68th Annual Meteoritical Society Meeting (2005) alpha_c-d.pdf

CONTENTS — C through D

Distinguishing Between Sulfur and Bearing Metallic Liquids During Histories N. L. Chabot, A. J. Campbell, M. Humayun, J. H. Jones, and H. V. Lauer...... 5021

Effects of Changing Composition on Li and B Behavior in Lunar Basalts: Implications for Magmas J. Chaklader and C. K. Shearer ...... 5253

Were Permian-Triassic Extinctions Sudden and Caused by Impact? C. R. Chapman ...... 5139

Li and B Isotopic Systematics in CAIs, and Differentiated M. Chaussidon, F. Robert, M. Gounelle, G. Kurat, and J.-A. Barrat...... 5183

Fine-grained Rims Around Chondrules and Refractory Inclusions in ALHA77307 are Compositionally Similar L. J. Chizmadia, E. R. D. Scott, and A. N. Krot...... 5268

Can be Used to Make Habitable? E. J. Clacey ...... 5121

James Smithson (c1765-1829): Smithsonian Institution Founder & Its First Meteorite Investigator R. S. Clarke Jr. and H. P. Ewing...... 5120

Lunar Organic Compounds: Search and Characterization S. J. Clemett, L. P. Keller, and D. S. McKay...... 5300

The History of Early Solar System Processes Recorded in the Structure of Meteoritic Organic Solids G. D. Cody, C. M. O’D Alexander, M. Fogel, T. Araki, and D. Kilcoyne...... 5163

More Impact-Melt Clasts in Feldspathic Lunar Meteorites B. A. Cohen ...... 5314

A Review of 62 Meteorites Recovered from Algeria, Libya and Western Sahara K. J. Cole, B. D. Dod, G. A. Jerman, R. Pelisson, R. Pelisson, and P. P. Sipiera...... 5320

Can Meteorite Porosity Provide Habitats for Interplanetary Transport of Microbes? G. J. Consolmagno SJ, L. J. Rothschild, M. M. Strait, and D. T. Britt...... 5101

Nickel Isotopic Composition of Meteoritic Metal: Implications for the Initial 60Fe/56Fe Ratio in the Early Solar System D. L. Cook, M. Wadhwa, R. N. Clayton, P. E. Janney, N. Dauphas, and A. M. Davis...... 5136

EET 83230: Relationship to Group IVA , and Styles and Timing of Oxidation C. M. Corrigan, T. J. McCoy, D. Rumble, W. McDonough, J. Goldstein, G. Benedix, J. Yang, R. Walker, R. Ash, and J. Honesto...... 5190

Mg Isotopic Study of Wark-Lovering Rims in Type A Inclusions from CV : Formation Mechanisms and Timing M. Cosarinsky, D. J. Taylor, K. D. McKeegan, and I. D. Hutcheon ...... 5284

68th Annual Meteoritical Society Meeting (2005) alpha_c-d.pdf

Highly Siderophile Elements in the Admire, , and Springwater L. R. Danielson, M. Humayun, and K. Righter...... 5276

The U-Th Age of the Milky Way N. Dauphas...... 5029

The Nucleosynthesis of Short-lived Isotopes in Asymptotic Giand Branch A. M. Davis and R. A. Gallino...... 5309

Petrogenesis of Martian MIL 03346 J. M. Day, L. A. Taylor, C. Floss, H. Y. McSween Jr., Y. Liu, and E. Hill ...... 5288

Textural Analysis and Crystallization Histories of La Paz Mare Basalt Meteorites J. M. Day, L. A. Taylor, E. Hill, and Y. Liu...... 5185

Mechanisms for Melt Vein Formation in Meteorites P. S DeCarli, Z. Xie, and T. G. Sharp ...... 5141

What is the Tycho Component at ? J. W. Delano, N. E. B. Zellner, T. D. Swindle, F. Barra, E. Olsen, and D. C. B. Whittet...... 5022

Fracturing in Terrestrial Impact Craters: The Relationship of Confining Pressure to Dynamic Tensile Fracture Strength M. R. Dence...... 5091

Limitations on the Production of Short-lived Radionuclides by Irradiation in the Early Solar System S. J. Desch...... 5265

The Meaning of 60: A Nearby Supernova Injected Radionuclides into Our Solar System S. J. Desch, N. Ouellette, and J. J. Hester...... 5264

Unusual Staurolite-rich Target Rocks and Glass-rich Suevite at the Lake Bosumtwi Impact Structure, Ghana, W. Africa A. Deutsch, F. Langenhorst, K. Heide, U. Bläß, and A. Sokol ...... 5172

Bulk Composition of the Moon: 2. Volatiles and Isotopes M. J. Drake and G. J. Taylor...... 5100

Carswell Impact Structure, Saskatchewan, Canada: Geological, Petrographical and Geophysical Results, and Implications for the Age of the Astrobleme I. Duhamel, S. Genest, F. Robert, and A. Tremblay ...... 5126

Assembly of the Descartes Terrane: Argon Ages of Lunar 67016 and 67455 R. A. Duncan and M. D. Norman ...... 5149

Identification of Alkalic Rocks Using Thermal Emission Spectroscopy: Applications to Martian Remote Sensing T. L. Dunn and H. Y. McSween Jr...... 5254

68th Annual Meteoritical Society Meeting (2005) 5021.pdf

DISTINGUISHING BETWEEN SULFUR AND CARBON BEARING METALLIC LIQUIDS DURING METEORITE HISTORIES. N. L. Chabot1, A. J. Campbell2, M. Humayun3, J. H. Jones4, and H. V. Lauer5. 1The Johns Hopkins University Applied Physics Laboratory, 11100 Johns Hopkins Road, Laurel, MD, 20723. E- mail: [email protected]. 2Department of the Geophysical Sciences, The University of Chicago, 5734 S. Ellis Ave., Chi- cago, IL, 60637. 3National High Magnetic Field Laboratory and Department of Geological Sciences, Florida State University, Tallahassee, FL, 32310. 4NASA Johnson Space Center, Mail Code KR, Houston, TX, 77058. 5ESCG/Barrios Technology, P.O. Box 58477, Houston, TX, 77258.

Many planetary processes involve a metallic liquid, such as the separation of metal from silicate during differentiation and the crystallization of metallic cores as planetary bodies cool. However, for many meteorite samples, separation from or re- moval of a metallic liquid is inferred in a meteorite’s history but often the metallic liquid itself is no longer present in the meteor- ite sample. This has been proposed as the case for a number of meteorite types. For example, some iron meteorites represent the solid metal that crystallized from the molten metallic cores of -sized parent bodies [1]. The siderophile element signa- ture of has been attributed to partial melting with the subsequent removal of a metallic liquid [2, 3]. More generally, the meteorite groups that derived from differentiated parent bodies sample the residual silicate material left behind following the early separation of a metallic liquid [e.g. 4]. Though the metallic liquids may no longer be present in these meteorite samples, it is possible to get information about the composition of the metallic liquids based on the element frac- tionations that the planetary processes left behind. Here we pre- sent solid metal-liquid metal partition coefficients from experi- ments involving C-bearing metallic liquids [5] and compare these results to previous S-bearing data [6]. We focus on the three ele- ments of Cu, Re, and W, for which S and C are observed to have distinctly different effects on the partitioning behaviors. Because different effects will result in different element fractionations in the meteorite samples, by specifically examining Cu, Re, and W concentrations in meteorites, insight can potentially be gained into the presence of S or C during a meteorite’s history. Distin- guishing between fractionations due to the presence of S versus C may be of specific interest to interpreting the history of ureilites, since ureilites contain C-bearing phases such as graphite [7] but also show evidence for loss of a S-rich metallic liquid in their history [2, 3]. Acknowledgements: Supported by NASA grant NAG5- 12831 to N. L. C., NSF grant EAR-0330591 to A. J. C., NASA grants NAG5-13133 and NNG05GB81G to M. H., and NASA RTOP 344-31-20-18 to J. H. J. References: [1] Scott E. R. D. 1972. Geochimica et Cosmo- chimica Acta 36:1205-1236. [2] Humayun M. et al. 2005. Ab- stract #2208. 36th Lunar & Conference. [3] Kallemeyn G. W. and Warren P. H. 2005. Abstract #2165. 36th Lunar & Planetary Science Conference. [4] Mittlefehldt D. W. et al. 1998. In Planetary Materials (J. J. Papike Ed.), Min. Soc. Amer., Wash. DC. [5] Chabot N. L. et al. 2005. Geochimica et Cosmochimica Acta submitted. [6] Chabot N. L. et al. 2003. Me- teoritics & Planetary Science 38:181-196. [7] Goodrich C. A. 1992. 27:327-352. 68th Annual Meteoritical Society Meeting (2005) 5253.pdf

EFFECTS OF CHANGING PYROXENE COMPOSITION ON LI & B BEHAVIOR IN LUNAR BASALTS: IMPLICATIONS FOR MARTIAN MAGMAS. J. Chaklader1 and C. K. Shearer1. 1Institute of Meteoritics, University of New Mexico, Albuquerque, NM 87131-1126. E-mail: [email protected].

Introduction: The late-stage magmatic rims of from some Martian basalts show a decrease in Li and B contents relative to earlier formed pyroxene cores [1-2]. Previous workers interpreted core to rim depletions in Li and B to reflect the loss of several weight percent magmatic water during basalt crystalliza- tion [1-2]. This has profound implications for recent exchange of volatiles between the Martian mantle and atmosphere. To assess alternative mechanisms that may influence Li and B behavior in the absence of aqueous fluid activity, we studied changing py- roxene composition during crystallization in lunar basalts. Here, we present major and trace element results from pyroxenes in lunar basalt samples 75035 (A-17) and 10017 (A-11). Methods: Pyroxenes were imaged with a JEOL JSM-5800 LV SEM and analyzed with a JEOL JXA-8200 EMP (15 kv, 20 nA, <1 µm beam). Prior to trace element analyses, thin sections were soaked in 1 % mannitol solution, rinsed in ultrapure (18 MΩ) water and rastered to reduce effects of B contamination. Pyroxenes were analyzed for 7Li, 9Be, 11B, 88Sr, 140Ce, 146Nd, and 174Yb using a primary beam of O- ions in a Cameca ims-4f (10 kV, 8-10 nA, 10 µm beam). Moderate energy filtering (75 V off- set, ± 25 V) was used to remove molecular ion interference. Results: A-17 pyroxenes have a single Ca depletion, Fe en- richment crystallization trend on the pyroxene quadrilateral with early augitic cores (Wo43En42Fs15), late-stage ferro-pigeonite rims (Wo9En4Fs87) and pyroxferroite as a late-stage mineral. In contrast, A-11 pyroxenes have a more restricted Ca depletion, Fe enrichment trend with early augitic cores (Wo40En44Fs16), late- stage ferro-pigeonite rims (Wo11En21Fs68), and no late-stage py- roxferroite. Lithium depletions are observed in late-stage rims and correspond to regions of high Fe, low Ca and low (Cr3+)VI in A-17 pyroxenes. In contrast, A-11 pyroxenes express relatively constant Li-values across core to rim transects. Boron depletions occur in late-stage rims of both A-17 and A-11 pyroxenes. Discussion: Lithium1+ (M2 site) and Cr3+ (M1 site) substitute jointly as coupled cations into A-17 pyroxenes. The compatibil- ity of Cr3+ into the M1 site decreases the Cr in the melt and late, Fe-rich pyroxene. This results in decreasing the importance of the Li1+ (M2 site) and Cr3+ (M1 site) couple substitution and in- creasing Li incompatibility during the crystallization of pyroxene rims. Alternatively, Ca is expelled during breakdown reactions of metastable pyroxferroite and Li may follow in A-17 pyroxenes. Since late-stage Fe enrichments are not as extensive in A-11 py- roxenes, metastable pyroxferroite is absent and Li loss does not occur. It is also possible that DLi during pyroxferroite crystalliza- tion is lower than DLi during pyroxene crystallization. Late-stage B depletions may reflect loss during eruption of lunar basalts [3]. Late-stage rims of Martian pyroxenes with Li depletions gener- ally exhibit similar extents of Fe enrichment as A-17 pyroxenes. Late-stage pyroxene rims in Nakhla and the A-11 basalt gener- ally have less enriched Fe-contents and no Li depletions. References: [1] McSween, H.Y. et al. (2001) Nature, 409:487-490. [2] Lentz, R.C.F. et al. (2001) Geochimica et Cos- mochimica Acta 65:4551-4565. [3] Meyer, C., Jr., & Schonfeld, E. (1977). 8th Lunar & Planetary Science Conference, p. 661-662. 68th Annual Meteoritical Society Meeting (2005) 5139.pdf

WERE PERMIAN-TRIASSIC EXTINCTIONS SUDDEN AND CAUSED BY IMPACT? C.R. Chapman. Southwest Research Inst., #400, 1050 Walnut St., Boulder CO 80302 USA. E-mail: [email protected].

