individual stones three of these fragments were classified as an ll4 5 of shock stage s2 now named misfits flat 001 one of which stone mf33 fell 8 1 1 3 ka ago based on the 14c terrestrial age assuming it came from a 20 80 cm diameter meteoroid in addition a small darkly crusted meteorite mf34 now named misfits flat 002 was found 820 m wsw from the main mass this meteorite is classified as an ll5 ordinary chondrite with shock stage s4 5 the meteorite is saturated in 14c at 63 dpm kg 1 suggesting it originated from the center of a 0 5 m diameter meteoroid or deep inside a 1 0 m meteoroid less than 300 yr ago accounts exist of a fireball seen at 13 15 ut on march 2 1895 that are consistent with the find location of misfits flat 002

tectonic control on sediment accretion and subduction off south central chile implications for coseismic rupture processes of the 1960 and 2010 megathrust earthquakes based on a compilation of published and new seismic refraction and multichannel seismic reflection data along the south central chile margin 33 46 s we study the processes of sediment accretion and subduction and their implications on megathrust seismicity in terms of the frontal accretionary prism fap size the marine south central chile fore arc can be divided in two main segments 1 the maule segment south of the juan fernandez ridge and north of the mocha block characterized by a relative large fap 20 40 km wide and 2 the chiloe segment south of the mocha block and north of the nazca antarctic south america plates junction characterized by a small fap 10 km wide in addition the maule and chiloe segments correlate with a thin 1 km thick and thick 1 5 km thick subduction channel respectively the mocha block lies between 37 5 and 40 s and is configured by the chile trench mocha and valdivia fracture zones this region separates young 0 25 ma oceanic lithosphere in the south from old 30 35 ma oceanic lithosphere in the north and it represents a fundamental tectonic boundary separating two different styles of sediment accretion and subduction respectively a process responsible for this segmentation could be related to differences in initial angles of subduction which in turn depend on the amplitude of the down deflected oceanic lithosphere under trench sediment loading on the other hand a small fap along the chiloe segment is coincident with the rupture area of the trans pacific tsunamigenic 1960 earthquake mw 9 5 while a relatively large fap along the maule segment is coincident with the rupture area of the 2010 earthquake mw 8 8 differences in earthquake and tsunami magnitudes between these events can be explained in terms of the fap size along the chiloe and maule segments that control the location of the updip limit of the seismogenic zone the rupture area of the 1960 event also correlates with a thick subduction channel chiloe segment that may provide enough smoothness at the subduction interface allowing long lateral earthquake rupture propagation

meteorite and meteoroid new comprehensive definitions abstract meteorites have traditionally been defined as solid objects that have fallen to earth from space this definition however is no longer adequate in recent decades man made objects have fallen to earth from space meteorites have been identified on the moon and mars and small interplanetary objects have impacted orbiting spacecraft taking these facts and other potential complications into consideration we offer new comprehensive definitions of the terms meteorite meteoroid and their smaller counterparts a meteoroid is a 10 m to 1 m size natural solid object moving in interplanetary space a micrometeoroid is a meteoroid 10 m to 2 mm in size a meteorite is a natural solid object larger than 10 m in size derived from a celestial body that was transported by natural means from the body on which it formed to a region outside the dominant gravitational influence of that body and that later collided with a natural or artificial body larger than itself even if it is the same body from which it was launched weathering and other secondary processes do not affect an object s status as a meteorite as long as something recognizable remains of its original minerals or structure an object loses its status as a meteorite if it is incorporated into a larger rock that becomes a meteorite itself a micrometeorite is a meteorite between 10 m and 2 mm in size meteorite a solid substance or body falling from the high regions of the atmosphere craig 1849 a mass of stone and iron that ha s been directly observed to have fallen down to the earth s surface translated from cohen 1894 a solid bod y which came to the earth from space farrington 1915 a mass of solid matter too small to be considered an asteroid either traveling through space as an unattached unit or having landed on the earth and still retaining its identity nininger 1933 a meteoroid which has reached the surface of the earth without being vaporized 1958 international astronomical union iau definition quoted by millman 1961 a solid body which has arrived on the earth from outer space mason 1962 a solid bod y which reach es the earth or the moon mars etc from interplanetary space and is large enough to survive passage through the earth s or mars etc atmosphere gomes and keil 1980 a meteoroid that survive s passage through the atmosphere and fall s to earth burke 1986 a recovered fragment of a meteoroid that has survived transit through the earth s atmosphere mcsween 1987 a solid bod y of extraterrestrial material that penetrate s the atmosphere and reach es the earth s surface krot et al 2003

