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

26al 26mg systematics in d orbigny and sahara 99555 angrites implications for high resolution chronology using extinct chronometers abstract we report on an investigation of the 26al 26mg isotope systematics in the d orbigny and sahara 99555 angrites high precision mg isotope compositions and al mg ratios were measured in mineral separates and whole rock samples from d orbigny and sahara 99555 using multiple collector inductively coupled plasma mass spectrometry mc icpms plagioclase separates from both angrites have resolvable excesses in 26mg 26mg that correlate with their respective al mg ratios 26al 26mg systematics in the mineral separates and whole rocks define precise isochrons that correspond to 26al 27al ratios of 5 06 0 92 10 7 and 5 13 1 90 10 7 and initial 26mg values of 0 006 0 040 and 0 016 0 047 for d orbigny and sahara 99555 respectively the slopes and initial 26mg values are identical for these two meteorites within errors and the data for both angrites considered together define an isochron corresponding to a 26al 27al ratio of 5 10 0 55 10 7 and initial 26mg value of 0 012 0 019 relative to the efremovka e60 cai the 26al 27al values reported here for these angrites imply 26al 26mg ages of 4562 42 0 29 ma and 4562 43 0 53 ma for d orbigny and sahara 99555 respectively these 26al 26mg ages are concordant with model ages determined using other extinct radionuclide chronometers e g 53mn 53cr and 182hf 182w but are 2 myr younger than the absolute 207pb 206pb ages that have been reported recently for these angrites the reason for this discrepancy is not presently known but may imply disturbance of one or more of the isotope systems under consideration or a possible bias in the 207pb 206pb ages of the angrites resulting from natural or analytical causes

unraveling the evolution of chondrite parent asteroids by precise u pb dating and thermal modeling u th pb isotopic data are reported for mineral fractions individual chondrules and fractions of chondrule fragments from the equilibrated ordinary chondrite richardton h5 chondrules and milligram sized fractions of pyroxene rich chondrule fragments contain highly radiogenic pb and concordant or nearly concordant u th pb isotopic systems and are suitable for precise pb pb age determinations olivine and sulfide have low u concentrations and contain less radiogenic pb the ages of individual chondrules pyroxene rich and phosphate fractions are determined using u pb and pb pb isochron and model date calculations the pb pb isochron date of 4562 7 1 7 ma of the richardton chondrules and chondrule fragments is resolved from the pb pb isochron date of 4550 7 2 6 ma obtained from multiple phosphate fractions possible biases of the isochron dates due to single stage approximation of multi stage evolution contamination with modern common pb and disturbance to the system by reheating are examined and are found to be insignificant the chondrule and phosphate dates are interpreted as the timing of cessation of pb diffusion during cooling following metamorphism in chondrite parent bodies the difference in estimated closure temperatures 950 1150 k for pyroxenes and 700 800 k for phosphates temperature estimates are based on published diffusion rates for pb in pyroxenes and apatite allows evaluation of the average cooling rate at 26 13 k million years for the richardton parent body over the period of 4563 4551 my thermal modeling of the h chondrite parent body which is assumed to be asteroid 6 hebe heated by decay of 26al suggests a scenario in which accretion initiated at 1 7 m y after formation of calcium aluminum rich inclusions and continued for 3 5 m y

ce anomalies in the lew85300 eucrite evidence for ree mobilization during antarctic weathering abstract there is abundant evidence for widespread ree mobilization in antarctic eucrites resulting in ce and eu anomalies and lower whole rock ree abundances relative to typical eucrites using secondary ion mass spectrometry sims we investigated the microdistribution of ce anomalies in the antarctic polymict eucrite lew85300 ce anomalies positive and or negative are present in all three of the minerals plagioclase pyroxene and silica analysed the anomalies occur in grains from all four clasts as well as in mineral and lithic fragments from the surrounding matrix thus there appears to be no lithologic association silica which has been heavily shocked and altered exhibits a lree enriched pattern with negative ce and eu anomalies consistent with a derivation of the ree from ca phosphate dissolution trivalent ree are leached from the phosphates with preferential retention of tetravalent ce and redeposited on silica pyroxene is also widely affected by ree mobilization due to an extensive shock induced microcrack network along cleavage planes a tendency for the largest ce anomalies to occur at low lree concentrations suggests that pyroxene itself experienced ree leaching with concomitant ce retention ce anomalies are rare in plagioclase because this mineral lacks an extensive network along which ree can be mobilized the widespread ree mobilization and evidence for other forms of weathering requires that trace element data be used cautiously especially for antarctic eucrites

chromium vanadium and titanium valence systematics in solar system pyroxene as a recorder of oxygen fugacity planetary provenance and processes pyroxene is arguably the most powerful single phase geochemical and petrologic recorder of solar system processes from nebular condensation through planetary evolution over a wide range of temperatures pressures and f o 2 it is an important mineral phase in the crusts and mantles of evolved planets in undifferentiated and differentiated asteroids and in refractory inclusions the earliest solar system materials here we review the valence state partitioning behavior of cr cr 2 cr 3 ti ti 3 ti 4 and v v 2 v 3 v 4 v 5 among crystallographic sites in pyroxene over a range of f o 2 from approximately fayalite magnetite quartz fmq to 7 log units below iron wustite iw 7 and decipher how pyroxene can be used as a recorder of conditions of planetary and nebular environments and planetary parentage the most important crystallographic site in pyroxene with respect to its influence on mineral melt partitioning is m2 its ca content has a huge effect on partitioning behavior because the large ca cation expands the structure as a result distribution coefficients d s for cr and v increase with increasing ca content from orthopyroxene to pigeonite to augite in addition it is noted that v 3 is favored over v 4 in olivine and pyroxene in pyroxene in refractory inclusions ti 3 is favored over ti 4 and incorporation of ti is facilitated by the high availability of al for coupled substitution the most important results from analysis of pyroxene in martian meteorites e g que 94201 are the oxygen fugacity estimates of iw 0 2 and iw 0 9 derived from partitioning and valence data for cr and v respectively obtained from experiments using appropriate temperatures and melt compositions in angrites changes in v valence state may translate to changes in f o 2 from iw 0 7 during early pyroxene crystallization to iw 0 5 during later episodes of pyroxene crystallization in addition to f o 2 the partitioning behavior of cr v and ti between pyroxene and melt is also dependent upon availability of other cations especially al for charge balancing coupled substitutions

minor and trace element partitioning between pyroxene and melt in rapidly cooled chondrules we present minor and trace element ree sr y and zr data for pyroxenes and mesostases in four porphyritic chondrules from the semarkona ordinary chondrite apparent partition coefficients for clinoenstatite orthoenstatite pigeonite and augite are compared with experimental and petrologic data from the literature and the effects on apparent partition coefficients of the rapid cooling rates at which chondrules crystallized are evaluated for most elements the effects of cooling at rates of hundreds of degrees per hour cannot be distinguished from variations in equilibrium data resulting from differences in temperature or composition however for lree apparent partition coefficients are significantly higher than comparable equilibrium data and the ratio of hree lree partition coefficients is lower particularly for ca poor pyroxene we attribute this flattening of ree patterns to the effect of rapid cooling apparent partition coefficients of all ree and y in augite are higher than equilibrium data particularly in one chondrule with a high al 2o3 content we suggest that this may be attributed to an increase in the uptake of trivalent trace element cations in the pyroxene crystal structure as a result of charge balanced substitutions with al 31 cations

mn cr isotope systematics of the d orbigny angrite we have conducted a detailed study of the mn cr systematics of the angrite d orbigny here we report cr isotopic abundances and mn cr ratios in olivine pyroxene glass chromite and bulk rock samples from d orbigny 53cr excesses in these samples correlate well with their respective mn cr ratios and define an isochron with a slope that corresponds to an initial 53mn 55mn ratio 3 24 0 04 x 10 6 and initial 53cr 52cr ratio of 53 0 30 0 03 at the time of isotopic closure the 53mn 55mn ratio of the d orbigny bulk rock is more than two fold the 53mn 55mn ratio of the angrites lewis cliff 86010 lew and angra dos reis ador and implies an older mn cr age of 4562 9 0 6 ma for d orbigny relative to a pb pb age of 4557 8 0 5 ma for lew and ador one of the most unusual aspects of d orbigny is the presence of glass a phase that has not been identified in any of the other angrites the mn cr data for glass and a pyroxene fraction found in druses indicate that they formed contemporaneously with the main phases of the meteorite since the mn cr age of d orbigny is 5 ma years older than the angrites lew and ador d orbigny likely represents an earlier stage in the evolution of the angrite parent body

petrogenesis of angrites abstract the recent discovery of two new angrites sahara 99555 and d orbigny has revived interest in this small group of achondrites we measured trace element abundances in the individual minerals of these two angrites and compared them with the three antarctic angrites lew 86010 lew 87051 and asuka 881371 trace element variations in four of these meteorites lew 87051 asuka 881371 sahara 99555 and d orbigny indicate rapid crystallization under near closed system conditions consistent with their mineralogical and textural features all four appear to be closely related and crystallized from very similar magmas discrepancies between their bulk ree compositions and melts calculated to be in equilibrium with the major phases may be due in part to kinetic effects of rapid crystallization prior crystallization of olivine and or plagioclase may also account for the elevated parent melt composition of clinopyroxene in some of the angrites such as asuka 881371 lew 86010 also crystallized from a melt and represents a liquid composition but trace element trends in clinopyroxene and olivine differ from those of the other angrites this meteorite seems to have crystallized from a different source magma

the system mg2sio4 ca2sio4 caal2o4 naalsio4 sio2 one atmosphere liquidus equilibria of analogs of alkaline mafic lavas one atmosphere liquidus relationships in the system mg2sio4 fo ca2sio4 la naalsio4 ne caal2o4 ca sio2 sil are presented as analogs for alkaline mafic lavas liquidus diagrams are constructed from electron microprobe analyses of quenched liquids and coexisting mineral phases produced in melting experiments and they are depicted in terms of sub projections within the pseudo quaternary system fo la ne ca sil the ne and ca components are combined to create a normative feldspathoid component defined as ne ne ne ca liquidus relations at ne 0 5 from this study are compared to relations at ne 0 0 and 1 0 from previous studies in general liquidus temperatures decrease and positions of liquidus boundaries involving feldspathic phases shift toward the ne ca component as ne increases the pseudoinvariant points fo di pl mel l and fo pl mel sp l exist at ne 0 5 these equilibria between forsterite plagioclase melilite liquid are not present in the system when ne 1 0 because a boundary curve fo di ne l separates the plagioclase and melilite liquidus fields the liquidus diagrams provide useful analogs for the crystallization sequences of natural primary alkali olivine basalts basanitoids basanites olivine nephelinites olivine melilite nephelinites and olivine melilitites

