labile trace elements in carbonaceous chondrites a survey we report radiochemical neutron activation analysis data for co au ga rb sb ag se cs te zn cd bi tl and in ordered by increasing putative volatility in primary nebular processes in 42 c2 c6 chondrites all but three from antarctica from these and literature data for 19 additional chondrites cl normalized concentrations of the nine most volatile elements ag in are quite constant in most meteorites trace element trends in 39 antarctic and 22 non antarctic carbonaceous chondrites are similar no evidence exists for substantial alteration by weathering of samples in antarctica nor do the data reflect modification by open system parent body metamorphism at 500 c volatile element concentrations and siderophile ratios au co and ga co define continua which correlate at statistically significant levels carbonaceous chondrites sample not a few compositionally distinct parents but rather a compositional continuum in which parent materials forming under more oxidizing conditions incorporated lesser complements of volatiles essentially unfractionated from cosmic composition this may well reflect the range of formation conditions temperature duration and water rock ratios represented by oxygen isotope variations during preterrestrial aqueous alteration of parent materials

the cr renazzo type carbonaceous chondrite group and its implications abstract a petrologic geochemical and oxygen isotopic study of eight meteorites identified as cr renazzo type chondrites reveals that they have a set of similar properties that distinguishes them from other chondrite groups and confirms cr as a carbonaceous chondrite group characteristics of the cr group include 1 1 abundant large multilayered fe ni metal rich type i chondrules 2 2 abundant matrix and dark inclusions di that contain microchondrules microfragments and magnetite framboids and platelets 3 3 unique assemblages of serpentine and chlorite rich phyllosilicates and ca carbonates 4 4 ca carbonate rims on chondrules 5 5 abundant fe ni metal with a positive ni vs co trend and a solar ni co ratio 6 6 low abundance of refractory rich inclusions 7 7 amoeboid olivine aggregates aoa with mn rich and mn poor forsterite and 8 8 oxygen isotopic compositions that form a unique mixing line the cr chondrites are breccias consisting of two major components the large layered chondrules and the matrix dark inclusions al rais is an anomalous member in having a higher abundance of the dark inclusion component 70 vol and this accounts for its having a higher volatile content than other members of the group the conditions that prevailed during aqueous alteration of the cr chondrites differed from those of other hydrated chondrite groups and may be the result of a higher temperature environment than that for the ci and cm chondrites the cr chondrite components chondrules matrix dark inclusions etc experienced aqueous alteration to differing degrees prior to assembly of the host chondrites and dark inclusions represent a lithology that was altered by water to a greater degree than the rest of the meteorite the overall degree of hydration in cr chondrites varies among meteorites with al rais being the most hydrated the oxygen isotopic variation of the whole rocks chondrules and matrices may be related to degree of hydration indicating that cr chondrites interacted with a water rich component having heavy oxygen and that was the same as ci and cm water

oxygen isotopes in r chondrite magnetite and olivine links between r chondrites and ordinary chondrites ion microprobe studies yield 17o 17o 0 52 18o values in magnetite from the rumurti chondrite rc pca91241 which is paired with pca91002 of 3 1 to 3 9 slightly higher than that in o from whole rock r samples despite 17o values in whole rock rcs that are much by ca 1 6 higher than in whole rock ll chondrites the 17o in r magnetite is much lower by ca 2 than the values 4 to 7 from ll3 semarkona and ngawi choi et al 1998 the 18o values in pca magnetite 15 to 10 are the lowest known in meteorites well below the range in semarkona 4 to 9 on a 17o 18o diagram both magnetite data sets form linear arrays with slopes of ca 0 7 indicating mixing of o from different isotopic reservoirs the slopes and intercepts of the two arrays are similar enough to permit them to be segments of a single array this suggests that in rcs and ll chondrites magnetite formed from the same raw materials by the same processes probably by aqueous alteration of metal in an asteroidal setting we observed 17o values in olivines and pyroxene from rcs ranging from 1 2 to 2 9 and 18o from 1 4 to 9 1 these compositions scatter in the same general range observed in chondrules from ordinary chondrites the similarity in the o isotopic composition of minerals that preserve a record of formation in the solar nebula supports a model in which rcs formed from nebular components similar to those in h chondrites but with a matrix chondrule ratio several times higher in the rcs and with more extensive aqueous alteration in the rcs than in known h chondrites we postulate that the matrix in r chondrites has 17o higher than whole rock values we suggest that the original 17o value of h2o in the rc body was similar to that incorporated into the ordinary chondrites previously estimated by choi et al 1998 to be ca 7 in the ll parent body

collisions with ice volatile objects geological implications a qualitative treatment abstract an aperiodic collision of the earth with extra terrestrial ice volatile bodies is proposed as a mechanism to produce rapid changes in the geologic record due to the volatile nature of these bodies evidence for their impacts particularly in the ocean might be subtle and best seen as spikes in the geochemical or fossil record against normal background differing effects would result depending on the site of the major break up of the object in the atmosphere on land or in the ocean this paper focuses on the effects of adding material to the seas oceans and atmosphere the treatment is largely qualitative however mass balance calculations were used to estimate the relative mass needed to affect changes in a variety of reservoirs although actual impactors probably have a variable composition the effects of water c n and s containing objects are discussed in the atmosphere effects could include increased rain acidity increased levels of nutrients and enhanced greenhouse warming cooling oceanic effects might include increased oceanic productivity nitrogen containing objects as a result of increased chemical weathering and or greenhouse effects increased temperatures coupled with enhanced productivity could result in wider spread oceanic anoxia or altered calcite aragonite stability possible examples of such impacts from the geologic record and potential biotic effects are given

a new kind of primitive chondrite allan hills 85085 abstract allan hills 85085 is a chemically and mineralogically unique chondrite whose components have suffered little metamorphism or alteration this chondrite is unique because it has fewer and smaller chondrules 4 wt mean diameter 16 m than any other chondrite more metallic fe ni 36 and lithic and mineral silicate fragments 56 and a lower abundance of troilite 2 and volatiles most chondrules are cryptocrystalline or glassy and are depleted in volatiles some small chondrules are also very depleted in refractory lithophiles matrix lumps 4 partly resemble ci and cm matrices and may be foreign to the parental asteroid despite these differences the components of alh 85085 have some features common to most type 2 and the least metamorphosed type 3 chondrites metallic fe ni grains that contain 0 1 1 wt cr si and p fe fe mg values of olivines pyroxenes and chondrules are concentrated in the range 1 6 at with a few percent in the range 7 30 porphyritic chondrules are chondritic in composition except for their low volatile abundances thus the components of alh 85085 probably have similar origins to those of components in other chondrites and their properties largely reflect nebular not asteroidal processes the bulk composition of alh 85085 fits none of the nine groups of chondrites it is richer in fe 1 4 ci levels when normalized to si and poorer in na and s 0 1 0 2 ci than other chondrites low volatile concentrations are due to a low matrix abundance and loss of volatiles during or prior to chondrule formation not to volatile loss during metamorphism chondrule textures imply extensive heating of chondrule melts above the liquidus consistent with loss of volatiles from small volumes of melt during chondrule formation the small size of chondrules is partly due to extensive fragmentation by impacts which may have occurred on the parent asteroid or in the solar nebula collisions between chondrule precursor aggregates in the nebula could also be responsible for the small sizes of chondrules assuming that alh 85085 is a representative sample of an asteroid its properties lend support to models for the origins of the earth eucrite parent body and volatile poor iron meteorites that invoke chondritic planetesimals depleted in volatiles the existence of alh 85085 and kakangari suggests that the nine chondrite groups may provide a remarkably poor sample of the primitive chondritic material from which the asteroids formed certain similarities between alh 85085 and bencubbin and weatherford suggest that the latter two primitive meteorites may actually be chondrites with even higher metal abundances 50 60 wt and very large partly fragmented chondrules

r chondrite bulk chemical compositions and diverse oxides implications for parent body processes abstract r chondrites are among the most oxidized chondrite groups they also have the highest 17o values known in whole rock meteorites we analyzed r chondrites six antarctic four hot desert by instrumental neutron activation analysis data for one of the former and three of the latter show large weathering effects but the remainder show only moderate scatter and permit us to determine trends and mean compositions for the group bulk r chondrite compositions are similar to those in h and l chondrites but the concentrations of several volatiles especially se and zn are higher the more volatile the element the higher the enrichment in r chondrites relative to h and l petrologic types in r chondrites extend as low as 3 6 we determined olivine compositional distributions and studied opaque oxides in 15 r chondrite thin sections including a newly discovered r4 clast in bencubbin adding to the diversity of chondritic clasts in this polymict breccia and an r clast in cm2 murchison opaque oxides in r chondrites include nearly pure magnetite al rich chromite magnetite chromite solid solution nearly pure chromite and ilmenite this diverse set of opaque phases reflects differing aqueous alteration conditions the least equilibrated r chondrites contain nearly pure magnetite but the spinels in metamorphosed r chondrites contain additional components e g cr2o3 and al2o3 and some minor cations the nio content in olivine correlates with the magnetite component in magnetite chromite solid solution in equilibrated r chondrites and is a function of the degree of oxidation the absence of metallic fe in a 881988 and lap 031156 indicates a high degree of oxidation the relatively low feo fa35 olivine in these rocks in part reflects the conversion of fe2 to fe3 and its partitioning into magnetite oxidation trends in r chondrites are affected by both aqueous alteration and thermal metamorphism the differing degrees of oxidation in this group reflect differences in local environments on the parent asteroid

nonporphyritic chondrules from equilibrated rumuruti and ordinary chondrites chemical evidence of secondary processing fil varela maria eugenia consejo nacional de investigaciones cientificas y tecnicas centro cientifico tecnologico conicet san juan instituto de ciencias astronomicas de la tierra y del espacio universidad nacional de san juan instituto de ciencias astronomicas de la tierra y del espacio argentina