The K-T mass extinction was very sudden (e.g., >70% of Cre- taceous forams went extinct simultaneously, within the precision of the marine fossil record [1]). The Chicxulub impact clearly caused the K-T boundary. But geologic records are less complete for other large, earlier mass extinctions and the chances are poor that causal craters remain. For the biggest one, the P-T, equivocal evidence for impact has been debated and many alternative causes have been advanced [cf. 2]. Here I evaluate a recent claim [3] that there was a gradual component to extinction of vertebrates before the P-T. I then discuss why impacts by near- objects (NEOs) should be regarded (a) as the "null hypothesis" or mostly likely cause of mass extinctions, barring disproof, rather than (b) as just one of many possible causes or even the explanation of last resort, which re- mains a common perspective among paleontologists. Ward et al. [3] argue for some P-T gradualism and also "that at least some species originated" before the boundary. Neither con- clusion is supported by their data. They define a zero-level plausi- bly marking the sudden event. They claim that vertical distribu- tions of 126 fossil skulls from 21 taxa collected in the Karoo Basin negate a wholly sudden mass extinction. Their case for gradualism rests on just 9 skulls in 3 taxa, distributed over 60m below zero. About 5 other taxa plausibly went extinct at zero, ~3 others passed through, and ~8 taxa originated above zero-level (the extinction opened ecological niches, plausibly fostering speciation). The uppermost skull of the 3 critical taxa was ~10m below zero. The case for gradualism depends on a statistically conclusive tendency for these skulls to be absent as the zero-level is ap- proached. Yet in 10 random trials distributing 9 items between 0 and -60, 3 show an even stronger avoidance of the zero-level than do the actual data. Plainly, there is no robust case for a gradual extinction. (One of the 3 taxa is actually useless, despite being claimed as having the highest confidence, 0.875, of all. Based on just 2 skulls from the same depth [~-52m], it provides no evidence about extinction. The other 2 taxa have claimed confidences of just 0.5.) Ward et al. violated their adopted methodology [4] in many ways. Even had correct methods been used, there would still be less than 1-sigma confidence that there was a gradual compo- nent to P-T extinctions. Statistics of 9 fossils are hardly worthy of a 5-page report in Science and wide coverage by the news media. Indeed, such statistics of fossils from a non-marine, terrestrial environment may reflect evolving Karoo ecology and simple mi- grations of species around Pangaea, rather than extinction. Astro- nomical evidence is that impact of one or more NEOs larger than the K-T boundary extinctor is statistically likely in the past 0.5 Gyr; the Earth can hardly have avoided the inevitable, horrific re- sulting consequences [5]. Thus, absent countervailing evidence or some other equally sudden, energetic modifier of the ecology (no terrestrial alternative is so sudden or energetic), presumption must favor the inevitable NEO impacts to explain mass extinctions. References: [1] Paul C.R.C. 2005. Palaeogeography, in press. [2] Erwin D.H. et al. 2002. USGS Spec. Paper 356, 363-383. [3] Ward P.D. et al. 2005. Science 307:709-714. [4] Wang S.C. & Marshall C.R. 2004. Paleobiology 30:5-18. [5] Chapman C.R. 2002. USGS Spec. Paper 356, 7-19. 68th Annual Meteoritical Society Meeting (2005) 5183.pdf

LI AND B ISOTOPIC SYSTEMATICS IN CAIS, CHONDRULES AND DIFFERENTIATED METEORITES. M. Chaussidon1 , F. Robert2, M. Gounelle2, G. Kurat3 and J.-A. Barrat4.1 CRPG-CNRS, BP20, 54501 Vandoeuvre-les-Nancy, France E-mail: [email protected]. 2 LEME-MNHN- CNRS, case postale 52, 57 rue Buffon, 75005 Paris, France 3Leystrasse 20C/4, A-1200 Wien, Austria. 4 CNRS UMR6538, UBO-IUEM place Nicolas Copernic, 29280 Plouzané Cedex, France.

Li and B show significant isotopic variations in the different components of meteorites. If part of these variations (in the 10 permil range) can be attributed to magmatic or post-magmatic processes (up to 15‰ variations likely due to diffusion processes have recently been detected for 7Li/6Li ratios in lunar and mar- tian meteorites [1, 2]), variations of higher amplitude (several tens of permil) reflect the presence in the solar system of Li and B having different nuclear sources. One of these nucleosynthetic source is of most interest for early solar system processes, namely the production of Li-Be-B elements from irradiation by solar cosmic rays of the gas and solids of the accreting disk. Such irradiation processes should theoretically produce 6Li-poor Li (7Li/6Li ≈ 2), 11B-rich B (11B/10B up to ≈ 5) and the short lived nuclides of Be, 10Be which decays to 10B with a half-life of 1.5Ma and 7Be which decays to 7Li with a half life of 53 days. We have previously presented evidences for (i) the presence in chondrules of Li and B isotopic variations [3-5], (ii) the pres- ence in CAIs of 10B excesses due to the in situ decay of 10Be [6] and (iii) the presence in CAIs of 7Li excesses which could be attributed to the in situ decay of 7Be [7]. All these observations can be reconciled in a model where a small fraction of the Li-Be- B elements is produced in the early solar system and mixed in various proportions in the nebula to the precursors of CAIs and chondrules [8]. If the presence of 10B in CAIs is well demon- strated [9, 10], its implication for the existence of irradiation processes in the early solar system is discussed [11]. We shall compare in this talk these previous data acquired on CAIs, chondrules with new data on CAIs and differentiated me- teorites (, , martian and lunar meteorites) to dis- cuss the following questions : (i) were Li and B isotopic compo- sitions homogenized in the nebula, (ii) what are the distribution of 10Be and 7Be in the nebula ? (iii) do the timescales implied by 26Al between CAIs and differentiated meteorites match those inferred from 10Be ? (iv) what is the fraction of the Li and B iso- topic variations which can be due to early irradiation processes around the young Sun and not to a recent exposure to galactic cosmic rays ? References: [1] Beck P. 2004. Geochimica Cosmochimica Acta 68, 2925-2933. [2] Barrat J.-A. et al. Geochimica Cosmo- chimica Acta (submitted). [3] Chaussidon M. & Robert F. 1995 Nature 374, 337-339. [4] Chaussidon M. & Robert F. 1998 Earth Planetary Science Letters 164, 577-589. [5] Robert F. & Chaus- sidon M. Abstract #1344. 34th Lunar & Planetary Science Con- ference. [6] McKeegan K. D. et al. 2000 Science 289, 1334- 1337. [7] Chaussidon M. et al. (submitted) Geochimica Cosmo- chimica Acta. [8] Chaussidon M. et al. (accepted) in Meteorites and Early Solar System II. [9] Sugiura N. et al. 2001 Meteoritics Planetary Sciences 36, 1397-1408. [10] MacPherson G. J. et al. 2003 Geochimica Cosmochimica Acta.67, 3165-3179. [11] Desh S. 2004 Astrophysical Journal 602, 528-542. 68th Annual Meteoritical Society Meeting (2005) 5268.pdf

FINE-GRAINED RIMS AROUND CHONDRULES AND REFRACTORY INCLUSIONS IN ALHA77307 ARE COMPOSITIONALLY SIMILAR. L. J. Chizmadia1, E. R. D. Scott2 and A. N. Krot2. IInstitute for Astronomy, University of Ha- wai’i. E-mail: [email protected]. 2Hawai’i Institute for Geo- physics and Planetology.

Introduction: Equilibrium thermodynamic condensation [1], O-isotopes [2] and Al-Mg chronology [3] suggest that chondrules and refractory inclusions (CAIs and AOAs) formed in distinct re- gions of the solar nebula separated in time and/or space. There are chemical signatures (e.g. wt%Si vs. wt%Mg) that suggest some genetic relationship between chondrules and matrix (interchondrule matrix and fine-grained rims) [4]. [5] demonstrated how the corre- lation between rim thickness and size indicates forma- tion in the nebula rather than from asteroid debris and in 100-1000 years. A question remains as to whether the there is a connection between the fine-grained rims and the central object: if chondrules formed 1-3 Ma after refractory inclusions, do the fine-grained rims around them reflect an evolution in the chemistry of the solar neb- ula? ALHA77307 was studied because it has repeatedly been shown to be primitive, exhibiting very little aqueous or thermal alteration [e.g. 6,7] and therefore any compositional differences in the rims should be retained. Results: Bulk compositions of 79 fine-grained rims around three types of chondrules (I, II and Al-rich) and two types of inclu- sions (CAIs and AOAs) were found to be indistinguishable on the ~10 micron scale, using the method of [6]. The fine-grained rims show a positive correlation between Al/Si-Fe/Si, S/Si-Fe/Si, Ni/Si- Fe/Si, and Na/Si-K/Si, and a negative correlation between Mg/Si- Fe/Si, Mn/Si-Fe/Si and Cr/Si-Fe/Si. When compared to the solar ratio and normalized to Si, the fine-grained rims are enriched in Al, K, Fe and Ni and depleted in Ca, Ti, Mg, Cr, Mn, Na, and S. The fine-grained rim data from [6] form a tighter population but are embedded within this data. Discussion: This study shows for the first time that regardless of the central object, the fine-grained rims are compositionally in- distinguishable. This implies that although the central objects formed under differing conditions and times, all of the rims were acquired in the same time/place. For example, Type I and II chon- drules are thought to have formed under different conditions (e.g. II show more oxidation and higher volatile contents) [8]. However, these differences are not reflected in the rim compositions. Also, if CAIs acquired rims in the time before chondrule formation, they must have been temporary. Therefore, the fine-grained rims do not carry information of the central object, Al-Ca and Na-K are decoupled from each other implying that 1) these systems are very sensitive to small amounts of aqueous alteration, 2) these systems were decoupled before rim formation or 3) terrestrial weathering has affected the fine-grained materials in ALH77307. Moreover, the fact that Na and S are depleted and Al is enriched in the fine-grained rims relative to the solar ratio opposes the previous assumption that volatile elements are enriched and refractory elements depleted [4]. References: [1] Grossman (1972) GCA v36 597-619; [2] Clay- ton (1999) GCA v63 2089-2104; [3] Huss et al. (2001) MAPS v37 975-997; [4] Huss et al. (2004) Wkshp on Chondrites & Proto- planetary Disk. Abstract #9078; [5] Cuzzi et al. (2004) Icarus v168 485; [6] Brearley (1993) GCA v57 1521-1550; [7] Scott & Jones (1990) GCA v54 2485-2503. Acknowledgements: This study was supported by NASA grant 5-10610 (A. Krot, P. I.) and 5-4212 (K. Keil, P. I.). 68th Annual Meteoritical Society Meeting (2005) 5121.pdf

CAN ASTEROIDS BE USED TO MAKE MARS HABITABLE? E. J. Clacey1. 1International Space University, 1 rue Jean-Dominique Cassini, 67400 Illkirch-Graffenstaden (Strasbourg), France. E-mail: [email protected]

Introduction: Undertaking an immense project such as changing a planet in order to sustain human life on the surface, i.e. terraforming, will require vast resources and effort. This pa- per shall discuss how impacting asteroids onto the surface of a planet, such as Mars, can greatly assist the terraforming effort. It will discuss issues of selecting an asteroid, how to move it to a Mars impact trajectory as well as the useful effects it will have on the planet. Discussion: In order to terraform Mars, it has been sug- gested to use asteroids [1, 2] to import critical elements that are lacking in the regolith. Nitrogen, associated with many life proc- esses, is one such element. This could be mined from the atmos- phere of several planetary moons, such as , or could be im- ported using nitrogen-rich asteroids. Using current data, however, the amount of nitrogen available in asteroids, such as P-type icy asteroids, appears to be limited. Thus, there may be a need for future searches for nitrogen-rich asteroids, possibly in the Kuiper belt and beyond. Using one large (>>10 km diameter) impact to import all the elements that are needed is not deemed practical as it would severely delay any terraforming efforts and negate any terraforming initiatives done prior to the impact. In order to allow humans to live on the surface during the impacts, it would be necessary to limit the size of the asteroid to a few kilometers in diameter. Using a small asteroid, however, the desired change to the planet will be minimal. Another option could, therefore, be to target an asteroid onto the southern pole of Mars [2]. Impacting it at the pole would benefit terraforming by covering the region with a dark regolith mat, thereby reducing the surface albedo and increasing the melting of the pole. The melt would mainly consist of CO2, which will outgas to the atmosphere and increase the mean surface temperature. Melted water may seep down cracks in the ice, taking heat with them, thus increasing the overall heat- ing effect. References: [1] McKay, C. P. & Zubrin, R. M 1993. Technological Re- quirements for Terraforming Mars, American Institute of Aero- nautics and Astronautics, http://www.users.globalnet.co.uk/ ~mfogg/zubrin.htm. [2] Clacey E. J. et al. 2005. Visysphere Mars: Terraforming meets engineered life adaptation. International Space University, available at: http://www.isunet.edu/EN/77

68th Annual Meteoritical Society Meeting (2005) 5120.pdf

JAMES SMITHSON (c1765-1829): SMITHSONIAN INSTITUTION FOUNDER & ITS FIRST METEORITE INVESTIGATOR. R. S. Clarke, Jr.1 and H. P. Ewing2. 1Department of Mineral Sciences, Smithsonian Institution, Washington, D.C. , USA. E-mail: [email protected]. 2Institutional History Division, SIA, Smithsonian Institution, Washington, D.C., USA.