exposure history and terrestrial ages of ordinary chondrites from the dar al gani region libya we measured the concentrations of noble gases in 32 ordinary chondrites from the dar al gani dag region libya as well as concentrations of the cosmogenic radionuclides 14c 10be 26al 36cl and 41ca in 18 of these samples although the trapped noble gases in five dag samples show ratios typical of solar or planetary gases in all other dag samples they are dominated by atmospheric contamination which increases with the degree of weathering cosmic ray exposure cre ages of dag chondrites range from 1 myr to 53 myr the cre age distribution of 10 dag l chondrites shows a cluster around 40 myr due to four members of a large l6 chondrite shower the cre age distribution of 19 dag h chondrites shows only three ages coinciding with the main h chondrite peak at 7 myr while seven ages are 5 myr two of these h chondrites with short cre ages dag 904 and 908 show evidence of a complex exposure history five of the h chondrites show evidence of high shielding conditions including low 22ne 21ne ratios and large contributions of neutron capture 36cl and 41ca these samples represent fragments of two or more large pre atmospheric objects which supports the hypothesis that the high h l chondrite ratio at dag is due to one or more large unrecognized showers the 14c concentrations correspond to terrestrial ages 35 kyr similar to terrestrial ages of chondrites from other regions in the sahara but younger than two dag achondrites despite the loss of cosmogenic 36cl and 41ca during oxidation of metal and troilite concentrations of 36cl and 41ca in the silicates are also consistent with 14c ages 35 kyr the only exception is dag 343 h4 which has a 41ca terrestrial age of 150 40 kyr this old age shows that not only iron meteorites and achondrites but also chondrites can survive the hot desert environment for more than 50 kyr a possible explanation is that older meteorites were covered by soils during wetter periods and were recently exhumed by removal of these soils due to deflation during more arid periods such as the current one which started 3000 years ago finally based on the 26al 21ne and 10be 21ne systematics in 16 dag meteorites we derived more reliable estimates of the 10be 21ne production rate ratio which seems more sensitive to shielding than was predicted by the semi empirical model of graf et al 1990 but less sensitive than was predicted by the purely physical model of leya et al 2000

heterogeneous plate locking in the south central chile subduction zone building up the next great earthquake abstract we use global positioning system gps velocities and kinematic finite element models fe models to infer the state of locking between the converging nazca and south america plates in south central chile 36 s 46 s and to evaluate its spatial and temporal variability gps velocities provide information on earthquake cycle deformation over the last decade in areas affected by the megathrust events of 1960 m w 9 5 and 2010 m w 8 8 our data confirm that a change in surface velocity patterns of these two seismotectonic segments can be related to their different stages in the seismic cycle accordingly the northern 2010 segment was in a final stage of interseismic loading whereas the southern 1960 segment is still in a postseismic stage and undergoes a prolonged viscoelastic mantle relaxation after correcting the signals for mantle relaxation the residual gps velocity pattern suggests that the plate interface accumulates slip deficit in a spatially and presumably temporally variable way towards the next great event though some similarity exist between locking and 1960 coseismic slip extrapolating the current decadal scale slip deficit accumulation towards the 300 yr recurrence times of giant events here does neither yield the slip distribution nor the moment magnitude of the 1960 earthquake this suggests that either the locking pattern is evolving in time to reconcile a slip deficit distribution similar to the 1960 earthquake or that some asperities are not persistent over multiple events the accumulated moment deficit since 1960 suggests that highly locked patches in the 1960 segment are already capable of producing a m 8 event if triggered to fail by stress transfer from the 2010 event

the flux of meteorites to the earth and weathering in hot desert ordinary chondrite finds abstract the abundance of ferric iron produced by weathering in ordinary chondrites collected from hot desert regions is related to their terrestrial age enabling a variety of processes involved in meteorite weathering to be deduced fe0 fe2 fe3 content was measured quantitatively by 57fe mossbauer spectroscopy it is observed that meteorites from different regions are oxidised at different rates we also propose the tentative hypothesis that one source of scatter in total oxidation versus terrestrial age for a region is climatic change a mechanism to explain the variable response to climatic conditions involves the high initial porosity of samples being reduced as ferric oxides and other alteration products are produced reliable recovery data from a meteorite accumulation site roosevelt county new mexico usa and a quantitative measure of weathering and terrestrial age permit an estimate of the flux of meteorites to the earth s surface having established a decay constant for meteorites and accounting for the area of searches and pairing we estimate an accumulation rate of 159 falls of mass greater than 20 g per 106 km2 per yr this calculation is distinct from but in broad agreement with previous estimates from camera observations suggesting that the accumulation rate of meteorite falls to the earth s surface has remained essentially unchanged over the last 50 000 years at between 59 and 159 falls of mass exceeding 20 g per 106 km2 per yr the error for both methods is approximately a factor of 2

