Sample records for achondrites

  1. Uranium and thorium in achondrites.

    Morgan, J. W.; Lovering, J. F.


    The abundances of U and Th in 19 achondrites and two pallasite olivines have been measured by radiochemical neutron activation analysis. Brecciated eucrites are enriched relative to chondrites in both elements by factors between 10 and 20, perhaps as a result of a magmatic differentiation process. Two unbrecciated eucrites are far less enriched, possibly due to their origin as igneous cumulates. The diogenites Johnstown and Shalka contain approximately chondritic levels of U and Th, but Ellemeet is 10 times lower. The abundances in three howardites are in good agreement with those expected from major element data for a mixing model with eucrite and diogenite end members. The high O-18 basaltic achondrites Nakhla, Shergotty and Angra dos Reis have a range of U and Th abundances similar to the brecciated eucrites and howardites, but have systematically higher Th/U ratios.

  2. Hf-W chronometry of primitive achondrites

    Schulz, T.; Münker, C.; Mezger, K.; Palme, H.


    Metal segregation and silicate melting on asteroids are the most incisive differentiation events in the early evolution of planetary bodies. The timing of these events can be constrained using the short-lived 182Hf- 182W radionuclide system. Here we present new 182Hf- 182W data for major types of primitive achondrites including acapulcoites, winonaites and one lodranite. These meteorites are of particular interest because they show only limited evidence for partial melting of silicates and are therefore intermediate between chondrites and achondrites. For acapulcoites we derived a 182Hf- 182W age of Δ tCAI = 4.1 +1.2/ -1.1 Ma. A model age for winonaite separates calculated from the intercept of the isochron defines an age of Δ tCAI = 4.8 +3.1/ -2.6 Ma (assuming a bulk Hf/W ratio of ˜1.2). Both ages most likely define primary magmatic events on the respective parent bodies, such as melting of metal, although metal stayed in place and did not segregate to form a core. A later thermal event is responsible for resetting of the winonaite isochron, yielding an age of Δ tCAI = 14.3 +2.7/ -2.2 Ma, significantly younger than the model age. Assuming a co-genetic relationship between winonaites and silicates present in IAB iron meteorites (based on oxygen isotope composition) and including data by Schulz et al. (2009), a common parent body chronology can be established. Magmatic activity occurred between ˜1.5 and 5 Ma after CAIs. More than 5 Ma later, intensive thermal metamorphism has redistributed Hf-W. Average cooling rates calculated for the winonaite/IAB parent asteroid range between ˜35 and ˜4 K/Ma, most likely reflecting different burial depths. Cooling rates obtained for acapulcoites were ˜40 K/Ma to ˜720 K and then ˜3 K/Ma to ˜550 K. Accretion and subsequent magmatism on the acapulcoite parent body occurred slightly later if compared to most achondrite parent bodies (e.g., angrites, ureilites and eucrites), in this case supporting the concept of an inverse

  3. Studying SNC achondrites: Looking for clues on Mars

    Moyano-Cambero, C. E.; Trigo-Rodríguez, J. M.; Mestres, N.; Chennaoui Aoudjehane, N.; Madiedo, J. M.


    We characterize here the main minerals forming four SNC achondrites (Zagami, Nakhla, Dar al Gani 735 and Tissint), studied with a petrographic microscope and a Raman spectrometer. Our goal is to obtain information on the physico-chemical processes that participated in their formation and delivery to Earth. We are also studying the ability of some minerals forming the different groups to retain Mars atmospheric gases during the post-shock stages in order to sample Mars' atmospheric evolution.

  4. Photochemical mass-independent sulfur isotopes in achondritic meteorites.

    Rai, Vinai K; Jackson, Teresa L; Thiemens, Mark H


    Sulfides from four achondrite meteorite groups are enriched in 33S (up to 0.040 per mil) as compared with primitive chondrites and terrestrial standards. Stellar nucleosynthesis and cosmic ray spallation are ruled out as causes of the anomaly, but photochemical reactions in the early solar nebula could produce the isotopic composition. The large 33S excess present in oldhamite from the Norton County aubrite (0.161 per mil) suggests that refractory sulfide minerals condensed from a nebular gas with an enhanced carbon-oxygen ratio, but otherwise solar composition is the carrier. The presence of a mass-independent sulfur effect in meteorites argues for a similar process that could account for oxygen isotopic anomalies observed in refractory inclusions in primitive chondrites.

  5. Geochemistry and chronology of the Bunburra Rockhole ungrouped achondrite

    Spivak-Birndorf, Lev J.; Bouvier, Audrey; Benedix, Gretchen K.; Hammond, Samantha; Brennecka, Gregory A.; Howard, Kieren; Rogers, Nick; Wadhwa, Meenakshi; Bland, Philip A.; Spurný, Pavel; Towner, Martin C.


    Bunburra Rockhole is a unique basaltic achondrite that has many mineralogical and petrographic characteristics in common with the noncumulate eucrites, but differs in its oxygen isotope composition. Here, we report a study of the mineralogy, petrology, geochemistry, and chronology of Bunburra Rockhole to better understand the petrogenesis of this meteorite and compare it to the eucrites. The geochemistry of bulk samples and of pyroxene, plagioclase, and Ca-phosphate in Bunburra Rockhole is similar to that of typical noncumulate eucrites. Chronological data for Bunburra Rockhole indicate early formation, followed by slow cooling and perhaps multiple subsequent heating events, which is also similar to some noncumulate eucrites. The 26Al-26Mg extinct radionuclide chronometer was reset in Bunburra Rockhole after the complete decay of 26Al, but a slight excess in the radiogenic 26Mg in a bulk sample allows the determination of a model 26Al-26Mg age that suggests formation of the parent melt for this meteorite from its source magma within the first ~3 Ma of the beginning of the solar system. The 207Pb-206Pb absolute chronometer is also disturbed in Bunburra Rockhole minerals, but a whole-rock isochron provides a re-equilibration age of ~4.1 Ga, most likely caused by impact heating. The mineralogy, geochemistry, and chronology of Bunburra Rockhole demonstrate the similarities of this achondrite to the eucrites, and suggest that it formed from a parent melt with a composition similar to that for noncumulate eucrites and subsequently experienced a thermal history and evolution comparable to that of eucritic basalts. This implies the formation of multiple differentiated parent bodies in the early solar system that had nearly identical bulk elemental compositions and petrogenetic histories, but different oxygen isotope compositions inherited from the solar nebula.

  6. In Situ Determination of Siderophile Trace Elements in Metals and Sulfides in Enstatite Achondrites

    vanAcken, D.; Humayun, M.; Brandon, A. D.; Peslier, A.


    Enstatite meteorites are identified by their extremely reduced mineralogy (1) and similar oxygen isotope composition (2). The enstatite meteorite clan incorporates both EH and EL chondrites, as well as a wide variety of enstatite achondrites, such as aubrites or anomalous enstatite meteorites (e.g. Mt. Egerton, Shallowater, Zaklodzie, NWA 2526). The role of nebular versus planetary processes in the formation of enstatite meteorites is still under debate (e.g. 3-5). Past studies showed a significant influence of metal segregation in the formation of enstatite achondrites. Casanova et al. (6) suggested incomplete metal-silicate segregation during core formation and attributed the unfractionated siderophile element patterns in aubrites metals to a lack of fractional crystallization in a planetary core. Recent studies suggest a significant role of impact melting in the formation of primitive enstatite chondrites (7) and identified NWA 2526 as a partial melt residue of an enstatite chondrite (8). To understand the nature of siderophile element-bearing phases in enstatite achondrites, establish links between enstatite achondrites and enstatite chondrites (9), and constrain planetary differentiation on their respective parent bodies and their petrogenetic histories, we present laser ablation ICP-MS measurements of metal and sulfide phases in Shallowater, Mt. Egerton, and the aubrites Aubres, Cumberland Falls, and Mayo Belwa.

  7. Assessing the Formation of Ungrouped Achondrite Northwest Africa 8186: Residue, Crystallization Product, or Recrystallized Chondrite?

    Srinivasan, P.; McCubbin, F. M.; Agee, C. B.


    The recent discoveries of primitive achondrites, metachondrites, and type 7 chondrites challenge the long held idea that all chondrites and achondrites form on separate parent bodies. These meteorites have experienced metamorphic temperatures above petrologic type 6 and have partially melted to various degrees. However, because of their isotopic and compositional similarities to both undifferentiated and differentiated groups, the provenance of these 'type 6+' meteorites remains largely unknown. CK and CV chondrites have recently been linked to a few achondrites due to their strong compositional, mineralogical, and isotopic similarities], suggesting a common origin between these meteorites. Although CVs have generally undergone low degrees of alteration near petrologic type 3, CKs have experienced a wide range of thermal alteration from petrologic type 3 to 6. Thermal evolution models on early accreting bodies predict that an early forming body can partially differentiate due to radiogenic heating, and, as a result, form radial layers of material increasing in thermal grade (types 3 to 6+) from the unmelted chondritic surface towards the differentiated core.Northwest Africa (NWA) 8186 is an ungrouped achondrite that provides compelling evidence for higher degrees of thermal processing and/or melting and differentiation on some CK/CV parent bodies. NWA 8186 plots on the CCAM line on a 3-oxygen isotope diagram directly with CK and CV chondrites and also plots with the CKs in regards to Cr isotopes. This meteorite is dominated by Nickel(II)Oxygen-rich olivine (less than 80%), lacks iron metal, and contains four oxide phases, indicating a high fOxygen (above FMQ) similar to the CKs. Additionally, NWA 8186 does not contain chondrules. We have further investigated the origins of NWA 8186 by examining and comparing the bulk composition of this CK-like achondrite with CK and CV chondrites, allowing us to assess the various scenarios in which NWA 8186 may have formed from

  8. Chips off of asteroid 4 Vesta - Evidence for the parent body of basaltic achondrite meteorites

    Binzel, Richard P.; Xu, Shui


    For more than two decades, asteroid 4 Vesta has been debated as the source for the eucrite, diogenite, and howardite classes of basaltic achondrite meteorites. Its basaltic achondrite spectral properties are unlike those of other large main-belt asteroids. Telescopic measurements have revealed 20 small main-belt asteroids that have distinctive optical reflectance spectral features similar to those of Vesta and eucrite and diogenite meteorites. Twelve have orbits that are similar to Vesta's and were previously predicted to be dynamically associated with Vesta. Eight bridge the orbital space between Vesta and the 3:1 resonance, a proposed source region for meteorites. These asteroids are most probably multikilometer-sized fragments excavated from Vesta through one or more impacts. The sizes, ejection velocities of 500 meters per second, and proximity of these fragments to the 3:1 resonance establish Vesta as a dynamically viable source for eucrite, diogenite, and howardite meteorites.

  9. Chemical fractionations in meteorites. V - Volatile and siderophile elements in achondrites and ocean ridge basalts.

    Laul, J. C.; Keays, R. R.; Ganapathy, R.; Anders, E.; Morgan, J. W.


    Eighteen achondrites and 4 terrestrial basalts (3 ocean ridge, 1 continental) were analyzed by radiochemical neutron activation analysis for Ag, Au, Bi, Br, Cd, Co, Cs, Cu, Ga, In, Ir, Rb, Se, Tl and Zn. Samples included 7 eucrites, 5 howardites, 2 nakhlites, 2 shergottites, an angrite, and an aubrite. Light and dark portions of the gas-rich meteorites Kapoeta and Pesyanoe were analyzed separately. Nakhlites and shergottites have volatile element abundances similar to those in ocean ridge basalts; eucrites, howardites, and angrites show greater depletions by an order of magnitude and less similar abundance patterns. In terms of a two-component model of planetary accretion, the parent planets contained the following percentages of low-temperature material: eucrites 0.8, nakhlites 38, shergottites 28. Shergottites may be genetically related to L-chondrites. The siderophile element pattern of achondrites resembles that of the moon, but with less extreme depletions.

  10. Unusual weathering products of oldhamite parentage in the Norton County enstatite achondrite

    Okada, A.; Keil, K.; Taylor, G. J.


    Oldhamite, CaS, is found only in enstatite chondrites and enstatite achondrites. During the course of a comprehensive study of Norton County, oldhamite was found in several polished thin sections of enstatite achondrite. Inspection of thousands of specimens of Norton County showed that occasionally white, pale-yellow and brown specks, generally a few millimeters in size, occur on their surfaces. X-ray powder analysis of these materials shows that they contain portlandite, Ca(OH)2, vaterite (CaCO3, hexagonal), calcite (CaCO3, trigonal), bassanite (CaSO4 1/2 H2O) and one unknown species. It is suggested that these minerals were produced by terrestrial weathering of oldhamite.

  11. Vestas Pinaria Region: Original Basaltic Achondrite Material Derived from Mixing Upper and Lower Crust

    Mcfadden, L. A.; Combe, Jean-Philippe; Ammannito, Eleonora; Frigeri, Alessandro; Stephan, Katrin; Longobardo, Andrea; Palomba, Ernesto; Tosi, Federico; Zambon, Francesca; Krohn, Katrin; DeSanctis, Cristina M.; Reddy, Vishnu; LeCorre, Lucille; Nathues, Andreas; Pieters, Carle M.; Prettyman, Thomas; Raymond, C. A.; Russell, C. T.


    Analysis of data from the Dawn mission shows that the Pinaria region of Vesta spanning a portion of the rim of the Rheasilvia basin is bright and anhydrous. Reflectance spectra, absorption band centers, and their variations, cover the range of pyroxenes from diogenite-rich to howardite and eucrite compositions, with no evidence of olivine in this region. By examining band centers and depths of the floor, walls and rims of six major craters in the region, we find a lane of diogenite-rich material next to howardite-eucrite material that does not follow the local topography. The source of this material is not clear and is probably ejecta from post-Rheasilvia impacts. Material of a howardite-eucrite composition originating from beyond the Rheasilvia basin is evident on the western edge of the region. Overall, the Pinaria region exposes the complete range of basaltic achondrite parent body material, with little evidence of contamination of non-basaltic achondrite material. With both high reflectance and low abundance of hydrated material, this region of Vesta may be considered the "Pinaria desert".

  12. Olivine-Orthopyroxene Equilibrium in Metal-rich Systems: Applications to Achondrites and Equilibrated Chondrites

    Lauretta, D. S.; Benedix, G. K.; McCoy, T. J.


    Olivine and orthopyroxene are major minerals in every type of stony meteorite. The majority of achondritic meteorites and silicate-bearing iron meteorites have experienced high temperatures. If these temperatures persisted for an extended period of time then the iron contents of olivine and orthopyroxene should be in equilibrium. In their study of ungrouped clasts and chondritic meteorites, suggested that the equilibrium compositions of olivine and orthopyroxene should fall on a mixing line between LL chondrites and aubrites. Here we show that this is not necessarily the case and that a range of FeO contents in olivine and orthopyroxene can be in equilibrium with each other. The key parameters that determine the equilibrium Fe content in these minerals are temperature, oxygen fugacity (fO2), and silica activity (aSiO2).

  13. Brachinite-Like Clast in the Kaidun Meteorite: First Report of Primitive Achondrite Material

    Higashi, K.; Hasegawa, H.; Mikouchi, T.; Zolensky, M. E.


    Kaidun is a brecciated meteorite containing many different types of meteorites. It is composed of carbonaceous, enstatite, ordinary and R chondrites with smaller amounts of basaltic achondrites, impact melt products and unknown [1, 2]. Because of the multiple components and high abundance of carbonaceous chondrites, the Kaidun parent body was probably a large C-type asteroid in order to have accumulated clasts of many unrelated asteroids, and thus Kaidun contains previously unknown materials[1]. It has been suggested that the Kaidun parent body trawled through different regions of the solar system [3], but the formation of Kaidun meteorite is still uncertain. In this abstract, we report the first discovery of a brachinite-like clast in Kaidun.

  14. Near Earth Object 2012XJ112 as a source of bright bolides of achondritic nature

    Madiedo, Jose M; Williams, Iwan P; Konovalova, Natalia; Ortiz, Jose L; Castro-Tirado, Alberto; Pastor, Sensi; Reyes, Jose A de los; Cabrera-Caño, Jesus


    We analyze the likely link between the recently discovered Near Earth Object 2012XJ112 and a bright fireball observed over the south of Spain on December 27, 2012. The bolide, with an absolute magnitude of -9 +- 1, was simultaneously imaged during the morning twilight from two meteor stations operated by the SPanish Meteor Network (SPMN). It was also observed by several casual witnesses. The emission spectrum produced during the ablation of the meteoroid in the atmosphere was also recorded. From its analysis the chemical nature of this particle was inferred. Although our orbital association software identified several potential parent bodies for this meteoroid, the analysis of the evolution of the orbital elements performed with the Mercury 6 symplectic integrator supports the idea that NEO 2012XJ112 is the source of this meteoroid. The implications of this potential association are discussed here. In particular, the meteoroid bulk chemistry is consistent with a basaltic achondrite, and this emphasizes the im...

  15. Igneous history of the aubrite parent asteroid - Evidence from the Norton County enstatite achondrite

    Okada, Akihiko; Keil, Klaus; Taylor, G. Jeffrey; Newsom, Horton


    Numerous specimens of the Norton County enstatite achondrite (aubrite) were studied by optical microscopy, electron microprobe, and neutron-activation analysis. Norton County is found to be a fragmental impact breccia, consisting of a clastic matrix made mostly of crushed enstatite, into which are embedded a variety of mineral and lithic clasts of both igneous and impact melt origin. The Norton County precursor materials were igneous rocks, mostly plutonic orthopyroxenites, not grains formed by condensation from the solar nebula. The Mg-silicate-rich aubrite parent body experienced extensive melting and igneous differentiation, causing formation of diverse lithologies including dunites, plutonic orthopyroxenites, plutonic pyroxenites, and plagioclase-silica rocks. The presence of impact melt breccias (the microporphyritic clasts and the diopside-plagioclase-silica clast) of still different compositions further attests to the lithologic diversity of the aubrite parent body.

  16. Petrography and petrogenesis of some Indian basaltic achondrites derived from the HED parent body: Insights from electron microprobe analyses

    Rajesh K Srivastava


    Three Indian achondrites, viz., Bholghati howardite, Lohawat howardite and Pipliya Kalan eucrite and two other achondrites, viz., Bé ré ba eucrite and Johnstown diogenite are studied for their petrography and mineral chemistry. All these achondrites are derived from the HED parent body. Both Bholghati and Lohawat howardites are polymict breccias and contain pieces of eucrites and diaogenites (lithic clasts), pyroxene and minor olivine as mineral clasts, and small proportion of ilmenite and pure iron metal. Eucrite clasts are noncumulate basaltic in nature, whereas diogenite clasts are mostly composed of orthopyroxene with minor clinopyroxene and anorthite. Both howardite samples contain orthopyroxene, pigeonite and augite. Notable characteristics observed in Lohawat howardite include crystallization of orthoenstatite first at a high-temperature followed by ferrosilite, pigeonite olivine and augite from a basaltic melt. Piplia Kalan eucrite is noncumulate, unbrecciated and basaltic in nature and display ophitic/sub-ophitic or hypidiomorphic textures. It contains ∼60% pyroxenes (clinoenstatite and pigeonite) and ∼40% plagioclase feldspars (bytownite to anorthite). The observed mineralogy in the Piplia Kalan eucrite suggests its crystallization from a high-temperature basaltic melt crystallized at low pressure. Two other achondrite samples, viz., Bé ré ba eucrite and Johnstown diogenite are also studied. The Bé ré ba eucrite shows cumulate nature which is probably formed by small-degree melts of ilmenitebearing gabbro, whereas the Johnstown diogenite crystallized from a slow cooling of a Ca-poor basaltic melt derived from cumulates formed from the magma ocean, similar to the origin of the noncumulate eucrites.

  17. U-Pb and Al-Mg systematics of the ungrouped achondrite Northwest Africa 7325

    Koefoed, Piers; Amelin, Yuri; Yin, Qing-Zhu; Wimpenny, Josh; Sanborn, Matthew E.; Iizuka, Tsuyoshi; Irving, Anthony J.


    Northwest Africa (NWA) 7325 is a unique ungrouped gabbroic achondrite which has characteristics consistent with a possible link to the planet Mercury. In order to understand the origin of this meteorite and the nature of its parent body, we have determined its crystallisation age using the long-lived U-Pb and short-lived Al-Mg chronometers. An internal Pb-Pb isochron defined by six acid leached pyroxene fractions yields an age of 4563.4 ± 2.6 Ma, assuming that the 238U/235U ratio for NWA 7325 is identical to the bulk Earth and Solar System value of 137.794. The Al-Mg isotope analyses of seven fractions (four plagioclase, one pyroxene, one olivine and one whole rock) define a regression line corresponding to 26Al/27Al0 = (3.03 ± 0.14) × 10-7 and an initial δ26Mg∗ of 0.093 ± 0.004‰. When anchored to the D'Orbigny angrite, this initial 26Al/27Al yields an age of 4563.09 ± 0.26 Ma. The Pb-Pb age of 4563.4 ± 2.6 Ma and Al-Mg age of 4563.09 ± 0.26 Ma are in complete agreement, but the low U concentrations of NWA 7325 resulted in a relatively low precision Pb-Pb age. The observed excess in initial δ26Mg∗ can be explained by 27Al/24Mg fractionation and subsequent Mg isotopic evolution after planetary differentiation. Furthermore, the parental magma of NWA 7325 most likely formed within 1.72 Ma after calcium-aluminium rich inclusion (CAI) formation. NWA 7325 formed near simultaneously with quenched angrites and a number of ungrouped achondrites at ∼4563 Ma, suggesting that a multitude of planetary bodies had formed and differentiated by ∼4-5 Myr after CAI formation. This ancient age may be interpreted as an argument against NWA 7325 originating from Mercury, however it does not completely rule it out.

  18. Thermoluminescence characteristics of a chondrite (Holbrook) and an aubrite achondrite (Norton County) meteorites.

    Bossin, Lily; Kazakis, Nikolaos A; Kitis, George; Tsirliganis, Nestor C


    The present study constitutes the first part of a meteorite project, currently in progress, towards the full and thorough dosimetric study (TL and OSL) of two different meteorites of recent fall, Norton County and Holbrook. Both meteorites exhibit strong TL sensitivity, linear dose response and no saturation for doses up to 2kGy. However, the two meteorites exhibited a very dissimilar TL glow curve and behaviour regarding sensitization and fading. Notably, the Norton County aubrite achondrite was found to exhibit a strong fading of the high-temperature peak (~300°C), attributed to anomalous fading, whereas Holbrook did not seem to show signs of anomalous fading. Since quantitative conclusions regarding the thermal and irradiation history of meteorites, require knowledge of the detailed peak structure of the glow curve and deeper understanding of the trapping mechanism, the glow curves, after irradiation in the range 10-2000Gy, were deconvoluted using general order kinetics. The fitting parameters extracted point towards complex non-strictly first order mechanisms with a multitude of traps acting very differently. All the above, combined with future OSL measurements, currently in progress, are expected to shed light on the nature of the involved traps in both phenomena (energy depth, light-resistance etc), which would allow to extract more concrete conclusions about their history. Copyright © 2017 Elsevier Ltd. All rights reserved.


    Wimpenny, Josh; Yin, Qing-zhu [Department of Earth and Planetary Sciences, University of California, One Shields Avenue, Davis, CA 95616 (United States); Amelin, Yuri, E-mail: [Research School of Earth Sciences, The Australian National University, Canberra, ACT 0200 (Australia)


    Studies of Lu–Hf isotope systematics in meteorites have produced apparent “ages” that are older than Pb–Pb ages and older than the estimated age of our solar system. One proposed explanation for this discrepancy is that irradiation by cosmic rays caused excitation of {sup 176}Lu to its short-lived isomer that then underwent rapid decay to {sup 176}Hf. This explanation can account for apparent excesses in {sup 176}Hf that correlate with Lu/Hf ratio. Mass balance requires that samples with measurable excess in {sup 176}Hf should also have measurable deficiencies in {sup 176}Lu on the order of 1‰–3‰. To unambiguously test the accelerated decay hypothesis, we have measured the {sup 176}Lu/{sup 175}Lu ratio in terrestrial materials and achondrites to search for evidence of depletion in {sup 176}Lu. To a precision of 0.1‰ terrestrial standards, cumulate and basaltic eucrites and angrites all have the same {sup 176}Lu/{sup 175}Lu ratio. Barring a subsequent mass-dependent fractionation event, these results suggest that the apparent excesses in {sup 176}Hf are not caused by accelerated decay of {sup 176}Lu, and so another hypothesis is required to explain apparently old Lu–Hf ages.

  20. Mineralogy of new Antarctic achondrites with affinity to Lodran and a model of their evolution in an asteroid

    Takeda, Hiroshi; Mori, Hiroshi; Hiroi, Takahiro; Saito, Jun


    We studied five new Antartic achondrites, MacAlpine Hills (MAC) 88177, Yamato (Y)74357, Y75274, Y791491 and Elephant Moraine (EET)84302 by mineralogical techniques to gain a better understanding of the mineral assemblages of a group of meteorites with an affinity to Lodran (stony-iron meteorite) and their formation processes. This group is being called lodranites. These meteorites contain major coarse-grained orthopyroxene (Opx) and olivine as in Lodran and variable amounts of FeNi metal and troilite etc. MAC88177 has more augite and less FeNi than Lodran; Y74357 has more olivine and contains minor augite; Y791491 contains in addition plagioclase. EET84302 has an Acapulco-like chondritic mineral assembladge and is enriched in FeNi metal and plagioclase, but one part is enriched in Opx and chromite. The EET84302 and MAC88177 Opx crystals have dusty cores as in Acapulco. EET84302 and Y75274 are more Mg-rich than other members of the lodranite group, and Y74357 is intermediate. Since these meteorites all have coarse-grained textures, similar major mineral assemblages, variable amounts of augite, plagioclase, FeNi metal, chromite and olivine, we suggest that they are related and are linked to a parent body with modified chondritic compositions. The variability of the abundances of these minerals are in line with a proposed model of the surface mineral assemblages of the S asteroids. The mineral assemblages can best be explained by differing degrees of loss or movements of lower temperature partial melts and recrystallization, and reduction. A portion of EET84302 rich in metal and plagioclase may represent a type of component removed from the lodranite group meteorites. Y791058 and Caddo County, which were studied for comparison, are plagioclase-rich silicate inclusions in IAB iron meteorites and may have been derived by similar process but in a different body.

  1. Crystal structure refinement of chromites from two achondrites, their T-f(O2) conditions, and implications

    Lenaz, Davide; Schmitz, Birger


    Six Cr-spinel grains from NWA 6077 brachinite-like and NWA 725 winonaite achondrites have been studied by single-crystal X-ray diffraction and structural refinement. From a chemical point of view, spinels from NWA 6077 show Cr/(Cr + Al) (i.e., Cr#) and Mg/(Mg + Fe2+) (i.e., Mg#) values similar to other brachinites, while the Cr# of NWA 725 is lower than that of literature winonaites. Spinels from NWA 6077 and NWA 725 meteorites show similar cell edges, while the oxygen positional parameter is rather different being about 0.2629 for NWA 6077 and 0.2622 for NWA 725. Considering both parameters, NWA 725 shows structural features that are close to some terrestrial spinel occurrences as in komatiites, kimberlites, or included in diamonds; those from NWA 6077 show values that have no terrestrial analogs. Olivine-chromite closure temperature ranges from 737 to 765° C for NWA 725, being similar to that of literature winonaites and 846 to 884° C for NWA 6077. The logfO2 ranges from -19.8 to -20.5 and -17.0 to -17.9 for the two meteorites, respectively. The u values for terrestrial samples can give information about the cooling history of the samples. For the extraterrestrial samples, it seems that it can give information about the cooling only for spinels where it is lower than 0.2625. For higher values, it appears related only to the chemistry of the spinels.

  2. Petrogenesis and provenance of ungrouped achondrite Northwest Africa 7325 from petrology, trace elements, oxygen, chromium and titanium isotopes, and mid-IR spectroscopy

    Goodrich, Cyrena A.; Kita, Noriko T.; Yin, Qing-Zhu; Sanborn, Matthew E.; Williams, Curtis D.; Nakashima, Daisuke; Lane, Melissa D.; Boyle, Shannon


    Northwest Africa (NWA) 7325 is an ungrouped achondrite that has recently been recognized as a sample of ancient differentiated crust from either Mercury or a previously unknown asteroid. In this work we augment data from previous investigations on petrography and mineral compositions, mid-IR spectroscopy, and oxygen isotope compositions of NWA 7325, and add constraints from Cr and Ti isotope compositions on the provenance of its parent body. In addition, we identify and discuss notable similarities between NWA 7325 and clasts of a rare xenolithic lithology found in polymict ureilites. NWA 7325 has a medium grained, protogranular to poikilitic texture, and consists of 10-15 vol.% Mg-rich olivine (Fo 98), 25-30 vol.% diopside (Wo 45, Mg# 98), 55-60 vol.% Ca-rich plagioclase (An 90), and trace Cr-rich sulfide and Fe,Ni metal. We interpret this meteorite to be a cumulate that crystallized at ⩾1200 °C and very low oxygen fugacity (similar to the most reduced ureilites) from a refractory, incompatible element-depleted melt. Modeling of trace elements in plagioclase suggests that this melt formed by fractional melting or multi-stage igneous evolution. A subsequent event (likely impact) resulted in plagioclase being substantially remelted, reacting with a small amount of pyroxene, and recrystallizing with a distinctive texture. The bulk oxygen isotope composition of NWA 7325 plots in the range of ureilites on the CCAM line, and also on a mass-dependent fractionation line extended from acapulcoites. The ε54Cr and ε50Ti values of NWA 7325 exhibit deficits relative to terrestrial composition, as do ordinary chondrites and most achondrites. Its ε54Cr value is distinct from that of any analyzed ureilite, but is not resolved from that of acapulcoites (as represented by Acapulco). In terms of all these properties, NWA 7325 is unlike any known achondrite. However, a rare population of clasts found in polymict ureilites (;the magnesian anorthitic lithology;) are strikingly

  3. Northwest Africa 6693: A new type of FeO-rich, low-Δ17O, poikilitic cumulate achondrite

    Warren, Paul H.; Rubin, Alan E.; Isa, Junko; Brittenham, Steve; Ahn, Insu; Choi, Byeon-Gak


    Northwest Africa 6693 is a new type of achondrite, with a unique combination of oxygen-isotopic composition (low Δ17O: -1.08‰; also δ17O = 1.19‰) and FeO-rich, low mg bulk composition. A mode (in vol%) shows 70% pyroxene, 16% olivine and 13% feldspar, along with 0.6% Cr-spinel, and 0.4% NiFe metal (awaruite). Its coarse-poikilitic texture, with pigeonite oikocrysts up to 14 mm, as well as the subchondritic MgO/SiO2 of the rock's bulk composition, indicate origin as an igneous cumulate. The cumulus phases included pigeonite and olivine, and the parent magma was probably also saturated with feldspar, which occurs mainly as anhedral, yet optically continuous, grains intergrown with the pyroxene. The mafic silicates are uniformly ferroan: pigeonite near En57Wo3.2 and olivine near Fo49. The feldspar is uniformly albitic, near Ab92, except for a single tiny grain of Ab57Or43. However, the albite features diverse K/Ca (Or/An) ratios: ranging from consistently ˜0.46 in one end of the oblong NWA 6693 stone, to 5.2 in an olivine-rich enclave that consists mostly of micrographic olivine-feldspar intergrowth. Also, siderophile and incompatible element data show heterogeneity among samples from different regions of this large cumulate. The rock was probably neither an orthocumulate nor an adcumulate, and the proportion of "trapped liquid" probably varied from place to place. After initial crystallization, a shock event caused very minor brecciation, and pervasively mobilized linear-arcuate trails of microinclusions (minute oxides, mostly) and bubbles. A minor proportion of additional melt was formed within, and/or infiltrated into, the rock and formed discrete overgrowth mantles, recognizable based on unusual scarcity of microinclusions, on some pyroxenes. Final cooling, based on mineral-equilibration temperatures, occurred at a moderate rate by intrusive-igneous standards. Olivine, metal, and sulfide phases are all very Ni-rich (e.g., olivine NiO averages 0.77 wt

  4. Titanium stable isotopic variations in chondrites, achondrites and lunar rocks

    Greber, Nicolas D.; Dauphas, Nicolas; Puchtel, Igor S.; Hofmann, Beda A.; Arndt, Nicholas T.


