• 2007 Barringer Medal for Christian Koeberl

      Reimold, Wolf Uwe (The Meteoritical Society, 2007-01-01)
    • 2007 Leonard Medal for Michel Maurette

      Brownlee, Donald (The Meteoritical Society, 2007-01-01)
    • 2008 Barringer Medal for Frank Kyte

      Claeys, Philippe (The Meteoritical Society, 2008-01-01)
    • 2008 Leonard Medal for Edward R. D. Scott

      Goldstein, Joseph I. (The Meteoritical Society, 2008-01-01)
    • 2008 Nier Prize for Shogo Tachibana

      Huss, Gary (The Meteoritical Society, 2008-01-01)
    • 2008 Pellas-Ryder Award for Mathieu Touboul

      Kleine, Thorsten (The Meteoritical Society, 2008-01-01)
    • 2008 Service Award for Drew Barringer

      Stöffler, Dieter; Kring, David A. (The Meteoritical Society, 2008-01-01)
    • 2009 Barringer Medal for Wolf Uwe Reimold

      Koeberl, Christian (The Meteoritical Society, 2009-01-01)
    • 2009 Leonard Medal for Lawrence Grossman

      Humayun, Munir (The Meteoritical Society, 2009-01-01)
    • 2009 Service Award for Derek Sears

      Drake, Michael J. (The Meteoritical Society, 2009-01-01)
    • 26Al-26Mg systematics of Ca-Al-rich inclusions, amoeboid olivine aggregates, and chondrules from the ungrouped carbonaceous chondrite Acfer 094

      Sugiura, N.; Krot, A. N. (The Meteoritical Society, 2007-01-01)
      We report in situ magnesium isotope measurements of 7 porphyritic magnesium-rich (type I) chondrules, 1 aluminum-rich chondrule, and 16 refractory inclusions (14 Ca-Al-rich inclusions [CAIs] and 2 amoeboid olivine aggregates [AOAs]) from the ungrouped carbonaceous chondrite Acfer 094 using a Cameca IMS 6f ion microprobe. Both AOAs and 9 CAIs show radiogenic 26Mg excesses corresponding to initial 26Al/27Al ratios between ~5 x 10^(5) and ~7 x 10^(5), suggesting that formation of the Acfer 094 CAIs may have lasted for ~300,000 years. Four CAIs show no evidence for radiogenic 26Mg; three of these inclusions (a corundum-rich, a grossite-rich, and a pyroxene-hibonite spherule CAI) are very refractory objects and show deficits in 26Mg, suggesting that they probably never contained 26Al. The fourth object without evidence for radiogenic 26Mg is an anorthite-rich, igneous (type degrees C) CAI that could have experienced late-stage melting that reset its Al-Mg systematics. Significant excesses in 26Mg were observed in two chondrules. The inferred 26Al/27Al ratios in these two chondrules are (10.3 +/- 7.4) 10^(6) and (6.0 +/- 3.8) 10^(6) (errors are 2-sigma), suggesting formation 1.6^(1.2 over 0.6) and 2.2^(-0.4 over 0.3) Myr after CAIs with the canonical 26Al/27Al ratio of 5 10^(5). These age differences are consistent with the inferred age differences between CAIs and chondrules in primitive ordinary (LL3.0-LL3.1) and carbonaceous (CO3.0) chondrites.
    • 26Mg-excess in hibonites of the Rumuruti chondrite Hughes 030