two layers of australasian impact ejecta in the indian ocean only 2 australasian tektites have been found in the indian ocean and both are associated with surficial sediments we collected cores from both locations where the tektites have been reported the microtektites in these cores and both the tektites as reported earlier have chemical compositions within the compositional range previously reported for australasian tektites and microtektites in both locations while the tektites are occurring at the sediment water interface the microtektites are found buried in older horizons beneath the seafloor at stratigraphic levels conforming to the radiometric age of the strewn field thus at first glance there appear to be 2 layers of australasian impact ejecta in the indian ocean however the manganese nodules are associated with the tektites which although millions of years old are invariably resting on recent sediments therefore the mechanism that retains nodules at the seafloor also seems to be operative on the tektites thus leading to this apparent age paradox of tektite microtektite distribution in the indian ocean although they both belong to the same impact event

oxygen isotopic composition and chemical correlations in meteorites and the terrestrial planets recent models attempting to explain non mass dependent oxygen isotopic anomalies in meteorites and planets posit that they may have originated within the gas phase of the solar nebula which suggests the potential for correlations of non mass dependent oxygen isotopic anomalies with other chemical fractionations generated during cooling and condensation of the nebula we have examined three specific issues possible correlations of 17o with i oxidation state ii bulk chondrite chemistry and iii bulk planetary properties isolated grains and chondrules from several carbonaceous chondrite groups exhibit good to weak positive correlations between 17o and olivine fayalite content and whole rock ureilite samples show a positive correlation of 17o with olivine fayalite content these are consistent with oxidation of fe metal by 17o 18o enriched oxygen in the precursor materials that formed these objects in contrast oxygen isotopic and major element compositions of ferromagnesian phases in ordinary chondrite chondrules and in bulk chondrites do not show a correlation thus there is no compelling evidence that oxidation of nebular materials was tightly linked to gas species carrying anomalous o using average chondrite group compositions we demonstrate that significant negative correlations of refractory lithophile element mg and refractory siderophile element ni with 17o exist refractory inclusions cais and aoas are modally rare in many chondrite types that exhibit substantial range in 17o thus the refractory component in these chondrites must occur in a crypto component e g material dissolved in chondrule melts during chondrule formation significant positive correlations of moderately volatile elements mg with 17o are not simply explained by incomplete mixing of 16o enriched refractory grains but are broadly consistent with nebula based mechanisms of non mass dependent oxygen isotope fractionation the estimated compositions of the primitive mantles of the earth mars and 4 vesta have some compositional redox and isotopic properties that vary with heliocentric distance however 17o does not vary monotonically in this sequence indicating a decoupling of planetary o isotopic composition from other compositional characteristics

alh85085 a unique volatile poor carbonaceous chondrite with possible implications for nebular fractionation processes abstract allan hills 85085 is a unique chondrite with affinities to the al rais renazzo clan of carbonaceous chondrites its constituents are less than 50 m in mean size chondrules and microchondrules of all textures are present nonporphyritic chondrules are unusually abundant the mean compositions of porphyritic nonporphyritic and barred olivine chondrules resemble those in ordinary chondrites except that they are depleted in volatile elements ca al rich inclusions are abundant and largely free of nebular alteration they comprise types similar to those in cm and co chondrites as well as unique types calcium dialuminate occurs in several inclusions metal silicate and sulfide compositions are close to those in cm co chondrites and al rais and renazzo c1 chondrite clasts and metal rich reduced clasts are present but opaque matrix is absent siderophile abundances in alh85085 are extremely high e g fe si 1 7 solar and volatiles are depleted e g na si 0 25 solar s si 0 03 solar nonvolatile lithophile abundances are similar to those in al rais renazzo and cm and co chondrites alh85085 agglomerated when temperatures in the nebula were near 1000 k in the same region where renazzo al rais and the ci chondrites formed agglomeration of high temperature material may thus be a mechanism by which the fractionation of refractory lithophiles occurred in the nebula chondrule formation must have occurred at high temperatures when clumps of precursors were small after agglomeration alh85085 was annealed and lightly shocked c1 and other clasts were subsequently incorporated during late stage brecciation

chondrules in the murray cm2 meteorite and compositional differences between cm co and ordinary chondrite chondrules abstract bulk compositions were determined by broad beam electron microprobe analysis for thirteen of the least aqueously altered chondrules in murray cm2 these and literature data reveal compositional differences between cm co and ordinary chondrite oc chondrules 1 a co chondrules are richer in refractory lithophiles and poorer in cr mn and volatile lithophiles than oc chondrules much lower refractory lithophile abundances in cm chondrules resulted from aqueous alteration 2 b in cm co chondrites abundances of refractory lithophiles are higher in nonporphyritic than porphyritic chondrules whereas in h l ll3 chondrites the converse is true 3 c cr ranges are greater and cr and mn correlate more strongly in chondrules in cm co than in h l ll3 chondrites we find evidence for two important lithophile precursor components of cm co chondrite chondrules 1 1 pyroxene and refractory rich feo poor 2 2 olivine rich refractory and feo poor the occurrence of a few feo rich chondrules attests to a third component similar to matrix olivine and feo rich refractories not characterized the first two components differ from those inferred for oc chondrules consistent with formation at different locations the pyroxene and refractory rich feo poor lithophile precursor component probably formed by an incomplete evaporation of presolar silicates that brought these materials into the enstatite stability field

magmatic unmixing in spinel from late precambrian concentrically zoned mafic ultramafic intrusions eastern desert egypt abstract spinel is widespread in the ultramafic core rocks of zoned late precambrian mafic ultramafic complexes from the eastern desert of egypt these complexes gabbro akarem genina gharbia and abu hamamid are precambrian analogues of alaskan type complexes they are not metamorphosed although weakly altered each intrusion is composed of a predotite core enveloped by pyroxenites and gabbros at the margin silicate mineralogy and chemistry suggest formation by crystal fractionation from a hydrous magma relatively high cr 2 o 3 contents are recorded in pyroxenes up to 1 1 wt and amphiboles up to 1 4 wt from the three plutons the chrome spinel crystallized at different stages of melt evolution as early cumulus inclusions in olivine inclusions in pyroxenes and amphiboles and late magmatic intercumulus phase the intercumulus chrome spinel is homogenous with narrow range of chemical composition mainly fe 3 rich spinel spinel inclusions in clinopyroxene and amphibole reveal a wide range of al 27 44 wt al 2 o 3 and mg 6 13 wt mgo contents and are commonly zoned the different chemistries of those spinels reflect various stages of melt evolution and re equilibration with the host minerals the early cumulus chrome spinel reveals a complex unmixing structures and compositions three types of unmixed spinels are recognized crystallographically oriented irregular and complete separation unmixing products are al rich type i and fe 3 rich type ii spinels with an extensive solid solution between the two end members the compositions of the unmixed spinels define a miscibility gap with respect to cr al fe 3 extending from the fe 3 al join towards the cr corner spinel unmixing occurs in response to cooling and the increase in oxidation state the chemistry and grain size of the initial spinel and the cooling rate control the type of unmixing and the chemistry of the final products causes of spinel unmixing during late magmatic stage are analogous to those in metamorphosed complexes the chemistry of the unmixed spinels is completely different from the initial spinel composition and is not useful in petrogenetic interpretations spinels from oxidized magmas are likely to re equilibrate during cooling and are not good tools for genetic considerations

mineralogical characterization of primitive type 3 lithologies in rumuruti chondrites rumuruti r chondrites constitute a new well established chondrite group different from the carbonaceous ordinary and enstatite chondrites many of these samples are gas rich regolith breccias showing the typical light dark structure and consist of abundant fragments of various parent body lithologies embedded in a fine grained olivine rich matrix unequilibrated type 3 lithologies among these fragments have frequently been mentioned in various publications in this study detailed mineralogical data on seven primitive fragments from the r chondrites dar al gani 013 and hughes 030 are presented the fragments range from 300 in size up to several millimeters generally the main characteristics can be summarized as follows 1 unequilibrated type 3 fragments have a well preserved chondritic texture with a chondrule to matrix ratio of 1 1 chondrules and chondrule fragments are embedded in a fine grained olivine rich matrix thus the texture is quite similar to that of type 3 carbonaceous chondrites 2 in all cases matrix olivines in type 3 fragments have a significantly higher fa content 44 57 mol than olivines in other equilibrated lithologies 38 40 mol fa 3 olivines and pyroxenes occurring within chondrules or as fragments are highly variable in composition fa0 65 and fs0 33 respectively and generally more magnesian than those found in equilibrated r chondrites agglomerated material of the r chondrite parent body or bodies was highly unequilibrated it is suggested that the material that accreted to form the parent body consisted of chondrules and chondrule fragments mainly having mg rich silicate constituents and fe rich highly oxidized fine grained materials the dominating phase of this fine grained material may have been fa rich olivine from the beginning the brecciated whole rocks the r chondrite regolith breccias were not significantly reheated subsequent to brecciation or during lithification as indicated by negligible degree of equilibration between matrix components and mg rich olivines and pyroxenes in primitive type 3 fragments

