CONTENTS — T through V - lpi.usra.edu · PDF fileCONTENTS — T through V...

CONTENTS — T through V

Cathodoluminescence and Thermoluminescence Studies of CR Chondrites K. Takeda and K. Ninagawa .................................................................................................................. 5030

Fractionated Highly Siderophile Elements in a Silicate Clast of Mesosiderite M. Tamaki, A. Yamaguchi, K. Misawa, and M. Ebihara........................................................................ 5206

Survey of Initial 26Al in Type A and B CAIs: Evidence for an Extended Formation Period for Refractory Inclusions

D. J. Taylor, M. Cosarinsky, M.-C. Liu, K. D. McKeegan, A. N. Krot, and I. D. Hutcheon ............................................................................................................... 5282

Bulk Composition of the Moon: 1. Refractory Elements, Iron, and Distinct Reservoirs G. J. Taylor and M. J. Drake.................................................................................................................. 5098

JSC-1 as the Lunar Soil Simulant of Choice L. A. Taylor, E. Hill, Y. Liu, and J. M. Day ............................................................................................ 5180

The Moon: A Taylor Perspective L. A. Taylor, S. R. Taylor, and G. J. Taylor ........................................................................................... 5283

The Moon: A Retrospective View S. R. Taylor............................................................................................................................................. 5020

In-Situ U-Pb Dating of Phosphates in Lunar Basaltic Breccia Elephant Moraine 87521 K. Terada and Y. Sano............................................................................................................................ 5062

Discovery of a New Strewn Field of Distal Ejecta in the Southern Parana Basin at the Permian Triassic Boundary

J. M. Thèry, E. Dransart, and M. Baron ............................................................................................... 5220

Hypervelocity Impact Experiments of Iron Projectiles on Dry and Water-bearing Sandstones K. Thoma, T. Behner, T. Kenkmann, D. Stöffler, R. T. Schmitt, and S. Mayr......................................... 5049

Nepheline Formation in Chondrules in CO3 Chondrites: Relationship to Parent-Body Processes

K. Tomeoka and D. Itoh ......................................................................................................................... 5080

Analytical Transmission Electron Microscopy of Experimentally Shocked Murchison CM Chondrite

N. Tomioka, K. Tomeoka, and K. Nakamura.......................................................................................... 5054

Ion Probe Analysis of Cation Concentration Profiles in Pallasite Olivine T. Tomiyama and G. R. Huss.................................................................................................................. 5326

Martian Rayed Craters: Implications for Martian Meteorite Source Regions L. L. Tornabene, H. Y. McSween Jr., J. E. Moersch, J. L. Piatek, K. A. Milam, A. S. McEwen, and P. R. Christensen..................................................................................................... 5078

Bulk Composition and Origin of a Gabbronorite Granulite Clast in Lunar Meteorite ALHA81005 A. H. Treiman, A. K. Maloy, and C. K. Shearer Jr................................................................................. 5241

68th Annual Meteoritical Society Meeting (2005) alpha_t-v.pdf

The Orbit of Villalbeto De La Peña: An L6 Chondrite Delivered by the 3:1 Resonance J. M. Trigo-Rodriguez, J. Borovička, P. Spurny, J. L. Ortiz, J. A. Docobo, A. J. Castro-Tirado, and J. Llorca ......................................................................................................... 5017

In-Situ Observation of Hypervelocity Particles Captured in a Silica Aerogel Collector Using Syncrotron-based Micro-Radiography

A. Tsuchiyama, K. Uesugi, T. Nakano, H. Yano, K. K. Okudaira, and T. Noguchi................................ 5204

LA-ICP-MS and EMPA Analysis of Melt Rock Particles from the Yaxcopoil-1 Borehole, Chicxulub Impact Structure, Mexico

M. G. Tuchscherer, W. U. Reimold, R. L. Gibson, and C. Koeberl ........................................................ 5104

Evidence of Enhanced Space Weathering Effect by Coexisting Metallic Iron Y. Ueda, T. Hiroi, S. Sasaki, and M. Miyamoto ..................................................................................... 5198

Chondrites from the Atacama Desert E. M. Valenzuela, P. A. Bland, S. S. Russell, C. Roeschmann, and D. Morata ...................................... 5096

Zinder: A New Pyroxene-bearing Pallasite D. van Niekerk........................................................................................................................................ 5328

Weathering Forms of Antarctic Stony Meteorite Finds: Terrestrial Weathering Brings Out Subtle Textures in Eucrites and Howardites

M. A. Velbel............................................................................................................................................ 5009

Aqueous Alteration in QUE93005 (CM2): Different Alteration Scales for Antarctic and Non-Antarctic CM Chondrites?