the meteoritical bulletin no 85 2001 september meteoritical bulletin no 85 lists information for 1376 newly classified meteorites comprising 658 from antarctica 409 from africa 265 from asia 262 of which are from oman 31 from north america 7 from south america 3 from australia and 3 from europe information is provided for 11 falls dergaon dunbogan gujba independence itqiy moravka oued el hadjar sayama sologne valera and worden noteworthy non antarctic specimens include 5 martian meteorites dar al gani 876 northwest africa 480 and 817 and sayh al uhaymir 051 and 094 6 lunar meteorites dhofar 081 280 and 287 and northwest africa 479 482 and 773 an ungrouped enstatite rich meteorite itqiy a bencubbin like meteorite gujba 9 iron meteorites and a wide variety of other interesting stony meteorites including ch ck cm co cr cv r enstatite and unequilibrated ordinary chondrites primitive achondrites hed achondrites and ureilites

rare earth elements in angra dos reis and lewis cliff 86010 two meteorites with similar but distinct magma evolutions abstract rare earth element ree and selected trace element abundances were measured with an ion microprobe in individual grains of merrillite fassaite olivine kirschsteinite and plagioclase of lew 86010 the second known angrite and compared with measurements in merrillite and fassaite of angra dos reis ador the rare merrillite is highly enriched in ree the ree patterns show steep decreases from la 3 300 cl to tm 100 cl in lew 86010 and from la 1 500 cl to tm 130 cl in ador ree patterns in fassaite of both meteorites are similar although concentrations are higher in ador whereas ador pyroxenes show a high degree of equilibration the lew 86010 pyroxenes show much variation in composition the abundances of the ree zr al and ti correlate positively with fe fe mg and those of cr sc and v correlate negatively consistent with an igneous origin in a closed system pyroxene and plagioclase cores in lew 86010 formed in equilibrium with a melt whose composition is close to that of the meteorite bulk composition the ador melt had higher ree concentrations but a lower fe mg ratio than that of lew 86010 despite numerous common characteristics the two meteorites were produced in separate magmatic events involving similar but distinct processes and parent melts the unusual angrite composition is not due to purely nebular processes

generation of abnormal trace element abundances in antarctic eucrites by weathering processes abstract based on rees antarctic eucrites can be divided into two groups those showing normal trace element characteristics e g similar to juvinas and those showing abnormal trace element abundances many antarctic eucrite polymict eucrite and basaltic clast samples show the abnormal trace element abundances with ree patterns exhibiting positive ce anomalies sometimes negative ce anomalies positive eu anomalies and low abundances of the remainder of the rees with the lrees generally being at lower relative abundances than the hrees most samples of crystalline clasts from the polymict eucrites lew85300 lew85302 and lew85303 show the abnormal patterns while the glassy matrixes of these meteorites show normal patterns exterior samples generally show more abnormal patterns larger anomalies greater depletions than interior samples from the same meteorites comparison of all basaltic eucrite literature data combined with our data shows that positive and negative ce anomalies and positive eu anomalies are found in about 61 of antarctic eucrite analyses and are virtually unknown in non antarctic eucrite analyses further positive ce anomalies and positive eu anomalies are commonly associated with antarctic eucrites having low ree concentrations consideration of mineral melt partition coefficients shows that it is unlikely that ce anomalies are magmatic features from the hed parent body cerium anomalies on earth are generally restricted to the weathering zone where the relative ease of oxidizing ce to the 4 state allows for fractionation of ce from the 3 rees we believe the unusual ree patterns of abnormal antarctic eucrites arise from weathering effects generated in or on the antarctic ice our suggested scenario involves formation of melt water and its equilibration with the atmosphere which promotes dissolution of ree rich phosphates and oxidation of ce tetravalent ce can then be fractionated from the trivalent ree in solution the details of the weathering process are unclear and will require detailed chemical and sem investigations of eucrites for their elucidation we predict that rapidly chilled eucrites with glassy rather than crystalline mesostases will be more likely to survive the antarctic environment without alteration of their ree patterns occasional s se and k enrichments are likely due to weathering in the antarctic environment as well but these enrichments are not well correlated with ce anomalies

mn cr dating of fe and ca rich olivine from quenched and plutonic angrite meteorites using secondary ion mass spectrometry this research was supported by grants dp034277 and dp0666751 from the australian research council to tri and ya and an australian national university phd research scholarship

experimental partial melting of the st severin ll and lost city h chondrites we have performed melting experiments between 1170 1325 c and at an oxygen fugacity of iw 1 on the ordinary chondrites lost city h and st severin ll in order to investigate the origin of diogenites and their possible relationship to eucrites low ca pyroxene disappears from the lost city residuum just above 1220 c at a mg near 66 accordingly lost city does not have a sufficiently large stability field for orthopyroxene to be a likely parent composition for melts which could crystallize diogenites in contrast orthopyroxene in st severin persists up to about 1325 c at which point it has a mg similar to that of typical diogenites 75 this is only marginally compatible with diogenite origins as the most magnesian pyroxenes from diogenites mg 82 and howardites mg 85 are more mgo rich than any pyroxene formed from a st severin melt accordingly if diogenites formed from a source having the bulk composition of an ordinary chondrite than either the fo2 had to be lower than that inferred for eucrite formation or more likely the parent body had a lower fesi ratio than that of an ll chondrite also low temperature melts of st severin are depleted in elements compatible with pyroxene and so while broadly eucritic do not closely match the compositions of eucrites that are thought to be primary partial melts hence it doesn t appear possible to produce both diogenites and eucrites from the same source region composition if eucrites are primary partial melts reconnaiss mce experiments at higher oxygen fugacity iw 2 produce broadly angritic melts for lost city as was observed for murchison and allende in contrast our na2o poor st severin charge produced a broadly eucritic melt at this higher fo2 this difference in melting behavior is probably because ll chondrites have a much lower bulk fesi ratio than the h cm or cv chondrites

age and isotopic relationships among the angrites lewis cliff 86010 and angra dos reis results of a wide ranging isotopic investigation of the unique antarctican angrite lew 86010 lew are presented together with a reassessment of the type angrite angra dos reis ador the principal objectives of this study are to obtain precise radiometric ages initial sr isotopic compositions and to search for the erstwhile presence of the short lived nuclei 146sm and 26al via their daughter products the isotopic compositions of sm u ca and ti were also measured this allows a detailed appraisal to be made of the relations between and the geneology of these two angrites lew proves to be severely contaminated with modern terrestrial pb which is shown to result from terrestrial weathering nevertheless concordant pb pb model ages of pyroxene separates were obtained 2 4 55784 52 ga for lew and 4 55780 42 ga for ador uranium isotopic compositions are normal within error the inferred initial pb isotopic composition is within error of primordial pb as defined by canon diablo troilite because of the extreme upb ratios of both angrites this places an upper limit of 2 ma on the time between volatile element loss of the angrite parent body or its precursor planetesimals and the final crystallization of the angrites as differentiates initial 87sr86sr ratios were found to be indistinguishable in lew ador and the cumulate eucrite moore county the derived initial 87sr86sr for all three meteorites is 0 698970 15 2 a 147sm 143nd isochron for lew was obtained yielding an age of 4 553 34 ga with an initial 143nd144nd of 0 506682 49 2 146sm142nd isotope systematics were also measured anomalies on 142nd arising from extinct 146sm were clearly resolved resulting in an initial 146sm144sm of 0 0071 17 with nd142 2 57 0 62 at the time of isotopic closure both of these sm nd methods imply derivation of lew from a reservoir with chondritic smnd ratio they are also quite consistent with the previously reported systematics for ador overall the age and isotopic similarities between lew and ador are striking it suggests almost simultaneous production on the same asteroid even though recent experimental studies imply that the two are not comagmatic calcium and titanium do not exhibit enrichments in the n rich isotopes in contrast to cais making it unlikely that the angrite parent body is inherently rich in early condensates from the solar nebula no evidence was found for live 26al in lew when combined with the pb pb age and initial 87sr86sr data this firmly excludes 26al being an important heat source in the early solar system heat supplied for for example 1 the differentiation of the angrite and eucrite parent bodies and 2 metamorphism of the chondrite parent bodies must come from some other source the debate over live vs extinct 26al in the earliest solar system remains unresolved by this new data from lew however both the angrite and eucrite parent bodies have extremely low rbsr and high upb ratios compared to the solar nebula therefore the common initial 87sr86sr of 0 698970 can be firmly associated with the u pb angrite age above and the formation of both bodies this enables an absolute chronology of the early solar system to be established based upon 87sr86sr differences the oldest cais are a minimum of 11 4 ma older than the angrites i e 4 569 5 ga the age and isotopic constraints are discussed with respect to current collapse condensation and accretion timescales calculated for the solar nebula

wave induced drag force on vegetation under shoaling random waves abstract this paper provides a practical method for estimating the drag force on a vegetation field in shoaling conditions beneath non breaking and breaking random waves this is achieved by using a simple drag formula based on two empirical drag coefficients given by mendez et al 1999 and mendez and losada 2004 respectively in conjunction with a stochastic approach here the waves are assumed to be a stationary narrow band random process and propagating in shallow waters the effects of shoaling and breaking waves are included by adopting the mendez et al 2004 wave height distribution results are presented and discussed for different slopes and an example of calculation is also provided to demonstrate the application of the method

