two cryogenian glacial successions compared aspects of the sturt and elatina sediment records of south australia abstract two cryogenian glacial sequences the sturt and elatina occur within the adelaide rift complex s australia and are part of an 8 km thick succession recording rodinia fragmentation and subsequent passive margin development we compare and contrast these glacial successions presenting new data including detailed logged sections for both glacial sequences facies analysis reveals a total of six facies associations recording a range of glacial and glacially related processes these are a diamictite facies association ice proximal debris flows a sheet sandstone facies association fluvial deposits a flaser and rhythmically bedded facies association tidal flat a hummocky cross stratified sandstone facies association shoreface to offshore transition zone deposits and an underflow facies association recording offshore deposition a sixth facies association a ferruginous lonestone bearing siltstone is restricted to the top of the elatina formation and records rapid environmental amelioration and emergence from glaciation in the central flinders ranges the sturt succession commences with a glacial erosion surface ges which in agreement with previous workers was probably enhanced by rifting this ges is overlain in ascending order by the pualco tillite holowilena ironstone and wilyerpa formation with the warcowie dolomite member at the base of this latter formation a second ges is preserved within this latter unit and is overlain by a stratigraphic motif that records an alternation of offshore transition zone and offshore deposits significant base level falls within the wilyerpa formation are identified by fluvial deposits sitting disconformably upon offshore deposits in contrast within the elatina formation a single ges is proposed which defines the base of the formation the elatina formation is split into two informal members on the basis of analysis of sediment stacking patterns and the recognition of a sharp stratigraphic surface that divides the formation apart from a locally preserved basal diamictite the lower member consists of fluvial deposits whereas the upper member is dominated by a mixture of tidal flat sediments and debris flow deposits the boundary between these units is therefore interpreted as a hybrid surface recording tidal ravinement in some areas and a glacial advance in others deglaciation left contrasting deposits the sturt deglaciation culminated in deposition of black shale of the tindelpina shale member of the tapley hill formation seemingly as a sheet like deposit over the adelaide rift complex and beyond into the amadeus basin of central australia the elatina deglaciation meanwhile began first with deposition of the sixth facies association ferruginous dropstone bearing siltstone then proceeded with deposition of cap dolostone of the nuccaleena formation

nebular and asteroidal modification of the iron isotope composition of chondritic components abstract the fe isotope signatures 56feirmm and 57feirmm of twelve chondrules three ca al rich inclusions cais and multiple matrix aliquots from two type 3 chondrites allende cv3 and chainpur ll3 were measured by mc icp ms the mass fractionation line for these samples is 57feirmm 1 45 0 05 56feirmm 0 01 0 02 with r2 0 9995 two processes appear to affect the fe isotope composition of these chondritic components initially short lived high temperature events within the solar nebula drove isotopic signatures towards isotopically heavier compositions subsequently metasomatism shifted isotopic signatures of chondrules and cais towards bulk like compositions the fe isotope composition of allende matrix 56feirmm 0 07 0 02 n 6 is similar to that of bulk allende 56feirmm 0 05 0 05 the range of chainpur matrix compositions is 0 03 56feirmm 0 02 this relatively homogeneous matrix composition appears to be governed by metasomatic exchange of iron although the possibility that matrix is heterogeneous on a scale smaller than the sample size cannot be ruled out cais from allende in which iron has been metasomatically introduced from the matrix are mainly unfractionated with respect to the bulk composition of allende the least altered cai which contains minor bulk feo 0 4 wt is isotopically lighter 56feirmm 0 16 with respect to bulk allende this signature may reflect condensation of isotopically light iron in the nebula or preferential incorporation of the lighter iron isotopes contained within the matrix chondrule fe isotope compositions 1 33 56feirmm 0 65 are driven by both high temperature nebular events and subsequent metasomatic exchange the relationship between compositional and isotopic signatures clearly points to an evaporation origin for type i chondrules which are isotopically heavier than type ii chondrules subsequent metasomatic exchange with matrix iron has driven some chondrules most notably the smaller chondrules towards a bulk like fe isotopic signature

demonstration of ree fractionation among individual chondrules from the allende cv3 chondrite abstract abundances of ree ba sr rb k mg and ca were determined by precise mass spectrometric isotope dilution techniques for 24 chondrules from the allende cv3 chondrite the ree abundances are 2 5 10 ci for barred olivine chondrules 2 8 ci for porphyritic and nonporphyritic pyroxene chondrules 0 15 4 ci for porphyritic olivine and porphyritic olivine pyroxene chondrules and are more or less similarly fractionated general ree fractionations and large up to 170 anomalies of ce eu and yb occur in all chondrule types particularly for barred olivine and pyroxene rich chondrules positive correlations of ree with the moderately volatile elements k and rb as well as other refractory elements ca sr and ba are independent of textural type and major chemical compositions each type of chondrule has large and systematic abundance variations of k and rb but shows a constant k rb ratio close to that of cis from these results the following constraints on the chemical characteristics of precursors and chondrule forming events are suggested 1 vaporization loss of alkalis accompanied by k rb fractionation did not occur during chondrule formation melting events 2 elemental abundances were basically established prior to melting events by accretion of alkali free components and alkali bearing refractory precursors with fractionated ree 3 gas solid or liquid processes yielding ree fractionations took place during the formation of refractory precursors

allochthonous salt initiation and advance in the northern flinders and eastern willouran ranges south australia using outcrops to test subsurface based models from the northern gulf of mexico the northern flinders ranges and eastern willouran ranges south australia expose neoproterozoic salt diapirs salt sheets and associated growth strata that provide a natural laboratory for testing and refining models of allochthonous salt initiation and emplacement the diapiric callanna group 850 800 ma comprises a lithologically diverse assemblage of brecciated rocks that were originally interbedded with evaporites that are now absent using stereonet analysis to derive three dimensional information from two dimensional outcrops of stratal geometries flanking salt diapirs and beneath salt sheets we evaluate 10 examples of the transition from steep diapirs to salt sheets 3 of ramp to flat geometries and 2 of flat to ramp transitions stratal geometries adjacent to feeder diapirs range from a minibasin scale megaflap to halokinetic drape folds to high angle truncations and appear to have no relationship to subsequent allochthonous salt development in all cases the transition from steep diapirs to salt sheets is abrupt and involved piston like breakthrough of thin roof strata which permitted salt to flow laterally we suggest two models to explain the transition from steep diapirs to subhorizontal salt 1 salt top breakout where salt rise occurs inboard of the salt flank thereby preserving part of the roof strata beneath the sheet and 2 salt edge breakout where rise occurs at the edge of the diapir with no roof preservation lateral emplacement of salt sheets is dependent on the interplay between the rate of salt supply to the front of the sheet and the sediment accumulation rate when the ratio of salt supply rate to sediment accumulation rate is high to moderate thrust advance produces base salt flats and truncation ramps respectively halokinetic folds are absent because the thrust emerges at the base of the sea floor scarp and mass transport complexes are rare as a result of relatively low scarp relief if the ratio is low pinned inflation leads to drape folding of the top salt and cover into a fold ramp with occasional slumping of the sheet and its roof and further breakout on thrust or reverse faults in the shallow water depositional environments of south australia lateral emplacement of salt sheets occurred through some combination of thrust advance extrusive advance and open toed advance with no evidence for subsalt thrust imbricates shear zones or continuous rubble zones in deep water environments such as the northern gulf of mexico thrust imbricates and rubble zones which represent slumped carapace are more common the presence of slumped carapace is caused primarily by higher topographic relief related to thicker hemipelagic roofs a lack of dissolution and gravity driven transport of overburden strata to the toes of large canopies

environmental interpretation and a sequence stratigraphic framework for the terminal proterozoic ediacara member within the rawnsley quartzite south australia abstract fossils of the ediacara biota are confined to preservational windows in the ediacara member of the rawnsley quartzite pound subgroup from the flinders ranges south australia the base of the ediacara member is a type 1 sequence boundary incised into the partly lithified chace quartzite member of the rawnsley quartzite the ediacara member and the upper half of the rawnsley quartzite comprise the rawnsley depositional sequence bounded above by the early cambrian uratanna depositional sequence the rawnsley sequence developed over an erosional surface cut into the chace quartzite member with some 250 m of relief southeasterly directed palaeovalleys are filled with a sequence of massive sandstone and laminated siltstone passing up into well bedded sandstone at lowstand local channels were filled by massive sand the highstand systems tract consists of several parasequence sets of laminated siltstone and channelized amalgamated massive sandstone overlain by interbedded siltstone and sandstone grading up into well bedded clean sandstone impressions of soft bodied ediacaran organisms are preserved above the valley fill facies on sandstone partings within upward shoaling delta front environments between storm and fairweather wavebase the ediacara member is in places conformably overlain by up to 500 m of sandstone of the same lithofacies as those underlying the member distinctive microbial mat bound sand laminae described as petee structures are characteristic of the rawnsley quartzite above and below the ediacara member during deposition of the ediacara member colonization of the deeper substrates by microbial mat communities enabled preservation of the ediacara biota the erosional surface at the base of the ediacara member is one of at least four incision events recorded in the terminal proterozoic and early cambrian succession of the adelaide geosyncline the similarity of incision filling lithofacies of the rawnsley and uratanna sequences has in condensed sections led to confusion between the depositional sequences characteristic trace and body fossil assemblages provide the only clear distinction between depositional cycles spanning the proterozoic cambrian boundary