      Bischoff, A.; Srinivasan, G. (The Meteoritical Society, 2003-01-01)
      The Rumuruti chondrites (R chondrites) constitute a new, well-established, chondrite group different from carbonaceous, ordinary, and enstatite chondrites. Most samples of this group are gas-rich regolith breccias showing the typical light/dark structure and consist of abundant fragments of various parent body lithologies embedded in a fine-grained, olivine-rich matrix. Most R chondrites contain the typical components of primitive chondrites including chondrules, chondrule and mineral fragments, sulfides, and rare calcium-aluminum-rich inclusions (CAIs). In Hughes 030, an interesting CAI consisting of abundant hibonite and spinel was found. Mg isotopic analyses revealed excess 26Mg in components of R chondrites for the first time. The hibonite grains with high Al/Mg values (~1500 to 2600) show resolved 26Mg excess. The slope of the correlation line yields an initial 26Al/ 27Al = (1.4 +/- 0.3) x 10^(-6), which is ~40 times lower than the initial value measured in CAIs from primitive meteorites. The inferred difference in 26Al abundance implies a time difference of ~4 million years for the closure of the Al-Mg system between CAIs from primitive chondrites and the Hughes 030 CAI. Based on mineralogy and the petrographic setting of the hibonite-rich CAI, it is suggested that 4 million years reflect the time interval between the formation of the CAI and the end of its secondary alteration. It is also suggested that most of this alteration may have occurred in the nebula (e.g. Zn- and Fe-incorporation in spinels). However, the CAI could not have survived in the nebula as a\ free floating object for a long period of time. Therefore, the possibility of storage in a precursor planetesimal for a few million years, resetting the magnesium-aluminum isotopic system, prior to impact brecciation, excavation, and accretion of the final R chondrite parent body cannot be ruled out.
    • 3-D elemental and isotopic composition of presolar silicon carbides

      Henkel, T.; Stephan, T.; Jessberger, E. K.; Hoppe, P.; Strebel, R.; Amari, S.; Lewis, R. S. (The Meteoritical Society, 2007-01-01)
      Thirteen presolar silicon carbide grains—three of supernova (SN) origin and ten of asymptotic giant branch (AGB) star origin—were examined with time-of-flightsecondary ion mass spectrometry (TOF-SIMS). The grains had been extracted from two different meteorites—Murchison and Tieschitz—using different acid residue methods. At high lateral resolution of ~300 nm, isotopic and elemental heterogeneities within the micrometer-sized grains were detected. The trace elemental abundances, when displayed in two-element correlation plots, of Li, Mg, K, and Ca show a clear distinction between the two different meteoritic sources. The different concentrations might be attributed to differences of the host meteorites and/or of extraction methods whereas the stellar source seems to be less decisive. In one SN grain with 26Mg-enrichment from extinct 26Al, the acid treatment, as part of the grain separation procedure, affected the Mg/Al ratio in the outer rim and therefore the inferred initial 26Al/27Al ratio. A second SN grain exhibits a lateral heterogeneity in 26Al/27Al, which either is due to residual Al-rich contamination on the grain surface or to the condensation chemistry in the SN ejecta.
    • 36Cl, 26Al, and O isotopes in an Allende type B2 CAI: Implications for multiple secondary alteration events in the early solar system

      Ushikubo, T.; Guan, Y.; Hiyagon, H.; Sugiura, N.; Leshin, L. A. (The Meteoritical Society, 2007-01-01)
      We measured 36Cl-36S and 26Al-26Mg systematics and O isotopes of secondary phases in a moderately altered type B2 CAI (CAI#2) from the Allende CV3 chondrite. CAI#2 has two distinct alteration domains: the anorthite-grossular (An-Grs) domain that mostly consists of anorthite and grossular, and the Na-rich domain that mostly consists of sodalite, anorthite, and Fe-bearing phases. Large 36S excesses (up to ~400) corresponding to an initial 36Cl/35Cl ratio of (1.4 +/- 0.3) x 10^(-6) were observed in sodalite of the Na-rich domain, but no resolvable 26Mg excesses were observed in anorthite and sodalite of the Na-rich domain (the initial 26Al/27Al ratio 4.4 x 10^(-7)). If we assume that the 36Cl-36S and the 26Al-26Mg systematics were closed simultaneously, the 36Cl/35Cl ratio would have to be on the order of ~10^(-2) when CAIs were formed. In contrast to sodalite in Na-rich domain, significant 26Mg excesses (up to ~35 ppm) corresponding to an initial 26Al/27Al ratio of (1.2 +/- 0.2) x 10^(-5) were identified in anorthite of the An-Grs domain. The 26Al-26Mg systematics of secondary phases in CAI#2 suggest that CAIs experienced multiple alteration events. Some of the alteration processes occurred while 36Cl (half-life is 0.3 Myr) and 26Al (half-life is 0.72 Myr) were still alive, whereas others took place much later. Assuming that 26Al was homogeneously distributed in the solar nebula, our study implies that alteration of CAIs occurred as early as within 1.5 Myr of CAI formation and as late as 5.7 Myr after.
    • 39Ar-40Ar "ages" and origin of excess 40Ar in Martian shergottites