corrosion of fe ni alloys by cl containing akaganeite beta feooh the antarctic meteorite case a suite of 12 iron and 8 stony meteorites from various environments and locations in antarctica was studied representing a range of compositions metallographic structures and degrees of weathering polished sections of meteoritic metal with adhering corrosion products were examined microscopically with the electron microprobe and sem and were used as samples for x ray diffraction examination the major corrosion products are cl containing akaganeite up to 5wtper thousand cl and goethite with minor amounts of lepidocrocite and maghemite cl is not native to the meteorites but owing to the electrochemical nature of the corrosion of fe ni alloys is attracted from the snow and ice or rocky soil environment that contains low amounts of cl akaganeite precipitates near the reaction front incorporating cl ions into ion exchange sites where they may be retained made available for further depassivating corrosive action or become flushed from the system with time and distance from the reaction surface akaganeite ages and transforms to mainly goethite and maghemite it is again argued that lawrencite fecl 2 is not a mineral in meteorites in the stormy antarctic wind blown terrestrial particles may become attached to the weathering products on the meteorite and in time themselves decompose delivering terrestrial ions to the meteorite corrosion system the ions may move a significant distance from the surface and in particular cl may be found along almost invisible cracks in the deep interior trace element work and age determinations 36 cl should take this problem into account

active faulting and heterogeneous deformation across a megathrust segment boundary from gps data south central chile 36 39 s 1 this study focuses on the present day deformation mechanisms of the south central chile margin at the transition zone between two megathrust earthquake segments defined from historical data the valdivia and concepcion sectors new gps data and finite element models with complex geometries constrained by geophysical data are presented to gain insight into forearc kinematics and to address the role of upper plate faults on contemporary deformation gps vectors are heterogeneously distributed in two domains that follow these two earthquake segments we find that models which simulate only interseismic locking on the plate interface fail to reproduce surface deformation in the entire study area in the concepcion domain models that include a crustal scale fault in the upper plate better reproduce the gps observations in the valdivia domain gps data show regional scale vertical axis rotations which could reflect postseismic deformation processes at the edge of the mw 9 5 earthquake that ruptured in 1960 and or activity of another crustal fault related to motion of a forearc sliver our study suggests that upper plate faults in addition to earthquake cycle transients may exert an important control on the surface velocity of subduction zone forearcs

teleseismic inversion for rupture process of the 27 february 2010 chile mw 8 8 earthquake the 27 february 2010 chile m w 8 8 earthquake is the fifth largest earthquake to strike during the age of seismological instrumentation the faulting geometry slip distribution seismic moment and moment rate function are estimated from broadband teleseismic p sh and rayleigh wave signals we explore some of the trade offs in the rupture process estimation due to model parameterizations limited teleseismic sampling of seismic phase velocities and uncertainty in fault geometry the average slip over the 81 500 km 2 rupture area is about 5 m with slip concentrations down dip up dip and southwest and up dip and north of the hypocenter relatively little slip occurred up dip offshore of the hypocenter the average rupture velocity is 2 0 2 5 km s

terrestrial 81kr kr ages of antarctic meteorites the production rate of 38ar in meteorites p 38 has been determined as a function of the sample s chemical composition from 81kr kr exposure ages of four eucrite falls the cosmogenic 78kr 83kr ratio is used to estimate the shielding dependence of p 38 from the true 38ar exposure ages and the apparent 81kr kr exposure ages of nine antarctic eucrite finds terrestrial ages are calculated they range from about 3 105a pecora escarpment 82502 to very recent falls thiel mountains 82502 polymict eucrites from the allan hills a78132 a79017 and a81009 have within the limits of error the same exposure age 15 2 106a and the same terrestrial age 1 1 105a this is taken as strong evidence that these meteorites are fragments of the same fall a similar case are the elephant moraine polymict eucrites a79005 a79006 and 82600 with an exposure age of 26 106a and a terrestrial age of 1 8 105a eeta79004 may be different from this group because its exposure age and terrestrial age are 21 106a and 2 5 105a respectively the distribution of terrestrial ages of allan hills meteorites is discussed meteorites from this blue ice field have two sources directly deposited falls and meteorites transported to the allan hills inside the moving antarctic ice sheet during the surface residence time meteorites decompose due to weathering processes the weathering half life is about 1 6 105a from the different age distributions of allan hills and yamato meteorites it is concluded that meteorite concentrations of different antarctic ice fields need different explanations