ultrarapid chondrite formation by hot chondrule accretion evidence from unequilibrated ordinary chondrites unequilibrated ordinary chondrites uocs of all groups h l ll contain unique chondrite clasts which are characterized by a close fit texture of deformed and indented chondrules these clasts termed cluster chondrites occur in 41 of the investigated samples with modal abundances between 5 and 90 vol and size variations between 1 mm and 10 cm they show the highest chondrule abundances compared with all chondrite classes 82 92 vol and only low amounts of fine grained interchondrule matrix and rims 3 9 vol the mean degree of chondrule deformation varies between 11 and 17 compared to 5 in the clastic portions of their host breccias and to values of 3 5 found in uoc literature respectively the maximum deformation of individual chondrules is about 50 a value which seemingly cannot be exceeded due to geometric limitations both viscous and brittle chondrule deformation is observed a model for cluster chondrite formation is proposed where hot and deformable chondrules together with only small amounts of co accreting matrix formed a planetesimal or reached the surface of an already existing body within hours to a few days after chondrule formation they deformed in a hot stage possibly due to collisional compression by accreting material later the resulting rocks were brecciated by impact processes thus cluster chondrite clasts are interpreted as relicts of primary accretionary rocks of unknown original dimensions if correct this places a severe constraint on chondrule forming conditions cluster chondrites would document local chondrule formation where chondrule forming heating events and the accretion of chondritic bodies were closely linked in time and space

the crystalline lunar spherules their formation and implications for the origin of meteoritic chondrules crystalline lunar spherules cls from three thin sections of apollo 14 regolith breccias 14318 6 14318 48 and 14315 20 have been examined the objects have been classified and their abundances size distributions bulk compositions and where possible plagioclase compositions determined by number 64 consist predominantly of very fine grained equant plagioclase grains but can also contain larger 50 m feldspar crystals type x while 22 contain plagioclase lathes in a fine grained mafic mesostasis type y plagioclase in both spherule types displays bright yellow cathodoluminescence that is conspicuous among the blue cl of the normal feldspar of the breccias type z spherules 5 contain feldspar with blue cl and minor amounts of olivine and pyroxene type q spherules 4 contain feldspar with yellow cl but in a luminescent mesostasis of quartz or feldspar a few spherules are mixtures of type y and type x textures most type x spherules and a few type y spherules have fine grained opaque rims compound objects were also found and consist of two or more cls that appear to have collided while still plastic or molten the cls are thought to be impact spherules that crystallized in free flight their coarse textures suggesting fairly slow cooling rates 1 c s the abundance of the cls resembles that of chondrules in the cm chondrite murchison and their cumulative size frequency distributions are very similar to those of the chondrules in several meteorite classes the bulk compositions of the cls do not resemble regoliths at any of the apollo sites including apollo 14 or any of the common impact glasses but they do resemble the bulk compositions of several lunar meteorites and the impact glasses they contain the apollo 14 site is located on a region containing imbrium ejecta and we suggest that the cls derive from the imbrium impact ballistic calculations indicate that only impact events of this size on the moon are capable of producing melt spherules with the required free flight times and slow cooling rates smaller impacts produce glassy spherules and agglutinates as has been pointed out many times the cls have many properties in common with meteoritic chondrules while much remains unclear difficulties with a nebular origin and new developments in chondrule chronology studies of asteroid surfaces and impact ejecta behavior and the present observations indicate that meteoritic chondrules could have formed by impact

the geological setting of tourmalinite at rum jungle n t australia genetic and economic implications tourmalinite is a common rock type associated with proterozoic strata bound mineral deposits although common it is often difficult to recognise in the field leading to misidentification it occurs as a conformable banded quartz tourmaline lithological unit comprising at least 15 and as much as 50 of the rock at rum jungle tourmalinite occurs within the oldest sediments arenites and magnesites as distinct lenses as facies equivalents of quartz magnetite units and mafic schists tuffs and distal equivalents of polymetallic sulfides distinct layering slump folding rip up clasts and the association with diagenetic pyrite suggest a sedimentary environment enechelon fracturing of the fine grained light green tourmaline crystals spectacularly supports pre deformation formation the crystals are optically and chemically zoned parallel to the c axis with irregular growth lamellae width which supports a pre regional metamorphic origin analyses show the tourmaline to be the mg rich variety dravite most tourmalinites are interpreted as subaqueous marine deposits it is more likely that they form in lacustrine shallow water evaporitic environments particularly continental rifts suitable b bearing fluids can be generated by hotspring activity and mobilized by co2 rich fluids association with chemical sediments suggests tourmalinites also have a chemical sediment precursor ample evidence at rum jungle supports the notion of a continental rift environment which was the site of deposition of fluvial arenites and alkaline evaporitic lake sediments localised hot spring activity contributed b bearing fluids which precipitated chemical sediments according to the pertaining ph temperature etc diagenetic alteration produced the tourmalinite now present these tourmalinites are comparable to those of similar age elsewhere e g sullivan broken hill they can be genetically modelled upon recent borate concentrations all of which occur in continental rift environments

coarse grained chondrule rims in type 3 chondrites abstract relatively coarse grained rims occur around all types of chondrules in type 3 carbonaceous and ordinary chondrites those in h l ll3 chondrites are composed primarily of olivine and low ca pyroxene those in cv3 chondrites contain much less low ca pyroxene average grain sizes range from 4 m in h l ll3 chondrites to 10 m in cv3 chondrites such rims surround 50 10 and 1 of chondrules in cv3 h l ll3 and co3 chondrites respectively but are rare 1 around cv3 ca al rich inclusions rim thicknesses average 150 m in h l ll3 chondrites and 400 m in cv3 chondrites the rims in h l ll3 chondrites are composed of material very similar to that which comprises darkzoned chondrules and recrysiallized matrix dark zoned chondrules and coarse grained rims probably formed in the solar nebula from clumps of opaque matrix material heated to sub solidus to sub liquidus temperatures during chondrule formation mechanisms capable of completely melting some material while only sintering other material require steep thermal gradients suitable processes are lightning reconnecting magnetic field lines and possibly aerodynamic drag heating cv chondrites may have formed in a region where the chondrule formation mechanism was less efficient probably at greater solar distances than the ordinary chondrites the lesser efficiency of heating could be responsible for the greater abundance of coarse grained rims around cv chondrules alternatively cv chondrules may have suffered fewer particle collisions prior to agglomeration

olivine growth rates in a tholeiitic basalt an experimental study of melt inclusions in plagioclase abstract basaltic glass inclusions trapped in plagioclase phenocrysts an 84 are remnant of their parent magmatic liquid they can be used as natural reactors for the experimental investigation of olivine growth rate as a function of temperature the growth of one olivine nucleus can be observed at constant temperature supercooling from 15 to 150 c have been investigated growth habits vary from equant to feather in qualitative agreement with previous studies growth rates vary from 10 m s 1 to 6 10 7 m s 1 they vary with the direction the growth process planar or dendritic and the degree of supercooling chemical analysis of crystal overgrowth and the remaining liquid composition enables a mass balance calculation which confirms the rates determined optically the small number of results obtained so far does not permit to draw inferences on the growth mechanisms

granoblastic olivine aggregates in magnesian chondrules planetesimal fragments or thermally annealed solar nebula condensates abstract granoblastic olivine aggregates goa have been discovered in some type i magnesian chondrules within carbonaceous chondrites by libourel and krot libourel g krot a n 2007 evidence for the presence of planetesimal material among the precursors of magnesian chondrules of nebular origin earth planet sci lett 254 1 8 who proposed an origin from pre existing planetesimals amoeboid olivine aggregates aoa generally considered as aggregates of solar nebula condensates and found within similar carbonaceous chondrites display similar equilibrium texture though on a finer scale for these reasons we conducted experiments to determine if annealing of olivine required time scales appropriate to planetesimal or nebular heating pressed 88 4 was isothermally heated at temperatures ranging from 1350 1550 c for 1 100 h the 100 h runs yield olivine aggregates with well developed granoblastic texture at all temperatures manifest as a network of randomly oriented and sutured olivine grains with 120 triple junctions individual olivine grains are 4 6 sided and polygonal by 1450 c and equigranular texture is developed at high temperature 1500 1550 c melting of olivine commences at 1450 1500 c and aids in ripening and suturing grain coarsening and grain boundary migration textural equilibrium is clearly met at 1550 c a planetesimal origin cannot be ruled out however the experimental evidence reveals that granoblastic texture can be reproduced in an interval not inconsistent with heating times for nebular objects goa may have experienced higher degrees of thermal processing than the finer grained aoa if the precursors were the same grain coarsening would have to be accompanied by modification to bulk and isotopic compositions however the precursors could have been olivine condensates formed later than aoa annealing may have been a widespread process operating in the primordial solar nebula responsible for thermal processing and formation of goa prior to their incorporation into chondrules