mineralogy and petrology of the angrite northwest africa 1296 we report on a new angrite northwest africa nwa 1296 a fine grained rock with a magmatic texture of rapid cooling dendritic olivine fo50 crystallized first in association with anorthite microcrysts an98100 forming composite chains separated from one another by intergrown al fe diopside hedenbergite pyroxenes in addition some olivines with lower mg and increased cao up to 12 are found between the chains as equant microphenocrysts pyroxenes and olivines are both normally zoned from mg 0 52 to less than 0 01 in the rims ca rich olivines are surrounded by intergrown with or replaced by subcalcic kirschsteinite they appear after plagioclase crystallization stopped at the end of the crystallization sequence minor phases are pyrrhotite fapatite and titanomagnetite pyroxene is the last silicate phase to grow interstitial to idiomorphic olivine kirschsteinite numerous small vesicles and some channels are filled with microcristalline carbonate the mode vol is about 28 olivine 3 kirschsteinite 32 anorthite 34 pyroxene and 3 of the minor phases close to that reported previously for d orbigny and sahara sah 99555 the bulk chemical composition of nwa 1296 is similar to d orbigny and sah 99555 nwa 1296 differs by its texture and mineralogy which are interpreted as resulting from rapid crystallization an evidence of impact melting angrites cannot be produced by partial melting of a cv source because segregation of a planetary core is necessary to explain the low feo mgo ratio of magnesian olivines neither the odd ca al ratio nor the very low sio2 content can be explained by conventional partial melting scenarios we suggest that carbonate is the key to angrite genesis this is supported by the striking similarities with terrestrial melilitites low sio2 superchondritic ca al ratio presence of carbonate the lack of alkalies could be the result of either loss after impact melting or absence of alkalies in the source

impact histories of angrites eucrites and their parent bodies abstract eucrites which are probably from 4 vesta and angrites are the two largest groups of basaltic meteorites from the asteroid belt the parent body of the angrites is not known but it may have been comparable in size to vesta as it retained basalts and had a core dynamo both bodies were melted early by 26al and formed basalts a few myr after they accreted despite these similarities the impact histories of the angrites and eucrites are very different angrites are very largely unshocked and none are breccias whereas most eucrites are breccias and many are shocked we attribute the lack of shocked and unbrecciated angrites to an impact possibly at 4558 myr ago the radiometric age of the younger angrites that extracted the angrites from their original parent body into smaller bodies these bodies which may have had a diameter of approximately 10 km suffered much less impact damage than vesta during the late heavy bombardment because small bodies retain shocked rocks less efficiently than large ones and because large bodies suffer near catastrophic impacts that deposit vastly more impact energy per kg of target our proposed history for the angrites is comparable to that proposed by bogard and garrison 2003 for the unbrecciated eucrites with ar ar ages of 4 48 gyr and that for unbrecciated eucrites with anomalous oxygen isotopic compositions that did not come from vesta we infer that the original parent bodies of the angrites and the anomalous eucrites were lost from the belt when the giant planets migrated and the total mass of asteroids was severely depleted alternatively their parent bodies may have formed in the terrestrial planet region and fragments of these bodies were scattered out to the primordial main belt as a consequence of terrestrial planet formation

evolution and future of the lusi mud eruption inferred from ground deformation 1 the ongoing eruption of the lusi mud volcano in east java indonesia offers the unprecedented opportunity to study a large eruption from its beginning to its eventual end we use new observations of ground deformation obtained from multitemporal interferometric analysis of l band synthetic aperture radar data to show that lusi will stop erupting much sooner than previously anticipated using principal component analysis we find that the rate of ground deformation and by implication pressure in the mud source region has been decaying exponentially with an e folding time scale of 2 1 0 4 years we anticipate that discharge will decrease to 10 of the present rate in 5 years

the univariant curve liquid forsterite anorthite diopside in the system cmas at 1 bar solid solutions and melt structure one atmosphere liquid present experiments were carried out in the cmas system using an ordinary quench furnace apparatus the runs including reversal and duplicate experiments describe the univariant curve l fo an di between the invariant points q l fo an di sp and f l fo an di oen located respectively at 1245 1 c and 1244 1 c the thermal divide on this curve m3 l fo an di is located at 1275 1 c and plots well within the silica saturated field in agreement with longhi s 1987 experiments along the univariant curve l fo an di liquid composition evolves away from the thermal divide either toward invariant points q or f and pierces the silica saturation plane i e the join di an en in the silica saturated field in this compositional range the al solubility in clinopyroxene changes drastically from one side of the thermal divide to the other with great increase of al solubility in the silica undersaturated field four endmembers must be used to describe the complex solid solution of anorthite caal2si2o8 camgsi3o8 mgal2si2o8 and si4o8 the last two of these are present only within the silica saturated field unlike clinopyroxene the mg content of anorthite is insensitive to the thermal barrier but is only sensitive to silica saturation plane olivine composition can be described by a binary solid solution of forsterite and monticellite with no ca in the m2 site as with anorthite olivine compositions exhibit a marked change with crossing of the silica saturation plane the above features imply that the solubility of minor elements in crystalline phases al in clinopyroxene ca in olivine and mg in anorthite selectively respond to only one or another of these particular plane results have many important consequences one is the likelihood of changes in melt speciation depending on position with respect to the thermal divide and the silica saturation plane

chronology of the angrite parent body and implications for core formation in protoplanets abstract angrites formed by some of the earliest igneous activity in the solar system and provide insights into the early stages of planetary melting and differentiation moreover they are pivotal reference points for early solar system chronology in order to study the processes and timescales of metal segregation in early protoplanets and to assess the distribution of short lived radionuclides in the early solar system the 182 hf 182 w system was applied to a comprehensive suite of angrites 182 hf 182 w isochron ages for angrites are in excellent agreement with previously reported 207 pb 206 pb and 53 mn 53 cr results but are 1 myr older than ages obtained from 26 al 26 mg chronometry these inconsistencies probably reflect a disturbance of the al mg system in the angrite feldspars but could alternatively be explained by a heterogeneous distribution of 26 al in the early solar system based on the hf w results four texturally and temporally resolved groups of angrites can be identified that were derived from at least two distinct mantle sources these mantle sources are the result of separate events of core formation both of which took place within 2 myr of cai formation thus core formation in the angrite parent body did not occur as a single event of metal segregation from a global magma ocean but rather took place under varying conditions by several more local events the disparate hf w systematics of the two distinct angrite source regions indicate that convection in the magma ocean was inefficient in homogenizing the composition of the mantle possibly as a result of a continuous bombardment with small planetesimals during ongoing core formation such impacts could have constantly removed primordial and earlier formed crust facilitating rapid cooling of the magma ocean which solidified as early as 3 6 0 7 myr after cai formation

the effects of feo on the system cmas at low pressure and implications for basalt crystallization processes the common occurrence of olivine clinopyroxene and plagioclase in natural basalts may suggest that crystallization of these phases exerts important controls on the evolution of natural basalts at low pressure in order to understand the effects of such an assemblage on the evolution of basalt an experimental study of the divariant assemblage 1 an cpx ol in the system cmas feo was undertaken at 1 bar and under very reducing conditions experiments have been performed along three isothernal sections detailed electron microprobe data have been collected on all the coexisting phases combining these data with available data in the system cmas the compositions of all the coexisting phases have been described as functions of temperature and cao content in the melt by applying a multiple linear regression method this allows a quantitative characterization of the divariant assemblage 1 an epx ol in the system cmas feo from 1275 c to 1160 c with liquid compositions ranging from mg 1 to mg 0 28 knowing the composition temperature relationships the basic t x configuration of the assemblage 1 an cpx ol has been analysed and mass balance calculations have been performed to examine the feo effect on different crystallization processes addition of feo to the system cmas transforms the thermal divide in the assemblage 1 an cpx ol to a thermal ridge and shifts the spine of the thermal ridge towards sio2 poor compositions with decreasing temperature this indicates that tholeiitic basalts can be relatively silica poor and evolve towards slightly more silica poor compositions with increasing feo content pigeonite replaces ortheonstatite as a crystallizing phase along the silica rich boundary of the assemblage 1 an cpx ol in some iron and silica rich composition olivine possibly terminates its crystallization or even starts resorption prior to pigeonite precipitation this suppresses silica enrichment in the melt crystallization paths of the assemblage 1 an cpx ol are determined by the detailed t x relations of the thermal ridge with the melt evolving away from the spine the liquid evolution trend depends strongly on the initial compositions a tholeiitic liquid can follow a moderate silica enrichment path at the same very reducing condition of there is a high modal proportion of olivine a fenner mechanism therefore is at work at the same place as a bowen mechanism

thermal histories of angrite meteorites trace element partitioning among silicate minerals in angra dos reis lewis cliff 86010 and experimental analogs we measured rare earth element ree abundances in selected silicate phases in the angrites angra dos reis ador and lewis cliff lew 86010 in order to further clarify the thermal history of ador we also carried out a preliminary experimental study designed to examine apparent ree partitioning between silicates fassaite olivine kirschsteinite and melt in synthetic analogs of angrites under disequilibrium conditions at liquidus temperatures silicates in ador are homogeneous with respect to major minor and trace elements which is consistent with the interpretation that ador underwent extensive subsolidus equilibration ree distributions in olivine and kirschsteinite in ador are similar to those in lew 86010 and are consistent with the formation of kirschsteinite by exsolution from olivine during cooling and or annealing there is no evidence for a disequilibrium trace element signature that could have been inherited from rapid cooling at liquidus temperatures this is supported by our petrographic observations of the occurrence of kirschsteinite within olivine aggregates in ador olivine kirschsteinite pairs in ador record closure temperatures around 600 650 c

petrogenesis and provenance of ungrouped achondrite northwest africa 7325 from petrology trace elements oxygen chromium and titanium isotopes and mid ir spectroscopy northwest africa nwa 7325 is an ungrouped achondrite that has recently been recognized as a sample of ancient differentiated crust from either mercury or a previously unknown asteroid in this work we augment data from previous investigations on petrography and mineral compositions mid ir spectroscopy and oxygen isotope compositions of nwa 7325 and add constraints from cr and ti isotope compositions on the provenance of its parent body in addition we identify and discuss notable similarities between nwa 7325 and clasts of a rare xenolithic lithology found in polymict ureilites nwa 7325 has a medium grained protogranular to poikilitic texture and consists of 10 15 vol mg rich olivine fo 98 25 30 vol diopside wo 45 mg 98 55 60 vol ca rich plagioclase an 90 and trace cr rich sulfide and fe ni metal we interpret this meteorite to be a cumulate that crystallized at 1200 c and very low oxygen fugacity similar to the most reduced ureilites from a refractory incompatible element depleted melt modeling of trace elements in plagioclase suggests that this melt formed by fractional melting or multi stage igneous evolution a subsequent event likely impact resulted in plagioclase being substantially remelted reacting with a small amount of pyroxene and recrystallizing with a distinctive texture the bulk oxygen isotope composition of nwa 7325 plots in the range of ureilites on the ccam line and also on a mass dependent fractionation line extended from acapulcoites the e54cr and e50ti values of nwa 7325 exhibit deficits relative to terrestrial composition as do ordinary chondrites and most achondrites its e54cr value is distinct from that of any analyzed ureilite but is not resolved from that of acapulcoites as represented by acapulco in terms of all these properties nwa 7325 is unlike any known achondrite however a rare population of clasts found in polymict ureilites the magnesian anorthitic lithology are strikingly similar to nwa 7325 in mineralogy and mineral compositions oxygen isotope compositions and internal textures in plagioclase these clasts are probably xenolithic in polymict ureilites and could be pieces of nwa 7325 like meteorites using constraints from chromium titanium and oxygen isotopes we discuss two possible models for the provenance of the nwa 7325 parent body 1 accretion in the inner solar system from a reservoir similar to that of acapulcoites in 17o e54cr and e50ti or 2 early 1 ma after cai formation accretion in the outer solar system beyond the snow line before 54cr and 50ti anomalies were introduced to this region of the solar system the mid ir emission spectrum of nwa 7325 obtained in this work matches its modal mineralogy and so can be compared with spectra of new meteorites or asteroids planets to help identify similar materials and or the parent body of nwa 7325