porosity and density of ordinary chondrites clues to the formation of friable and porous ordinary chondrites densities and porosities of meteorites are physical properties that can be used to infer characteristics of asteroid interiors we report density and porosity measurements of 42 pieces of 30 ordinary chondrites and provide a quantification of the errors of the gas pycnometer method used in this study based on our measurements we find that no significant correlation exists between porosity and petrologic grade chemical group sample mass bulk and grain density or shock level to investigate variations in porosity and density between pieces of a meteorite we examined stones from two showers holbrook and pultusk examination of nine samples of holbrook suggests relative homogeneity in porosity and density between pieces of this shower measurements of three samples of pultusk show homogeneity in bulk density in contrast to wilkison and robinson 2000 a study that reported significant variations in bulk density between 11 samples of pultusk finally examination of two friable ordinary chondrites bjurbole and allegan reveal variability in friability and porosity among pieces of the same fall we suggest that friable ordinary chondrites may have formed in a regolith or fault zone of an asteroid

an impact origin for the foliation of chondrites abstract the origin of the foliation of ordinary chondrites is addressed through the study of the anisotropy of magnetic susceptibility ams of these meteorites based on a database of 295 different meteorites including 35 achondrites hed and snc ams is a reliable proxy for preferred orientation in ordinary chondrites moreover the intensity of magnetic anisotropy is constant over a given chondrite the intensity of l chondrite petrofabric evaluated by means of ams measurements and shock stage determined independently by microscopic observation of shock features in silicates appear to be positively correlated this suggests that the oblate petrofabric in l chondrites is shock induced the inverse correlation between porosity and ams intensity suggests that hypervelocity impacts compacted and lithified an originally loose material causing the deformation of metallic fe ni grains ll and h ordinary chondrites cannot be studied as easily as l chondrites tetrataenite in ll chondrites affects the ams in an unpredictable way and shape anisotropy due to the strong susceptibility of h chondrites imposes strong constraints on sample shape our limited dataset for carbonaceous chondrites is compatible with a shock induced foliation model the very low degrees of ams in rumuruti chondrites testify that surprisingly the easily deformable fe sulfides in these chondrites show almost no deformation suggesting that sulfidation is a secondary phenomenon that occurred after the major impacts on the rumuruti parent body the weak magnetic anisotropy of martian meteorites implies that no significant macroscopic deformation took place during the severe impacts suffered by these rocks which is explained by the weak initial porosity and high compressive strength of these igneous products

an interdisciplinary study of weathering effects in ordinary chondrites from the acfer region algeria weathering effects on meteorite finds from the acfer region were studied by various analytical techniques and in dependence on the depth of sampling in thin sections of weathered meteorites weathering effects usually decrease from the outside to the interior of the meteorite the results of evolved gas analysis indicate that variation in weathering between surface and core is not significant in respect to the formation of fe oxyhydroxides the secondary alteration effects in the noble gases are distributed unevenly throughout the specimens as seen in the nonsystematic differences observed for the heavy noble gases chemical analyses show significant enrichment of ba and sr in the outer parts of the weathered samples due to element contamination through aqueous solution iron ni and co are partly flushed from the system as the metal oxidation proceeds oxygen isotopes show increases in d180 and d17o with increasing terrestrial age for a set of h3 chondrites the degree of weathering determined from the water content was correlated with terrestrial ages and is discussed with respect to possible weathering mechanisms