An enigmatic Englishman, James Smithson, bequeathed a large fortune to the United States that led to the founding of the Smithsonian Institution in Washington in 1846. He had never visited the US and was completely unknown here, and his motivations are still mysterious. His extensive personal archive and large meteorite-containing mineral collection were included in the bequest and traveled successfully from London to Washington in 1838. Tragically, they were both lost a few years later, in 1865, in a disastrous fire in the Smithsonian Institution Building before they could reveal their stories. All that remained of his meteorites is a tantalizing quotation: “The [mineral] cabinet also contains a valuable suite of meteoric stones, which appear to be suites of most of the important meteorites which have fallen in Europe during several centuries.” Smithson’s mature years spanned late 18th century Enlightenment with its skepticism about meteorites and passed into the early 19th century period of serious discussion of their origins: a transformation from an Aristotelian view that space was empty to the realization that small bodies fall from space to the Earth’s surface. He was there at the beginning of modern meteoritics, and recent archival research reveals that he was an active participant in the scientific discussion as well as a meteorite collector [1]. William Thomson (1761-1806) was a mentor of Smithson during his student years at Oxford, 1782-1786, and became a life- long friend. Thomson left England in 1790 for residence in Naples where he became an active investigator of Mt. Vesuvius. He was monitoring the Vesuvius’s massive June 15, 1894 eruption when the Siena meteorite fell the next day, on June 16, 200 km to the north. Smithson was residing in Florence at the time and went immediately over the Chianti Hills to investigate this seminal fall that Thomson later described. Reports from the period show Smithson to have been very highly regarded by his Italian scientific colleagues. Smithson spent much of his life on the Continent, particularly in Paris where he was acquainted with the scientific leadership of the day. There were also periods in other French locations, and in various locations in Italy and Germany, all interspersed with periods in London. His contacts in these places were the scientific leadership of the area. He knew and was known by the leading mineralogists of the day, and Smithsoin was regarded by them as an accomplished mineral collector, mineralogist, and particularly as an accomplished chemical analyst of minerals. Although he apparently never worked on meteorites himself, he actively followed the developing science throughout his life. References: [1] Ewing, H. P. 2005. Manuscript of Smithson biography in preparation to be published by Bloomsbery, London, 2006. 68th Annual Meteoritical Society Meeting (2005) 5300.pdf

LUNAR ORGANIC COMPOUNDS: SEARCH AND CHARACTERIZATION. S.J. Clemett1, L.P. Keller2 & D.S. McKay2; 1ERC Inc., 2NASA JSC, ARES, Houston, TX 77058. E-mail: simon.j.clemett@.gov

Introduction: With the exception of CH4 [1-2] no complex indigenous organic matter has been positively identified in any Apollo lunar sample. Yet several processes should contribute to the lunar organic inventory: (1) meteoritic carbonaceous accre- tion; (2) organic synthesis driven by energetic cosmic, solar and planetary magnetospheric radiation (UV, keV H+ & He2+ and more massive keV to MeV ions). Both effects would have been enhanced in an early transient lunar protoatmosphere, but con- tinue albeit slowly to the present day. Using a recently completed ultra-fast laser desorbtion / laser ionization mass spectrometer (ultra-L2MS), we are revisiting the search for, and characteriza- tion of, indigenous lunar organic matter. Strategy: Previous non-detection of lunar organics may be a consequence of not only its paucity, but also its heterogeneous distribution. If the sample size required for a measurement is large in scale relative to the localization of organics detection becomes limited not by ultimate sensitivity but rather by the ability to distinguish an indigenous signature from background contamination (~0.1 ng.g-1 [3]) and simple mass dilution, both effects scaling proportionally with sample size. Whilst ultra- L2MS is not intrinsically more sensitive than techniques used previously to characterize lunar samples, it has the virtue of be- ing capable of spatially resolved measurement on a significantly smaller sample mass (10-9 g vs. 10-2 g). Hence ultra-L2MS detec- tion can detect localized organics which previously would have been obscured by background contamination and mass dilution effects.

Preliminary Results: An ultra-L2MS spectrum (see above) from several particulates of Apollo 16 mature highland soil 64501, (<20 µm dry-sieved fraction) mounted on KBr. Mass peaks at 39, 41, 118, 120, 157, 159 and 161 amu are due to K and KBr cluster ions from the KBr substrate, while peaks at 27, 56 and 70 are due to Al, Fe, and Al2O from the lunar grains. Under- lying these peaks is a suite of simple 1-, 2-, 3- and 4-ring aro- matic species. Styrene and dimethoxybenzene are almost cer- tainly organic contaminants from the sample, however, benezene, phenol, naphthalene, phenanthrene and pyrene appear indigenous and are present at concentrations of < 1 ppm. References: [1] Lipsky, et al. (1970) Science 167, 778 and subsequent papers in issue; [2] Cadogan, et al. (1973) LPSC IV 2,1493; [3] Allton (1999) LPSC XXIX, 1857. 68th Annual Meteoritical Society Meeting (2005) 5163.pdf

THE HISTORY OF EARLY SOLAR SYSTEM PROCESSES RECORDED IN THE STRUCTURE OF METEORITIC ORGANIC SOLIDS. G. D. Cody1, C. M. O’ D. Alexander2. M. Fogel2, T. Araki3, D. Kilcoyne3 1Geophysical Laboratory, Carnegie Institution of Washington, Washington DC. [email protected] 2Department of Terrestrial Magnetism, Car- negie Institution of Washington, 3Advanced Light Source, Law- rence Berkeley Laboratory.

Introduction: In our earlier study of insoluble organic mat- ter (IOM) from Murchison [1] we showed that we could thor- oughly dissect the organic functional group information in mete- oritic IOM. However, the study of highly complex organic matter from a single meteorite can only shed a little information on the chemical history of the early solar system. Consequently, we have expanded our studies to include IOM samples from differ- ent meteorite groups and petrologic grade in order to establish the chemical pathways recorded in this complex material. Analy- sis of pure meteorite IOM from four different groups, (CI1), EET92042 (CR2), Murchison (CM2), and (C2-ungrouped) reveal considerable variation in bulk organic composition across the different meteorite group’s IOM. The fraction of aromatic carbon increases as CR2 < CI1 < CM2 < Tagish Lake. The increases in aromatic carbon are offset by re- 3 ductions in aliphatic (sp ) carbon moieties, e.g, “CHx”, and 2 “CHx(O,N)”. Oxidized sp bonded carbon, e.g. carboxyls and ketones grouped as “CO”, are largely conservative across these meteorite groups. The variation in chemistry across these four meteorite groups is consistent with alteration by low temperature chemical oxidation that occurred in the meteorite parent body [2]. We have expanded these studies to include a suite of IOM derived from aqueously altered CM chondrites including Kives- varra, Murchison, Bells, Cold Bokkeveld, Mighei, Murray, ALH83100, and MET01070. Remarkably, we find that in spite of the large range in the extent of aqueous alteration, e.g. from Kivesvaara to MET01070 (a CM1) [3] only subtle differences in the organic structure of the IOM are observed. It would appear that low temperature aqueous alteration alone has minimal effect on the chemical structure of IOM. We have also analyzed IOM isolated from CV and CO chondrites. The chemistry of IOM in these groups of meteorites provide extremely valuable informa- tion regarding the thermal history of respective parent bodies. Furthermore, although the IOM hydrogen contents in CV’s and CO’s are lower than the CR’s, CI’s, and CM’s we have studied, this IOM contains significant organic oxygen and nitrogen, and is, therefore, still organic. To date, we have acquired NMR data on IOM from the CV’s Leoville, Vigarano and Allende, and C-, N-, and O-XANES on Kaba, Mokoia, Leoville, Vigarano, Al- lende, and the CO’s ALH77307, ALH77003, and Isna. As ex- pected, the chemical structure of IOM from both the CV’s and CO’s differ enormously from that of the CR, CI, CM’s, and Tagish Lake. The chemical structures of CV and CO IOM do reveal, however, spectroscopic signatures indicative of the extent of thermal metamorphism. These novel spectral features may allow us to independently rank the extent of thermal metamor- phism using IOM as recorder. References: [1] Cody G. D. et al. 2002. Geochim. Cosmo- chim. Acta :66, 1851. [2] Cody G. D. and Alexander C. M.O’D. 2005 Geochim. Cosmochim. Acta. 69, 1085. [3] Zolensky M. and Le. L. 2003 Abstract # 1235 34th Lunar & Planetary Science Conference. 68th Annual Meteoritical Society Meeting (2005) 5314.pdf

MORE IMPACT-MELT CLASTS IN FELDSPATHIC LUNAR METEORITES. B. A. Cohen, Inst. of Meteoritics, Univ. of New Mexico, Albuquerque, NM 87131 ([email protected]).

Introduction: Impact-melt clasts in breccias yield ages of impacts occurring in the vicinity of the until its lithification [1]. Major-element chemistry of the clasts distin- guishes the source terrane of the breccia. This study reports on 13 clasts in five new meteorites, identified using the petrographic mi- croscope and backscattered-electron imaging and using the electron microprobe to obtain major-element chemistry via a grid of defo- cused beam analyses. Most analyses have low totals due to cracks; therefore, all analyses totalling 85-101% were normalized and av- eraged to yield the bulk composition of the clast. These clasts will be extracted from the meteorites for 40Ar-39Ar analysis. Results: Yamato 86032, Dhofar 910, Dhofar 911, and Kalahari 008 are feldspathic breccias with varying amounts of regolith and impact-melt components [2]; both Dhofar meteorites may be paired with various other Dhofar meteorites. Impact-melt clasts in these meteorites are high in Al2O3 and have compositions within the range of Apollo 16 feldspathic breccias (Fig. 1), consistent with an origin in the feldspathic lunar highlands either prior to, or far away from, the nearside KREEP-rich terrane that produced mafic im- pact-melt rocks. Sayh al Uhaymir (SaU) 169 [3] is mostly a KREEP-rich mafic impact melt breccia, probably originating from the nearside KREEP terrane. The SAU 169 rock also contains adhering regolith breccia, a sample of which was used for this study. Impact-melt clasts within SAU 169 include both feldspathic and KREEPy clasts (Fig. 1) derived from the lunar nearside.

References: [1] Cohen et al. (2005) MAPS, in press. [2] Koro- tev (2005) http://epsc.wustl.edu/admin/resources/moon_ meteor- ites.html. [3] Gnos et al. (2004) Science 305, 657–659.

68th Annual Meteoritical Society Meeting (2005) 5320.pdf

A REVIEW OF 62 METEORITES RECOVERED FROM ALGERIA, LIBYA AND WESTERN SAHARA. K. J. Cole1 B.D. Dod2, G.A. Jerman3, R. Pelisson4, R. Pelisson4, and P.P. Sipiera1. 1Schmitt Meteorite Research Group, Harper College, Palatine, Il 60067. [email protected]. 2Metallurgical Diagnostic Facility, NASA Marshall Space Flight Center, Huntsville, AL 35812, USA, 3Dept. of Physics and Earth Sciences, Mercer Uni- versity, Macon, GA 35812, USA, 4SaharaMet., LaTerrasse, France.

Introduction: During the years 1998 through 2004 the Har- rison H. Schmitt Meteorite Research Group at Harper College has classified 62 meteorites recovered by Richard and Roland Pelisson (SaharaMet) as a result of their systematic searches in Algeria (Acfer), Libya (Dar al Gani and Hammada al Hamra), and Western Sahara [1], [2], [3], [4]. These include three random finds in Libya by others. In contrast to the undocumented NWA finds from Algeria and Morocco, these 62 meteorites are well documented and provide accurate data to construct maps which contribute to the determination of possible pairings of individual finds. Results: The 62 meteorites analyzed by the Schmitt Meteor- ite Research Group record 16 H, 21 L, and 11 LL type chon- drites; 4 paired CO3 chondrites (DaG 749, 858, 1006, 1028); 2 CR chondrites (DaG 974 and Acfer 324); and 1 EL6 (Acfer 356). In addition, six consisting of 4 eucrites (Acfer 353 and DaG 863, 872, 973) [5] and two urielites (DaG 874 and 1010) were identified, along with one (DaG 962). Among the more significant finds is Acfer 353, an 11,935 gram individual which represents the only among the 363 me- teorites found in the Acfer region. Another eucrite (DaG 872) appears to have oxygen isotope ratios more characteristic of a lunar origin [6]. Although Acfer 324 is most likely paired with several other Acfer CR 2’s, it has many interesting characteristics that may point to a separate origin and needs further study [7]. DaG 749 represents only one of several paired specimens from a CO3 strewn field which has been well documented by the Pelis- son brother’s field maps. Summary and Conclusions: Given the large number of me- teorites coming out of the deserts of North Africa and Oman, great care should be taken to collect these specimens in a manner that contributes to the over-all understanding of the find. The care taken in the recording these 62 finds clearly provides the data necessary to make a complete analytical evaluation of each specimen. Random collection and analysis of undocumented specimens adds little to the meteorite database other than new numbers and should be discouraged. References: [1] Sipiera, P.P. et al, 1999. Meteoritics and Planetary Science 34: A109-110, [2] Sipiera, P.P. et al, 2001. Meteoritics and Planetary Science 36: A190-191, [3] Cole, K.J. et al, 2002. Meteoritics and Planetary Science 37: A132, [4] Cole, K.J. et al, 2003. Meteoritics and Planetary Science 38: A71, [5] Sipiera, P.P., 2001. Meteoritics and Planetary Science 36: A190, [6], Patzer et al, 2002. Abstract #1106. 33rd Lunar & Planetary Science Conference, [7] Sipiera, P.P. and K. J. Cole, 2004. Abstract 1063, 35th Lunar and Planetary Science Confer- ence. 68th Annual Meteoritical Society Meeting (2005) 5101.pdf

CAN METEORITE POROSITY PROVIDE HABITATS FOR INTERPLANETARY TRANSPORT OF MICROBES? G. J. Consolmagno SJ1, L. J. Rothschild2, M. M. Strait3, and D. T. Britt4. 1Specola Vaticana, V-00120, Vatican City State. E-mail: [email protected] 2NASA Ames Research Center. 3Alma College, Alma, MI. 4University of Central Florida, Orlando FL.