      Bogard, D.; Park, J.; Garrison, D. (The Meteoritical Society, 2009-01-01)
      We report new 39Ar-40Ar measurements on 15 plagioclase, pyroxene, and/or whole rock samples of 8 Martian shergottites. All age spectra suggest ages older than the meteorite formation ages, as defined by Sm-Nd and Rb-Sr isochrons. Employing isochron plots, only Los Angeles plagioclase and possibly Northwest Africa (NWA) 3171 plagioclase give ages in agreement with their formation ages. Isochrons for all shergottite samples reveal the presence of trapped Martian 40Ar(40Arxs), which exists in variable amounts in different lattice locations. Some 40Arxs is uniformly distributed throughout the lattice, resulting in a positive isochron intercept, and other 40Arxs occurs in association with K-bearing minerals and increases the isochron slope. These samples demonstrate situations where linear Ar isochrons give false ages that are too old. After subtracting 40Ar* that would accumulate by 40K decay since meteorite formation and small amounts of terrestrial 40Ar, all young age samples give similar 40Arxs concentrations of ~1-2 x 10^(-6) cm^3/g, but a variation in K content by a factor of ~80. Previously reported NASA Johnson Space Center data for Zagami, Shergotty, Yamato (Y-) 000097, Y-793605, and Queen Alexandra Range (QUE) 94201 shergottites show similar concentrations of 40Arxs to the new meteorite data reported here. Similar 40Arxs in different minerals and meteorites cannot be explained as arising from Martian atmosphere carried in strongly shocked phases such as melt veins. We invoke the explanation given by Bogard and Park (2008) for Zagami, that this 40Arxs in shergottites was acquired from the magma. Similarity in 40Arxs among shergottites may reveal common magma sources and/or similar magma generation and emplacement processes.
    • 39Ar-40Ar ages of eucrites and thermal history of asteroid 4 Vesta

      Bogard, D. D.; Garrison, D. H. (The Meteoritical Society, 2003-01-01)
      Eucrite meteorites are igneous rocks that derived from a large asteroid, probably 4 Vesta. Past studies have shown that after most eucrites formed, they underwent metamorphism in temperatures up to greater than or equal to 800 degrees C. Much later, many were brecciated and heated by large impacts into the parent body surface. The less common basaltic, unbrecciated eucrites also formed near the surface but, presumably, escaped later brecciation, while the cumulate eucrites formed at depths where metamorphism may havepersisted for a considerable period. To further understand the complex HED parent body thermal history, we determined new 39Ar- 40Ar ages for 9 eucrites classified as basaltic but unbrecciated, 6 eucrites classified as cumulate, and several basaltic-brecciated eucrites. Precise Ar-Ar ages of 2 cumulate eucrites (Moama and EET 87520) and 4 unbrecciated eucrites give a tight cluster at 4.48 +/- 0.02 Gyr (not including any uncertainties in the flux monitor age). Ar-Ar ages of 6 additional unbrecciated eucrites are consistent with this age within theirrelatively larger age uncertainties. By contrast, available literature data on Pb-Pb isochron ages of 4 cumulate eucrites and 1 unbrecciated eucrite vary over 4.4-4.515 Gyr, and 147Sm-143Nd isochron ages of 4 cumulate and 3 unbrecciated eucrites vary over 4.41-4.55 Gyr. Similar Ar-Ar ages for cumulate and unbrecciated eucrites imply that cumulate eucrites do not have a younger formation age than basaltic eucrites, as was previously proposed. We suggest that these cumulate and unbrecciated eucrites resided at a depth where parent body temperatures were sufficiently high to cause the K-Ar and some other chronometers to remain as open diffusion systems. From the strong clustering of Ar-Ar ages at ~4.48 Gyr, we propose that these meteorites were excavated from depth in a single large impact event ~4.48 Gyr ago, which quickly cooled the samples and started the K-Ar chronometer. A large (~460 km) crater postulated to exist on Vesta may be the source of these eucrites and of many smaller asteroids thought to be spectrally or physically associated with Vesta. Some Pb-Pb and Sm-Nd ages of cumulate and unbrecciated eucrites are consistent with the Ar-Ar age of 4.48 Gyr, and the few older Pb-Pb and Sm-Nd ages may reflect an isotopic closure before the large cratering event. One cumulate eucrite gives an Ar-Ar age of 4.25 Gyr; 3 additional cumulate eucrites give Ar-Ar ages of 3.4-3.7 Gyr; and 2 unbrecciated eucrites give Ar-Ar ages of ~3.55 Gyr. We attribute these younger ages to a later impact heating. Furthermore, the Ar-Ar impact-reset ages of several brecciated eucrites and eucritic clasts in howardites fall within the range of 3.5-4.1 Gyr. Among these, Piplia Kalan, the first eucrite to show evidence for extinct 26Al, was strongly impact heated ~3.5 Gyr ago. When these data are combined with eucrite Ar-Ar ages in the literature, they confirm that several large impact heating events occurred on Vesta between ~4.1-3.4 Gyr ago. The onset of major impact heating may have occurred at similar times for both Vesta and the moon, but impact heating appears to have persisted for a somewhat later time on Vesta.
    • 39Ar-40Ar chronology of R chondrites