M. A. Velbel, E. K. Tonui, and M. E. Zolensky ....................................................................................... 5191

Popigai Fluidizite Dykes: Data on Volatiles S. A. Vishnevsky, N. A. Gibsher, J. Raitala, S. G. Simakin, and N. A. Palchik....................................... 5036

Significance of Low Silicon Contents in Iron Meteorites I. A. Vogel, A. Pack, B. Luais, and H. Palme ......................................................................................... 5239

High Resolution 40Ar/39Ar Dating of Plagioclase Separates from IAB Silicate Inclusions — New Methodological and Thermochronological Insights

N. Vogel and P. R. Renne ....................................................................................................................... 5195

Development and First Test Results of a Low-Volume UV-Laser Noble Gas Extraction Line N. Vogel, I. Leya, H. Lüthi, and J. A. Whitby ......................................................................................... 5177

68th Annual Meteoritical Society Meeting (2005) alpha_t-v.pdf

CATHODOLUMINESCENCE AND THERMOLUMINES-CENCE STUDIES OF CR CHONDRITES. K. Takeda1 and K. Ninagawa1. 1Department of Applied Physics, Okayama Univ. of Science. E-mail: [email protected].

Introduction: Cathodoluminescence (CL) is the light emit-

ted from phosphor excited with an electron beam, and its appear-ance could be attributed to impurity, especially transition metal elements and rare earth elements, and to lattice defects in the structure. Chondrules in ordinary chondrites are classified by compositions of forsterite and mesostasis together with CL colors to A1-5 and B1-3 [1,2]. However, A1 and A2 chondrules, anor-thite-rich chondrules with yellow CL on mesostasis, are rare in the ordinary chondrites except Semarkona and RC 075[3]. On the other hand, anorthite-rich chondrules are fairly common in CR chondrites [4]. Thermoluminescence (TL) is the light emitted from the phosphor during heating after natural and laboratory dose of radiation. Sensitivity of induced TL, the response to a laboratory dose of radiation, is used to determine the petrologic subtype of type 3 ordinary chondrites [5, 6], and CO chondrites [7]. In the present study we measured CL and TL of CR chon-drites, NWA801 (CR2) and Sahara00182 (CR3), comparing with those of an A1 chondrule in Semarkona.

Cathodoluminescence: CL images of the chondrites were measured by Luminoscope (Premier American Technologies) with cooled CCD camera. NWA801 (CR2) showed mainly yel-low CL on mesostasis with red and dull red CL on forsterite. A1 and A2 chondrules were main constituents in the NWA801 (CR2). On the other hand, Sahara00182 (CR3) showed mainly blue CL on mesostasis with no CL on forsterite. A4 and A5 chondrules were main constituents. NWA801 (CR2) shows in-homogeneous yellow CL in each chondrule. Mesostasis of outer region in each chondrule is relatively brighter than that of inner region. This feature is the same as an A1 chondrule in Semarkona [8]. Manganese, emission center of yellow CL, might be concen-trated on circumference of chondrules. This yellow CL profile of A1 and A2 chondrules in the CR chondrite suggests that they have been formed in the same reduction and recondensation process of the A1 chondrule in Semarkona.

Thermoluminescence: TL images and local TL glow curves of the chondrites were measured by 2D TL readout system. A1 and A2 chondrules in NWA801 (CR2) showed weak and uncer-tain TL glow curves. Devitrification has not proceeded in mesostases of NWA801 (CR2). These TL glow curves are differ-ent from those observed in Semarkona and Bishunpur [9]. These TL glow curves suggest that depth of trap is different from the chondrules in Semarkona and Bishunpur, and detailed formation conditions were different from those of the chondrules. TL inten-sity of Sahara00182 (CR3) has relatively strong emission, and has low temperature TL peaks near 100oC. Devitrification has proceeded in this chondrite.

References: [1] Sears D. W. G. et al. 1992. Nature 357: 207-211. [2] DeHart J. M. et al. 1992. GCA 56: 3791-3807. [3] Sears D. W. G. et al. 1995. EPSL 131: 27-39. [4] Krot A. N. et al. 2002. Meteoritics & Planetary Science 32: 1451-1490. [5] Sears et al. 1980. Nature 287: 791-795. [6] Benoit et al., 2002. Meteor-itics & Planetary Science 37: 793-805. [7] Sears D. W. G. et al. 1991. Proc. NIPR Symp. Antarct. Meteorites 4: 319-343. [8] Ma-tsunami S. et al. 1993 GCA 57: 2102–2110. [9] Ninagawa K. et al. 1992. Proc. NIPR Symp. Antarct. Meteorites 5: 281–289.