    Titanium isotopes are potential tracers of processes of evaporation/condensation in the solar nebula and magmatic differentiation in planetary bodies. To gain new insights into the processes that control Ti isotopic variations in planetary materials, 25 komatiites, 15 chondrites, 11 HED-clan meteorites, 5 angrites, 6 aubrites, a martian shergottite, and a KREEP-rich impact melt breccia have been analyzed for their mass-dependent Ti isotopic compositions, presented using the δ49Ti notation (deviation in permil of the 49Ti/47Ti ratio relative to the OL-Ti standard). No significant variation in δ49Ti is found among ordinary, enstatite, and carbonaceous chondrites, and the average chondritic δ49Ti value of +0.004 ± 0.010‰ is in excellent agreement with the published estimate for the bulk silicate Earth, the Moon, Mars, and the HED and angrite parent-bodies. The average δ49Ti value of komatiites of -0.001 ± 0.019‰ is also identical to that of the bulk silicate Earth and chondrites. OL-Ti has a Ti isotopic composition that is indistinguishable from chondrites and is therefore a suitable material for reporting δ49Ti values. Previously published isotope data on another highly refractory element, Ca, show measurable variations among chondrites. The decoupling between Ca and Ti isotope systematics most likely occurred during condensation in the solar nebula. Aubrites exhibit significant variations in δ49Ti, from -0.07 to +0.24‰. This is likely due to the uniquely reducing conditions under which the aubrite parent-body differentiated, allowing chalcophile Ti3+ and lithophile Ti4+ to co-exist. Consequently, the observed negative correlation between δ49Ti values and MgO concentrations among aubrites is interpreted to be the result of isotope fractionation driven by the different oxidation states of Ti in this environment, such that isotopically heavy Ti4+ was concentrated in the residual liquid during magmatic differentiation. Finally, KREEPy impact melt breccia SaU 169 exhibits a heavy δ49Ti value of +0.330 ± 0.034‰ which is interpreted to result from Ti isotopic fractionation during ilmenite precipitation in the late stages of lunar magma ocean crystallization. A Rayleigh distillation calculation predicts that a δ49Ti value of +0.330‰ is achieved after removal of 94% of Ti in ilmenite.

  5. Petrology of enstatite chondrites and anomalous enstatite achondrites

    van Niekerk, Deon


    Chondrites are meteorites that represent unmelted portions of asteroids. The enstatite chondrites are one class of chondrites. They consist of reduced mineral assemblages that formed under low oxygen fugacity in the solar nebula, prior to accretion into asteroids. There are two groups of enstatite chondrites---EH and EL. I studied EL3 meteorites, which are understood to be unmetamorphosed and thus to only preserve primitive nebular products. I show in a petrographic study that the EL3s are in fact melt--breccias in which impact-melting produced new mineral assemblages and textures in portions of the host chondrites, after accretion. I document meta- land sulfide assemblages that are intergrown with silicate minerals (which are often euhedral), and occur outside chondrules; these assemblages probably represent impact-melting products, and are different from those in EH3 chondrites that probably represent nebular products. In situ siderophile trace element compositions of the metal in EL3s, obtained by laser ablation inductively coupled plasma mass spectrometry, are consistent with an impact-melting hypothesis. The trace element concentrations show no clear volatility trend, and are thus probably not the result of volatile-driven petrogenetic processes that operated in the solar nebula. Trace element modeling suggests that the character of the trace element patterns together with deviations from the mean bulk EL metal pattern is consistent with metal that crystallized in a coexisting liquid-solid metal system in which dissolved carbon influenced element partitioning. I also conducted a petrographic and mineral-chemistry study of several anomalous enstatite meteorites. These have igneous textures, but unfractionated mineralogy similar to unmelted chondrites. I show that with the exception of one, the meteorites are related to each other, and probably formed by crystallization from an impact melt instead of metamorphism through the decay of short lived radionuclides. The broad importance of these studies lies in documenting the petrology of extraterrestrial materials that reveal the geological history of the young solar system prior to the existence of planets. Furthermore, they serve to identify which mineral assemblages record nebular processes and which record processes on asteroids, so that future studies may select the correct material to address particular questions.

  6. Heterogeneous Neutron Capture Record of the Norton County Enstatite Achondrite

    Hidaka, H.; Yoneda, S.


    Large and heterogeneous isotopic variations of Sm and Gd due to neutron capture reactions caused by cosmic-ray irradiation were found in chemical and mineral separates from the Norton County meteorite.

  7. Petrologic and Oxygen-Isotopic Investigations of Eucritic and Anomalous Mafic Achondrites

    Mittlefehldt, D. W.; Greenwood, R. C.; Peng, Z. X.; Ross, D. K.; Berger, E. L.; Barrett, T. J.


    The most common asteroidal igneous meteorites are eucrite-type basalts and gabbros rocks composed of ferroan pigeonite and augite, calcic plagioclase, silica, ilmenite, troilite, Ca-phosphate, chromite and Fe-metal. These rocks are thought to have formed on a single asteroid along with howardites and diogenites (HEDs). However, Northwest Africa (NWA) 011 is mineralogically identical to eucrites, but has an O-isotopic composition distinct from them and was derived from a different asteroid. Modern analyses with higher precision have shown that some eucrites have smaller O-isotopic differences that are nevertheless well-resolved from the group mean.

  8. Cosmic-ray exposure history of the Norton County enstatite achondrite

    Herzog, G. F.; Albrecht, Achim; Ma, Peixue; Fink, David; Klein, Jeffrey; Middleton, Roy; Bogard, Donald D.; Nyquist, L. E.; Shih, C.-Y.; Garrison, D. H.; Reese, Young; Masarik, J.; Reedy, R. C.; Rugel, G.; Faestermann, T.; Korschinek, G.


    Abstract- We report measurements of cosmogenic nuclides in up to 11 bulk samples from various depths in Norton County. The activities of 36Cl, 41Ca, 26Al, and 10Be were measured by accelerator mass spectrometry; the concentrations of the stable isotopes of He, Ne, Ar, and Sm were measured by electron and thermal ionization mass spectrometry, respectively. Production rates for the nuclides were modeled using the LAHET and the Monte Carlo N-Particle codes. Assuming a one-stage irradiation of a meteoroid with a pre-atmospheric radius of approximately 50 cm, the model satisfactorily reproduces the depth profiles of 10Be, 26Al, and 53Mn (Norton County at a depth of 88 cm in a large body for 140 Ma prior to its liberation as a meteoroid with a radius of 50 cm and further CRE for 100 Ma.

  9. Petrogenesis of anomalous Queen Alexandra Range enstatite meteorites and their relation to enstatite chondrites, primitive enstatite achondrites, and aubrites

    Niekerk, Deon; Keil, Klaus; Humayun, Munir


    Queen Alexandra Range (QUE) meteorite 94204 is an anomalous enstatite meteorite whose petrogenesis has been ascribed to either partial melting or impact melting. We studied the meteorite pairs QUE 94204, 97289/97348, 99059/99122/99157/99158/99387, and Yamato (Y)-793225; these were previously suggested to represent a new grouplet. We present new data for mineral abundances, mineral chemistries, and siderophile trace element compositions (of Fe,Ni metal) in these meteorites. We find that the texture and composition of Y-793225 are related to EL6, and that this meteorite is unrelated to the QUEs. The mineralogy and siderophile element compositions of the QUEs are consistent with petrogenesis from an enstatite chondrite precursor. We caution that potential re-equilibration during melting and recrystallization of enstatite chondrite melt-rocks make it unreliable to use mineral chemistries to assign a specific parent body affinity (i.e., EH or EL). The QUEs have similar mineral chemistries among themselves, while slight variations in texture and modal abundances exist between them. They are dominated by inclusion-bearing millimeter-sized enstatite (average En99.1-99.5) with interstitial spaces filled predominantly by oligoclase feldspar (sometimes zoned), kamacite (Si approximately 2.4 wt%), troilite (≤2.4 wt% Ti), and cristobalite. Siderophile elements that partition compatibly between solid metal and liquid metal are not enriched like in partial melt residues Itqiy and Northwest Africa (NWA) 2526. We find that the modal compositions of the QUEs are broadly unfractionated with respect to enstatite chondrites. We conclude that a petrogenesis by impact melting, not partial melting, is most consistent with our observations.

  10. Characterization of crust formation on a parent body of achondrites and the moon by pyroxene crystallography and chemistry

    Takeda, H.; Miyamoto, M.; Ishii, T.; Reid, A. M.


    Single crystal X-ray diffraction and electron microprobe techniques were used to study lunar crustal pyroxenes in a cataclastic norite, a pyroxene-rich clast, and anorthosite lunar samples, and also in meteorites including diogenites, eucrites, and the Yamoto (1) howardite. The crystallographic and chemical characteristics of pyroxenes in these materials are compared and are discussed in terms of the lower stability limit of pigeonite. A mechanical mixing model of howardite is proposed.

  11. Noble gases in 18 Martian meteorites and angrite Northwest Africa 7812—Exposure ages, trapped gases, and a re-evaluation of the evidence for solar cosmic ray-produced neon in shergottites and other achondrites

    Wieler, R.; Huber, L.; Busemann, H.; Seiler, S.; Leya, I.; Maden, C.; Masarik, J.; Meier, M. M. M.; Nagao, K.; Trappitsch, R.; Irving, A. J.


    We present noble gas data for 16 shergottites, 2 nakhlites (NWA 5790, NWA 10153), and 1 angrite (NWA 7812). Noble gas exposure ages of the shergottites fall in the 1-6 Ma range found in previous studies. Three depleted olivine-phyric shergottites (Tissint, NWA 6162, NWA 7635) have exposure ages of ~1 Ma, in agreement with published data for similar specimens. The exposure age of NWA 10153 (~12.2 Ma) falls in the range of 9-13 Ma reported for other nakhlites. Our preferred age of ~7.3 Ma for NWA 5790 is lower than this range, and it is possible that NWA 5790 represents a distinct ejection event. A Tissint glass sample contains Xe from the Martian atmosphere. Several samples show a remarkably low (21Ne/22Ne)cos ratio SCR Ne) in addition to the commonly found galactic cosmic ray-produced Ne, implying very low preatmospheric shielding and ablation loss. We revisit this by comparing measured (21Ne/22Ne)cos ratios with predictions by cosmogenic nuclide production models. Indeed, several shergottites, acalpulcoites/lodranites, angrites (including NWA 7812), and the Brachina-like meteorite LEW 88763 likely contain SCR Ne, as previously postulated for many of them. The SCR contribution may influence the calculation of exposure ages. One likely reason that SCR nuclides are predominantly detected in meteorites from rare classes is because they usually are analyzed for cosmogenic nuclides even if they had a very small (preatmospheric) mass and hence low ablation loss.

  12. Almahata Sitta News: Well-Known Varieties and New Species in the Zoo

    Bischoff, A.; Ebert, S.; Patzek, M.; Horstmann, M.; Pack, A.; Decker, S.


    Mineralogical characteristics of 18 new samples from the Almahata Sitta strewn field are presented. Among the samples are 5 E chondrites, 12 samples of ureilitic origin (including a new trachyandesite), and an enstatite- and metal-rich achondrite.

  13. The Meteoritical Bulletin, No. 103

    Ruzicka, Alex; Grossman, Jeffrey; Bouvier, Audrey; Agee, Carl B.


    Meteoritical Bulletin 103 contains 2582 meteorites including 10 falls (Ardón, Demsa, Jinju, Križevci, Kuresoi, Novato, Tinajdad, Tirhert, Vicência, Wolcott), with 2174 ordinary chondrites, 130 HED achondrites, 113 carbonaceous chondrites, 41 ureilites, 27 lunar meteorites, 24 enstatite chondrites, 21 iron meteorites, 15 primitive achondrites, 11 mesosiderites, 10 Martian meteorites, 6 Rumuruti chondrites, 5 ungrouped achondrites, 2 enstatite achondrites, 1 relict meteorite, 1 pallasite, and 1 angrite, and with 1511 from Antarctica, 588 from Africa, 361 from Asia, 86 from South America, 28 from North America, and 6 from Europe. Note: 1 meteorite from Russia was counted as European. The complete contents of this bulletin (244 pages) are available on line. Information about approved meteorites can be obtained from the Meteoritical Bulletin Database (MBD) available on line at

  14. Infrared spectroscopy of circumstellar dust: signs of differentiated materials?

    Morlok, A.; Köhler, M; Grady, Monica


    Mid-infrared absorption spectra of powdered achondrites are compared with the astronomical spectra of dust around young, evolving stars, to find evidence (or not) of dust formed in collisional cascades of material from planetesimals.

  15. Aioun el Atrouss - Evidence for thermal recrystallization of a eurite breccia. [meteoritic mineralogy

    Duke, M. B.


    The Aioun el Atrouss meteorite is a breccia consisting largely of angular fragments of green orthopyroxene and containing scattered clasts of basaltic composition (mostly pigeonite and calcic plagioclase). It appears to be a physical mixture of two meteorite types - diogenite (hypersthene achondrite) and eucrite (basaltic achondrite). The results of a mineral analysis are tabulated, and typical pyroxene compositions in orthopyroxene (diogenite), subophitic and granoblastic portions of the meteorite are presented.

  16. Rare meteorites common in the Ordovician period

    Heck, Philipp R.; Schmitz, Birger; Bottke, William F.; Rout, Surya S.; Kita, Noriko T.; Cronholm, Anders; Defouilloy, Céline; Dronov, Andrei; Terfelt, Fredrik


    Most meteorites that fall today are H and L type ordinary chondrites, yet the main belt asteroids best positioned to deliver meteorites are LL chondrites 1,2 . This suggests that the current meteorite flux is dominated by fragments from recent asteroid breakup events 3,4 and therefore is not representative over longer (100-Myr) timescales. Here we present the first reconstruction of the composition of the background meteorite flux to Earth on such timescales. From limestone that formed about one million years before the breakup of the L-chondrite parent body 466 Myr ago, we have recovered relict minerals from coarse micrometeorites. By elemental and oxygen-isotopic analyses, we show that before 466 Myr ago, achondrites from different asteroidal sources had similar or higher abundances than ordinary chondrites. The primitive achondrites, such as lodranites and acapulcoites, together with related ungrouped achondrites, made up ~15-34% of the flux compared with only ~0.45% today. Another group of abundant achondrites may be linked to a 500-km cratering event on (4) Vesta that filled the inner main belt with basaltic fragments a billion years ago 5 . Our data show that the meteorite flux has varied over geological time as asteroid disruptions create new fragment populations that then slowly fade away from collisional and dynamical evolution. The current flux favours disruption events that are larger, younger and/or highly efficient at delivering material to Earth.

  17. A model composition for Mars derived from the oxygen isotopic ratios of martian/SNC meteorites. [Abstract only

    Delaney, J. S.


    Oxygen is the most abundant element in most meteorites, yet the ratios of its isotopes are seldom used to constrain the compositional history of achondrites. The two major achondrite groups have O isotope signatures that differ from any plausible chondritic precursors and lie between the ordinary and carbonaceous chondrite domains. If the assumption is made that the present global sampling of chondritic meteorites reflects the variability of O reservoirs at the time of planetessimal/planet aggregation in the early nebula, then the O in these groups must reflect mixing between known chondritic reservoirs. This approach, in combination with constraints based on Fe-Mn-Mg systematics, has been used previously to model the composition of the basaltic achondrite parent body (BAP) and provides a model precursor composition that is generally consistent with previous eucrite parent body (EPB) estimates. The same approach is applied to Mars exploiting the assumption that the SNC and related meteorites sample the martian lithosphere. Model planet and planetesimal compositions can be derived by mixing of known chondritic components using O isotope ratios as the fundamental compositional constraint. The major- and minor-element composition for Mars derived here and that derived previously for the basaltic achondrite parent body are, in many respects, compatible with model compositions generated using completely independent constraints. The role of volatile elements and alkalis in particular remains a major difficulty in applying such models.

  18. Mineralogical Characterization of Baptistina Asteroid Family: Implications for K/T Impactor Source

    Reddy, Vishnu; Lazzaro, Daniela; Michtchenko, Tatiana A; Gaffey, Michael J; Kelley, Michael S; Diniz, Thais Mothé; Candal, Alvaro Alvarez; Moskovitz, Nicholas A; Cloutis, Edward A; Ryan, Erin L; 10.1016/j.icarus.2011.08.027


    Bottke et al. (2007) linked the catastrophic formation of Baptistina Asteroid Family (BAF) to the K/T impact event. This linkage was based on dynamical and compositional evidence, which suggested the impactor had a composition similar to CM2 carbonaceous chondrites. However, our recent study (Reddy et al. 2009) suggests that the composition of (298) Baptistina is similar to LL-type ordinary chondrites rather than CM2 carbonaceous chondrites. This rules out any possibility of it being related to the source of the K/T impactor, if the impactor was of CM-type composition. Mineralogical study of asteroids in the vicinity of BAF has revealed a plethora of compositional types suggesting a complex formation and evolution environment. A detailed compositional analysis of 16 asteroids suggests several distinct surface assemblages including ordinary chondrites (Gaffey SIV subtype), primitive achondrites (Gaffey SIII subtype), basaltic achondrites (Gaffey SVII subtype and V-type), and a carbonaceous chondrite. Based on ...

  19. The Meteoritical Bulletin, no. 85, 2001 September

    Grossman, J.N.; Zipfel, J.


    Meteoritical Bulletin No. 85 lists information for 1376 newly classified meteorites, comprising 658 from Antarctica, 409 from Africa, 265 from Asia (262 of which are from Oman), 31 from North America, 7 from South America, 3 from Australia, and 3 from Europe. Information is provided for 11 falls (Dergaon, Dunbogan, Gujba, Independence, Itqiy, Mora??vka, Oued el Hadjar, Sayama, Sologne, Valera, and Worden). Noteworthy non-Antarctic specimens include 5 martian meteorites (Dar al Gani 876, Northwest Africa 480 and 817, and Sayh al Uhaymir 051 and 094); 6 lunar meteorites (Dhofar 081, 280, and 287, and Northwest Africa 479, 482, and 773); an ungrouped enstatite-rich meteorite (Itqiy); a Bencubbin-like meteorite (Gujba); 9 iron meteorites; and a wide variety of other interesting stony meteorites, including CH, CK, CM, CO, CR, CV, R, enstatite, and unequilibrated ordinary chondrites, primitive achondrites, HED achondrites, and ureilites.

  20. Rb-Sr and Sm-Nd Study of Asuka 881394: Evidence of "Late" Metamorphism

    Nyquist, L. E.; Shih, C.-Y.; Reese, Y.; Takeda, H.


    The Asuka 881394 achondrite contains fossil Al-26 and Mn-53 [1,2,3] and has a Pb-207/Pb-206 age of 4566.5 plus or minus 0.2 Ma [3], the oldest for an achondrite. Preliminary results showed initial Sm-146/Sm-144 = (7.4 plus or minus 1.2) x 10(exp -3), indicative of an ancient age, but Rb-87 - Sr-87 and Sm-147 - Nd-143 ages of 4370 plus or minus 60 and 4490 plus or minus 20 Ma, resp. [1], were younger than expected from the presence of short-lived nuclides. We revisit the Rb-Sr and Sm-Nd chronology of A881394 in an attempt to establish whether late metamorphism led to inconsistency in its apparent ages.

  1. Chronological and chemical studies on several differentiated meteorites. Bunkashita inseki no kagakuteki/nendaigakuteki kenkyu

    Takahashi, K. (The Inst. of Physical and Chemical Research, Saitama (Japan). Earth Science Lab.)


    Materials on the earth generally pass though the metamorphosing, igneous and the weathering action in a long time, meteorites were considered to faithfully reflect occurrence from the birth to the first stage of the solar system according to the chemical composition. Meteorites are divided into the original chondrites and the differentiated meteorites. In the studies on the origin and evolution of planets, the differentiated meteorites can mainly give the important informations. In the differentiated meteorites, the lithic material is called as achondrites, only five to six kinds have been known until now. With the development of recent researches, discover of meteorites related to the origin of Mars and moon, kinds of meteorites become variety, and studies are also more detailed. In this paper, concerning to the origin of three kinds of achondrites such as eucrites, howardites and diogenites in the differentiated meteorites, the age measurement made by authors was mainly described. 21 refs., 10 figs., 2 tabs.

  2. The geologic classification of the meteorites

    Elston, Donald Parker


    The meteorite classes of Prior and Mason are assigned to three proposed genetic groups on the basis of a combination of compositional, mineralogical, and elemental characteristics: l) the calcium-poor, volatile-rich carbonaceous chondrites and achondrites; 2) the calcium-poor, volatile-poor chondrites (enstatite, bronzite, hypersthene, and pigeonite), achondrites (enstatite, hypersthene, and pigeonite), stonyirons (pallasites, siderophyre), and irons; and, 3) the calcium-rich (basaltic) achondrites. Chondrites are correlated with calcium-poor achondrites and the silicate phase of the pallasitic meteorites on Fe contents of olivine and pyroxene; and with metal of the stony-irons and irons on the basis of trace elements (Ga and Ge). Transitions in structure and texture between the chondrites and achondrites are recognized. The Van Schmus-Wood chemical-petrologic classification of the chondrites has been modified and expanded to a mineralogic-petrologic classification of the chondrites and calcium-poor achondrites. Chondrites apparently are the first rocks of the solar system. Paragenetic and textural relations in the Murray carbonaceous chondrite shed new light on the manner of accretion, and on the character of dispersed solid materials ('dust', and chondrules and metal) that existed in the solar system before accretion. Two pre-accretionary mineral assemblages (components) are recognized in the carbonaceous chondrites and in the unequilibrated volatile-poor chondrites. They are: 1) a 'low temperature' water-, rare gas-, and carbon-bearing component; and, 2) a high temperature anhydrous silicate and metal component. Paragenetic relations indicate that component 2 materials predate chondrite formation. An accretionary assemblage (component 3) also is recognized in the carbonaceous chondrites and in the unequilibrated volatile-poor chondrites. Component 3 consists of very fine grains of olivine and pyroxene, which occur as pervasive disseminations, as small irregular

  3. Fractionation and fragmentation of glass cosmic spherules during atmospheric entry

    Rudraswami, N.G.; ShyamPrasad, M.; Babu, E.V.S.S.K.; VijayaKumar, T.; Feng, W.; Plane, J.M.C.

    of these elements during atmospheric entry (Fig. 7). However, the bulk chemical compositions of Al, Ca, Mg, Fe are generally CI-like except for some volatile elements, which rules out an achondritic parent body. Taylor et al. (2007) reported anorthite with low... entry with the exception of the particles having high velocities and low zenith angles (Love and Brownlee, 1991; Vondrak et al., 2008). Larger micrometeorites have undergone ablation leading to siderophile and volatile element depletion, and mass...

  4. 1991 Urey Prize Lecture: Physical evolution in the solar system - Present observations as a key to the past

    Binzel, Richard P.


    The present evaluation of the use of new observational methods for exploring solar system evolutionary processes gives attention to illustrative cases from the constraining of near-earth asteroid sources and the discovery of main-belt asteroid fragments which indicate Vesta to be a source of basaltic achondrite meteorites. The coupling of observational constraints with numerical models clarifies cratering and collisional evolution for both main-belt and Trojan asteroids.

  5. Geochemical arguments for an Earth-like Moon-forming impactor

    Dauphas, Nicolas; Burkhardt, Christoph; Warren, Paul H.; Fang-Zhen, Teng


    Geochemical evidence suggests that the material accreted by the Earth did not change in nature during Earth's accretion, presumably because the inner protoplanetary disc had uniform isotopic composition similar to enstatite chondrites, aubrites and ungrouped achondrite NWA 5363/5400. Enstatite meteorites and the Earth were derived from the same nebular reservoir but diverged in their chemical evolutions, so no chondrite sample in meteorite collections is representative of the Earth's building...

  6. Rapid timescales for magma ocean crystallization on the howardite-eucrite-diogenite parent body

    Schiller, M.; Paton, C.; Bizzarro, Martin


    Asteroid 4 Vesta has long been postulated as the source for the howardite-eucrite-diogenite (HED) achondrite meteorites. Here we show that Al-free diogenite meteorites record variability in the mass-independent abundance of Mg ( Mg*) that is correlated with their mineral chemistry. This suggests...... occurred within the following 2-3Myr. Thermal models predict that such rapid cooling and magma ocean crystallization could only occur on small asteroids (...

  7. Hungaria Asteroid Region Telescopic Spectral Survey (HARTSS): Stony Asteroids Abundant in the Background and Family Populations

    Lucas, Michael P.; Emery, Joshua P.; Pinilla-Alonso, Noemi; Lindsay, Sean S.; Lorenzi, Vania


    The Hungaria region represents a "purgatory" for the closest, preserved samples of the material from which the terrestrial planets accreted. The Hungaria region harbors a collisional family of Xe-type asteroids, which are situated among a background of predominantly S-complex asteroids. Deciphering their surface composition may provide constraints on the nature of the primordial building blocks of the terrestrial planets. We hypothesize that planetesimals in the inner part of the primordial asteroid belt experienced partial- to full-melting and differentiation, the Hungaria region should retain any petrologically-evolved material that formed there.We have undertaken an observational campaign entitled the Hungaria Asteroid Region Telescopic Spectral Survey (HARTSS) to record near-infrared (NIR) spectra to characterize taxonomy, surface mineralogy, and potential meteorite analogs. We used NIR instruments at two ground-based facilities (NASA IRTF; TNG). Our data set includes spectra of 82 Hungaria asteroids (61 background; 21 family), 65 were observed during HARTSS. We compare S-complex background asteroids to calibrations developed via laboratory analyses of ordinary chondrites, and to our analyses (EPMA, XRD, VIS+NIR spectra) of 11 primitive achondrite (acapulcoite-lodranite clan) meteorites.We find that stony S-complex asteroids dominate the Hungaria background population (~80%). Background objects exhibit considerable spectral diversity, when quantified by spectral band parameter measurements, translates to a variety of surface compositions. Two main meteorite groups are represented within the Hungaria background: unmelted, nebular L chondrites (and/or L chondrites), and partially-melted primitive achondrites. H-chondrite mineralogies appear to be absent from the Hungaria background. Xe-type Hungaria family members exhibit spectral homogeneity, consistent with the hypothesis that the family was derived from the disruption of a parent body analogous to an enstatite

  8. Iron Mossbauer spectral study of weathered Antarctic and SNC meteorites

    Solberg, T. C.; Burns, R. G.


    Mossbauer spectral measurements were made on suites of finds from Antarctica and falls collected elsewhere in order to distinguish preterrestrial oxidation products formed on parent meteorite bodies from secondary minerals derived from chemical weathering on earth. Ferric iron is shown to be present throughout the interiors of all the specimens, in amounts ranging from less than 1 to greater than 30 percent Fe(3+). The results indicate that achondrites found to date did not originate from the outermost surface of Mars.

  9. An ejection model for SNC meteorites: An indication for recent volcanism on Mars

    Manker, J. P.


    When compared to other achondrites, Shergotty-Nakhla-Chassigny (SNC) meteorites are viewed as anomalous objects. This conclusion is based mainly on their extremely young crystallization ages and their short cosmic ray exposure times. Further, SNC's noble gas and nitrogen components indicate a martian origin for these objects. If these meteorites are from Mars, then the most confounding question facing the planetary science community is how were they ejected from the planet's surface. The following is an investigation of that question.

  10. Comparison of lunar rocks and meteorites: Implications to histories of the moon and parent meteorite bodies

    Prinz, M.; Fodor, R. V.; Keil, K.


    There are many similarities between lunar samples and stone meteorites. Lunar samples, especially from the highlands, indicate that they have been affected by complex and repeated impact processes. Similar complex and repeated impact processes have also been operative on the achondritic and chondritic meteorites. Similarities between lunar and meteoritic rocks are discussed as follows: (1) Monomict and polymict breccias occur in lunar rocks, as well as in achondritic and chondritic meteorites, having resulted from complex and repeated impact processes; (2) Chondrules are present in lunar meteorites, as well as in a few achondritic and most chondritic meteorites. They apparently crystallized spontaneously from molten highly supercooled droplets which may have formed from impact melts or, perhaps, volcanic processes (as well as from the solar nebula, in the case of meteoritic chondrites); (3) Lithic fragments vary from little modified (relative to the apparent original texture) to partly or completely melted and recrystallized lithic fragments. Their detailed study allows conclusions to be drawn about their parent rock types and their origin, thereby gaining insight into preimpact histories of lunar and meteoritic breccias. There is evidence that cumulate rocks were involved in the early history of both moon and parent meteorite bodies.

  11. Petrologic and Minerochemical Trends of Acapulcoites, Winonaites and Lodranites: New Evidence from Image Analysis and EMPA Investigations

    Vanni Moggi Cecchi


    Full Text Available A comprehensive classification of primitive achondrites is difficult due to the high compositional and textural variability and the low number of samples available. Besides oxygen isotopic analysis, other minerochemical and textural parameters may provide a useful tool to solve taxonomic and genetic problems related to these achondrites. The results of a detailed modal, textural and minerochemical analysis of a set of primitive achondrites are presented and compared with literature data. All the samples show an extremely variable modal composition among both silicate and opaque phases. A general trend of troilite depletion vs. silicate fraction enrichment has been observed, with differences among coarse-grained and fine-grained meteorites. In regard to the mineral chemistry, olivine shows marked differences between the acapulcoite-lodranite and winonaite groups, while a compositional equilibrium between matrix and chondrules for both groups, probably due to the scarce influence of metamorphic grade on this phase, was observed. The analysis of Cr and Mn in clinopyroxene revealed two separate clusters for the acapulcoite/lodranite and winonaite groups, while the analysis of the reduction state highlighted three separate clusters. An estimate of equilibrium temperatures for the acapulcoite-lodranite and winonaite groups is provided. Finally, proposals regarding the genetic processes of these groups are discussed.

  12. Petrology of Anomalous Eucrites

    Mittlefehldt, D. W.; Peng, Z. X.; Ross, D. K.


    Most mafic achondrites can be broadly categorized as being "eucritic", that is, they are composed of a ferroan low-Ca clinopyroxene, high-Ca plagioclase and a silica phase. They are petrologically distinct from angritic basalts, which are composed of high-Ca, Al-Ti-rich clinopyroxene, Carich olivine, nearly pure anorthite and kirschsteinite, or from what might be called brachinitic basalts, which are composed of ferroan orthopyroxene and high-Ca clinopyroxene, intermediate-Ca plagioclase and ferroan olivine. Because of their similar mineralogy and composition, eucrite-like mafic achondrites formed on compositionally similar asteroids under similar conditions of temperature, pressure and oxygen fugacity. Some of them have distinctive isotopic compositions and petrologic characteristics that demonstrate formation on asteroids different from the parent of the HED clan (e.g., Ibitira, Northwest Africa (NWA) 011). Others show smaller oxygen isotopic distinctions but are otherwise petrologically and compositionally indistinguishable from basaltic eucrites (e.g., Pasamonte, Pecora Escarpment (PCA) 91007). The degree of uniformity in delta O-17 of eucrites and diogenites is one piece of evidence considered to favor of a magma-ocean scenario for their petrogenesis. Given that the O isotopic differences separating Pasamonte and PCA 91007 from other eucrites are small, and that there is an absence of other distinguishing characteristics, a legitimate question is: Did the HED parent asteroid fail to homogenize via a magma-ocean stage, thus explaining outliers like Pasamonte? We are initiating a program of study of anomalous eucrite-like achondrites as one part of our effort to seek a resolution of this issue. Here we present preliminary petrologic information on Asuka (A-) 881394, Elephant Moraine (EET) 87520 and EET 87542. We will have studied several more by conference time.

  13. Samarium-neodymium systematics in kimberlites and in the minerals of garnet lherzolite inclusions

    Basu, A.R.; Tatsumoto, M.


    The initial ratios of neodymium-143 to neodymium-144 in kimberlites ranging in age between 90 ?? 106 to 1300 ?? 106 years from South Africa, India, and the United States are different from the corresponding ratios in the minerals of peridotite inclusions in the kimberlites but are identical to the ratios in the basaltic achondrite Juvinas at the times of emplacement of the respective kimberlite pipes. This correlation between the kimberlites and Juvinas, which represents the bulk chondritic earth in rare-earth elements, strongly indicates that the kimberlite's source in the mantle is chondritic in rare-earth elements and relatively primeval in composition. Copyright ?? 1979 AAAS.

  14. The meteorite collection at Museo di Storia Naturale, Pisa University, Italy

    Perchiazzi, Natale; D'Orazio, Massimo; Folco, Luigi


    The historical meteorite collection of Museo di Storia Naturale, Pisa University, is presented in this catalog. Dating back to at least 1860, the collection currently (as of June 2003) contains 30 specimens of 26 individual meteorites, representing about 50 kg of extraterrestrial material. The collection includes 2 carbonaceous chondrites, 12 ordinary chondrites, 1 achondrite, 4 stony-iron meteorites, and 7 iron meteorites, including three remarkable specimens: the main mass of Bagnone (48 kg), the fourth largest mass of Quenggouk (717.5 g), and a large (nearly) complete individual of the Siena showerfall (318.8 g).

