late glacial stage and holocene tropical ice core records from huascaran peru two ice cores from the col of huascaran in the north central andes of peru contain a paleoclimatic history extending well into the wisconsinan wurm glacial stage and include evidence of the younger dryas cool phase glacial stage conditions at high elevations in the tropics appear to have been as much as 8 to 12 c cooler than today the atmosphere contained about 200 times as much dust and the amazon basin forest cover may have been much less extensive differences in both the oxygen isotope ratio 18o 8 per mil and the deuterium excess 4 5 per mil from the late glacial stage to the holocene are comparable with polar ice core records these data imply that the tropical atlantic was possibly 5 to 6 c cooler during the late glacial stage that the climate was warmest from 8400 to 5200 years before present and that it cooled gradually culminating with the little ice age 200 to 500 years before present a strong warming has dominated the last two centuries

the noble gas concentrations of the martian meteorites grv 99027 and paired nwa 7906 nwa 7907 here we present the isotopic concentrations of he ne ar kr and xe for the three martian meteorites namely grove mountains 99027 grv 99027 northwest africa 7906 nwa 7906 and northwest africa 7907 nwa 7907 the cosmic ray exposure cre age for grv 99027 of 5 7 0 4 ma 1 is consistent with cre ages for other poikilitic basaltic shergottites and suggests that all were ejected in a single event 5 6 ma ago after correcting for an estimated variable sodium concentration the cre ages for nwa 7906 and nwa 7907 of 5 4 0 4 and 4 9 0 4 ma 1 respectively are in good agreement with the cre age of 5 ma favored by cartwright et al 2014 for nwa 7034 the data therefore support the conclusion that all three basaltic regolith breccias are paired the 40ar gas retention age for nwa 7907 of 1 3 ga is in accord with cartwright et al 2014 for nwa 7906 we were unable to determine a 40ar gas retention age the 4he gas retention ages for nwa 7906 and 7907 are in the range of 200 ma and are much shorter than the 40ar gas retention age of nwa 7907 indicating that about 86 88 of the radiogenic 4he has been lost the kr and xe isotopic concentrations in grv 99027 are composed almost exclusively of martian interior mi gases while for nwa 7906 and nwa 7907 they indicate gases from the mi elementally fractionated air and possibly martian atmosphere

tropical climates in the game of two hemispheres revealed by abrupt climatic change the climatically sensitive equatorial regions provide important information for evaluation of the phasing between high and low latitude climate variability a high resolution pollen record from northern brazil demonstrates a significant abrupt and rapid environmental change associated with the northern hemisphere younger dryas temperature reversal this finding is consistent with the model in which the younger dryas had a stronger influence on temperature in the northern hemisphere than south of the equator because of the larger temperature gradient between pole and equator in the northern hemisphere than in the southern hemisphere one consequence of the younger dryas changes would be the location of the intertropical convergence zone in a southern position so that even tropical regions would have been under arctic influence

shock induced melting recrystallization and exsolution in plagioclase from the martian lherzolitic shergottite grv 99027 plagioclase in the martian lherzolitic shergottite grove mountains grv 99027 was shocked melted and recrystallized the recrystallized plagioclase contains lamellae of pyroxene olivine and minor ilmenite 1 m wide both the pyroxene and the olivine inclusions enclosed in plagioclase and grains neighboring the plagioclase were partially melted into plagioclase melt pools the formation of these lamellar inclusions in plagioclase is attributed to exsolution from recrystallizing melt distinct from other martian meteorites grv 99027 contains no maskelynite but does contain recrystallized plagioclase this shows that the meteorite experienced a slower cooling than maskelynite bearing meteorites we suggest that the parent rock of grv 99027 could have been embedded in hot rocks which facilitated a more protracted cooling history

three late quaternary pollen diagrams from southern patagonia and their palaeoecological implications abstract diagrams of fossil pollen in three deposits postdating glacial recession of the last ice age provide an account of late glacial and holocene vegetation and palaeoclimate in southern patagonia sites are mires located along the estrecho de magallanes at punta arenas 53 09 s 70 57 w and puerto del hambre 53 36 s 70 55 w and an intermittent lake some 300 km to the north at torres del paine 50 59 s 72 40 w chronostratigraphy is controlled by 20 radiocarbon dates the oldest site puerto del hambre covering close to 16 000 years charcoal from the sites and carbonate torres del paine as well as tephra layers and an instance of marine incursion puerto del hambre supply additional data of interpretive value accompanying the fossil pollen records is a reference survey of modern pollen fallout from 43 surface sample localities late glacial vegetation during deglaciation consisted mostly of tundra dominated by communities of empetrum acaena gunnera and tubuliflorae compositae under a relatively cold dry climate nothofagus although present in numbers initially at puerto del hambre did not expand until the close of the late glacial at punta arenas expansion of nothofagus was episodic occurring during apparent warmer intervals of the last three millennia of steppe tundra holocene vegetation is depicted at first as a patchwork of nothofagus woodland and steppe subject to climate of relative warmth and limited moisture except at torres del paine where moisture levels were apparently higher than at sites to the south closed nothofagus forest communities subsequently are best developed in the late holocene under a climate with generally cooler wetter parameters fire believed to be caused mostly by palaeoindians has had an important role in shaping vegetation sequences in the holocene formidable however in the development of vegetation are the latitudinal displacements variable intensities of atmospheric conditions caused by shifting storm tracks of the southern westerlies