petrogenesis of lunar highlands meteorites dhofar 025 dhofar 081 dar al gani 262 and dar al gani 400 the petrogenesis of four lunar highlands meteorites dhofar 025 dho 025 dhofar 081 dho 081 dar al gani 262 dag 262 and dar al gani 400 dag 400 were studied for dho 025 measured oxygen isotopic values and fe mn ratios for mafic minerals provide corroboratory evidence that it originated on the moon similarly fe mn ratios in the mafic minerals of dho 081 indicate lunar origin lithologies in dho 025 and dho 081 include lithic clasts granulites and mineral fragments a large number of lithic clasts have plagioclase an and coexisting mafic mineral mg that plot within the gap separating ferroan anorthosite suite fan and high magnesium suite hms rocks this is consistent with whole rock ti sm ratios for dho 025 dho 081 and dag 262 which are also intermediate compared to fan and hms lithologies although ion microprobe analyses performed on dho 025 dho 081 dag 262 and dag 400 clasts and minerals show far stronger fan affinities than whole rock data suggest most clasts indicate admixture of 12 hms component based on geochemical modeling in addition coexisting plagioclase pyroxene ree concentration ratios in several clasts were compared to experimentally determined plagioclase pyroxene ree distribution coefficient ratios two dho 025 clasts have concordant plagioclase pyroxene profiles indicating that equilibrium between these minerals has been sustained despite shock metamorphism one clast has an intermediate fan hms composition these lunar meteorites appear to represent a type of highland terrain that differs substantially from the kreep signatured impact breccias that dominate the lunar database from remote sensing data it is inferred that the lunar far side appears to have appropriate geochemical signatures and lithologies to be the source regions for these rocks although the near side cannot be completely excluded as a possibility if these rocks are indeed from the far side their geochemical characteristics may have far reaching implications for our current scientific understanding of the moon

effect of hot desert weathering on the bulk rock iron isotope composition of l6 and h5 ordinary chondrites abstract although iron isotopes are increasingly used for meteorites studies no attempt has been made to evaluate the effect of terrestrial weathering on this isotopic tracer we have thus conducted a petrographic chemical and iron isotopic study of equilibrated ordinary chondrites oc recovered from hot moroccan and algerian saharan deserts environment as previously noticed we observe that terrestrial desertic weathering is characterized by the oxidation of fe ni metal fe0 sulfide and fe2 occurring in olivine and pyroxene it produces fe oxides and oxyhydroxides that partially replace metal sulfide grains and also fill fractures the bulk chemical compositions of the ordinary chondrites studied show a strong sr and ba enrichment and a s depletion during weathering bulk meteoritic iron isotope compositions are well correlated with the degree of weathering and s sr and ba contents most weathered chondrites display the heaviest isotopic composition by up to 0 1 which is of similar magnitude to the isotopic variations resulting from meteorite parent bodies formation and evolution this is probably due to the release of isotopically light fe2 to waters on the earth s surface hence when subtle fe isotopic effects have to be studied in chondrites meteorites with weathering grade above w2 should be avoided

interannual variability in the hydrography of the norwegian atlantic current frontal versus advective response to atmospheric forcing 1 the warm and saline inflow of the north atlantic current to the nordic seas is highly relevant for the region and the global climate north of the greenland scotland ridge the norwegian atlantic current consists of two 40 60 km wide branches situated at the slope and 150 200 km offshore respectively to interpret changes in these branches in terms of climate variability in the northern north atlantic it is important to understand their spatiotemporal response to both atmospheric forcing and advection we analyzed three decades of synoptic hydrographic observations of the branches variability with particular focus on the response to the north atlantic oscillation nao and related wind stress curl changes in the nordic seas to do so we separated the effect of fluctuating position and thickness of the branches from the variability in temperature and salinity in the spatially fluctuating cores as a rapid response to the nao we find a deflection of both branches toward the coast which is consistent with an enhanced basin wide cyclonic circulation while the immediate correlation between hydrographic properties and the nao is weak we find a significant negative correlation when the nao leads temperature and salinity by 4 6 years we attribute the overall delayed response to the advection of anomalies generated in the northwestern north atlantic through nao induced air sea interaction and changes in the position of the subpolar front

kinematic constraints on intra arc shear and strain partitioning in the southern andes between 38 s and 42 s latitude 1 on the basis of structural field work fault kinematic analysis and the analysis of digital imagery we describe the northern part of the southern andean intra arc liquine ofqui fault zone lofz as an sc like fault zone system accommodating part of the nazca south american plate convergence obliquity kinematic modeling suggests that the lofz accommodated 124 24 21 km of dextral displacement between 40 s and 42 s and 67 13 11 km between 38 s and 40 s since the pliocene associated vertical axis rotations are 31 4 clockwise and 9 1 counterclockwise along synthetic and antithetic faults respectively mean pliocene to recent shear rates along the lofz decrease northward from 32 6 mm yr to 13 3 mm yr compatible with partitioning of half of the convergence obliquity into the intra arc zone north of 40 s and complete partitioning to the south the displacement gradient along the intra arc zone results in margin parallel shortening of the fore arc