cosmogenic mega tsunami in the australia region are they supported by aboriginal and maori legends mega tsunami have affected much of the coastline of australia over the past millennium such catastrophic waves have left an imprint consisting predominently of bedrock sculpturing of the rocky coastline and deposition of marine sediments to elevations reaching 130 mabove sea level one of the largest of these events occurred in eastern australia in the fifteenth century this event may be related to the mahuika impact crater found at 48 38 s 166 48 e on the continental shelf 250 km south of new zealand a comet at least 500 m in diameter formed the crater maori and aboriginal legends allude to significant cosmogenic events in the region while aboriginal legends about tsunami are common along the eastern australian coast evidence for legends that could describe the impact of a cosmogenic tsunami also exists in nw australia here geological evidence of a single megatsunami as recent as in the seventeenth century covers 1500 km of coastline we term this event wandjina after the artwork related to the legends more attention should be given to oral traditions in searching globally for other sites of significant mega tsunami

fe mg fe mn relations of meteorites and primary heterogeneity of primitive achondrite parent bodies abstract we examine fe mg mn relations of meteorites as represented on plots of molar fe mg ratio vs molar fe mn ratio and use them to consider whether it is meaningful to classify achondrites as primitive or evolved first we demonstrate that fe mg fe mn plots can be used to identify some of the major processes that have affected meteorite parent bodies during both the nebular condensation and accretion and the planetary igneous stages of their evolution examination of compositions of chondrites on this diagram reveals distinct patterns that result from three nebular processes 1 volatility controlled mn mg fractionation 2 metal silicate fractionation under highly reducing conditions and 3 subsequent oxidation leading to variations in feo mgo ratio ordinary chondrites ocs show a characteristic pattern that records all three of these processes and suggests that the latter two are coupled examination of the compositions of achondrites on this diagram shows that all of those that have been classified as primitive lodranites acapulcoites winonaites iab silicate inclusions brachinites and ureilites are easily distinguished from those that have been classified as evolved sncs heds and lunar basalts the mn mg ratios of the former are chondritic while those of the latter are superchondritic hence they plot in two graphically distinct regions of the fe mg fe mn diagram a simple melting calculation reveals that this distinction results principally because the former are residues and the latter are melts or cumulate products of melts rather than because the latter are more evolved additionally however some of the groups classified as primitive achondrites show fe mg fe mn patterns similar to that of ocs constant but distinct mno mgo ratios over large ranges of feo mgo ratio we argue that these trends reflect primary heterogeneity resulting from the same nebular processes as those that affected ocs and therefore preserve evidence that more of the materials that accreted to form planetesimals experienced these processes than is apparent from known chondrites this evidence is preserved principally because these meteorites are residues in contrast groups commonly classified as evolved achondrites show fe mg fe mn patterns that reflect only igneous processing and any evidence for primary heterogeneity of their parent bodies has been obliterated again this is principally because these meteorites represent melts rather than beause they are more evolved usage of the terms primitive and evolved to describe achondrites should be clearly defined

physical properties of chondrules in different chondrite groups implications for multiple melting events in dusty environments chondrite groups cv ck cr with large average chondrule sizes have low proportions of rp plus c chondrules high proportions of enveloping compound chondrules high proportions of chondrules with thick igneous rims and relatively low proportions of type i chondrules containing sulfide in contrast chondrite groups cm co oc r eh el with smaller average chondrule sizes have the opposite properties equilibrated ck chondrites have plagioclase with relatively low na equilibrated oc r eh and el chondrites have more sodic plagioclase enveloping compound chondrules and chondrules with igneous rims formed during a remelting event after the primary chondrule was incorporated into a dustball repeated episodes of remelting after chondrules were surrounded by dust would tend to produce large chondrules rp and c chondrules formed by complete melting of their precursor assemblages remelting of rp and c chondrules surrounded by dust would tend to produce porphyritic chondrules as small dust particles mixed with the melt providing nuclei for crystallizing phenocrysts this process would tend to diminish the numbers of rp and c chondrules correlations among these chondrule physical properties suggest that chondrite groups with large chondrules were typically surrounded by thick dust rich mantles that formed in locally dusty nebular environments chondrules that were surrounded by thick dust mantles tended to cool more slowly because heat could not quickly radiate away slow cooling led to enhanced migration of sulfide to chondrule surfaces and more extensive sulfide evaporation these chondrules also lost na the plagioclase that formed from equilibrated ck chondrites was thus depleted in na

collisional modification of the acapulcoite lodranite parent body revealed by the iodine xenon system in lodranites the i xe system of three lodranites has been investigated samples of gibson yielded no isochrons and late model ages are attributed to late addition of iodine two metal and one silicate separate from the transitional lodranite graves nunataks gra 95209 gave ages that are consistent with each other and with the literature i xe age of acapulco feldspar these yield a mean closure age 4 19 0 53 ma after the shallowater enstatite reference age 4562 3 0 4 ma such identical i xe ages from distinct phases imply that the parent material underwent a period of rapid cooling the absolute age of this event being 4558 1 0 7 ma such rapid cooling indicates an increase in the rate at which heat could be conducted away requiring a significant modification of the parent body we suggest the parent body was modified by an impact at or close to the time recorded by the i xe system an age of 10 4 2 3 ma after shallowater has been determined for one whole rock sample of lewis cliff lew 88280 since the release pattern is similar to that of gra 95209 this hints that the larger grain size of this sample may reflect slower cooling due to deeper post impact burial

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

allan hills 77081 an unusual stony meteorite abstract allan hills alha 77081 is achondritic in texture while the mineral composition and the chemistry are chondritic with the exception of a few elements an assignment to one specific group of ordinary chondrites is therefore difficult in many respects this meteorite is similar to the unusual stone meteorite acapulco the ree pattern of alha 77081 is essentially flat and the distribution ratios of siderophile elements between metal and silicates are high compared to ordinary chondrites gas retention ages are 3 5 0 5 ae for u th he and 4 50 0 15 ae for k ar in spite of the high degree of recrystallisation the meteorite contains trapped noble gases in amounts comparable to type 4 chondrites cosmic ray tracks and spallogenic noble gases indicate a small preatmospheric radius of about 2 3 cm spallogenic nuclides produced by solar cosmic rays or stopped solar flare ions may be present

the matrices of unequilibrated ordinary chondrites implications for the origin and history of chondrites abstract the matrices of sixteen unequilibrated ordinary chondrites all witnessed falls were studied microscopically in transmitted and reflected light and analyzed by electron microprobe selected specimens were also studied by scanning electron microscopy these studies indicate that the fine grained opaque silicate matrix of type 3 unequilibrated chondrites is compositionally mineralogically and texturally distinct from the chondrules and chondrule fragments and may be the low temperature condensate proposed by larimer and anders 1967 1970 examination of the matrices of unequilibrated chondrites also shows that each meteorite has been metamorphosed with the alteration ranging in intensity from quite mild where the matrix has been only slightly altered to a more severe metamorphism that has completely recrystallized the opaque matrix most of the metamorphic changes in the matrix occurred without significant effects on the compositions or textures of the chondrules the metamorphic alteration probably resulted from a combination of processes including thermal metamorphism and the passage of shock waves the present appearance of each unequilibrated chondrite is a result of the particular temperature and pressure conditions under which it and its components formed plus the subsequent metamorphic alteration it experienced

the chromite deposit of the ipueira medrado sill sao francisco craton bahia state brazil the ipueira medrado mafic ultramafic sill hosts the largest chromite deposit in brazil the sill is a 7 km long and 300 m thick elongated body consisting mainly of interlayered dunite and harzburgite but also containing minor mafic rocks the most distinctive feature of the ipueira medrado sill is a continuous 5 to 8 m thick massive chromitite layer that is currently being mined the anomalous thickness of this chromitite layer provides important constraints on current genetic models for the origin of massive chromitites the sill is divided into three zones marginal ultramafic and mafic the marginal zone 5 20 m thick consists of sheared gabbro and orthopyroxene rich harzburgite the ultramafic zone up to 250 m thick is subdivided into the lower ultramafic unit the main chromitite layer and the upper ultramafic unit the lower ultramafic unit consists of dunite with minor harzburgite and chain textured chromitite the main chromitite layer is composed of chain textured and massive chromitites and the upper ultramafic unit consists mainly of harzburgite but also minor chain textured chromitite and dunite pyroxene abundance increases toward the top in this zone and grades to an orthopyroxenite at the top the presence of magmatic intercumulus amphibole is significant up to 20 vol in this unit the mafic zone up to 40 m thick consists of leuconorites to melanorites that are partially metamorphosed under amphibolite facies conditions the variation of olivine and orthopyroxene compositions throughout the sill layers reveals two intervals of distinct magmatic evolution the interval located below the main chromitite layer is characterized by gradual upward evolution of mineral compositions toward more mg rich compositions fo93 and en94 the interval located above the main chromitite layer is characterized by rapid evolution toward more fe rich compositions fo85 and en84 with increasing stratigraphic height the interval below the main chromitite layer suggests crystallization in a dynamic magma chamber undergoing frequent replenishment with primitive magma the interval above the main chromitite layer suggests crystallization in a mainly closed fractionating magma chamber mass balance considerations suggest that an enormous amount of magma 10 000 m thick was associated with the formation of the main chromitite layer at the ipueira medrado sill such a volume of magma is obviously not represented in the stratigraphy of the ipueira medrado sill mineral chemistry data indicate that the composition of the resident magma was most primitive at the stratigraphic interval immediately below the main chromitite layer we suggest that the sill acted as a conduit through which a large volume of magma flowed under these conditions contamination of the parental magma with crustal material and fluids is a likely mechanism for explaining the origin of the chromitite abundant intercumulus amphibole in the upper ultramafic unit and high fe3 in chromites intercumulus orthopyroxene in main chromitite layer chromitites and sm nd and re os isotope data for silicate rocks and chromitites respectively indicate that the ipueira medrado sill formed from magmas contaminated by crustal material the host rocks of the ipueira medrado sill consist mainly of high grade gneiss and marbles that would have been appropriate source of fluids and sio2 and could have caused the increase in f o2

geochemical and oxygen isotope perspective of a new r chondrite dhofar 1671 affinity with ordinary chondrites dhofar 1671 is a relatively new meteorite that previous studies suggest belongs to the rumuruti chondrite class major and ree compositions are generally in agreement with average values of the r chondrites rcs moderately volatile elements such as se and zn abundances are lower than the r chondrite values that are similar to those in ordinary chondrites ocs porphyritic olivine pyroxene pop radial pyroxene rp and barred olivine bo chondrules are embedded in a proportionately equal volume of matrix one of the characteristic features of rcs microprobe analyses demonstrate compositional zoning in chondrule and matrix olivines showing fa poor interior and fa rich outer zones precise oxygen isotope data for chondrules and matrix obtained by laser assisted fluorination show a genetic isotopic relationship between ocs and rcs on the basis of our data we propose a strong affinity between these groups and suggest that oc chondrule precursors could have interacted with a 17o rich matrix to form rc chondrules i e 17o shifts from 1 to 3 these interactions could have occurred at the same time as exotic clasts in brecciated samples formed such as nwa 10214 ll3 6 parnallee ll3 pca91241 r3 8 6 and dhofar 1671 r3 6 we also infer that the source of the oxidation and 17o enrichment is the matrix which may have been enriched in 17o rich water the abundance of matrix in rcs relative to ocs ensured that these rocks would be apparently more oxidized and appreciably 17o enriched in situ analysis of dhofar 1671 is recommended to further strengthen the link between ocs and rcs