chronology and petrogenesis of young achondrites shergotty zagami and alha77005 late magmatism on a geologically active planet a study was undertaken to determine the chronology petrogenesis and relationships among the shergottites shergotty and zagami and the unique achondrite alha77005 these meteorites are the product of a variety of complex processes petrogenesis chondrite normalized abundance patterns of shergotty and zagami are very similar and show pronounced depletions of both the light ree la nd and heavy ree dy lu relative to sm gd these characteristic depletions are even more pronounced for alha77005 the light ree depletion is qualitatively consistent with the presence of cumulus pyroxene and or olivine in these meteorites but trace element models show that the parental magmas of all three meteorites were probably also light ree depleted both trace element model calculations and combined rb sr and sm nd isotopic systematics show that the meteorites could not have been co magmatic nor can alha77005 be representative of the source material of the shergottites light ree depletion of the parental magmas also implies light ree depletion of the source material the sm nd systematics of the shergottites require a time averaged sub chondritic light ree enriched sm nd ratio since 4 6 ae ago the sm nd systematics of alha77005 permit a time averaged super chondritic light ree depleted sm nd ratio if its crystallization age is less than tice 0 72 ae chronology rb sr internal isochrons for all three meteorites and a sm nd internal isochron for zagami are concordant at 180 myr 39ar 40ar plateau ages of shergotty and zagami maskelynite are 250 260 myr these ages apparently reflect resetting of these isotopic systems by shock metamorphism which converted the feldspar to maskelynite the concordance of these ages suggests a single shock event during which the meteorites were in close physical proximity the time of this event is most precisely given by the rb sr age of 180 4 myr for zagami the crystallization ages of the meteorites were not precisely determined extreme upper limits are determined by sm nd model ages relative to an eucrite initial 143nd144nd 0 505835 at 4 6 ae ago these model ages for shergotty zagami and alha77005 are 3600 3500 and 2850 myr respectively the sm nd whole rock age of 1340 60 myr for the three meteorites gives the crystallization age if the sm nd ratios of the precursor materials were always the same we consider this 1340 myr age as a best estimate upper limit best estimate lower limits for shergotty and zagami are taken from the average 39ar 40ar ages of 1200 and 900 myr of pyroxene separates the average 39ar 40ar age of a whole rock sample of alha77005 was 1600 myr and can be partitioned between a low temperature feldspar phase and a high temperature olivine pyroxene inclusions phase the average apparent 39ar 40ar age of the low temperature phase is 1050 myr which is chosen as the best estimate lower limit to the age the crystallization ages of shergotty zagami and alha77005 probably lie within the ranges of 1200 1300 900 1300 and 1000 1300 myr respectively the rb sr whole rock age of 4400 400 myr and single stage babi model ages of 4800 5100 myr are interpreted as reflecting differentiation of the parent body at 4600 myr ago the complex geochemical and isotopic evolution recorded by these meteorites suggests a geologically active parent body capable of sustaining melting at two or more epochs in its history

bulk chemical composition of lherzolitic shergottite grove mountains 99027 constraints on the mantle of mars we report the concentration of 50 elements including rare earth elements rees and platinum group elements pges in bulk samples of the grove mountains grv 99027 lherzolitic shergottite the abundances of rees are distinctly lower than those of allan hills alh a77005 and other lherzolitic shergottites indicating that grv 99027 is not paired with them it may nevertheless sample the same igneous unit as the others lin et al 2005b wang and chen 2006 the ci normalized elemental pattern of grv 99027 reveals low 0 004 0 008 ci and unfractionated pges except for pd of 0 018 ci without depletion of w or ga relative to lithophile element trends fractionation between siderophile and lithophile elements become less pronounced with increase of volatility except for high abundances of ni and co these characteristics are probably representative of the mantle of mars which is consistent with previous work that the martian mantle formed in a deep magma ocean followed by a later accretion of chondritic materials