Introduction: Most stony meteorites have a measured porosity on the order of 10% [1]. The bulk of the porosity occurs as a net- work of interconnected microcracks which permeate the fabric of the rock (cf. [2]), most likely the result of the moderate (a few GPa) shock events typical for extraterrestrial samples subjected to impacts and launched into Earth-crossing orbits [3]. Could extrater- restrial life enter these microcracks, seal off a small volume within them, and thus be both protected from the vacuum environment and shielded from the cosmic ray and UV environment by the centime- ters of rock between it and interplanetary space? Previous models: Modeling [4] suggests that microbes could survive the impact and forces needed to cause a sample to be jetti- soned from a planet, escape to space, and survive the impact of landing on Earth. They predict a substantial survival rate of bacte- rial endospores after a simulated meteorite impact at shock pres- sures of 32 GPa. Further, spores of B. subtilis mixed with minerals representing the of meteorites survive in the space en- vironment better than unprotected spores [5]. Crack width vs. microbe size: Typical widths for microcracks range from 0.5 µm to >5 µm. For example, in 56 measurements of cracks in Barratta (L3.8), we found widths to range from 0.6 µm to 3.8 µm (averaging 2.0 µm ± 0.7). The cracks were narrower for Knyahinya (L/LL5): 0.82 µm ± 0.45, ranging from 0.33 µm to 3.2 µm based on 51 measurements in one large grain. Bishopville () cracks ranged from 0.4 µm to 6.5 µm (average width 2.2 µm ± 1.4) based on 67 measurements. (SNC) had larger cracks, averaging 4.9 µm ± 2.3 with a range from 1.7 µm to 9.6 µm based on 32 measurements. In addition to cracks, small holes are also present in some achondrites; in Bishopville the average diame- ter of 17 such holes is 14.7 µm ± 7.6 with a range from 5.4 µm to 32.9 µm. Bacteria and archeae sizes mostly range from 0.2 µm to 10 µm. Eukaryotic cells can be very small (picoeukaryotes, perhaps the most abundant eukaryotes on Earth, are between 0.2 µm and 2-3 µm in diameter) or very large (> 1 cm) but tend to range from 5- 100 µm in diameter. Virus diameters are about 0.05-0.1 µm. Future Work: We plan to test the suitability of meteorite mi- crocrack pore spaces for microbe habitat and transport. Destructive experiments on SNC meteorites are impractical, but the geometry of their porosity is similar to that of ordinary chondrites [6]. We will measure a suitable ordinary for porosity; then, at NASA-ARC, it will be heat sterilized and a known and easily traceable type of microbe (e.g. Synechococcus, Bacillus subtilis, or yeast) will be introduced into it. The meteorite will be exposed to simulated space conditions, then cored or cut to determine the sur- vival characteristics of the microbes, as a function of time of expo- sure and depth within the rock. References: [1] Britt D. T. and Consolmagno G. J. 2003. Me- teoritics and Planetary Science 38:1161–1180. [2] Strait M. M. and Consolmagno G. J. 2005. Abstract #2073, 36th Lunar and Planetary Science Conference. [3] DeCarli P. et al. 2001. Meteoritics and Planetary Science 36:A47. [4] Mileikowsky C. et al. 2000. Icarus 145:391–427. [5] Horneck G. et al. 2001. Icarus 149:285–290. [6] Strait M. M. and Consolmagno G. J. 2004. Meteoritics and Plane- tary Science 39:A100. 68th Annual Meteoritical Society Meeting (2005) 5136.pdf

NICKEL ISOTOPIC COMPOSITION OF METEORITIC METAL: IMPLICATIONS FOR THE INITIAL 60FE/56FE RATIO IN THE EARLY SOLAR SYSTEM. D. L. Cook1,2, M. Wadhwa2,3, R. N. Clayton1,2,4, P. E. Janney2,3, N. Dauphas1,2,4, and A. M. Davis1,2,4. 1Dept. of the Geophysical Sciences, The University of Chicago, Chicago, IL 60637 (dave- [email protected]). 2Chicago Center for Cosmochemistry, Chicago, IL 60637. 3Dept. of Geology, The Field Museum, Chi- cago, IL, 60605. 4Enrico Fermi Institute, The University of Chi- cago, Chicago, IL, 60637.

Introduction: The former presence of the short-lived ra- 60 dionuclide Fe (t1/2 = 1.49 My) has been reported from numerous meteoritic components. Excesses of the daughter isotope, 60Ni, have been found in chondrites [1-3] and eucrites [3, 4]. Recently, variations of up to 1.5 ε in the 60Ni/58Ni ratio (attributed to the decay of 60Fe) were reported for Fe-Ni metal from several iron meteorites [5] and ordinary chondrites [6]; these were the first reports of excess 60Ni in meteoritic metal. However, our recent analyses of metal from a suite of 8 iron meteorites and the Bren- ham revealed no resolvable excesses of 60Ni [7]. We report here the Ni isotopic composition of metal from 8 addi- tional meteorites to determine if excesses of 60Ni are present. Results and Discussion: Iron-nickel metal from the follow- ing meteorites was analyzed: (IAB), Bella Roca (IIIAB), Yanhuitlan (IVA), Eagle Station (pallasite), Forest Vale (H4), Bishunpur (LL3.1), Renazzo (CR), and Gujba (CBa). All samples were processed at the Field Museum except Toluca. An elevated 60Ni/58Ni ratio of ≈ 1 ε was reported by [6, F. Moynier, pers. comm.] for this meteorite and, therefore, two separate aliquots from a single digestion were obtained from Lyon for inter- laboratory comparison. One aliquot had been chemically proc- essed in Lyon for Ni separation, and the other was unprocessed; the latter was processed at the Field Museum and both aliquots were analyzed. Nickel isotope measurements were made by MC- ICP-MS at the Isotope Geochemistry Laboratory of the Field Museum. As in our previous report [7], no 60Ni excesses were detected in any of the meteoritic metal samples (including both aliquots of Toluca obtained from Lyon) beyond our external pre- cision of ±16 ppm (2σ). On a 60Fe-60Ni isochron plot, the slope of the best-fit line through all our data [6, this study] yields an up- per limit on the 60Fe/56Fe ratio of ≤4 × 10–7, consistent with some estimates from ion microprobe studies of components in ordinary chondrites (e.g., [1]). Thus, the Ni isotopic compositions of metal in iron meteorites, pallasites and chondrites do not provide any evidence for an initial 60Fe/56Fe ratio as high as ~3 × 10–6, as re- cently proposed by [6], at the time of Fe-Ni fractionation in the early solar system. Acknowledgement: We thank F. Moynier and F. Albarède (Ecole Normale Supérieure de Lyon) for generously providing aliquots from their solutions of Toluca. References: [1] Tachibana S. and Huss G. R. 2003. Astro- physical Journal 588:L41-L44. [2] Guan Y. et al. 2003. Meteorit- ics & Planetary Science 38: A138. [3] Mostefaoui S. et al. 2004. New Astronomy Reviews 48: 155-159. [4] Shukolyukov A. and Lugmair G. W. 1993. Science 259:1138-1142. [5] Moynier F. et al. 2004. Abstract #1286. 35th Lunar & Planetary Science Con- ference. [6] Moynier F. et al. 2005. Abstract #1593. 36th Lunar & Planetary Science Conference. [7] Cook D. L. et al. 2005. Ab- stract #1779. 36th Lunar & Planetary Science Conference. 68th Annual Meteoritical Society Meeting (2005) 5190.pdf

EET 83230: RELATIONSHIP TO GROUP IVA IRONS, AND STYLES AND TIMING OF PARENT BODY OXIDATION. C. M. Corrigan1, T. J. McCoy2 . D. Rumble3, W. McDonough4, J. Goldstein5, G. Benedix6, J. Yang5, R. Walker4, R. Ash4, J. Honesto4. 1JHU/Applied Physics Lab., Laurel, MD 20723, USA. ([email protected]). 2National Museum of Natural History, Smithsonian Inst., Washington, DC 20560, USA. 3Geophysical Lab., Carnegie Inst. of Washington, Wash- ington DC, 20015, USA. 4Dept. of Geology, Univ. of Maryland, College Park, MD 20742 USA. 5Dept. of Mech. & Indust. Eng., Univ. of Massachusetts, Amherst, MA 01003, USA. 6Dept. of Earth & Plan. Sci., Wash. Univ., St Louis, MO 63130, USA.

Introduction: We recently examined Ni-rich ungrouped iron meteorites, including Tishomingo [1, 2] and now EET 83230 to determine whether or not they are extensions of the main groups IVA and/or IVB. Our findings suggest that oxi- dation is a key process in the formation of high-Ni irons. Results: According to [3], siderophile elements in EET 83230 are consistent with it being the result of extreme fractional crystallization of a IVA iron, while PGE abundances [4] require mixing of late stage liquids and middle stage solids of IVA irons to explain the composition of EET 83230. We have measured the oxygen isotope compositions of phosphates in EET 83230, and they fall into the IVA iron group [5]. With the exception of the presence of large phosphates, EET 83230 structurally resem- bles a IVB, perhaps as a reflection of it containing higher Ni than most IVAs (16 wt.% vs. 8-12 wt.%). Additionally, we have measured the full suite of siderophile elements in EET 83230 and the resulting pattern mimics that of IVA irons. Discussion: The link between EET 83230 and IVA irons provides another perspective on the role of oxidation (particu- larly of P) during parent body differentiation. Oxidation appears to be a widespread phenomenon during core formation and crys- tallization, though different styles are observed. We previously argued [1,2] that the Ni-rich, P-poor ungrouped iron, Tisho- mingo, experienced oxidation of ~70% of its metallic iron and all of its P prior to core formation. This early oxidation produced an iron meteorite lacking either phosphides or phosphates. In EET 83230, phosphides are absent, but iron phosphates are present, suggesting that oxidation occurred later in the history of the IVAs, during crystallization. In this case, trace quantities of in- compatible oxygen dissolved in the core probably reached satura- tion during late-stage crystallization, resulting in P oxidation. Given the silicate-poor nature of the core, the only available cation was Fe, producing iron phosphates. This situation differs from that of IAB [6] and IIICD [7] irons, where low-Ni, early- crystallizing members often contain phosphides, and high-Ni members contain a variety of complex Na,Ca,Mg-phosphates. These almost certainly formed by the same mechanisms observed in EET 83230, but this oxidized P scavenged cations from the abundant silicate minerals in IAB and IIICD irons. Thus, while each of these groups records the role of oxidation, this oxidation appears to have occurred at different times and manifests itself in fundamentally different chemical and mineralogical properties. References: [1] Corrigan et al. (2005) LPSC XXXVI, #2062. [2] Corrigan & McCoy (2005) LPI Contrib. 1267, 7023. [3] Scott et al. (1996) GCA 60, 1615 [4] Walker et al. (2005) LPSC XXXVI, 1313. [5] Rumble et al. (2005) this vol. [6] Benedix et al. (2000) MAPS 35, 1127. [7] McCoy et al. (1993) Meteoritics 28, 552. 68th Annual Meteoritical Society Meeting (2005) 5284.pdf

Mg ISOTOPIC STUDY OF WARK-LOVERING RIMS IN TYPE A INCLUSIONS FROM CV CHONDRITES: FORMATION MECHANISMS AND TIMING. M. Cosarinsky1, D. J. Taylor1, K. D. McKeegan1 and I. D. Hutcheon2. 1Dept. Earth & Space Sciences, UCLA, Los Angeles, CA 90095-1567; 2Chemical Biol- ogy & Nuclear Science Division, LLNL, Livermore, CA 94551-0808. [email protected].