laboratory hydration of condensed magnesiosilica smokes with implications for hydrated silicates in idps and comets samples of silica rich and mgo rich condensed amorphous magnesiosilica smokes were hydrated to monitor systematic mineralogical and chemical changes as a function of time and temperature controlled by their unique metastable eutectic compositions their porous texture and the ultrafine nanometer grain size of all entities at water supersaturated conditions proto phyllosilicates formed by spinodal type homogeneous nucleation their formation and subsequent growth was entirely determined by the availability of water via pore spaces inherited from the original smokes and the textural continuity of magnesiosilica material with a mostly smectite dehydroxylate composition the results may have implications for the hydration of proto ci material the presence of rare periclase and brucite in primitive solar system bodies and the pervasiveness of hydrated amorphous magnesiosilica dust and saponite proto phyllosilicates in icy protoplanets such as comet nuclei

the cooling history of the lewis cliff 86010 angrite as inferred from kirschsteinite lamellae in olivine olivine in the angritic meteorite lewis cliff lew 86010 contains abundant exsolution lamellae of kirschsteinite compositional gradients adjacent to the interface in both host and lamellae were formed by diffusion of chemical components into and out of the lamellae during cooling and growth we have compared these gradients with compositional profiles calculated from diffusion and heat flow equations to estimate the cooling rate and burial depth of the sample the resulting values for cooling rate and burial depth depend on which values are used for the diffusion rate of ca in olivine and how measured diffusivities are extrapolated to the lower temperatures at which the lamellae grew if the highest diffusion coefficients are used the cooling rates obtained from seven different lamellae range from 30 to 52 c year with an average of 42 c year and burial depths assuming an overburden with a thermal diffusivity typical of solid rock range from 14 to 17 m with an average of 15 m if the lowest reasonable diffusion coefficients are used the cooling rates range from 1 4 to 2 2 c year with an average of 1 7 c year and the depths range from 68 to 83 m with an average of 75 m for the highest ca diffusivities details of the compositional profiles near the olivine kirschsteinite interface suggest that continuous cooling was greatly accelerated at a temperature near 600 700 c the simplest physical explanation for such an acceleration is excavation of the sample from its original burial depth by an impact event if ca diffusivities are lower a two stage cooling history is not required

trace element distributions within ordinary chondrite chondrules implications for chondrule formation conditions and precursors the concentrations of thirty six lithophile elements in the major silicate phases of chondrules have been determined by ion microprobe two types of porphyritic chondrule olivines normal and incompatible rich have been identified the incompatible rich olivines which have forsterite contents that are greater than fo98 appear to have formed under highly reducing conditions the olivine and low ca pyroxene grains in porphyritic chondrules have relatively unfractionated l chondrite normalized ree abundances compared to expectations from equilibrium distribution coefficients this is consistent with porphyritic chondrules having formed at cooling rates of the order of 1000 c h or faster the alkali metal na k rb and cs to al ratios in chondrule glasses vary by two orders of magnitude the lower values possibly being the result of volatile loss from chondrules no correlation was found between alkali metal depletions in chondrule glasses and enrichments in the surrounding rims but any such correlation may have been destroyed by the diffusive redistribution of these elements in rims that is likely to occur even under mild metamorphic conditions the refractory lithophiles with the exception of mg are all highly incompatible in silicate melts and are as a result concentrated in the chondrule glasses the refractory lithophiles in the glass are in most cases unfractionated from one another suggesting that neither vapor phase nor crystal liquid fractionation played a major role in the formation of chondrules or their precursors based largely on the observation that the refractory lithophiles are concentrated in the chondrule glasses it is suggested that previously reported correlations between these elements in bulk chondrule analyses are due to chondrules themselves as opposed to refractory condensates having been their own immediate precursors a simple monte carlo simulation using the compositions of the major chondrule silicate phases reported here supports this hypothesis it is argued that the upper limit of about one observed in the atomic na al ratios of chondule glasses is not due to an albitic precursor but simply reflects that for na to be incorporated into the structure of the melt it must take part in the coupled substitution naalo2 sio2

dynamic crystallization experiments on the angra dos reis achondritic meteorite abstract with the recent discovery of angrite meteorites in the antarctic collection which clearly have a melt origin the hypothesis that angra dos reis ador itself is a cumulate is being reconsidered a recent model suggests that ador is a porphyry not a cumulate dynamic crystallization experiments have been conducted to determine whether a melt of ador composition can crystallize with porphyritic textures at reasonable cooling rates under appropriate heterogeneous nucleation conditions the nucleation conditions were varied by melting the starting material at different degrees of superheat porphyritic textures were produced if nuclei are absent from the melt and embryos are few in number if some degree of supercooling is developed while the embryos are growing to critical size the phenocrysts grow with skeletal shapes fassaitic pyroxene grows over a large temperature interval before the appearance of kirschsteinite spinel and a pyroxferroite like phase alternatively if the nucleation density is high and irregularity distributed at the beginning of cooling a granular texture very similar to ador is produced in this case the large fassaites would grow later and poikilitic enclose the early formed granular fassaite the phases present and their composition depend on the oxygen fugacity and a complex redox history for ador can be inferred olivine is not present in quantities compatible with ador and kirschsteinite appears to have been stabilized kinetically in the experiments while a volcanic or hypabyssal history for ador is possible based on the experiments the presence of olivine particularly as a phenocryst remains unexplained

plant patch hydrodynamics in streams mean flow turbulence and drag forces 1 this paper investigates the effects of a finite size vegetation patch on flow turbulence variations in drag forces experienced by individual plants within the patch and flow drag interrelations the experiments were conducted in a 32 m long laboratory flume with a 2 8 m long artificial patch the plants were arranged to form a staggered pattern and three flow scenarios were tested velocities were recorded with an acoustic doppler velocimeter whereas specifically designed devices were used to simultaneously measure the drag forces acting on nine plants within the patch for all studied cases the results show zones of increased turbulent energy close to the leading edge and along the patch canopy top where turbulence shear production is enhanced zones of negative reynolds stresses u w are found inside the patch and they reflect the influence of plant morphology which affects the shape of the longitudinal velocity profile and associated turbulent fluxes modifications to the power spectral densities of velocity by the plants indicate the emergence of two plant induced mechanisms of energy production which are most likely related to the wake turbulence and shear layer turbulence drag fluctuations appear to be correlated with the velocity field with this correlation being especially profound at the highest studied flow rate the data suggest that the highlighted correlation stems from flow plant interactions at the top of the vegetation canopy likely due to the presence of large three dimensional coherent structures

diffusion kinetics of cr in olivine and 53mn 53cr thermochronology of early solar system objects we have determined the diffusion coefficient of cr in olivine as function of temperature oxygen fugacity fo2 and crystallographic orientation and used these data to develop a quantitative understanding of the resetting of the short lived 53 mn 53 cr decay system in olivine during cooling within meteorite parent body the diffusion of cr in olivine was found to be anisotropic and effectively indepen dent of fo2 between wustite iron buffer and two orders of magnitude above this buffer the diffusion data were used to calculate the spatially averaged mean closure temperature of the 53 mn 53 cr decay system in olivine as function of the initial temperature cooling rate and grain size and also the closure age profile of this system in olivine single crystal as function of radial distance and a dimensionless parameter that incorporates the effects of various parameters that affect the closure age we also present a thermochronolgic formulation that permits retrieval of cooling rates from the extent of resetting of the bulk 53 mn 53 cr closure age of olivine during cooling this method was applied to determine the cooling rate of the pallasite omolon which showed 53 mn 53 cr bulk age of olivine that is 10 myr younger than the age of the solar system the calculated cooling rate which is 20 40 c myr at 985 1000 c is in good agreement with the metallographic cooling rate at 500 c when the two results are considered in terms of a cooling model in which the reciprocal temperature increases linearly with time the inferred cooling rate of omolon which seems to be a sample from the core mantle boun dary yields a burial depth of 30 km in a parent body of at least 100 km radius

numerical model for coastal wave propagation through mild slope zone in the presence of rigid vegetation abstract the study of wave propagation on coastal vegetation field is fundamental to assessing the effectiveness and limitations of vegetation in coastal protection this paper presents a refraction diffraction wave model for the investigation of wave propagation through a coastal mild slope zone in the presence of rigid vegetation via numerical simulation the model is based on the implementation of a module for vegetation induced wave energy dissipation in the parabolic mild slope equation the model is capable of simulating both wave refraction and diffraction and economical in computation and may bridge the gap between the wave energy spectrum and the phase resolved models for wave propagation through coastal vegetation fields the model is validated through by comparison with experimental results the model is subsequently applied to a simulation of a wave propagating on a plane in the presence of different patterns of rigid vegetation the sensitivity of the wave height to the plant height the diameter and the stem density is investigated by comparison of the numerical results for wave height attenuation that results from different patterns of rigid vegetation the numerical results show that wave height attenuation due to rigid vegetation has a higher variability for the different rigid plant conditions and that the attenuation of the wave height due to the rigid vegetation increases alongside the plant height under water as well as the diameter and plant stem density the results further indicate that for wave propagates through coastal rigid vegetation zones with a high plant height under water large diameter and high stem density the wave height along the propagating direction is decreased nonlinearly with the increase of the wave propagating distance and nonlinearity is more obvious for the plant with a higher height under water as well as a larger diameter and higher stem density