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

analysis of the mahuika comet impact tsunami hypothesis abstract a comet impact on february 13 1491 ad 250 km sw of new zealand named mahuika has been proposed as the tsunamigenic source for an alleged large 15th century tsunami along the new zealand and east australian coastlines this hypothesis has been based on astronomic and atmospheric evidence and data from near the putative impact site but the underpinning documentation has never been fully presented we outline the current mahuika comet impact tsunami hypothesis and analyse the original data sources geophysical evidence for a crater has never been documented tektites are widespread in south pacific sediments and provide no indication of the event age and far field evidence for any comet impact in the 15th century is unconvincing all the evidence reviewed indicates that no comet mahuika or otherwise struck the earth on february 13 1491 ad based upon our reassessment the origin of apparent tsunami deposits along the coasts of new zealand and east australia needs to be reassessed they are not tsunami deposits the mahuika comet impact tsunami hypothesis should be treated with extreme caution until stronger evidence is presented

mineralogy of meteorite groups approximately 275 mineral species have been identified in meteorites reflecting diverse redox environments and in some cases unusual nebular formation conditions anhydrous ordinary carbonaceous and r chondrites contain major olivine pyroxene and plagioclase major opaque phases include metallic fe ni troilite and chromite primitive achondrites are mineralogically similar the highly reduced enstatite chondrites and achondrites contain major enstatite plagioclase free silica and kamacite as well as nitrides a silicide and ca mg mn na cr k and ti rich sulfides aqueously altered carbonaceous chondrites contain major amounts of hydrous phyllosilicates complex organic compounds magnetite various sulfates and sulfides and carbonates in addition to kamacite and taenite iron meteorites contain carbides elemental c nitrides phosphates phosphides chromite and sulfides silicate inclusions in iab iiicd and iie iron meteorites consist of mafic silicates plagioclase and various sulfides oxides and phosphates eucrites howardites and diogenites have basaltic to orthopyroxenitic compositions and consist of major pyroxene and calcic plagioclase and several accessory oxides ureilites are made up mainly of calcic chromian olivine and low ca clinopyroxene embedded in a carbonaceous matrix accessory phases include the c polymorphs graphite diamond lonsdaleite and chaoite as well as metallic fe ni troilite and halides angrites are achondrites rich in fassaitic pyroxene i e al ti diopside minor olivine with included magnesian kirschsteinite is also present martian meteorites comprise basalts lherzolites a dunite and an orthopyroxenite major phases include various pyroxenes and olivine minor to accessory phases include various sulfides magnetite chromite and ca phosphates lunar meteorites comprise mare basalts with major augite and calcic plagioclase and anorthositic breccias with major calcic plagioclase several meteoritic phases were formed by shock metamorphism martensite 2 fe ni has a distorted body centered cubic structure and formed by a shear transformation from taenite during shock reheating and rapid cooling the c polymorphs diamond lonsdaleite and chaoite formed by shock from graphite suessite formed in the north haig ureilite by reduction of fe and si possibly from olivine via reaction with carbonaceous matrix material ringwoodite the spinel form of mg fe 2sio4 and majorite a polymorph of mg fe sio3 with the garnet structure formed inside shock veins in highly shocked ordinary chondrites secondary minerals in meteorite finds that formed during terrestrial weathering include oxides and hydroxides formed directly from metallic fe ni by oxidation phosphates formed by the alteration of schreibersite and sulfates formed by alteration of troilite

reaction relationships of chrome spinels in igneous rocks further evidence from the layered intrusions of rhum and mull inner hebrides scotland compositions of chrome spinels in peridotites from the layered igneous rocks of rhum and of the ben buie intrusion mull show evidence of post depositional reaction relationships with the cumulus olivine and or the intercumulus liquid some seam forming spinels in the ben buie intrusion are highly aluminous more so than those in the rhum intrusion occasional zoned spinels in both intrusions show enrichment in al towards their rims the evidence suggests that the spinel reaction trend involving cr al exchange proceeds in the direction of al enrichment equilibrium between chrome spinel and cumulus olivine appears to have been attained rarely thus limiting the application of the olivine spinel geothermometer

the kemi stratiform chromitite deposit northern finland the kemi chromite deposit is hosted by an early proterozoic 2 44 ga layered intrusion the lower part of the intrusion is composed of peridotitic and pyroxenitic cumulates and chromitite layers olivine and chromite have not been observed in the upper part where plagioclase is the predominant cumulus phase occurring either alone or together with pyroxenes the intrusion was metamorphosed during the svecokarelidic orogeny mafic minerals of the lower and upper parts of the complex are completely altered to chlorite serpentine talc amphiboles and carbonates whereas the middle part is well preserved the chromite grains too suffered from alteration but the cores of the grains still exhibit primary compositions a continuous chromitite layer can be traced for the entire length of 15 km of the intrusion it varies in thickness from a few millimeters to as much as 90 m in the central part of the intrusion the mineable thicker part of the main chromitite layer is about 4 5 km long the main chromitite layer is overlain by a sequence of thin chromite rich layers which continues upward to the stratigraphic level of 500 m above the basal contact of the intrusion the upper part of the main chromitite is layered but the lower part is more massive and brecciated the ore reserves for open pit mining are ca 40 million metric tons with an average grade of 26 6 percent cr 2 o 3 and a cr fe ratio of 1 53 the whole area has additional reserves of about 110 million metric tons of ore the ore zone is intensely fractured the host rocks have undergone alteration which has degraded the quality of the ore the present surface section of the kemi intrusion is interpreted as a cross section typical of a funnel shaped intrusion and plunging about 70 degrees to the northwest the cumulate sequence especially the main chromitite layer is at its thickest in the middle of the intrusion and the magmatic conduit which fed the intrusion is also thought to have been located just below this thickening it is suggested that the chromitite was deposited when the input of magma into the kemi intrusion was contaminated by salic material from the underlying basement complex this magma mixed with the fresh input of primitive magma resulting in chromite saturation the chromite crystals formed during mixing in a plume according to the model of huppert et al 1986 and accumulated preferentially around the magmatic conduit evidence of contamination is found in chromite grains in the form of small inclusions rich in alkalies which are thought to represent trapped droplets of the contaminant salic melt

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

textural and compositional features of chromite in the lower and critical zones of the bushveld complex south of potgietersrus chromite is developed as an accessory mineral in a 1 700 m thick sequence of lower and lower critical zone cumulates in the area south of potgietersrus and as a major constituent in a number of chromitite layers within this sequence the lower zone consists of a 1 500 m thick sequence of ultramafic rocks characterized by varying proportions of olivine orthopyroxene and chromite which allows the pile of cumulates to be subdivided into 37 cyclic units the critical zone on the other hand is only 350 m thick of which only the lower 150 m contains chromite bearing lithologies electron microprobe analyses of chromite and coexisting silicates indicate a strong positive correlation between the mg mg fe super 2 and cr fe super 2 fe super 3 ratios of chromite and the mg mg fe super 2 ratio of the mafic silicates the composition of the chromite is also strongly influenced by the mineralogical composition of the host rock and probably reflects conditions within the parental magma during crystallization of these rocks the analytical data have also shown the tio 2 content of the disseminated chromite to be the most informative indicator of the degree of differentiation of the magma a detailed investigation of the chromite across the contact of a thin chromitite layer has shown that the chromitite layers crystallized in response to an influx of magma and that chromite crystallization could have been enhanced by an increase in the f sub o 2 and a rise in the cr 2 o 3 content of the liquid thereby causing an increase in the cr 2 o 3 content of the chromite within the chromitite layers postcumulus modification of the chromitite layers is extensive and primary textural features have been obliterated essentially by sintering sintering took place in the presence of a reactive mg rich liquid which resulted in an increase in the mg mg fe super 2 ratio of the chromite this process resulted in a densification of the chromitite layers from an estimated initial porosity of 30 to 45 percent to less than 10 percent