Introduction: The abundance of 26Al in chondritic materials in principle permits a determination of the relative timing of events that occurred during the early stages of solar system formation [1]. In particular, Ca-Al-rich inclusions (CAIs) from CV chondrites experienced complex histories and many underwent high temperature processing that resulted in the formation of Wark-Lovering rims (WLRs), or sequences of thin single-mineral layers, by flash thermal events [2] or condensation [3,4]. Analytical techniques to resolve excess 26Mg in the low Al/Mg phases characteristic of WLRs have only recently been developed and these few studies suggest that the high temperature processes occurred several ×105 years after CAI formation [3,5,6]. We report here ion microprobe Mg isotope measurements of WLRs around type A CAIs and consider the implications for the timing and nature of WLR formation. Results and Discussion: WLRs completely surround the Viga- rano 1623-2, and Efremovka E44L and E44N compact type A (CTA) CAIs as well as each nodule of the fluffy type A (FTA) Vigarano 477-5 and Allende TS24 and TS25 CAIs. These WLRs consist of an innermost layer of spinel intergrown with hibonite blades and minor perovskite, an intermediate layer of melilite, pervasively replaced by anorthite, and an outermost layer of Ti-Al-rich pyroxene grading outwards to Al-diopside. WLR phases yield well-correlated Al-Mg isochrons, corresponding to initial 26Al/27Al abundances of 5.5, 4.4, and 4.4 (×10–5) for the FTAs TS25, TS24 and V477-5, respectively, and of 5.2, 5.0, and 4.8 (×10–5) for the CTAs V1623-2, E44N, and E44L (uncertainties are in the range 0.1-0.2×10–5). The CAI interior phases also yield apparent isochrons [6] and, in all cases but one (TS25), there is a resolvable time difference between CAI and WLR formation ranging from ~0.5 to 3×105 years. Our data suggest that these CAIs did not form at a single time [7], especially in the case of the never molten FTAs [8], and also that rim formation occurred over ~2×105 years. Some CAIs (e.g., TS25) apparently acquired their WLRs even before other CAIs achieved isotopic closure (e.g., V477- 5). Small fractionations between individual WLR layers are seen: pyroxene is lighter (δ25Mg= –2.2 to 1.6 ‰) than spinel (δ25Mg=0.2 to 6.2 ‰) in all rims. These results may be difficult to reconcile with condensation models [3] but could be explained by flash heating and subsequent reequilibration with ambient gas by diffusion of light Mg into the pyroxene layer [2]. Such high temperature events could have been produced by shock waves [9] or by flare events close to the proto-sun [10]. In summary, the data suggest a dynamic environment for WLR formation which persisted for a long period of time. References: [1] MacPherson G.J. et al. (1995) Meteoritics, 30, 365-386; [2] Wark D. and Boynton W.V. (2001) MAPS 36, 1135- 1166; [3] Simon J.I. et al. (2005) LPSC 36, #2068; [4] Dyl K.A. et al. (2005) LPSC 36, #1531; [5] Cosarinsky M. et al. (2205) LPSC 36, #2105; [6] Taylor D.J. et al. (2005) LPSC 36, #2121; [7] Taylor D.J. et al. (2005) MAPS, this issue; [8] MacPherson G.J. and Grossman L. (1984) GCA 48, 29-46; [9] Desch S.J. and Connolly H.C. (2002) MAPS 37, 183; [10] Shu F.H. et al. (2001) ApJ 548, 1029-1050. 68th Annual Meteoritical Society Meeting (2005) 5276.pdf

HIGHLY SIDEROPHILE ELEMENTS IN THE ADMIRE, IMILAC, AND SPRINGWATER PALLASITES. L. R. Daniel- son1 , M. Humayun2, and K. Righter1. 1Mail Code KT, NASA JSC, 2101 NASA Rd 1, Houston, TX 77058. E-mail: [email protected]. 2National High Magnetic Field Labora- tory and Dept. of Geological Sciences, Florida State University, Tallahassee, FL 32310.

Introduction: Pallasites are long thought to represent a metal- lic core-silicate mantle boundary, where the IIIAB irons are linked to the crystallization history of the metallic fraction, and the HED meteorites may be linked to the silicate fraction [1,2,3]. However, measurement of trace elements in individual metallic and silicate phases is necessary in order to fully understand the petrogenetic history of pallasites, as well as any magmatic processes which may link pallasites to both IIIAB irons and HED meteorites. In order to achieve this objective, we measured abundances of a suite of ele- ments, including the highly siderophile elements, in (K), (T), (Tr), and (ol) for the pallasites Admire, Imilac, and Springwater. Analytical: Trace element microanalysis was performed using a CETAC LSX-200 laser ablation system coupled to a Finnigan Element™ at the NHMFL, FSU, following procedures modified from Campbell and Humayun [4]. Elemental abundances were determined in line scan mode, from the isotopes: 53Cr, 57Fe, 59Co, 60Ni, 63Cu, 69Ga, 74Ge, 75As, 95Mo, 102Ru, 103Rh, 105Pd, 184W, 185Re, 192Os, 193Ir, 195Pt, and 197Au. Ablated tracks across individual min- eral grains ranged from 100 µm to 2.36 mm long, and 30 to 110 µm wide, depending on the grain size. Standards were Filomena, Hoba and SRM-612. Results: Some zoning was noted at phase boundaries, so parti- tion coefficients (D) were extracted by using average values of elements for flat portions of each traverse. D(Os,Re,Ru,Pt,Rh)T/K range from 1.0 to 1.7, while Cr, Co, As, and W partitioned prefer- entially into kamacite. D(HSE)metal/Tr for all three pallasites ranged from ~10 to 100, except Cr, Cu, Mo and Re which partitioned pref- erentially into troilite. 4 D(HSE)metal/ol are generally < 10 , spanning two orders of mag- nitude within individual meteorites. The metal composition is con- stant; the variation may be due to fine metal inclusions in the sili- cate. There was consistent variation between pallasites, where Ad- mire < Springwater < Imilac. Discussion: D(HSE)T/K for Imilac is in good agreement with previous studies for , IAB and IIIAB irons, in which D’s cluster around 1.5 [5,6]. However, D(Re,Os)metal/Tr are several or- ders of magnitude less than the 103-104 for IAB irons [7]. D(HSE)metal/ol is generally less than reported by [8], >104. The zoning (e.g., Cr, Cu, W, Re) across multiple phases in metals may be the result of diffusion on quench or post quench magmatic interaction. In the variation in HSE abundances is consistent with inclusions of metal. Some previous large scale variation (Ir, Ni, for example) in pallasites may be resolved by fur- ther analyses on individual phases. References: [1] Scott, 1977, Geochim. Cosmochim. Acta, 41: 349-360. [2] Mittlefeldt et al., 1998, In: Planetary Materilas, Papike J.J. (Ed), p. 195. [3] Wasson and Choi, 2003, Geochim. Cosmochim. Acta, 67: 3079-3096. [4] Campbell and Humayun, 1999, Anal. Chem., 71: 939-946. [5] Hsu et al., 2000, Geochim. Cosmochim. Acta, 64: 1133-1147. [6] Hirata and Nesbitt, 1997, Earth. Planet. Sci. Lett., 147: 11-24. [7] Shen et al., 1996, Geo- chim. Cosmochim. Acta, 60: 2887-2900. [8] Hillebrand et al., 2004, LPSC XXXV, No. 1278. 68th Annual Meteoritical Society Meeting (2005) 5029.pdf

THE U-Th AGE OF THE MILKY WAY. N. Dauphas. Origins Lab., Dept. Geophysical Sci., Enrico Fermi Inst., and Chicago Ctr. Cosmochemistry, Univ. of Chicago, Chi- cago IL 60637, USA. E-mail: [email protected].

Introduction: Much progress has been made since the pio- neering work of Patterson [1] for determining the age of the solar system. Using modern mass spectrometric methods, the earliest solids formed in the solar nebula can now be dated with a preci- sion of 0.6 My [2]. The application of similar radiometric meth- ods to the determination of the age of the Milky Way has been less successful. Two methods exist for dating the Galaxy. One relies on the determination of the 238U/232Th (U/Th) ratio in the spectra of low metallicity stars in the halo of the Galaxy [3,4]. The other relies on the determination of the U/Th ratio in meteor- ites [5,6] and modeling of the nucleosynthesis of actinides in the Galaxy through time [7,8]. These two approaches use the U/Th production ratio as an input parameter in the calculations. Acti- nides are produced by the r-process, which involves exotic nu- clides on the neutron-rich side of the valley of β-stability [9,10]. When propagated, the nuclear physics uncertainties on the U/Th production ratio (0.4-0.7) lead to large uncertainties for the calcu- lated ages. The U/Th ratios measured in meteorites and low met- allicity halo stars can be used together to estimate the U/Th pro- duction ratio and the age of the Milky Way with better precisions [11]. Two equations in two unknowns: The U/Th ratio measured in low metallicity halo stars depends on the U/Th ratio in the when it formed and on the time since formation of the star [3,4]. Low metallicity halo stars formed early in the galactic history. Their age can be taken to be the age of the Milky Way (TG) and the U/Th ratio that they inherited from the ISM at their formation must be close to the production ratio (PU/Th). It is therefore possi- U/Th ble to define a relationship between TG and P . The U/Th ratio measured in meteorites represents the composition of the ISM in the solar neighborhood at solar system birth. This value reflects nucleosynthesis of actinides in stars, ejection of newly synthe- sized matter in the ISM, and decay integrated over the age of the galaxy. If the history of nucleosynthesis is prescribed, then it is U/Th possible to derive a second relationship between TG and P using the U/Th ratio measured in meteorites. There are two equa- tions in two unknowns and it is therefore possible to solve the system. Conclusions: The radiometric age of the Milky Way is 14.5+2.8 Gy. The large uncertainty stems primarily from the un- -2.2 certainty in the U/Th ratio measurement of low metallicity halo stars [3,4], which will hopefully be improved in the near future. The U/Th production ratio is 0.571+0.037 . This value can be used -0.031 in future studies to restrict the possible mass laws used in r- process calculations, to determine the source of galactic cosmic rays, and to date . [1] Patterson C.C. 1956 GCA 10: 230-237. [2] Amelin Y., et al. 2002 Science 297: 1678-1683. [3] Cayrel R. et al. 2001 Na- ture 409: 691-692. [4] Hill V. et al. 2002 A&A 387: 560-579. [5] Chen J.H. et al. 1993 LPSC XXIV: 277-278. [6] Goreva J.S. and Burnett D.S. 2001 MPS 36: 63-74. [7] Yokoi K. et al. 1983 A&A 117: 65-82. [8] Clayton D.D. 1988 Mon. Not. R. Astron. Soc. 234:1-36. [9] Goriely S. and Arnould M. 2001 A&A 379:1113-1122. [10] Schatz H. et al. 2002 ApJ 579:626-638. [11] Dauphas N. 2005 Nature in press. 68th Annual Meteoritical Society Meeting (2005) 5309.pdf

THE NUCLEOSYNTHESIS OF SHORT-LIVED ISOTOPES IN ASYMPTOTIC GIANT BRANCH STARS. A. M. Davis1 and R. Gallino2. 1 Enrico Fermi Inst., Dept. of Geophysical Sciences, and Chicago Center for Cosmochemistry, University of Chicago, Chicago, IL, USA. [email protected]. 2Diparti-mento di Fisica Generale, Universitá di Torino, Torino, Italy.

Asymptotic giant branch (AGB) stars have been considered as sources of short-lived nuclides in the early solar system [1]. Here we consider the short-lived nuclides made by the s-process in the

ejecta of low mass (1.5–3 M) solar metallicity AGB stars that may be of importance for mainstream presolar SiC grains. 26 26 27 Al (t1/2=0.73 My): Low mass AGB stars yield Al/ Al ratios up to 3×10–3, consistent with mainstream SiC data [2]. 41 41 40 Ca (t1/2=0.13 My): The Ca/ Ca ratio produced in the ejecta of low mass AGB stars is ~3×10–4. Presolar hibonite, likely from such stars, has initial 41Ca/40Ca ratios of <2×10–6–4×10–4 [3] 60 60 56 Fe (t1/2=1.5 My): The Fe/ Fe ratio produced in the ejecta –6 –5 of 1.5 and 3 M AGB stars is 2–3×10 and 1–3×10 , respectively. Presolar grains contain a few hundred ppm Fe and Ni [4], so it is unlikely that 60Ni techniques will be observable. 93 Zr (t1/2=1.5 My): This isotope is on the main s-process path, because its half-life is long enough that it behaves as if it were sta- ble. 93Zr decays to monoisotopic 93Nb, in fact most of the latter iso- tope is made in this way. Trace element data on presolar SiC show that most grains have the expected Nb/Zr ratio [4]. 99 Tc (t1/2=210 ky): This isotopic is also on the main s-process path. Ruthenium isotopic data are consistent with 99Tc having been live when presolar SiC condensed [5]. 107 Pd (t1/2=6.5 My): AGB stars produce copious amounts of this isotope: the predicted 107Pd/108Pd ratios are ~0.1, far higher than the early solar system ratio of ~5×10–5. Since Ag is a rela- tively volatile element, there may be a chance to detect radiogenic 107Ag in presolar grains and better constrain AGB stars as potential sources of early solar system 107Pd. 135 Cs (t1/2=2 My): Cs is a volatile element that does not con- dense into SiC. Ba isotopic data on presolar SiC aggregates [6] are consistent with grain condensation before 135Cs decay [7]. 146 Sm (t1/2=103 My): This isotope is normally thought of as only being produced by the p-process, however neutron capture on p-only 144Sm initially present in the star produces 146Sm/144Sm ra- tios of ~0.0015, comparable to the early solar system ratio. Since this ratio is still low and 142Nd is relatively abundant, evidence for 146Sm decay is hard to detect in AGB grains. 182 182 180 Hf (t1/2=9 My): Low mass AGB stars yield Hf/ Hf ratios of 0.008–0.025, considerably higher than the early solar system value of ~10–4. If both Hf and W condense fully into presolar SiC, 182Hf decay would shift 182W/184W ratios by 1 to 3%. This shift is likely undetectable, given that the s-process also modifies 182W/184W ratios. If significant Hf/W enhancement occurs through condensation, radiogenic 182Hf might be detectable. 205 Pb (t1/2=15 My): Although low mass AGB stars may yield 205Pb/204Pb ratios of up to 1, both Pb and Tl are volatile and effects are unlikely to be detected in presolar SiC. References: [1] Wasserburg G. J. et al. 2005. Nuclear Physics A, in press. [2] Zinner E. 2003. In Treatise on Geochemistry Vol. 1 (Oxford: Elsevier), 17–39. [3] Nittler L. R. et al. 2005. Absract #2200. 36th Lunar and Planetary Science Conference. [4] Kashiv Y. 2004. Ph.D. Diss., Univ. of Chicago. [5] Savina M. R. et al. 2004. Science 303: 649–652. [6] Prombo C. A. et al. 1992. Astrophysical Journal 410: 393–399. [7] Lugaro M. et al. 2003. Astrophysical Journal 593: 486–508. 68th Annual Meteoritical Society Meeting (2005) 5288.pdf