plant stiffness and biomass as drivers for drag forces under extreme wave loading a flume study on mimics abstract moving water exerts drag forces on vegetation the susceptibility of vegetation to bending and breakage determines its flow resistance and chances of survival under hydrodynamic loading to evaluate the role of individual vegetation parameters in this water vegetation interaction we conducted drag force measurements under a wide range of wave loadings in a large wave flume artificial vegetation elements were used to manipulate stiffness frontal area in still water and material volume as a proxy for biomass the aim was to compare i identical volume but different still frontal area ii identical stiffness but different still frontal area and iii identical still frontal area but different volume comparison of mimic arrangements showed that stiffness and the dynamic frontal area i e frontal area resulting from bending which depends on stiffness and hydrodynamic forcing determine drag forces only at low orbital flow velocities did the still frontal area dominate the force velocity relationship and it is hypothesised that no mimic bending took place under these conditions mimic arrangements with identical stiffness but different overall material volume and still frontal area showed that forces do not increase linearly with increasing material volume and it is proposed that short distances between mimics cause their interaction and result in additional drag forces a model based on effective leaf length and characteristic plant width developed for unidirectional flow performed well for the force time series under both regular and irregular waves however its uncertainty increased with increasing interaction of neighbouring mimics

sediment retention by a mediterranean posidonia oceanica meadow the balance between deposition and resuspension the role of posidonia oceanica in promoting sediment stability and accretion was studied in a 15 m deep meadow at fanals point nw mediterranean spain by comparing particle deposition within the meadow and adjacent bare sediment small sediment traps were used to measure deposition within and above the meadow and over bare sand a model based on measurements of particle deposition at increasing distances from the bottom was used to partition the total depositional flux between primary sediment particles deposited for the first time at the measuring site and resuspended deposition sediment particles that have been previously deposited at the measuring site measurements were conducted monthly over a year to establish the magnitude and seasonality of deposition and to form a balance of particle transport at the annual time scale significant differences in total deposition were found over time ranging from 1 5 to 500 g dw m 2 d 1 including those between bare and vegetated sediments the effect of p oceanica in increasing primary deposition at an annual scale was modest however p oceanica significantly buffered sediment resuspension which was reduced more than three fold compared to the unvegetated bottom the annual flux of deposition was dominated by settling of resuspended materials which represented 85 of the total flux within the meadow but 95 of the total deposition on bare sand thus seagrass meadows reduce resuspension in the nw mediterranean littoral thereby contributing to increased sediment retention and therefore reducing erosion in the coastal zone

pb diffusion in cr diopside augite and enstatite and consideration of the dependence of cation diffusion in pyroxene on oxygen fugacity abstract chemical diffusion of pb under anhydrous po2 buffered conditions has been measured in natural pyroxenes of three different compositions a chromian diopside an augitic clinopyroxene and a near end member enstatite sources of diffusant consisted of pbs powder and ground pyroxene mixed together pre reacted in evacuated silica capsules at 1050 c and re ground prepared sample capsules were annealed for times ranging from several hours to a few months at temperatures from 850 c to 1050 c the pb distributions in the pyroxene specimens were profiled by rutherford backscattering spectrometry rbs the following arrhenius relations are obtained for pb diffusion in the pyroxenes when buffered at qfm d c 8 7 10 7 exp 351 36 kj mol 1 rt m 2 s 1 cr diopside d a 3 8 10 5 exp 372 15 kj mol 1 rt m 2 s 1 augite d e 6 6 10 7 exp 366 29 kj mol 1 rt m 2 s 1 enstatite in all cases diffusion is measured perpendicular to the c axis diffusion in cr diopside does not appear to be strongly anisotropic as diffusion rates for transport parallel to c are similar to the 110 results above diffusion in the augite is faster by nearly an order of magnitude than pb diffusion in the cr diopside diffusion tends to be faster in pyroxenes with higher iron contents as was evident in our earlier work chemical geology 150 1998a 105 but simple correlations are not obvious pb diffusion in enstatite is considerably slower than in the clinopyroxene compositions studied to investigate the fo2 dependence of pb diffusion in pyroxene experiments using the cr diopside augite and enstatite as well as the near end member diopside and a more iron rich clinopyroxene employed in a recent diffusion study chemical geology 150 1998a 105 were run at 950 c under oxygen fugacities ranging from 10 6 to 10 16 all of the pyroxenes exhibited a positive dependence of pb diffusion rate on fo2 with values of m ranging from 0 14 to 0 20 given d fo2 m interestingly the exponential term for diopside is 0 19 in good agreement with the value 3 16 determined from point defect models for diffusion mechanisms controlled by cation vacancies j geophys res 99 1994 9423 the activation energies for pb diffusion in all of the pyroxenes studied are relatively high and pb diffusivities slow when compared with the extant diffusion data for most other minerals it follows as consequence of these comparatively slow diffusivities that pb closure temperatures are higher in pyroxenes than for the majority of minerals with the exception of a few phases such as zircon monazite and garnet the slightly faster diffusivities that characterize fe rich clinopyroxenes will lead to somewhat depressed closure temperatures but pyroxenes in general should be fairly retentive of pb isotopic information when subjected to all but the most extreme thermal events

subsidence associated with the lusi mud eruption east java investigated by sar interferometry abstract a mud volcano lusi initiated its eruption on 29 may 2006 adjacent to a hydrocarbon exploration well in east java ground subsidence in the vicinity of the lusi eruptive vent was well recorded by a synthetic aperture radar sar palsar onboard the japanese alos satellite we apply an interferometric sar insar technique on ten palsar data scenes acquired between 19 may 2006 and 21 may 2007 in order to obtain continuous maps of ground displacements around lusi although the displacements in the area closest to the eruptive vent spatial extension of about 1 5 km are not detectable because of the erupted mud all the processed interferograms indicate subsidence in an ellipsoidal area of approximately 4 km north south 3 km east west centered at the main eruptive vent in particular interferograms spanning the first four months until 4 oct 2006 and the subsequent 46 days between 4 oct 2006 and 19 nov 2006 show at least about 70 cm and 80 cm of displacements away from the satellite respectively possible causes of the subsidence i e 1 loading effect of the erupted mud 2 creation of a cylindrical mud conduit and 3 pressure decrease and depletion of materials at depth are investigated the effects of the first two causes are found to be insufficient to explain the total amount of subsidence observed in the first six months the third possibility is quantitatively examined using a boundary element approach by modeling the source of deformation as a deflating oblate spheroid the spheroid is estimated to lie at depths of a few hundred to a thousand meters the estimated depths are significantly shallower than determined from analyses of erupted mud samples the difference is explained by presence of significant amount of inelastic deformation including compaction and downward transfer of material

metamorphic angrite northwest africa 3164 5167 compared to magmatic angrites abstract northwest africa nwa 3164 and 5167 are two angrites with a granulitic texture unlike that of other angrites with a variable up to millimeter grain size besides mineralogical and chemical similarities to other angrites nwa 3164 and 5167 exhibit unique characteristics ca rich olivine dominates in nwa 3164 49 vol fo57 nwa 5167 40 vol fo59 fassaitic clinopyroxene is the second major phase in nwa 3164 29 vol in nwa 5167 36 vol with a significant tschermak component in addition two al rich phases are present plagioclase an99 and hercynitic spinel 6 and 7 vol respectively for nwa 3164 17 and 4 vol respectively for nwa 5167 heavily weathered iron sulfide and kamacite 9 wt in nwa 3164 4 wt in nwa 5167 are the remaining minor phases a unique feature among angrites all mineral phases are homogeneous like other angrites nwa 3164 and 5167 exhibit a superchondritic ca al ratio with negligible amounts of alkalis and very low silica content the presence of metal results from the incorporation of exogenous iron following impact subsequent annealing resulted in the observed granulitic texture major element composition indicates that both nwa 3164 and 5167 are derived from a picritic angrite precursor after incorporation of metal and annealing after correction for iron and fo90 olivine incorporation bulk rock ree abundances of both nwa 3164 and nwa 5167 appear lower than those of quenched angrites showing the lowest absolute abundances among angrites laser ablation inductively coupled plasma mass spectrometry la icp ms analyses of clinopyroxene olivine and anorthite indicate that difference of rare earth element ree abundances between nwa 3164 and nwa 5167 can be explained by adding traces of phosphate to nwa 3164 nwa 3164 5167 trace elements abundances are similar showing depletion in volatile elements and enrichment in refractory lithophile elements such as ca ti and al the most incompatible elements are depleted as well unlike other angrites this indicates that the source of these younger angrites was more depleted in incompatible elements when compared to the older magmatic angrites the low hf w is understood as the result of exogenous iron incorporation and therefore the hf w and w isotopic heterogeneity of the angrite parent body apb mantle is secondary comparison with other angrites suggests that iron incorporation may be necessary to explain their low hf w and w isotopic compositions

drag force on a vegetation field due to long crested and short crested nonlinear random waves this paper provides a practical method for estimating the drag force on a vegetation field exposed to long crested 2d and short crested 3d nonlinear random waves this is achieved by using a simple drag formula together with an empirical drag coefficient given by mendez et al 1999 in conjunction with a stochastic approach here the waves are assumed to be a stationary narrow band random process effects of nonlinear waves are included by adopting the forristall 2000 wave crest height distribution representing both 2d and 3d random waves

distinct 238 u 235 u ratios and ree patterns in plutonic and volcanic angrites geochronologic implications and evidence for u isotope fractionation during magmatic processes angrites are differentiated meteorites that formed between 4 and 11 myr after solar systemformation when several short lived nuclides e g 26 al 26 mg 53 mn 53 cr 182 hf 182 w were still alive as such angrites are prime anchors to tie the relative chronology inferred from these short lived radionuclides to the absolute pb pb clock the discovery of variable u isotopic composition at the sub permil level calls for a revision of pb pb ages calculated using an assumed constant 238 u 235 u ratio i e pb pb ages published before 2009 2010 in this paper we report high precision u isotope measurement for six angrite samples nwa 4590 nwa 4801 nwa 6291 angra dos reis d orbigny and sahara 99555 using multi collector inductively coupled plasma mass spectrometry and the irmm 3636 u double spike the age corrections range from 0 17 to 1 20 myr depending on the samples after correction concordance between the revised pb pb and hf w and mn cr ages of plutonic and quenched angrites is good and the initial 53 mn 55 mn 0 ratio in the early solar system ess is recalculated as being 7 1 10 6 at the formation of the solar system the error bar incorporates uncertainty in the absolute age of calcium aluminum rich inclusions cais an uncertainty remains as to whether the al mg and pb pb systems agree in large part due to uncertainties in the pb pb age of cais a systematic difference is found in the u isotopic compositions of quenched and plutonic angrites of 0 17 a difference is also found between the rare earth element ree patterns of these two angrite subgroups the 238 u values are consistent with fractionationduring magmatic evolution of the angrite parent melt stable u isotope fractionation due to a change in the coordination environment of u during incorporation into pyroxene could be responsible for such a fractionation in this context pb pb ages derived from pyroxenes fraction should be corrected using the u isotope composition measured in the same pyroxene fraction