quantifying the error of 2d bulk chondrule analyses using a computer model to simulate chondrules simchon bulk chondrule compositions are important to many questions in cosmochemistry however the number of available bulk chondrule data sets is still small a main reason for this is the difficulties of determining bulk chondrule compositions a commonly used technique is to obtain 2d bulk chondrule compositions from meteorite sections this technique has an error that we quantify here for the first time using a mathematical model of a chondrule called simchon the theoretically calculated errors are compared to errors that we determined from serial sectioning of eight efremovka chondrules the errors obtained from both approaches are in excellent agreement proving that our mathematical model produces reliable errors that can be assigned to 2d bulk chondrule compositions these errors allow a much better interpretation of 2d bulk chondrule data we provide a table that contains typical errors for 2d bulk compositions of porphyritic chondrules the errors are in the range of 1 30 relative this should be acceptable for many problems in cosmochemistry the effect of a chemical layering inside chondrules and the occurrence of a rim around them as well as the occurrence of opaque and other accessory phases have been studied a spreadsheet is provided that enables the calculation of errors for any desired chondrule mineral composition bo chondrules have a negligible error but it is impossible to provide reasonable error estimates for bo chondrules with an igneous rim radial pyroxene chondrules have negligible errors

the formation and alteration of the renazzo like carbonaceous chondrites ii linking o isotope composition and oxidation state of chondrule olivine abstract to better understand the formation conditions of type i and type ii chondrules in the renazzo like carbonaceous cr chondrites an in situ major and minor element and o isotope study was conducted twenty one ferromagnesian chondrules from three cr chondrites gra 95229 gra 06100 and que 99177 were analyzed to establish an internally consistent data set from this study we infer that type ii chondrule precursors contained enhanced s bearing dust and ice abundances relative to type i chondrules there is a relationship between the o isotope composition and oxidation state of olivine which may be related to the amount of 16 o poor ice and reduced carbon accreted by chondrule precursors before melting type ii chondrules formed under h 2 o h 2 ratios of 230 740 times solar in contrast type i chondrules formed under more reducing conditions with lower h 2 o h 2 ratios of 10 100 times solar we find a relationship between type ii chondrule petrology relict free vs relict grain bearing and o isotope composition which is due to degree of melting and exchange with a 16 o poor gas reservoir the 16 o poor gas that interacted with both type i and type ii chondrules is estimated to have an isotopic composition between 18 o g 13 27 and 17 o g 10 22 different from the o isotope composition of the water accreted by the cr chondrite parent body due to partial melting type i chondrules and relict grain bearing type ii chondrules exchanged with the 16 o poor gas to a lower degree than relict free type ii chondrules

microchondrule bearing clast in the piancaldoli ll3 meteorite a new kind of type 3 chondrite and its relevance to the history of chondrules in the piancaldoli ll3 chondrite we found a mm sized clast containing 100 chondrules 0 2 64 m in apparent diameter much smaller than any previously reported that are all of the same textural type radial pyroxene fs1 17 this clast like other type 3 chondrites has a fine grained ferich opaque silicate matrix sharply defined chondrules abundant low ca clinopyroxene and minor troilite and si and cr bearing metallic fe ni however the very high modal matrix abundance 63 8 vol unique characteristics of the chondrules and absence of microscopically observable olivine indicate that the clast is a new kind of type 3 chondrite most chondrules have feo rich edges and chondrule size is inversely correlated with chondrule core feo concentration the first reported correlation of chondrule size and composition chondrules acquired fe by diffusion from fe rich matrix material during mild metamorphism possibly before final consolidation of the rock microchondrules those chondrules 100 m in diameter are also abundant in another new kind of type 3 chondrite clast in the rio negro l chondrite regolith breccia in other type 3 chondrite groups microchondrule abundance appears to be anticorrelated with mean chondrule size viz 0 02 0 04 vol in h and co chondrites and 0 006 vol in l ll and cv chondrites microchondrules probably formed by the same process that formed normal sized droplet chondrules melting of pre existing dustballs because most compound chondrules in the clast and other type 3 chondrites formed by collisions between chondrules of the same textural type we suggest that dust grains were mineralogically sorted in the nebula before aggregating into dustballs the sizes of compound chondrules and chondrule craters which resulted from collisions of similarly sized chondrules while they were plastic indicate that size sorting of dustballs occurred before chondrule formation probably by aerodynamic processes in the nebula we predict that other kinds of type 3 chondrites exist which contain chondrule abundances size ranges and proportions of textural types different from known chondrite groups

characterizing halokinesis and timing of salt movement in the abu musa salt diapir persian gulf offshore iran abstract geometric and stratigraphic characteristics of halokinetic sequences adjacent to the salt diapirs highlight the sedimentation response to variation in the rate of salt rise the style of salt movement sedimentation interaction and episodes of salt movement can be reconstructed by mapping these halokinetic sequences adjacent to the diapirs detailed interpretation of 2d seismic profiles adjacent to the abu musa salt diapir within the persian gulf basin offshore iran indicates that this diapir originated from the miocene fars salt which created a central and several ring like peripheral salt structures our results show that the evolution of the salt structures take place in three stages mound dome and post dome associated with sedimentation cycles periodically by passive and active rising to present the pattern of these halokinetic sequences reveals that the fars salt rose since mid miocene coeval sedimentation of the gachsaran formation the main mechanism of driving salt body has been the differential loading caused by down building processes

basin geometry and salt diapirs in the flinders ranges south australia insights gained from geologically constrained modelling of potential field data abstract the adelaide basin in australia is a complex of late neoproterozoic to early cambrian rift and sag basins which was inverted during the cambro ordovician delamerian orogeny the deposition of evaporitic sediments during the earliest stage of basin development in the late neoproterozoic willouran age played a major role in the subsequent tectonic evolution of the basin previous studies have shown that early mobilization vertical transport and withdrawal of the evaporites influenced the sedimentation during the late neoproterozoic and early cambrian the evaporites also influenced deformation during the inversion of the basin and the development of the delamerian fold and thrust belt however the control exerted by basement structures in the deposition of the evaporitic beds and the role of these tectonic structures in the later inversion of the basin have been poorly constrained in this work we use a combination of published and original geological observations along with the interpretation of potential field datasets total magnetic intensity and bouguer anomaly data to better constrain the geology of the basin at depth we construct two and a half dimensional forward models of the potential field data along selected profiles across the adelaide basin these models are constrained by the geology at the surface drill hole data and measured petrophysical properties specific gravity and magnetic susceptibility we achieved the best fit between observed and modelled potential fields with a model favouring thick skinned deformation where the diapirs are not randomly distributed but located directly above basement penetrating normal faults furthermore these normal faults were probably active during the sedimentation of the late neoproterozoic and early cambrian sediments and underwent partial or total inversion during the cambro ordovician delamerian orogeny mobilisation and withdrawal of the evaporites was therefore initiated and facilitated by the extension coeval with the opening of the basin and continued during the subsequent delamerian orogeny

the origin of chondrules and chondrites debris from low velocity impacts between molten planetesimals we investigate the hypothesis that many chondrules are frozen droplets of spray from impact plumes launched when thin shelled largely molten planetesimals collided at low speed during accretion this scenario here dubbed splashing stems from evidence that such planetesimals intensely heated by 26al were abundant in the protoplanetary disk when chondrules were being formed approximately 2 myr after calcium aluminum rich inclusions cais and that chondrites far from sampling the earliest planetesimals are made from material that accreted later when 26al could no longer induce melting we show how splashing is reconcilable with many features of chondrules including their ages chemistry peak temperatures abundances sizes cooling rates indented shapes relict grains igneous rims and metal blebs and is also reconcilable with features that challenge the conventional view that chondrules are flash melted dust clumps particularly the high concentrations of na and feo in chondrules but also including chondrule diversity large phenocrysts macrochondrules scarcity of dust clumps and heating we speculate that type i feo poor chondrules come from planetesimals that accreted early in the reduced partially condensed hot inner nebula and that type ii feo rich chondrules come from planetesimals that accreted in a later or more distal cool nebular setting where incorporation of water ice with high 17o aided oxidation during heating we propose that multiple collisions and repeated re accretion of chondrules and other debris within restricted annular zones gave each chondrite group its distinctive properties and led to so called complementarity and metal depletion in chondrites we suggest that differentiated meteorites are numerically rare compared with chondrites because their initially plentiful molten parent bodies were mostly destroyed during chondrule formation