39ar 40ar chronology of r chondrites this study presents the first determinations of 39ar 40ar ages of r chondrites for the purpose of understanding the thermal history of the r chondrite parent body the 39ar 40ar ages were determined on whole rock samples of four r chondrites carlisle lakes rumuruti acfer 217 and pecora escarpment 91002 pca 91002 all samples are breccias except for carlisle lakes the age spectra are complicated by recoil and diffusive loss to various extents the peak 39ar 40ar ages of the four chondrites are 4 35 4 47 0 02 4 30 0 07 ga and 4 37 ga respectively these ages are similar to ar ar ages of relatively unshocked ordinary chondrites 4 52 4 38 ga and are older than ar ar ages of most shocked ordinary chondrites 4 2 ga because the meteorites with the oldest rumuruti 4 47 ga and the youngest acfer 217 4 30 ga ages are both breccias these ages probably do not record slow cooling within an undisrupted asteroidal parent body instead the process of breccia formation may have differentially reset the ages of the constituent material or the differences in their age spectra may arise from mixtures of material that had different ages two end member type situations may be envisioned to explain the age range observed in the r chondrites the first is if the impact s that reset the ages of acfer 217 and rumuruti was very early in this case the 170 ma maximum age difference between these meteorites may have been produced by much deeper burial of acfer 217 than rumuruti within an impact induced thick regolith layer or within a rubble pile type parent body following parent body re assembly the second preferred scenario is if the impact that reset the age of acfer 217 was much later than that which reset rumuruti then acfer 217 may have cooled more rapidly within a much thinner regolith layer in either scenario the oldest age obtained here from rumuruti provides evidence for relatively early 4 47 ga impact events and breccia formation on the r chondrite parent body

the cooling history of the acapulco meteorite as recorded by the 244pu and 40ar 39ar chronometers 244pu fission track densities recorded in phosphates merrillite and apatite and in orthopyroxenes adjacent to phosphates along with 40ar 39ar dating were used to retrace the cooling evolution in the low temperature regime of the acapulco meteorite over a time interval of 110 ma high resolution 40ar 39ar dating yielded a plateau age of 4514 16 ma and a precise 40ar closure temperature of 560 20 k in plagioclase this ar closure temperature is essentially indistinguishable from the 50 retention temperature of fission tracks registered in orthopyroxene 550 25 k this allows us to anchor the floating relative 244pu timescale to the absolute timescale defined by the 40ar 39ar chronometer plutonium contents of bulk phosphates inferred from fission xenon are 2x higher than those inferred from tracks in the same phosphates reflecting the low track retention temperatures of phosphates however the pu contents from tracks in orthopyroxenes adjacent to phosphates agree with those from fission xenon suggesting similar retention temperatures and times our results together with an estimated peak metamorphic temperature 1300 k and the u pbpb datum of acapulco phosphates gopel et al 1992 outline an early thermochronological history of acapulco that is more detailed than obtained by earlier attempts and spans a time of 160 ma fast cooling in the high temperature regime 1300 720 k of 100 40 k ma was followed by a drastic change of the cooling rate between 720 and 560 k 3 7 k ma down to a very slow cooling 1 7 0 5 k ma from 550 to 360 k the fast cooling at high temperatures shared also by other acapulcoite lodranites a l suggests that the parent body of acapulco was distinctly smaller than the h chondrite asteroid in contrast the very slow cooling in the low temperature regime should imply that acapulco like material became effectively insulated during a later stage of its history 6 ma after the asteroid formation if a formation time of 4565 ma is assumed for the a l body extrapolations back in time of the pu contents of phosphates give initial 244pu 238u ratios of 0 4 10 2 and 11 10 2 for apatite and merrillite respectively for the bulk phosphates an initial pu u value of 0 8 0 16 10 2 is obtained for acapulco which is in full agreement with the preferred chondritic ratio of 0 7 10 2 proposed by hagee et al 1990 trapped ar contents are surprisingly high both primordial 36ar at levels of type 4 ordinary chondrites and excess radiogenic 40ar were detected in our sample as in some acapulcoites by other authors this partial closed system behaviour could be the result of the partial melt and sintering effects that the high peak metamorphic temperatures have induced in a l meteorites in addition the spread in the early peak temperatures 1300 1450 k as reflected by the diverse degrees of partial melting observed in a l meteorites suggests heterogeneously distributed short lived heating sources 26al60fe and disfavours the homogeneous heating expected from an electromagnetic induction arising from an active pre main sequence sun the possibility that some specific collisional event s with or without disruption of the a l planetesimal could satisfactorily explain the thermal histories and diverse characteristics of these meteorites appears difficult to envision in the absence of evident shock effects in most if not all a l meteorites

a strongly hydrated microclast in the rumuruti chondrite nwa 6828 implications for the distribution of hydrous material in the solar system hydrous carbonaceous microclasts are by far the most abundant foreign fragments in stony meteorites and mostly resemble ci1 cm2 or cr2 like material their occurrence is of great importance for understanding the distribution and migration of water bearing volatile rich matter in the solar system this paper reports the first finding of a strongly hydrated microclast in a rumuruti chondrite the r3 6 chondrite northwest africa 6828 contains a 420 325 m sized angular foreign fragment exhibiting sharp boundaries to the surrounding r type matrix the clast is dominantly composed of magnetite pyrrhotite rare ca carbonate and very rare mg rich olivine set in an abundant fine grained phyllosilicate rich matrix phyllosilicates are serpentine and saponite one region of the clast is dominated by forsteritic olivine fa 1 au between the formation regions of ordinary and carbonaceous chondrites the occurrence of a hydrous microclast in an r chondrite attests to the presence of such material also in this region at least at some point in time and documents the wide distribution of water bearing possibly zodiacal cloud material in the solar system

tsunami hazard assessment and risk in aotearoa new zealand a systematic review ad 1868 2012 abstract this paper presents a systematic review of peer reviewed journal articles scientific reports books and research theses covering tsunami hazard assessment and risk in aotearoa new zealand a nz fifteen electronic databases were examined using an array of keyword search strings to comprehensively gather all available sources of information spanning 1868 2012 ad 222 references were identified as directly relevant to tsunami hazard assessment and risk in a nz with a further 51 references identified by scrutinising the original 222 references the amount of information as well as the emphasis of the science contained in these 273 references differs greatly between documents a meta analysis of this collective scholarship shows six principal areas of scientific endeavour i observation and cataloguing of modern and historical tsunami impacts caused by earthquakes and landslides ii modelling and evaluation of near and far field generated tsunamis iii detailed mapping and assessment of offshore seismic and other geological structures responsible for near field tsunami generation iv investigation and cross referencing of holocene palaeo records of tsunami deposits preserved in wetlands dunes and other coastal landforms v survey and reconnaissance of modern and historical tsunami impacts and vi guidance for tsunami hazard mitigation preparedness and land use planning synthesising all of these references it is clear that a nz has been affected by remote regional and locally generated tsunami during the historic pre written and pre human periods further scientific knowledge of tsunami risk and the forces responsible for tsunami generation has greatly improved however in spite of the many scientific advances detailed in this review much more remains to be done to better understand and deal with the diverse tsunami hazard and risk facing a nz

carlisle lakes and allan hills 85151 members of a new chondrite grouplet carlisle lakes and allan hills 85151 alh85151 are members of a new grouplet of chondrites characterized by feo rich silicates olivine fa 38 41 mol unusual oxygen isotopic composition and abundant 35 vol recrystallized matrix material yamato 75302 is not as well characterized but is probably also a member of this grouplet siderophile elements in carlisle lakes and alh85151 are fractionated relative to ci chondrites refractory and common siderophiles are at 1 ci ga and as are lower 0 6 0 9 ci and au is very low 0 17 ci and 0 36 ci in carlisle lakes and alh85151 respectively the low au abundance may indicate that au resided mainly in fine grained metal particles that were suspended in the nebular gas during the time these chondrites agglomerated the oxidation state of chondrites may be controlled by the presence of oxidizing agents e g magnetite in agglomerated matrix material the high matrix abundance that characterizes this new grouplet may thus be responsible for the high oxidation state of these meteorites

do manganese nodules grow or dissolve after burial results from the central indian ocean basin abstract fifty buried manganese nodules at different depth intervals were recovered in 12 sediment cores from the central indian ocean basin ciob a maximum of 15 buried nodules were encountered in one sediment core aas 22 gc 07 and the deepest nodule was recovered at 5 50 m below seafloor in core aas 04 gc 5a approximately 80 of the buried nodules are small in size 2 cm diameter in contrast to the atlantic ocean and peru basin pacific ocean where the majority of the buried nodules are large 8 cm and 6 cm respectively buried nodule size decreases with core depth and this distribution appears to be similar to the phenomenon of brazil nut effect buried nodules exhibit both smooth and rough surface textures and are ellipsoidal elongated rounded sub rounded irregular and polynucleated buried nodules from siliceous ooze are enriched in mn cu ni zn mo ga v and rb whereas those from red clay are enriched in fe co ti u th y cr nb and rare earth elements ree buried nodules from siliceous ooze suggest their formation under hydrogenetic early digenetic and diagenetic processes whereas those from red clay are of hydrogenetic origin ree are enriched more than 1 5 times in buried nodules from red clay compared to siliceous ooze however the mode of incorporation of ree into buried nodules from both sedimentary environments is by a single authigenic phase consisting of fe ti p shale normalized ree patterns and ce anomalies suggest that nodules from siliceous ooze formed under more oxidizing conditions than those from red clay nodules buried at depths between 1 5 and 2 5 m are diagenetic mn fe ratio 10 15 formed in highly oxic environments large positive ce anomalies and record aeolian dust high eu anomalies chemical composition surface texture and morphology of buried nodules are similar to those of surface nodules from the same basin furthermore buried nodule compositions do not exhibit any distinct patterns within the core depth suggesting that buried nodules neither grow nor dissolve after their burial in the sediment column