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

chemical isotopic and mineralogical evidence for the origin of matrix in ordinary chondrites abstract we report the first combined chemical isotopic and mineralogical study of fine grained opaque matrix material from a type 3 ordinary chondrite allan hills a77299 h3 7 electron microprobe and instrumental neutron activation analysis of a large matrix lump show that it has a major element composition typical of matrix material in type 3 chondrites unlike chondrules it shows no siderophile element depletions and is remarkably unfractionated relative to ci chondrites suggesting that it is primitive solar system material the matrix lump has an unique oxygen isotopic composition which lies below the terrestrial fractionation line and differs markedly from the composition of fine grained matrix lumps and chondrule rims from semarkona grossman et al 1987 transmission electron microscope tem studies of microtomed samples of the fine grained fraction m of the matrix lump show that it consists of rare angular clastic grains 1 m of pyroxene and olivine embedded within a groundmass of rounded fine grained m olivines the mineralogy and textures of the matrix lump are typical of other occurrences of fine grained matrix studied by tem in other type 3 ordinary chondrites we conclude that the matrix lump in alha 77299 consists largely of material that formed by annealing of amorphous presolar dust or nebular condensates and could not have been derived from chondrules by any reasonable mechanism however the observed compositional differences between the matrix lump and chondrules in ordinary chondrites are consistent with the idea that some chondrules formed by melting of matrix like material accompanied by loss of siderophile and volatile elements

lusi mud eruption triggered by geometric focusing of seismic waves the lusi mud eruption in indonesia has been ongoing since 2006 numerical simulations show that a parabolic shaped layer in the rock surrounding the site of the lusi eruption could have amplified and focussed incoming seismic energy from an earthquake which then triggered the mud eruption

reassessing the origin and chronology of the unique achondrite asuka 881394 implications for distribution of 26al in the early solar system abstract the achondrite asuka 881394 has mineralogy broadly similar to that of eucrites but is isotopically chemically and texturally distinct from them previous u pb chronology shows that it is very old forming within the first 0 8 ma of the formation of calcium aluminum rich inclusions cais however the age difference between asuka 881394 and other very old solar system materials cais quenched angrites measured with the 26al 26mg and 53mn 53cr extinct radionuclide chronometers and 207pb 206pb chronometer is not the same this could be interpreted to reflect heterogeneity in the distribution of 26al and 53mn in the early solar system given the significant implications for the early solar system chronology if 26al and 53mn are indeed heterogeneously distributed in this study we further investigate the origin of asuka 881394 and the apparent age discordance between short lived and absolute chronometers by focusing on measurement of its e54cr composition renewed measurements of the absolute pb pb age and new high precision measurements of its 26al 26mg systematics new cr isotope data places additional constraints on the origin of asuka 881394 its e 54cr value of 0 37 0 10e is resolvable outside of uncertainty from hed meteorites 0 72 0 10e reinforcing evidence from oxygen isotopic analyses that suggest it originated from a distinct parent body unlikely to be 4 vesta new pb pb analyses combined with using a directly measured 238u 235u ratio for age calculation result in a recalculated pb pb age of 4564 95 0 53 ma 1 5 ma younger than the previously reported age with this age asuka 881394 remains one of the oldest known achondrites in our solar system new high precision 26al 26mg data produce an initial 26al 27al ratio of 1 48 0 12 10 6 within error of previous data this ratio corresponds to an al mg age of 4563 69 0 36 ma or 4564 83 0 21 ma relative to cais and the d orbigny angrite respectively thus depending on which age anchor is used the 26al 26mg age is either 1 26 ma or 0 12 ma younger than the new pb pb age the latter being unresolved within analytical uncertainty though a potential age discrepancy between 26al 26mg and pb pb could be a result of heterogeneous distribution of 26al we demonstrate with our new high precision mg isotope data in conjunction with petrographic evidence that the mg isotope system has been disturbed in asuka 881394 we suggest that the 26al 26mg system closed to diffusion after the u pb system either due to slow cooling on the parent body or low grade metamorphic re equilibration of mg thus we can satisfactorily explain the observed age discrepancy between 26al 26mg and u pb systems in asuka 881394 without invoking heterogeneous distribution of 26al 27al ratio in the early solar system comparison of the asuka 881394 data with that of other anomalous achondrites from distinct parent bodies suggests that these could also have evolved from a source region with a canonical 26al 27al ratio because these achondrites have significant differences in their e54cr 17o systematics which could be indicative of location within the early protoplanetary disk it is consistent with homogeneous distribution of 26al in the early solar system angrites remain an outlier either because they evolved from a source with a lower 26al 27al ratio or because their 26al 26mg or pb pb data are problematic in either case this suggests that basaltic angrites are questionable as the age anchor for the entire solar system as a whole and other very old well preserved achondrites should be considered for that role

petrology of alh85085 a chondrite with unique characteristics abstract alh85085 has several characteristics which set it apart from any known chondritic group its chondrules are smaller 25 75 m the majority are cryptocrystalline and all are volatile na k s depleted feni metal is more abundant 40 9 wt than in any other chondrite and sulfide abundance is low 1 1 matrix material does not surround the chondrules and fragments but occurs as lithic clasts lumps up to 300 m across the bulk composition of alh85085 is lower in na si and s si and higher in ni si fe si and mg si than in other chondritic groups the ca si al si and mg si ratios are closest to those of the renazzo chondrite grouplet cr matrix lumps are most similar to cr and murchison group cm chondrite matrices survival of this fragile matrix material as lithic clasts indicates that they were added just prior to the agglomeration of the chondrite all components chondrules fragments matrix lumps fall within a narrow size range which may be the result of aerodynamic sorting if so the sorting must have occurred after chondrule solidification and following a period of chondrule breakage since fragments from larger chondrules are present the ni vs co trend in the feni metal overlaps that of metal in cr chondrites and bencubbin these trends are similar to those of calculated nebular condensation paths indicating a nebular origin the cryptocrystalline texture and volatile depletion of the chondrules indicate that most chondrules were heated to temperatures above the liquidus although alh85085 cannot now be assigned to any known chondrite group it shares many similarities with cr chondrites and the bencubbin metal silicate chondritic assemblage and may be part of a chondritic group closely related to these meteorites

olivinites in the angrite d orbigny vestiges of pristine reducing conditions during angrite formation abstract olivinites together with olivine megacrysts are the most magnesian phases found in angrites their chemical composition mg 90 is out of equilibrium with the groundmass and far away from that of possible precipitates from angrite parent melts therefore olivinites as well as olivine megacrysts were considered as xenoliths and xenocrysts we report here a detailed study of five olivinites from the angrite d orbigny our results indicate that d orbigny experienced metasomatic alteration processes which led to enrichments in feo and mno relative to the original composition changing the initial mg rich composition of the olivines to the one seen now as this process took place in equilibrium with a chondritic reservoir e g fe mn ratios spreading around primitive values the primitive mg rich olivine chemical composition was changed towards a more fayalitic one while preserving a chondritic signature this chondritic signature was preserved in the fe mn ratio of the olivinites olivine megacrysts augite grains in olivinites and groundmass olivine of d orbigny therefore the fayalite content of about 35 mol that characterizes the groundmass olivine of this rock as well as other angrites does not correspond to its original composition but may be the result of a late metasomatic process that affected these rocks if so olivinites and mg rich olivines might not be compositionally exotic phases but are an early constituent phase that retained the pristine more reducing conditions that have been preserved in some angrites where they form either a small part of the rock e g asuka 881371 and d orbigny or the majority of it nwa 8535

the goshogake mud volcano field tohoku northern japan an acidic high temperature system related to magmatic volcanism abstract the high temperature 33 98 c highly acidic ph 2 44 2 94 goshogake mud volcano field in akita prefecture northern japan is a mud volcano system associated with the quaternary andesitic composite volcano akita yakeyama the mud volcano features observed in goshogake include salsa ponds gryphons and mud pots this is a rare example of mud volcano systems linked with magmatic volcanism with the full range of landforms observed primarily in low temperature mud volcanism in sedimentary settings the goshogake mud volcano field is probably not a simple hydrothermal system related to a magmatic volcano instead it appears to be a hybrid system sedimentary volcanism linked with deep mud sources and strongly influenced by its surrounding magmatic volcanism the identified mineral species in the sampled mud include quartz group hydrous silica muscovite kaolinite pyrite and sulfur the presence of high temperature silica polymorphs tridymite and cristobalite and or microcrystalline opals opal c opal ct and an amorphous form of silica opal a in the mineralogy indicates that the mud volcano system likely involves conditions and processes such as high temperature hydrothermal circulation dehydration reaction at certain depths underneath the goshogake mud volcano field although the source of the mud is not clearly determined possible options include 1 hydrothermal alteration products of host rocks and sediments 2 fine grained sedimentary layer s at depth or 3 a combination of 1 and 2 in situ measurement of emitted gases from vents detected methane which is possibly linked with the organic rich sedimentary layer s aside from being a product of thermodynamic equilibrium with co2 under the subsurface pressure temperature conditions the increases in d and 18o of water in goshogake mud volcanoes with respect to the values of current meteoric water indicates that the water was derived not only from meteoric water and deviation of the values may be explained by processes such as evaporation and mixing of other waters from deeper sources regarding the driving mechanisms at the goshogake mud volcanoes buoyancy of muddy sediment high fluid pressure under overpressured or under compacted conditions due to rapid sedimentation together with the presence of a gas phase in the sediment could be key factors although the goshogake mud volcano field currently maintains a low level activity resulting in only minor morphological changes of the mud volcano landforms enhanced activities have been documented in the last half century the historical records are inconclusive about the relationship between earthquakes and activity in the goshogake mud volcano field