  15. 35 seasons of US antarctic meteorites (1976-2010) a pictorial guide to the collection

    Righter, Kevin; McCoy, Timothy; Harvey, Ralph; Harvey, Ralph


    The US Antarctic meteorite collection exists due to a cooperative program involving the National Science Foundation (NSF), the National Aeronautics and Space Administration (NASA), and the Smithsonian Institution.  Since 1976, meteorites have been collected by a NSF-funded field team, shipped for curation, characterization, distribution, and storage at NASA, and classified and stored for long term at the Smithsonian.  It is the largest collection in the world with many significant samples including lunar, martian, many interesting chondrites and achondrites, and even several unusual one-of-

  16. Early stages of core segregation recorded by Fe isotopes in an asteroidal mantle

    Barrat, Jean-Alix; Rouxel, O; Wang, K; Moynier, F; Yamaguchi, A; Bischoff, A; Langlade, J


    International audience; Ureilites displays  56 Fe values higher than average chondrite. 29-Segregation of Fe-sulfide melts explains the high  56 Fe values in ureilites. 30-Formation of a core can begin at very low degrees of melting through the circulation of a Fe-S melt 31 through a silicate mantle. 32 33 Earth and Planetary Science Letters, in press (11/3/15). 34 2 35 Abstract 36 37 Ureilite meteorites are achondrites that are debris of the mantle of a now disrupted 38 differentiated aste...

  17. Porphyritic Olivine-Pyroxene Clast in Kaidun: First Discovery of an Ordinary Chondrite Clast?

    Mikouchi, T.; Makishima, J.; Koizumi, E.; Zolensky, M. E.


    Kaidun is an enigmatic meteorite showing a micro-brecciated texture composed of variable kinds of lithic clasts and mineral fragments. The constituent components range from primitive chondritic materials to differentiated achondritic materials, and thus believed to have originated from a large parent body accumulating materials from many different bodies in the asteroid belt. One of the interesting observations is that no ordinary chondrite component has been found yet, although C and E chondrites components are abundant. In this abstract, we report mineralogy of the clast (Kaidun #15415- 01.3.13a) showing a porphyritic olivine-pyroxene chondrule-like texture similar to those found in unequilibrated ordinary chondrites.

  18. Petrology of Diogenite NWA 5480, A Pristine Olivine-Rich Deformed Harzburgite

    Peslier, A. H.; Brandon, A. D.; Tarduno, J. A.; Mittlefehldt, D. W.


    Diogenites are achondrites that are part of the HED (howardite, eucrite, diogenite) meteorite group thought to originate from asteroid Vesta. This suite of igneous rocks offers a glimpse of early planetary differentiation and subsequent igneous processes. While eucrites represent asteroidal basaltic crust and howardites the impact brecciated surface, diogenites are samples of the mantle and lower crust. Most of them are orthopyroxene (Opx) dominated cumulates, although harzburgites and rare dunites have also been found. The majority of diogenites are impact breccias. This study describes NWA 5480, a pristine, i.e. hardly altered and minimally shocked, harzburgitic diogenite.

  19. Oxygen isotopic composition of relict olivine grains in cosmic spherules: Links to chondrules from carbonaceous chondrites

    Rudraswami, N.G.; ShyamPrasad, M.; Nagashima, K.; Jones, R.H.

    evidence of evolved asteroids, similar to chondritic or achondritic parent bodies (e.g., Taylor et al., 2007; Genge et al., 2008; Gounelle et al., 2009; Badjukov et al., 2010; Cordier et al., 2011a, b, 2012; Suavet et al., 2010; Van Ginneken et al., 2012... is much less (Taylor et al., 2000; Yada et al., 2004; Prasad et al., 2013). They are expected to have sampled a wide variety of parent bodies, including those known to us through meteorite studies, and some that have not yet been sampled (Brownlee...

  20. Structure, tectonic and petrology of mid-oceanic ridges and the Indian scenario

    Iyer, S.D.; Ray, Dwijesh

    to basaltic achondrite 6 as also attested by REE and K ? Rb contents. The major elements Si, Al, Fe, Mg, Ca and Na play an important role, while Ti sometimes qualifies and at times behaves purely as a trace element . SiO 2 has a narrow range (49 ? 52...) while the most evolved basalt contains MgO as low as 6% and Fe up to 13.5% with Mg# 45. TiO 2 (0.7 ? 2%) acts as an incompatible trace ele - ment in the more magnesian lavas but in the Fe - rich ones it occurs in an oxide phase and/or in amphibo le...

  1. Annual review of earth and planetary sciences. Volume 17

    Wetherill, G.W.; Albee, A.L.; Stehli, F.G.


    Recent advances in earth and planetary science are examined in reviews by leading experts. The subjects discussed include geochemistry and the dynamics of the Yellowstone hydrothermal system, Alpine and Himalayan blueschists, pressure solution during diagenesis, achondrites and igneous processes on asteroids, Sr isotopes in seawater, sediment magnetization and the evolution of magnetite biomineralization, active deformation of the continents, the nature of deep-focus earthquakes, and the use of Raman spectroscopy in mineralogy and geochemistry. Consideration is given to the mechanics of faulting, the crustal structure of western Europe, gases in diamonds, metamorphic fluids in the deep crust, faunal dynamics of pleistocene mammals, magma chambers, and the nature of the Mohorovicic discontinuity.

  2. Meteorite falls in Bulgaria: Reappraisal of mineralogy, chemistry, and classification

    Dekov, Vesselin; Rochette, Pierre; Gattacceca, JéRôMe


    We present a summary of the mineralogy, mineral chemistry, and magnetic characteristics of all the five Bulgarian meteorite falls. We report the first mineralogical descriptions, chemical analyses, and magnetic measurements of the Konevo (1931) and Silistra (1917) meteorites. We classify Konevo as LL5, and Silistra as an ungrouped achondrite with HED affinities. Pavel (1966; previously classified as an H5) is reclassified as H3-anomalous. We also provide precise mineralogy and mineral chemistry of the Virba meteorite (1873, L6), and more details on the mineral chemistry of Gumoschnik (1904, H5).

  3. The Kenna ureilite - An ultramafic rock with evidence for igneous, metamorphic, and shock origin

    Berkley, J. L.; Brown, H. G.; Keil, K.; Carter, N. L.; Mercier, J.-C. C.; Huss, G.


    Ureilites are a rare group of achondrites. They are composed mainly of olivine and pigeonite in a matrix of carbonaceous material, including graphite, lonsdaleite, diamond, and metal. In most respects Kenna is a typical ureilite with the requisite mineralogical and chemical properties of the group. Differences of the Kenna ureilite from previously studied ureilites are related to a greater density, the occurrence of exceedingly minute quantities of feldspar, and a very strong elongation lineation of the silicate minerals. A description is presented of a study which indicates a complex history for Kenna, including igneous, mild metamorphic, and shock processes.

  4. Planetary Protection Considerations in EVA System Design

    Eppler, Dean B.; Kosmo, Joseph J.


    To better constrain their origin, we have performed systematic studies of the siderophile element distribution in metal from Enstatite achondrites and iron-rich meteorites linked to Enstatite achondrites. Humayun (2010) reported 20 siderophile elements in the metal of Horse Creek, Mt. Egerton and Tucson, three iron meteorites known for their high Si content in their metal. The Horse Creek and Mt. Egerton irons have elemental patterns identical to metallic solids derived from partially molten enstatite chondrites. Tucson has an unusual siderophile element pattern that is reminiscent of IVA irons, except for the most volatile siderophiles with condensation temperatures below that of Cu (Sb, Ge, Sn) which are more depleted. The origin of Tucson metal is likely linked to an impact involving a reduced chondritic body that provided the silicates, and IVA iron. In a related study, van Acken et al. (2010) reported siderophile element abundances in metal and sulfides from aubrites, chondritic inclusions in aubrites, and other enstatite achondrites (including a separate section of Mt. Egerton). They found that aubrite metal was linked to metal in enstatite chondrites by low degree partial melting forming sulfur-rich metallic liquids. A restite origin of aubrites is not consistent with these metal compositions. The link between the metal compositions and cumulate silicates is not simple. The metal must have been incorporated from enstatite chondritic material that was assimilated by the aubrite magma. A manuscript is in preparation (van Acken et al., 2010). In a related study, van Acken et al. (2010, submitted) reported new precise Os isotope ratios and highly siderophile element abundances in Enstatite chondrites, Enstatite achondrites, Rumurutite chondrites to explore the range of nucleosynthetic variation in s-process Os. They observed nucleosynthetic anomalies, deficiencies of s-process Os, in most primitive enstatite chondrites, but showed the Rumurutite chondrites have

  5. Moessbauer spectroscopy of the SNC meteorite Zagami

    Agerkvist, D. P.; Vistisen, L.


    We have performed Mossbauer spectroscopy on two different pieces of the meteorite Zagami belonging to the group of SNC meteorites. In one of the samples we found a substantial amount of olivine inter grown with one kind of pyroxene, and also another kind of pyroxene very similar to the pyroxene in the other sample we examined. Both samples showed less than 1 percent of Fe(3+) in the silicate phase. The group of SNC meteorites called shergottites, to which Zagami belongs, are achondrites whose texture, mineralogy and composition resembles those of terrestrial diabases. The results from the investigation are presented.

  6. Overview of Mars: SNC meteorite results

    Waenke, H.


    The SNC meteorites according to their oxygen isotope ratios and various trace element ratios form a distinct group of 8 achondrites. Their young crystallization ages and fractionated REE pattern which exclude an asteroidal origin, were the first observations to point towards Mars as their parent body. In spite of the many arguments for Mars as the parent body of the SNC meteorites there does not exist a generally accepted model for the ejecting process and other dynamical problems involved. In this discussion it is, however, assumed that Mars is the SNC parent body. The chemical composition of Mars is examined.

  7. The Foreign Clast Populations of Anomalous Polymict Urelite Almahata Sitta (Asteroid 2008 TC(sub3) and Typical Polymict Ureilites: Implications for Asteroid-Meteorite Connections

    Goodrich, C. A.; Treiman, A. H.; Zolensky, M.; Kita, N. T.; Defouilloy, C.; Fioretti, A. M.; O'Brien, D. P.; Jenniskens, P.; Shaddad, M. H.


    Almahata Sitta (AhS) is the first meteorite to originate from an asteroid (2008 TC3) that had been studied in space before it hit Earth [1,2]. It is also unique because the fallen fragments comprise a variety of types: approximately 69% ureilites (achondrites) and 31% chondrites [3]. Two models have been proposed for the origin 2008 TC3: 1) an accretionary model [3,4]; or 2) a regolith model [5,6]. Typical polymict ureilites are interpreted to represent regolith, and contain a few % foreign clasts [7,8]. The most common are dark (CC matrix-like) clasts similar to those in many meteoritic breccias [9]. A variety of other chondrites, as well as achondrites (angrites), have also been reported [7,9,10]. We have been working to determine the full diversity of these clasts [10-13] for comparison with AhS. We discuss implications for mixing of materials in the early solar system and the origin of 2008 TC3.

  8. Bunburra Rockhole: Exploring the Geology of a New Differentiated Basaltic Asteroid

    Benedix, G.K.; Bland, P. A.; Friedrich, J. M.; Mittlefehldt, D.; Sanborn, M. E.; Yin, Q.-Z.; Greenwood, R. C; Franchi, L. A.; Bevan, A. W. R.; Towner, M. C.; Perotta, Grace C.


    Bunburra Rockhole (BR) is the first recovered meteorite of the Desert Fireball Network. It was initially classified as a basaltic eucrite, based on texture, mineralogy, and mineral chemistry but subsequent O isotopic analyses showed that BR's composition lies significantly far away from the HED group of meteorites. This suggested that BR was not a piece of the HED parent body (4 Vesta), but other explanations could also account for the observed oxygen signatures. Possible scenarios include contamination by components from other bodies (chondrites or other achondrites) or that 4 Vesta may not be as equilibrated as hypothesized. After examining multiple pieces with different instruments (CT scans and x-ray maps), no obvious evidence of contamination was found. If BR is not from Vesta, a conundrum exists as no unusual features were found in mineral and bulk trace element chemistry as exist for other anomalous basaltic achondrites such as Ibitira or Asuka 881394. These meteorites have distinct petrological and geochemical characteristics, in addition to their anomalous O isotope compositions, that set them apart from eucrites. Thus, early results provided a somewhat ambiguous picture of BR's petrogenesis and parentage. To clarify the nature of the relationship, if any, between BR and eucrites, we have performed a correlated stable isotope and bulk chemical study of several lithologic fragments.

  9. V Xanes in Spinels as an Oxy-Barometer in Meteorites with Implications for Redox Variations in the Inner Solar System

    Righter, K.; Sutton, S.; Danielson, L.; Pando, K.; Le, L.; Newville, M.


    The variation of oxygen fugacity within inner solar system materials spans a range of nearly 15 orders of magnitude. Igneous and metamorphic rocks commonly contain a mineral assemblage that allows oxygen fugacity to be calculated or con-strained such as FeTi oxides, olivine-opx-spinel, or some other oxy-barometer. Some rocks, however, contain a limited mineral assemblage and do not provide constraints on fO2 using mineral equilibria. Good examples of the latter are orthopyroxenites or dunites, such as diogenites, ALH 84001, chassignites, or brachinites. In fact it is no surprise that the fO2 of many of these achondrites is not well known, other than being "reduced" and below the metal saturation value. In order to bridge this gap in our understanding, we have initiated a study of V in chromites in achondrite. Because the V pre-edge peak intensity and energy in chromites varies with fO2, and this has been calibrated over a large fO2 range, we can apply this relation to rocks for which we otherwise have no fO2 constraints.

  10. The initial abundance and distribution of 92Nb in the Solar System

    Iizuka, Tsuyoshi; Akram, Waheed; Amelin, Yuri; Schönbächler, Maria


    Niobium-92 is an extinct proton-rich nuclide, which decays to 92Zr with a half-life of 37 Ma. This radionuclide potentially offers a unique opportunity to determine the timescales of early Solar System processes and the site(s) of nucleosynthesis for p-nuclei, once its initial abundance and distribution in the Solar System are well established. Here we present internal Nb-Zr isochrons for three basaltic achondrites with known U-Pb ages: the angrite NWA 4590, the eucrite Agoult, and the ungrouped achondrite Ibitira. Our results show that the relative Nb-Zr isochron ages of the three meteorites are consistent with the time intervals obtained from the Pb-Pb chronometer for pyroxene and plagioclase, indicating that 92Nb was homogeneously distributed among their source regions. The Nb-Zr and Pb-Pb data for NWA 4590 yield the most reliable and precise reference point for anchoring the Nb-Zr chronometer to the absolute timescale: an initial 92Nb/93Nb ratio of $(1.4 \\pm 0.5) \\times 10^{-5}$ at $4557.93 \\pm 0.36$ Ma, ...

  11. Sm-Nd and Initial Sr-87/Sr-86 Isotopic Systematics of Asuka 881394 and Cumulate Eucrites Yamato 980318/433 Compared

    Nyquist, L. E.; Shih, C-Y; Young, Y. D.; Takeda, H.


    The Asuka 881394 achondrite contains fossil Al-26 and Mn-53 and has a Pb-206/Pb-207 age of 4566.5 +/- 0.2 Ma, the oldest for an achondrite. Recent re-investigation of A881394 yielded revised initial Sm-146/Sm-144 = (9.1 +/- 1.4) x 10(exp -3), a Sm-147-Nd-143 age of 4525 +/- 58 Ma, a Rb-87-Sr-87 age of 4490 +/- 130 Ma, and initial Sr-87/Sr-86 = 0.698991 +/- 19, respectively. The relatively large uncertainties in the Sm-Nd and Rb-Sr ages are due to disturbances of the isotopic systematics of tridymite and other minor phases. A preliminary value for the Sm-147-Nd-143 age of the Yamato 980318 cumulate eucrite of 4560 +/- 150 Ma was refined in later work to 4567 +/- 24 Ma as reported orally at LPSC 35. Similarly, a preliminary value for Sm-146/Sm-144 = (7.7 +/- 1.2) x 10 (exp -3) was refined to (6.0 +/- 0.3) x 10(exp -3). For Yamato 980433, a Sm-147-Nd-143 age of 4542 +/-42 Ma and Sm-146/Sm-144 = (5.7 +/- 0.5) x 10(exp -3) has been reported. Because these two cumulate eucrites are paired, we consider them to represent one igneous rock and present their combined isotopic data here.

  12. A Model for Siderophile Element Distribution in Planetary Differentiation

    Humayun, M.; Rushmer, T.; Rankenburg, K.; Brandon, A. D.


    Planetary differentiation begins with partial melting of small planetesimals. At low degrees of partial melting, a sulfur-rich liquid segregates by physical mechanisms including deformation-assisted porous flow. Experimental studies of the physical mechanisms by which Fe-S melts segregate from the silicate matrix of a molten H chondrite are part of a companion paper. Geochemical studies of these experimental products revealed that metallic liquids were in equilibrium with residual metal in the H chondrite matrix. This contribution explores the geochemical signatures produced by early stages of core formation. Particularly, low-degree partial melt segregation of Fe-S liquids leaves residual metal in the silicate matrix. Some achondrites appear to be residues of partial melting, e.g., ureilites, which are known to contain metal. The metal in these achondrites may show a distinct elemental signature. To quantify the effect of sulfur on siderophile element contents of residual metal we have developed a model based on recent parametrizations of equilibrium solid metal-liquid metal partitioning experiments.

  13. PIXE and light element analysis (C,N) in glass inclusions trapped in meteorites with the nuclear microprobe

    Varela, M.E.; Mosbah, M. E-mail:; Metrich, N.; Duraud, J.P.; Kurat, G


    Proton-induced X-ray emission (PIXE) and light element analysis have been performed with the nuclear microprobe at the Laboratoire Pierre Suee (Saclay-France) in glass inclusions of the carbonaceous chondrites: Allende, Kaba and Renazzo, and in the achondrite meteorite: Chassigny. Carbon contents in olivine of chondrules are below the nuclear reactions analysis (NRA) detection limit, however, glasses from glass inclusions hosted by these grains, contain an appreciable and highly variable quantities of carbon (200-1600 ppm). This could indicate variable amounts of C trapped during glass inclusion formation. On the other hand, nitrogen is present in highly variable amounts in glasses of both, chondrites and achondrites minerals. Its abundance, correlated with depth from the section surface which suggests loss of N during analyses and therefore the possible existence of a very mobile (volatile?) species. A chondritic Rb/Sr and K/Rb ratio obtained by PIXE analyses in the glass-bearing inclusions of the Chassigny meteorite points towards a primitive source for the glass precursor of Chassigny inclusions.

  14. Hungaria asteroid region telescopic spectral survey (HARTSS) I: Stony asteroids abundant in the Hungaria background population

    Lucas, Michael P.; Emery, Joshua P.; Pinilla-Alonso, Noemi; Lindsay, Sean S.; Lorenzi, Vania


    different S-subtypes are represented therein, which translates to a variety of surface compositions. We identify the Gaffey S-subtype (Gaffey et al. [1993]. Icarus 106, 573-602) and potential meteorite analogs for 24 of these S-complex background asteroids. Additionally, we estimate the olivine and orthopyroxene mineralogy for 18 of these objects using spectral band parameter analysis established from laboratory-based studies of ordinary chondrite meteorites. Nine of the asteroids have band parameters that are not consistent with ordinary chondrites. We compared these to the band parameters measured from laboratory VIS+NIR spectra of six primitive achondrite (acapulcoite-lodranite) meteorites. These comparisons suggest that two main meteorite groups are represented among the Hungaria background asteroids: unmelted, nebular L- (and possibly LL-ordinary chondrites), and partially-melted primitive achondrites of the acapulcoite-lodranite meteorite clan. Our results suggest a source region for L chondrite like material from within the Hungarias, with delivery to Earth via leakage from the inner boundary of the Hungaria region. H chondrite like mineralogies appear to be absent from the Hungaria background asteroids. We therefore conclude that the Hungaria region is not a source for H chondrite meteorites. Seven Hungaria background asteroids have spectral band parameters consistent with partially-melted primitive achondrites, but the probable source region of the acapulcoite-lodranite parent body remains inconclusive. If the proposed connection with the Hungaria family to fully-melted enstatite achondrite meteorites (i.e., aubrites) is accurate (Gaffey et al. [1992]. Icarus 100, 95-109; Kelley and Gaffey [2002]. Meteorit. Planet. Sci. 37, 1815-1827), then asteroids in the Hungaria region exhibit a full range of petrologic evolution: from nebular, unmelted ordinary chondrites, through partially-melted primitive achondrites, to fully-melted igneous aubrite meteorites.


    侯渭; 谢鸿森; 周文戈


    In recent 40 years, meteorite taxology has undergone thre e development stages. In the 1960-1970s, chemical-petrologic classification of chondrites and chemical classification of iron meteorite were established. In the 1970-1980s, achondrites, stony irons and irons were considered to be from differentiated meteorite bodies. In the 1980-1990s,the oxygen isotopic compositions of meteorites were taken as an important foundation for meteorite classification, so meteorite taxology entered a new original classification stage. In this paper, R chondrite, K chondrite, CR chondrite and CK chondrite are reported to be new chemical groups distinguished in recent 20 years, and A-L achondrite, Winonaite achondrite and Brachinite achondrite,to be primitive achondrites based on the oxygen isotopic compositions. Finally, significance of meteorite classification in earth science is discussed,calling earth scientists to pay attention to the developments on meteoritics and meteorite taxology.%近40年来陨石分类学经历了3个发展阶段:60~70年代,由根据陨石的矿物结构的分类方法发展为球粒陨石的化学—岩石学分类法和铁陨石的化学群分类法;70~80年代,提出了分异型陨石和未分异型陨石的概念。球粒陨石被认为是未分异型陨石,而其它陨石(铁陨石、石铁陨石和无球粒陨石)大多被划入分异型陨石;80~90年代以来,陨石氧同位素组成成为了陨石成因分类的一个主要依据,使陨石分类学进入了一个新的成因分类阶段。作者对80~90年代以来新确立的R群、K小群、CR群和CK群球粒陨石,以及根据氧同位素划分出的原始型无球粒陨石系列:A-L无球粒陨石、Winonaites无球粒陨石和Brachinites无球粒陨石进行了介绍。笔者对陨石研究和陨石分类学的发展在估算地球整体成分,探讨地球成因和早期演化历史方面的重要意义进行了说明,并建议

  16. Petrology and Geochemistry of LEW 88663 and PAT 91501: High Petrologic L Chondrites

    Mittlefehldt, D. W.; Lindstrom, M. M.; Field, S. W.


    Primitive achondrites (e.g., Acapulco, Lodran) are believed to be highly metamorphosed chondritic materials, perhaps up to the point of anatexis in some types. Low petrologic grade equivalents of these achondrites are unknown, so the petrologic transition from chondritic to achondritic material cannot be documented. However, there are rare L chondrites of petrologic grade 7 that may have experienced igneous processes, and study of these may yield information relevant to the formation of primitive achondrites, and perhaps basaltic achondrites, from chondritic precursors. We have begun the study of the L7 chondrites LEW 88663 and PAT 91501 as part of our broader study of primitive achondrites. Here, we present our preliminary petrologic and geochemical data on these meteorites. Petrology and Mineral Compositions: LEW 88663 is a granular achondrite composed of equant, subhedral to anhedral olivine grains poikilitically enclosed in networks of orthopyroxene and plagioclase. Small grains of clinopyroxene are spatially associated with orthopyroxene. Troilite occurs as large anhedral and small rounded grains. The smaller troilite grains are associated with the orthopyroxene-plagioclase networks. PAT 91501 is a vesicular stone containing centimeter-sized troilite +/- metal nodules. Its texture consists of anhedral to euhedral olivine grains, anhedral orthopyroxene grains (some with euhedral clinopyroxene overgrowths), anhedral to euhedral clinopyroxene, and interstitial plagioclase and SiO2-Al2O3-K2O- rich glass. In some areas, olivine is poikilitically enclosed in orthopyroxene. Fine-grained troilite, metal, and euhedral chromite occur interstitial to the silicates. Average mineral compositions for LEW 88663 are olivine Fo(sub)75.8, orthopyroxene Wo(sub)3.4En(sub)76.2Fs(sub)20.4, clinopyroxene Wo(sub)42.6En(sub)47.8Fs(sub)9.6, plagioclase Ab(sub)75.0An(sub)21.6Or(sub)3.4. Mineral compositions for PAT 91501 are olivine Fo(sub)73.8, orthopyroxene Wo(sub)4.5En(sub)74.8Fs

  17. Medium Rare or Well Done? Asteroid Melting in the Hungaria Region

    Lucas, Michael P.; Emery, Joshua P.; Lorenzi, Vania; Pinilla-Alonso, Noemí; Lindsay, Sean S.


    The Hungaria region is located interior to the Main Belt and contains ~12,000 small asteroids (D inhabited by the Hungaria family of mainly Xe-type asteroids, which comprises a significant fraction of the regional population. However, this family is situated among a spectrally diverse asteroid background. Among the asteroids with semi-major axes interior to the Main Belt (e.g., Hungarias, Mars-crossers, and near-Earth asteroids), only Hungarias are located in relatively stable orbital space. Therefore, these objects may represent the closest remaining reservoir of the material that accreted to form the terrestrial planets. Deciphering the mineralogy of the Hungaria asteroids may place constraints on the nature of this material.Partially-melted or differentiated bodies that originated in the terrestrial planet region were either accreted or scattered out of this region early in solar system history. We hypothesize that planetesimals in the inner part of the solar nebula (terrestrial planet region) underwent significant melting - the Hungaria region should retain this petrologically-evolved material. We test this hypothesis by performing detailed spectral band parameter analyses on Hungaria asteroid spectra and on primitive achondrite meteorite spectra obtained from the RELAB database.Through an ongoing near-infrared survey of Hungaria asteroids at the IRTF and TNG telescopes we have acquired a spectral sample of 36 objects (32 background, 4 family). Preliminary results indicate a compositionally diverse background population dominated by S- and S-subtypes (23 out of 32). Band parameter analyses of 19 of these S-types show that two main meteorite groups appear to be represented, unmelted ordinary chondrites; and partially-melted primitive achondrite meteorites acapulcoites/lodranites. Furthermore, three of four family members are X-types, likely consistent with the largest collisional fragment 434 Hungaria. Xe-subtypes in the Hungaria region are thought to be related

  18. Curious kinetic behavior in silica polymorphs solves seifertite puzzle in shocked meteorite.

    Kubo, Tomoaki; Kato, Takumi; Higo, Yuji; Funakoshi, Ken-Ichi


    The presence of seifertite, one of the high-pressure polymorphs of silica, in achondritic shocked meteorites has been problematic because this phase is thermodynamically stable at more than ~100 GPa, unrealistically high-pressure conditions for the shock events in the early solar system. We conducted in situ x-ray diffraction measurements at high pressure and temperatures, and found that it metastably appears down to ~11 GPa owing to the clear difference in kinetics between the metastable seifertite and stable stishovite formations. The temperature-insensitive but time-sensitive kinetics for the formation of seifertite uniquely constrains that the critical shock duration and size of the impactor on differentiated parental bodies are at least ~0.01 s and ~50 to 100 m, respectively, from the presence of seifertite.

  19. Low γ activity measurement of meteorites using HPGe–NaI detector system

    Colombetti, P. [Dipartimento di Fisica dell' Università di Torino (Italy); Osservatorio Astrofisico di Torino – INAF, Torino (Italy); Taricco, C., E-mail: [Dipartimento di Fisica dell' Università di Torino (Italy); Osservatorio Astrofisico di Torino – INAF, Torino (Italy); Bhandari, N. [Basic Sciences Research Institute, Navrangpura, Ahmedabad (India); Sinha, N. [Department of Science, Wentworth Institute of Technology, Boston (United States); Di Martino, M.; Cora, A. [Osservatorio Astrofisico di Torino – INAF, Torino (Italy); Vivaldo, G. [Dipartimento di Fisica dell' Università di Torino (Italy)


    The radioactivity in natural samples like cosmogenic isotopes in meteorites, in Moon samples, in earth and ice in Antarctica, produced by protons, neutrons, μ mesons and other charged particles, is very low, usually below 0.001 disintegration per minute per gram. Therefore, very special techniques are required, particularly if the sample cannot be destroyed for chemical separation and system must have possibility of counting large amount of sample. For this purpose we have developed a highly selective Ge–NaI coincidence spectrometer, operating in the underground Laboratory of Monte dei Cappuccini (INAF) in Torino. We have then improved it by developing a multiparametric acquisition system, which allows better selectivity of the coincidence windows (e.g., in meteorites, to disentangle cosmogenic {sup 44}Ti signal from overlapping {sup 214}Bi, originated by naturally occurring {sup 238}U). Applications of this system to the study of meteorites (chondrite, achondrite and iron samples) are described.

  20. Chondrule size and related physical properties: a compilation and evaluation of current data across all meteorite groups

    Friedrich, Jon M; Ebel, Denton S; Biltz, Alison E; Corbett, Bernadette M; Iotzov, Ivan V; Khan, Wajiha S; Wolman, Matthew D


    The examination of the physical properties of chondrules has generally received less emphasis than other properties of meteorites such as their mineralogy, petrology, and chemical and isotopic compositions. Among the various physical properties of chondrules, chondrule size is especially important for the classification of chondrites into chemical groups, since each chemical group possesses a distinct size-frequency distribution of chondrules. Knowledge of the physical properties of chondrules is also vital for the development of astrophysical models for chondrule formation, and for understanding how to utilize asteroidal resources in space exploration. To examine our current knowledge of chondrule sizes, we have compiled and provide commentary on available chondrule dimension literature data. We include all chondrite chemical groups as well as the acapulcoite primitive achondrites, some of which contain relict chondrules. We also compile and review current literature data for other astrophysically-relevant p...

  1. Mineralogy and Surface Composition of Asteroids

    Reddy, Vishnu; Thomas, Cristina A; Moskovitz, Nicholas A; Burbine, Thomas H


    Methods to constrain the surface mineralogy of asteroids have seen considerable development during the last decade with advancement in laboratory spectral calibrations and validation of our interpretive methodologies by spacecraft rendezvous missions. This has enabled the accurate identification of several meteorite parent bodies in the main asteroid belt and helped constrain the mineral chemistries and abundances in ordinary chondrites and basaltic achondrites. With better quantification of spectral effects due to temperature, phase angle, and grain size, systematic discrepancies due to non-compositional factors can now be virtually eliminated for mafic silicate-bearing asteroids. Interpretation of spectrally featureless asteroids remains a challenge. This paper presents a review of all mineralogical interpretive tools currently in use and outlines procedures for their application.

  2. Pomozdino - An anomalous, high-MgO/FeO, yet REE-rich eucrite

    Warren, P. H.; Jerde, E. A.; Migdisova, L. F.; Iaroshevskii, A. A.


    A new chemical analysis and petrographic data for the Pomozdino basaltic achondrite are presented. Earlier indications that Pomozdino is a eucrite and that it is a monomict breccia with an anomalous, REE-rich, yet high-MgO/FeO bulk composition, are confirmed. Characteristics such as texture, composition, and REE concentration are examined and compared to those in other publications. A model for the origin of this meteorite, as a partial cumulate with an uncommonly high content of trapped liquid, is found to be preferable. Two alternatives of the origin are suggested, one of which implies that the parent melt is roughly similar in composition to Stannern. The other considers Pomozdino as a possible primary partial melt, derived from a source region far more magnesian than generally envisaged for the sources of primary eucritic partial melts. It is concluded that at least some Stannern-like eucrites were involved in fractional crystallization, and thus do not represent primary partial melts.

  3. Mercury (Hg) in meteorites: variations in abundance, thermal release profile, mass-dependent and mass-independent isotopic fractionation

    Meier, Matthias M M; Marty, Bernard


    We have measured the concentration, isotopic composition and thermal release profiles of Mercury (Hg) in a suite of meteorites, including both chondrites and achondrites. We find large variations in Hg concentration between different meteorites (ca. 10 ppb to 14'000 ppb), with the highest concentration orders of magnitude above the expected bulk solar system silicates value. From the presence of several different Hg carrier phases in thermal release profiles (150 to 650 {\\deg}C), we argue that these variations are unlikely to be mainly due to terrestrial contamination. The Hg abundance of meteorites shows no correlation with petrographic type, or mass-dependent fractionation of Hg isotopes. Most carbonaceous chondrites show mass-independent enrichments in the odd-numbered isotopes 199Hg and 201Hg. We show that the enrichments are not nucleosynthetic, as we do not find corresponding nucleosynthetic deficits of 196Hg. Instead, they can partially be explained by Hg evaporation and redeposition during heating of ...

  4. Meteorites - A petrologic-chemical synthesis

    Dodd, Robert T.

    In this book, an attempt has been made to summarize current knowledge and understanding about meteorites in a manner comprehensible to both professional scientists and university students. Attention is given to the flux of meteoritic material, major meteorite types, sources of meteorites, the recovery of meteorites, meteorite nomenclature, and literature. The chemistry and classification of the chondrites is considered along with details regarding carbonaceous chondrites, ordinary chondrites, the enstatite chondrite-achondrite association, and questions regarding time and process in the evolution of chondrites. The eucrite association is discussed, taking into account eucrites, diogenites, howardites, mesosiderites, the radiometric ages of eucrites and their associates, and the chemical evolution of the eucrite association. Differentiated meteorites are considered along with source objects, and parent bodies.