shock and annealing in the amphibole and mica bearing r chondrites mil 11207 r6 and lap 04840 r6 contain hornblende and phlogopite mil 07440 r6 contains accessory titan phlogopite and no hornblende all three meteorites have been shocked mil 11207 contains extensive sulfide veins pyroxene that formed from dehydrated hornblende and an extensive network of plagioclase glass mil 07440 contains chromite plagioclase assemblages chromite veinlets and blebs pincer shaped plagioclase patches but no sulfide veins lap 04840 contains olivine grains with chromite bleb laden cores and opaque free rims rare grains of pyroxene that formed from dehydrated hornblende and no sulfide veins these meteorites appear to have been heated to maximum temperatures of approximately 700 900 c under conditions of moderately high ph2o perhaps 250 500 bars all three samples underwent postshock annealing during this process olivine crystal lattices healed giving the rocks the appearance of shock stage s1 and diffusion of fe and s from thin sulfide veins to coarse sulfide grains caused the veins to disappear in mil 07440 and lap 04840 this latter process apparently also occurred in most s1 s2 ordinary chondrites of high petrologic type the pressure temperature conditions responsible for forming the amphibole and mica in these rocks may have been present at depths of a few tens of kilometers as suggested in the literature a giant impact or a series of smaller impacts would then have been required to excavate the hornblende and biotite bearing rocks and bring them closer to the surface it was in that latter location where the samples were shocked deposited in a hot ejecta blanket of low thermal diffusivity and annealed

a synthesis and review of the geological evidence for palaeotsunamis along the coast of southeast australia the evidence issues and potential ways forward abstract in recent years the role of extreme events such as tsunamis and storms in shaping coastal evolution and change has been increasingly appreciated around the world tsunami geologists are increasingly recognising the signatures of palaeotsunamis almost everywhere they look and in many cases base their interpretations on similar evidence for quaternary tsunamis first identified in australia geological research suggests that the coast of south east australia and others worldwide may have been impacted by palaeotsunamis many times larger than the catastrophic 2004 indian ocean and 2011 t hoku events in australia the debate centres on the hypothesis that the coast of south east australia preserves evidence for repeated large magnitude quaternary tsunamis if independently validated this hypothesis has profound implications for risk despite the potential importance of this hypothesis no synthesis or comprehensive review of the proposed geological evidence and chronology exists as a result it is difficult to assess the evidence and to draw conclusions about the nature of the hazard and risk along the coast this synthesis details the spatial distribution of reported palaeotsunami deposits along the coast of new south wales south east australia and summarises the distribution of different types of sedimentary and erosional evidence the age range of reported palaeotsunami deposits is identified and mapped before discussing same age chronologically correlated deposits these data are then used to draw broad conclusions about the evidence and identify future research questions to aid in the testing of the hypothesis for repeated tsunami inundation we show that 60 sites are purported to contain evidence of tsunami inundation over 650 km of the south east australian coast with a spatial concentration south of sydney geomorphic evidence distinctly different to that used elsewhere in global palaeotsunami studies is reported at 54 sites with erosional features described as the most frequent indication of inundation proposed tsunami deposits are evident at 44 sites with the dominant deposit type being imbricated boulder stacks radiocarbon dating at 39 of the sites led to a proposition of nine events during the quaternary eight of which occurred during the holocene interestingly 18 sites have no chronological data associated with them alternative interpretations are offered at six type field sites purported to contain palaeotsunami evidence attention is drawn to the disjunct between historical and geological scales of tsunami inundation in the region in addition to the contrast between the scale of reported palaeotsunamis and the robust evidence of smaller events a synthesis of research into the nature of the evidence is offered including critiques of evidence type and mechanisms a critical review of the chronological data is also presented in addition to the recalibration and analysis of published radiocarbon data the paper concludes with an outline of research questions for further work on proposed palaeotsunami sites in australia as well as a statement about likely risk in south east australia it also advocates the need for caution when interpreting evidence for palaeotsunamis elsewhere around the world when those interpretations are based on signatures originally reported in south east australia

rumuruti chondrites noble gases exposure ages pairing and parent body history in this paper we present concentration and isotopic composition of the light noble gases he ne and ar as well as of 84kr 132xe and 129xe in bulk samples of 33 rumuruti r chondrites together with previously published data of six r chondrites exposure ages are calculated and compared with those of ordinary chondrites a number of pairings especially between those from northwest africa nwa are suggested so that only 23 individual falls are represented by the 39 r chondrites discussed here eleven of these meteorites or almost 50 contain solar gases and are thus regolithic breccias this percentage is higher than that of ordinary chondrites howardites or aubrites this may imply that the parent body of r chondrites has a relatively thick regolith concentrations of heavy noble gases especially of kr are affected by the terrestrial atmospheric component which resides in weathering products compared to ordinary chondrites 129xe 132xe ratios of r chondrites are high

petrogenesis of acapulcoites and lodranites a shock melting model abstract acapulcoites are modeled as having formed by shock melting cr like carbonaceous chondrite precursors the degree of melting of some acapulcoites was low enough to allow the preservation of 3 6 vol relict chondrules shock effects in acapulcoites include veins of metallic fe ni and troilite polycrystalline kamacite fine grained metal troilite assemblages metallic cu and irregularly shaped troilite grains within metallic fe ni while at elevated temperatures acapulcoites experienced appreciable reduction because graphite is present in some acapulcoites and lodranites it seems likely that carbon was the principal reducing agent reduction is responsible for the low contents of olivine fa 4 14 mol and low ca pyroxene fs 3 13 mol in the acapulcoites the observation that in more than two thirds of the acapulcoites the fa value is lower than the fs value in contrast to the case for equilibrated ordinary chondrites the low feo mno ratios in acapulcoite olivine 16 18 compared to 32 38 in equilibrated h chondrites the relatively high modal orthopyroxene olivine ratios e g 1 7 in monument draw compared to 0 74 in h chondrites and reverse zoning in some mafic silicate grains lodranites formed in a similar manner to acapulcoites but suffered more extensive heating loss of plagioclase and loss of an fe ni s melt acapulcoites and lodranites experienced moderate post shock annealing presumably resulting from burial beneath material of low thermal diffusivity the annealing process repaired damaged olivine crystal lattices lending acapulcoites and lodranites the appearance of unshocked i e shock stage s1 rocks any high pressure phases that may have formed during initial shock reverted to their low pressure polymorphs during annealing some samples were subsequently shocked again several acapulcoites reached shock stage s2 levels alh 84190 reached s3 and the lodranite mac 88177 reached s5

clastic matrix in eh3 chondrites patches of clastic matrix 15 to 730 m in size constitute 4 9 vol of eh3 yamato y 691 and 11 7 vol of eh3 allan hills alh 81189 individual patches in y 691 consist of 1 25 vol relatively coarse opaque grain fragments and polycrystalline assemblages of kamacite schreibersite perryite troilite some grains with daubreelite exsolution lamellae niningerite oldhamite and caswellsilverite 2 30 vol relatively coarse silicate grains including enstatite albitic plagioclase silica and diopside and 3 an inferred fine nebular component 45 vol comprised of submicrometer size grains clastic matrix patches in alh 81189 contain relatively coarse grains of opaques 20 vol kamacite schreibersite perryite and troilite and silicates 30 vol enstatite silica and forsterite as well as an inferred fine nebular component 50 vol the o isotopic composition of clastic matrix in y 691 is indistinguishable from that of olivine and pyroxene grains in adjacent chondrules both sets of objects lie on the terrestrial mass fractionation line on the standard three isotope graph some patches of fine grained matrix in y 691 have distinguishable bulk concentrations of na and k inferred to be inherited from the solar nebula some patches in alh 81189 differ in their bulk concentrations of ca cr mn and ni the average compositions of matrix material in y 691 and alh 81189 are similar but not identical matrix in alh 81189 is much richer in mn 0 23 0 05 versus 0 07 0 02 wt and appreciably richer in ni 0 36 0 10 versus 0 18 0 05 wt than matrix in y 691 each of the two whole rocks exhibits a petrofabric probably produced by shock processes on their parent asteroid

geological and historical records of tsunami in australia abstract the indian ocean tsunami iot of 2004 has resulted in significant interest within australia about the record of tsunami for the continent because an understanding of tsunami hazard begins with a catalogue of past events here a preliminary catalogue of tsunami affecting australia is presented the catalogue contains entries for 57 tsunami events the oldest event is dated at 3 47 ga the most recent is the july 17th 2006 forty four tsunami were recorded on the new south wales coast although the nw coast of western australia records a significant number of events forty seven events have affected australia since ad1858 maximum run up for an historic event is 6 m asl whilst the maximum run up for a palaeotsunami event is reported at an elevation of at least 100 m asl twenty three percent of historic australian tsunami were generated by unknown causes and papua new guinea the solomon islands and indonesia collectively represent the most important source area of historic tsunami for australia geological records for palaeo and historic tsunami are identified and summarised the geological record of tsunami represents a potentially important source of information for australian tsunami however at the present time the geological record is both limited and controversial and future research should seek to re examine proposed geological evidence of tsunami from an analysis of this preliminary catalogue of australian tsunami a series of key research priorities have been identified to guide future research in the region

reaction rims of orthopyroxene and plagioclase around chrome spinels in olivine from skye and rhum nw scotland reaction between chrome spinel and its supernatant magma due to changes in magmatic composition or temperature is well known its effects can be observed in these rocks however evidence of solid solid reaction between chrome spinels and enclosing olivine is also present in the form of relict diffusion profiles in some of the olivines and an orthopyroxene reaction product rimming the spinel in addition the rhum specimens contain rims of plagioclase resulting from solid liquid reaction around chrome spinels within the margins of olivine detailed microprobe traverses and analysis of reaction products have been made in an attempt to determine the equations for these reactions