laboratory experiments on the weathering of iron meteorites and carbonaceous chondrites by iron oxidizing bacteria batch culture experiments were performed to investigate the weathering of meteoritic material by iron oxidizing bacteria the aerobic acidophilic iron oxidizer a ferrooxidans was capable of oxidizing iron from both carbonaceous chondrites murchison and cold bokkeveld and iron meteorites york and casas grandes preliminary iron isotope results clearly show contrasted iron pathways during oxidation with and without bacteria suggesting that a biological role in meteorite weathering could be distinguished isotopically anaerobic iron oxidizers growing under ph neutral conditions oxidized iron from iron meteorites these results show that rapid biologically mediated alteration of extraterrestrial materials can occur in both aerobic and anaerobic environments these results also demonstrate that iron can act as a source of energy for microorganisms from both iron and carbonaceous chondrites in aerobic and anaerobic conditions with implications for life on the early earth and the possible use of microorganisms to extract minerals from asteroidal material

chemical alteration and ree mobilization in meteorites from hot and cold deserts the effects of terrestrial weathering on ree mobilization are evaluated for a variety of uncommon meteorites found in antarctica and in hot deserts the meteorites analyzed include 7 non cumulate eucrites 10 shergottites 3 nakhlites 2 lunar meteorites 4 angrites 10 acapulcoites 1 winonaite and 1 brachinite in situ concentration measurements of lanthanides and selected other minor and trace elements were made on individual grains by secondary ion mass spectrometry sims in antarctic meteorites oxidation converts ce 3 to ce 4 which is less soluble than the trivalent ree resulting in ce anomalies the mineral most affected is low ca pyroxene however not all grains of a given mineral are and distinct analyses of a single grain can even yield ree patterns with and without ce anomalies the effect is most pronounced for antarctic eucrites in which ce anomalies are observed not only in individual minerals but also in whole rock samples although ce anomalies are observed in meteorites from hot deserts as well the most characteristic signs of chemical alteration in this environment are a lree enrichment with a typical crustal signature as well as sr ba and u contaminations these can modify the whole rock ree patterns and disturb the isotope systematics used to date these objects the lree contamination is highly heterogeneous affecting some grains and not others of a given mineral mainly olivine and low ca pyroxene the two minerals with the lowest ree concentrations the major conduit for ree movement is through shock induced cracks and defects and the highest levels of contamination are found in altered material filling such veins and cracks meteorites that experienced low shock levels and those that are highly recrystallized are the least altered copyright 2003 elsevier ltd

pleistocene climatic change in southern australia and its effect on speleothem deposition in some nullarbor caves activity ratios of 234u 238u 230th 234u and 230th 232th have been determined for calcite gypsum and halite speleothems from caves of the nullarbor plain mostly in the area n and nw of mundrabilla station for the purpose of u series dating all calcite speleothems contain adequate amounts of uranium for dating but some show an excess of 230th stratigraphic relationships indicate that there were at least three phases of calcium carbonate deposition in the nullarbor caves the calcite samples with one possible exception have ages in excess of ca 400000 yrs bp this suggests that no significant amounts of calcium carbonate deposition have taken place during the last 400ka at present active deposition of speleothems is restricted almost entirely to gypsum and halite the only gypsum speleothem dated was found to have a finite age of ca 185 ka six dates on a small halite speleothem containing insect and arachnid remains indicate that it formed rapidly during holocene time

the densest meteorite collection area in hot deserts the san juan meteorite field atacama desert chile we describe the geological morphological and climatic setting of the san juan meteorite collection area in the central depression of the atacama desert chile our recovery activities yielded 48 meteorites corresponding to a minimum of 36 different falls within a 3 88 km 2 area the recovery density is in the range 9 12 falls km 2 depending on pairing making it the densest among meteorite collection areas in hot deserts this high meteorite concentration is linked to the long standing hyperaridity of the area the stability of the surface pebbles ma and very low erosion rates of surface pebbles approximately 30 cm ma 1 maximum the san juan meteorite population is characterized by old terrestrial ages that range from zero to beyond 40 ka and limited weathering compared with other dense collection areas in hot desert chemical weathering in san juan is slow and mainly controlled by the initial porosity of meteorites as in the antarctic and other hot deserts there is an overabundance of h chondrites and a shortage of ll chondrites compared with the modern falls population suggesting a recent few ka change in the composition of the meteorite flux to earth