  5. Antarctic Meteorite Newsletter, Volume 31, No. 1

    Satterwhite, Cecilia (Editor); Righter, Kevin (Editor)


    This newsletter reports 418 new meteorites from the 2004 and 2006 ANSMET seasons from the Cumulus Hills (CMS), LaPaz Ice Field (LAP), Graves Nunataks (GRA), Grosvenor Mountains (GRO), Larkman Nunatak (LAR), MacAlpine Hills (MAC), Miller Range (MIL), Roberts Massif (RBT), and Scott Glacier (SCO). These new samples include one iron, 1 eucrite, 1 mesosiderite, 6 CK chondrites (2 with pairing), 2 CV3 chondrites, 1 CM1, 7 CM2 (4 with pairing), 3 CR2 (2 with pairing), and one each of a type 3 L and H chondrites. The CK6 chondrites (LAR 06869, 06872, 06873) are unusual in that they have no discernable chondrules, extremely fine-grained texture, and are full of veins. This newsletter represents a break from recent newsletters in which we have announced many unusual and popular samples, including new lunar and martian meteorites, an unusual achondrite (GRA 06128 and 06129 the topic of a special session at this years LPSC).

  6. Ubiquitous brecciation after metamorphism in equilibrated ordinary chondrites

    Scott, E. R. D.; Lusby, D.; Keil, K.


    Ten objects with aberrant Fe/(Fe + Mg) ratios have been found in apparently unbrecciated types 4-6 H and L chondrites. Since the Fe/(Fe + Mg) ratios of these objects are incompatible with the metamorphic history of the host chondrites, it is concluded that a high proportion of ordinary chondrites are breccias that were lithified after peak metamorphism. This is consistent with the results of Scott (1984), who concluded that most type three ordinary chondrites are breccias of materials with diverse thermal histories, even though they do not show prominent brecciation. It is found that the classification scheme of Van Schmus and Wood (1967) does not identify chondrites with similar thermal histories; the petrologic type of a chondrite is only a measure of the average thermal history of its ingredients. Chondrite and achondrite breccias are also compared in order to understand how brecciation of chondrites after metamorphism is so well camouflaged.

  7. Alkali elements in the Earth's core: Evidence from enstatite meteorites

    Lodders, K.


    The abundances of alkali elements in the Earth's core are predicted by assuming that accretion of the Earth started from material similar in composition to enstatite chondrites and that enstatite achondrites (aubrites) provide a natural laboratory to study core-mantle differentiation under extremely reducing conditions. If core formation on the aubrite parent body is comparable with core formation on the early Earth, it is found that 2600 (+/- 1000) ppm Na, 550 (+/- 260) ppm K, 3.4 (+/- 2.1) ppm Rb, and 0.31 (+/- 0.24) ppm Cs can reside in the Earth's core. The alkali-element abundances are consistent with those predicted by independent estimates based on nebula condensation calculations and heat flow data.

  8. In Situ Analysis of Orthopyroxene in Diogenites Using Laser Ablation ICP-MS

    Elk, Mattias; Quinn, J. E.; Mittlefehldt, D. W.


    Howardites, eucrites and diogenites (HED) form a suit of igneous achondrite meteorites that are thought to have formed on a single asteroidal body. While there have been many different models proposed for the formation of the HED parent asteroid they can be generalized into two end member models. One is the magma ocean model (e.g. [1]) in which the entire HED parent body was continuously fractionated from a planet wide magma ocean with diogenites representing the lower crust and eucrites being upper crustal rocks. The second model hypothesizes that diogenites and eucrites were formed as a series of intrusions and/or extrusions of partial melts of a primitive proto-Vesta [2]. We use in situ trace element analysis together with major and minor element analysis to try and distinguish between these different hypotheses for the evolution of the HED parent body.

  9. Composition of the L5 Mars Trojans: Neighbors, not Siblings

    Rivkin, Andrew S; Thomas, Cristina A; DeMeo, Francesca; Spahr, Timothy B; Binzel, Richard P


    Mars is the only terrestrial planet known to have Tro jan (co-orbiting) asteroids, with a confirmed population of at least 4 objects. The origin of these objects is not known; while several have orbits that are stable on solar-system timescales, work by Rivkin et al. (2003) showed they have compositions that suggest separate origins from one another. We have obtained infrared (0.8-2.5 micron) spectroscopy of the two largest L5 Mars Tro jans, and confirm and extend the results of Rivkin et al. (2003). We suggest that the differentiated angrite meteorites are good spectral analogs for 5261 Eureka, the largest Mars Trojan. Meteorite analogs for 101429 1998 VF31 are more varied and include primitive achondrites and mesosiderites.

  10. Early inner solar system origin for anomalous sulfur isotopes in differentiated protoplanets.

    Antonelli, Michael A; Kim, Sang-Tae; Peters, Marc; Labidi, Jabrane; Cartigny, Pierre; Walker, Richard J; Lyons, James R; Hoek, Joost; Farquhar, James


    Achondrite meteorites have anomalous enrichments in (33)S, relative to chondrites, which have been attributed to photochemistry in the solar nebula. However, the putative photochemical reactions remain elusive, and predicted accompanying (33)S depletions have not previously been found, which could indicate an erroneous assumption regarding the origins of the (33)S anomalies, or of the bulk solar system S-isotope composition. Here, we report well-resolved anomalous (33)S depletions in IIIF iron meteorites (solar system (solar system S-isotope composition was chondritic (consistent with IAB iron meteorites, Earth, Moon, and Mars). The range of mass-independent sulfur isotope compositions may reflect spatial or temporal changes influenced by photochemical processes. A tentative correlation between S isotopes and Hf-W core segregation ages suggests that the two systems may be influenced by common factors, such as nebular location and volatile content.

  11. Meteorite-catalyzed syntheses of nucleosides and of other prebiotic compounds from formamide under proton irradiation.

    Saladino, Raffaele; Carota, Eleonora; Botta, Giorgia; Kapralov, Mikhail; Timoshenko, Gennady N; Rozanov, Alexei Y; Krasavin, Eugene; Di Mauro, Ernesto


    Liquid formamide has been irradiated by high-energy proton beams in the presence of powdered meteorites, and the products of the catalyzed resulting syntheses were analyzed by mass spectrometry. Relative to the controls (no radiation, or no formamide, or no catalyst), an extremely rich, variegate, and prebiotically relevant panel of compounds was observed. The meteorites tested were representative of the four major classes: iron, stony iron, chondrites, and achondrites. The products obtained were amino acids, carboxylic acids, nucleobases, sugars, and, most notably, four nucleosides: cytidine, uridine, adenosine, and thymidine. In accordance with theoretical studies, the detection of HCN oligomers suggests the occurrence of mechanisms based on the generation of radical cyanide species (CN·) for the synthesis of nucleobases. Given that many of the compounds obtained are key components of extant organisms, these observations contribute to outline plausible exogenous high-energy-based prebiotic scenarios and their possible boundary conditions, as discussed.

  12. Noble gas contents of shergottites and implications for the Martian origin of SNC meteorites

    Bogard, D. D.; Nyquist, L. E.; Johnson, P.


    Three meteorites belonging to the rare group of SNC achondrites, which may have originated in the planet Mars, have been subjected to noble gas isotopic concentration measurements. The elemental and isotopic ratios obtained are unlike those for any other noble gas components except those obtained in analyses of the Martian atmosphere by Viking spacecraft. It is hypothesized that the Kr and Xe gases represent a portion of the Martian atmosphere which was shock-implanted in the case of Elephant Moraine A79001, and that they constitute direct evidence of a Martian origin for the shergottite meteorites. If the SNC meteorites were ejected from Mars at the shergottite shock age of about 180 My ago, they must have been objects more than 6 m in diameter which experienced at least three space collisions to initiate cosmic ray exposure.

  13. SNC Meteorites: Atmosphere Implantation Ages and the Climatic Evolution of Mars

    Moyano-Cambero, C. E.; Trigo-Rodríguez, Josep M.; Martín-Torres, F. Javier

    SNC meteorites are Martian rocks that provide valuable information about the atmospheric composition of Mars over time. These meteorites experienced significant shock during the impact that released them from Mars, and during the flight through the Martian atmosphere some of the gases were retained in the melted shock-altered glasses. As using different radiogenic systems can precisely date such shock processes, SNC achondrites can be considered time capsules capable of providing significant insight into the atmospheric evolution of Mars. Different SNCs were released by impacts at different times, having then different atmosphere-implantation ages, so in practice we can obtain clues on the composition of Mars' atmosphere at different times. Taking this information into account, we have developed a 1D model of the evolution of Martian Mars' atmosphere mass, near surface temperature and pressure.

  14. Hungaria asteroid family as the source of aubrite meteorites

    Ćuk, Matija; Gladman, Brett J.; Nesvorný, David


    The Hungaria asteroids are interior to the main asteroid belt, with semimajor axes between 1.8 and 2 AU, low eccentricities and inclinations of 16-35°. Small asteroids in the Hungaria region are dominated by a collisional family associated with (434) Hungaria. The dominant spectral type of the Hungaria group is the E or X-type (Warner et al. [2009]. Icarus, 204, 172-182), mostly due to the E-type composition of Hungaria and its genetic family. It is widely believed the E-type asteroids are related to the aubrite meteorites, also known as enstatite achondrites (Gaffey et al. [1992]. Icarus, 100, 95-109). Here we explore the hypothesis that aubrites originate in the Hungaria family. In order to test this connection, we compare model Cosmic Ray Exposure ages from orbital integrations of model meteoroids with those of aubrites. We show that long CRE ages of aubrites (longest among stony meteorite groups) reflect the delivery route of meteoroids from Hungarias to Earth being different than those from main-belt asteroids. We find that the meteoroids from Hungarias predominantly reach Earth by Yarkovsky-drifting across the orbit of Mars, with no assistance from orbital resonances. We conclude that the CRE ages of aubrites are fully consistent with a dominant source at the inner boundary of the Hungaria family at 1.7 AU. From here, meteoroids reach Earth through the Mars-crossing region, with relatively quick delivery times favored due to collisions (with Hungarias and the inner main-belt objects). We find that, after Vesta, (434) Hungaria is the best candidate for an asteroidal source of an achondrite group.

  15. Geologic History of Asteroid 4 Vesta

    Mittlefehldt, David W.


    Some types of meteorites - most irons, stony irons, some achondrites - hail from asteroids that were heated to the point where magmatism occurred within a very few million years of the formation of the earliest solids in the solar system. The largest clan of achondrites, the howardite, eucrite and diogenite (HED) meteorites, represent the crust of their parent asteroid]. Diogenites are cumulate harzburgites and orthopyroxenites from the lower crust whilst eucrites are basalts, diabases and cumulate gabbros from the upper crust. Howardites are impact-engendered breccias mostly of diogenites and eucrites. There remains only one large asteroid with a basaltic crust, 4 Vesta, which is thought to be the source of the HED clan. Differentiation models for Vesta are based on HED compositions. Proto-Vesta consisted of chondritic materials containing Al-26, a potent, short-lived heat source. Inferences from compositional data are that Vesta was melted to high degree (=50%) allowing homogenization of the silicate phase and separation of a metallic core. Convection of the silicate magma ocean allowed equilibrium crystallization, forming a harzburgitic mantle. After convective lockup occurred, melt collected between the mantle and the cool thermal boundary layer and underwent fractional crystallization forming an orthopyroxene-rich (diogenite) lower crust. The initial thermal boundary layer of chondritic material was replaced by a mafic upper crust through impact disruption and foundering. The mafic crust thickened over time as additional residual magma intrudes and penetrates the mafic crust forming plutons, dikes, sills and flows of cumulate and basaltic eucrite composition. This magmatic history may have taken only 2-3 Myr. This magma ocean scenario is at odds with a model of heat and magma transport that indicates that small degrees of melt would be rapidly expelled from source regions, precluding development of a magma ocean. Constraints from radiogenic Mg-26 distibutions

  16. Khatyrka, a new CV3 find from the Koryak Mountains, Eastern Russia

    MacPherson, Glenn J.; Andronicos, Christopher L.; Bindi, Luca; Distler, Vadim V.; Eddy, Michael P.; Eiler, John M.; Guan, Yunbin; Hollister, Lincoln S.; Kostin, Alexander; Kryachko, Valery; Steinhardt, William M.; Yudovskaya, Marina; Steinhardt, Paul J.


    A new meteorite find, named Khatyrka, was recovered from eastern Siberia as a result of a search for naturally occurring quasicrystals. The meteorite occurs as clastic grains within postglacial clay-rich layers along the banks of a small stream in the Koryak Mountains, Chukotka Autonomous Okrug of far eastern Russia. Some of the grains are clearly chondritic and contain Type IA porphyritic olivine chondrules enclosed in matrices that have the characteristic platy olivine texture, matrix olivine composition, and mineralogy (olivine, pentlandite, nickel-rich iron-nickel metal, nepheline, and calcic pyroxene [diopside-hedenbergite solid solution]) of oxidized-subgroup CV3 chondrites. A few grains are fine-grained spinel-rich calcium-aluminum-rich inclusions with mineral oxygen isotopic compositions again typical of such objects in CV3 chondrites. The chondritic and CAI grains contain small fragments of metallic copper-aluminum-iron alloys that include the quasicrystalline phase icosahedrite. One grain is an achondritic intergrowth of Cu-Al metal alloys and forsteritic olivine ± diopsidic pyroxene, both of which have meteoritic (CV3-like) oxygen isotopic compositions. Finally, some grains consist almost entirely of metallic alloys of aluminum + copper ± iron. The Cu-Al-Fe metal alloys and the alloy-bearing achondrite clast are interpreted to be an accretionary component of what otherwise is a fairly normal CV3 (oxidized) chondrite. This association of CV3 chondritic grains with metallic copper-aluminum alloys makes Khatyrka a unique meteorite, perhaps best described as a complex CV3 (ox) breccia.

  17. Mercury (Hg) in meteorites: Variations in abundance, thermal release profile, mass-dependent and mass-independent isotopic fractionation

    Meier, Matthias M. M.; Cloquet, Christophe; Marty, Bernard


    We have measured the concentration, isotopic composition and thermal release profiles of Mercury (Hg) in a suite of meteorites, including both chondrites and achondrites. We find large variations in Hg concentration between different meteorites (ca. 10 ppb to 14,000 ppb), with the highest concentration orders of magnitude above the expected bulk solar system silicates value. From the presence of several different Hg carrier phases in thermal release profiles (150-650 °C), we argue that these variations are unlikely to be mainly due to terrestrial contamination. The Hg abundance of meteorites shows no correlation with petrographic type, or mass-dependent fractionation of Hg isotopes. Most carbonaceous chondrites show mass-independent enrichments in the odd-numbered isotopes 199Hg and 201Hg. We show that the enrichments are not nucleosynthetic, as we do not find corresponding nucleosynthetic deficits of 196Hg. Instead, they can partially be explained by Hg evaporation and redeposition during heating of asteroids from primordial radionuclides and late-stage impact heating. Non-carbonaceous chondrites, most achondrites and the Earth do not show these enrichments in vapor-phase Hg. All meteorites studied here have however isotopically light Hg (δ202Hg = ∼-7 to -1) relative to the Earth's average crustal values, which could suggest that the Earth has lost a significant fraction of its primordial Hg. However, the late accretion of carbonaceous chondritic material on the order of ∼2%, which has been suggested to account for the water, carbon, nitrogen and noble gas inventories of the Earth, can also contribute most or all of the Earth's current Hg budget. In this case, the isotopically heavy Hg of the Earth's crust would have to be the result of isotopic fractionation between surface and deep-Earth reservoirs.

  18. The iron isotope composition of enstatite meteorites: Implications for their origin and the metal/sulfide Fe isotopic fractionation factor

    Wang, Kun; Savage, Paul S.; Moynier, Frédéric


    Despite their unusual chemical composition, it is often proposed that the enstatite chondrites represent a significant component of Earth’s building materials, based on their terrestrial similarity for numerous isotope systems. In order to investigate a possible genetic relationship between the Fe isotope composition of enstatite chondrites and the Earth, we have analyzed 22 samples from different subgroups of the enstatite meteorites, including EH and EL chondrites, aubrites (main group and Shallowater) and the Happy Canyon impact melt. We have also analyzed the Fe isotopic compositions of separated (magnetic and non-magnetic) phases from both enstatite chondrites and achondrites. On average, EH3-5 chondrites (δ56Fe = 0.003 ± 0.042‰; 2 standard deviation; n = 9; including previous literature data) as well as EL3 chondrites (δ56Fe = 0.030 ± 0.038‰; 2 SD; n = 2) have identical and homogeneous Fe isotopic compositions, indistinguishable from those of the carbonaceous chondrites and average terrestrial peridotite. In contrast, EL6 chondrites display a larger range of isotopic compositions (-0.180‰ < δ56Fe < 0.181‰; n = 11), a result of mixing between isotopically distinct mineral phases (metal, sulfide and silicate). The large Fe isotopic heterogeneity of EL6 is best explained by chemical/mineralogical fragmentation and brecciation during the complex impact history of the EL parent body. Enstatite achondrites (aubrites) also exhibit a relatively large range of Fe isotope compositions: all main group aubrites are enriched in the light Fe isotopes (δ56Fe = -0.170 ± 0.189‰; 2 SD; n = 6), while Shallowater is, isotopically, relatively heavy (δ56Fe = 0.045 ± 0.101‰; 2 SD; n = 4; number of chips). We take this variation to suggest that the main group aubrite parent body formed a discreet heavy Fe isotope-enriched core, whilst the Shallowater meteorite is most likely from a different parent body where core and silicate material remixed. This could be

  19. Proceedings of the 38th Lunar and Planetary Science Conference


    The sessions in the conference include: Titan, Mars Volcanism, Mars Polar Layered Deposits, Early Solar System Isotopes, SPECIAL SESSION: Mars Reconnaissance Orbiter: New Ways of Studying the Red Planet, Achondrites: Exploring Oxygen Isotopes and Parent-Body Processes, Solar System Formation and Evolution, SPECIAL SESSION: SMART-1, . Impact Cratering: Observations and Experiments, SPECIAL SESSION: Volcanism and Tectonism on Saturnian Satellites, Solar Nebula Composition, Mars Fluvial Geomorphology, Asteroid Observations: Spectra, Mostly, Mars Sediments and Geochemistry: View from the Surface, Mars Tectonics and Crustal Dichotomy, Stardust: Wild-2 Revealed, Impact Cratering from Observations and Interpretations, Mars Sediments and Geochemistry: The Map View, Chondrules and Their Formation, Enceladus, Asteroids and Deep Impact: Structure, Dynamics, and Experiments, Mars Surface Process and Evolution, Martian Meteorites: Nakhlites, Experiments, and the Great Shergottite Age Debate, Stardust: Mainly Mineralogy, Astrobiology, Wind-Surface Interactions on Mars and Earth, Icy Satellite Surfaces, Venus, Lunar Remote Sensing, Space Weathering, and Impact Effects, Interplanetary Dust/Genesis, Mars Cratering: Counts and Catastrophes?, Chondrites: Secondary Processes, Mars Sediments and Geochemistry: Atmosphere, Soils, Brines, and Minerals, Lunar Interior and Differentiation, Mars Magnetics and Atmosphere: Core to Ionosphere, Metal-rich Chondrites, Organics in Chondrites, Lunar Impacts and Meteorites, Presolar/Solar Grains, Topics for Print Only papers are: Outer Planets/Satellites, Early Solar System, Interplanetary Dust, Comets and Kuiper Belt Objects, Asteroids and Meteoroids, Chondrites, Achondrites, Meteorite Related, Mars Reconnaissance Orbiter, Mars, Astrobiology, Planetary Differentiation, Impacts, Mercury, Lunar Samples and Modeling, Venus, Missions and Instruments, Global Warming, Education and Public Outreach, Poster sessions are: Asteroids/Kuiper Belt Objects

  20. Partial melting of a C-rich asteroid: Lithophile trace elements in ureilites

    Barrat, Jean-Alix; Jambon, Albert; Yamaguchi, Akira; Bischoff, Addi; Rouget, Marie-Laure; Liorzou, Céline


    Ureilites are among the most common achondrites and are widely believed to sample the mantle of a single, now-disrupted, C-rich body. We analyzed 17 ureilite samples, mostly Antarctic finds, and determined their incompatible trace element abundances. In order to remove or reduce the terrestrial contamination, which is marked among Antarctic ureilites by light-REE enrichment, we leached the powdered samples with nitric acid. The residues display consistent abundances, which strongly resemble those of the pristine rocks. All the analyzed samples display light-REE depletions, negative Eu anomalies, low (Sr/Eu∗)n, and (Zr/Eu∗)n ratios which are correlated. Two groups of ureilites (groups A and B) are defined. Compared to group A, group B ureilites, which are the less numerous, tend to be richer in heavy REEs, more light-REE depleted, and display among the deepest Eu anomalies. In addition, olivine cores in group B ureilites tend to be more forsteritic (Mg# = 81.9-95.2) than in group A ureilites (Mg# = 74.7-86.1). Incompatible trace element systematics supports the view that ureilites are mantle restites. REE modeling suggests that their precursors were rather REE-rich (ca. 1.8-2 × CI) and contained a phosphate phase, possibly merrillite. The REE abundances in ureilites can be explained if at least two distinct types of magmas were removed successively from their precursors: aluminous and alkali-rich melts as exemplified by the Almahata Sitta trachyandesite (ALM-A), and Al and alkali-poor melts produced after the exhaustion of plagioclase from the source. Partial melting was near fractional (group B ureilites, which are probably among the least residual samples) to dynamic with melt porosities that did not exceed a couple of percent (group A ureilites). The ureilite parent body (UPB) was almost certainly covered by a crust formed chiefly from the extrusion products of the aluminous and alkali-rich magmas. It is currently uncertain whether the Al and alkali

  1. Asteroid 4 Vesta: A Fully Differentiated Dwarf Planet

    Mittlefehldt, David


    One conclusion derived from the study of meteorites is that some of them - most irons, stony irons, some achondrites - hail from asteroids that were heated to the point where metallic cores and basaltic crusts were formed. Telescopic observations show that there remains only one large asteroid with a basaltic crust, 4 Vesta; present day mean radius 263 km. The largest clan of achondrites, the howardite, eucrite and diogenite (HED) meteorites, represent the crust of their parent asteroid. Diogenites are cumulate harzburgites and orthopyroxenites from the lower crust whilst eucrites are cumulate gabbros, diabases and basalts from the upper crust. Howardites are impact-engendered breccias of diogenites and eucrites. A strong case can be made that HEDs are derived from Vesta. The NASA Dawn spacecraft orbited Vesta for 14 months returning data allowing geological, mineralogical, compositional and geophysical interpretations of Vesta's surface and structure. Combined with geochemical and petrological observations of HED meteorites, differentiation models for Vesta can be developed. Proto-Vesta probably consisted of primitive chondritic materials. Compositional evidence, primarily from basaltic eucrites, indicates that Vesta was melted to high degree (>=50%) which facilitated homogenization of the silicate phase and separation of immiscible Fe,Ni metal plus Fe sulphide into a core. Geophysical models based on Dawn data support a core of 110 km radius. The silicate melt vigorously convected and initially followed a path of equilibrium crystallization forming a harzburgitic mantle, possibly overlying a dunitic restite. Once the fraction of crystals was sufficient to cause convective lockup, the remaining melt collected between the mantle and the cool thermal boundary layer. This melt undergoes fractional crystallization to form a dominantly orthopyroxenite (diogenite) lower crust. The initial thermal boundary layer of primitive chondritic material is gradually replaced by a

  2. Differentiation of Planetesimals and the Thermal Consequences of Melt Migration

    Moskovitz, Nicholas


    We model the heating of a primordial planetesimal by decay of the short-lived radionuclides Al-26 and Fe-60 to determine (i) the timescale on which melting will occur; (ii) the minimum size of a body that will produce silicate melt and differentiate; (iii) the migration rate of molten material within the interior; and (iv) the thermal consequences of the transport of Al-26 in partial melt. Our models incorporate results from previous studies of planetary differentiation and are constrained by petrologic (i.e. grain size distributions), isotopic (e.g. Pb-Pb and Hf-W ages) and mineralogical properties of differentiated achondrites. We show that formation of a basaltic crust via melt percolation was limited by the formation time of the body, matrix grain size and viscosity of the melt. We show that low viscosity (100 km in size. Differentiation would be mos t likely for planetesimals larger than 20 km in diameter that accreted within ~2.7 Myr of CAI formation.

  3. The effect of temperature and pressure on the distribution of iron group elements between metal and olivine phases in the process of differentiation of protoplanetary material

    Vinogradov, A. P.; Ilyin, N. P.; Kolomeytsava, L. N.


    The distribution patterns of Ni, Co, Mn, and Cr were studied in olivines of various origins: from meteorites (chondrites, achondrites, pallasites), which are likely analogs of the protoplanetary material, to peridotite inclusions in kimberlite pipes, which are analogs of mantle material. According to X-ray microanalysis data, nickel is concentrated in peridotite olivines, while manganese is concentrated in meteoritic olivines. The maximum chromium content was found in ureilites, which were formed under reducing conditions. Experiments at pressures of 20 to 70 kbar and temperatures of 1100 to 2000 C have shown that in a mixture of olivine and Ni metal or NiO, nickel enters the silicate phase, displacing Fe into the metallic phase. Equilibrium temperatures were estimated from the Fe, Ni distribution coefficients between the metal and olivine: 1500 K for pallasites, 1600 K for olivine-bronzite H6 chondrites, 1200 K for olivine-hypersthene L6, 900 K for LL6, and 1900 K for ureilites (at P = 1 atm). The equilibrium conditions of peridotites are close to T = 1800 K and P over 100 kbar. It is concluded that there is a sharp difference between the conditions of differentiation of the protoplanetary material at the time meteorites were formed and the conditions of differentiation of the planets into concentric layers.

  4. Vesta's Elemental Composition

    Prettyman, T. H.; Beck, A. W.; Feldman, W. C.; Lawrence, D. J.; McCoy, T. J.; McSween, H. Y.; Mittlefehldt, D. W.; Peplowski, P. N.; Raymond, C. A.; Reedy, R. C.; Russell, C. T.; Titus, T. N.; Toplis, M. J.; Yamashita, N.


    Many lines of evidence (e.g. common geochemistry, chronology, O-isotope trends, and the presence of different HED rock types in polymict breccias) indicate that the howardite, eucrite, and diogenite (HED) meteorites originated from a single parent body. Meteorite studies show that this protoplanet underwent igneous differentiation to form a metallic core, an ultramafic mantle, and a basaltic crust. A spectroscopic match between the HEDs and 4 Vesta along with a plausible mechanism for their transfer to Earth, perhaps as chips off V-type asteroids ejected from Vesta's southern impact basin, supports the consensus view that many of these achondritic meteorites are samples of Vesta's crust and upper mantle. The HED-Vesta connection was put to the test by the NASA Dawn mission, which spent a year in close proximity to Vesta. Measurements by Dawn's three instruments, redundant Framing Cameras (FC), a Visible-InfraRed (VIR) spectrometer, and a Gamma Ray and Neutron Detector (GRaND), along with radio science have strengthened the link. Gravity measurements by Dawn are consistent with a differentiated, silicate body, with a dense Fe-rich core. The range of pyroxene compositions determined by VIR overlaps that of the howardites. Elemental abundances determined by nuclear spectroscopy are also consistent with HED-compositions. Observations by GRaND provided a new view of Vesta inaccessible by telescopic observations. Here, we summarize the results of Dawn's geochemical investigation of Vesta and their implications.

  5. Genesis of Augite-Bearing Ureilites: Evidence From LA-ICP-MS Analyses of Pyroxenes and Olivine

    Herrin, J. S.; Lee, C-T. A.; Mittlefehldt, D. W.


    Ureilites are ultramafic achondrites composed primarily of coarse-grained low-Ca pyroxene and olivine with interstitial carbonaceous material, but a number of them contain augite [1]. Ureilites are considered to be restites after partial melting of a chondritic precursor, although at least some augite-bearing ureilites may be partially cumulate [1, 2]. In this scenario, the augite is a cumulus phase derived from a melt that infiltrated a restite composed of typical ureilite material (olivine+low-Ca pyroxene) [2]. To test this hypothesis, we examined the major and trace element compositions of silicate minerals in select augite-bearing ureilites with differing mg#. Polished thick sections of the augite-bearing ureilites ALH 84136 , EET 87511, EET 96293, LEW 88201, and META78008 and augite-free typical ureilite EET 90019 were examined by EPMA for major and minor elements and laser ablation ICP-MS (LA-ICP-MS) for trace elements, REE in particular. Although EET 87511 is reported to contain augite, the polished section that we obtained did not.

  6. Highly Siderophile Elements and Osmium Isotope Systematics in Ureilites: Are the Carbonaceous Veins Primary Components?

    Rankenburg, K.; Brandon, A. D.; Humayun, M.


    Ureilites are an enigmatic group of primitive carbon-bearing achondrites of ultramafic composition. The majority of the 143 ureilite meteorites consist primarily of olivine and pyroxene (and occasionally chromite) [1]. They are coarse-grained, slowly cooled, and depleted in incompatible lithophile elements. Minor amounts of dark interstitial material consisting of carbon, metal, sulfides, and fine-grained silicates occur primarily along silicate grain boundaries, but also intrude the silicates along fractures and cleavage planes. Variable degrees of impact shock features have also been imparted on ureilites. The prevailing two origins proposed for these rocks are either as melting residues of carbonaceous chondritic material [2], [3], or alternatively, derivation as mineral cumulates from such melts [4], [5], [6]. It has recently been proposed that ureilites are the residues of a smelting event, i.e. residues of a partial melting event under highly reducing conditions, where a solid Fe-bearing phase reacts with a melt and carbon to form Fe metal and carbon monoxide [7]. Rapid, localized extraction and loss of the basaltic component into space resulting from high eruption velocities could preserve unequilibrated oxygen isotopes and produce the observed olivine-pyroxene residues via 25-30% partial melting of chondritic-like precursor material.

  7. Rubidium isotopic composition of the Earth, meteorites, and the Moon: Evidence for the origin of volatile loss during planetary accretion

    Pringle, Emily A.; Moynier, Frédéric


    Understanding the origin of volatile element variations in the inner Solar System has long been a goal of cosmochemistry, but many early studies searching for the fingerprint of volatile loss using stable isotope systems failed to find any resolvable variations. An improved method for the chemical purification of Rb for high-precision isotope ratio measurements by multi-collector inductively-coupled-plasma mass-spectrometry. This method has been used to measure the Rb isotopic composition for a suite of planetary materials, including carbonaceous, ordinary, and enstatite chondrites, as well as achondrites (eucrite, angrite), terrestrial igneous rocks (basalt, andesite, granite), and Apollo lunar samples (mare basalts, alkali suite). Volatile depleted bodies (e.g. HED parent body, thermally metamorphosed meteorites) are enriched in the heavy isotope of Rb by up to several per mil compared to chondrites, suggesting volatile loss by evaporation at the surface of planetesimals. In addition, the Moon is isotopically distinct from the Moon in Rb. The variations in Rb isotope compositions in the volatile-poor samples are attributed to volatile loss from planetesimals during accretion. This suggests that either the Rb (and other volatile elements) were lost during or following the giant impact or by evaporation earlier during the accretion history of Theia.

  8. U-Pb Dating of Zircons and Phosphates in Lunar Meteorites, Acapulcoites and Angrites

    Zhou, Q.; Zeigler, R. A.; Yin, Q. Z.; Korotev, R. L.; Joliff, B. L.; Amelin, Y.; Marti, K.; Wu, F. Y.; Li, X. H.; Li, Q. L.; Lin, Y. T.; Liu, Y.; Tang, G. Q.


    Zircon U-Pb geochronology has made a great contribution to the timing of magmatism in the early Solar System [1-3]. Ca phosphates are another group of common accessory minerals in meteorites with great potential for U-Pb geochronology. Compared to zircons, the lower closure temperatures of the U-Pb system for apatite and merrillite (the most common phosphates in achondrites) makes them susceptible to resetting during thermal metamorphism. The different closure temperatures of the U-Pb system for zircon and apatite provide us an opportunity to discover the evolutionary history of meteoritic parent bodies, such as the crystallization ages of magmatism, as well as later impact events and thermal metamorphism. We have developed techniques using the Cameca IMS-1280 ion microprobe to date both zircon and phosphate grains in meteorites. Here we report U-Pb dating results for zircons and phosphates from lunar meteorites Dhofar 1442 and SaU 169. To test and verify the reliability of the newly developed phosphate dating technique, two additional meteorites, Acapulco, obtained from Acapulco consortium, and angrite NWA 4590 were also selected for this study as both have precisely known phosphate U-Pb ages by TIMS [4,5]. Both meteorites are from very fast cooled parent bodies with no sign of resetting [4,5], satisfying a necessity for precise dating.

  9. Thulium anomalies and rare earth element patterns in meteorites and Earth: Nebular fractionation and the nugget effect

    Dauphas, N


    This study reports the bulk rare earth element (REEs, La-Lu) compositions of 41 chondrites, including 32 falls and 9 finds from carbonaceous (CI, CM, CO and CV), enstatite (EH and EL) and ordinary (H, L and LL) groups, as well as 2 enstatite achondrites (aubrite). The CI-chondrite-normalized REE patterns and Eu anomalies in ordinary and enstatite chondrites show more scatter in more metamorphosed than in unequilibrated chondrites. This is due to parent-body redistribution of the REEs in various carrier phases during metamorphism. The dispersion in REE patterns of equilibrated ordinary chondrites is explained by the nugget effect associated with concentration of REEs in minor phosphate grains. Terrestrial rocks and samples from ordinary and enstatite chondrites display negative Tm anomalies of ~-4.5 % relative to ca chondrites. In contrast, CM, CO and CV (except Allende) show no significant Tm anomalies. Allende CV chondrite shows large excess Tm (~+10 %). These anomalies are similar to those found in group II...