the ksar ghilane 002 shergottite the 100th registered martian meteorite fragment we report on the discovery of a new shergottite from tunisia ksar ghilane kg 002 this single stone weighing 538 g is a coarse grained basaltic shergottite mainly composed of maskelynitized plagioclase approximately 52 vol and pyroxene approximately 37 vol it also contains fe rich olivine approximately 4 5 vol large ca phosphates including both merrillites and cl apatites approximately 3 4 vol minor amounts of silica or sio 2 normative k rich glass pyrrhotite ti magnetite ilmenite and accessory baddeleyite the largest crystals of pyroxene and plagioclase reach sizes of approximately 4 to 5 mm pyroxenes fs 26 96 en 5 50 wo 2 41 they typically range from cores of about fs 29 en 41 wo 30 to rims of about fs 68 en 14 wo 17 maskelynite is ab 41 49 an 39 58 or 1 7 in composition but some can be as anorthitic as an 93 olivine fa 91 96 occurs mainly within symplectitic intergrowths in paragenesis with ilmenite or at neighboring areas of symplectites kg 002 is heavily shocked s5 as indicated by mosaic extinction of pyroxenes maskelynitized plagioclase the occurrence of localized shock melt glass pockets and low radiogenic he concentration oxygen isotopes confirm that it is a normal member of the snc suite kg 002 is slightly depleted in lree and shows a positive eu anomaly providing evidence for complex magma genesis and mantle processes on mars noble gases with a composition thought to be characteristic for martian interior is a dominant component measurements of 10 be 26 al and 53 mn and comparison with monte carlo calculations of production rates indicate that kg 002 has been exposed to cosmic rays most likely as a single meteoroid body of 35 65 cm radius kg 002 strongly resembles los angeles and nwa 2800 basaltic shergottites in element composition petrography and mineral chemistry suggesting a possible launch pairing the similar cre ages of kg 002 and los angeles may suggest an ejection event at approximately 3 0 ma

the gisp2 δ18o climate record of the past 16 500 years and the role of the sun ocean and volcanoes measured 18o 16o ratios from the greenland ice sheet project 2 gisp2 ice core extending back to 16 500 cal yr b p provide a continuous record of climate change since the last glaciation high resolution annual 18o 16o results were obtained for most of the current millennium a d 818 1985 and record the medieval warm period the little ice age and a distinct 11 yr 18o 16o cycle volcanic aerosols depress central greenland annual temperature 1 5 c maximally and annual 18o 16o for about 4 yr after each major eruptive event on a bidecadal to millennial time scale the contribution of solar variability to holocene greenlandic temperature change is 0 4 c the role of thermohaline circulation change on climate problematic during the holocene is more distinct for the 16 500 10 000 cal yr b p interval analogous to 14c age calibration terminology we express time in calibrated cal yr b p a d 1950 0 cal yr b p the oldest dryas bolling older dryas allerod younger dryas sequence appears in great detail bidecadal variance in 18o 16o but not necessarily in temperature is enhanced during the last phase of lateglacial time and the younger dryas interval suggesting switches of air mass transport between jet stream branches the branched system is nearly instantaneously replaced at the beginning of the bolling and holocene at 14 670 and 11 650 cal yr b p respectively by an atmospheric circulation system in which 18o 16o and annual accumulation initially track each other closely thermodynamic considerations of the accumulation rate temperature relationship can be used to evaluate the 18 o 16o temperature relationship the gisp2 ice layer count years of major gisp2 climate transitions also support the use of coral 14c ages for age calibration

common asteroid break up events of eucrites diogenites and howardites and cosmic ray production rates for noble gases in achondrites we determined the cosmic ray produced noble gas abundances in eight diogenites four eucrites and four howardites using these and additional noble gas and chemical data from the literature composition and shielding dependent production rates of achondrites for 3he 21ne 38ar 78kr 83kr and126xe were derived based on 81krkr exposure ages the cosmogenic ratio 22ne 21ne is found to be a valid shielding indicator for all howardites eucrites and diogenites heds this ratio correlates with other shielding dependent ratios such as 78kr 83kr 80kr 83kr 124xe 131xe 126xe 131xe and 128xe 131xe we show that strong correlations for these ratios also exist for basaltic lunar rocks the new production rates were used for the calculation of exposure ages for all heds with known noble gas abundances two major exposure age clusters at 21 ma and 38 ma are observed in all three classes we find that five asteroid break up events characterized by exposure ages 6 1 ma 12 2 ma 21 4 ma 38 8 ma and 73 3 ma produced all diogenites fifteen out of seventeen howardites and twenty eight out of thirty nine eucrites we conclude that asteroidal or cometary impact events at such times on one or several parent bodies are responsible for the ejection of eucrites howardites and diogenites probable parent bodies are multiple 4 vesta derived kilometer sized objects of basaltic achondritic composition reaching the 3 1 resonance region a proposed source area for meteorites the direct ejection from vesta and capture by earth of basaltic meteorites has been shown to be dynamically difficult in such a scenario large events 38 ma and 21 ma ago are required liberating simultaneously material representing vesta s surface eucrites howardites and interior regions diogenites

the two step shape and timing of the last deglaciation in antarctica the two step character of the last deglaciation is well recognized in western europe in greenland and in the north atlantic for example in greenland a gradual temperature decrease started at the bolling b around 14 5 ky bp spanned through the allerod a and was followed by the cold younger dryas yd event which terminated abruptly around 11 5 ky bp recent results suggest that this ba yd sequence may have extended throughout all the northern hemisphere but the evidence of a late transition cooling is still poor for the southern hemisphere here we present a detailed isotopic record analyzed in a new ice core drilled at dome b in east antarctica that fully demonstrates the existence of an antarctic cold reversal acr these results suggest that the two step shape of the last deglaciation has a worldwide character but they also point to noticeable interhemispheric differences thus the coldest part of the acr which shows a temperature drop about three times weaker than that recorded during the yd in greenland may have preceded the yd antarctica did not experienced abrupt changes and the two warming periods started there before they started in greenland the links between southern and northern hemisphere climates throughout this period are discussed in the light of additional information derived from the antarctic dust record