a study of ordinary chondrites by mossbauer spectroscopy with high velocity resolution an improvement in the velocity resolution and quality of mssbauer spectra has been applied to a group of ordinary chondrites this improvement permitted us to carry out a more detailed study of the iron bearing phases in these samples than has previously been possible mssbauer spectra of 11 ordinary chondrites of l and h chemical groups were measured using 4096 channels and presented for further analysis in 1024 channels subspectra of the metal grains of several chondrites demonstrated the presence of at least two magnetic sextets related to the main fe ni co phases moreover mssbauer study of extracted metal grains from tsarev l5 revealed three sextets and one singlet spectral components related to various fe ni co fe ni co 2 fe ni co and fe ni co phases each subspectrum of olivine and pyroxene in mssbauer spectra of ordinary chondrites was fitted by superposition of two quadrupole doublets related to m1 and m2 sites in minerals for the first time an analysis of relative areas and mssbauer hyperfine parameters was performed and some differences for l and h chondrites as well as for m1 and m2 sites were observed mssbauer parameters of troilite and oxidized iron were analyzed in contrast to a previous study with 512 channel spectra the presence of oxidized iron was found in all chondrites

meteorites from the united arab emirates description weathering and terrestrial ages we report on the first meteorite search campaign in the united arab emirates uae the geology and proximity of our search region suggest that it is the north western extension of the oman meteorite fields we found 26 ordinary chondrites bringing the total number of official meteorites from the uae to 28 the campaign was organized and conducted in close cooperation with the uae government and the main masses of the meteorites remained in the country where they will become part of an exhibition the bulk composition of five meteorite and three soil samples indicates an uptake of u mo sr ba li and pb from the soil into the meteorites during terrestrial weathering terrestrial ages determined from 14c decay of 21 meteorites range from recent falls to 24 4 ka with two meteorites having 37 ka and approximately 39 ka respectively weak correlations between weathering degree meteorite bulk chemical composition and terrestrial age suggest highly localized weathering conditions possibly related to abundant occurrences of sabkhas in the search region

climate and rock weathering a study of terrestrial age dated ordinary chondritic meteorites from hot desert regions abstract ordinary chondrites oc recovered from the desert areas of roosevelt county new mexico the nullarbor region of western australia and the algerian and libyan sahara for which 14c terrestrial ages have been determined were examined by 57fe mossbauer spectroscopy oc were chosen as a standard sample to investigate weathering processes as their well constrained trace and bulk element chemistry normative mineralogy and isotopic composition define a known pre weathering starting composition given that terrestrial ages are known it is possible to compare initially very similar samples that have been subsequently weathered in a range of climatic regimes from the present day to 44 ka bp in addition recently fallen equilibrated oc contain iron only as fe0 and fe2 thus the abundance of ferric iron is directly related to the level of terrestrial weathering mossbauer spectroscopy identifies two broad types of ferric alteration paramagnetic phases akaganeite lepidocrocite and goethite and magnetically ordered principally magnetite and maghemite oc finds show a range in the percentage of total fe existing as fe3 from zero to over 80 however oxidation is comparable between fragments of the same oc separated since their time of fall i e paired meteorites our results indicate several features of meteorite weathering that may result from climatic or geomorphologic conditions at the accumulation site 1 saharan samples are overall less weathered than non saharan samples which may be related to the relatively recent age ca 20 ka of the saharan accumulation surface 2 broad differences between sites in the rate of weathering arising from regional differences in climate 3 consistent differences in the weathering products between samples that fell during humid periods and those that fell during more arid periods those falling during humid periods contain a higher proportion of magnetically ordered ferric oxides 4 one region the nullarbor that shows a variation in the total amount of ferric species that closely matches the climatic record for this area of australia for the last 30 ka points 3 and 4 may be related to the identification of a rapid initial weathering phase the majority of weathering occurs in the first few hundred years after fall followed by passivation of weathering by porosity reduction porosity reduction and the associated restriction in the ability of water to penetrate the sample appears to be the mechanism whereby a weathering assemblage formed during the brief initial period of oxidation is preserved through subsequent climatic cycles over the terrestrial lifetime of the sample

the 410 000 year terrestrial age of eucrite rio cuarto 001 we have measured a surprisingly long terrestrial age of 410 000 20 000 45 000 years 410 20 45 ka for basaltic eucrite ro cuarto 001 using accelerator mass spectrometry of 26al 36cl and 41ca though many meteorites are known to have survived for tens or hundreds of ka in antarctica or hot deserts the mean annual precipitation of 815 mm in ro cuarto cordoba province argentina makes the long survival of this meteorite remarkable we propose two explanations for the exceptional preservation of ro cuarto 001 first the meteorite contains only trace amounts of metal so the weathering and oxidation of metallic fe which commonly destroys chondrites is ineffective in this case second the meteorite was found in a relatively young deflation basin and may have been exhumed only recently from beneath a protective layer of soil insofar as the survival on earth of ro cuarto 001 is due to environmental factors there may be other meteorites with comparably long terrestrial ages still to be discovered in the vicinity