  10. Evidence for a Single Ureilite Parent Asteroid from a Petrologic Study of Polymict Ureilites

    Downes, Hilary; Mittlefehldt, David W.


    Ureilites are ultramafic achondrites composed of olivine and pyroxene, with minor elemental C, mostly as graphite [1]. The silicate composition indicates loss of a basaltic component through igneous processing, yet the suite is very heterogeneous in O isotopic composition inherited from nebular processes [2]. Because of this, it has not yet been established whether ureilites were derived from a single parent asteroid or from multiple parents. Most researchers tacitly assume a single parent asteroid, but the wide variation in mineral and oxygen isotope compositions could be readily explained by an origin in multiple parent asteroids that had experienced a similar evolution. Numerous ureilite meteorites have been found in Antarctica, among them several that are clearly paired (Fig. 1) and two that are strongly brecciated (EET 83309, EET 87720). We have begun a detailed petrologic study of these latter two samples in order to characterize the range of materials in them. One goal is to attempt to determine whether ureilites were derived from a single parent asteroid.

  11. Lunar and Meteorite Sample Disk for Educators

    Foxworth, Suzanne; Luckey, M.; McInturff, B.; Allen, J.; Kascak, A.


    NASA Johnson Space Center (JSC) has the unique responsibility to curate NASA's extraterrestrial samples from past and future missions. Curation includes documentation, preservation, preparation and distribution of samples for research, education and public outreach. Between 1969 and 1972 six Apollo missions brought back 382 kilograms of lunar rocks, core and regolith samples, from the lunar surface. JSC also curates meteorites collected from a US cooperative effort among NASA, the National Science Foundation (NSF) and the Smithsonian Institution that funds expeditions to Antarctica. The meteorites that are collected include rocks from Moon, Mars, and many asteroids including Vesta. The sample disks for educational use include these different samples. Active relevant learning has always been important to teachers and the Lunar and Meteorite Sample Disk Program provides this active style of learning for students and the general public. The Lunar and Meteorite Sample Disks permit students to conduct investigations comparable to actual scientists. The Lunar Sample Disk contains 6 samples; Basalt, Breccia, Highland Regolith, Anorthosite, Mare Regolith and Orange Soil. The Meteorite Sample Disk contains 6 samples; Chondrite L3, Chondrite H5, Carbonaceous Chondrite, Basaltic Achondrite, Iron and Stony-Iron. Teachers are given different activities that adhere to their standards with the disks. During a Sample Disk Certification Workshop, teachers participate in the activities as students gain insight into the history, formation and geologic processes of the moon, asteroids and meteorites.

  12. REE Partition Coefficients from Synthetic Diogenite-Like Enstatite and the Implications of Petrogenetic Modeling

    Schwandt, C. S.; McKay, G. A.


    Determining the petrogenesis of eucrites (basaltic achondrites) and diogenites (orthopyroxenites) and the possible links between the meteorite types was initiated 30 years ago by Mason. Since then, most investigators have worked on this question. A few contrasting theories have emerged, with the important distinction being whether or not there is a direct genetic link between eucrites and diogenites. One theory suggests that diogenites are cumulates resulting from the fractional crystallization of a parent magma with the eucrites crystallizing, from the residual magma after separation from the diogenite cumulates. Another model proposes that diogenites are cumulates formed from partial melts derived from a source region depleted by the prior generation of eucrite melts. It has also been proposed that the diogenites may not be directly linked to the eucrites and that they are cumulates derived from melts that are more orthopyroxene normative than the eucrites. This last theory has recently received more analytical and experimental support. One of the difficulties with petrogenetic modeling is that it requires appropriate partition coefficients for modeling because they are dependent on temperature, pressure, and composition. For this reason, we set out to determine minor- and trace-element partition coefficients for diogenite-like orthopyroxene. We have accomplished this task and now have enstatite/melt partition coefficients for Al, Cr, Ti, La, Ce, Nd, Sm, Eu, Dy, Er, Yb, and La.

  13. Oriented Mineral Transformation in a Dark Inclusion from the Leoville Meteorite

    Buchanan, P. C.; Zolensky, M. E.; Weisberg, M. K.; Hagiya, K.; Mikouchi, T.; Takenouchi, A.; Hasegawa, H.; Ono, H.; Higashi, K.; Ohsumi, K.


    Dark inclusions (DIs) in chondrites and achondrites are dark gray to black fragments that include a wide variety of materials that have experienced very different petrologic histories. Based on the law of inclusions, they are rocks that accreted prior to and are older than their host meteorites and possibly rep-resent an earlier generation of material. The origin of these inclusions and their relationship to their host meteorites is not always clear. They are interesting in that they represent lithologies that experienced different parent body histories than their host meteorites and are either exotic components or originated from different regions of the meteorite parent body. In many cases, DIs in CV chondrites have been altered to greater degrees than their host meteorites suggesting pre accretionary alteration [e.g., 1,2,3]. There is debate concerning whether or not these DIs record an earlier era of aqueous alteration and subsequent thermal metamorphism, and how these processes may have also affected the host CV materials. The present study is a description of a dark inclusion found in the Leoville meteorite (specifically, thin section USNM 3535-1). This inclusion has some interesting features that have considerable relevance for this discussion.

  14. A Martian origin for the Mars Trojan asteroids

    Polishook, D.; Jacobson, S. A.; Morbidelli, A.; Aharonson, O.


    Seven of the nine known Mars Trojan asteroids belong to an orbital cluster1,2 named after its largest member, (5261) Eureka. Eureka is probably the progenitor of the whole cluster, which formed at least 1 Gyr ago3. It has been suggested3 that the thermal YORP (Yarkovsky-O'Keefe-Radzievskii-Paddack) effect spun up Eureka, resulting in fragments being ejected by the rotational-fission mechanism. Eureka's spectrum exhibits a broad and deep absorption band around 1 μm, indicating an olivine-rich composition4. Here we show evidence that the Trojan Eureka cluster progenitor could have originated as impact debris excavated from the Martian mantle. We present new near-infrared observations of two Trojans ((311999) 2007 NS2 and (385250) 2001 DH47) and find that both exhibit an olivine-rich reflectance spectrum similar to Eureka's. These measurements confirm that the progenitor of the cluster has an achondritic composition4. Olivine-rich reflectance spectra are rare amongst asteroids5 but are seen around the largest basins on Mars6. They are also consistent with some Martian meteorites (for example, Chassigny7) and with the material comprising much of the Martian mantle8,9. Using numerical simulations, we show that the Mars Trojans are more likely to be impact ejecta from Mars than captured olivine-rich asteroids transported from the main belt. This result directly links specific asteroids to debris from the forming planets.

  15. Hungaria Asteroid Family as the Source of Aubrite Meteorites

    Ćuk, Matija; Nesvorný, David


    The Hungaria asteroids are interior to the main asteroid belt, with semimajor axes between 1.8 and 2 AU, low eccentricities and inclinations of 16-35 degrees. Small asteroids in the Hungaria region are dominated by a collisional family associated with (434) Hungaria. The dominant spectral type of the Hungaria group is the E or X-type (Warner et al, 2009), mostly due to the E-type composition of Hungaria and its genetic family. It is widely believed the E-type asteroids are related to the aubrite meteorites, also known as enstatite achondrites (Gaffey et al, 1992). Here we explore the hypothesis that aubrites originate in the Hungaria family. In order to test this connection, we compare model Cosmic Ray Exposure ages from orbital integrations of model meteoroids with those of aubrites. We show that long CRE ages of aubrites (longest among stony meteorite groups) reflect the delivery route of meteoroids from Hungarias to Earth being different than those from main-belt asteroids. We find that the meteoroids from...

  16. Iodine-xenon analysis of ordinary chondrite halide: implications for early solar system water

    Busfield, A.; Gilmour, J. D.; Whitby, J. A.; Turner, G.


    We report the results of iodine-xenon analyses of irradiated halide grains extracted from the H-chondrite Monahans (1998) and compare them with those from Zag ( Whitby et al., 2000) to address the timing of aqueous processing on the H-chondrite parent body. Xe isotopic analyses were carried out using the RELAX mass spectrometer with laser stepped heating. The initial 129I/ 127I ratio in the Monahans halide was determined to be (9.37 ± 0.06) × 10 -5 with an iodine concentration of ˜400 ppb. Significant scatter, especially in the Zag data, indicates that a simple interpretation as a formation age is unreliable. Instead we propose a model whereby halide minerals in both meteorites formed ˜5 Ma after the enstatite achondrite Shallowater (at an absolute age of 4559 Ma). This age is in agreement with the timing of aqueous alteration on the carbonaceous chondrite parent bodies and ordinary chondrite metamorphism and is consistent with the decay of 26Al as a heat source for heating and mobilisation of brines on the H-chondrite parent body. Post accretion surface impact events may have also contributed to the heat source.

  17. Assessing the Behavior of Typically Lithophile Elements Under Highly Reducing Conditions Relevant to the Planet Mercury

    Rowland, Rick, II; Vander Kaaden, Kathleen E.; McCubbin, Francis M.; Danielson, Lisa R.


    With the data returned from the MErcury Surface, Space ENvironment, GEochemistry, and Ranging (MESSENGER) mission, there are now numerous constraints on the physical and chemical properties of Mercury, including its surface composition (e.g., Evans et al. 2012; Nittler et al. 201 l; Peplowski et al. 2012; Weider et al. 2012). The high Sand low FeO contents observed from MESSENGER on the planet's surface suggests a low oxygen fugacity of the present planetary materials. Estimates of the oxygen fugacity for Mercurian magmas are approximately 3- 7 log units below the Iron-Wiistite (Fe-FeO) oxygen buffer (McCubbin et al. 2012; Zolotov et al. 2013), several orders of magnitude more reducing than other terrestrial bodies we have data from such as the Earth, Moon, or Mars (Herd 2008; Sharp, McCubbin, and Shearer 2013; Wadhwa 2008). Most of our understanding of elemental partitioning behavior comes from observations made on terrestrial rocks, but Mercury's oxygen fugacity is far outside the conditions of those samples. With limited oxygen available, lithophile elements may instead exhibit chalcophile, halophile, or siderophile behaviors. Furthermore, very few natural samples of rocks that formed under reducing conditions are available in our collections (e.g., enstatite chondrites, achondrites, aubrites). The goal of this study is to conduct experiments at high pressure and temperature conditions to determine the elemental partitioning behavior of typically lithophile elements as a function of decreasing oxygen fugacity.

  18. Si isotope homogeneity of the solar nebula

    Pringle, Emily A.; Savage, Paul S.; Moynier, Frédéric [Department of Earth and Planetary Sciences and McDonnell Center for the Space Sciences, Washington University in St. Louis, One Brookings Drive, St. Louis, MO 63130 (United States); Jackson, Matthew G. [Department of Earth Science, University of California, Santa Barbara, CA 93109 (United States); Barrat, Jean-Alix, E-mail:, E-mail:, E-mail:, E-mail:, E-mail:, E-mail: [Université Européenne de Bretagne, Université de Brest, CNRS UMR 6538 (Domaines Océaniques), I.U.E.M., Place Nicolas Copernic, F-29280 Plouzané Cedex (France)


    The presence or absence of variations in the mass-independent abundances of Si isotopes in bulk meteorites provides important clues concerning the evolution of the early solar system. No Si isotopic anomalies have been found within the level of analytical precision of 15 ppm in {sup 29}Si/{sup 28}Si across a wide range of inner solar system materials, including terrestrial basalts, chondrites, and achondrites. A possible exception is the angrites, which may exhibit small excesses of {sup 29}Si. However, the general absence of anomalies suggests that primitive meteorites and differentiated planetesimals formed in a reservoir that was isotopically homogenous with respect to Si. Furthermore, the lack of resolvable anomalies in the calcium-aluminum-rich inclusion measured here suggests that any nucleosynthetic anomalies in Si isotopes were erased through mixing in the solar nebula prior to the formation of refractory solids. The homogeneity exhibited by Si isotopes may have implications for the distribution of Mg isotopes in the solar nebula. Based on supernova nucleosynthetic yield calculations, the expected magnitude of heavy-isotope overabundance is larger for Si than for Mg, suggesting that any potential Mg heterogeneity, if present, exists below the 15 ppm level.

  19. Petrology and Geochemistry of New Ureilites and Ureilite Genesis

    Mittlefehldt, David W.; Herrin, J. S.; Downes, H.


    Ureilites are C-bearing, basalt-depleted olivine+pyroxene achondrites from a differentiated asteroid. The group is heterogeneous, exhibiting ranges in O isotopic composition, Fe/Mg, Fe/Mn, pyx/ol, siderophile and lithophile trace element content, and C content and isotopic composition [1]. Some of these characteristics are nebular in origin; others were strongly overprinted by asteroidal igneous processes. The consensus view is that most ureilites are melt-residues, but some are partial cumulates or have interacted with a melt [1,2]. An "unroofing" event occurred while the parent asteroid was hot that froze in mineral core com-positions and resulted in FeO reduction at olivine grain margins. We have studied several new ureilites, but will focus here on two anomalous stones; LAR 04315 and NWA 1241. LAR 04315 is texturally unusual. It contains olivine with angular subdomains, and low-Ca pyroxene riddled with wormy inclusions of metal+troilite, graphite, and possibly other phases, and irregular inclusions of high-Ca pyroxene. Reduction occurred along olivine grain margins and internal fractures, but not along subdomain boundaries. Although texturally odd, LAR 04351 is a typical ureilite in mineral and bulk composition. The olivine is Fo80.8 and falls on the ureilite Fe/Mn-Fe/Mg trend. Its olivine composition falls within the range of the majority of ureilites, and it is typical of these ureilites in bulk rock lithophile and siderophile element contents.

  20. Abundance, distribution, and origin of 60Fe in the solar protoplanetary disk

    Tang, Haolan; 10.1016/j.epsl.2012.10.011


    Meteorites contain relict decay products of short-lived radionuclides that were present in the protoplanetary disk when asteroids and planets formed. Several studies reported a high abundance of 60Fe (t1/2=2.62+/-0.04 Myr) in chondrites (60Fe/56Fe~6*10-7), suggesting that planetary materials incorporated fresh products of stellar nucleosynthesis ejected by one or several massive stars that exploded in the vicinity of the newborn Sun. We measured 58Fe/54Fe and 60Ni/58Ni isotope ratios in whole rocks and constituents of differentiated achondrites (ureilites, aubrites, HEDs, and angrites), unequilibrated ordinary chondrites Semarkona (LL3.0) and NWA 5717 (ungrouped petrologic type 3.05), metal-rich carbonaceous chondrite Gujba (CBa), and several other meteorites (CV, EL H, LL chondrites; IIIAB, IVA, IVB iron meteorites). We derive from these measurements a much lower initial 60Fe/56Fe ratio of (11.5+/-2.6)*10-9 and conclude that 60Fe was homogeneously distributed among planetary bodies. This low ratio is consist...

  1. Potassium-bearing Iron-Nickel Sulfides in Nature and High-Pressure Experiments: Geochemical Consequences of Potassium in the Earth's Core

    Keshav, S.; Corgne, A.; McDonough, W. F.; Fei, Y.


    Introduction: Potassium (K) as a large ion lithophile element has dominantly been concentrated in the Earth s crust and the mantle through differentiation, and in the form of K-40 contributes to the planet s heat budget. However, whether or not K also enters core-forming phases, has been debated for over three decades. Arguments favoring entry of K in the core are based on: (1) K-sulfide (with Fe, Ni, Cu, Na, and Cl; djerfisherite) found in highly reduced enstatite chondrites (or aubrites, enstatite achondrites); (2) demonstration that K, owing to an s-d electronic switch at high-pressure, exhibits transition- element like character, (3) solubility of measurable K in Fe-Ni-S liquids at high pressure, temperature conditions, and (4) models of cooling of the core that seem to require, besides convection, some form of radioactivity, and thus lending support to the experimental work. In this contribution, we assess the effect of sequestering K in the core, as it is perhaps an element that is a key to reconciling geochemistry, paleomagnetism, accretion, and thermal evolution models for the planet.

  2. Minor elements in relict olivine grains of deep-sea spheres: Match with Mg-rich olivines from C2 meteorites

    Smith, J. V.; Steele, I. M.; Brownlee, D. E.


    The bulk composition and relict minerals of meteoroid ablation spheres from deep sea sediments can be related to the parental material, and bulk compositions and elemental ratios favor a CI/CM affinity for most spheres. Although largely melted, some deep sea spheres (DSS) have retained rare grains apparently unmodified chemically by ablation heating or seawater alteration. Minor elements in relict olivines for comparison with compositions of olivines in known meteorites were analyzed. All relict olivines are very Mg rich. No terrestrial olivines match the chemical features which reinforces other evidence for an extraterrestrial origin. There is no match with achondritic olivines. Mg rich olivines occur in all types of carbonaceous meteorites, but the minor elements of most DSS olivines do not match with those for Allende (C3) olivines, and fit poorly with those of Murchison (C2) olivines. There is a good fit for Fe and Cr with those of the olivines in the unusual Belgica 7904 (C2) meteorite (3). It seems likely that the relict olivines of at least many deep sea spheres are chemically related to olivines in at least one C2 meteorite.

  3. Radioelements on Vesta: An Update

    Prettyman, T. H.; Yamashita, N.; Reedy, R. C.; McSween, H. Y.; Mittlefehldt, D. W.


    The main-belt asteroid 4 Vesta is the putative parent body of the howardite, eucrite, and diogenite (HED) meteorites. Because these achondrites have similar petrology, geochemistry, chronology, and O-isotope compositions, it is thought that most HEDs originated from a single parent body. The connection to Vesta is supported by a close spectroscopic match between Vesta and the HEDs and a credible mechanism for their delivery to Earth. Studies of the HEDs show that Vesta underwent igneous differentiation, forming a Fe-rich core, ultramafic mantle, and basaltic crust. Here we present the results of peak analyses applied to a gamma ray difference spectrum to determine the absolute abundances of K and Th. Data are compared to meteorite whole-rock compositions and other inner solar system bodies. The results, while preliminary, represent our present best estimates for these elements. Because the element signatures are near detection limits and not fully resolved, further analysis (e.g. using spectral unmixing) will be required for improved accuracy and to characterize systematic errors.

  4. On the puzzle of space weathering alteration of basaltic asteroids

    Marchi, S; Lazzarin, M; Magrin, S


    The majority of basaltic asteroids are found in the inner main belt, although a few have also been observed in the outer main belt and near-Earth space. These asteroids -referred to as V-types- have surface compositions that resemble that of the 530km sized asteroid Vesta. Besides the compositional similarity, dynamical evidence also links many V-type asteroids to Vesta. Moreover, Vesta is one of the few asteroids to have been identified as source of specific classes of meteorites, the howardite, eucrite, diogenite achondrites (HEDs). Despite the general consensus on the outlined scenario, several questions remain unresolved. In particular, it is not clear if the observed spectral diversity among Vesta, V-types and HEDs is due to space weathering, as is thought to be the case for S-type asteroids. In this paper, SDSS photometry is used to address the question of whether the spectral diversity among candidate V-types and HEDs can be explained by space weathering. We show that visible spectral slopes of V-types...

  5. A Breccia of Ureilitic and C2 Carbonaceous Chondrite Materials from Almahata Sitta: Implications for the Regolith of Urelitic Asteroids

    Goodrich, C. A.; Fioretti, A. M.; Zolensky, M.; Fries, M.; Shaddad, M.; Kohl, I.; Young, E.; Jenniskens, P.


    The Almahata Sitta (AhS) polymict ureilite is the first meteorite to originate from a spectrally classified asteroid (2008 TC3) [1-3], and provides an unprecedented opportunity to correlate properties of meteorites with those of their parent asteroid. AhS is also unique because its fragments comprise a wide variety of meteorite types. Of approximately140 stones studied to-date, 70% are ureilites (carbon-rich ultramafic achondrites) and 30% are various types of chondrites [4,5]. None of these show contacts between ureilitic and chondritic lithologies. It has been inferred that 2008 TC3 was loosely aggregated, so that it disintegrated in the atmosphere and only its most coherent clasts fell as individual stones [1,3,5]. Understanding the structure and composition of this asteroid is critical for missions to sample asteroid surfaces. We are studying [6] the University of Khartoum collection of AhS [3] to test hypotheses for the nature of 2008 TC3. We describe a sample that consists of both ureilitic and chondritic materials.

  6. Asteroid 2008 TC3 Breakup and Meteorite Fractions

    Goodrich, C.; Jenniskens, P.; Shaddad, M. H.; Zolensky, M. E.; Fioretti, A. M.


    The recovery of meteorites from the impact of asteroid 2008 TC3 in the Nubian Desert of Sudan on October 7, 2008, marked the first time meteorites were collected from an asteroid observed in space by astronomical techniques before impacting. Search teams from the University of Khartoum traced the location of the strewn field and collected about 660 meteorites in four expeditions to the fall region, all of which have known fall coordinates. Upon further study, the Almahata Sitta meteorites proved to be a mixed bag of mostly ureilites (course grained, fine grained, and sulfide-metal assemblages), enstatite chondrites (EL3-6, EH3, EH5, breccias) and ordinary chondrites (H5-6, L4-5). One bencubbinite-like carbonaceous chondrite was identified, as well as one unique Rumuruti-like chondrite and an Enstatite achondrite. New analysis: The analysed meteorites so far suggest a high 30-40 percent fraction of non-ureilites among the recovered samples, but that high fraction does not appear to be in agreement with the meteorites in the University of Khartoum (UoK) collection. Ureilites dominate the meteorites that were recovered by the Sudanese teams. To better understand the fraction of recovered materials that fell to Earth, a program has been initiated to type the meteorites in the UoK collection in defined search areas. At this meeting, we will present some preliminary results from that investigation.

  7. An unusual clast in lunar meteorite MacAlpine Hills 88105: A unique lunar sample or projectile debris?

    Joy, K. H.; Crawford, I. A.; Huss, G. R.; Nagashima, K.; Taylor, G. J.


    Lunar meteorite MacAlpine Hills (MAC) 88105 is a well-studied feldspathic regolith breccia dominated by rock and mineral fragments from the lunar highlands. Thin section MAC 88105,159 contains a small rock fragment, 400 × 350 μm in size, which is compositionally anomalous compared with other MAC 88105 lithic components. The clast is composed of olivine and plagioclase with minor pyroxene and interstitial devitrified glass component. It is magnesian, akin to samples in the lunar High Mg-Suite, and also alkali-rich, akin to samples in the lunar High Alkali Suite. It could represent a small fragment of late-stage interstitial melt from an Mg-Suite parent lithology. However, olivine and pyroxene in the clast have Fe/Mn ratios and minor element concentrations that are different from known types of lunar lithologies. As Fe/Mn ratios are notably indicative of planetary origin, the clast could either (1) have a unique lunar magmatic source, or (2) have a nonlunar origin (i.e., consist of achondritic meteorite debris that survived delivery to the lunar surface). Both hypotheses are considered and discussed.

  8. Petrology of Zircon-Bearing Diogenite Northwest Africa 10666

    Tanner, T. B.; Jeffcoat, C. R.; Righter, M.; Berger, E. L.; Lapen, T. J.; Irving, A. J.; Kuehner, S. M.; Fujihara, G.


    The howardite, eucrite, and diogenite (HED) meteorites are a group of achondrites thought to be derived from the asteroid 4 Vesta, though there is active debate as to whether all diogenites are part of the HED suite. Petrologic investigation of the HED meteorite group provides a means of understanding early planetary differentiation processes and early evolution of planets in our solar system. Diogenites are predominantly coarse grained ortho-pyroxenites with some samples containing appreciable amounts of clinopyroxene, olivine, chromite, and plagioclase. Accessory metal, troilite, and apatite are common. Many diogenites are brecciated, however, there are few poorly to unbrecciated samples. Diogenites are important because they may represent the lower crust of 4 Vesta. Although Mg isotope data indicates that the sources of diogenites are ancient, their crystallization ages are difficult to constrain due to their protracted thermal histories. The limited chronologic data for diogenites also limits the ability to test petrogenetic connections with eucrites and even parent body. A reliable and high closure-temperature isotope system, such as U-Pb in zircon, is needed to address the timing of diogenite igneous crystallization. Description of the textures and mineralogy of diogenites are essential to their classification and understanding their formation, in particular, whether all phases are petrogenetically related. Here, we present detailed petrographic data from a rare zircon-bearing feldspathic diogenite, Northwest Africa (NWA) 10666 and provide textural evidence for igneous crystallization of the zircon.

  9. Evidence of atmospheric sulphur in the martian regolith from sulphur isotopes in meteorites.

    Farquhar, J; Savarino, J; Jackson, T L; Thiemens, M H


    Sulphur is abundant at the martian surface, yet its origin and evolution over time remain poorly constrained. This sulphur is likely to have originated in atmospheric chemical reactions, and so should provide records of the evolution of the martian atmosphere, the cycling of sulphur between the atmosphere and crust, and the mobility of sulphur in the martian regolith. Moreover, the atmospheric deposition of oxidized sulphur species could establish chemical potential gradients in the martian near-surface environment, and so provide a potential energy source for chemolithoautotrophic organisms. Here we present measurements of sulphur isotopes in oxidized and reduced phases from the SNC meteorites--the group of related achondrite meteorites believed to have originated on Mars--together with the results of laboratory photolysis studies of two important martian atmospheric sulphur species (SO2 and H2S). The photolysis experiments can account for the observed sulphur-isotope compositions in the SNC meteorites, and so identify a mechanism for producing large abiogenic 34S fractionations in the surface sulphur reservoirs. We conclude that the sulphur data from the SNC meteorites reflects deposition of oxidized sulphur species produced by atmospheric chemical reactions, followed by incorporation, reaction and mobilization of the sulphur within the regolith.

  10. Extraterrestrial Amino Acids in Ureilites Including Almahata Sitta

    Burton, A. S.; Glavin, D. P.; Callahan, M. P.; Dworkin, J. P.


    Ureilites are a class of meteorites that lack chondrules (achondrites) but have relatively high carbon abundances, averaging approx.3 wt %. Using highly sensitive liquid chromatography coupled with UV fluorescence and time-of-flight mass spectrometry (LC-FD/ToF-MS), it was recently determined that there are amino acids in. fragment 94 of the Almahata Sitta ureilite[l]. Based on the presence of amino acids that are rare in the Earth's biosphere, as well as the near-racemic enantiomeric ratios of marry of the more common amino acids, it was concluded that most of the detected amino acids were indigenous to the meteorite. Although the composition of the Almahata Sitta ureilite appears to be unlike other recovered ureilites, the discovery of amino acids in this meteorite raises the question of whether other ureilites rnav also contain amino acids. Herein we present the results of LC-FDlTo.F-MS analyses of: a sand sample from the Almahata Sitta strewn held, Almahata Sitta fragments 425 (an ordinary H5 chondrite) and 427 (ureilite), as well as an Antarctic ureilite (Allan lulls, ALHA 77257).

  11. Micro-IL and micro-PIXE studies of rich diamond meteorites at Legnaro nuclear microprobe

    Lo Giudice, A. E-mail:; Pratesi, G.; Olivero, P.; Paolini, C.; Vittone, E.; Manfredotti, C.; Sammiceli, F.; Rigato, V


    A combination of micro-ionoluminescence (micro-IL) and micro-PIXE was used to characterize diamond grains inside a type of meteorites known as ureilites. Ureilites are a group of achondrites unique in containing relatively large amounts of carbon occurring as diamond, graphite or lonsdaleite. A shock origin for ureilitic diamonds has been widely accepted though an exact knowledge of the conditions during high-pressure graphite conversion is not yet achieved. Micro-IL is a very powerful technique for material investigation and particularly for diamond analysis. Using this technique we were able to identify the occurrence of the diamond phase inside carbon meteoritic inclusions and to perform micro-PIXE analysis on single diamond grains. In fact, IL in low nitrogen content diamonds is dominated by A-band emission (centered at about 2.9 eV) and so, considering only IL monochromatic map at such a spectral band, it was possible to identify them. By making measurements directly on the meteorites, contamination during chemical extraction processes was avoided and it was possible to study not only the diamond phase, but also its distribution inside carbon inclusions.

  12. Studies on Al Kidirate and Kapoeta meteorites

    Gismelseed, A.M. [Sudan Atomic Energy Commission, Khartoum (Sudan); Khangi, F. [Sudan Atomic Energy Commission, Khartoum (Sudan); Ibrahim, A. [Sudan Atomic Energy Commission, Khartoum (Sudan); Yousif, A.A. [Coll. of Science, Sultan Qaboos Univ., Alkhoud (Oman); Worthing, M.A. [Coll. of Science, Sultan Qaboos Univ., Alkhoud (Oman); Rais, A. [Coll. of Science, Sultan Qaboos Univ., Alkhoud (Oman); Elzain, M.E. [Coll. of Science, Sultan Qaboos Univ., Alkhoud (Oman); Brooks, C.K. [Coll. of Science, Sultan Qaboos Univ., Alkhoud (Oman); Sutherland, H.H. [Coll. of Science, Sultan Qaboos Univ., Alkhoud (Oman)


    Moessbauer spectroscopy (20-300 K), magnetic susceptibility measurements (77-350 K), scanning electron microscopy and X-ray diffraction experiments have been performed on two meteorite samples: one from an old fall (Kapoeta) and another from a very recent fall (Al Kidirate). The two specimens differ in their mineralogy. Chondrules appear to be absent in Kapoeta and it is probably a pyroxene-plagioclase achondrite with ferrohypersthene as the most abundant mineral. On the other hand, the Al Kidirate meteorite is an ordinary chondrite and the specimen consists of olivine, orthopyroxene, troilite and kamacite. The Moessbauer measurements confirm the above characterization, showing a paramagnetic doublet for the Kapoeta sample and at least two paramagnetic doublets and magnetic sextets for the Al Kidirate specimens. The former were assigned to Fe in pyroxene sites, while the latter was assigned to Fe in pyroxene, olivine, Fe-S and Fe-Ni alloys. The difference in the mineralogy of the two meteorites has also been reflected in the temperature-dependent magnetic susceptibility. The magnetization and the hyperfine interaction parameters will be discussed in relation to the mineralogy. (orig.)

  13. SNC meteorites - Clues to Martian petrologic evolution?. [Shergottites, Nakhlites and Chassigny

    Mcsween, H. Y., Jr.


    Shergottites, nakhlites and the Chassigny meteorites (SNC group) may have originated on Mars. The shergottites are medium-grained basalts, the nakhlites are pyroxenites and the Chassigny is a dunite. The SNC group is petrologically diverse but differs from all other known achondrites in terms of mineral chemistry, the redox state, the oxygen isotopic composition and the radiometric ages. The SNC stones are mafic and ultramafic cumulate rocks with mineralogies that indicate rapid cooling and crystallization from tholeiitic magmas which contained water and experienced a high degree of oxidation. The characteristics suggest formation from a large parent body, i.e., a planet, but not earth. The estimated ages for the rocks match the estimated ages for several mapped Martian volcanoes in the Tharsis region. Additionally, the elemental and isotopic abundances of atmospheric gases embedded in melts in the SNC stones match Viking Lander data for the Martian atmosphere. However, reasons are cited for discounting the possibility that a large meteorite(s) collided with Mars about 180 myr ago and served as the mechanism for ejecting the SNC stones to earth.

  14. Origin of igneous meteorites and differentiated asteroids

    Scott, E.; Goldstein, J.; Asphaug, E.; Bottke, W.; Moskovitz, N.; Keil, K.