68th Annual Meteoritical Society Meeting (2005) 5030.pdf

FRACTIONATED HIGHLY SIDEROPHILE ELEMENTS IN A SILICATE CLAST OF MESOSIDERITE. M. Tamaki1, A. Yamaguchi1,2, K. Misawa1,2 and M. Ebihara3. 1 Grad. Univ. Advanced Studies, Tokyo 173-8515, Japan. E-mail: [email protected]. 2 National Institute of Polar Research, Tokyo 173-8515, Japan. 3 Grad. School of Sci., Tokyo Metropolitan University, Hachiouji, Tokyo, 192-0372, Japan.

Introduction: Mesosiderites are an enigmatic group of stony-

iron meteorites. Although numerous formation models have been proposed so far [1-3], the exact formation history of mesoside-rites remains unclear. The major complicating factor in elucida-tion of the origin is that they have undergone multiple episodes of variable degrees of thermal metamorphism which may have changed the textures and bulk chemistries [4]. Coupled with min-eralogical study, we determined siderophile elements in a basaltic clast of Mount Padbury by INAA and ID-ICP-MS to better un-derstand the association between secondary thermal metamor-phism and redistribution of siderophile element abundances.

Results and Discussion: The basaltic clast in Mount Padbury shows an extremely fractionated siderophile element pattern. The abundances of Os and Ir are below detection limits (0.01ppb). The CI-normalized Co/Ni (=1.3) ratio is similar to that of mesosiderite metallic portion (=1.17). However, the CI-normalized highly siderophile element/Ni ratio (e.g., Pt/Ni=0.0096) is different from that of mesosiderite metallic por-tion (=1.19). The SEM observation suggests that a carrier phase of siderophile elements, Fe-Ni metal occurs as fine-grained drop-let or curvilinear trails coexisting with troilite throughout sili-cates. These textures may have been formed by injection of mol-ten metal from mesosiderite metallic portion as observed in shocked ordinary chondrites.

An obvious potential source of the metal and sulfide is mesosiderite metallic portion. If metallic liquid penetrated through silicate portions during metal-silicate mixing, the sidero-phile element pattern should be parallel to that of mesosiderite metallic portion. However, the CI-normalized siderophile ele-ment pattern of the clast is highly fractionated, compared to those of mesosiderite metallic portions which show relatively flat pat-terns with a very limited compositional range of ~10 x CI-chondrite. The partitioning of many siderophile elements be-tween solid metal and liquid metal-sulfide is markedly dependent on the S content [5]. If metallic portion underwent such metal-liquid fractionation, highly siderophile elements strongly deplete in S-bearing metal-liquid. The pattern in the basaltic clast can be explained by such melt. It is likely that metallic liquid had al-ready been fractionated before silicate-metal mixing. This argues with the idea that metallic portions were largely molten during metal-silicate mixing. Alternatively, mesosiderite was reheated that cause partial melting of Fe-FeS eutectic liquid mobilized into silicate portion along cracks and fractures by later impacts. Our results suggest that the thermal history of mesosdierites is more complicated than previously thought.

References: [1] Powell B.N. 1971. Geochimica et Cosmo-chimica Acta 35: 5-34. [2] Hewins R. H. 1983. J. Geophys. Res.88: B257-B266. [3] Delaney J. S. 1983. Meteoritics & Plane-tary Science 18: 289-290. [4] Wadhwa M. et al. 2003. Geo-chimica et Cosmochimica Acta 67: 5049-5069. [5] Chabot N. L. and Jones J. H. 2003 Meteoritics & Planetary Science 38: 1425-1436.


SURVEY OF INITIAL 26Al IN TYPE A AND B CAIs: EVIDENCE FOR AN EXTENDED FORMATION PERIOD FOR REFRACTORY INCLUSIONS. D. J. Taylor1, M. Cosarin-sky1, M.-C. Liu1, K. D. McKeegan1, A.N. Krot2 and I. D. Hutcheon3. 1Dept. Earth & Space Sciences, UCLA, Los Angeles, CA; 2HIGP/SOEST, University of Hawai’i at Manoa, HI; 3Chemical Biology & Nuclear Sci-ence Division, LLNL, Livermore, CA. [email protected].