potential glacial evidence for the younger dryas event in the cordillera of north and south america there is debate as to whether or not the younger dryas yd climatic event affected areas outside of the north atlantic region the potential of alpine glacial deposits to record the yd is of interest because alpine glaciers would be likely to leave a morainal record even during minor short lived advances caused by a period of deteriorating climate in the cordilleran ranges of north and south america there are several candidate moraines many bracketed between radiocarbon ages of ca 12 and 10 ka which may be yd in age the best examples are in the canadian and american rockies the ecuadorian peruvian and bolivian andes and around the patagonian ice cap in most cases temporal brackets are not narrow enough and some radiocarbon ages may not be accurate enough to allow correlation at the present time there are two cases of lateglacial readvance whose ages are interpreted to match or fall within the yd interval an advance of the crowfoot glacier in canada is interpreted to have occurred within the period ca 11 3 and 10 14c ka bp and an advance of the reschreiter glacier in ecuador is interpreted to have culminated in the period ca 11 to 10 6 14c ka bp the latter interpretation depends on an assumption that lake level variations were caused by glacier advances and retreats

ejection ages from krypton 81 krypton 83 dating and pre atmospheric sizes of martian meteorites cosmic ray exposure cre ages and mars ejection times were calculated from the radionuclide 81 and stable kr isotopes for seven martian meteorites the following 8lkr kr cre ages were obtained los angeles 3 35 0 70 ma queen alexandra range 94201 2 22 0 35 ma shergotty 3 05 0 50 ma zagami 2 98 0 30 ma nakhla 10 8 4 0 8 ma chassigny 10 6 2 0 ma and allan hills 84001 15 4 5 0 ma comparison of these ages with previously obtained cre ages from the stable noble gas nuclei 3he 21ne and 38ar shows excellent agreement this indicates that the method for the production rate calculation for the stable nuclei is reliable in all martian meteorites we observe effects induced by secondary cosmic ray produced epithennal neutrons epithermal neutron fluxes 30 300 ev are calculated based on the reaction 79br n yp gokr we show that the neutron capture effects were induced in free space during mars earth transfer of the meteoroids and that they are not due to a pre exposure on mars before ejection of the meteoritic material neutron fluxes and slowing down densities experienced by the meteoroids are calculated and pre atmospheric sizes are estimated we obtain minimum radii in the range of 22 25 cm and minimum masses of 150 220 kg these results are in good agreement with the mean sizes reported for model calculations using current semiempirical data

modern atmospheric signatures in 4 4 ga martian meteorite nwa 7034 the nwa 7034 martian basaltic breccia dated at 4 4 ga 4 4 ga represents an entirely new type of martian meteorite however due to the unique make up of nwa 7034 compared to other martian meteorite types including its anomalous oxygen isotope ratios noble gas analyses a key tool for martian meteorite identification are important to confirm its martian origin here we report the first noble gas results for nwa 7034 which show the presence of a trapped component that resembles the current martian atmosphere this trapped component is also similar in composition to trapped gases found in the much younger shergottites 150 600 ma 150 600 ma our formation ages for the sample suggest events at 1 6 ga k ar and 170 ma u th he which are considerably younger than those observed by rb sr 2 1 ga and sm nd 4 4 ga zircons 4 4 ga however our k ar age is similar to a disturbance in the u pb zircon data at 1 7 ga which could hint that both chronometers have been subjected to disturbance by a common process or event the u th he age of 170 ma could relate to complete loss of radiogenic 4he at this time and is a similar age to the crystallisation age of most shergottites while this may be coincidental it could indicate that a single event is responsible for both shergottite formation and nwa 7034 thermal metamorphism as for cosmic ray exposure ages our favoured age is 5 ma which is outside the ranges for other martian meteorite groups and may suggest a distinct ejection event nwa 7034 shows evidence for neutron capture on br which has caused elevations in kr isotopes 80 kr and 82 kr these elevated abundances indicate significant shielding and could relate to either a large meteoroid size and or shielding in relation to a regolithic origin we have also applied similar neutron capture corrections to ar and xe data which further refine the likelihood of a modern atmospheric component though such corrections remain speculative cosmogenic production rates and noble gas data are consistent with a meteoroid radius of 50 cm fission contributions are clear in the xe data with evidence to suggest that nwa 7034 contains both 238 u and 244 pu derived fission xe components if the gas in nwa 7034 was trapped at its ancient igneous formation this would suggest little evolution of the martian atmosphere between 4 4 ga and present day however as nwa 7034 is a regolith breccia with multiple lithologies and a strong compositional similarity to gusev soils the timing and incorporation of trapped atmospheric gases is unclear with hints of resetting events at 1 5 2 1 ga 1 5 2 1 ga the atmospheric component may have been incorporated during breccia formation possibly in the amazonian though it could also have been incorporated on ejection from the surface