chondrules matrix and coarse grained chondrule rims in the allende meteorite origin interrelationships and possible precursor components bulk compositions of 20 chondrules 13 coarse grained chondrule rims and two composite samples of matrix material from cv3 allende were determined by instrumental neutron activation analysis three rare nonporphyritic cv chondrules from allende leoville and vigarano were analyzed by broad beam electron microprobe analysis chondrule precursor components deduced from chondrule compositions are characterized by 1 refractory and semi refractory lithophiles with low feo 2 common siderophiles and chalcophiles 3 common to slightly volatile lithophiles si cr mn and modal pyroxene with moderately high feo feo mgo 4 moderately volatile siderophiles and 5 alkalies these precursor components can be explained by plausible processes occurring in the solar nebula the precursor components of coarsegrained rims are apparently the same as those of chondrules these components differ from those inferred previously for oc eh or cm co chondrules in general the compositions of coarse grained rims are more similar to the mean chondrule composition than to those of the chondrules they enclose rim siderophile contents are generally 2 5x greater than those in the chondrules and 0 5 to 2x those in bulk allende rims as a group are more homogeneous than chondrules suggesting that rims formed from finer grained precursors several chondrules and rims have fractionated rare earth patterns and may have been affected by metamorphism the enclosure of some coarse grained rims by fine grained matrix like rims that are almost certainly of nebular origin indicates that coarse grained rims were also formed in the nebula two matrix samples are similar in composition to some coarse grained rims suggesting that matrix was derived from similar compositional reservoirs of nebular dust chondrules with coarse grained rims were reheated in space following the accretion of dusty coatings this restricts plausible chondrule forming mechanisms to those that allow multiple nebular heating events

oxygen isotope systematics of chondrule phenocrysts from the co3 0 chondrite yamato 81020 evidence for two distinct oxygen isotope reservoirs high precision oxygen three isotope measurements of olivine and pyroxene were performed on 33 chondrules in the yamato 81020 co3 0 chondrite by secondary ion mass spectrometry in chondrules where oxygen isotopes were measured in both olivine and pyroxene the majority of grains have similar values indicating co magmatic crystallization however many chondrules contain relict grains with unique oxygen isotope ratios a striking feature of yamato 81020 chondrules is a bimodal distribution of oxygen isotope ratios as those with mg 97 phenocrysts range in 17o from 4 8 to 6 5 5 5 group and those with mg 96 36 phenocrysts have 17o values of 2 1 to 3 0 2 5 group a single mg 99 6 barred olivine chondrule has a 17o of 3 3 we discuss that 17o 5 5 chondrules are derivative of a reservoir with limited dust enrichment 100 solar system which yielded a relatively reduced chondrule forming environment in contrast the 17o 2 5 chondrules may have been influenced by 16o poor h2o ice that sublimed and then homogenized with precursor material the addition of h2o when combined with high dust enrichment 1000 solar system and greater bulk fe content could have induced an oxidized environment at high temperatures forming mg 96 36 chondrules among the 33 chondrules studied the al mg relative ages of 20 had been obtained previously comparing the oxygen isotope ratios and the 26al ages of these chondrules it is likely that the 5 5 and 2 5 oxygen isotope reservoirs existed contemporaneously this implies that the snow line was spatially fixed during chondrule formation and separated the co chondrite accretion region into two distinct volumes of precursors

role of gas melt interaction during chondrule formation abstract it is generally believed that most chondrules formed in the protoplanetary disk by melting of fine grained solid precursor materials and that during these melting events chondrules behaved as closed systems both chemically and isotopically i e the observed range in chondrule bulk chemistry and modal mineralogy was entirely inherited from solid precursors that experienced melting to varying degrees followed by igneous crystallization accompanied by very limited if any evaporation recondensation our mineralogical and chemical study of magnesium rich porphyritic type i chondrules in primitive ordinary and carbonaceous chondrites revealed that chondrule glasses are not located on the subtraction lines of olivine or low ca pyroxene in appropriate phase diagrams indicating that type i chondrules do not obey closed system crystallization we suggest that gas melt interaction played a major role in evolution of mineralogy bulk chemical and isotopic compositions of type i chondrules chondrules are thus complex objects composed of an inherited solid component and a melt component that equilibrated with nebular gas suggesting that chondrules formed in regions with high ambient gas partial pressures as a result chondrule glasses melts are therefore thermochemical and isotopic sensors of the surrounding nebular gas in the chondrule forming regions of the protoplanetary disk and can be used for evaluating its physico chemical conditions

mechanics of active salt diapirism abstract an active diapir forcefully intrudes its overburden driven by diapir pressure that overcomes the resistance of the overburden strength possible causes for the driving pressure are differential loading of the source layer and a density contrast with the overburden possible resisting forces derive from the mass of the roof block and resistance to the faulting and folding that accommodate the intrusion for a typical density contrast between salt and a sedimentary overburden a simple force balance demonstrates that the diapir height must be more than two thirds to three quarters the thickness of the surrounding overburden to initiate substantial active diapirism narrow diapirs must be even taller physical and numerical modeling show that typical structures of active diapirism are a central crestal graben flanked by relatively unstrained flaps that rotate upward and outward curved reverse faults can separate the flaps from the regional overburden normal faults in the crestal graben propagate downward with new faults created farther outward as the roof arches over the rising diapir thin wide roofs develop multiple grabens separating a relatively flat roof from the rotating flaps in cases leading to emergence the piercing diapir evolves from a pointed crest to a progressively rounded and widening crest as the flaps rotate outward the numerical models show that overburden flexure contributes to early formation of active diapir structures but piercement does not continue to emergence unless the diapir is very wide or tall relative to the overburden thickness active diapirism becomes progressively more difficult for diapir crests ranging from a rectangle a round cornered rectangle a semicircle to a triangle with a pointed crest

ubiquitous low feo relict grains in type ii chondrules and limited overgrowths on phenocrysts following the final melting event type ii porphyritic chondrules commonly contain several large 40 m olivine phenocrysts furnace based cooling rates based on the assumption that these phenocrysts grew in a single stage melting cooling event yield chondrule cooling rate estimates of 0 01 1 k s 1 because other evidence indicates much higher cooling rates we examined type ii chondrules in the co3 0 chondrites that have experienced only minimal parent body alteration we discovered three kinds of evidence indicating that only minor 4 10 m olivine growth occurred after the final melting event 1 nearly all 90 type ii chondrules in co3 0 chondrites contain low feo relict grains overgrowths on these relicts are narrow in the range of 2 12 m 2 most type ii chondrules contain some feo rich olivine grains with decurved surfaces and acute angles between faces indicating that the grains are fragments from an earlier generation of chondrules the limited overgrowth thicknesses following the last melting event are too thin to disguise the shard like nature of these grains 3 most type ii chondrules contain many small 40 m high feo phenocrysts are relicts from earlier generations of chondrules and that cooling rates after the last melting event were much more rapid than indicated by models based on a single melting event these observations are thus inconsistent with the classic igneous model of formation of type ii porphyritic chondrules by near total melting of a precursor mix followed by olivine nucleation on a very limited number of nuclei say 10 and by growth to produce the large phenocrysts during a period of monotonic and roughly linear cooling our observations that recycled chondrule materials constitute a large component of the phenocrysts of type ii chondrules also imply that this kind of chondrule formed relatively late during the chondrule forming period

internal kinematics of salt diapirs the internal structure of intrusive and extrusive salt bodies elucidates their external shape and the mechanism and history of diapiric emplacement information relevant to petroleum exploration trace amounts of brine can act like heat to weaken salt and promote geologic creep by solution transfer mechanisms we compare natural strain markers in salt with the artificial markers used by fluid dynamicists stream lines are the smooth flow paths followed by fluid particles stream surfaces separate flow laminae and contain the stream lines grain shape fabrics in salt anneal readily and have strain memories so short that lineations map the stream lines and foliations map the stream surfaces of the last stages of deformation by contrast larger structures like folded beddi g have much longer strain memories as a result multiple generations of tonguelike recumbent flow folds formed by unsteady flow in the mother source layer rotate to upright sheath folds or spines in the stems of diapirs here they are constricted and refolded into steep curtain folds to form crescentic and other interference patterns visible in the roofs of salt mines mature diapirs can form crestal bulbs which may be balloon or mushroom shaped and which potentially form larger petroleum traps than previously supposed screens of country rock may be entrained between the stem and peripheral overhanging lobes caused by episodic sedimentation

contemporaneous formation of chondrules in distinct oxygen isotope reservoirs we investigated the 26al 26mg systematics of type i feo poor chondrules from one of the most primitive carbonaceous chondrites acfer 094 the inferred initial 26al 27al ratios of chondrules from acfer 094 ranged from 4 2 2 0 10 6 to 9 0 1 5 10 6 these chondrules have distinct oxygen isotope ratios 17o 5 2 and 0 though no correlation between inferred initial 26al 27al ratios and oxygen isotope ratios were observed these results indicate the regional oxygen isotope heterogeneity in the solar nebula over the duration of chondrule formation a few low ca pyroxene grains in chondrules have small but resolvable 26mg excesses at the level of 0 1 which may be the result of a partial melting of chondrules by reheating events if this is the case the true inferred initial 26al 27al ratios of these particular chondrule could be slightly lower 10 than estimates using mg isotope ratios of coexisting plagioclase and olivine stable isotope ratios of mg 25mg 24mg of many olivine grains in chondrules are positively fractionated by 1 relative to those in other phases within the same chondrules this suggests that olivine preserved a positively fractionated mg isotope ratios of the chondrule forming melt prior to significant condensation during the cooling stage of chondrule formation