stony meteorite porosities and densities a review of the data through 2001 in this review we summarize the data published up to december 2001 on the porosity and density of stony meteorites these data were taken from 925 samples of 454 different meteorites by a variety of techniques most meteorites have densities on the order of 3 to 4 g cm 3 with lower densities only for some volatile rich carbonaceous meteorites and higher densities for stony irons for the vast majority of stones porosity data alone cannot distinguish between different meteorite compositions average porosities for most meteorite classes are around 10 though individual samples can range as high as 30 porosity unbrecciated basaltic achondrites appear to be systematically less porous unless vesicles are present the measured density of ordinary chondrites is strongly controlled by the amount of terrestrial weathering the sample has undergone with porosities steadily dropping with exposure to the terrestrial environment a theoretical grain density based on composition can model pre weathered porosities the average model porosity for h and ll chondrites is 10 while l chondrite model porosities average only 6 a statistically significant difference

weathering of ordinary chondrites from oman correlation of weathering parameters with 14c terrestrial ages and a refined weathering scale we have investigated 128 14c dated ordinary chondrites from oman for macroscopically visible weathering parameters for thin section based weathering degrees and for chemical weathering parameters as analyzed with handheld x ray fluorescence these 128 14c dated meteorites show an abundance maximum of terrestrial age at 19 9 ka with a mean of 21 0 ka and a pronounced lack of samples between 0 and 10 ka the weathering degree is evaluated in thin section using a refined weathering scale based on the current w0 to w6 classification of wlotzka 1993 with five newly included intermediate steps resulting in a total of nine formerly six steps we find significant correlations between terrestrial ages and several macroscopic weathering parameters the correlation of various chemical parameters including sr and ba with terrestrial age is not very pronounced the microscopic weathering degree of metal and sulfides with newly added intermediate steps shows the best correlation with 14c terrestrial ages demonstrating the significance of the newly defined weathering steps we demonstrate that the observed 14c terrestrial age distribution can be modeled from the abundance of meteorites with different weathering degrees allowing the evaluation of an age frequency distribution for the whole meteorite population

distribution of terrestrial age and petrologic type of meteorites from western libya abstract a group of 54 meteorites have been recovered from daraj western libya after assessment of pairing of samples using petrologic criteria 14 c terrestrial ages were obtained on 13 samples selected from 9 different fall events eleven of the ages range from 3500 to 7600 years with only two samples having ages in excess of 10 000 years the cut off in ages may be related to the timing of climatic changes in the hammadah al hamra

rapid weathering in holbrook an iron 57 mossbauer spectroscopy study samples of holbrook an l6 chondrite that fell in arizona in 1912 were analysed by 57fe mossbauer spectroscopy to determine the proportion of the total fe that had been converted to fe3 by weathering processes although samples recovered in 1912 showed negligible 40 ka a linear rate of weathering is unrealistic rapidly producing very high levels of oxidation in samples with low terrestrial ages however if weathering follows an approximate power law then we can model a rapid initial phase and the levels of oxidation that are more typical in samples with much longer terrestrial residence times recovered from roosevelt county our analysis together with work on terrestrial age dated samples indicates that hot desert weathering of ordinary chondrites is at least a two stage process with an initial rapid phase lasting 500 years before oxidation is passivated

northwest africa 011 a eucritic basalt from a non eucrite parent body we have carried out a detailed petrographic mineralogical and trace element study of northwest africa nwa 011 this meteorite bears many similarities to the eucrites it was initially identified with although oxygen isotopic compositions rule out a genetic relationship like many eucrites nwa 011 crystallized from a source with approximately chondritic proportions of ree although a slightly lree enriched bulk composition with a small positive eu anomaly as well as highly fractionated fe mg ratios and depleted sc abundances korotchantseva et al 2003 suggest that the nwa 011 source experienced some pyroxene and or olivine fractionation thermal metamorphism resulted in homogenization of ree abundances within grains but nwa 011 did not experience the intergrain ree redistribution seen in some highly metamorphosed eucrites despite a similarity in oxygen isotopic compositions nwa 011 does not represent a basaltic partial melt from the acapulcoite lodranite parent body the material from which nwa 011 originated may have been like some ch or cb chondrites members of the cr chondrite clan which are all related through oxygen isotopic compositions the nwa 011 parent body is probably of asteroidal origin possibly the basaltic asteroid 1459 magnya