    Introduction: Igneously formed meteorites and asteroids provide major challenges to our understanding of the formation and evolution of the asteroid belt. The numbers and types of differentiated meteorites and non-chondritic asteroids appear to be incompatible with an origin by fragmentation of numerous Vesta-like bodies by hypervelocity impacts in the asteroid belt over 4 Gyr. We lack asteroids and achondrites from the olivine-rich mantles of the parent bodies of the 12 groups of iron meteorites and the ˜70 ungrouped irons, the 2 groups of pallasites and the 4--6 ungrouped pallasites. We lack mantle and core samples from the parent asteroids of the basaltic achondrites that do not come from Vesta, viz., angrites and the ungrouped eucrites like NWA 011 and Ibitira. How could core samples have been extracted from numerous differentiated bodies when Vesta's basaltic crust was preserved? Where is the missing Psyche family of differentiated asteroids including the complementary mantle and crustal asteroids [1]? Why are meteorites derived from far more differentiated parent bodies than chondritic parent bodies even though C and S class chondritic asteroids dominate the asteroid belt? New paradigm. Our studies of meteorites, impact modeling, and dynamical studies suggest a new paradigm in which differentiated asteroids accreted at 1--2 au less than 2 Myr after CAI formation [2]. They were rapidly melted by 26Al and disrupted by hit-and-run impacts [3] while still molten or semi-molten when planetary embryos were accreting. Metallic Fe-Ni bodies derived from core material cooled rapidly with little or no silicate insulation less than 4 Myr after CAI formation [4]. Fragments of differentiated planetesimals were subsequently tossed into the asteroid belt. Meteorite evidence for early disruption of differentiated asteroids. If iron meteorites were samples of Fe-Ni cores of bodies that cooled slowly inside silicate mantles over ˜50--100 Myr, irons from each core would have

  15. Lunar and Planetary Science XXXVI, Part 19


    The topics include: 1) The abundances of Iron-60 in Pyroxene Chondrules from Unequilibrated Ordinary Chondrites; 2) LL-Ordinary Chondrite Impact on the Moon: Results from the 3.9 Ga Impact Melt at the Landing Site of Appolo 17; 3) Evaluation of Chemical Methods for Projectile Identification in Terrestrial and Lunar Impactites; 4) Impact Cratering Experiments in Microgravity Environment; 5) New Achondrites with High-Calcium Pyroxene and Its implication for Igneous Differentiation of Asteroids; 6) Climate History of the Polar Regions of Mars Deduced form Geologic Mapping Results; 7) The crater Production Function for Mars: A-2 Cumulative Power-Law Slope for Pristine Craters Greater than 5 km in Diameter Based on Crater Distribution for Northern Plains Materials; 8) High Resolution Al-26 Chronology: Resolved Time Interval Between Rim and Interior of a Highly Fractionated Compact Type a CAI from Efremovka; 9) Assessing Aqueous Alteration on Mars Using Global Distributions of K and Th; 10) FeNi Metal Grains in LaPaz Mare Basalt Meteorites and Appolo 12 Basalts; 11) Unique Properties of Lunar Soil for In Situ Resource Utilization on the Moon; 12) U-Pb Systematics of Phosphates in Nakhlites; 13) Measurements of Sound Speed in Granular Materials Simulated Regolith; 14) The Effects of Oxygen, Sulphur and Silicon on the Dihedral Angles Between Fe-rich Liquid Metal and Olivine, Ringwoodite and Silicate Perovskite: Implications for Planetary Core Formation; 15) Seismic Shaking Removal of Craters 0.2-0.5 km in Diameter on Asteroid 433 Eros; 16) Focused Ion Beam Microscoopy of ALH84001 Carbonate Disks; 17) Simulating Micro-Gravity in the Laboratory; 18) Mars Atmospheric Sample Return Instrument Development; 19) Combined Remote LIBS and Raman Spectroscopy Measurements; 20) Unusual Radar Backscatter Properties Along the Northern Rim of Imbrium Basin; 21) The Mars Express/NASAS Project at JPL; 22) The Geology of the Viking 2 Lander Site Revisited; 23) An Impact Genesis for Loki

  16. Proceedings of the 39th Lunar and Planetary Science Conference


    Sessions with oral presentations include: A SPECIAL SESSION: MESSENGER at Mercury, Mars: Pingos, Polygons, and Other Puzzles, Solar Wind and Genesis: Measurements and Interpretation, Asteroids, Comets, and Small Bodies, Mars: Ice On the Ground and In the Ground, SPECIAL SESSION: Results from Kaguya (SELENE) Mission to the Moon, Outer Planet Satellites: Not Titan, Not Enceladus, SPECIAL SESSION: Lunar Science: Past, Present, and Future, Mars: North Pole, South Pole - Structure and Evolution, Refractory Inclusions, Impact Events: Modeling, Experiments, and Observations, Mars Sedimentary Processes from Victoria Crater to the Columbia Hills, Formation and Alteration of Carbonaceous Chondrites, New Achondrite GRA 06128/GRA 06129 - Origins Unknown, The Science Behind Lunar Missions, Mars Volcanics and Tectonics, From Dust to Planets (Planetary Formation and Planetesimals):When, Where, and Kaboom! Astrobiology: Biosignatures, Impacts, Habitability, Excavating a Comet, Mars Interior Dynamics to Exterior Impacts, Achondrites, Lunar Remote Sensing, Mars Aeolian Processes and Gully Formation Mechanisms, Solar Nebula Shake and Bake: Mixing and Isotopes, Lunar Geophysics, Meteorites from Mars: Shergottite and Nakhlite Invasion, Mars Fluvial Geomorphology, Chondrules and Chondrule Formation, Lunar Samples: Chronology, Geochemistry, and Petrology, Enceladus, Venus: Resurfacing and Topography (with Pancakes!), Overview of the Lunar Reconnaissance Orbiter Mission, Mars Sulfates, Phyllosilicates, and Their Aqueous Sources, Ordinary and Enstatite Chondrites, Impact Calibration and Effects, Comparative Planetology, Analogs: Environments and Materials, Mars: The Orbital View of Sediments and Aqueous Mineralogy, Planetary Differentiation, Titan, Presolar Grains: Still More Isotopes Out of This World, Poster sessions include: Education and Public Outreach Programs, Early Solar System and Planet Formation, Solar Wind and Genesis, Asteroids, Comets, and Small Bodies, Carbonaceous

  17. Ultraviolet Spectroscopy of Asteroid(4) Vesta

    Li, Jian-Yang; Bodewits, Dennis; Feaga, Lori M.; Landsman, Wayne; A'Hearn, Michael F.; Mutchler, Max J.; Russell, Christopher T.; McFadden, Lucy A.; Raymond, Carol A.


    We report a comprehensive review of the UV-visible spectrum and rotational lightcurve of Vesta combining new observations by Hubble Space Telescope and Swift with archival International Ultraviolet Explorer observations. The geometric albedos of Vesta from 220 nm to 953 nm arc derived by carefully comparing these observations from various instruments at different times and observing geometries. Vesta has a rotationally averaged geometric albedo of 0.09 at 250 nm, 0.14 at 300 nm, 0.26 at 373 nm, 0.38 at 673 nm, and 0.30 at 950 nm. The linear spectral slope in the ultraviolet displays a sharp minimum ncar sub-Earth longitude of 20deg, and maximum in the eastern hemisphere. This is completely consistent with the distribution of the spectral slope in the visible wavelength. The uncertainty of the measurement in the ultraviolet is approx.20%, and in the visible wavelengths better than 10%. The amplitude of Vesta's rotational lightcurves is approx.10% throughout the range of wavelengths we observed, but is smaller at 950 nm (approx.6%) ncar the 1-micron mafic band center. Contrary to earlier reports, we found no evidence for any difference between the phasing of the ultraviolet and visible/ncar-infrared lightcurves with respect to sub-Earth longitude. Vesta's average spectrum between 220 and 950 nm can well be described by measured reflectance spectra of fine particle howardite-like materials of basaltic achondrite meteorites. Combining this with the in-phase behavior of the ultraviolet, visible. and ncar-infrared lightcurves, and the spectral slopes with respect to the rotational phase, we conclude that there is no global ultraviolet/visible reversal on Vesta. Consequently, this implies lack of global space weathering on Vesta. Keyword,: Asteroid Vesta; Spectrophotometry; Spectroscopy; Ultraviolet observations; Hubble Space Telescope observations

  18. Geochemical identification of projectiles in impact rocks

    Tagle, Roald; Hecht, Lutz


    The three major geochemical methods for impactor identification are evaluated with respect to their potential and limitations with regards to the precise detection and identification of meteoritic material in impactites. The identification of a projectile component in impactites can be achieved by determining certain isotopic and elemental ratios in contaminated impactites. The isotopic methods are based on Os and Cr isotopic ratios. Osmium isotopes are highly sensitive for the detection of minute amounts of extraterrestrial components of even isotopic method requires the relatively highest projectile contamination (several wt%) in order to detect an extraterrestrial component, but may allow the identification of three different groups of extraterrestrial materials, ordinary chondrites, an enstatite chondrites, and differentiated achondrites. A significant advantage of this method is its independence of the target lithology and post-impact alteration. The use of elemental ratios, including platinum group elements (PGE: Os, Ir, Ru, Pt, Rh, Pd), in combination with Ni and Cr represents a very powerful method for the detection and identification of projectiles in terrestrial and lunar impactites. For most projectile types, this method is almost independent of the target composition, especially if PGE ratios are considered. This holds true even in cases of terrestrial target lithologies with a high component of upper mantle material. The identification of the projectile is achieved by comparison of the "projectile elemental ratio" derived from the slope of the mixing line (target-projectile) with the elemental ratio in the different types of possible projectiles (e.g., chondrites). However, this requires a set of impactite samples of various degree of projectile contamination.

  19. Rotationally Resolved Photometry of the V-type Near-Earth Asteroid 4055 Magellan (1985 DO2)

    Garcia, Karen; Truong, T.; Hicks, M. D.; Barajas, T.; Foster, J.


    The Near-Earth Asteroid (NEA) 4055 Magellan was discovered by Glo Helin at Palomar Mountain (IAUC 4638) and was one of the first known minor planets with surface reflectance properties comparable to that of 4 Vesta (Tholen, 1988). Broad-band photometry and near-IR spectroscopy revealed strong 0.9 and 1.9 micron proxene bands, suggesting a compositional similarity of 4055 Magellan with that of 4 Vesta and the basaltic achondrite meteorites (Cruikshank et al. 1991). In anticipation of the Dawn mission to 4 Vesta we obtained 5 partial nights, 2010 August 9/10/12/13/14, of Bessel R photometry of 4055 Magellan at the Jet Propulsion Laboratory Table Mountain 0.6-m telescope (TMO). We measured a synodic period of 7.488+/-0.001 hr, similar to the 7.475+-0.001 hr period obtained by Pravec et al. ( ppravec/newres.txt). Our object exhibited a large lightcurve amplitude (delta_M 0.8 mag) implying a highly elongated shape. We used our TMO photometry and the absolute magnitude as tabulated by the Minor Planet Center to construct a rudimentary solar phase curve. We derived a phase parameter g=0.30, similar to the phase behavior as measured by Pravec and colleagues ( ppravec/neo.html). Our high g implies a shallow solar phase slope, consistent with the object's high albeldo (rho=0.31) obtained from thermal measurements (Delbo et al. 2003). The photometric properties of the V-type 4055 Magellan , such as shallow phase slope and high albedo, are consistent with 4 Vesta, giving us confidence in using NEA vestoids as photometric analogs for 4 Vesta.

  20. Exsolution of ferromagnesian olivine in the Divnoe meteorite

    Petaev, M. I.; Brearley, A. J.


    The Divnoe meteorite is a granoblastic olivine-rich primitive achondrite whose textural and mineralogical characteristics suggest extensive recrystallization during slow cooling in the temperature range from approximately 1000 to approximately 500 C and lower. Olivine grains in this meteorite show a lamellar appearance in BSE images, caused by minor micrometer-scale chemical variations in Fe, Mg, and Mn contents between adjacent lamellae. Ten grains of lamellar olivine were studied in detail by Electron Probe Microanalysis (EPMA) and optical microscopy and two of these by Transmission Electron Microscopy (TEM). The olivine grains studied are essentially free of minor elements (Ti, Al, Cr, Ni, Ca, Na) except for Mn, and fall in the compositional range found by an earlier study. While the compositional ranges of Fe-poor and Fe-rich lamellae overlap, the differences between lamellae richest and poorest in Fe are quite similar, suggestive of their formation by an equilibrium process. Fine-scale microprobing has confirmed earlier compositional data, but has reduced lamella thicknesses to a few micrometers, which is in a good agreement with TEM observations. The structural and compositional data obtained strongly suggest that the lamellar structure in these olivine grains was produced by an exsolution process, which is in qualitative agreement with a recent thermodynamic analysis of phrase relations in the system Mg2SiO4-FeSiO2. Cracks in Fe-rich lamellae could result from expansion during the exsolution process due to the volume difference between Fe-rich and Fe-poor lamellae.

  1. Assessing the Behavior of Typically Lithophile Elements Under Highly Reducing Conditions Relevant to the Planet Mercury

    Rowland, Rick, II; Vander Kaaden, Kathleen E.; McCubbin, Francis M.; Danielson, Lisa R.


    With the data returned from the MErcury Surface, Space ENvironment, GEochemistry, and Ranging (MESSENGER) mission, there are now numerous constraints on the physical and chemical properties of Mercury, including its surface composition. The high Sand low FeO contents observed from MESSENGER suggest a low oxygen fugacity of the present materials on the planet's surface. Most of our understanding of elemental partitioning behavior comes from observations made on terrestrial rocks, but Mercury's oxygen fugacity is far outside the conditions of those samples, estimated at approximately 3-7 log units below the Iron-Wtistite (lW) oxygen buffer, several orders of magnitude more reducing than other terrestrial bodies we have data from. With limited oxygen available, lithophile elements may instead exhibit chalcophile, halophile, or siderophile behaviors. Furthermore, very few natural samples of rocks that formed under reducing conditions (e.g., enstatite chondrites, achondrites, aubrites) are available in our collections for examination of this change in geochemical affinity. Our goal is to determine the elemental partitioning behavior of typically lithophile elements at lower oxygen fugacity as a function of temperature and pressure. Experiments were conducted at I GPa in a 13 mm QUICKpress piston cylinder and at 4 GPa in an 880-ton multianvil press, at temperatures up to 1850degC. The composition of starting materials for the experiments were designed so the final run products contained metal, silicate melt, and sulfide melt phases. Oxygen fugacity was controlled in the experiments by adding silicon metal to the samples, in order to utilize the Si-Si02 buffer, which is approximately 5 log units more reducing than the IW buffer at our temperatures of interest. The target silicate melt composition was diopside (CaMgSi206) because measured surface compositions indicate partial melting of a pyroxene-rich mantle. The results of our experiments will aid in our understanding of

  2. Chromium isotope anomaly in an impactite sample from the El'gygytgyn structure, Russia: Evidence for a ureilite projectile?

    Foriel, Julien; Moynier, Frederic; Schulz, Toni; Koeberl, Christian


    The 3.6 Ma, 18-km-diameter El'gygytgyn impact structure (Arctic Russia) is unique among the currently known terrestrial impact craters in that it is the only one that was formed in acid volcanic rocks. Previous analyses of impactites from El'gygytgyn showed minor enrichments of the siderophile elements, including Ir, which, together with distinct Cr enrichments, gave rise to speculation that an achondritic projectile was involved. We studied the major and trace element composition in samples from the new ICDP drill core obtained near the center of the structure, as well as the chromium isotopic composition of an impact glass sample collected on the surface. Several suevitic breccias from the upper part of the suevite sequence in the drill core show higher Cr and Ni contents compared with felsic volcanic rocks in the lower part of the core and from surface samples. However, it is difficult to unambiguously establish a meteoritic component from trace element data, as input from (rare) mafic target rocks is a possibility. In contrast, the Cr isotopic composition of the impact glass sample yielded a nonterrestrial ɛ54Cr value of -0.72 ± 0.31 (2 std. err.). This negative ɛ54Cr is different from known carbonaceous chondrite values (ɛ54Cr of +0.95 to +1.65), but is nearly identical to reported values for ureilites (approximately -0.77). The value is, however, also within analytical error of eucrites (approximately -0.38) and ordinary chondrites (approximately -0.42). Given the chemical signatures found in previous analyses of El'gytgytgyn impactites and the similarity of our Cr isotopic data to ureilites, we suggest that the impacting asteroid could have been an F-type asteroid of mixed composition, similar to the recent Almahata Sitta fall in Sudan.

  3. s-Process Os isotope enrichment in ureilites by planetary processing

    Goderis, S.; Brandon, A. D.; Mayer, B.; Humayun, M.


    Ubiquitous nucleosynthetic isotope anomalies relative to the terrestrial isotopic composition in Mo, Ru, and other elements are known from both bulk chondrites and differentiated meteorites, but Os isotope ratios reported from such meteorites have been found to be indistinguishable from the terrestrial value. The carriers of s- and r-process Os must thus have been homogeneously distributed in the solar nebula. As large Os isotope anomalies are known from acid leachates and residues of primitive chondrites, the constant relative proportions of presolar s- and r-process carriers in such chondrites must have been maintained during nebular processes. It has long been assumed that partial melting of primitive chondrites would homogenize the isotopic heterogeneity carried by presolar grains. Here, ureilites, carbon-rich ultramafic achondrites dominantly composed of olivine and low-Ca pyroxene, are shown to be the first differentiated bulk Solar System materials for which nucleosynthetic Os isotope anomalies have been identified. These anomalies consist of enrichment in s-process Os heterogeneously distributed in different ureilites. Given the observed homogeneity of Os isotopes in all types of primitive chondrites, this Os isotope variability among ureilites must have been caused by selective removal of s-process-poor Os host phases, probably metal, during rapid localized melting on the ureilite parent body. While Mo and Ru isotope anomalies for all meteorites measured so far exhibit s-process deficits relative to the Earth, the opposite holds for the Os isotope anomalies in ureilites reported here. This might indicate that the Earth preferentially accreted olivine-rich restites and inherited a s-process excess relative to smaller meteorite bodies, consistent with Earth's high Mg/Si ratio and enrichment of s-process nuclides in Mo, Ru, and Nd isotopes. Our new Os isotope results imply that caution must be used when applying nucleosynthetic isotope anomalies as provenance

  4. Stable chromium isotopic composition of meteorites and metal-silicate experiments: Implications for fractionation during core formation

    Bonnand, P.; Williams, H. M.; Parkinson, I. J.; Wood, B. J.; Halliday, A. N.


    We present new mass independent and mass dependent Cr isotope compositions for meteorites measured by double spike thermal ionisation mass spectrometry. Small differences in both mass independent 53Cr and 54Cr relative to the Bulk Silicate Earth are reported and are very similar to previously published values. Carbonaceous chondrites are characterised by an excess in 54Cr compared to ordinary and enstatite chondrites which make mass independent Cr isotopes a useful tool for distinguishing between meteoritic groups. Mass dependent stable Cr isotope compositions for the same samples are also reported. Carbonaceous and ordinary chondrites are identical within uncertainty with average δ53 Cr values of - 0.118 ± 0.040 ‰ and - 0.143 ± 0.074 ‰ respectively. The heaviest isotope compositions are recorded by an enstatite chondrite and a CO carbonaceous chondrite, both of which have relatively reduced chemical compositions implying some stable Cr isotope fractionation related to redox processes in the circumstellar disk. The average δ53 Cr values for chondrites are within error of the estimate for the Bulk Silicate Earth (BSE) also determined by double spiking. The lack of isotopic difference between chondritic material and the BSE provides evidence that Cr isotopes were not fractionated during core formation on Earth. A series of high-pressure experiments was also carried out to investigate stable Cr isotope fractionation between metal and silicate and no demonstrable fractionation was observed, consistent with our meteorites data. Mass dependent Cr isotope data for achondrites suggest that Cr isotopes are fractionated during magmatic differentiation and therefore further work is required to constrain the Cr isotopic compositions of the mantles of Vesta and Mars.

  5. The stable Cr isotopic compositions of chondrites and silicate planetary reservoirs

    Schoenberg, Ronny; Merdian, Alexandra; Holmden, Chris; Kleinhanns, Ilka C.; Haßler, Kathrin; Wille, Martin; Reitter, Elmar


    The depletion of chromium in Earth's mantle (∼2700 ppm) in comparison to chondrites (∼4400 ppm) indicates significant incorporation of chromium into the core during our planet's metal-silicate differentiation, assuming that there was no significant escape of the moderately volatile element chromium during the accretionary phase of Earth. Stable Cr isotope compositions - expressed as the ‰-difference in 53Cr/52Cr from the terrestrial reference material SRM979 (δ53/52CrSRM979 values) - of planetary silicate reservoirs might thus yield information about the conditions of planetary metal segregation processes when compared to chondrites. The stable Cr isotopic compositions of 7 carbonaceous chondrites, 11 ordinary chondrites, 5 HED achondrites and 2 martian meteorites determined by a double spike MC-ICP-MS method are within uncertainties indistinguishable from each other and from the previously determined δ53/52CrSRM979 value of -0.124 ± 0.101‰ for the igneous silicate Earth. Extensive quality tests support the accuracy of the stable Cr isotope determinations of various meteorites and terrestrial silicates reported here. The uniformity in stable Cr isotope compositions of samples from planetary silicate mantles and undifferentiated meteorites indicates that metal-silicate differentiation of Earth, Mars and the HED parent body did not cause measurable stable Cr isotope fractionation between these two reservoirs. Our results also imply that the accretionary disc, at least in the inner solar system, was homogeneous in its stable Cr isotopic composition and that potential volatility loss of chromium during accretion of the terrestrial planets was not accompanied by measurable stable isotopic fractionation. Small but reproducible variations in δ53/52CrSRM979 values of terrestrial magmatic rocks point to natural stable Cr isotope variations within Earth's silicate reservoirs. Further and more detailed studies are required to investigate whether silicate

  6. Geophysics of Small Planetary Bodies

    Asphaug, Erik I.


    As a SETI Institute PI from 1996-1998, Erik Asphaug studied impact and tidal physics and other geophysical processes associated with small (low-gravity) planetary bodies. This work included: a numerical impact simulation linking basaltic achondrite meteorites to asteroid 4 Vesta (Asphaug 1997), which laid the groundwork for an ongoing study of Martian meteorite ejection; cratering and catastrophic evolution of small bodies (with implications for their internal structure; Asphaug et al. 1996); genesis of grooved and degraded terrains in response to impact; maturation of regolith (Asphaug et al. 1997a); and the variation of crater outcome with impact angle, speed, and target structure. Research of impacts into porous, layered and prefractured targets (Asphaug et al. 1997b, 1998a) showed how shape, rheology and structure dramatically affects sizes and velocities of ejecta, and the survivability and impact-modification of comets and asteroids (Asphaug et al. 1998a). As an affiliate of the Galileo SSI Team, the PI studied problems related to cratering, tectonics, and regolith evolution, including an estimate of the impactor flux around Jupiter and the effect of impact on local and regional tectonics (Asphaug et al. 1998b). Other research included tidal breakup modeling (Asphaug and Benz 1996; Schenk et al. 1996), which is leading to a general understanding of the role of tides in planetesimal evolution. As a Guest Computational Investigator for NASA's BPCC/ESS supercomputer testbed, helped graft SPH3D onto an existing tree code tuned for the massively parallel Cray T3E (Olson and Asphaug, in preparation), obtaining a factor xIO00 speedup in code execution time (on 512 cpus). Runs which once took months are now completed in hours.

  7. Late Chondritic Additions and Planet and Planetesimal Growth: Evaluation of Physical and Chemical Mechanisms

    Righter, Kevin


    Studies of terrestrial peridotite and martian and achondritic meteorites have led to the conclusion that addition of chondritic material to growing planets or planetesimals, after core formation, occurred on Earth, Mars, asteroid 4 Vesta, and the parent body of the angritic meteorites [1-4]. One study even proposed that this was a common process in the final stages of growth [5]. These conclusions are based almost entirely on the highly siderophile elements (HSE; Re, Au, Pt, Pd, Rh, Ru, Ir, Os). The HSE are a group of eight elements that have been used to argue for late accretion of chondritic material to the Earth after core formation was complete (e.g., [6]). This idea was originally proposed because the D(metal/silicate) values for the HSE are so high, yet their concentration in the mantle is too high to be consistent with such high Ds. The HSE also are present in chondritic relative abundances and hence require similar Ds if this is the result of core-mantle equilibration. Since the work of [6] there has been a realization that core formation at high PT conditions can explain the abundances of many siderophile elements in the mantle (e.g., [7]), but such detailed high PT partitioning data are lacking for many of the HSE to evaluate whether such ideas are viable for all four bodies. Consideration of other chemical parameters reveals larger problems that are difficult to overcome, but must be addressed in any scenario which calls on the addition of chondritic material to a reduced mantle. Yet these problems are rarely discussed or emphasized, making the late chondritic (or late veneer) addition hypothesis suspect.

  8. The global elemental composition of 433 Eros: First results from the NEAR gamma-ray spectrometer orbital dataset

    Peplowski, Patrick N.


    A primary goal of the Near-Earth Asteroid Rendezvous (NEAR) mission was to compare the elemental composition of the S-type asteroid 433 Eros to the chemical compositions of meteorites, with the specific objective of testing the hypothesis that the S-type asteroids are the source of the ordinary chondrite (OC) meteorites. To that end, NEAR carried an X-ray and Gamma-ray Spectrometer (XGRS) to measure the elemental composition of Eros from orbit. To date, no Eros-originating signal had been reported in GRS orbital measurements, a consequence of NEAR's high orbital altitudes about Eros. A reanalysis of the NEAR GRS orbital dataset, particularly data collected during a series of low-altitude flyovers, has finally revealed the first positively identified gamma-ray signals from Eros. This dataset, which amounts to just 10 h of data collection, was used to produce the first GRS-derived global elemental composition values. Results include the first absolute concentrations of Fe and Th, and the first global K concentration. The data confirm prior conclusions that the elemental composition of Eros' surface is inconsistent with achondritic and volatile-rich carbonaceous chondritic compositions. In contrast, ordinary chondrites, volatile-poor carbonaceous chondrites, and enstatite chondrites have compositions that are consistent with Eros' gamma-ray emissions. When placed in the context of other gamma-ray spectrometer investigations, this analysis indicates that successful gamma-ray spectroscopy investigations require extended periods of time (≥10 days) at orbital altitudes less than or equal to the radius of the target body.

  9. 40 Years of Processing Pieces of Space

    Satterwhite, C. E.; Funk, R. C.; Righter, K.; Harrington, R. H.


    This year marks the 40th year anniversary for the Antarctic Search for Meteorite (ANSMET) program. In 1976, the ANSMET program led the first expedition to Antarctica. The ANSMET program is a US-led field-based science project that recovers meteorite samples from Antarctica. Once a year from late November to late January, a field team consisting of 8 to 12 people, spends 6-8 weeks camping on the ice and collecting meteorites. Since 1976, more than 22,000 meteorite samples have been recovered. These meteorites come from asteroids, planets and other bodies of the solar system. Once collected, the Antarctic meteorites are shipped to NASA/Johnson Space Center (JSC) Houston, TX. in a refrigerated truck and are kept frozen to minimize oxidation until they are ready for initial processing. In Antarctica each meteorite is given a field tag which consists of numbers, once in the lab, this is replaced by an official tag, consisting of the Antarctic field location and year collected. The types and numbers of meteorites that have been classified include 849 carbonaceous chondrites, 135 enstatites, 512 achondrites, 64 stony, 115 irons, 48 others (27 R chondrites, 7 ungrouped), 6,161 H chondrites, 7,668 L chondrites, and 4,589 LL chondrites. Although 80-85 percent of the collected meteorites fall in the ordinary chondrite group, the other approximately 15 percent represent rare types of achondrites and carbonaceous chondrites. These rare meteorites include 25 lunar meteorites, 15 Martian meteorites, scores of various types of carbonaceous chondrites, and unique achondrites. The Antarctic meteorites that have been collected are processed in the Meteorite Processing Lab at JSC in Houston, TX. Initial processing of the meteorites begins with thawing/drying the meteorites in a nitrogen glove box for 24 to 48 hours. The meteorites are then photographed, measured, weighed and a description of the interior and exterior of each meteorite is written. The meteorite is broken and a

  10. Solar wind and other gases in the regoliths of the Pesyanoe parent object and the moon

    Mathew, K. J.; Marti, K.


    We report new data from Pesyanoe-90,1 (dark lithology) on the isotopic signature of solar wind (SW) Xe as recorded in this enstatite achondrite which represents a soil-breccia of an asteroidal regolith. The low temperature (800 deg C) steps define the Pesyanoe-S xenon component, which is isotopically consistent with SW Xe reported for the lunar regolith. This implies that the SW Xe isotopic signature was the same at two distinct solar system locations and, importantly, also at different times of solar irradiation. Further, we compare the calculated average solar wind "SW-Xe" signature to Chass-S Xe, the indigenous Xe observed in SNC (Mars) meteorites. Again, a close agreement between these compositions is observed, which implies that a mass-dependent differential fractionation of Xe between SW-Xe and Chass-S Xe is document a fission component due to extinct 244Pu. Interestingly, the Pesyanoe-F Xe component is revealed only at the highest temperatures (>1200 deg C). The Pesyanoe-F gas reveals Xe isotopic signatures that are consistent with lunar solar energetic particles (SEP) data and may indicate a distinct solar energetic particle radiation as was inferred for the moon. However, we cannot rule out fractionation processes due to parent body processes. We note that ratios 36Ar/38Ar 5 are also consistent with SEP data. Calculated abundances of the fission component correlate well with radiogenic 40Ar concentrations, revealing rather constant 244Pu/K ratios in Pesyanoe, and separates thereof, and indicate that both components were retained. We identify a nitrogen component (15N = 44) of non-solar origin with an isotopic signature distinct from indigenous N (15N = -33). While large excesses at 128Xe and 129Xe are observed in the lunar regolith samples, these excesses in Pesyanoe are small. On the other hand, significant 126Xe isotopic excesses, comparable to relative excesses observed in lunar soils and breccias, are prominent in the intermediate temperature steps of

  11. Variable microstructural response of baddeleyite to shock metamorphism in young basaltic shergottite NWA 5298 and improved U-Pb dating of Solar System events

    Darling, James R.; Moser, Desmond E.; Barker, Ivan R.; Tait, Kim T.; Chamberlain, Kevin R.; Schmitt, Axel K.; Hyde, Brendt C.


    The accurate dating of igneous and impact events is vital for the understanding of Solar System evolution, but has been hampered by limited knowledge of how shock metamorphism affects mineral and whole-rock isotopic systems used for geochronology. Baddeleyite (monoclinic ZrO2) is a refractory mineral chronometer of great potential to date these processes due to its widespread occurrence in achondrites and robust U-Pb isotopic systematics, but there is little understanding of shock-effects on this phase. Here we present new nano-structural measurements of baddeleyite grains in a thin-section of the highly-shocked basaltic shergottite Northwest Africa (NWA) 5298, using high-resolution electron backscattered diffraction (EBSD) and scanning transmission electron microscopy (STEM) techniques, to investigate shock-effects and their linkage with U-Pb isotopic disturbance that has previously been documented by in-situ U-Pb isotopic analyses. The shock-altered state of originally igneous baddeleyite grains is highly variable across the thin-section and often within single grains. Analyzed grains range from those that preserve primary (magmatic) twinning and trace-element zonation (baddeleyite shock Group 1), to quasi-amorphous ZrO2 (Group 2) and to recrystallized micro-granular domains of baddeleyite (Group 3). These groups correlate closely with measured U-Pb isotope compositions. Primary igneous features in Group 1 baddeleyites (n = 5) are retained in high shock impedance grain environments, and an average of these grains yields a revised late-Amazonian magmatic crystallization age of 175 ± 30 Ma for this shergottite. The youngest U-Pb dates occur from Group 3 recrystallized nano- to micro-granular baddeleyite grains, indicating that it is post-shock heating and new mineral growth that drives much of the isotopic disturbance, rather than just shock deformation and phase transitions. Our data demonstrate that a systematic multi-stage microstructural evolution in

  12. Vesta Is Not an Intact Protoplanet

    Consolmagno, Guy; Turrini, Diego; Golabeck, Gregor; Jutzi, Martin; Sirono, Sin-iti; Svetsov, Vladimir; Tsiganis, Kleomenis


    Asteroid 4 Vesta has been identified as the likely source of howardite, eucrite, and diogenite (HED) basaltic achondrite meteorites, whose parent body differentiated and started solidifying within 3 Ma after the condensation of the Ca-Al-rich inclusions (CAIs). The formation of Jupiter and the disk-driven migration of the giant planets also occurred during this period; thus it was expected that Vesta could provide an intact record of large-scale early episodes of planetary migration and bombardment as in the proposed Jovian Early Bombardment and the “Grand Tack” scenarios. However, the results of the Dawn mission detailing Vesta’s mass, volume, density, and surface characteristics provide challenges for modeling the structure and evolution of this asteroid. All proposed models for the generation of the HEDs require the presence of a substantial olivine-rich mantle. But recent work on the depth of excavation of the large basins at the south pole of Vesta suggests that because there is not abundant mantle olivine visible on Vesta or in the Vestoid family asteroids, the crust of Vesta must be at least 80 km thick. Such a thick crust is radically at odds with previous models; should it exist, it ought to manifest itself in other ways such as Vesta’s density structure and bulk chemical composition. However, we find that no Vesta model of iron core, olivine-rich mantle, and HED crust can match the joint constraints of (a) Vesta’s density as derived from the gravity field observed by Dawn; (b) the observed depletion of sodium and potassium and trace element enrichments of the HED meteorites; and (c) the absence of exposed olivine on Vesta’s surface, among Vestoid asteroids, or in our collection of basaltic meteorites. Either Vesta was subjected to a radical change in composition, presumably due to the intense collisional environment where and when it formed, or the asteroid we see today is in fact a reaccretion of material formed elsewhere from now

  13. Curie's hypotheses concerning radioactivity and the origin of the elements

    Kuroda, P.K.