      Dixon, E. T.; Bogard, D. D.; Garrison, D. H. (The Meteoritical Society, 2003-01-01)
      This study presents the first determinations of 39Ar-40Ar ages of R chondrites for the purpose of understanding the thermal history of the R chondrite parent body. The 39Ar-40Ar ages were determined on whole-rock samples of four R chondrites: Carlisle Lakes, Rumuruti, Acfer 217, and Pecora Escarpment #91002 (PCA 91002). All samples are breccias except for Carlisle Lakes. The age spectra are complicated by recoil and diffusive loss to various extents. The peak 39Ar-40Ar ages of the four chondrites are greater than or equal to 4.35, ~4.47 +/- 0.02, 4.30 +/- 0.07 Ga, and greater than or equal to 4.37 Ga, respectively. These ages are similar to Ar-Ar ages of relatively unshocked ordinary chondrites (4.52-4.38 Ga) and are older than Ar-Ar ages of most shocked ordinary chondrites (<<4.2 Ga). Because the meteorites with the oldest (Rumuruti, ~4.47 Ga) and the youngest (Acfer 217, ~4.30 Ga) ages are both breccias, these ages probably do not record slow cooling within an undisrupted asteroidal parent body. Instead, the process of breccia formation may have differentially reset the ages of the constituent material, or the differences in their age spectra may arise from mixtures of material that had different ages. Two end-member type situations may be envisioned to explain the age range observed in the R chondrites. The first is if the impact(s) that reset the ages of Acfer 217 and Rumuruti was very early. In this case, the ~170 Ma maximum age difference between these meteorites may have been produced by much deeper burial of Acfer 217 than Rumuruti within an impact-induced thick regolith layer, or within a rubble pile type parent body following parent body re-assembly. The second, preferred scenario is if the impact that reset the age of Acfer 217 was much later than that which reset Rumuruti, then Acfer 217 may have cooled more rapidly within a much thinner regolith layer. In either scenario, the oldest age obtained here, from Rumuruti, provides evidence for relatively early (~4.47 Ga) impact events and breccia formation on the R chondrite parent body.
    • 39Ar-40Ar dating of the Zagami Martian shergottite and implications for magma origin of excess 40Ar