the u pb systematics of angrite sahara 99555 abstract angrite sahara 99555 hereafter sah precisely dated by baker et al baker j bizzarro m wittig n connelly j and haack h 2005 early planetesimal melting from an age of 4 5662 gyr for differentiated meteorites nature 436 1127 1131 has been proposed as a new reference point for the early solar system timescale and for calculation of the revised minimum age of our solar system the pb pb age of sah of 4566 18 0 14 ma reported by baker et al differs from the pb pb age of d orbigny another basaltic angrite of 4564 42 0 12 ma amelin y 2008 u pb ages of angrites geochim cosmochim acta 72 221 232 despite the fact that the relative 53mn 53cr and 182hf 182w ages of these meteorites are identical here i report u pb data for 21 whole rock and pyroxene fractions from sah analyzed using the same approach as d orbigny amelin 2008 these fractions contain between 1 3 and 8 9 pg of total common pb slightly more than analytical blank measured 206pb 204pb ratios are between 625 and 2817 for d orbigny blank corrected 206pb 204pb ratios are between 1173 and 6675 eight acid washed whole rock fractions yielded an isochron age of 4564 86 0 38 ma mswd 1 5 data for pyroxene fractions plot mostly above the whole rock isochron and do not form a linear array in 207pb 206pb vs 204pb 206pb isochron coordinates the 207pb 206pb model dates of the pyroxene fractions vary from 4563 8 0 3 to 4567 1 0 5 ma the difference between whole rock and pyroxene u pb systematics may be a result of re distribution of radiogenic pb at a mineral grain scale several million years after crystallization complexities of sm nd lu hf and possibly 26al 26mg mineral systematics of sah described previously may be related to the same process that caused the re distribution of radiogenic pb disturbance of isotopic chronometers renders sah an imperfect anchor for the early solar system timescale the problems with age determination revealed by the studies of sah call for greater attention in pb isotopic dating of angrites and other achondrites

subsidence and uplift of sidoarjo east java due to the eruption of the lusi mud volcano 2006 present global positioning system gps and satellite based insar interferometric synthetic aperture radar measurements of the subsidence and uplift of a populated area of sidoarjo east java are due to the eruption of the lusi mud volcano 2006 present these data are the first direct quantitative measurements of deformation due to the growth of a mud volcano edifice the gps data were recorded over periods of a few hours to several months and show that between june 2006 and september 2007 the earth s surface has been subsiding at rates of 0 1 4 cm day maximum rates of subsidence occurred in an area 300 400 m to the northwest of the main mud volcano vent horizontal displacements were 0 03 0 9 cm day and were also towards this area in general uplifts of up to 0 09 cm day were recorded in areas outside of the edifice changes in elevation measured using satellite imagery insar technique provide regional datasets of subsidence and uplift they confirm that during the first year a roughly circular area was undergoing sag like subsidence centered to the northwest of the main vent and that uplift was occurring 3 4 months after the initiation of the eruption due to the movement watukosek fault system subsidence occurred due to the weight of mud and man made dams and the collapse of the overburden due to removal of mud from the subsurface assuming constant rates of subsidence of 4 cm day then in the centre of the edifice there would be up to 44 m of subsidence in 3 years and up to 16 m in 10 years the mud volcano is now in a self organizing state with new fluid conduits forming as a result of the collapse

phase equilibrium constraints on angrite petrogenesis parameterizations of liquidus boundaries and solid solution in the cmas fe system shi 1992 have been employed to depict the liquidus equilibria relevant to the petrogenesis of angrites angrites are basaltic achondrites characterized by highly aluminous augite fassaite intermediate mg fe olivine and late stage cafe olivine kirschsteinite two important features of the equilibria on the olivine liquidus surface relevant to angrite petrogenesis are 1 the presence of a thermal divide on the ol aug plag liq boundary curve which separates the compositions of source materials that produce low silica angritic melts that crystallize highly aluminous augite from those that produce higher silica melts with tholeiitic to eucritic crystallization patterns and 2 the change in the pseudo invariant point on the low silica side of the thermal divide from a plagioclase peritectic involving spinel ol aug plag sp liq at high to intermediate mg mg mg fe to two pseudo eutectics involving kirschsteinite ol aug plag kir liq and ol kir plag sp liq at low mg the fassaitic aluminous augite pyroxene composition in angra dos reis ador the presence of minor green spinel and the absence of primary kirschsteinite prinz et al 1977 indicate that crystallization of the ador parental liquid was governed by the intermediate mg set of equilibria such that following crystallization of ol aug plag the plagioclase reacted completely at the plagioclase peritectic with the interstitial liquid which subsequently crystallized beyond the plagioclase peritectic onto the ol aug sp liquidus boundary curve the ador bulk composition is consistent with trapping 10 of the parental liquid in a cumulate with cotectic proportions of fassaite and olivine lewis cliff lew 86010 crystallized from a liquid with mg similar to that of ador but on the ol plag cotectic closer to the thermal divide such that the first pyroxene to crystallize had much lower al content than that of ador in the late stages of crystallization the 86010 residual liquid and that of lew87051 encountered the low mg set of equilibria involving kirschsteinite these relationships require either a higher degree of melting for the 86010 parent magma or source region different than ador s these relationships are also consistent with compositionally dependent ree partition coefficients between fassaite and the ador liquid being as much as 1 5 2 times higher than those for the 86010 liquid at the onset of pyroxene crystallization the combination of a trapped liquid component higher partition coefficients and smaller degrees of melting help to explain the observation that ador an apparent cumulate has ree concentrations twice as high as those in 86010 mittlefehdlt and lindstrom 1990 an apparent chilled liquid the absence of a strong negative eu anomaly in the ador parent liquid however requires relatively high degrees of partial melting to eliminate plagioclase in the source region resorption of plagioclase at the peritectic eliminates the eu anomaly that develops during crystallization so ultimately different source regions are required progressive iron loss from devolatilized primitive chondrites allende murchison produces source regions capable of producing a wide range of melt compositions with angritic to eucritic crystallization behavior the compositions of carbonaceous and ordinary chondrite provide a similar range of potential source region compositions however primitive chondrite fe source regions that produce angrite like melts have mg that is too low whereas chondrite fe sources that have mg sufficiently high to yield the mg in angrite minerals have too much silica or orthopyroxene component to yield angrite like liquids no single group of meteorites fe simultaneously satisfies the constraints of mg and silica component however mixtures of fe depleted chondrite plus a low silica component similar to ca al rich inclusions cais can satisfy the constraints the absence in angrites of 48ca and 50ti anomalies typical of cais lugmair and galer 1992 suggests that the low silica component was not simply an enrichment of cais but was the result of direct accretion of high temperature condensate grossman 1972 into sizable thermally shielded planetesimals thus angrites cryptically record mixing of planetesimal sized heterogeneities in the early solar system

reactive transport modeling an essential tool and a new research approach for the earth sciences abstract reactive transport modeling is an essential tool for the analysis of coupled physical chemical and biological processes in earth systems and has additional potential to better integrate the results from focused fundamental research on earth materials appropriately designed models can describe the interactions of competing processes at a range of spatial and time scales and hence are critical for connecting the advancing capabilities for materials characterization at the atomic scale with the macroscopic behavior of complex earth systems reactive transport modeling has had a significant impact on the treatment of contaminant retardation in the subsurface the description of elemental and nutrient fluxes between major earth reservoirs and in the treatment of deep earth processes such as metamorphism and magma transport active topics of research include the development of pore scale and hybrid or multiple continua models to capture the scale dependence of coupled reactive transport processes frontier research questions that are only now being addressed include the effects of chemical microenvironments coupled thermal mechanical chemical processes controls on mineral fluid reaction rates in natural media and scaling of reactive transport processes from the microscopic to pore to field scale

excess hafnium 176 in meteorites and the early earth zircon record 1 the long lived176lu to 176hf decay system is a powerful tool to understand ancient chemical fractionation events associated with planetary differentiation detrital hadean zircons 3 8 gyr from the jack hills metasedimentary belt of western australia record extremely enriched hf isotope signals suggesting early extraction of a continental crust 4 5 gyr but fail to identify a prevalent complementary depleted mantle reservoir suggesting that crust formation processes in the early earth were fundamentally distinct from today however this conclusion assumes that the hf isotope composition of bulk chondrite meteorites can be used to estimate the composition of earth prior to its differentiation into major silicate reservoirs namely the bulk silicate earth bse we report a176lu 176hf internal mineral isochron age of 4869 34 myr for the pristine sah99555 angrite meteorite this age is 300 myr older than the age of the solar system confirming the existence of an energetic process yielding excess 176hf in affected early formed solar system objects through the production of the 176lu isomer t1 2 3 9 hours thus chondrite meteorites contain excess 176hf and their present day composition cannot be used to infer the lu hf parameters of bse using a revised bse estimate based on the sah99555 isochron we show that earth s oldest zircons preserve a record of coexisting enriched and depleted hafnium reservoirs as early as 4 3 gyr in earth s history with little evidence for the existence of continental crust prior to 4 4 gyr this new view suggests continuous juvenile crustal growth and recycling throughout the hadean and archean eras perhaps analogous to modern plate tectonics

hydrodynamics induced by wind waves in a vegetation field the wave induced kinematics and dynamics of a submerged or emerged vegetation field is analyzed using potential flow and an eigenfunction expansion the problem is solved considering regular as well as irregular incident waves the model takes into account the vegetation motion and solves for the complete wave system on the vegetation field and in its vicinity the model is validated against experimental laboratory data obtained by other authors showing a much better agreement than previous theoretical models in this paper the model is used to evaluate wave height evolution damping vegetation and fluid motion and forces and moments on the vegetation furthermore the inclusion of irregular waves provides force and moment distributions on the vegetation field depending on the wave climate statistics