    Pierre Curie gave two hypotheses at first; (1) It can be supposed that the radioactive substances borrow the energy, which they release, from an external radiation, and their radiation would then be a secondary radiation, (2) It can be supposed that the radioactive substances draw from themselves the energy which they release. The second hypothesis has shown the more fertile in explaining the properties of the radioactive substances. Consequently, the first hypothesis became more or less forgotten. It appears, however, the first hypothesis should play an important role in explaining the phenomena concerning the origin of the elements. The Oklo Phenomenon has demonstrated that a nuclear fire had once existed on our planet earth and formation of heavy elements was occurring in nature. The author pointed out that the difference in the isotopic compositions of xenon found in meteorites, lunar samples and in the earth's atmosphere can only be explained as due to the alterations of the isotropic compositions of xenon by combined effect of (a) mass-fractionation, (b) spallation, and (c) stellar temperature neutron-capture reactions. The strange xenon components are not isotopically pure substance. Instead, xenon-HL is a mixture of the {sup 244}Pu fission xenon and the xenon whose isotopic compositions is severely altered by a combined effect of the processes (a), (b) and (c) mentioned above. These results also indicate that C1 carbonaceous chondrites, which is generally as the most primitive sample of the solar system material, began to retain its xenon 5.1 billion years ago, when the plutonium to uranium ratio in the solar system was as high as almost 0.6 (atom/atom), while the C2 carbonaceous chondrite began to retain their xenon about 150 million years later and the ordinary chondrites and achondrite about 500 to 600 million years later. This means that the birth of the solar system began soon after the last supernova exploded about 5.1 billion years ago, and the

  14. Re-analysis of previous laboratory phase curves: 2. Connections between opposition effect morphology and spectral features of stony meteorites

    Déau, Estelle; Spilker, Linda J.; Flandes, Alberto


    We investigate connections between the opposition phase curves and the spectra from ultraviolet to near infrared wavelengths of stony meteorites. We use two datasets: the reflectance dataset of Capaccioni et al. ([1990] Icarus, 83, 325), which consists of optical phase curves (from 2° to 45°) of 17 stony meteorites (three carbonaceous chondrites, 11 ordinary chondrites, and three achondrites), and the spectral dataset from the RELAB database consisting of near-ultraviolet to near-infrared spectra of the same meteorites. We re-analyzed the first dataset and fit it with two morphological models to derive the amplitude A, the angular width HWHM of the surge and the slope S of the linear part. Our re-analysis confirms that stony meteorites have a non-monotonic behavior of the surge amplitude with albedo, which is also observed in planetary surfaces (Déau et al. [2013] Icarus, 226, 1465), laboratory samples (Nelson et al. [2004] Proc. Lunar Sci. Conf., 35, p. 1089) and asteroids (Belskaya and Shevchenko [2000] Icarus, 147, 94). We find a very strong correlation between the opposition effect morphological parameters and the slope of the spectra between 0.75 μm and 0.95 μm. In particular, we found that meteorites with a positive amplitude-albedo correlation have a positive spectral slope between 0.75 μm and 0.95 μm, while meteorites with a negative amplitude-albedo correlation have a negative spectral slope between 0.75 μm and 0.95 μm. We have ruled out the role of the meteorite samples' macro-properties (grain size, porosity and macroscopic roughness) in the correlations found because these properties were constant during the preparation of the samples. If this hypothesis is correct, this implies that other properties like the composition or the micro-properties (grain inclusions, grain shape or microscopic roughness) could have a preponderant role in the non-monotonic behavior of the surge morphology with albedo at small and moderate phase angles. Further

  15. A geochemical study of the winonaites: Evidence for limited partial melting and constraints on the precursor composition

    Hunt, Alison C.; Benedix, Gretchen K.; Hammond, Samantha J.; Bland, Philip A.; Rehkämper, Mark; Kreissig, Katharina; Strekopytov, Stanislav


    The winonaites are primitive achondrites which are associated with the IAB iron meteorites. Textural evidence implies heating to at least the Fe, Ni-FeS cotectic, but previous geochemical studies are ambiguous about the extent of silicate melting in these samples. Oxygen isotope evidence indicates that the precursor material may be related to the carbonaceous chondrites. Here we analysed a suite of winonaites for modal mineralogy and bulk major- and trace-element chemistry in order to assess the extent of thermal processing as well as constrain the precursor composition of the winonaite-IAB parent asteroid. Modal mineralogy and geochemical data are presented for eight winonaites. Textural analysis reveals that, for our sub-set of samples, all except the most primitive winonaite (Northwest Africa 1463) reached the Fe, Ni-FeS cotectic. However, only one (Tierra Blanca) shows geochemical evidence for silicate melting processes. Tierra Blanca is interpreted as a residue of small-degree silicate melting. Our sample of Winona shows geochemical evidence for extensive terrestrial weathering. All other winonaites studied here (Fortuna, Queen Alexander Range 94535, Hammadah al Hamra 193, Pontlyfni and NWA 1463) have chondritic major-element ratios and flat CI-normalised bulk rare-earth element patterns, suggesting that most of the winonaites did not reach the silicate melting temperature. The majority of winonaites were therefore heated to a narrow temperature range of between ∼1220 (the Fe, Ni-FeS cotectic temperature) and ∼1370 K (the basaltic partial melting temperature). Silicate inclusions in the IAB irons demonstrate partial melting did occur in some parts of the parent body (Ruzicka and Hutson, 2010), thereby implying heterogeneous heat distribution within this asteroid. Together, this indicates that melting was the result of internal heating by short-lived radionuclides. The brecciated nature of the winonaites suggests that the parent body was later disrupted by

  16. Meteorite Source Regions as Revealed by the Near-Earth Object Population

    Binzel, Richard P.; DeMeo, Francesca E.; Burt, Brian J.; Polishook, David; Burbine, Thomas H.; Bus, Schelte J.; Tokunaga, Alan; Birlan, Mirel


    Spectroscopic and taxonomic information is now available for 1000 near-Earth objects, having been obtained through both targeted surveys (e.g. [1], [2], [3]) or resulting from all-sky surveys (e.g. [4]). We determine their taxonomic types in the Bus-DeMeo system [5] [6] and subsequently examine meteorite correlations based on spectral analysis (e.g. [7],[8]). We correlate our spectral findings with the source region probabilities calculated using the methods of Bottke et al. [9]. In terms of taxonomy, very clear sources are indicated: Q-, Sq-, and S-types most strongly associated with ordinary chondrite meteorites show clear source signatures through the inner main-belt. V-types are relatively equally balanced between nu6 and 3:1 resonance sources, consistent with the orbital dispersion of the Vesta family. B- and C-types show distinct source region preferences for the outer belt and for Jupiter family comets. A Jupiter family comet source predominates for the D-type near-Earth objects, implying these "asteroidal" bodies may be extinct or dormant comets [10]. Similarly, near-Earth objects falling in the spectrally featureless "X-type" category also show a strong outer belt and Jupiter family comet source region preference. Finally the Xe-class near-Earth objects, which most closely match the spectral properties of enstatite achondrite (aubrite) meteorites seen in the Hungaria region[11], show a source region preference consistent with a Hungaria origin by entering near-Earth space through the Mars crossing and nu6 resonance pathways. This work supported by the National Science Foundation Grant 0907766 and NASA Grant NNX10AG27G.[1] Lazzarin, M. et al. (2004), Mem. S. A. It. Suppl. 5, 21. [2] Thomas, C. A. et al. (2014), Icarus 228, 217. [3] Tokunaga, A. et al. (2006) BAAS 38, 59.07. [4] Hasselmann, P. H., Carvano, J. M., Lazzaro, D. (2011) NASA PDS, EAR-A-I0035-5-SDSSTAX-V1.0. [5] Bus, S.J., Binzel, R.P. (2002). Icarus 158, 146. [6] DeMeo, F.E. et al. (2009), Icarus

  17. Evidence from Polymict Ureilite Meteorites for a Single "Rubble-Pile" Ureilite Parent Asteroid Gardened by Several Distinct Impactors

    Downes, Hilary; Mittlefehldt, David W.; Kita, Noriko T.; Valley, John W.


    Ureilites are ultramafic achondrite meteorites that have experienced igneous processing whilst retaining heterogeneity in mg# and oxygen isotope ratios. Polymict ureilites represent material derived from the surface of the ureilite parent asteroid(s). Electron microprobe analysis of more than 500 olivine and pyroxene clasts in six polymict ureilites reveals that they cover a statistically identical range of compositions to that shown by all known monomict ureilites. This is considered to be convincing evidence for derivation from a single parent asteroid. Many of the polymict ureilites also contain clasts that have identical compositions to the anomalously high Mn/Mg olivines and pyroxenes from the Hughes 009 monomict ureilite (here termed the Hughes cluster ). Four of the six samples also contain distinctive ferroan lithic clasts that have been derived from oxidized impactors. The presence of several common distinctive lithologies within the polymict ureilites is additional evidence that the ureilites were derived from a single parent asteroid. Olivine in a large lithic clast of augite-bearing ureilitic has an mg# of 97, extending the compositional range of known ureilite material. Our study confirms that ureilitic olivine clasts with mg#s 85, which also show more variable Mn contents, including the melt-inclusion bearing "Hughes cluster" ureilites. We interpret this to indicate that the parent ureilite asteroid was disrupted by a major impact at a time when melt was still present in regions with a bulk mg# > 85, giving rise to the two types of ureilites: common ferroan ones that were already residual after melting and less common magnesian ones that were still partially molten when disruption occurred, some of which are the result of interaction of melts with residual mantle during disruption. A single daughter asteroid re-accreted from the disrupted remnants of the mantle of the proto-ureilite asteroid, giving rise to a "rubble-pile" body that had material of a

  18. Oxygen and Magnesium Isotopic Compositions of Asteroidal Materials Returned from Itokawa by the Hayabusa Mission

    Yurimoto, H; Abe, M.; Ebihara, M.; Fujimura, A.; Hashizume, K.; Ireland, T. R.; Itoh, S.; Kawaguchi, K.; Kitajima, F.; Mukai, T.; Nagao, K.; Nakamura, T.; Naraoka, H.; Noguchi, T.; Okazaki, R.; Sakamoto, N.; Seto, Y.; Tsuchiyama, A.; Uesugi, M.; Yada, T.; Yoshikawa, M.; Zolensky, M.


    The Hayabusa spacecraft made two touchdowns on the surface of Asteroid 25143 Itokawa on November 20th and 26th, 2005. The Asteroid 25143 Itokawa is classified as an S-type asteroid and inferred to consist of materials similar to ordinary chondrites or primitive achondrites [1]. Near-infrared spectroscopy by the Hayabusa spacecraft proposed that the surface of this body has an olivine-rich mineral assemblage potentially similar to that of LL5 or LL6 chondrites with different degrees of space weathering [2]. The spacecraft made the reentry into the Earth s atmosphere on June 12th, 2010 and the sample capsule was successfully recovered in Australia on June 13th, 2010. Although the sample collection processes on the Itokawa surface had not been made by the designed operations, more than 1,500 grains were identified as rocky particles in the sample curation facility of JAXA, and most of them were judged to be of extraterrestrial origin, and definitely from Asteroid Itokawa on November 17th, 2010 [3]. Although their sizes are mostly less than 10 microns, some larger grains of about 100 microns or larger were also included. The mineral assembly is olivine, pyroxene, plagioclase, iron sulfide and iron metal. The mean mineral compositions are consistent with the results of near-infrared spectroscopy from Hayabusa spacecraft [2], but the variations suggest that the petrologic type may be smaller than the spectroscopic results. Several tens of grains of relatively large sizes among the 1,500 grains will be selected by the Hayabusa sample curation team for preliminary examination [4]. Each grain will be subjected to one set of preliminary examinations, i.e., micro-tomography, XRD, XRF, TEM, SEM, EPMA and SIMS in this sequence. The preliminary examination will start from the last week of January 2011. Therefore, samples for isotope analyses in this study will start from the last week of February 2011. By the time of the LPSC meeting we will have measured the oxygen and

  19. Heliocentric zoning of the asteroid belt by aluminum-26 heating

    Grimm, R. E.; Mcsween, H. Y., Jr.


    Variations in petrology among meteorites attest to a strong heating event early in solar system history, but the heat source has remained unresolved. Aluminum-26 has been considered the most likely high-energy, short-lived radionuclide (half-life 0.72 million years) since the discovery of its decay product - excess Mg-26 - in Allende CAI's. Furthermore, observation of relict Mg-26 in an achondritic clast and in feldspars within ordinary chondrites (3,4) provided strong evidence for live Al-26 in meteorite parent bodies and not just in refractory nebular condensates. The inferred amount of Al-26 is consistent with constraints on the thermal evolution of both ordinary and carbonaceous chondrite parent objects up to a few hundred kilometers in diameter. Meteorites can constrain the early thermal evolution of their parent body locations, provided that a link can be established between asteroid spectrophotometric signature and meteorite class. Asteroid compositions are heliocentrically distributed: objects thought to have experienced high metamorphic or even melting temperatures are located closer to the sun, whereas apparently unaltered or mildly heated asteroids are located farther away. Heliocentric zoning could be the result of Al-26 heating if the initial amount of the radionuclide incorporated into planetesimals was controlled by accretion time, which in turn varies with semimajor axis. Analytic expressions for planetary accretion may be integrated to given the time, tau, required for a planetesimal to grow to a specified radius: tau varies as a(sup n), where n = 1.5 to 3 depending on the assumptions about variations in the surface density of the planetesimal swarm. Numerical simulations of planetesimal accretion at fixed semimajor axis demonstrate that variations in accretion time among small planetesimals can be strongly nonlinear depending on the initial conditions and model assumptions. The general relationship with semimajor axis remains valid because it

  20. Accretional Impact Melt From the L-Chondrite Parent Body

    Wittmann, A.; Weirich, J. R.; Swindle, T. D.; Rumble, D.; Kring, D. A.


    MIL 05029, a unique achondritic Antarctic meteorite with L-chondritic affinity, has a medium-grained, well equilibrated texture of large poikilitic low-Ca pyroxenes that overgrew smaller, euhedral olivines. Plagioclase filled interstitial spaces and has an abundance that is twice that typical for L-chondrites, while Fe-Ni metal and troilite are strongly depleted in that respect. No relic clasts or shock features were found in the thin section analyzed. However, based on its chemical affinity to L-chondrites, MIL 05029 was classified as an impact melt. This is confirmed by its olivine and low-Ca pyroxene compositions, the Co content in Fe-Ni metal, and its oxygen isotopic composition that lies very close to that of L-chondrites. An igneous origin of MIL 05029 cannot be ruled out but would have to be reconciled with thermochronometric constraints for the formation of the ordinary chondrite parent bodies. These studies infer delayed accretion of the parent asteroids of the ordinary chondrites and, thus, insufficient heating from short-lived radiogenic isotopes to produce endogenic magmatism. Metallographic cooling rates of ˜2-22 °C/Ma in the temperature range between ˜700-400°C were determined on five zoned metal particles of MIL 05029. Thermal modeling showed that such cooling rates relate to metamorphic conditions at depths of 5-12 km on the L-chondrite parent body. For an impact to deposit material at this depth, scaling relationships for an impact event on the 100-200 km diameter parent asteroid require a 15 to 60 km diameter simple crater that produced a basal melt pool, in which MIL 05029 crystallized. Further constraints for the formation conditions of MIL 05029 were derived from three whole-rock samples that gave well-defined Ar-Ar plateau ages of 4.53±0.02 Ga. This age indicates the time at which MIL 05029 cooled below ˜180°C, the Ar-closure temperature of plagioclase. Considering its slow metallographic cooling, the impact event that formed MIL 05029

  1. Highly Reducing Partitioning Experiments Relevant to the Planet Mercury

    Rowland, Rick, II; Vander Kaaden, Kathleen E.; McCubbin, Francis M.; Danielson, Lisa R.


    With the data returned from the MErcury Surface Space ENvironment GEochemistry and Ranging (MESSENGER) mission, there are now numerous constraints on the physical and chemical properties of Mercury, including its surface composition. The high S and low FeO contents observed from MESSENGER on the planet's surface suggests a low oxygen fugacity of the present planetary materials. Estimates of the oxygen fugacity for Mercurian magmas are approximately 3-7 log units below the Iron-Wüstite (Fe-FeO) oxygen buffer, several orders of magnitude more reducing than other terrestrial bodies we have data from such as the Earth, Moon, or Mars. Most of our understanding of elemental partitioning behavior comes from observations made on terrestrial rocks, but Mercury's oxygen fugacity is far outside the conditions of those samples. With limited oxygen available, lithophile elements may instead exhibit chalcophile, halophile, or siderophile behaviors. Furthermore, very few natural samples of rocks that formed under reducing conditions are available in our collections (e.g., enstatite chondrites, achondrites, aubrites). With this limited amount of material, we must perform experiments to determine the elemental partitioning behavior of typically lithophile elements as a function of decreasing oxygen fugacity. Experiments are being conducted at 4 GPa in an 880-ton multi-anvil press, at temperatures up to 1850degC. The composition of starting materials for the experiments were selected for the final run products to contain metal, silicate melt, and sulfide melt phases. Oxygen fugacity is controlled in the experiments by adding silicon metal to the samples, using the Si-SiO2 oxygen buffer, which is approximately 5 log units more reducing than the Fe-FeO oxygen buffer at our temperatures of interest. The target silicate melt compositional is diopside (CaMgSi2O6) because measured surface compositions indicate partial melting of a pyroxene-rich mantle. Elements detected on Mercury

  2. Experimental Constraints on a Vesta Magma Ocean

    Hoff, C.; Jones, J. H.; Le, L.


    A magma ocean model was devised to relate eucrites (basalts) and diogenites (orthopyroxenites), which are found mixed together as clasts in a suite of polymict breccias known as howardites. The intimate association of eucritic and diogenitic clasts in howardites argues strongly that these three classes of achondritic meteorites all originated from the same planetoid. Reflectance spectral evidence (including that from the DAWN mission) has long suggested that Vesta is indeed the Eucrite Parent Body. Specifically, the magma ocean model was generated as follows: (i) the bulk Vesta composition was taken to be 0.3 CV chondrite + 0.7 L chondrite but using only 10% of the Na2O from this mixture; (ii) this composition is allowed to crystallize at 500 bar until approx. 80% of the system is solid olivine + low-Ca pyroxene; (iii) the remaining 20% liquid crystallizes at one bar from 1250C to 1110C, a temperature slightly above the eucrite solidus. All crystallization calculations were performed using MELTS. In this model, diogenites are produced by cocrystallization of olivine and pyroxene in the >1250C temperature regime, with Main Group eucrite liquids being generated in the 1300-1250C temperature interval. Low-Ca pyroxene reappears at 1210C in the one-bar calculations and fractionates the residual liquid to produce evolved eucrite compositions (Stannern Trend). We have attempted to experimentally reproduce the Vesta magma ocean. In the MELTS calculation, the change from 500 bar to one bar results in a shift of the olivine:low-Ca pyroxene boundary so that the 1250C liquid is now in the olivine field and, consequently, olivine should be the first-crystallizing phase, followed by low-Ca pyroxene at 1210C, and plagioclase at 1170C. Because at one bar the olivine:low-Ca pyroxene boundary is a peritectic, fractional crystallization of the 1210C liquid proceeds with only pyroxene crystallization until plagioclase appears. Thus, the predictions of the MELTS calculation are clear

  3. Light element controlled iron isotope fractionation in planetary cores

    Shahar, A.; Hillgren, V. J.; Horan, M. F.; Duke, L.; Mock, T. D.


    Using iron isotope fractionations measured in planetary and meteorite samples to trace planetary differentiation or formation has yielded contradictory results. Iron from high-Ti lunar basalts is more enriched in 57Fe/54Fe than mantle-derived terrestrial samples, in contrast to the isotopic similarity for almost every other element between the Earth and Moon. SNC (Shergottite, Nakhlite, Chassigny) and HED (Howardite, Eucrite, Diogenite) meteorites, which are thought to be derived from the mantles of Mars and Vesta, respectively, show no isotopic fractionation relative to chondrites. While the Bulk Silicate Earth (BSE) value is debated, recent work has shown effectively that basalts (mid-ocean ridge basalts, terrestrial basalts, and ocean island basalts) are enriched in 57Fe/54Fe relative to chondrites, but the causes of that fractionation are unclear (Craddock et al. 2013). Angrites, basaltic achondrite meteorites, also show enrichment in δ57Fe (Wang et al. 2012). Possible mechanisms include high-pressure core formation, oxidation during perovskite disproportionation, evaporation during the giant impact, and mantle melting. It is important to reconcile why the Earth's basalts are enriched in 57Fe/54Fe but the meteorites from Mars and Vesta are not. One possible explanation is that Mars and Vesta are smaller and the lower pressure attenuated the potential Fe fractionation during core formation. A second possibility is that the intrinsic oxidation states of the planets are causing the differences. However, another option is that the light elements (e.g. S, C, O, H, Si) in the cores of differentiated bodies control the iron isotope fractionation during differentiation. We have conducted experiments at 1 GPa and 1650-1800°C in a piston cylinder apparatus to address how sulfur, carbon and silicon alloyed with iron affect the iron isotopic fractionation between metallic alloy and silicate melt. We find that sulfur has the greatest effect on the iron isotopic

  4. Precise measurement of chromium isotopes by MC-ICPMS.

    Schiller, Martin; Van Kooten, Elishevah; Holst, Jesper C; Olsen, Mia B; Bizzarro, Martin


    We report novel analytical procedures allowing for the concurrent determination of the stable and mass-independent Cr isotopic composition of silicate materials by multiple collector inductively coupled mass spectrometry (MC-ICPMS). In particular, we focus on improved precision of the measurement of the neutron-rich isotope (54)Cr. Because nitride and oxide interferences are a major obstacle to precise and accurate (54)Cr measurements by MC-ICPMS, our approach is designed to minimize these interferences. Based on repeat measurements of standards, we show that the mass-independent (53)Cr and (54)Cr compositions can be routinely determined with an external reproducibility better than 2.5 and 5.8 ppm (2 sd), respectively. This represents at least a two-fold improvement compared to previous studies. Although this approach uses significantly more Cr (30-60 μg) than analysis by thermal ionization mass spectrometry (TIMS), our result indicate that it is possible to obtain an external reproducibility of 19 ppm for the μ(54)Cr when consuming amounts similar to that typically analyzed by TIMS (1 μg). In addition, the amount of time required for analysis by MC-ICPMS is much shorter thereby enabling a higher sample throughput. As a result of the improved analytical precision, we identified small apparent mass-independent differences between different synthetic Cr standards and bulk silicate Earth (BSE) when using the kinetic law for the mass bias correction. These differences are attributed to the Cr loss by equilibrium processes during production of the synthetic standards. The stable isotope data concurrently obtained have a precision of 0.05‰ Da (-1), which is comparable to earlier studies. Comparison of the measured isotopic composition of four meteorites with published data indicates that Cr isotope data measured by the technique described here are accurate to stated uncertainties. The stable Cr composition of the Bilanga and NWA 2999 achondrites suggests that the

  5. Sulfur Isotopic Fractionation During Vacuum Ultraviolet Photolysis of SO2: Implication for Meteorites and Early Earth

    Chakraborty, S.; Jackson, T. L.; Rude, B.; Ahmed, M.; Thiemens, M. H.


    Several sulfur bearing gas phase species existed in the solar nebula, including H2S, SO2, SiS, OCS, CS2, CS, NS and SO as a consequence of multiple available chemical valence states (S2- to S6+). Sulfur directly condensed into refractory phases in the solar nebula under reducing conditions. Mass independent (MI) sulfur isotopic compositions have been measured in chondrules and organics from chondritic meteorites. Large 33S excesses in sulfides from achondrite meteoritic groups have also been found suggesting that refractory sulfide minerals condensed from a nebular gas with an enhanced carbon to oxygen ratio. Photochemical reactions in the early solar nebula have been inferred to be a leading process in generating MI sulfur compositions. Previously, we have reported wavelength dependent mass-independent sulfur isotopic compositions (with a varying degree in D33S and D36S) in the product elemental sulfur during vacuum ultraviolet (VUV) photodissociation of H2S. Recently we performed photodissociation of SO2 experiments in the wavelength region 98 to 200 nm at low pressures (0.5 torr) using the VUV photons from the Advanced Light Source Synchrotron in a differentially pumped reaction chamber. To our knowledge, this is the first ever experiment to determine the isotopic fractionation in VUV photodissociation of SO2. At VUV energy region, SO2 is mostly predissociative. The measured sulfur isotopic compositions in the product elemental sulfur are MI and dependent on the wavelength. These new results support the previous finding from photodissociation of other di- and tri-atomic molecules (CO, N2, H2S) that predissociative photodissociation produces MI isotopic products and is a quantum mechanically driven selective phenomenon. These new results are useful because (i) they are important in interpreting meteoritic data and decipher sulfur chemistry in the early nebula which is indicative of the redox condition of the nebula (ii) SO2 photolysis in the atmosphere of early

  6. Origin, Internal Structure and Evolution of 4 Vesta

    Zuber, Maria T.; McSween, Harry Y.; Binzel, Richard P.; Elkins-Tanton, Linda T.; Konopliv, Alexander S.; Pieters, Carle M.; Smith, David E.


    Asteroid 4 Vesta is the only preserved intact example of a large, differentiated protoplanet like those believed to be the building blocks of terrestrial planet accretion. Vesta accreted rapidly from the solar nebula in the inner asteroid belt and likely melted due to heat released due to the decay of 26Al. Analyses of meteorites from the howardite-eucrite-diogenite (HED) suite, which have been both spectroscopically and dynamically linked to Vesta, lead to a model of the asteroid with a basaltic crust that overlies a depleted peridotitic mantle and an iron core. Vesta’s crust may become more mafic with depth and might have been intruded by plutons arising from mantle melting. Constraints on the asteroid’s moments of inertia from the long-wavelength gravity field, pole position and rotation, informed by bulk composition estimates, allow tradeoffs between mantle density and core size; cores of up to half the planetary radius can be consistent with plausible mantle compositions. The asteroid’s present surface is expected to consist of widespread volcanic terrain, modified extensively by impacts that exposed the underlying crust or possibly the mantle. Hemispheric heterogeneity has been observed by poorly resolved imaging of the surface that suggests the possibility of a physiographic dichotomy as occurs on other terrestrial planets. Vesta might have had an early magma ocean but details of the early thermal structure are far from clear owing to model uncertainties and paradoxical observations from the HEDs. Petrological analysis of the eucrites coupled with thermal evolution modeling recognizes two possible mechanisms of silicate-metal differentiation leading to the formation of the basaltic achondrites: equilibrium partial melting or crystallization of residual liquid from the cooling magma ocean. A firmer understanding the plethora of complex physical and chemical processes that contribute to melting and crystallization will ultimately be required to

  7. What do Meteorite Falls Tell Us about the Strength of Asteroid Boulders

    Britt, Daniel; Demasi, Michael; Kring, David


    One possible source of data on the strength of a boulder on an asteroid's surface is the meteorite collection and the observations of meteorite falls. Since highly fractured boulders should breakup in the atmosphere and arrive as meteorite showers, the relative ratio of boulders to showers can provide insight into boulder strength. Since about 85-95% of the mass of a meteoroid is lost during atmospheric entry, we have chosen to investigate only those falls with a final recovered mass of at least 10 kg. This corresponds to a minimum pre-atmospheric mass of 100-200 kg and roughly 25 centimeter minimum diameter. Using the Catalogue of Meteorites and the Meteoritical Bulletins we compiled a list of observed meteorite falls with a total recovered mass greater than or equal to 10 kg. We found a total of 269 meteorites that met these criteria, of which 263 entries reported or estimated the number of fragments associated with their falls. The overall percentage of observed showers was found to be around 34%. The ratio of "boulders" to showers was determined to be around 1.94:1. Comparing the percentage of showers within the meteorite types shows a trend in strength with irons (showers only 4.3%) very rarely exhibit reported showers, stony-irons (25%), ordinary chondrites (28.5%), achondrites (35.7%), and carbonaceous chondrites (70%) are dominantly showers.The meteorite fall data primarily sample the "boulder" population of meteoroids roughly 0.25 meters to a few meters in their pre-atmospheric diameter because of the 85-95% atmospheric loss. The relative rarity of showers seems to indicate that most meteoroids that survive to produce meteorites in this size range are fairly strong and coherent. Not surprisingly, irons and stony-irons are the strongest class which is consistent with the overwhelmingly high production of Earth's smallest impact craters by iron meteorites. Carbonaceous chondrites are by far the weakest and most fracture-prone meteorite class with 70% of the

  8. The SNC Meteorites

    Varela, M. E.