a neoproterozoic fringing stromatolite reef complex flinders ranges south australia abstract a series of 14 microbial buildups outcrop in stark topographic relief along the western edge of the enorama diapir in the central flinders zone of the adelaide geosyncline south australia the enclosing stratigraphic unit the enorama shale is in the locally named interglacial succession between the sturtian and marinoan varanger equivalent glacigenic units thereby placing the reefs within the upper cryogenian locally derived conglomerates showing progressive cannibalisation indicate that this diapir was active during reef and mound growth apparent gradual onlap of the enorama shale against the diapir controlled in part by the present structural disposition has allowed good resolution of the individual buildups movement of the diapir during and after reef growth has turned the succession to vertical so that the features are seen in section view provision of a clean stable substrate controlled the establishment of the buildups a core facies of cumulate stromatolite domes first formed mounds which interfingered with the surrounding sediments then reefs which stood well above the sea floor not all mounds progressed to reefs as the edge of the active diapir was unstable at times the maximum size of a mound plus reef is ca 50 m high and 200 m across the base at a microscopic scale the core facies shows distinctive clotted textures reminiscent of the calcimicrobes epiphyton and renalcis although a contribution to the stromatolitic domes from microbial activity is also possible the entire reef complex has been completely dolomitised probably by solutions emanating from the diapir early dolomite cement has allowed the preservation of the sedimentary textures and some porosity the reefs grew during a time of sea level rise and show a close relationship with the enorama diapir the diapir provided an area of shallow water around an island at a time when deeper water shale was being deposited in the rest of the basin the mound to reef transition shows catch up and keep up growth habit but the sudden demise of individual reefs appears related to pulses of movement on the diapir

tetrad effects in ree abundance patterns of chondrules from cm meteorites implications for aqueous alteration on the cm parent asteroid abstract lanthanide tetrad effect in bulk chondrules from two moderately altered cm chondrites murchison and yamato 793321 y 793321 are reported for the first time twenty three chondrules were petrographically characterized and analyzed for 10 rare earth elements ree and other trace and major elements ba sr rb k ca mg and fe using the precise isotope dilution technique the results indicate systematic depletion several times of alkali and alkaline earths compared to cv and co chondrules most of the porphyritic olivine 8 po and olivine pyroxene 4 pop porphyritic and radial pyroxene 2 pp 1 rp and granular olivine 1 go chondrules show a light ree l ree depleted heavy ree h ree smoothly fractionated pattern composed of four upward convex segments possessing a relatively large negative eu anomaly ci normalized la sm lu er and eu eu ratios 0 3 1 eu normal value on the other hand all barred olivine 5 bo chondrules a few po and pop indicate almost a flat l ree pattern in addition regardless of their textural types nearly half of the chondrules have a variable degree of ce and yb anomalies and or l h ree discontinuity which is similar to cv and co chondrules the observed l and h convex ree patterns accompanied with the negative eu anomaly is the first known case for chondrules as well as meteoritic materials but have been previously reported for geological samples such as sedimentary rocks late stage igneous and metamorphic rocks and are explained as the lanthanide tetrad effect which plausibly results from fluid rock interaction we suggest that the marked ree fractionations occurred by the selective incorporation of l h rees and eu into alteration products in the matrix during alteration processes on the cm parent body but that the gas solid ree fractionation characteristics established in the nebula have basically remained unchanged we suggest that the tetrad effects observed here represent a new index of physico chemical conditions of fluid rock interactions prevalent on the cm parent body

sulfur and sulfides in chondrules abstract the nature and distribution of sulfides within type i po pop and pp chondrules of the carbonaceous chondrite vigarano cv3 have been studied by secondary electron microscopy and electron microprobe they occur predominantly as spheroidal blebs composed entirely of low ni iron sulfide troilite fes or troilite magnetite but in less abundance in association with metallic fe ni beads in opaque assemblages troilites are mainly located within the low ca pyroxene outer zone and their amounts increase with the abundance of low ca pyroxene within chondrules suggesting co crystallization of troilite and low ca pyroxene during high temperature events we show that sulfur concentration and sulfide occurrence in chondrules obey high temperature sulfur solubility and saturation laws depending on the f s 2 and f o 2 of the surrounding gas and on the melt composition mainly the feo content sulfur dissolved in chondrule melts may eventually reach a concentration limit the sulfur content at sulfide saturation scss at which an immiscible iron sulfide liquid separates from the silicate melt the occurrence of both a silicate melt and an immiscible iron sulfide liquid is further supported by the non wetting behavior of sulfides on silicate phases in chondrules due to the high interfacial tension between their precursor iron sulfide liquid droplets and the surrounding silicate melt during the high temperature chondrule forming event the evolution of chondrule melts from po to pp towards more silicic compositions very likely due to high p sio g of the surrounding nebular gas induces saturation of fes at much lower s content in pp than in po chondrules leading to the co crystallization of iron sulfides and low ca pyroxenes conditions of co saturation of low ca pyroxene and fes are only achieved in non canonical environments characterized by high partial pressures of sulfur and sio and redox conditions more oxidizing than iw 3 fe and s mass balance calculations also suggest the occurrence of an external source of iron very likely gaseous during chondrule formation we therefore propose that enrichments in sulfur and other volatile and moderately volatile elements from po to pp type i bulk chondrule compositions towards chondritic values result from progressive reaction between partially depleted olivine bearing precursors and a volatile rich gas phase

melted micrometeorites from antarctic ice with evidence for the separation of immiscible fe ni s liquids during entry heating we report the discovery of four large 50 m cosmic spherules css and a single scoriaceous micrometeorite smm that contain evidence for the separation of immiscible fe ni s liquids during atmospheric entry heating the particles contain segregated fe rich regions dominated by either ni s bearing fe oxides or iron sulphides and have textural relations that suggest these separated from the silicate portions of the particles as metallic liquids the oxides which may be hydrous are thought to result from alteration of metal and sulphide the compositions of the silicate portions of the css are equivalent to spherules without fe rich regions implying that metallic liquids are exsolved during the heating of most spherules but completely separate the single smm has a very different composition from other scoriaceous particles and the occurrence of an exsolved metallic liquid probably indicates extreme reduction during entry heating the pyrolysis of carbonaceous materials is the most likely explanation for reduction and suggests that the precursor material of this particle was unusually c rich this smm might be therefore an appropriate candidate for a large melted anhydrous or smectite interplanetary dust particle idp the exsolution of immiscible fe ni s liquids during entry heating will result in systematic changes in the compositions of the remaining silicate melt

trace element geochemistry of ordinary chondrite chondrules the type i type ii chondrule dichotomy we report trace element concentrations of silicate phases in chondrules from ll3 ordinary chondrites bishunpur and semarkona results are similar to previously reported data for carbonaceous chondrites with rare earth element ree concentrations increasing in the sequence olivine 10 k h than type i chondrules appreciable na concentrations 3 221 ppm are measured in olivine from both chondrule types type ii chondrules seem to have behaved as closed systems which may require chondrule formation in the vicinity of protoplanets or planetesimals at any rate higher solid concentrations in type ii chondrule forming regions may explain the higher oxygen fugacities they record compared to type i chondrules type i and type ii chondrules formed in different environments and the correlation between high solid concentrations and or oxygen fugacities with rapid cooling rates is a key constraint that chondrule formation models must account for

cooling rate of chondrules in ordinary chondrites revisited by a new geospeedometer based on the compensation rule abstract for several decades efforts to constrain chondrite cooling rates from diffusion zoning in olivine gave rise to a range of values from 5 to 8400 k h desch s j connolly jr h c 2002 a model for the thermal processing of particles in solar nebula shocks application to cooling rates of chondrules meteorit planet sci 37 183 208 greeney s ruzicka a 2004 relict forsterite in chondrules implications for cooling rates lunar planet sci xxxv abstract 1246 such large uncertainties directly reflect the variability of diffusion data alternatively from this variability results a compensation rule log d 0 a be diffusion coefficients are written d d 0 exp e rt we test a new geospeemetry approach based on this rule on cooling of chondrules in chondrites sahara 97210 ll 3 2 and wells ll 3 3 greeney and ruzicka 2004 matched fe mg diffusion profiles in olivine from these chondrites with cooling rates between 200 and 6000 k h in our geospeedometry model the use of the compensation rule greatly reduces the uncertainties by avoiding the choice of one diffusion coefficient among many the cooling rates we found are between 700 and 3600 k h for sahara and 700 1600 k h for wells finally we discuss the influence of our analytical model parameters on our cooling rate estimates

restoration of cross sections above intrusive salt domes the applicability of bed length restoration to the sequence above a vertical intrusion of salt was tested on an experimental model that included deposition of units during uplift restoration of the model resulted in an apparently unbalanced cross section due to excess bed length in the pre growth interval the excess bed length was due to significant internal strain for a correct restoration it is thus important to distinguish between the growth and pre growth sequences the thinning index which quantifies the thinning onto the uplift aids in making this distinction a thinning index vs depth curve has a sharp inflection at the top of the pre growth sequence the pre growth sequence is restored by area balancing the growth sequence deforms mainly by formation of a restal graben with little other strain sequential restoration of growth intervals shows the growth history of the dome when applied to the pool creek salt dome from the mississippi interior salt basin the methods developed for the model served to separate the pre growth from the growth sequence and to indicate a growth history of vertical intrusion changing through time to vertical intrusion plus regional extension