PETROGENESIS OF MARTIAN NAKHLITE MIL 03346 James M.D. Day1, Lawrence A. Taylor1, Christine Floss2, Harry Y. McSween Jr.1, Yang Liu1, Eddy Hill1 1Planetary Geosciences Institute, Department of Earth and Planetary Sciences, University of Tennessee, Knoxville, TN 37996. E-mail: [email protected] 2Laboratory for Space Sciences, Washington University, St Louis, MO 63130

Introduction: Antarctic meteorite MIL 03346 is a nakhlite composed of 79% clinopyroxene, ~1% olivine and 20% vitrophyric intercumulus material. We have performed a detailed petrologic and geochemical study of this nakhlite [1] and demonstrate a near identical petrogenetic history to previously discovered from Mars. Data and Discussion: Quantitative textural study of MIL 03346 indicates long (> 1×101 yr) residence times for the cumulus augite, whereas the skeletal Fe-Ti oxide, fayalite and sulfide, and vitrophyric appearance of the intercumulus matrix suggests rapid cooling, most probably as a flow. From the relatively high forsterite contents in olivine (up to Fo43) and the compositions of augite cores (Wo38-42En35-40Fs22-28) and their Ca- Fe-rich rims, we suggest that MIL 03346 is part of the same cumulate-rich lava flow as the other nakhlites on Mars. However, MIL 03346 has experienced less equilibration and faster cooling than the other nakhlites discovered to date. Calculated trace element concentrations based upon modal abundances of MIL 03346 and ion microprobe analysis of its constituent minerals are identical to whole-rock trace element abundances measured by ICP-MS [1]. Parental melts for augite lie parallel with whole rock and intercumulus melt trace-element compositions using experimentally defined partition coefficients [2]. This parallelism has been considered to reflect closed system crystallization for Nakhla [3], where the only significant petrogenetic process between crystallization of the augite and the eruption and emplacement of the nakhlite flow has been fractional crystallization. A simple model for the petrogenesis of MIL 03346 and the other nakhlites (Nakhla, Governador Valadares, Lafayette, , NWA 817 and NWA 998) would include (1) partial melting and ascent of melt generated from a long-term LREE depleted source [3-5], (2) crystallization of cumulus augite (± olivine, ± magnetite, ± pyrrhotite) in a shallow-level martian magma chamber, (3) eruption of the crystal-rich nakhlite magma on to the surface of Mars, (4) cooling, crystal settling, overgrowth and partial equilibration to different extents within the flow, (5) secondary alteration of the flow through hydrothermal processes, possibly immediately succeeding or even during emplacement of the flow. Ultimately, MIL 03346 and the other nakhlites preserve a record of magmatic processes in volcanic rocks on Mars with analogous petrogenetic histories to pyroxene-rich terrestrial lava flows (e.g., [6]) and to Komatiites. References: [1] Day J.M.D. et al. (2005) Meteoritics and Planetary Science, submitted. [2] McKay G. et al. (1994) Lunar Planet. Sci. Conf. (Ab.) XXV, 883-884. [3] Wadhwa M., Crozaz G. (1995) Geochimica et Cosmochimica Acta, 59, 3629-3645. [4] Longhi J. (1991) Proc. Lunar Planet. Sci. Conf. 21st, 695-709. [5] Shih C.-Y. et al. (1999) Meteoritics and Planetary Science, 34, 647-655. [6] Lentz R.C.F et al. (1999) Meteoritics and Planetary Science, 34, 919-932.

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TEXTURAL ANALYSIS AND CRYSTALLIZATION HISTORIES OF LA PAZ MARE BASALT METEORITES. James M.D. Day1, Lawrence A. Taylor1, Eddy Hill1, Yang Liu1 1Planetary Geosciences Institute, Department of Earth and Planetary Science, University of Tennessee, Knoxville, TN 37996, E-mail: [email protected]

Introduction: La Paz mare basalts, LAP 02-205, -224, -226, -436 and 03-632, are a suite of paired Antarctic meteorites with identical mineral and whole-rock major- and trace-element compositions, modal distributions and textures [1]. We present a quantitative textural study of lunar basalts that further constrains crystallization histories and cooling rates, providing clues to mare basalt lava flow geometries. Methods: Crystal Size Distribution (CSD) and Spatial Distribution Pattern (SDP) analyses were performed by digitizing the mono-mineralic textures and processing them with image- analysis software using methods outlined in Jerram et al. [2]. Crystallization: The La Paz mare basalts are holocrystalline, intergranular to subophitic basalts predominantly composed of pigeonite, augite, ferro-pyroxene, plagioclase and ilmenite [1]. Pyroxene (0.28×0.17mm), plagioclase (0.27×0.10mm) and ilmenite (0.20×0.06mm) fractions all possess nearly straight CSDs indicating continuous nucleation and growth during crystallization. Slight downturns for smaller size-fractions are consistent with either shock-induced annealing or cessation of nucleation accompanied by continued growth. Pyroxenes possess the highest R-values (sample/random nearest neighbor distance) and lowest melt porosity (touching crystal framework) whilst ilmenites have lower R-values and higher melt porosity than plagioclase consistent with the crystallization sequence of these minerals (plagioclase ≥ pyroxene > ilmenite). Comparison of Modal Data: Modal data for La Paz basalts [1] collected using the method of Taylor et al. [3] is in good agreement with modal percentages derived from CSD. The modal percentages calculated from CSD are slightly overestimated and are related to the calculated 3-D shape of crystal populations. Cooling and Growth Rates: Using growth rates of crystals in terrestrial lava lakes with well-constrained P-T histories [4], cooling rates for La Paz pyroxene, plagioclase and ilmenite can be calculated at 0.2ºC/Hr, 0.15ºC/Hr and 1.3ºC/Hr respectively. These are similar to independent cooling rate calculations for the La Paz basalts using the methods of Grove and Walker [5] and Lofgren et al. [6]. The fast cooling rate of ilmenite probably reflects differences in the cooling rate of terrestrial ilmenites from which the growth rate was derived, but could also represent more rapid cooling of the magma body on the Moon with increasing crystallization. Calculated residence times are ~0.9yrs for plagioclase, ~0.7yrs for pyroxene and ~0.1 yrs for ilmenite, using these growth rates. Assuming the magma body was a lava flow, cooling rates are consistent with it being 5-20m thick. Employing independently calculated cooling rates [5,6], growth rates for La Paz pyroxenes, plagioclase and ilmenite can be calculated at to be 3×10-9 to 3×10-8 mm/s, consistent with estimates of minerals in terrestrial basalt lava flows [4]. References: [1] Day J.M.D. et al. (2005) Geochimica et Cosmochimica, submitted. [2] Jerram D.A. et al. (2003) J. Petrol. 44, 2033-2051. [3] Taylor L.A. et al. (1996) Icarus. 124, 500- 512. [4] Cashman K., Marsh B.D. (1988) Contrib. Min. Petrol. 99, 292-305. [5] Grove T.L., Walker D. (1977) Proc. Lunar. Sci. Conf. 8th, 1501-1520. [6] Lofgren G.E. et al. (1975) Proc. Lunar Sci. Conf. 6th, 79-99. 68th Annual Meteoritical Society Meeting (2005) 5141.pdf

MECHANISMS FOR MELT VEIN FORMATION IN METEORITES. P. S. DeCarli1, Z. Xie2, and T. G. Sharp2 1SRI International, Menlo Park, CA94025/University College London, E-mail: [email protected], 2Arizona State University, Tempe, AZ

Introduction: So-called shock melt veins are observed in many chondrites and Martian meteorites. Since the initial publi- cation of the results of shock recovery experiments by Fredriks- son et al. [1], it has become generally accepted that these veins resulted from shock compression. Recent studies indicate that the presence of high-pressure minerals within a vein may constrain the shock history of the vein-forming event [2],[3]. It is therefore important to give serious consideration to the detailed mecha- nisms by which melt veins may form. Fredriksson et al. [1] sug- gested that the veins could be caused by colliding shocks. Lan- genhorst et al. [4] have experimentally investigated the possibil- ity of generating shock veins by shear melting. The Problems with Experiments: One problem with labora- tory shock loading experiments is that they explore only a narrow range of the shock conditions to which meteorites could have been exposed. Laboratory experiments are limited to µs-duration pressures; evidence from some meteorites implies pressure dura- tions >0.01 s [3], [5]. In most shock recovery experiments, the samples are contained in high shock impedance metal containers. The resulting thermodynamic loading paths differ markedly from the loading paths expected in natural events [6]. Another problem that we have just begun to appreciate is that laboratory experi- ments do not adequately reproduce the pressure release environ- ment experienced by most meteorites Possible Vein Formation Mechanisms: Our current studies of veins in meteorites indicate that there are significant differ- ences among the veins in a single meteorite, even in the same thin section. Some veins contain high-pressure phases whereas others do not. One possibility is that there were several veining events. Another possibility is that there are several mechanisms for vein formation. We suggest that those veins that do contain high-pressure phases formed upon shock arrival via jetting at cracks and pores. Simple energy balance calculations indicate that this mechanism is consistent with the Law of Conservation of Energy. The second mechanism, heating via localized shear deformation, is well established [7]. However, it is associated with deformation that takes place during release of pressure. References: [1] Fredriksson, K. et al., 1963. Space Research III, ed. Priester, W., North-Holland Publishing Co.-Amsterdam, pp 974-983. [2] Langenhorst, F. and Poirier, J.P., 2000. Earth and Planetary Science Letters 184:37-55, [3] Xie, Z. and Sharp, T. G., 2004, Meteoritics & Planetary Science 39:2043-2054, [4] Langenhorst et al., 2002, Meteoritics & Planetary Science 37:1541-1553 [5] Sharp, T. G. et al., 2003, Abstract #1278. 34th Lunar & Planetary Science Conference. [6] Milton, D. J. and DeCarli, P. S., 1963. Science 140:670-671, [7] Zener, C. and Hollomon, J. H., 1944, Journal of Applied Physics 15:22-32 68th Annual Meteoritical Society Meeting (2005) 5022.pdf

WHAT IS THE TYCHO COMPONENT AT APOLLO 17? J. W. Delano1, N. E. B. Zellner2, T. D. Swindle3, F. Barra3, E. Olsen3, and D. C. B. Whittet4. 1Dept. of Earth and Atmospheric Sciences, University at Albany (SUNY), Albany, NY 12222. jde- [email protected]. 2Dept. of Physics, Albion College, Al- , MI; 3Lunar and Planetary Laboratory, University of Ari- zona, Tucson, AZ; 4Dept. of Physics and Astronomy, Rensselaer Polytechnic Institute, Troy, NY

Introduction: A cluster of secondary craters (Central Clus- ter) at the Apollo 17 landing site is generally regarded as being the result of impacts by Tycho ejecta [e.g., 1-3]. Cosmic ray ex- posure ages of samples returned from the rims of craters belong- ing to that cluster of secondaries (90-115 Ma) are presumed to be the age of the Tycho in the remote southern high- lands of the Moon [1,4]. Exotic components from Tycho have been sought within the Apollo 17 sample collection by previous investigators [e.g., 5-7]. Results: Impact glasses from Apollo 17 regolith, 71501, were extracted and analyzed by electron microprobe. A subset of those impact glasses was also isotopically dated by the laser 40Ar/39Ar method. One of these glasses yielded an isotopic age of 130 ± 25 Ma (95% of 39Ar released; 102 ± 11 Ma with 62% of 39Ar released). Its composition is similar to that of a chemically unique, friable, highlands regolith breccia, 73131, containing lit- tle-to-no mare component [8]. This impact glass spherule has the following chemical composition (wt %): SiO2=45.9; TiO2=0.82; Al2O3=23.3; Cr2O3=0.20; FeO=6.07; MnO=0.08; MgO=9.83; CaO=13.9; Na2O=0.75; K2O=0.10. Discussion: Since material from Tycho is likely to be a di- lute component in the Apollo 17 regolith [e.g., 2], it is interesting that this impact glass belongs to a compositional grouping com- prising only 2% of the Apollo 17 glass population. This compo- sition is also broadly consistent with geochemical constraints on the Tycho region obtained by the Clementine and Lunar Prospec- tor missions [e.g., 9,10]. This composition is also consistent with previous suggestions [e.g., 5,6] that the Tycho component at Apollo 17 was likely to be anorthositic troctolite to anorthositic norite in composition. References: [1] Arvidson R. et al. 1976. Proc. 7th Lunar & Planetary Science Conference, 2817-2832. [2] Lucchitta B. 1977. Icarus, 30, 80-96. [3] Wolfe et al. 1981. USGS Prof. Paper 1080, 280pp. [4] Drozd R. J. et al. 1977. Proc. 8th Lunar & Planetary Science Conference, 3027-3043. [5] Fruland R. M. et al. 1977. Proc. 8th Lunar & Planetary Science Conference, 3095-3111. [6] Jolliff B. L. et al. 1998. Lunar and Planetary Science-XXIX, 1734.pdf. [7] Vaniman D. T. et al. 1979. Proc. 10th Lunar & Planetary Science Conference, 1185-1227. [8] Korotev R. L. and Kresmer D. T. 1992. Proc. 22nd Lunar & Planetary Science Con- ference, 275-301. [9] Lucey P. G. et al. 2004. Lunar and Plane- tary Science-XXXV, 1717.pdf. [10] Le Mouélic S. et al. 2002. J. Geophysical Research, 107, 5074, doi:10.1029/20000JE001484.