the last glacial holocene transition in southern chile warming at the last glacial termination in the north atlantic region was interrupted by a period of renewed glacial activity during the younger dryas chronozone ydc the underlying mechanism of this cooling remains elusive but hypotheses turn on whether it was a global or a north atlantic phenomenon chronological sedimentological and palaeoecological records from sediments of small lakes in oceanic southern chile demonstrate that there was no ydc cooling in southern chile it is therefore likely that there was little or no cooling in southern pacific surface waters and hence that ydc cooling in the north atlantic was a regional rather than global phenomenon

noble gases and chemical composition of shergotty mineral fractions chassigny and yamato 793605 the trapped argon 40 argon 36 ratio and ejection times of martian meteorites we report the elemental and isotopic composition of the noble gases as well as the chemical abundances in pyroxene maskelynite mesostasis glass and bulk material of shergotty and of bulk samples from chassigny and yamato 793605 the 40k 40ar isochron for the shergotty minerals yields a gas retention age of 196 ma which is within errors in agreement with previously determined rb sr internal isochron ages argon that was trapped at this time has a 40ar 36ar ratio of 1100 for chassigny and y 793605 we obtain trapped 40ar 36ar ratios of 1380 and 950 respectively using these results and literature data we show that the three shergottites shergotty zagami and que 94001 the lherzolites alh 77005 lew 88516 and y 793605 as well as chassigny and alh 84001 contain a mixture of martian mantle and atmospheric ar whereas the trapped 40ar 36ar ratio of the nakhlites nakhla lafayette and governador valadares cannot be determined with the present data we show that martian atmospheric trapped ar in martian meteorites is correlated with the shock pressure that they experienced hence we conclude that the martian atmospheric gases were introduced by shock into the meteoritic material for the shergotty minerals we obtain 3he 21ne and 38ar based cosmic ray exposure ages of 3 0 ma and for the lherzolite y 793605 4 0 ma which confirms our earlier conclusion that the lherzolites were ejected from mars 1 ma before the shergottites chassigny yields the previously known ejection age of 11 6 ma

noble gases and nitrogen in martian meteorites dar al gani 476 sayh al uhaymir 005 and lewis cliff 88516 efa and extra neon meteorite finds from the terrestrial hot deserts have become a major contributor to the inventory of martian meteorites in order to understand their nitrogen and noble gas components we have carried out stepped heating experiments on samples from two martian meteorites collected from hot deserts we measured interior and surface bulk samples glassy and non glassy portions of dar al gani 476 and sayh al uhaymir 005 we have also analyzed noble gases released from the antarctic shergottite lewis cliff 88516 by crushing and stepped heating for the hot desert meteorites significant terrestrial ar kr xe contamination is observed with an elementally fractionated air efa component dominating the low temperature releases the extremely low ar kr xe ratios of efa may be the result of multiple episodes of trapping loss during terrestrial alteration involving aqueous fluids we suggest fractionation processes similar to those in hot deserts to have acted on mars with acidic weathering on the latter possibly even more effective in producing elementally fractionated components addition from fission xenon is apparent in dag 476 and sau 005 the ar kr xe patterns for lew 88516 show trends as typically observed in shergottites including evidence for a crush released component similar to that observed in eeta 79001 a trapped ne component most prominent in the surface sample of dag 476 may represent air contamination it is accompanied by little trapped ar 20ne 36ar 50 and literature data suggest its presence also in some antarctic finds data for lew 88516 and literature data on the other hand suggest the presence of two trapped ne components of martian origin characterized by different 20ne 22ne possibly related to the atmosphere and the interior caution is recommended in interpreting nitrogen and noble gas isotopic signatures of martian meteorites from hot deserts in terms of extraterrestrial sources and processes nevertheless our results provide hope that vice versa via noble gases and nitrogen in meteorites and other relevant samples from terrestrial deserts martian secondary processes can be studied

the meteoritical bulletin no 102 meteoritical bulletin 102 contains 3141 meteorites including 12 falls boumdeid 2003 boumdeid 2011 braunschweig chelyabinsk dongyang draveil heyetang indian butte katol ladkee ouadangou xining with 2611 ordinary chondrites 264 hed achondrites 124 carbonaceous chondrites 30 ureilites 20 martian meteorites 16 primitive achondrites 16 rumuruti chondrites 15 mesosiderites 12 iron meteorites 10 lunar meteorites 9 enstatite chondrites 4 enstatite achondrites 4 pallasites 4 ungrouped achondrites and 2 angrites and with 1708 from antarctica 956 from africa 294 from south america 126 from asia 47 from north america 6 from europe including russia and 4 from oceania information about approved meteorites can be obtained from the meteoritical bulletin database mbd available on line at http www lpi usra edu meteor