      Bogard, D. D.; Park, J. (The Meteoritical Society, 2008-01-01)
      The Zagami shergottite experienced a complex, petrogenetic formation history (McCoy et al. 1992, 1999). Like several shergottites, Zagami contains excess 40Ar relative to its formation age. To understand the origin of this excess 40Ar, we made 39Ar-40Ar analyses on plagioclase and pyroxene minerals from two phases representing different stages in the magma evolution. Surprisingly, all these separates show similar concentrations of excess 40Ar, ~1 x 10^(-6) cm^(3)/g. We present arguments against this excess 40Ar having been introduced from the Martian atmosphere as impact glass. We also present evidence against excess 40Ar being a partially degassed residue from a basalt that actually formed ~4 Gyr ago. We utilize our experimental data on Ar diffusion in Zagami and evidence that it was shock-heated to only ~70 degrees C, and we assume this heating occurred during an ejection from Mars ~3 Myr ago. With these constraints, thermal considerations necessitates either that its ejected mass was impossibly large, or that its shock-heating temperature was an order of magnitude higher than that measured. We suggest that this excess 40Ar was inherited from the Zagami magma, and that it was introduced into the magma either by degassing of a larger volume of material or by early assimilation of old, K-rich crustal material. Similar concentrations of excess 40Ar in the analyzed separates imply that this magma maintained a relatively constant 40Ar concentration throughout its crystallization. This likely occurred through volatile degassing as the magma rose toward the surface and lithostatic pressure was released. These concepts have implications for excess 40Ar in other shergottites.
    • 3He, 20,21,22Ne, 14C, 10Be, 26Al, and 36Cl in magnetic fractions

      Jull, A. J. T.; Lal, D.; Taylor, S.; Wieler, R.; Grimberg, A.; Vacher, L.; McHargue, L. R.; Freeman, S. P. H. T.; Maden, C.; Schnabel, C.; et al. (The Meteoritical Society, 2007-01-01)
      We report on studies of the concentrations of cosmogenic nuclides in the magnetic fraction of cosmic dust particles recovered from the South Pole Water Well (SPWW) and from Greenland. Our results confirm that cosmic dust material from these locations contains measurable amounts of cosmogenic nuclides.The Antarctic particles (and possibly those from Greenland as well) also contain minor amounts of solar Ne. Concentrations of cosmogenic nuclides are consistent with irradiation of this material as small objects in space, with exposure ages similar to the expected Poynting-Robertson (P-R) lifetimes of 50-200 kyr for particles 25-100 micrometers in size.
    • 40Ar-39Ar age determinations of lunar basalt meteorites Asuka 881757, Yamato 793169, Miller Range 05035, La Paz Icefield 02205, Northwest Africa 479, and basaltic breccia Elephant Moraine 96008

      Fernandes, V. A.; Burgess, R.; Morris, A. (The Meteoritical Society, 2009-01-01)
      40Ar-39Ar data are presented for the unbrecciated lunar basalatic meteorites Asuka (A-) 881757, Yamato (Y-) 793169, Miller Range (MIL) 05035, LaPaz Icefield (LAP) 02205, Northwest Africa (NWA) 479 (paired with NWA 032), and basaltic fragmental breccia Elephant Moraine (EET) 96008. Stepped heating 40Ar-39Ar analyses of several bulk fragments of related meteorites A-881757, Y-793169 and MIL 05035 give crystallization ages of 3.763 +/- 0.046 Ga, 3.811 +/- 0.098 Ga and 3.845 +/- 0.014 Ga, which are comparable with previous age determinations by Sm-Nd, U-Pb Th-Pb, Pb-Pb, and Rb-Sr methods. These three meteorites differ in the degree of secondary 40Ar loss with Y-793169 showing relatively high Ar loss probably during an impact event ~200 Ma ago, lower Ar loss in MIL 05035 and no loss in A-881757. Bulk and impact melt glass-bearing sapmles of LAP 02205 gave similar ages (2.985 +/- 0.016 Ga and 2.874 +/- 0.056 Ga) and are consistent with ages previously determined using other isotope pairs. The basaltic portion of EET 96008 gives an age of 2.650 +/- 0.086 Ga which is considered to be the crystallization age of the basalt in this meteorite. The Ar release for fragmental basaltic breccia EET 96008 shows evidence of an impact event at 631 +/- 20 Ma. The crystallization age of 2.721 +/- 0.040 Ga determined for NWA 479 is indistinguishable from the weighted mean age obtained from three samples of NWA 032 supporting the proposal that these meteorites are paired. The similarity of 40Ar-39Ar ages with ages determined by other isotopic systems for multiple meteorites suggests that the K-Ar isotopic system is robust for meteorites that have experienced a significant shock event and not a prolonged heating regime.