68th Annual Meteoritical Society Meeting (2005) 5091.pdf

FRACTURING IN TERRESTRIAL IMPACT CRATERS: THE RELATIONSHIP OF CONFINING PRESSURE TO DYNAMIC TENSILE FRACTURE STRENGTH Michael R. Dence. 824 Nesbitt Place, Ottawa, Ontario, Canada. K2C 0K1. E-mail: [email protected]

Introduction: In strong target materials the size of the transient crater created by shock wave interactions is critically dependent on the intrinsic dynamic tensile fracture strength of the medium and the confining pressure imposed by the depth of overburden. Here these are estimated from observations at terrestrial hypervelocity impact craters and the measurements of Ai and Ahrens [1]. Observations: Their experiments measured the shock pressure at room pressure and temperature both for the onset of fracturing and for complete fragmentation. The latter can be observed at some natural impact sites as a reasonably sharp gradation from breccia to autochthonous country rocks, whereas the lower limit of dynamic fracturing is difficult to distinguish from the additional fracturing caused by late-stage deformation. At simple craters, such as Brent (diameter D = 3.8km), the lowest part of the breccia fill in the center provides a direct estimate of the depth and the shock pressure at the limit of fragmentation [2]. In complex craters, such as Charlevoix (D = 54km), an indirect estimate is given by shock metamorphism levels in unfragmented rocks at the center of the central uplift. From these and other craters in the Canadian Shield, ranging from Deep Bay (D = 9.5km) to Manicouagan (D = 80km), it is observed that the estimated shock pressure, P (in GPa) at the fragmentation limit increases with crater size, with P = 3.5 D 0.5 (D in km). With increasing impact energy the down-axis limit of fragmentation occurs at progressively higher shock pressures. Analysis: The original depth of the rocks when shocked can be derived from their observed level of shock metamorphism and the inferred rate of shock pressure attenuation [3]. Calculation of the respective transient craters shows the limit of fragmentation is also progressively deeper with increasing crater size. A straightforward explanation is that the increase in the limit relative to shock is related to increasing confining pressure. An average density of 2700 Kg.m-3 is used to calculate the pressure at depth in typical Canadian Shield rocks. When combined with the data from [1] for gabbro and eclogite an estimate for the relationship between dynamic tensile fracture strength (TFS) of strong crystalline rocks and confining pressure (CP) is given (in Pa) by TFS = 7.94 x 105 CP0.53. It follows that, with increasing crater size, a smaller proportion of the shocked target material is disrupted and displaced as breccia while more is compressed and then unloaded during central uplift formation. More generally, shock levels observed in central peaks are dependent on gravity and target material properties as well as crater size. References: [1] Ai, H.A. and Ahrens, T.J. 2004. Meteoritics and Planetary Science. 39: 233-246. [2] Dence, M.R. 2002. In Meteorite impacts in Precambrian shields, J. Plado and L.J. Pesonen, Editors. Springer-Verlag: Berlin. pp. 59-79. [3] Dence, M.R. 2004. Meteoritics and Planetary Science. 39: 267-286.

68th Annual Meteoritical Society Meeting (2005) 5265.pdf

LIMITATIONS ON THE PRODUCTION OF SHORT-LIVED RADIONUCLIDES BY IRRADIATION IN THE EARLY SOLAR SYSTEM: S. J. Desch 1Department of Physics and As- tronomy, Arizona State University, Tempe AZ E-mail: [email protected].

Introduction: Isotopic analyses of meteorites reveal that our early Solar System held many short-lived (t1/2 ~ 1 Myr) radionu- clides, including: 41Ca, 36Cl, 26Al, 10Be and 53Mn, all found in cal- cium-aluminum-rich inclusions (CAIs); as well as 60Fe, 107Pd, 182Hf, and 129I in other meteoritic components (see reviews by 7 [1,2]). Evidence [3] for other radionuclides, Be (t1/2 = 57 days) in particular, awaits confirmation. One possible explanation for the presence of these radionuclides is that magnetic flares on the early Sun accelerated protons and other ions to kinetic energies of many tens of MeV/nucleon, thereby irradiating gas and solids. This irra- diation can drive nuclear reactions that create the short-lived ra- dionuclides. Here we explore the limitations of this hypothesis. Irradiation in the disk at 2-3 AU: Protostars probably emit energetic particles at 105 times the rate today's Sun does, or about 1048 particles with E > 10 MeV/nucleon in 1 Myr [4]. A proto- planetary disk will intercept about 1047 particles, but well over 99% of these particles merely ionize the gas, and do not lead to nuclear reactions [5]. Comparing the rates of reactions like 26Mg(p,n)26Al to ionization losses by the Bethe formula, we can demonstrate that at most 1 in 104 energetic particles can produce 26Al, for a maxi- mum of 1043 26Al atoms. This is to be compared to the number of 26Al atoms in the disk; for solar abundances [6] and the canoni- cal ratio 26Al / 27Al = 5 x 10-5, the total number of 26Al atoms in a 0.01 M disk is 1045. Irradiation models severely underproduce ~ radionuclides if the irradiation occurs in the presence of gas. Irradiation within the Stellar Magnetosphere: Irradiation of only rocky material (actually, CAIs) within the stellar magneto- sphere (where gas is heated to 107 K and quickly removed) has been proposed as the source of the radionuclides in CAIs (the "X- wind" model of [7,8]). Here we list some problems with the X- wind model. (1) CAIs formed in a reducing gas with near-solar oxygen fugacity [9], but in this model the CAIs form in gas > 105 times more oxidizing. (2) Production of 26Al, 41Ca and 53Mn at meteoritic levels overproduces 10Be, especially in light of updated 24Mg(3He,p)26Al reaction rates [10] and identified alternative sources of 10Be [11]. (3) Concordant production of 26Al and 41Ca in this model invokes immiscible melts of ferromagnesian silicate and Ca,Al-silicates that do not exist (see discussion in [12]). (4) Temperatures of solids in the X-wind region are typically > 1200 K [7], much higher than the condensation temperature of 36Cl (750 K), or the target nuclei that produce 36Cl (Cl, Ar, K) [7], so the presence of 36Cl in CAIs is unexplained. (5) Irradiation models fail to produce any significant quantities of 60Fe or 182Hf [13]. (6) Transport of irradiated CAIs to the 2-3 AU region is problematic and has not been quantitatively demonstrated. References: [1] McKeegan & Davis 2003 Treat Geochemistry [2] Lin Y et al 2005 PNAS 102, 1306 [3] Chaussidon M et al 2004 LPSC 35, 1568 [4] Feigelson ED et al 2002 SpJ 572, 335 [5] Nath BB & Biermann PL 1994 MNRAS 267, 447 [6] Lodders K 2003 ApJ 591, 1220 [7] Shu FH et al 2001 ApJ 548, 1029 [8] Gounelle M et al 2001 ApJ 548, 1051 [9] Krot AN et al 2000 PP IV, 1019 [10] Fitoussi C et al 2004 LPSC 35, 1586 [11] Desch SJ et al 2004 ApJ 602, 528 [12] Simon SB et al 2002 MAPS 37, 533 [13] Leya I et al. 2003 ApJ 594, 605 68th Annual Meteoritical Society Meeting (2005) 5264.pdf

THE MEANING OF IRON 60: A NEARBY SUPERNOVA INJECTED RADIONUCLIDES INTO OUR SOLAR SYSTEM. S. J. Desch, N. Ouellette, and J. Hester. 1Department of Physics and Astronomy, Arizona State University., Tempe AZ E-mail: [email protected].

Introduction: The recent discovery that the early Solar Sys- 60 tem contained the short-lived (t1/2 = 1.5 Myr) radionuclide Fe at a level 60Fe / 56Fe ≈ 5 x 10-7 [1,2] demands a stellar nucleosyn- thetic source, almost certainly a supernova. Astronomically, the most plausible time and place for the supernova is < 1 pc away, ~ 1 Myr after the Solar System’s protoplanetary disk had formed. Sources of Radionuclides: Possible sources of radionuclides are: inheritance from our molecular cloud material, in which some radionuclides are maintained in steady state abundance by continuous Galactic nucleosynthesis; production within the Solar System by energetic particle irradiation; and injection of ra- dionuclides from a nearby stellar source. Inheritance cannot ex- plain the abundance of 60Fe, since our molecular cloud had to be isolated from Galactic nucleosynthesis sources for ~ 108 years to avoid over production of 129I; 60Fe is not inherited at all [3,4]. Irradiation fails to explain the meteoritic abundance of 60Fe by six orders of magnitude [5,6]. Injection from an asymptotic giant branch (AGB) star is extremely improbable, < 3 x 10-6 [7], but a nearby supernova can account for the meteoritic 60Fe, and can reasonably account for most other radionuclides as well [8,9]. Time and Location of the Supernova: At the time of the supernova, the early Solar System was probably analogous to the protoplanetary disks seen in HST images < 1 pc from the massive (40 M ) star θ1 Ori C (which will go supernova in ~1 Myr), in ~ the Orion Nebula [10]. Most (50-90%) solar-mass stars form in such environments [11]. That protoplanetary disks, including our early Solar System’s disk, should be found near massive stars that will soon go supernova is easily understood as a natural con- sequence of star formation in such environments [12,13]. Injec- tion after the protoplanetary disk has formed is therefore proba- bly common, and is also consistent with the meteoritic evidence for “late injection” [14]: Disk Survival: We have conducted 2-D hydrodynamics simulations (to be presented) that show that a 0.013 M disk, 55 ~ AU in radius, located 0.3 pc from a supernova, will be stripped by its 2000 km/s ejecta to only 40 AU, but will survive the su- pernova. If the effective cross section of the disk for receiving supernova ejecta (with a 25 M progenitor composition calcu- ~ lated by [15]) is π(30 AU)2, then 60Fe/56Fe = 5 x 10-7 in the disk. That is, a protoplanetary disk 0.3 pc from a supernova can receive enough ejecta to explain the initial 60Fe in our Solar System, without being destroyed. References: [1] Tachibana S & Huss G 2003 ApJ 588, L41 [2] Mostefaoui S et al. 2004, New Astron Rev 48, 155 [3] Harper C 1996 ApJ 466, 1026 [4] Wasserburg et al 1996 ApJ 466, 1026 [5] Lee T et al. 1998 ApJ 506, 898 [6] Leya I et al 2003 ApJ 594, 605 [7] Kastner JH & Myers, PC 1994 ApJ 421, 605 [8] Meyer BS & Clayton DD 2000 Space Sci Rev 92, 133 [9] Ouellette N et al 2005, in Chondrites and the Protoplanetary Disk, in press [10] McCaughrean MJ & O’Dell CR 1996 AJ 111, 1977 [11] Lada CJ & Lada EA 2003 ARAA 41, 57 [12] Hester J et al 2004 Science 304, 1116 [13] Hester JJ & Desch 2005 in Chondrites Proto- planetary Disk, in press. [14] Sahijpal S & Goswami JN 1998 ApJ 509 L137 [15] Rauscher T et al 2002 ApJ 576, 323 68th Annual Meteoritical Society Meeting (2005) 5172.pdf

UNUSUAL STAUROLITE-RICH TARGET ROCKS AND GLASS-RICH SUEVITE AT THE LAKE BOSUMTWI IMPACT STRUCTURE, GHANA, W. AFRICA A. Deutsch1, F. Langenhorst2, K. Heide2, U. Bläß2 and A. Sokol1. 1Institut f. Planetologie, Univ. Münster, D-48149 Münster, Germany. E- mail: [email protected]. 2Institut f. Geowissenschaften, Univ. Jena, D-07749 Jena, Germany.

Introduction: The well-preserved, 1.07Ga complex Bosum- twi impact structure was target of an ICDP drilling project that successfully commenced in fall 2004 [1]. Geochemical-petro- graphic analysis of the two cores into the annular moat, and the central uplift is currently performed by several research groups. Bedrock geology at Lake Bosumtwi: Following descrip- tions given by [2-4, with refs. therein and geologic map], target rocks in the Bosumtwi area are mainly greywackes, carbon-rich phyllites, quartzites, and subordinately meta-volcanics of the ~2.1 Ga Birimian Supergroup. To the SE of the crater, coarser clastic sedimentary rocks of the younger Tarkwaian Supergroup occur. In addition syndeformational granitic intrusions are known which include hornblende diorites, and two mica granites as well. Newly discovered lithologies: Boulders of a staurolite-rich mica-schist were found N of the crater rim (Fig. 1). The occur- rence of this index mineral indicates that pT conditions at the peak of regional metamorphism in the Bosumtwi area were higher than so far assumed. The staurolite mica schist forms also mm-sized clasts in suevites and may represent metamorphic basement material excavated from deep levels of the target. Other clasts in suevites are diaplectic quartz, extremely rich in coesite, and vesicular mineral glasses. The correlation of these glasses and target lithologies with Ivory Coast tektites is under way.

Fig. 1: Photomicrograph of mica-schist sample BOT 6 with ≤20 vol% twinned staurolite-xx, altered to muscovite; //nicols. Sam- pling locality: S of the unpaved road between Nyameani and Nkowinkwanta about 2.7 km off the N lake shore outside the morphologic rim of the Lake Bosumtwi impact structure, Ghana.