physical modeling of structures formed by salt withdrawal implications for deformation caused by salt dissolution by creating 15 physical models we investigated deformation above subsiding tabular salt salt walls and salt stocks dry quartz sand simulated a brittle sedimentary roof above viscous silicone representing salt the modeled diapiric walls had linear planforms and rectangular semicircular triangular or leaning cross sectional shapes the stock was cylindrical in models where the source layer or allochthonous salt sheet was initially tabular a gentle flat bottomed syncline bounded by monoclinal flexures formed above a linear zone where the silicone was locally removed above all subsiding diapirs the deformed roof was bounded by an inner zone of steep convex upward reverse faults and an outer zone of normal faults above subsiding diapiric walls extensional and contractional zones were balanced above the subsiding salt stock conical concentric fault zones comprised inner reverse faults and outer normal faults sediments were added both before prekinematic and during synkinematic salt withdrawal in entirely prekinematic roofs reverse fault zones and normal fault zones both widened with time reverse faults propagated upward from the corners of the withdrawing diapirs new reverse faults formed in the footwalls of reverse faults each nearer the center of the deepening roof trough conversely new normal faults formed successively outward from the sagging trough synkinematic deposition retarded faulting but the pattern of inner reverse and outer normal faults was repeated however reverse faults formed successively outward whereas normal faults formed inward new conceptual models suggest that salt dissolution forms similar structures to those physically modeled for salt withdrawal the appropriate physical models resemble natural dissolution structures above tabular salt extension alone above diapirs is not caused merely by salt withdrawal or dissolution but by regional extension or active diapirism

proterozoic canyons of the flinders ranges south australia submarine canyons or drowned river valleys abstract a number of kilometer sized erosional incisions canyons occur within a specific stratigraphic interval in the late proterozoic succession of the adelaide geosyncline flinders ranges south australia this paper describes in detail four adjacent east west orientated incisions in the northern flinders ranges which are interpreted to be part of an ancient sinuously meandering canyon system at least 600 m of siltstones and fine sandstones of the bunyeroo and the brachina formations were removed during the erosional event that produced the canyon infilling sediments which exhibit a similar succession in each incision were deposited during emplacement of the wonoka formation although an identical sedimentary succession occurs within each incision palaeocurrents determined from flute casts at the bases of sandstone beds alternate by close to 180 from one erosional feature to the next basal infilling sediments commonly contain lenticular breccias interpreted as slumps derived from the brachina formation which forms the incision walls it is significant that clasts in these breccias preserve evidence of lithification predating the erosional event that produced the incisions channel filling debris flow units which occur mainly above the basal slumps along with associated sandstones were most likely emplaced episodically asymmetric ripple cross laminae in the sandstone beds above and within debris flow units commonly are wave modified isolated occurrences of hummocky cross stratification are observed in most units of the incision fill a thin

structure and evolution of upheaval dome a pinched off salt diapir upheaval dome canyonlands national park utah is an enigmatic structure previously attributed to underlying salt doming cryptovolcanic explosion fluid escape or meteoritic impact we propose that an overhanging diapir of partly extrusive salt was pinched off from its stem and subsequently eroded many features support this inference especially synsedimentary structures that indicate jurassic growth of the dome over at least 20 m y conversely evidence favoring other hypotheses seems sparse and equivocal in the rim syncline strata were thinned by circumferentially striking low angle extensional faults verging both inward toward the center of the dome and outward near the dome s core radial shortening produced constrictional bulk strain forming an inward verging thrust duplex and tight to isoclinal circumferentially trending folds farther inward circumferential shortening predominated radially trending growth folds and imbricate thrusts pass inward into steep clastic dikes in the dome s core we infer that abortive salt glaciers spread from a passive salt stock during late triassic and early jurassic time during middle jurassic time the allochthonous salt spread into a pancake shaped glacier inferred to be 3 km in diameter diapiric pinch off may have involved inward gravitational collapse of the country rocks which intensely constricted the center of the dome sediments in the axial shear zone beneath the glacier steepened to near vertical the central uplift is inferred to be the toe of the convergent gravity spreading system

chondrules and other components in c o and e chondrites similarities in their properties and origins we describe three types of chondrules that are common to h3 ll3 cm2 co3 and cv3 chondrites low and high feo porphyritic olivine chondrules contain olivine with fa0 3 8 and fa5 50 respectively and can easily be distinguished petrographically poikilitic pyroxene chondrules have 1 20 vol olivine fa0 2 8 enclosed by low ca pyroxene fs0 5 7 and also occur in e chondrites these three types formed in separate nebular regions which had dimensions and spacings such that a few percent of the chondrules that collided to form compound chondrules were of different types sorting of chondrule precursor material and mixing of chondrule types probably account for most variations in bulk and mineral chemistry among chondrite groups metallic fe ni grains containing 0 1 1 cr si and p are present in low feo olivine chondrules from all type 2 and least metamorphosed type 3 chondrites metal compositions reflect reduction during chondrule formation in the nebula not nebular condensation opaque matrices in type 3 ordinary and carbonaceous chondrites are somewhat similar in composition and mineralogy and probably have related origins we conclude that chondrules in all known chondrite groups share similar nebular origins

geochemistry of synsedimentary cements in early cambrian reefs abstract synsedimentary fibrous calcite cements in reefs representing different periods of early cambrian time from eastern siberia southern australia and eastern canada were analyzed to determine whether they retained information about the chemical and isotopic compositions of the seawater from which they precipitated although petrographically similar the sr o and c isotopic compositions as well as the sr and mg contents of the cements from the three areas are different such differences can be attributed to varying degrees of diagenesis of the cements that correlate with the tectonic history of each area cements from the siberian craton are the least altered cements from near the appalachian orogen are partially altered and cements from the flinders fold and thrust belt are extensively altered strontium contents of the fibrous cements generally increase with mg contents although the correlation among these two elements is more variable than that reported for devonian or holocene cements those cements with sr mg ratios near 0 04 which include clear fibrous calcite have the lowest 87 sr 86 sr ratios and have been least altered strontium isotopic ratios in the least altered cements are lower than whole rock ratios and probably approach the original values of early cambrian seawater 18o values in the cements are variable because of exchange with diagenetic fluids whereas 13c values exhibit local variations that do not match temporal curves constructed from whole rock data for the same regions thus most of the original chemical and isotopic compositions of these cements have been variably changed through diagenesis although limited information about the composition of early cambrian seawater such as sr and c isotopic compositions have been retained in some samples

zoned chondrules in semarkona evidence for high and low temperature processing at least 15 of the 10w feo chondrules in semarkona ll3 0 have mesostases that are concentrically zoned in na with enrichments near the outer margins we have studied zoned chondrules using electron microprobe methods x ray mapping plus quantitative analysis ion microprobe analysis for trace elements and hydrogen isotopes cathodoluminescence imaging and transmission electron microscopy in order to determine what these objects can tell us about the environment in which chondrules formed and evolved mesostases in these chondrules are strongly zoned in all moderately volatile elements and h interpreted as water calcium is depleted in areas ofvolatile enrichment titanium and cr generally decrease toward the chondrule surfaces whereas al and si may either increase or decrease generally in opposite directions to one another mn follows na in some chondru1es but not in others fe and mg are unzoned d h ratios increase in the water rich areas of zoned chondrules mesostasis shows cathodoluminescence zoning in most zoned chondrules with the brightest yellow color near the outside mesostasis in zoned chondrules appears to be glassy with no evidence for devitrification systematic variations in zoning patterns among pyroxene and olivine rich chondrules may indicate that fractionation oflow and high ca pyroxene played some role in ti cr mn si ai and some ca zoning but direct condensation ofelements into hot chondrules secondary melting oflate condensates into the outer portions of chondrules and subsolidus diffusion of elements into warm chondrules cannot account for the sub parallel zoning profiles ofmany elements the presence ofh20 or elemental abundance patterns zoning ofmoderately volatile elements and ca may have been produced by hydration ofchondrule glass without devitrification during aqueous alteration on the parent asteroid this could have induced structural changes in the glass allowing rapid diffusion and exchange of elements between altered glass and surrounding matrix and rim material calcium was mainly lost during this process and other nonvolatile elements may have been mobile as well some unzoned 10w feo chondrules appear to have fully altered mesostasis

the cryogenian record of glaciation and deglaciation in south australia abstract this paper reviews the state of our current knowledge of the cryogenian glacial and deglacial sedimentary records of south australia two distinct glacial intervals are recognised within rocks of cryogenian 850 630 ma age separated by an interglacial succession that by definition lacks glacial facies the glacial successions were laid down during the sturt and elatina glaciations each of these glaciations is arguably of global extent under the snowball earth hypothesis hoffman and schrag 2002 evidence for glaciation has been known for over one hundred years from the sturt tillite howchin 1900 when compared like for like in a systematic facies analysis both glacial successions show some similarities notably the occurrence of diamictites representing glacial deposition and slope reflux and dropstone bearing intervals but also show some dramatic differences notably deposition of the sturt succession was strongly influenced by extensional tectonics for which evidence is provided by dramatic thickness variations either side of major faults and palaeocurrent data sub basins formed during regional extension contain diamictites 4 6000 m thick e g the yudnamutana and baratta troughs in the northern and central flinders ranges respectively deposition of the younger elatina glacial deposits was locally influenced by diapirism in the central flinders ranges but otherwise these younger deposits seem to maintain a relatively constant thickness of