the case for old basaltic shergottites abstract the crystallization age of shergottites is currently not agreed upon although mineral 87 rb 87 sr 147 sm 143 nd 176 lu 176 hf and u pb isochrons all give very young ages typically in the range of 160 180 ma 207 pb 206 pb data support a much older crystallization age at 4 1 ga which is consistent with published whole rock 87 rb 87 sr data on basaltic shergottites different isotopic systems present different complexities but crater counting chronology which shows that a substantial fraction of the martian surface was resurfaced during the late heavy bombardment is in favor of an old martian lithosphere with ages in accordance with pb pb and rb sr isotopic data a 4 1 ga pb pb age of shergottites also agrees with the 142 nd and 182 w anomalies found in these rocks and concur with the presence of an actively convecting mantle during the first 500 myr of the planet s history we here present new sm nd lu hf and pb pb mineral isochrons for the basaltic shergottites shergotty and los angeles complementing our previous results on zagami bouvier a blichert toft j vervoort j d and albarede f 2005 the age of snc meteorites and the antiquity of the martian surface earth planet sci lett 240 221 233 the internal 147 sm 143 nd and 176 lu 176 hf isochrons give young ages of respectively 172 40 mswd 2 0 and 188 91 mswd 3 1 for shergotty and 181 13 mswd 0 14 and 159 42 mswd 0 01 for los angeles in contrast the pb isotope compositions of the leached whole rock fragments and maskelynite separates of shergotty and los angeles fall on the whole rock isochron previously established for zagami and other shergottite samples and collectively yield a pb pb age of 4050 70 ma for the crystallization of the basaltic shergottite suite the contrast between the 170 ma ages of internal isochrons and the 4 1 ga age supported by pb pb and 87 rb 87 sr on whole rocks simply reflects that the younger age dates the perturbation of a suite of rocks of noachian age the internal rb sr sm nd lu hf and u pb errorchrons are heavily biased by the presence of disseminated phosphate minerals and inclusions for which d h ratios d 4600 indicate strong interaction with martian subsurface waters in contrast baddeleyite occasionally present in sncs and also having extremely young u pb ages reflect resetting under the shock conditions that prevailed either during shergottite extraction from the planet or from impacts associated with a major break up event of planetesimals in the main asteroid belt we finally also re examine 39 ar 40 ar data on snc meteorites and suggest that they as well support old crystallization ages

martian meteorite chronology and the evolution of the interior of mars abstract the earth moon and mars are the only three planets for which satellite and ground observations can be confronted with extensive chronological and geochemical observations of rock samples here we use new pb isotope data on shergottites nakhlites chassigny and the alh 84001 orthopyroxenite to reassess chronological evidence and discuss its bearing on the evolution of the interior of mars we find that the depleted shergottites formed at 4 3 ga i e 170 ma after the last equilibration of pyroxene rich cumulates with the magma ocean while the younger enriched and intermediate shergottites as well as alh 84001 formed 200 ma later at 4 1 ga after the residual part of the mantle had been largely mixed back into these cumulates we also demonstrate that the th u ratios inferred from pb isotopes require shergottite ages older than 4 0 ga we finally reexamine the implications of this new chronological framework for the interpretation of 142 nd and 182 w anomalies in martian meteorites we conclude that shergottites represent samples that derived from a volcanic basement subsequently shattered by the 3 9 ga late heavy bombardment lhb although the magmatic activity of mars had strongly declined by the time of the lhb the new chronology of martian meteorites proposed here allows the martian mantle to be convective until today the 1 3 ga old emplacement of nakhlites and chassignites corresponds to decompression melting of ilmenite rich mantle domains and not to renewed global magmatic activity of the planet with the exception of this event the history of the interior of mars therefore somewhat resembles that of the moon

unique meteorite from early amazonian mars water rich basaltic breccia northwest africa 7034 we report data on the martian meteorite northwest africa nwa 7034 which shares some petrologic and geochemical characteristics with known martian meteorites of the snc i e shergottite nakhlite and chassignite group but also has some unique characteristics that would exclude it from that group nwa 7034 is a geochemically enriched crustal rock compositionally similar to basalts and average martian crust measured by recent rover and orbiter missions it formed 2 089 0 081 billion years ago during the early amazonian epoch in mars9 geologic history nwa 7034 has an order of magnitude more indigenous water than most snc meteorites with up to 6000 parts per million extraterrestrial h2o released during stepped heating it also has bulk oxygen isotope values of 17o 0 58 0 05 per mil and a heat released water oxygen isotope average value of 17o 0 330 0 011 per mil suggesting the existence of multiple oxygen reservoirs on mars

earthquake nucleation size evidence of loading rate dependence in laboratory faults recent gps observations of major earthquakes such as the 2014 chile megathrust show a slow pre slip phase releasing a significant portion of the total moment ruiz et al 2014 despite advances from theoretical stability analysis rubin ampuero 2005 ruina 1983 and modeling kaneko carpenter nielsen 2017 it is not fully understood what controls the prevalence and the amount of slip in the nucleation process here we present laboratory observations of slow slip preceding dynamic rupture where we observe a dependence of nucleation size and position on the loading rate laboratory equivalent of tectonic loading rate the setup is composed of two polycarbonate plates under direct shear with a 30 centimeters long slip interface the results of our laboratory experiments are in agreement with the pre slip model outlined by ellsworth and beroza 1995 and observed in laboratory experiments latour schubnel nielsen madariaga vinciguerra 2013 nielsen taddeucci vinciguerra 2010 ohnaka kuwahara 1990 which show a slow slip followed by an acceleration up to dynamic rupture velocity however further complexity arises from the effect of 1 rate of shear loading and 2 inhomogeneities on the fault surface in particular we show that when the loading rate is increased from 10 2 mpa s 1 to 6 mpa s 1 the nucleation length can shrink by a factor of three and the rupture nucleates consistently on higher shear stress areas the nucleation lengths measured fall within the range of the theoretical limits lb and l derived by rubin and ampuero 2005 for rate and state friction laws