References: [1] Koeberl C., Milkereit B. et al. (2002) Pro- posal to ICDP 65pp.; Koeberl C. et al. (2005) Abstract #1830 35th Lunar and Planetary Science Conference. [2] Boamah D. (2001) Ph.D. Thesis, Univ. Vienna, Austria, 269pp.. [3] Plado J. et al. (2000) Meteoritics and Planetary Science 35, 723-732; Koeberl C. et al. (1998) Geochimica et Cosmochimica Acta 62, 2179-2196. [4] Woodfield P.D. (1966) Ghana Geological Survey Bulletin 30; Moon P.A. and Mason D. (1967) Ghana Geological Survey Bulletin 31, 1-51. 68th Annual Meteoritical Society Meeting (2005) 5100.pdf

BULK COMPOSITION OF THE MOON: 2. VOLATILES AND ISOTOPES. M. J. Drake1 and G. J. Taylor2. 1Lunar and Planetary Lab, U. Arizona. E-mail: [email protected]. 2Hawaii Inst. of Geophysics and Planetology, U. Hawaii.

The bulk composition of the Moon informs us about the processes that operated prior to and during the moon-forming event, planetary accretion and the composition of at least one planetary embryo, and how the Moon differentiated. Here we discuss the abundances of volatile elements and compounds, and of diagnostic isotopes in the Moon and Earth. Depleted in volatiles: The Moon is depleted in volatile ele- ments, as shown by its low K/Th (360 vs 1000 for HED meteor- ites [asteroid 4 Vesta], 2800 for Earth, and 5500 for Mars). Con- ventional suggests that this depletion is the result of va- porization during formation of the Moon by a giant impact. Some authors argue that the depletion in volatiles in HED meteorites indicates that volatile depletion might be a primary feature of some planetesimals in the inner solar system, and that a giant impact is not needed. Whatever process depleted volatiles it did not fractionate potassium isotopes. The low initial Sr isotopic composition in lunar anorthosites (lower than BABI in eucrites) indicates that volatile Rb fractionated from Sr very early in solar system history. It is an open question as to whether this fractiona- tion reflects the composition of materials accreting to the moon- forming planetesimal, or reflects formation of the Moon early in the accretion stage in which embroys became planets. Although Cs is more volatile than Rb, the Cs/Rb ratio in mare basalts is higher than MORB. This might reflect processes in the hot debris surrounding the Earth after the giant impact, but both experi- ments and modeling are needed to test this idea. Isotopes: The isotopic composition of oxygen is identical in the Earth and Moon. Cr isotopic composition is also the same in the Earth and Moon. The isotopic compositions of O and Cr vary throughout the solar system, indicating that the Earth, Moon, and impactor formed from the same reservoir in the nebula. If the Earth accreted “wet”, as suggested by some authors, then the im- pactor must also have been hydrous and the current anhydrous state of at least the outer part of the Moon must be a consequence of giant impact energetics. Iron isotopic composition is generally similar in Earth and Moon, both of which have higher 57Fe/54Fe than SNC and HED meteorites. Tungsten isotopic compositions of most lunar samples show that short-lived 182Hf was present due to extraction of siderophile 182W from the silicate portion of the Moon, either in the giant impactor or during formation of a small lunar core. Some open questions: One cannot make definitive state- ments about the compositional features discussed above. For ex- ample, the similarity in O and Cr isotopes in Earth and the Moon might reflect (i) formation of the giant impactor and the Earth from the same narrow feeding zone, or (ii) equilibration of the Earth with the very hot melt-vapor cloud from which the Moon formed. There is a complicated interplay between the accretion of the planetesimals that subsequently accreted to form the Earth and Moon-forming planetary embryo, processes (e.g., core for- mation) that happened in them, and the processes that operated during a giant impact. 68th Annual Meteoritical Society Meeting (2005) 5126.pdf

CARSWELL IMPACT STRUCTURE, SASKATCHEWAN, CANADA: GEOLOGICAL, PETROGRAPHICAL AND GEOPHYSICAL RESULTS, AND IMPLICATIONS FOR THE AGE OF THE ASTROBLEME. I. Duhamel,1,2 S. Genest,2 F. Robert,2 and A. Tremblay1. 1Université du Québec à Montréal, Département des Sciences de la Terre, 201 Ave. Président-Kennedy, local PK-6125, 6e étage, Montréal (Québec), H2X 3Y7, Canada. E-mail: [email protected]; [email protected]. 2Omégalpha, 539 Route 131, Joliette (Québec), J6E 7Y8, Canada. E-mail: [email protected].

The Carswell astrobleme, in northern Saskatchewan, is a 39 km wide complex impact structure located in the Athabasca Ba- sin of Proterozoic age which shows an 18 km diameter central uplift composed of Aphebian gneisses and granitoids. During the past two decades, controversy has been raging over the age of the Carswell structure. Two dating hypotheses have been proposed: an Ordovician age impact event sustained by the regular shape of the astrobleme in the sedimentary units [1, 2] and an older catastrophe event, possibly pre-Athabasca, suggested by the lack of impact breccias and shock metamor- phism effects in the Proterozoic cover [3, 4]. Our group has carried out field works and an extensive petrographic study on the Carswell impact lithologies encoun- tered in drill cores and hand samples of the Athabasca sediments, the basal conglomerate surrounding the central uplift and the highly brecciated basement lithologies. The basement rocks in the central uplift show evidence of shock metamorphic features ranging from 2 to a minimum of 45 GPa (shatter cones, multiple sets of PDFs, diaplectic glasses, mineral melts). The quartz grains of the basal conglomerate show PDFs and cataclastic textures. On the other hand, the proximal proterozoic sedimentary cover, viewed as to have been impacted by earlier workers (the younger age hypothesis), shows no evidence of shock metamorphism nor of any deformation. In addition, vertical derivative Bouguer gravity anomalies [5] indicate that the central uplift is well expressed by its positive signature. It is also surrounded by a strongly defined negative well followed by a ring of small positive anomalies probably re- lated to subsidiary basement uplifts. This peak ring is more or less located beneath a pristine stromatolitic reefs unit which con- fers a circular shape to the sediments surrounding the central peak. Furthermore, paleogeographic features throughout the Atha- basca Basin (paleocurrents and isopach maps [6]) suggest that the sedimentation of the Athabasca Group has been controlled by a bowl shape basin roughly centered on the Carswell central uplift, acting then as a paleo-high. Therefore, our research suggests that the Carswell event is older than the deposition of the Athabasca Basin and that the ac- tual circular structure is quite probably the central peak, a local expression of a larger multi-ring impact structure hidden beneath the sediments. References: [1] Pagel M. 1975. Thèse Doc Spéc., Univ. Nancy I, France, 157 p. [2] Harper C. T. 1983. Ph.D. thesis, Colo. School Mines, Golden, Colorado. [3] Currie K. L. 1967. Nature, Lond., 213: 56-57. [4] Duhamel I. et al. 2004. Meteorit- ics & Planetary Science 39(8) Supp., p. A32 (Abs.) [5] Miles W. and Slimmon W. L. 2000. Geological Atlas of Saskatchewan Web page. GSC and Sask. Ind. Res. [6] Ramaekers P. 1990 Sask. Geol. Surv., Sask. En. Min., Rep. 195, 49 p. 68th Annual Meteoritical Society Meeting (2005) 5149.pdf

ASSEMBLY OF THE DESCARTES TERRANE: ARGON AGES OF LUNAR BRECCIAS 67016 AND 67455. R. A. Duncan1 and M. D. Norman2,3. 1Oregon State University, Corval- lis OR 97331 USA. [email protected]. 2Australian National University, Canberra 0200 AU 3Lunar and Planetary Institute, Houston TX 77058 USA

Introduction: The upper crust of the Moon records an inte- grated history of impact events extending from soon after the main accretionary phase of planet formation to the present day. An accurate reading of this impact history is important for several reasons, including a better understanding of the significance of large impact events for crust formation and biologic evolution on Earth, establishing absolute timescales of geological events on other planets, and understanding large-scale planetary dynamics of the Solar System. For example, recent models have linked a late cataclysmic bombardment of the inner Solar System at ~4.0 Ga to migration of the outer planets [1], despite the continuing debate over whether such a cataclysm really occurred [2]. In order to improve our understanding of the impact history and development of crustal terranes on the Moon, we measured 40Ar-39Ar ages of clasts from two Apollo 16 feldspathic fragmen- tal breccias (FFB’s; 67016, 67455). These breccias are composed of anorthositic and melt breccia clasts in a fine-grained clastic matrix. They represent the Descartes terrane, a regional unit of the central nearside highlands. Clasts in these breccias sampled ancient crustal lithologies, including ferroan noritic anorthosites with ages of 4.4-4.5 Ga [3], and magnesian impact melts that pre- date at least some of the nearside basins [4]. Methods: This project was initiated by Graham Ryder who separated chips of anorthositic and melt breccia clasts for Ar iso- topic analysis. 0.8 to 3.7 mg of material from 28 samples were encapsulated in evacuated quartz vials and irradiated for 300 hr in the OSU experimental TRIGA reactor. Neutron fluence was monitored with Mmhb-1 hornblende (513.5 Ma). Samples were heated by a continuous power CO2 laser in 20-35 temperature increments; ages calculated from the released gas at these heating steps formed “plateaus’ comprising from 30-100% of the total. Uncertainties (2σ) for individual ages are typically 20-40 Ma. Results: Four anorthositic clasts from 67016 yielded well- defined ages ranging from 3842 to 3875 Ma (average 3862+12 Ma, 1σ SD). There is little evidence for older components in the Ar spectra of these clasts. In contrast, melt breccia clasts from 67016 (n=8) have more diverse spectra, with apparent ages of 4.1 to 4.2 Ga and evidence for older material (to 4.5 Ga,) in the high- T fractions. Release spectra for 67455 were not as well behaved. Plateau ages of 3801 to 4012 Ma for three anorthositic clasts and 3987 Ma for one melt breccia clast were obtained. Conclusions: The Ar data are consistent with assembly of these FFB’s at ~3.9 Ga, coincident with many lunar impact melts. An assembly age of ~3860 Ma based on the 67016 anorthositic clasts would be younger than the age of Serenitatis inferred from Apollo 17 poikilitic melt breccias [3893 Ma; 5], possibly impli- cating a role for Imbrium or local craters in the formation of the Descartes breccias, rather than emplacement as Nectaris ejecta [5]. Older ages for melt breccia clasts may indicate incomplete degassing rather than the emplacement age of the breccias. References: [1] Gomes et al. 2005. Nature 435:466-469. [2] Norman 2005. Australian J. Earth Sci, in press. [3] Norman et al. 2003. Meteoritics Planet. Sci. 38:645-661. [4] Norman et al. 2005. 68th Meteoritical Soc. Conf., this volume. [5] Stöffler and Ryder 2001. Space Sci. Rev. 96:9-54. 68th Annual Meteoritical Society Meeting (2005) 5254.pdf

Identification of Alkalic Rocks Using Thermal Emission Spectroscopy: Applications to Martian Remote Sensing. T.L. Dunn1 and H.Y. McSween, Jr1.1 Department of Earth and Plane- tary Sciences, University of Tennessee, Knoxville, TN 37996. [email protected].

Introduction: Most of what we know about martian volcan- ism is based on geochemical evidence from SNC martian meteor- ites and remote sensing data collected by the Thermal Emission Spectrometer (TES). SNC meteorites first suggested that martian magmatism was primarily basaltic [1]. This was later supported by TES data, which identified two distinct subalkaline components, a basalt [2] and an andesite or weathered basalt [2,3]. However, because SNC meteorites represent only a limited sampling of martian surface material, and because TES surface types were derived using an end-member suite consisting primarily of subalkaline minerals [2,3], one cannot dismiss the possibility that alkalic volcanism may have once been active on the surface of Mars. This assertion is supported by recent geo- chemical evidence, which indicates that the Chassigny shares many similarities with terrestrial intra-plate al- kalic magmas [4]. However, before TES can be used to search for alkalic rocks on Mars, we must first determine if linear de- convolution of thermal emission spectra [5] is capable of distin- guishing between alkalic and subalkalic rocks. Methods: Here we present a detailed study examining the accuracy of using linear deconvolution of thermal emission spec- tra (5-25 µm) to identify and classify alkalic volcanic rocks at both laboratory resolution (2 cm-1) and TES instrument resolution (10 cm-1). Modal and derived bulk rock chemistries of a suite of terrestrial alkalic rocks were determined using linear deconvolution of thermal emission spectra. Modeled values were compared to measured mineralogies and chemistries to access the ability of using the linear deconvolution technique to reproduce measured data. Derived mineralogies and chemistries were then applied to several volcanic rock classification schemes to deter- mine if infrared spectra of terrestrial basalts, trachyandesites, trachytes, and rhyolites can be used for petrologic classification. Results: Results indicate that linear deconvolution of thermal emissivity spectra can successfully be used to identify and clas- sify alkalic rocks. Modeled mineralogies and derived bulk chem- istries accurately reproduce measured values and can be success- fully applied to several terrestrial volcanic rock classification schemes. Results obtained at 10 cm-1 spectral sampling are simi- lar to those at 2 cm-1, indicating that degradation of spectral data does not adversely affect modal mineralogies and chemistries derived from linear deconvolution. Overall, our results indicate that the TES instrument can successfully distinguish between subalkaline and alkalic rocks and can be used to search for signs of past alkalic . References: [1] McSween H.Y. 1985. Reviews of Geophys- ics 23:391-416. [2] Bandfield J.L. et al. 2000. Science 287:1626- 1630. [3] Wyatt M.B. and McSween H.Y. 2002. Nature 417:263- 266. [4] Nekvasil H. et al. 2004. Abstract #1280. 35th Lunar & Planetary Science Conference. [5] Ramsey M. and Christensen P.R. 1998. Journal of Geophysical Research 103:577-596.