chondrules precursors and interactions with the nebular gas chondrule compositions suggest either ferroan precursors and evaporation or magnesian precursors and condensation type i chondrule precursors include granoblastic olivine aggregates planetary or nebular and fine grained dustball precursors in carbonaceous chondrites type i chondrule precursors were s free while type ii chondrules have higher fe mn than in ordinary chondrites many type ii chondrules contain diverse forsteritic relicts consistent with polymict dustball precursors the relationship between finer and coarser grained type i chondrules in ordinary chondrites suggests more evaporation from more highly melted chondrules fe metal in type i and na and s in type ii chondrules indicate high partial pressures in ambient gas as they are rapidly evaporated at canonical conditions the occurrence of metal sulfide or low ca pyroxene on chondrule rims suggests re condensation in semarkona type ii chondrules na rich olivine cores na poor melt inclusions and na rich mesostases suggest evaporation followed by recondensation type ii chondrules have correlated feo and mno consistent with condensation onto forsteritic precursors but with different ratios in carbonaceous chondrites and ordinary chondrites indicating different redox history the high partial pressures of lithophile elements require large dense clouds either clumps in the protoplanetary disk impact plumes or bow shocks around protoplanets in ordinary chondrites clusters of type i and type ii chondrules indicate high number densities and their similar oxygen isotopic compositions suggest recycling together in carbonaceous chondrites the much less abundant type ii chondrules were probably added late to batches of type i chondrules from different o isotopic reservoirs

basement cover interaction in the adelaide foldbelt south australia the development of an arcuate foldbelt abstract the upper proterozoic to cambrian aged sedimentary and volcanic rocks comprising the adelaide foldbelt were deformed and in places metamorphosed during the cambro ordovician delamerian orogeny tectonic fabrics developed in the central portion of the foldbelt mt lofty ranges demonstrate westward transport during the orogeny the sigmoidal shape outlined by the kangaroo is mt lofty ranges olary portion of the foldbelt is interpreted to have been the result of dextral wrench faulting in the lower to mid proterozoic basement thus cover rocks overlying such basement wrench fault zones would have suffered a transpressional stress regime giving rise to the observed fold axis oriented at an oblique angle to the thrust boundary in the northern portion of the foldbelt northern flinders ranges wrench faulting is interpreted to have accommodated considerable basement shortening which initiated a basement cover decollement and resulted in thrust bound pop up structures in the cover

retention of sodium during chondrule melting abstract type i chondrules in unequilibrated ordinary and carbonaceous chondrites tend to be enriched in refractory elements and depleted in volatiles relative to bulk ci type ii chondrules show chondritic concentrations of major and minor lithophile elements with na in particular at or slightly above the appropriate bulk rock values element ratio diagrams for chondrule bulk compositions show that type ii chondrules plot on a mixing line between forsterite and a na phase with na al 1 1 whereas type i compositions can be explained by mixing forsterite with melilite or cai or other refractory component with little na calcium in type ii chondrules must have been added as an al free phase such as diopside if their bulk compositions are manipulated subtracting ca as diopside and fe mg as olivine the residue is 90 albite and 10 silica which would be in pyroxene albite was incorporated into the precursors of type ii chondrules which clearly have not been depleted in na although their initial temperatures overlap with those of type i there is no negative correlation between type i liquidus temperatures 1450 1900 c and na al ratios and hence no indication of na loss from the melt if type i precursors contained albite the most aluminous chondrules would have suffered the most extreme na loss but these have the lowest liquidus temperatures their precursors were na depleted whereas those of type ii were na enriched as a function of the abundance of albite the simplest way to obtain the bulk compositions of chondrules is to assemble condensates into precursors at different temperatures and concentration of solids in the nebula or exceptionally rapid heating is required to preserve na in chondrules after melting substantial exchange of na occurred between chondrules and chondrite matrix during parent body metamorphism to petrologic type 3 6

physical modeling of sedimentation adjacent to diapirs and comparison with late precambrian oratunga breccia body in central flinders ranges south australia the interaction of sedimentation with the change in shape of a developing diapir is modeled in a series of simple sandbox experiments this model replicates the pillow diapir and postdiapir stages of salt movement modeling produced rim synclines crestal unconformities and turtle structure anticlines all features known to be associated with diapirs by changing experimental parameters such as diapir shape sedimentation was simulated around various diapiric situations one experiment closely matches the sediment distribution around the oratunga diapir one of the controversial breccia bodies in the late precambrian cambrian adelaide geosyncline exposed in the flinders ranges of south australia rim synclines unconformities and bedding attitude around oratunga resemble those described around salt domes in addition the distribution size orientation and lithology of breccia within the oratunga diapir resemble breccia associated with active salt diapirs in iran these data suggest the breccia was emplaced as a salt diapir

ree bearing sulfide in bishunpur ll3 1 a highly unequilibrated ordinary chondrite abstract this is a report of the first unambiguous discovery of rare earth elements ree in iron sulfide fes in an ordinary chondrite the content and the pattern of ree as well as the reduced state of the chondrules with the ree containing sulfide suggest that the sulfide inside the bishunpur ll3 1 chondrules is of igneous origin formed during crystallization of the chondrule melts the similarities in the content and the pattern of ree between chondrule sulfide and matrix sulfide in bishunpur indicate a genetic relationship the presence of igneous sulfide inside chondrules provides constraints on the ambient nebular temperature and the duration of chondrule formation the results of this study allow on the basis of ree content and pattern discrimination of igneous sulfide from condensate and secondary sulfide in chondrites and other interplanetary materials

kinetic stability of a melted iron globule during chondrule formation i non rotating model we have investigated the kinematics of the separation of iron globules from chondrules during chondrule formation a simple model which assumes that the system has no angular momentum was used to calculate the energy of a system with an iron globule and a chondrule the energies of three different states were calculated 1 a melted iron globule fully embedded in a melted chondrule 2 a melted iron globule on the surface of a melted chondrule and 3 a melted iron globule being separated from a melted chondrule we also calculated the lowest energy shape for a melted iron globule on the surface of a melted chondrule and compared our result with the shapes of four natural samples of chondrules and iron globules in thin sections the shapes were calculated using an assumed value for the interface energy between the four couples of melted chondrules and the iron globules and agree well with the natural shapes of chondrules and iron globules the results of our calculations show that the iron globules of these four samples would be strongly bound to the surface of the melted chondrule during chondrule formation and separation would be difficult if the iron globules had been on the surface of precursors of these chondrules our results also show that if these iron globules were initially inside and transported to the surface of the melted chondrule most of them would be ejected from the inside to outside because of surface tension forces as long as the energy losses due to viscous dissipation when the globules pass through the surface of melted chondrules were sufficiently small although further improvement of the model is required our results demonstrate that this ejection process may be responsible for the depletion of siderophile elements in natural chondrules

the elatina glaciation late cryogenian marinoan epoch south australia sedimentary facies and palaeoenvironments abstract the late cryogenian elatina glaciation in south australia of marinoan age is named after the elatina formation of the glaciogenic yerelina subgroup which covers 200 000 km2 in the adelaide geosyncline and on the cratonic stuart shelf and is up to 1500 m thick the elatina glaciation is marked by numerous facies that are like those of phanerozoic glaciations basal diamictite displaying glacitectonites with penetrative deformation of preglacial beds indicating grounded ice or scouring by icebergs glaciomarine diamictites containing numerous faceted and striated clasts up to several metres across of intrabasinal and extrabasinal origin laminated siltstone and mudstone containing scattered ice rafted dropstones in outer marine shelf environments sandstones deposited in fluvial deltaic and inner marine shelf settings tidalites deposited in estuaries and on tidal deltas during interstadial rise of sea level with cyclic tidal rhythmites recording the annual oscillation of sea level and displaying wave generated ripple marks which together indicate long lived and extensive open seas siltstone containing acicular crystal pseudomorphs implying the formation of evaporite minerals in littoral deposits permafrost regolith of frost shattered quartzite breccia 20 m deep displaying large scale periglacial structures including primary sand wedges 3 m deep that indicate a frigid strongly seasonal climate near sea level periglacial aeolian sandstone covering 25 000 km2 and containing primary sand wedges near its base these deposits record a spectrum of settings ranging from permafrost regolith and periglacial sand sheet on the stuart shelf in the west through fluvial deltaic and inner marine shelf in the western and central parts of the adelaide geosyncline to outer marine shelf in the north and southeast the widespread and persistent rainout of fine grained sediment and ice rafted debris indicates that the sea was not frozen over during the elatina glaciation no direct age determination is available for the elatina glaciation and only maximum and minimum age limits of 640 and 580 ma respectively can at present be applied high quality palaeomagnetic data for red beds from the elatina formation supported by positive fold tests on soft sediment slump folds that demonstrate the early acquisition of magnetic remanence indicate deposition within 10 of the palaeoequator the yerelina subgroup in the adelaide geosyncline and on the stuart shelf is disconformably to unconformably overlain by the nuccaleena formation cap carbonate that marks the early ediacaran post glacial marine transgression the presence in near equatorial palaeolatitudes of glaciomarine deposition grounded ice and permafrost near sea level a strongly seasonal periglacial climate and widespread open seas implies a paradoxical palaeoclimate and palaeogeographic setting for the elatina glaciation the strong evidence for a non actualistic late cryogenian glacial climate in south australia has been a stimulus to worldwide multidisciplinary research on cryogenian glaciogenic successions