geochemistry and mineralogy of platinum group elements in the ransko gabbro peridotite massif bohemian massif czech republic the ransko gabbro peridotite massif in eastern bohemia is a strongly differentiated intrusive complex of lower cambrian age the complex hosts low grade ni cu ores mainly developed close to the contact of olivine rich rocks with gabbros in troctolites and to a much lesser extent in both pyroxene and olivine gabbros and plagioclase rich peridotites the ore zone is characterized by strong serpentinization and uralitization the total ni cu locally reaches up to 4 wt anomalous concentrations of platinum group elements pge s maximum 532 ppb pd 182 ppb pt 53 ppb rh 15 ppb ru 41 ppb ir were detected in samples of cu ni and ni cu ores maximum 2 63 wt ni and 2 31 wt cu from the jezirka orebody the main ore paragenesis includes pyrrhotite pentlandite chalcopyrite cubanite pyrite magnetite mackinawite valleriite ilmenite and sphalerite during this work michenerite froodite sperrylite gold native bismuth altaite tsumoite hessite an unnamed bi ni telluride cobaltite gersdorffite and galena were newly identified the host rocks originated through partial melting of a slightly depleted mantle source with noble metals scavenged from this primitive magma prior to the development of these rocks

tsunami and palaeotsunami depositional signatures and their potential value in understanding the late holocene tsunami record in recent years much research on modern and palaeotsunami deposits has been published from these studies a range of signature types has been identified identifying and dating such deposits is an important element in understanding late holocene tsunami hazard and risk however important questions such as do modern and palaeotsunami leave similar or dissimilar traces do tsunami leave the same signatures all around the world or are there significant variations and what is the actual record of tsunami in different parts of the world still remain answering these questions is not an easy task but examining megatsunami flood deposits should shed some light on these questions because such high magnitude events should leave very clear and detailed traces within the coastal landscape the coast of se australia is reported to have been affected by numerous palaeomegatsunami in the late holocene as such the coast of new south wales offers an important natural laboratory to examine in detail deposits associated with such events here we summarize the published characteristics of modern and palaeotsunami deposits globally and within australia we briefly outline the tsunami risk to australia before examining a site called minnamurra point on the coastline of se australia south of sydney that has previously been described as containing evidence for a palaeomegatsunami of an unknown age we describe the results of a detailed coastal survey field stratigraphic investigation and various standard laboratory analyses surprisingly we are unable to replicate the previously reported findings of tsunami deposits whilst we prefer the interpretation that the sequence is an in situ soil the sediment sequence examined contains none of the usually reported lines of evidence to demonstrate tsunami provenance we recognize and discuss the significance and difficulty of identifying tsunami deposits in the field and consider the implications of our findings to the wider debate about the preservation of tsunami deposited sediments

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

earth impact effects program a web based computer program for calculating the regional environmental consequences of a meteoroid impact on earth we have developed a web based program for quickly estimating the regional environmental consequences of a comet or asteroid impact on earth www lpl arizona edu impacteffects this paper details the observations assumptions and equations upon which the program is based it describes our approach to quantifying the principal impact processes that might affect the people buildings and landscape in the vicinity of an impact event and discusses the uncertainty in our predictions the program requires six inputs impactor diameter impactor density impact velocity before atmospheric entry impact angle the distance from the impact at which the environmental effects are to be calculated and the target type sedimentary rock crystalline rock or a water layer above rock the program includes novel algorithms for estimating the fate of the impactor during atmospheric traverse the thermal radiation emitted by the impact generated vapor plume fireball and the intensity of seismic shaking the program also approximates various dimensions of the impact crater and ejecta deposit as well as estimating the severity of the air blast in both crater forming and airburst impacts we illustrate the utility of our program by examining the predicted environmental consequences across the united states of hypothetical impact scenarios occurring in los angeles we find that the most wide reaching environmental consequence is seismic shaking both ejecta deposit thickness and air blast pressure decay much more rapidly with distance than with seismic ground motion close to the impact site the most devastating effect is from thermal radiation however the curvature of the earth implies that distant localities are shielded from direct thermal radiation because the fireball is below the horizon

evolution and classification of acapulcoites and lodranites from a chemical point of view we examined 15 bulk samples of the acapulcoite lodranite clan for their major minor and trace element concentrations using inaa techniques among the analyzed meteorites are 2 new acapulcoites dhofar dho 290 thiel mountains til 99002 as well as an additional acapulcoite that has been described previously only in very brief form graves nunataks gra 98028 the petrographic attributes of these 3 samples are addressed thoroughly we also include petrographic information on 2 acapulcoites from africa northwest africa nwa 725 and nwa 1058 in general our study strongly supports the widely accepted idea that acapulcoites and lodranites evolved through partial melting and melt migration of metal sulfide phases and plagioclase furthermore we concur with previous researchers that the original bimodal classification scheme for acapulcoites and lodranites proves to be too simple based on our data set we introduce an alternative extended scheme with respect to their elemental distribution patterns we distinguish 5 subtypes comprising primitive typical transitional and enriched acapulcoites on one hand and lodranites on the other the chemical distinction between the primitive typical and transitional acapulcoites is rather subtle and gradual it stands in contrast to the clear modifications observed for the signatures of the enriched acapulcoites and the lodranites the definition of subcategories basically reflects the concentrations of 2 key elements k and se we note however that the assignment of subgroups may not be exclusively inferred from elemental abundances but should also consider additional petrographic information

compositional effects on the solubility of minor and trace elements in oxide spinel minerals insights from crystal crystal partition coefficients in chromite exsolution chromite from los congos and los guanacos in the eastern pampean ranges of cordoba argentinian central andes shows homogenous and exsolution textures the composition of the exsolved phases in chromite approaches the end members of spinel mgal 2 o 4 spl and magnetite fe 2 fe 2 3 o 4 mag that define the corners of the spinel prism at relatively constant cr 3 r 3 ratio where r 3 is cr al fe 3 the exsolution of these phases from the original chromite is estimated to have accounted at 600 c on the basis of the major element compositions of chromite with homogenous and exsolution textures that are in equilibrium with forsterite rich olivine fo 95 the relatively large size of the exsolved phases in chromite up to ca 200 m provided for the first time the ability to conduct in situ analysis with laser ablation inductively coupled plasma mass spectrometry for a suite of minor and trace elements to constrain their crystal crystal partition coefficient between the spinel rich and magnetite rich phases d i spl mag minor and trace elements listed in increasing order of compatibility with the spinel rich phase are ti sc ni v ge mn cu sn co ga and zn d i spl mag values span more than an order of magnitude from d ti spl mag 0 30 0 06 to d zn spl mag 5 48 0 63 our results are in remarkable agreement with data available for exsolutions of spinel rich and magnetite rich phases in other chromite from nature despite their different cr 3 r 3 ratio the estimated crystal crystal partitioning coefficients reflect the effect that crystal chemistry of the exsolved phases from chromite imposes on all investigated elements excepting cu and sc and only slightly for mn the observed preferential partitioning of ti and sc into the magnetite rich phase is consistent with high temperature chromite melt experiments and suggests a significant dependence on fe 3 substitution in the spinel structure a compositional effect of major elements on ga co and zn is observed in the exsolved phases from chromite but not in the experiments this might be due to crystal chemistry differences along the mgfe 1 al 2 fe 2 3 exchange vector which is poorly covered experimentally this inference is supported by the strong covariance of ga co and zn observed only in chromite from layered intrusions where this exchange vector is important a systematic increase of zn and co coupled with a net decrease in ga during hydrous metamorphism of chromitite bodies cannot be explained exclusively by compositional changes of major elements in the chromite which are enriched in the magnetite component the most likely explanation is that the contents of minor and trace elements in chromite from metamorphosed chromitites are controlled by interactions with metamorphic fluids involved in the formation of chlorite

platinum group mineral inclusions in chromite from the bird river sill manitoba platinum group minerals pgm have been identified as inclusions in chromite from the bird river sill manitoba the inclusions are small 20 microns and are commonly euhedral the pgm inclusions are ru os ir s2 laurite and os ir ru alloy rutheniridosmine laurites contain up to 2 99 wt palladium arsenic content is negligible and no platinum or rhodium has been detected one platinum group element alloy contains 0 96 wt rhodium but neither platinum nor palladium has been detected laurite inclusions in chromite from the ultramafic zone record two compositional trends first increasing and then decreasing ru ru os ir up section pgm inclusions and other solid inclusions occur as discrete phases in chromite and are part of the chromite precipitation event increasing oxygen fugacity by wall rock assimilation or new magma injection initiates chromite precipitation locally increasing the sulphur content of the magma to convert pge alloys to sulphides

ca al rich inclusions in rumuruti r chondrites rumuruti chondrites r chondrites constitute a well characterized chondrite group different from carbonaceous ordinary and enstatite chondrites many of these meteorites are breccias containing primitive type 3 fragments as well as fragments of higher petrologic type ca al rich inclusions cais occur within all lithologies here we present the results of our search for and analysis of al rich objects in rumuruti chondrites we studied 20 r chondrites and found 126 ca al rich objects 101 cais 19 al rich chondrules and 6 spinel rich fragments based on mineralogical characterization and analysis by sem and electron microprobe the inclusions can be grouped into six different types 1 simple concentric spinel rich inclusions 42 2 fassaite rich spherules 3 complex spinel rich cais 53 4 complex diopside rich inclusions 5 al rich chondrules and 6 al rich spinel rich fragments the simple concentric and complex spinel rich cais have abundant spinel and based on the presence or absence of different major phases fassaite hibonite na al cl rich alteration products can be subdivided into several subgroups although there are some similarities between cais from r chondrites and inclusions from other chondrite groups with respect to their mineral assemblages abundance and size the overall assemblage of cais is distinct to the r chondrite group some ca al rich inclusions appear to be primitive e g low feo contents in spinel low abundances of na al cl rich alteration products abundant perovskite whereas others were highly altered by nebular and or parent body processes e g high concentrations of feo and zno in spinel ilmenite instead of perovskite abundant na al cl rich alteration products there is complete absence of grossite and melilite which are common in cais from most other groups cais from equilibrated r chondrite lithologies have abundant secondary ab rich plagioclase oligoclase and differ from those in unequilibrated type 3 lithologies which have nepheline and sodalite instead