the age of snc meteorites and the antiquity of the martian surface we report new sm nd lu hf and pb pb mineral and whole rock isotope data for the basaltic shergottite zagami as well as pb pb whole rock isotope data for the basaltic shergottite los angeles the lherzolitic shergottite dar al gani 476 dag 476 and the clinopyroxenite nakhla in agreement with previous findings our new sm nd and lu hf mineral ages on the martian meteorite zagami are young 155 and 185 ma respectively the 207pb 206pb 204pb 206pb compositions of the insoluble fractions of shergottites zagami los angeles and literature data for shergotty and eeta79001 form an excellent alignment indicative of a 4 0 ga crystallization age the range of pb isotope compositions observed in the leachates of these samples attests to negligible contamination of the shergottites by terrestrial pb and argues against mixing relationships the age of 4 048 0 017 ga mswd 1 5 provided by the pb isotope compositions of the zagami whole rock and residues is therefore taken to date the crystallization of this rock which so far was believed to be only not vert similar 180 ma old based on this result we argue that the lithosphere of mars is extremely old and that most mineral ages were reset recently by acidic aqueous solutions percolating through the martian surface this interpretation is consistent with photographic interpretations of erosional features on mars it also relieves the constraint imposed by the presence of anomalies of 142nd and 182w both products of extinct radioactive nuclides that the martian mantle should have preserved primordial isotopic heterogeneities thus allowing for the planet interior to be actively convecting

climate impact of late quaternary equatorial pacific sea surface temperature variations magnesium calcium data from planktonic foraminifera in equatorial pacific sediment cores demonstrate that tropical pacific sea surface temperatures ssts were 2 8 0 7 c colder than the present at the last glacial maximum glacial interglacial temperature differences as great as 5 c are observed over the last 450 thousand years changes in sst coincide with changes in antarctic air temperature and precede changes in continental ice volume by about 3 thousand years suggesting that tropical cooling played a major role in driving ice age climate comparison of sst estimates from eastern and western sites indicates that the equatorial pacific zonal sst gradient was similar or somewhat larger during glacial episodes extraction of a salinity proxy from the magnesium calcium and oxygen isotope data indicates that transport of water vapor into the western pacific was enhanced during glacial episodes

rb sr and sm nd isotopic systematics of the lherzolitic shergottite grv 99027 abstract rb sr and sm nd isotopic analyses of the lherzolitic shergottite grove mountains grv 99027 are reported grv 99027 yields a rb sr mineral isochron age of 177 5 2 ma and an initial 87sr 86sr ratio isr of 0 710364 11 2 due to larger uncertainties of the sm nd isotopic data no sm nd isochron age was obtained for grv 99027 the e143nd value is estimated approximately 12 2 assuming an age of 177 ma the isr of grv 99027 is distinguishable from other lherzolitic shergottites confirming our previous conclusion that it is not paired with them lin et al 2005 the new data of grv 99027 support the same age of approximately 180 ma for most lherzolitic shergottites and fill the small gap of isr between allan hills a77005 and lewis cliff 88516 borg et al 2002 all available data are consistent with a single igneous source for the intermediate subgroup of lherzolitic shergottites

the el abra stadial a younger dryas equivalent in colombia abstract a survey of radiocarbon dated palynological stratigraphical and glacio morphological evidence from colombia is presented showing a cold climatic fluctuation most likely between 10 900 and 10 100 bp immediately preceding the initiation of the holocene this fluctuation called the el abra stadial is characterized by lower temperatures and less precipitation and occurs after the late glacial guantiva interstadial average annual temperature during the guantiva interstadial may have been 2 c lower than today and during the el abra stadial from 4 to 6 c lower than today the upper forest line during the el abra stadial was some 400 to 500 m lower than during the guantiva interstadial and some 600 to 800 m lower than today the guantiva interstadial el abra stadial early holocene sequence is radiocarbon dated by some 45 dates and evidence is shown from 14 areas mostly located at high elevations 2000 4000 m in the eastern and central cordillera and in the sierra nevada de santa marta but some from the tropical low lands although more precise dating of the boundaries is desirable we interpret the guantiva el abra climatic fluctuations as equivalents in time and climatic phenomena to the allerod younger dryas sequence in europe

evidence against a significant younger dryas cooling event in new zealand pollen records of deglacial sequences from northwest nelson new zealand demonstrate that there was no significant temperature decline associated with the younger dryas in new zealand records of glacial advances at this time were either the product of increased snow accumulation under enhanced precipitation regimes or random variation rather than the result of a regional thermal decline this finding supports those models of younger dryas initiation that require neither enhanced westerly circulation nor significant thermal decline in the southern hemisphere