multiple melting in a four layered barred olivine chondrule with compositionally heterogeneous glass from ll3 0 semarkona chondrule k7p from ll3 0 semarkona consists of four nested barred olivine bo chondrules the innermost bo chondrule chondrule 1 formed by complete melting of an olivine rich dustball after formation the chondrule was incorporated into another olivine rich dustball a second heating event caused this second dustball to melt the mesostasis and some of the olivine in chondrule 1 were probably also melted at this time but the chondrule 1 structure remained largely intact at this stage the object was an enveloping compound bo chondrule this two step process of melting and dustball enshrouding repeated two more times the different proportions of olivine and glass in chondrules 1 4 suggest that the individual precursor dustballs differed in the amounts of chondrule fragments they contained and the mineral proportions in those fragments the final dustball which ultimately formed chondrule 4 was somewhat more ferroan after melting crystallizing and quenching chondrule 4 contained olivine and glass with higher feo and mno contents than those of the earlier formed chondrules subsequent aqueous alteration on the ll parent body transformed the abundant metal blebs and stringers at the chondrule surface into carbide iron oxide and minor ni rich metal portions of the mesostasis underwent dissolution producing holes and adjacent blades of more resistant material much of the glass in the chondrule remained isotropic even after minor hydration and leaching the sharp moderately lobate boundary between the extensively altered mesostasis and the isotropic glass represents the reaction front beyond which there was little or no glass dissolution

cooling rates of porphyritic olivine chondrules in the semarkona ll3 00 ordinary chondrite a model for diffusional equilibration of olivine during fractional crystallization cooling rates of chondrules provide important constraints on the formation process of chondrite components at high temperatures although many dynamic crystallization experiments have been performed to obtain the cooling rate of chondrules these only provide a possible range of cooling rates rather than providing actual measured values from natural chondrules we have developed a new model to calculate chondrule cooling rates by using the fe mg chemical zoning profile of olivine considering diffusional modification of zoning profiles as crystals grow by fractional crystallization from a chondrule melt the model was successfully verified by reproducing the fe mg zoning profiles obtained in dynamic crystallization experiments on analogs for type ii chondrules in semarkona we applied the model to calculating cooling rates for olivine grains of type ii porphyritic olivine chondrules in the semarkona ll3 00 ordinary chondrite calculated cooling rates show a wide range from 0 7 c h to 2400 c h and are broadly consistent with those obtained by dynamic crystallization experiments 10 1000 c h variations in cooling rates in individual chondrules can be attributed to the fact that we modeled grains with different core fa compositions that are more fe rich either because of sectioning effects or because of delayed nucleation variations in cooling rates among chondrules suggest that each chondrule formed in different conditions for example in regions with varying gas density and assembled in the semarkona parent body after chondrule formation

formation of solar nebula reservoirs by mixing chondritic components we determined proportions of type i reduced and type ii oxidized chondrules in ordinary chondrites oc and found linear relationships between chondrule abundances and chondrite bulk chemical and oxygen isotopic compositions similar relationships exist between bulk oxygen isotopic compositions of carbonaceous chondrites and modal abundances of their chondritic components matrix type i and type ii chondrules refractory calcium aluminium rich inclusions and amoeboid olivine aggregates these correlations can be used to predict the bulk oxygen isotopic composition of chondrites based on their petrology we can also define model isotopic compositions associated with each petrologic component which are not their current actual isotopic compositions due to alteration or mixing these compositions for refractory inclusions and chondrules plot close to a slope 1 line consistent with refractory inclusions ri forming from an early 16o rich gas the evolution of the gas to more 16o poor compositions possibly involving photodissociation and subsequent ice transport followed by chondrule formation our results open a new understanding of the oxygen 3 isotope space and explain the unique position of oc as well as the differences between h l and ll chondrites they indicate that major chemical and isotopic variations between chondritic reservoirs were established after chondrule and cai formation they may have some bearing on the formation of planetary reservoirs the 17o calculated for type i chondrules is appropriate for terrestrial planet progenitors consistent with their chemical similarity to earth mantle

petrographic constraints on the diversity of chondrule reservoirs in the protoplanetary disk abstract chondrules from different chondrite groups show characteristic properties including abundances of different chondrule textural types chondrule sizes oxygen isotope compositions chondrule bulk compositions and petrographic properties of type i and type ii chondrules including abundances of relict grains overall it can be argued that each chondrite group sampled a unique chondrule reservoir and that chondrite groups may represent fractions of larger reservoirs that are represented by chondrite classes these observations provide constraints for models of the early solar system in which it is necessary to establish multiple separate chondrule reservoirs and maintain them over extended time periods models for accretion of chondrite parent bodies must be able to account for localized accretion of chondrules that were formed in spatially or temporally separated reservoirs

physical modelling of overburden deformation around salt diapirs abstract salt diapirs produce highly complex deformation patterns in the surrounding overburden which are difficult to image seismically or model numerically to further the understanding of deformation around salt structures we have used physical models with brittle granular overburdens and simulated sedimentation accompanying diapiric rise rigid linear indentors produce a crestal horst above the indentor with two flanking graben large amounts of indentation produce predominantly reverse faults along the margins of the diapir and extensional faults over the crest in contrast hemispherical indentors produced inward dipping concentric reverse faults forefully intruded polymer diapirs produce a narrow crestal graben above the diapir crest downbuilt polymer diapirs produce extensional faults on the flanks of the diapirs which offset the diapir walls no clear secondary rim synclines were developed as polymer is withdrawn evenly from the whole of the polymer layer across the model strong and anisotropic layered overburden were simulated using cohesive clay and mica respectively detachments were formed along mica layers which suppressed faults with large throws cohesive layer deformation began with tensile fractures permitting rotation of fractured rafts around the sides of the diapir these progressively slip off the crest and create large gaps in the stratigraphy

geo and cosmochemistry of the twin elements yttrium and holmium we have analyzed the y ho ratios in bulk chondrites chondrules and four ca and al rich inclusions cais from carbonaceous and unequilibrated ordinary and enstatite chondrites ec by laser ablation inductively coupled mass spectrometry la icpms we demonstrate that bulk rock sample preparation by containerless melting is a suitable method for preparation of bulk rock samples for high precision la icpms bulk chondrites have variable y ho ratios carbonaceous chondrites ci1 cm2 cv3 and ck4 have a common y ho ratio 25 94 0 08 2 that is regarded as the solar system y ho ratio the y ho ratio increases from carbonaceous through ordinary ll l h to enstatite chondrites el6 which show the highest y ho ratio of 27 25 we discuss the result with respect to the origin of fractionation of re and os between chondrite groups within analytical error y and ho show a good correlation in oc and cv3 chondrules and define an y ho ratio of 26 22 0 40 2 y ho fractionation in ca and al rich inclusions is related to differences in volatility the bulk silicate earth is suggested to have a solar y ho ratio and links the earth with carbonaceous chondrites y ho variations in primitive and differentiated terrestrial igneous rocks are discussed in framework of incompatibility of y and ho during partial melting applicability of y ho as tracer for or against a sedimentary origin of the putative host rock of the earth s oldest traces of life from the island of akilia is briefly discussed

fe mn systematics of type iia chondrules in unequilibrated co cr and ordinary chondrites we have examined fe mn systematics of 34 type iia chondrules in eight highly unequilibrated co cr and ordinary chondrites using new data from this study and prior studies from our laboratory olivine grains from type iia chondrules in co chondrites and unequilibrated ordinary chondrites uoc have significantly different fe mn ratios with mean molar fe mn 99 and 44 respectively olivine analyses from both these chondrite groups show well defined trends in mn versus fe afu and molar fe mn versus fe mg diagrams in general type iia chondrules in cr chondrites have properties intermediate between those in uoc and co chondrites in most uoc and cr type iia chondrules the fe mn ratio of olivine decreases during crystallization whereas in co chondrites the fe mn ratio does not appear to change it is difficult to interpret the observed fe mn trends in terms of differing moderately volatile element depletions inherited from precursor materials instead we suggest that significant differences in the abundances of silicates and sulfides metals in the precursor material as well as open system behavior during chondrule formation were responsible for establishing the different fe mn trends using fe mn mg systematics we are able to identify relict grains in type iia chondrules which could be derived from previous generations of chondrules including chondrules from other chondrite groups and possibly chondritic reservoirs that have not been sampled previously