    The SNC (Shergotty-Nakhla-Chassigny) group, are achondritic meteorites. Of all SNC meteorites recognized up to date, shergottites are the most abundant group. The petrographic study of Shergotty began several years ago when Tschermak, (1872) identified this rock as an extraterrestrial basalt. Oxygen isotopes in SNC meteorites indicate that these rocks are from a single planetary body (Clayton and Mayeda, 1983). Because the abundance patterns of rare gases trapped in glasses from shock melts (e.g., Pepin, 1985) turned out to be very similar to the Martian atmosphere (as analyzed by the Viking landers, Owen, 1976), the SNC meteorites are believed to originate from Mars (e.g. McSween, 1994). Possibly, they were ejected from the Martian surface either in a giant impact or in several impact events (Meyer 2006). Although there is a broad consensus for nakhlites and chassignites being -1.3Ga old, the age of the shergottites is a matter of ongoing debates. Different lines of evidences indicate that these rocks are young (180Ma and 330-475Ma), or very old (> 4Ga). However, the young age in shergottites could be the result of a resetting of these chronometers by either strong impacts or fluid percolation on these rocks (Bouvier et al., 2005-2009). Thus, it is important to check the presence of secondary processes, such as re-equilibration or pressure-induce metamorphism (El Goresy et al., 2013) that can produce major changes in compositions and obscure the primary information. A useful tool, that is used to reconstruct the condition prevailing during the formation of early phases or the secondary processes to which the rock was exposed, is the study of glass-bearing inclusions hosted by different mineral phases. I will discuss the identification of extreme compositional variations in many of these inclusions (Varela et al. 2007-2013) that constrain the assumption that these objects are the result of closed-system crystallization. The question then arises whether these

  9. Micrometer-scale U–Pb age domains in eucrite zircons, impact re-setting, and the thermal history of the HED parent body

    Hopkins, M.D.; Mojzsis, S.J.; Bottke, W.F.; Abramov, Oleg


    Meteoritic zircons are rare, but some are documented to occur in asteroidal meteorites, including those of the howardite–eucrite–diogenite (HED) achondrite clan (Rubin, A. [1997]. Meteorit. Planet. Sci. 32, 231–247). The HEDs are widely considered to originate from the Asteroid 4 Vesta. Vesta and the other large main belt asteroids record an early bombardment history. To explore this record, we describe sub-micrometer distributions of trace elements (U, Th) and 235,238U–207,206Pb ages from four zircons (>7–40 μm ∅) separated from bulk samples of the brecciated eucrite Millbillillie. Ultra-high resolution (∼100 nm) ion microprobe depth profiles reveal different zircon age domains correlative to mineral chemistry and to possible impact scenarios. Our new U–Pb zircon geochronology shows that Vesta’s crust solidified within a few million years of Solar System formation (4561 ± 13 Ma), in good agreement with previous work (e.g. Carlson, R.W., Lugmair, G.W. [2000]. Timescales of planetesimal formation and differentiation based on extinct and extant radioisotopes. In: Canup, R., Righter, K. (Eds.), Origin of the Earth and Moon. University of Arizona Press, Tucson, pp. 25–44). Younger zircon age domains (ca. 4530 Ma) also record crustal processes, but these are interpreted to be exogenous because they are well after the effective extinction of 26Al (t1/2 = 0.72 Myr). An origin via impact-resetting was evaluated with a suite of analytical impact models. Output shows that if a single impactor was responsible for the ca. 4530 Ma zircon ages, it had to have been ⩾10 km in diameter and at high enough velocity (>5 km s−1) to account for the thermal field required to re-set U–Pb ages. Such an impact would have penetrated at least 10 km into Vesta’s crust. Later events at ca. 4200 Ma are documented in HED apatite 235,238U–207,206Pb ages (Zhou, Q. et al. [2011]. Early basaltic volcanism and Late Heavy Bombardment on Vesta: U–Pb ages of small

  10. Proceedings of the 40th Lunar and Planetary Science Conference


    ; Seek Out and Explore: Upcoming and Future Missions; Mars: Early History and Impact Processes; Mars Analogs II: Chemical and Spectral; Achondrites and their Parent Bodies; and Planning for Future Exploration of the Moon The poster sessions were: Lunar Missions: Results from Kaguya, Chang'e-1, and Chandrayaan-1; LRO and LCROSS; Geophysical Analysis of the Lunar Surface and Interior; Remote Observation and Geologic Mapping of the Lunar Surface; Lunar Spectroscopy; Venus Geology, Geophysics, Mapping, and Sampling; Planetary Differentiation; Bunburra and Buzzard Coulee: Recent Meteorite Falls; Meteorites: Terrestrial History; CAIs and Chondrules: Records of Early Solar System Processes; Volatile and Organic Compounds in Chondrites; Crashing Chondrites: Impact, Shock, and Melting; Ureilite Studies; Petrology and Mineralogy of the SNC Meteorites; Martian Meteorites; Phoenix Landing Site: Perchlorate and Other Tasty Treats; Mars Polar Atmospheres and Climate Modeling; Mars Polar Investigations; Mars Near-Surface Ice; Mars: A Volatile-Rich Planet; Mars: Geochemistry and Alteration Processes; Martian Phyllosilicates: Identification, Formation, and Alteration; Astrobiology; Instrument Concepts, Systems, and Probes for Investigating Rocks and Regolith; Seeing is Believing: UV, VIS, IR, X- and Gamma-Ray Camera and Spectrometer Instruments; Up Close and Personal: In Situ Analysis with Laser-Induced Breakdown Spectroscopy and Mass Spectrometry; Jupiter and Inscrutable Io; Tantalizing Titan; Enigmatic Enceladus and Intriguing Iapetus; Icy Satellites: Cryptic Craters; Icy Satellites: Gelid Geology/Geophysics; Icy Satellites: Cool Chemistry and Spectacular Spectroscopy; Asteroids and Comets; Comet Wild 2: Mineralogy and More; Hypervelocity Impacts: Stardust Models, LDEF, and ISPE; Presolar Grains; Early Nebular Processes: Models and Isotopes; Solar Wind and Genesis: Measurements and Interpretation; Education and Public Outreach; Mercury; Pursuing Lunar Exploration; Sources and Eruptionf

  11. Proceedings of the 40th Lunar and Planetary Science Conference


    ; Seek Out and Explore: Upcoming and Future Missions; Mars: Early History and Impact Processes; Mars Analogs II: Chemical and Spectral; Achondrites and their Parent Bodies; and Planning for Future Exploration of the Moon The poster sessions were: Lunar Missions: Results from Kaguya, Chang'e-1, and Chandrayaan-1; LRO and LCROSS; Geophysical Analysis of the Lunar Surface and Interior; Remote Observation and Geologic Mapping of the Lunar Surface; Lunar Spectroscopy; Venus Geology, Geophysics, Mapping, and Sampling; Planetary Differentiation; Bunburra and Buzzard Coulee: Recent Meteorite Falls; Meteorites: Terrestrial History; CAIs and Chondrules: Records of Early Solar System Processes; Volatile and Organic Compounds in Chondrites; Crashing Chondrites: Impact, Shock, and Melting; Ureilite Studies; Petrology and Mineralogy of the SNC Meteorites; Martian Meteorites; Phoenix Landing Site: Perchlorate and Other Tasty Treats; Mars Polar Atmospheres and Climate Modeling; Mars Polar Investigations; Mars Near-Surface Ice; Mars: A Volatile-Rich Planet; Mars: Geochemistry and Alteration Processes; Martian Phyllosilicates: Identification, Formation, and Alteration; Astrobiology; Instrument Concepts, Systems, and Probes for Investigating Rocks and Regolith; Seeing is Believing: UV, VIS, IR, X- and Gamma-Ray Camera and Spectrometer Instruments; Up Close and Personal: In Situ Analysis with Laser-Induced Breakdown Spectroscopy and Mass Spectrometry; Jupiter and Inscrutable Io; Tantalizing Titan; Enigmatic Enceladus and Intriguing Iapetus; Icy Satellites: Cryptic Craters; Icy Satellites: Gelid Geology/Geophysics; Icy Satellites: Cool Chemistry and Spectacular Spectroscopy; Asteroids and Comets; Comet Wild 2: Mineralogy and More; Hypervelocity Impacts: Stardust Models, LDEF, and ISPE; Presolar Grains; Early Nebular Processes: Models and Isotopes; Solar Wind and Genesis: Measurements and Interpretation; Education and Public Outreach; Mercury; Pursuing Lunar Exploration; Sources and Eruptionf

  12. On the existence of near-Earth-object meteoroid complexes producing meteorites

    Trigo-Rodriguez, J.; Madiedo, J.; Williams, I.


    is fracturing. Many asteroids are known to be rubble piles and such structures can be unstable during a close approach to a planet due to tidal forces. The irregular shape of many fast-rotators can allow the YORP effect to increase the spin rate, also leading to fracturing [7]. The escape speed from a fragmenting asteroid is considerably smaller than the orbital velocity so a large amount of the initial mass can be ejected. The fragmentation process is likely to produce many metre-sized rocks as well as few tens of meters fragmental asteroids that could form a complex of fragments, all moving on nearly identical orbits. The lifetime of such orbital complexes is quite short (few tens of thousand of years) as consequence of planetary perturbations[8], except perhaps for those cases exhibiting orbits with high inclination, where lifetimes can be considerably higher [9]. Catastrophic disruptions in the main asteroid belt have been extensively studied, but little is known about the relevance of the process in the NEO population. The Spanish Fireball Network (SPMN) regularly monitors the skies and is obtaining evidence that NEO complexes can be a source of meteorites. By performing backward integrations of meteoroid orbits and NEO candidates, previously identified by using our ORAS software to compute several orbital similarity criteria, we have identified several complexes associated with NEOs of chondritic nature [10-12] and even one, 2012 XJ_{112} of likely achondritic nature [13]. Another recent example was probably the Feb 15th, 2013 Chelyabinsk superbolide. The meteorites recovered were shocked to a very high level [14,15], and the ˜19-meter-diameter Chelyabinsk NEA was probably a monolithic single stone produced from its presumable progenitor, the 2.2 km in diameter asteroid (86039) [16]. This association should, however, be tested by performing backward integrations of both orbits.

  13. Lunar and Meteorite Sample Education Disk Program - Space Rocks for Classrooms, Museums, Science Centers, and Libraries

    Allen, Jaclyn; Luckey, M.; McInturff, B.; Huynh, P.; Tobola, K.; Loftin, L.


    violent impact history of the Moon. The disks also include two regolith soils and orange glass from a pyroclastic deposit. Each Meteorite Disk contains two ordinary chondrites, one carbonaceous chondrite, one iron, one stony iron, and one achondrite. These samples will help educators share the early history of the solar system with students and the public. Educators may borrow either lunar or meteorite disks and the accompanying education materials through the Johnson Space Center Curatorial Office. In trainings provided by the NASA Aerospace Education Services Program specialists, educators certified to borrow the disk learn about education resources, the proper use of the samples, and the special security for care and shipping of the disks. The Lunar and Meteorite Sample Education Disk Program will take NASA exploration to more people. Getting Space Rocks out to the public and inspiring the public about new space exploration is the focus of the NASA disk loan program.

  14. A Tale of Two Melt Rocks: Equilibration and Metal/Sulfide-Silicate Segregation in the L7 Chondrites PAT 91501 and LEW 88663

    Harvey, R. P.


    Type 7 ordinary chondrites have experienced temperatures near or beyond those necessary for partial melting. Two recently collected Antarctic specimens, PAT91501 (PAT) and LEW88663 (LEW), have been tentatively identified as L7 chondrites based on mineral and oxygen isotope compositions [1,2]. The petrology and mineralogy of these meteorites suggests that they have undergone significant metal/sulfide-silicate segregation, with implications for meteorite parent bodies. PAT consists of an equigranular contact-framework of nearly euhedral olivine grains, with interstitial spaces filled by plagioclase, pyroxenes, and several minor phases. Ortho- and clinopyroxene occur in an exsolution relationship. Olivine and pyroxene are highly equilibrated, varying PAT using the methods of [3] are self-consistent at about 1180 degrees C. In thin section, PAT contains only traces of metal, as tiny isolated blebs in sulfide grains; large (>1 cm) globular sulfide inclusions are seen in hand-sample [1], but are not present in the section examined. LEW was originally classified as an achondrite with olivine and pyroxene compositions similar to those in L chondrites [2]. Metal is absent in LEW, although the specimen is small and heavily rusted, making it impossible to gauge the original metal content. Olivine grains are commonly rounded in shape and seldom in contact with more than a few other grains. LEW olivine and pyroxene are also highly equilibrated. Veins of Ni-bearing metal oxides and sulfides are common. Both low- and high-Ca pyroxene occur as discrete grains, orthopyroxene often poikilitically enclosing olivine. Pyroxene equilibration temperatures for LEW are more variable than those for PAT and consistently lower, with an average around 900 degrees C. The various textural and compositional characteristics of PAT and LEW suggest they have experienced partial melting to varying degrees. Both visually resemble charges from experimental melting of ordinary chondrites [4-6]. The

  15. Modelling the thermal evolution and differentiation of the parent body of acapulcoites and lodranites

    Neumann, Wladimir; Breuer, Doris; Spohn, Tilman; Henke, Stephan; Gail, Hans-Peter; Schwarz, Winfried; Trieloff, Mario; Hopp, Jens


    The acapulcoites and lodranites are rare groups of achondritic meteorites. Several characteristics such as unique oxygen isotope composition and similar cosmic ray exposure ages indicate that these meteorites originate from a common parent body (Weigel et al. 1999). By contrast to both undifferentiated and differentiated meteorites, acapulcoites and lodranites are especially interesting because they experienced melting that was, however, not complete (McCoy et al. 2006). Thus, unravelling their origin contributes directly to the understanding of the initial differentiation stage of planetary objects in the Solar system. The information preserved in the structure and composition of meteorites can be recovered by modelling the evolution of their parent bodies and comparing the results with the laboratory investigations. Model calculations for the thermal evolution of the parent body of the Acapulco and Lodran-like meteorite clan were performed using two numerical models. Both models (from [3] and [4], termed (a) and (b), respectively) solve a 1D heat conduction equation in spherical symmetry considering heating by short- and long-lived radioactive isotopes, temperature- and porosity-dependent parameters, compaction of initially porous material, and melting. The calculations with (a) were compared to the maximum metamorphic temperatures and thermo-chronological data available for acapulcoites and lodranites. Applying a genetic algorithm, an optimised set of parameters of a common parent body was determined, which fits to the data for the cooling histories of these meteorites. The optimum fit corresponds to a body with the radius of 270 km and a formation time of 1.66 Ma after the CAIs. Using the model by (b) that considers differentiation by porous flow and magmatic heat transport, the differentiation of the optimum fit body was calculated. The resulting structure consists of a metallic core, a silicate mantle, a partially differentiated layer, an undifferentiated

  16. Chondrites as samples of differentiated planetesimals

    Elkins-Tanton, Linda; Weiss, Benjamin P.; Zuber, Maria T.


    talc and the absence of serpentine indicate peak temperatures of ~300-350°C. Subsequent to the analysis of natural remanent magnetization in angrites, Carporzen et al. (2009, submitted, and this conference) have described how unidirectional magnetization in Allende is consistent with a long-lived internally generated field. The metamorphic, magnetic, and exposure age data collectively indicate a new model for the CV chondrite parent body in which interior melting is incomplete and the magma ocean remains capped by an undifferentiated chondritic shell. This conductive lid insulates the internal magma ocean, slowing its cooling and solidification by orders of magnitude while still allowing sufficient heat flux out of the core to produce a dynamo with intensities consistent with magnetization in Allende. Materials in the undifferentiated lid experienced varying metamorphic conditions. Bodies that are internally differentiated in the manner described here may well exist undetected in the asteroid belt. The shapes and masses of the two largest asteroids, 1 Ceres and 2 Pallas, can be consistent with differentiated interiors, conceivably with small iron cores with hydrated silicate or ice-silicate mantles. Other asteroids may have lost their hydrostatic shapes through later impacts, and their surfaces may never have been covered with erupted basalt; surfaces of these bodies may have remained chondritic throughout this process. Such surfaces will therefore be irregular, space-weathered primitive material, perhaps with highly altered or even differentiated material at the bottoms of the largest craters and in crater ejecta. This scenario can explain the mismatch between the enormous diversity (> 130) of parent bodies represented by achondrites and the paucity (< 10) of basaltic asteroids.

  17. Effect of parent body evolution on equilibrium and kinetic isotope fractionation: a combined Ni and Fe isotope study of iron and stony-iron meteorites

    Chernonozhkin, Stepan M.; Goderis, Steven; Costas-Rodríguez, Marta; Claeys, Philippe; Vanhaecke, Frank


    Various iron and stony-iron meteorites have been characterized for their Ni and Fe isotopic compositions using multi-collector inductively coupled plasma-mass spectrometry (MC-ICP-MS) after sample digestion and chromatographic separation of the target elements in an attempt to further constrain the planetary differentiation processes that shifted these isotope ratios and to shed light on the formational history and evolution of selected achondrite parent body asteroids. Emphasis was placed on spatially resolved isotopic analysis of iron meteorites, known to be inhomogeneous at the μm to mm scale, and on the isotopic characterization of adjacent metal and silicate phases in main group pallasites (PMG), mesosiderites, and the IIE and IAB complex silicate-bearing iron meteorites. In a 3-isotope plot of 60/58Ni versus62/58Ni, the slope of the best-fitting straight line through the laterally resolved Ni isotope ratio data for iron meteorites reveals kinetically controlled isotope fractionation (βexper = 1.981 ± 0.039, 1 SD), predominantly resulting from sub-solidus diffusion (with the fractionation exponent β connecting the isotope fractionation factors, as α62/58 =α60/58β). The observed relation between δ56/54Fe and Ir concentration in the metal fractions of PMGs and in IIIAB iron meteorites indicates a dependence of the bulk Fe isotopic composition on the fractional crystallization of an asteroidal metal core. No such fractional crystallization trends were found for the corresponding Ni isotope ratios or for other iron meteorite groups, such as the IIABs. In the case of the IIE and IAB silicate-bearing iron meteorites, the Fe and Ni isotopic signatures potentially reflect the influence of impact processes, as the degree of diffusion-controlled Ni isotope fractionation is closer to that of Fe compared to what is observed for magmatic iron meteorite types. Between the metal and olivine counterparts of pallasites, the Fe and Ni isotopic compositions show clearly

  18. Evidence for Mo isotope fractionation in the solar nebula and during planetary differentiation

    Burkhardt, Christoph; Hin, Remco C.; Kleine, Thorsten; Bourdon, Bernard


    Mass-dependent Mo isotope fractionation has been investigated for a wide range of meteorites including chondrites (enstatite, ordinary and carbonaceous chondrites), iron meteorites, and achondrites (eucrites, angrites and martian meteorites), as well as for lunar and terrestrial samples. Magmatic iron meteorites together with enstatite, ordinary and most carbonaceous chondrites define a common δMo value of -0.16±0.02‰ (relative to the NIST SRM 3134 Mo standard), which is interpreted to reflect the Mo isotope composition of bulk planetary bodies in the inner solar system. Heavy Mo isotope compositions for IAB iron meteorites most likely reflect impact-induced evaporative losses of Mo from these meteorites. Carbonaceous chondrites define an inverse correlation between δMo and metal content, and a positive correlation between δMo and matrix abundance. These correlations are mainly defined by CM and CK chondrites, and may reflect the heterogeneous distribution of an isotopically light metal and/or an isotopically heavy matrix component in the formation region of carbonaceous chondrites. Alternatively, the elevated δMo of the CM and CK chondrites could result from the loss of volatile, isotopically light Mo oxides, that formed under oxidized conditions typical for the formation of these chondrites. The Mo isotope compositions of samples derived from the silicate portion of differentiated planetary bodies are heavy compared to the mean composition of chondrites and iron meteorites. This difference is qualitatively consistent with experimental evidence for Mo isotope fractionation between metal and silicate. The common δMo values of -0.05±0.03‰ of lunar samples derived from different geochemical reservoirs indicate the absence of significant Mo isotope fractionation by silicate differentiation or impact metamorphism/volatilization on the Moon. The most straightforward interpretation of the Mo isotope composition of the lunar mantle corresponds to the formation

  19. Constraints on the Composition and Evolution of the Lunar Crust from Meteorite NWA 3163

    McLeod, C. L.; Brandon, A. D.; Fernandes, V. A.; Peslier, A. H.; Lapen, T. J.; Irving, A. J.


    The lunar meteorite NWA 3163 (paired with NWA 4881, 4483) is a ferroan, feldspathic granulitic breccia characterized by pigeonite, augite, olivine, maskelynite and accessory Tichromite, ilmenite and troilite. Bulk rock geochemical signatures indicate the lack of a KREEP- derived component (Eu/Eu* = 3.47), consistent with previously studied lunar granulites and anorthosites. Bulk rock chondrite-normalized signatures are however distinct from the anorthosites and granulites sampled by Apollo missions and are relatively REE-depleted. In-situ analyses of maskelynite reveal little variation in anorthite content (average An% is 96.9 +/- 1.6, 2 sigma). Olivine is relatively ferroan and exhibits very little variation in forsterite content with mean Fo% of 57.7 +/- 2.0 (2 sigma). The majority of pyroxene is low-Ca pigeonite (En57Fs33Wo10). Augite (En46Fs21Wo33) is less common, comprising approximately 10% of analyzed pyroxene. Two pyroxene thermometry on co-existing orthopyroxene and augite yield an equilibrium temperature of 1070C which is in reasonable agreement with temperatures of 1096C estimated from pigeonite compositions. Rb-Sr isotopic systematics of separated fractions yield an average measured Sr-87/Sr-87 of 0.699282+/-0.000007 (2 sigma). Sr model ages are calculated using a modern day Sr-87/Sr-86 Basaltic Achondrite Best Initial (BABI) value of 0.70475, from an initial BABI value Sr-87/Sr-86 of 0.69891 and a corresponding Rb-87/Sr-97 of 0.08716. The Sr model Thermomechanical analysis (TMA) age, which represents the time of separation of a melt from a source reservoir having chondritic evolution, is 4.56+/-0.1 Ga. A Sr model T(sub RD) age, which is a Rb depletion age and assumes no contribution from Rb in the sample in the calculation, yields 4.34+/-0.1 Ga (i.e. a minimum age). The Ar-Ar dating of paired meteorite NWA 4881 reveals an age of c. 2 Ga, likely representing the last thermal event this meteorite experienced. An older Ar-40/Ar-39 age of c. 3.5 Ga may

  20. Cometary Refractory Grains: Interstellar and Nebular Sources

    Wooden, D. H.


    with asteroids, the Stardust Fe-bearing and Fe-rich crystalline silicates suggests partial aqueous alteration in comet nuclei. However, aqueous alteration transforms Fe-rich olivine to phyllosilicates before Mg-rich olivine, and Stardust has Mg-rich and Fe-rich olivine and no phyllosilicates. Hence, we look to a nebular source for the moderately Fe-rich to nearly pure-Fe crystalline silicates. Primitive matrices have Mg-Fe silicates but no phyllosilicates, supporting the idea that Mg-Fe silicates but not phyllosilicates are products of water-rich shocks. Chondrule-formation is a late stage process in our protoplanetary disk. Stardust samples show comet 81P/Wild 2 formed at least as late to incorporate a few chondrules, requiring radial transport of chondrules out to perhaps >20 AU. By similar radial transport mechanisms, collisional fragments of aqueously altered asteroids, in particular achondrites that formed earlier than chondrules, might reach the comet-forming zones. However, Stardust samples do not have phyllosilicates and chondrules are rare. Hence, the nebular refractory grains in comet 81P/Wild 2, as well as other comets, appear to be pre-accretionary with respect to asteroid parent bodies. By discussing nebular pathways for the formation of Fe-rich crystalline silicates, and also phyllosilicates and carbonates, we put forth the view that comets contain both the interstellar ingredients for and the products of nebular transmutation.

  1. Mineralogical and Geochemical Analysis of Howardite DaG 779: understanding geological evolution of asteroid (4) Vesta

    Marcel Müller, Christian; Mengel, Kurt; Singh Thangjam, Guneshwar; Weckwerth, Gerd


    The HED meteorites, a clan of stony achondrites, are believed to originate from asteroid (4) Vesta (e.g. Mittlefehldt et al. (2015)). Recent evolution models (e.g. Toplis et al. (2013)) and observations from Dawn spacecraft data (e.g., Prettyman et al. (2013)) indicate that diogenites form the lower crust and uppermost mantle of (4) Vesta. Deep seated material excavated by large impacts such as the Rheasilvia- and Veneneiaforming event should be present in howardites. We analysed a slice of howardite DaG 779 which had been recovered from the Libyan Desert in 1999 and was briefly described by Grossmann (2000). The data presented here include electron microprobe, bulk-rock XRD and XRF as well as trace element analysis by ICP-MS and INA. The petrographic results confirm earlier observations that DaG 779 is polymict and mainly contains diogenite and eucrite clasts. Mass balance calculations using bulk-rock and microprobe major element data reveal a modal mineralogy of 77% orthopyroxene, 8% plagioclase, 7% clinopyroxene and 2% spinels, the rest being olivine, SiO2-phases, sulphides, and native Fe(Ni). When compared with the element compilation recently reported by Mittlefehldt (2015) the 39 trace element analysed here (including REE and PGE) confirm that this howardite is clearly dominated by diogenite. Beside the modal petrographic information, a number of more detailed observations obtained from microprobe investigations reveal fresh and recrystallized glasses, troilite-orthopyroxene symplectites from a mixed silicate-sulphide melt giving rise to graphic intergrowths as well as vermicular and reticular FeS in highly disrupted clasts. While the origin of the FeS in these clasts is not clear yet, its particular shape and distribution indicates that this mineral has been (partially) molten and recrystallized from a sulphide melt. The silicate minerals around these FeS occurrences are recrystallized but there is no indication for a partial silicate melt. Further

  2. Isotopic constraints on the age and early differentiation of the Earth.

    McCulloch, M T


    The Earth's age and early differentiation history are re-evaluated using updated isotopic constraints. From the most primitive terrestrial Pb isotopic compositions found at Isua Greenland, and the Pilbara of Western Australia, combined with precise geochronology of these localities, an age 4.49 +/- 0.02 Ga is obtained. This is interpreted as the mean age of core formation as U/Pb is fractionated due to sequestering of Pb into the Earth's core. The long-lived Rb-Sr isotopic system provides constraints on the time interval for the accretion of the Earth as Rb underwent significant depletion by volatile loss during accretion of the Earth or its precursor planetesimals. A primitive measured 87Sr/86Sr initial ratio of 0.700502 +/- 10 has been obtained for an early Archean (3.46 Ga) barite from the Pilbara Block of Western Australia. Using conservative models for the evolution of Rb/Sr in the early Archean mantle allows an estimate to be placed on the Earth's initial Sr ratio at approximately 4.50 Ga, of 0.69940 +/- 10. This is significantly higher than that measured for the Moon (0.69900 +/- 2) or in the achondrite, Angra dos Reis (0.69894 +/- 2) and for a Rb/Sr ratio of approximately 1/2 of chondrites corresponds to a mean age for accretion of the Earth of 4.48 + /- 0.04 Ga. The now extinct 146Sm-142Nd (T1/2(146)=103 l0(6)yrs) combined with the long-lived 147Sm-143Nd isotopic systematics can also be used to provide limits on the time of early differentiation of the Earth. High precision analyses of the oldest (3.8-3.9 Ga) Archean gneisses from Greenland (Amitsoq and Akilia gneisses), and Canada (Acasta gneiss) do not show measurable (> +/- l0ppm) variations of 142Nd, in contrast to the 33 ppm 142Nd excess reported for an Archean sample. The general lack of 142Nd variations, combined with the presence of highly positive epsilon 143 values (+4.0) at 3.9 Ga, indicates that the record of large-scale Sm/Nd fractionation events was not preserved in the early-Earth from 4

  3. Evolution of asteroid (4) Vesta in the light of Dawn

    Thangjam, Guneshwar; Mengel, Kurt; Nathues, Andreas; Schmidt, Kai H.; Hoffmann, Martin


    Asteroid (4) Vesta has been visited by the NASA Dawn spacecraft in 2011/12. The combination of compositional/elemental information from the three onboard instruments with mineralogical information from the howardite-eucrite-diogenite (HED) clan of stony achondrites has shed new light on the surface lithologic heterogeneity and the early evolution. Although petrologic/chemical models have tried to unravel the evolutionary processes, inconsistencies exist for some chemical major element/phase [e.g., 1, 2]. A revised evolutionary model is presented here [3]. The three oxygen isotope signature of HEDs and, thus, of proto-Vesta is best met by a mixture of 80% ordinary plus 20 % CV chondrites. Assuming a 27Al-triggered magma ocean within the first MA after accretion and taking into account the reliable major element data of the silicate fraction of the chondritic mixture results a crystallization sequence that differs from the earlier models [1, 2, 3]. The crystallized phase obtained by 'MELTS' software [4] starts with olivine and continues with minor olivine plus orthopyroxene until the liquid reaches a Kd value (partition coefficient) of 0.31 where the fractionated melt is in equilibrium with the residual liquid [5]. The abundance of minerals and rocks formed in this model are converted in volume proportions assuming a spherical shape of early Vesta (262 km radius) with a core (FeNi, FeNiS) radius of 110 km [6]. Two scenarios are considered to describe the early bulk silicate Vesta. First, the early-crystallized olivine accumulated at the base of the silicate shell is accounted for a dunitic lower mantle having a thickness of 46 km while the later crystallized phases form an orthopyroxenitic upper mantle and a crust of thickness 84 and 22 km, respectively. Second, an olivine-rich lower mantle that gradually changes to orthopyroxene-rich upper mantle is expected having an overall shell thickness of 137 km, with a 15 km thick crust. An important result is that the deep

  4. Re-Evaluation of HSE DATA in Light of High P-T Partitioning Data: Late Chondritic Addition to Inner Solar System Bodies Not Always Required for HSE

    Righter, K.


    Studies of terrestrial peridotite and martian and achondritic meteorites have led to the conclusion that addition of chondritic material to growing planets or planetesimals, after core formation, occurred on Earth, Moon, Mars, asteroid 4 Vesta, and the parent body of the angritic meteorites. One study even proposed that this was a common process in the final stages of growth. These conclusions are based al-most entirely on the 8 highly siderophile elements (HSE; Re, Au, Pt, Pd, Rh, Ru, Ir, Os), which have been used to argue for late accretion of chondritic material to the Earth after core formation was complete. This idea was originally proposed because the D(metal/silicate) values for the HSE are very high (greater than 10,000), yet their concentration in the terrestrial mantle is too high to be consistent with such high Ds. The HSE in the terrestrial mantle also are present in chondritic relative abundances and hence require similar Ds if this was the result of core-mantle equilibration. The conclusion that late chondritic additions are required for all five of these bodies is based on the chondritic relative abundances of the HSE, as well as their elevated concentrations in the samples. An easy solution is to call upon addition of chondritic material to the mantle of each body, just after core formation; however, in practice this means similar additions of chondritic materials to each body just after core formation which ranges from approximately 4-5 Ma after T(sub 0) for 4 Vesta and the angrites, to 10-25 Ma for Mars, to 35 to 60 Ma for Moon and perhaps the Earth. Since the work of there has been a realization that high PT conditions can lower the partition coefficients of many siderophile elements, indicating that high PT conditions (magma ocean stage) can potentially explain elevated siderophile element abundances. However, detailed high PT partitioning data have been lacking for many of the HSE to evaluate whether such ideas are viable for all four bodies

  5. Analysis of ground-based and VIRTIS-M/ROSETTA reflectance spectra of asteroid 2687 Šteins: A comparison

    Markus, K.; Arnold, G.; Hiesinger, H.; Capaccioni, F.


    [II]-subclass. E-type asteroids are linked to aubrites, which are nearly monomineralic enstatite achondrites [11]. This interpretation is supported by comparative laboratory reflectance measurements. Although aubrites give the best agreement with Šteins spectra, several spectral features cannot be assigned unambiguously. Ti-rich minerals or space weathering implanted products were alternatively proposed to reproduce the observed spectral characteristics [1, 12]. Currently no meteorite in our present collection fits the Šteins spectra, indicating that Šteins is probably not the parent body of these meteorites. Because Šteins is a reduced anhydrous body, it can be argued that it formed in the inner planetary system and was scattered to the main belt. This opens interesting parallels between the E-type population and the formation of Mercury. [1] Barucci et al. (2005) A&A, 430, 313-317. [2] Dotto et al. (2009) A&A, 494, L29-L32. [3] Fornasier et al. (2007) A&A, 474, L29-L32. [4] Fornasier et al. (2008) Icarus, 196, 119-134. [5] Nedelcu et al. (2007) A&A, 473, L33-L36. [6] Weissman et al. (2008) Met. Planet. Sci, 43, 905-914. [7] Burbine at al. (2002) Met. Planet. Sci., 37, 1233-1244. [8] Tholen D. J. (1989) in Asteroids II, 1139-1150. [9] Gaffey and Kelley (2004) LPSC XXXV. Abstract #1812. [10] Bus and Binzel (2002) Icarus, 158, 146-177. [11] Keil (2010) Chem. Erde-Geochem., 70, 295-317. [12] Shestopalov et al. (2010) Planet. Space Sci., 58, 1400-1403.

  6. A New Type of Foreign Clast in A Polymict Ureilite: A CAI or AL-Rich Chondrule

    Goodrich, C. A.; Ross, D. K.; Treiman, A. H.


    Introduction: Polymict ureilites are breccias interpreted to represent regolith formed on a ureilitic asteroid [1-3]. They consist of approximately 90-95% clasts of various ureilite types (olivine-pyroxene rocks with Fo 75-95), a few % indigenous feldspathic clasts, and a few % foreign clasts [4-20]. The foreign clasts are diverse, including fragments of H, L, LL and R chondrites, angrites, other achondrites, and dark clasts similar to CC [6,7,9-19]. We report a new type of foreign clast in polymict ureilite DaG 999. Methods: Clast 8 in Dar al Gani (DaG) 999/1 (Museum fur Naturkunde) was discovered during a survey of feldspathic clasts in polymict ureilites [19,20]. It was studied by BEI, EMPA, and X-ray mapping on the JEOL 8530F electron microprobe at ARES, JSC. Petrography and Mineral Compositions: Clast 8 is sub-rounded to irregular in shape, approximately 85 micrometers in diameter, and consists of approximately 68% pyroxene and 32% mesostasis (by area). Part of the pyroxene (top half of clast in Fig. 1a and 2) shows a coarse dendritic morphology; the rest appears massive. Mesostasis may be glassy and contains fine needles/grains of pyroxene. The pyroxene has very high CaO (23.5 wt.%) and Al2O3 (19.7 wt.%), with the formula: (Ca(0.91)Mg(0.63)Fe(0.01)Al(sup VI) (0.38)Cr(0.01)Ti(0.05)1.99 Si2O6. The bulk mesostasis also has very high Al2O3 (approximately 26 wt.%). A bulk composition for the clast was obtained by combining modal abundances with phase compositions (Table 1, Fig. 3). Discussion: The pyroxene in clast 8 has a Ca-Al-(Ti)- rich (fassaitic) composition that is clearly distinct from compositions of pyroxenes in main group ureilites [22] or indigenous feldspathic clasts in polymict ureilites [4-8]. It also has significantly higher Al than fassaite in angrites (up to approximately 12 wt.% [23]), which occur as xenoliths in polymict ureilites. Ca-Al-Ti rich pyroxenes are most commonly found in CAIs, Al-rich chondrules and other types of refractory

  7. Phase equilibrium constraints on angrite petrogenesis

    Longhi, John


    Parameterizations of liquidus boundaries and solid solution in the CMAS + Fe system (Shi, 1992) have been employed to depict the liquidus equilibria relevant to the petrogenesis of angrites. Angrites are basaltic achondrites characterized by highly aluminous augite (fassaite), intermediate Mg-Fe olivine, and late-stage CaFe-olivine (kirschsteinite). Two important features of the equilibria on the olivine liquidus surface relevant to angrite petrogenesis are: 1) the presence of a thermal divide on the ol + aug + plag + liq boundary curve, which separates the compositions of source materials that produce low-silica angritic melts that crystallize highly aluminous augite from those that produce higher silica melts with tholeiitic to eucritic crystallization patterns; and 2) the change in the pseudo-invariant point on the low-silica side of the thermal divide from a plagioclase-peritectic involving spinel ( ol + aug + plag + sp + liq) at high to intermediate Mg' (Mg/[Mg + Fe]) to two pseudo-eutectics involving kirschsteinite ( ol + aug + plag + kir + liq and ol + kir + plag + sp + liq) at low Mg'. The fassaitic (aluminous augite) pyroxene composition in Angra Dos Reis (ADOR), the presence of minor green spinel, and the absence of primary kirschsteinite (Prinz et al., 1977) indicate that crystallization of the ADOR parental liquid was governed by the intermediate-Mg' set of equilibria such that, following crystallization of ol + aug + plag, the plagioclase reacted completely at the plagioclase-peritectic with the interstitial liquid, which subsequently crystallized beyond the plagioclase-peritectic onto the ol + aug + sp liquidus boundary curve. The ADOR bulk composition is consistent with trapping ˜10% of the parental liquid in a cumulate with cotectic proportions of fassaite and olivine. Lewis Cliff (LEW)86010 crystallized from a liquid with Mg' similar to that of ADOR, but on the ol + plag cotectic closer to the thermal divide such that the first pyroxene to