petrology geochemistry and cosmic ray exposure age of lherzolitic shergottite northwest africa 1950 northwest africa nwa 1950 is a new member of the lherzolitic shergottite clan of the martian meteorites recently found in the atlas mountains the petrological mineralogical and geochemical data are very close to those of the other known lherzolitic shergottites the meteorite has a cumulate gabbroic texture and its mineralogy consists of olivine fo66 to fo75 low and high ca pyroxenes en 78 fs 19 wo 2 en 60 fs 26 w 14 en 53 fs 16 wo 31 en 45 fs 14 wo 41 and plagioclase an 57 ab 41 or 1 to an 40 ab 57 or 3 entirely converted into maskelynite during intense shock metamorphism accessory minerals include phosphates merrillite chromite and spinels sulfides and a glass rich in potassium the oxygen isotopic values lie on the fractional line defined by the other snc meteorites delta 17 o 0 312 parts per thousand the composition of nwa 1950 is very similar to the other lherzolitic shergottites and suggests an origin from the same magmatic system or at least crystallization from a close parental melt cosmogenic ages indicate an ejection age similar to those of the other lherzolitic shergottites the intensity of the shock is similar to that observed in other shergottites as shown by the occurrence of small melt pockets containing glass interwoven with stishovite

ejection times of martian meteorites noble gas isotopic analyses were made for four meteorites whose origin is mars basaltic shergottites queen alexandra range 94201 zagami the iherzolite lew88516 and orthopyroxenite allan hills 84001 the latter one was separated into orthopyroxene chromite and maskelynite fractions ejection times were calculated for all martian meteorites using cosmic ray exposure ages based on 3he 21ne and 38ar concentrations and literature data on the terrestrial ages we discuss the arguments for a scenario in which they were ejected from mars by asteroidal or cometary impact as small meteoroids and were delivered to earth within and up to 15 million years the basaltic shergottites que94201 shergotty and zagami show an ejection age cluster at 2 76 ma the fourth basaltic shergottite eet79001 being younger 0 82 ma lherzolites lew88516 and alh77005 were ejected by a later event 3 84 ma ago all nakhlites nakhla governador valadares and lafayette originate from an event 11 0 ma ago although chassigny is chemically distinct from the nakhlites its ejection age is 11 6 ma whether this is a separate event cannot be decided from the available data finally orthopyroxenite alh84001 was launched from mars 14 4 ma ago the distribution of the delivery times for martian meteorites to earth reflect individual impact events onto five or six different source terrains this result is significant in the context of a comprehensive knowledge of the martian crust composition finally we derived the k 40ar gas retention age of alh84001 mineral fractions adopting two different models assuming a component of martian atmospheric ar with 40ar36ar 1790 trapped by this meteorite we obtained an age of 3390 ma on the other hand assuming no contribution of martian atmospheric ar the resulting k 40ar age is about 4100 ma that is roughly 500 ma younger than the reported sm nd crystallization age

volatiles nitrogen noble gases in recently discovered snc meteorites extinct radioactivities and evolution abstract we report noble gas and nitrogen analyses of newly discovered snc meteorites one nakhlite nwa817 and four shergottites nwa480 nwa856 nwa1068 and sau 005 the k ar age 1 3 ga as well as the cosmic ray exposure cre age 10 0 1 3 ma of nakhlite nwa817 agree with data of nakhla the cre ages of nwa480 nwa856 and nwa1068 2 35 0 20 2 60 0 21 and 2 01 0 65 ma respectively are consistent within uncertainties with other basaltic shergottites but the cre age of sau 005 1 25 0 07 ma is distinct and indicates a different ejection event bulk k ar ages of all shergottites exceed the reported radiometric ages and reveal the presence of inherited radiogenic 40 ar in basaltic lavas the isotopic composition of nitrogen trapped in these snc meteorites is not homogeneous since 15 n values of either 15 to 20 or 45 indicate different nitrogen reservoirs all shergottites contain fission xenon from 238 u and fission xe of extinct t 1 2 82 ma 244 pu previously identified in alh84001 in chassigny and in nakhla is also present in at least one shergottite nwa856 the shergottites contain less fissiogenic xe than other snc suggesting that either their source was more degassed or that the magma source region closed at a later time in nakhlites fission xenon from 244 pu correlates with uranium a geochemical proxy of plutonium thus it is possible that fissiogenic xe was not inherited during magma differentiation but rather was produced in situ and retained in refractory mineral assemblages in this interpretation the magma evolution that settled the mineralogy and geochemistry of nakhlites took place at a time when 244 pu was alive and pre dated the late events recorded in their radiometric ages alternatively fissiogenic xenon was trapped from a mantle source during closed system evolution of the parent magmas in which case such evolution might have taken place at considerable depth pressure in order to inhibit magma degassing during the course of differentiation

synchronous radiocarbon and climate shifts during the last deglaciation radiocarbon data from the cariaco basin provide calibration of the carbon 14 time scale across the period of deglaciation 15 000 to 10 000 years ago with resolution available previously only from holocene tree rings reconstructed changes in atmospheric carbon 14 are larger than previously thought with the largest change occurring simultaneously with the sudden climatic cooling of the younger dryas event carbon 14 and published beryllium 10 data together suggest that concurrent climate and carbon 14 changes were predominantly the result of abrupt shifts in deep ocean ventilation