the non igneous genesis of angrites support from trace element distribution between phases in d orbigny d orbigny is an exceptional angrite chemically it resembles other angrites such as asuka 881371 sahara 99555 lewis cliff lew 87051 and lew 86010 but its structure and texture are peculiar it has a compact and porous lithology abundant glasses augite bearing druses and chemical and mineralogical properties that are highly unusual for igneous rocks our previous studies led us to a new view on angrites they can possibly be considered as cais that grew to larger sizes than the ones we know from carbonaceous chondrites thus angrites may bear a record of rare and special conditions in some part of the early solar nebula here we report trace element contents of d orbigny phases trace element data were obtained from both the porous and the compact part of this meteorite we have confronted our results with the popular igneous genetic model according to this model if all phases of d orbigny crystallized from the same system as an igneous origin implies a record of this genesis should be expressed in the distribution of trace elements among early and late phases our results show that the trace element distribution of the two contemporaneous phases olivine and plagioclase which form the backbone of the rock seem to require liquids of different composition abundances of highly incompatible elements in all olivines including the megacrysts indicate disequilibrium with the bulk rock and suggest liquids very rich in these elements 10 000 x ci which is much richer than any fractional crystallization could possibly produce in addition trace element contents of late phases are incompatible with formation from the bulk systems residual melt these results add additional severe constraints to the many conflicts that existed previously between an igneous model for the origin of angrites and the mineralogical and chemical observations this new trace element content data reported here corroborate our previous results based on the shape structure mineralogy chemical and isotopic data of the whole meteorite as well as on a petrographic and chemical composition study of all types of glasses and give strength to a new genetic model that postulates that d orbigny and possibly all angrites could have formed in the solar nebula under changing redox conditions more akin to chondritic constituents e g cais than to planetary differentiated rock

u pb ages of angrites abstract precise u pb ages determined with double spike 202 pb 205 pb thermal ionization m1ass spectrometry are reported for angrites angra dos reis ador lewis cliff 86010 lew and d orbigny nineteen of 23 acid washed pyroxene fractions from these meteorites and whole rock fractions from d orbigny contain between 0 5 and 1 3 pg of total common pb indistinguishable from analytical blank measured 206 pb 204 pb ratios in these fractions are between 6300 and 14 100 for ador 1160 4500 for lew and 608 8500 for d orbigny blank corrected 206 pb 204 pb ratios for all three meteorites vary from 2160 to over 100 000 these fractions yielded precise and reproducible 207 pb 206 pb dates with the average values of 4557 65 0 13 ma for ador 4558 55 0 15 ma for lew and 4564 42 0 12 ma for d orbigny pb pb isochrons including data with slightly elevated common pb and u pb upper concordia intercepts yield similar dates the implications of these new pb isotopic ages of angrites are threefold first they demonstrate that ador and lew are not coeval and the group of slowly cooled angrites is therefore genetically diverse second the new age of lew suggests an upward revision of 53 mn 53 cr absolute ages by 0 7 ma third a precise age of d orbigny allows consistent linking of the 53 mn 53 cr and 26 al 26 mg extinct nuclide chronometers to the absolute lime scale

reconciliation of the excess 176 hf conundrum in meteorites recent disturbances of the lu hf and sm nd isotope systematics abstract the long lived 176 lu 176 hf and 147 sm 143 nd radioisotope systems are commonly used chronometers but when applied to meteorites they can reveal disturbances specifically lu hf isochrons commonly yield dates up to 300 myr older than the solar system and varying initial 176 hf 177 hf values we investigated this problem by attempting to construct mineral and whole rock isochrons for eucrites and angrites meteorites from different parent bodies exhibit similar disturbance features suggesting that a common process is responsible minerals scatter away from isochron regressions for both meteorite classes with low hf phases such as plagioclase and olivine typically being most displaced above or left of reference isochrons relatively hf rich pyroxene is less disturbed but still to the point of steepening lu hf errorchrons using our lu hf and sm nd data we tested various hf and lu redistribution scenarios and found that decoupling of lu hf from 176 hf 177 hf must postdate the accumulation of significant radiogenic 176 hf therefore early irradiation or diffusion cannot explain the excess 176 hf instead disturbed meteorite isochrons are more likely caused by terrestrial weathering contamination or common laboratory procedures the partial dissolution of phosphate minerals may predominantly remove rare earth elements including lu leaving relatively immobile and radiogenic hf behind robust lu hf and improved sm nd meteorite geochronology will require the development of chemical or physical methods for removing unsupported radiogenic hf and silicate hosted terrestrial contaminants without disturbing parent daughter ratios

petrology and geochemistry of d orbigny geochemistry of sahara 99555 and the origin of angrites petrology and geochemistry of d orbigny geochemistry of sahara 99555 and the origin of angrites

geochemistry and genesis of the angrites the angrites angra dos reis lew86010 and lew87051 are petrologically and compositionally similar achondrites all angrites have high feomno ratios of 80 94 and very low ci normalized na sm ratios of 0 001 0 003 high abundances of oxidized fe and low abundances of moderately volatile na most likely resulted from parent body processes such as magmatic outgassing rather than nebular processes all angrites have fractionated ca al ratios with angra dos reis exhibiting the most extreme ratio 3 1 ci this ca al fractionation may be due to small amounts of residual spinel in the source region after removal of the angrite melts or to crystallization of spinel from precursor melts for lew86010 and lew87051 the fractionated ca al ratios are not caused by the presence of significant cumulus material for angra dos reis cumulus material may be the cause of the high ca al ratio refractory element ca eu al sc la ce sm tb yb lu ti hf th and ta abundances of lew86010 and lew87051 show similar patterns while angra dos reis has both greater enrichments in these elements and more fractionated patterns compositional and petrologic constraints indicate that lew86010 and lew87051 are related via olivine control the refractory element abundances and mg of lew86010 can be approximated by removal of olivine from lew87051 suggesting that lew86010 may be a residual melt from a lew87051 like precursor alternatively lew87051 may have formed via olivine accumulation from a lew86010 like precursor the origin of the unusual refractory element pattern in angra dos reis remains obscure the differences between the lew86010 lew87051 duo and angra dos reis suggest that either the angrite parent body was heterogeneous or that angra dos reis was formed on a separate parent body based on feomno ratios and normative mineralogies the angrite parent body ies may be similar in bulk composition to one of the carbonaceous chondrite groups particularly ci cm co

magnetic classification of stony meteorites 3 achondrites a database of magnetic susceptibility measurements of stony achondrites acapulcoitelodranite clan winonaites ureilites angrites aubrites brachinites howardite eucrite diogenite hed clan and martian meteorites except lunar meteorites is presented and compared to our previous work on chondrites this database provides an exhaustive study of the amount of iron nickel magnetic phases essentially metal and more rarely pyrrhotite and titanomagnetite in these meteorites except for ureilites achondrites appear much more heterogeneous than chondrites in metal content both at the meteorite scale and at the parent body scale we propose a model to explain the lack of or inefficient metal segregation in a low gravity context the relationship between grain density and magnetic susceptibility is discussed saturation remanence appears quite weak in most metal bearing achondrites hed and aubrites compared to martian meteorites ureilites are a notable exception and can carry a strong remanence similar to most chondrites

petrogenesis of d orbigny like angrite meteorites and the role of spinel in the angrite source this research was supported by an australian national university phd scholarship to smck who is currently a postdoctoral fellow of the research foundation flanders

petrology and mineralogy of the angrite northwest africa 1670 northwest africa nwa 1670 contains olivines of up to 5 mm in size representing about 30 of the studied section with subordinate clinopyroxene and chrome spinel microphenocrysts 0 2 0 5 mm they represent a xenocrystic association phenocrysts are surrounded by a groundmass predominantly comprising bundles of plagioclase and clinopyroxene typically 20 x 200 m crystals olivine and kirschsteinite are present in the groundmass in lesser amounts the olivine xenocrysts fo90 are significantly fractured and show mosaicism for their major part the remaining showing faint undulatory extinction they are surrounded with a rim of 100200 m zoned down to fo80 and overgrown with serrated olivine fo80 to fo60 about 100 m olivine in the groundmass is zoned from mg 0 55 to 0 15 its cao content ranges 2 0 to 8 4 subcalcic kirschsteinite is zoned from mg 0 13 to 0 03 cao increasing from 15 8 to 21 3 pyroxenes xenocrysts mg 0 77 are superseded in the groundmass by less magnesian pyroxenes mg 0 61 to 0 17 with an average feo mno of 98 their compositions range from en30fs22wo27al ts28ti ts2 to en2fs37wo22al ts40ti ts1 anorthite microcrysts an99 100 are restricted to the groundmass accessories are pyrrhotite kamacite ca phosphate titanomagnetite hercynite and ca carbonate the bulk chemical composition confirms that nwa 1670 corresponds to a normal angrite melt that incorporated olivine high mg olivine xenocrysts and the associated mineralogy are typical of angrites we suggest that it is an impact melt with relict phenocrysts the strong silica undersaturation the presence of fo90 olivine xenocrysts and carbonate support their derivation as melilite like melts in the presence of carbonate

numerical models of the thermomechanical evolution of planetesimals application to the acapulcoite lodranite parent body the acapulcoite lodranite meteorites are members of the primitive achondrite class the observation of partial melting and resulting partial removal of fe fes indicates that this meteorite group could be an important link between achondrite and iron meteorites on the one hand and chondrite meteorites on the other thus a better understanding of the thermomechanical evolution of the parent body of this meteorite group can help improve our understanding of the evolution of early planetesimals here we use 2 d and 3 d finite difference numerical models to determine the formation time initial radius of the parent body of the acapulcoite lodranite meteorites and their formation depth inside the body by applying available geochronological thermal and textural constraints to our numerical data our results indicate that the best fit to the data can be obtained for a parent body with 25 65 km radius which formed around 1 3 ma after calcium aluminum rich inclusions the 2 d and 3 d results considering various initial temperatures and the effect of porosity indicate possible formation depths of the acapulcoite lodranite meteorites of 9 19 and 14 25 km respectively our data also suggest that other meteorite classes could form at different depths inside the same parent body supporting recently proposed models elkins tanton et al 2011 weiss and elkins tanton 2013

strike slip faulting as a trigger mechanism for overpressure release through piercement structures implications for the lusi mud volcano indonesia piercement structures such as hydrothermal vent complexes pockmarks and mud volcanoes are found in various geological settings but are often associated with faults or other fluid focussing features this article aims to investigate and understand the mechanisms responsible for the formation of piercement structures in sedimentary basins and the role of strike slip faulting as a triggering mechanism for fluidization for this purpose four different approaches were combined fieldwork analogue experiments and math