petrology of types 4 6 carbonaceous chondrites we have studied the petrology of three type 4 carbonaceous chondrites coolidge karoonda and pecora escarpment 82500 which was previously classified as an ll6 chondrite and compared them to published descriptions of the other known metamorphosed c chondrites yamato 6903 and mulga west all except coolidge have abundant matrix typically 80 vol composed largely of homogeneous olivine fa 29 33 and surprisingly heterogeneous plagioclase mostly an 20 75 their opaque mineralogy indicates high oxygen fugacities during metamorphism metallic fe ni and troilite are rare and magnetite and pentlandite are abundant with accessory pyrrhotite chalcopyrite and pyrite possibly because of a lower matrix abundance coolidge has more reduced minerals metallic fe ni and olivine with fa 14 the properties of all c4 6 chondrites appear to be consistent with an origin by metamorphism of c3 like precursors by processes analogous to those operating in ordinary chondrite parent bodies or planetesimals however type 4 6 material was not well mixed with type 3 material in the cv3 parent body as it was in the ordinary chondrite parent bodies conceivably c4 6 chondrites come from one or more separate parent bodies

the compositional classification of chondrites vii the r chondrite group bulk compositional and petrographic data clearly define the new r rumuruti group of chondrites consisting of rumuruti the only fall alh85151 acfer 217 carlisle lakes dar al gani 013 pca91002 pca91241 y 75302 y 793575 and y 82002 compositional petrographic rare gas and 0 isotopic data strongly suggest that pca91002 and pca91241 are paired the yamato specimens are probably not paired the matrices of the known r chondrites have experienced similar minor degrees of metamorphism petrographic types are 3 8 3 9 with the exception of alh85151 3 6 all except carlisle lakes contain equilibrated r5 r6 clasts petrographically the r chondrites are characterized by a low chondrule matrix modal abundance ratio high states of oxidation reflected by abundant nio bearing olivine with fa37 40 relatively small chondrules mean apparent diameters of 400 abundant up to 11 wt sulfides mainly pyrrhotite and pentlandite and negligible amounts of metallic fe ni refractory lithophile abundances are 0 95 x cl intermediate between those in ordinary chondrites oc and ci chondrites abundances of the volatile elements se and zn are greatly enhanced relative to oc the r chondrites are clearly distinguished from other chondrite groups on the basis of al mn and zn mn abundance ratios the oxygen isotopic data plot roughly along a slope 12 line with whole rock 17o values higher than for any other chondrite group rumuruti acfer 217 alh85151 pca91002 and pca91241 have light dark structures and solar wind implanted rare gases indicating that they are regolith breccias the yamato specimens also have light dark structures and are inferred to be regolith breccias carlisle lakes lacks solar rare gases and is unbrecciated based on similarities in refractory lithophile abundances 00 95 x ci oxygen isotope compositions 17o 0 and refractory inclusion abundances 0 1 vol none have been reported the r chondrites probably belong to a noncarbonaceous superclan of chondrites that also includes ordinary and enstatite chondrites the high oxidation state high matrix chondrule modal abundance ratio relatively low abundance of droplet chondrules and high 17o composition suggest that the r chondrites formed at greater heliocentric distances than the oc

chevrons are not mega tsunami deposits a sedimentologic assessment since the introduction of the term chevron for large v or u shaped bed forms in egypt and the bahamas others have adopted the term to describe large scale coastal bed forms in australia madagascar and elsewhere these authors interpret chevron bed forms as deposits of mega tsunamis resulting from holocene oceanic asteroid impacts we reason that chevron type bed forms are common and are present far enough from the coast to preclude tsunami genesis moreover we argue that chevrons are not mega tsunami deposits by modeling tsunami behavior and evaluating sediment transport conditions under which such features formed we model the southern madagascar case with an impact source in the indian ocean and show that a modeled wave approach is inconsistent with chevron orientation we then evaluate sediment transport conditions under which these chevron bed forms could persist i e bed load transport in our analysis no conditions specified generate pure bed load transport and most result in pure suspended load transport

the case for significant numbers of extraterrestrial impacts through the late holocene when astronomers tell us that there should have been numerous impacts from space during the last five millennia when impact craters exist on land and more impacts can be assumed over the oceans why are historians archaeologists and palaeoecologists not diligently seeking evidence for these impacts and their effects this article reviews just some of the relevant evidence for impacts in turn this suggests that ablation material background material from space and micro tektites should all be present in ocean cores ice cores peat and lake sediments it seems that almost no efforts have been made to find evidence that might link to the known crater fields or to identify and date periods of enhanced cosmic activity the question must be why copyright 2007 john wiley sons ltd

the carlisle lakes type chondrites a new grouplet with high δ17o and evidence for nebular oxidation abstract carlisle lakes alh85151 and y75302 are similar ungrouped chondrites which have petrologic and bulk compositional similarities to the ordinary chondrites but are more oxidized and their oxygen isotopic compositions differ they represent a new grouplet which we call the carlisle lakes type chondrites they have the highest 17o values up to 2 91 measured to date the whole chondrites and most of their chondrules plot on the same mass fractionation line on an oxygen 3 isotope diagram they are olivine rich 70 vol essentially metal free and most olivine is feo rich equilibrated at fa38 rare olivine and pyroxene grains in chondrules and fragments are zoned and these are important in discerning the history of these chondrites the zoning does not appear to have formed during crystallization from a melt droplet chondrule but post dated chondrule formation two hypotheses are postulated to explain the zoning 1 1 parent body thermal metamorphism 2 2 nebular gas solid exchange reactions accompanied by condensation of new feo rich olivine utilizing existing olivine surfaces as nucleation sites the occurrence of steep fe mg compositional gradients of core to rim profiles oscillatory zoning in olivine fayalitic rims of fa45 that exceed instead of approach the equilibrium composition of the matrix fa38 and olivine filled veins in zoned pyroxenes are more compatible with the nebular hypothesis the carlisle lakes type chondrites may have originally been derived from an ordinary chondrite like precursor which was later oxidized prior to its final lithification however the oxygen isotopic compositions of the whole chondrites and most of their chondrules suggest that the precursor probably formed in an oxygen isotopically distinct environment

ages and composition of gas trapped in allan hills and byrd core ice gas is extracted from large 6 31 kg antarctic ice samples to obtain sufficient co2 for14c measurements with small low level proportional counters the14c ages of byrd core ice are in accord with glaciological estimates ranging from 2 2 1 1 1 4 103 yr at 271 m depth to more than 8 103 yr at 1071 m depth the co2 abundances in gas extracted from byrd core ice range from 0 0216 to 0 051 with below present day atmosphere co2 abundances for ice from 1068 and 1469 m depths the co2 abundance in gas from allan hills surface ice samples ranges between four and six times the atmospheric value and the co2 had a specific activity three times that of contemporary carbon a possible explanation for the anomalously high specific activity is surface melting with the incorporation into co2 of14c produced by cosmic ray spallation of oxygen in ice the co2 abundance in gas extracted from subsurface allan hills ice ranged from 0 030 to 0 065 and the specific activities are below contemporary carbon indicating ages greater than 5 103 yr the18o 16o ratio of oxygen in the trapped gas is the same as that of atmospheric oxygen and differs markedly from the18o 16o ratio in the ice the o2 n2 and ar abundances and isotopic compositions are similar to those in contemporary air except for positive15n 14n ratios in a few samples

the chromite deposits of the troodos complex cyprus evidence for the role of a fluid phase accompanying chromite formation the troodos ophiolite of cyprus hosts chromite deposits both as podiform bodies within the basal harzburgite and as lesser layers and schlieren within the overlying dunites and clinopyroxene dunites of the metacumulate sequence all chromitite types have been studied from both field and mineralogical aspects with particular emphasis on the chemistry of the ubiquitous silicate inclusions within chromite grains two distinct inclusion assemblages have been documented chromites from podiform bodies contain abundant hornblende serpentine ortho and clinopyroxene and lesser olivine while those from the metacumulates host pargasite albite serpentine and rare pyroxenes this implies that no single silicate inclusion assemblage in chromite can be considered typically ophiolitic the presence of an alkalirich fluid phase during chromite crystallization as evidenced by the unusual mineralogy of these inclusions has already been widely discussed in the literature however the marked stratigraphic control of inclusion types in chromite as reported here enables more complete modelling of the evolution of this phase to be made

chromian spinel mineralogy of the stare ransko gabbro peridotite czech republic and its implications for sulfide mineralization chromian spinels from the stare ransko gabbro peridotite czech republic display a distinct development trend from primary cr rich spinels towards ferro ferri ti enriched magnetite and magnesio alumina spinel sensu stricto spinels zoning in the spinels is thought to be the result of a combination of exsolution postdepositional diffusion and replacement processes multiphase globular silicate inclusions mainly biotite and amphibole also orthopyroxene serpentine and chlorite are present in euhedral largely homogeneous chromian spinels which occur in a matrix of poikilitic amphibole the enclosed minerals have similar compositions to the minerals in the host rock these silicate inclusions are interpreted as being due to a late magmatic introduction of a hydrous k ca rich melt phase contaminated by wall rock interaction into a semi solidified olivine pyroxenes cumulate