The timing of formation and thermal processing of refrac-tory Ca-, Al-rich inclusions (CAIs) plays an important role in models of early solar system evolution. Recently reported high-precision Al-Mg isotope data have led to divergent answers re-garding the periods of time over which CAIs could have formed, with bulk data indicating an extremely short period of ~50,000 years [1] and laser-ablation in situ data implying a much longer interval (~300,000 years [2]). Other ICPMS data on bulk CAIs [3] suggest high initial 26Al/27Al values, apparently in conflict with [1]. We have conducted an ion microprobe survey of 8 ig-neous and 3 non-igneous CAIs from CV3 meteorites in order to document the range of initial 26Al/27Al values preserved in these inclusions. Analyses are obtained by high mass resolution multi-ple-collector Faraday cup measurements on ~20 µm spots and have typical precision and accuracy in the range ~0.1‰ for ∆26Mg* in low Al/Mg phases.

With the exception of three of the type B CAIs which have apparently undergone multiple reheating episodes resulting in internal redistribution of Mg isotopes, there is very good correla-tion between Al/Mg ratios and excess ∆26Mg* in spinel, pyrox-ene and hibonite phases. Three fluffy type A (FTA) samples (Vigarano 477-5, and Allende TS24 and TS25) are composed of small individual melilite+spinel+hibonite nodules which have never been melted, each surrounded by a Wark-Lovering rim (WLR). The inferred initial 26Al/27Al ratios for the interiors of the nodules range from 5.1×10-5 (V477-5) to 5.9×10-5 (TS24). We also studied three igneous-textured compact type A CAIs (CTA): Vigarano 1623-2, and Efremovka E44L and E44N. Well-correlated initial 26Al/27Al ratios for the interiors range from 5.30×10-5 (E44N) to 6.26±0.47×10-5 for E44L, an unusual, highly-fractionated CAI in which the melilite shows no evidence for isotope exchange. In several of these CAIs there are resolv-able time differences between the formation of the CAI interiors and their surrounding WLRs [4]. Five of the samples, Efremovka E38 and E107, and Allende TS23, TS34 and MC1 have typical B1 igneous textures and display a spread of inferred 26Al/27Al ratios at isotopic closure ranging from 3.9×10-5 for TS23 to 5.7×10-5 for E38.

Isotope resetting can explain the low initial 26Al/27Al values for some of the type B CAIs. However the high initial values and also the spread in values seen in the FTA inclusions, the individ-ual nodules of which have not been melted, and in the CTA in-clusions are not apparently compatible with a well-defined (new ‘canonical’) initial 26Al/27Al value of 5.2×10-5 [1]. Instead, our data suggest not only that the thermal recycling of CAIs lasted for a long time, in agreement with [2], but also that whatever nebular processes were responsible for the formation and thermal modification of CAIs, they continued for a period of time span-ning at least a few 105 years. References: [1] Bizzarro M. et al. (2004) Nature 431,275-278; [2] Young E.D. et al. (2005) Science 308, 223-227; [3] Galy A. et al. (2004) LPSC 35, #1790; [4] Cosarinsky, M. et al. (2005), MAPS, this issue.


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BULK COMPOSITION OF THE MOON: 1. REFRACTORY ELEMENTS, IRON, AND DISTINCT RESERVOIRS. G. J. Taylor1 and M. J. Drake2. 1Hawaii Inst. of Geophysics and Planetology, U. Hawaii. E-mail: [email protected]. 2Lunar and Planetary Lab, U. Arizona.

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 refractory elements and iron, and show that we do not have a complete picture of Moon’s composition.

Refractory elements: If refractory elements occur in chon-dritic proportions, pinning down the abundance on one element allows us to use the geochemical behavior of the others to deci-pher the differentiation of the Moon and Earth. We have global data for Th and Al (indirectly from the Fe concentration) and ad-ditional data from lunar samples and experiments on mare ba-salts. We also have a good idea of the distribution of major lithologic types on the lunar surface, reasonable estimates of the total volume of those lithologies, and a good estimate of the thickness of the crust (45-52 km on average) and the size of the core (1-3 % of the lunar mass). This allows us to use a mass bal-ance approach to estimate Al and Th in the bulk silicate Moon. Our calculations suggest that Al could be the same as in Earth, but is likely to be somewhat enriched. However, no reasonable combination of lithologic volumes or compositions results in the same enrichment of Al and Th, unless Th is quantitatively se-questered into the crust (a crustal average abundance of 50 times that of the mantle). For this crustal enrichment to be correct, all mare basalts and highland Mg-suite magmas must have obtained their Th (and, hence, their REE and other incompatibles) via in-teraction with crustal materials.

Iron: The lunar density and moment of inertia imply that the Moon is enriched in FeO (about 11-13 wt%) compared to Earth (8 wt%). Source regions of mare basalts were rich in FeO (about 18 wt%), but geophysical factors rule out the entire mantle hav-ing that much FeO. Parent magmas of Mg-suite rocks might be produced from mantle sources with considerably less FeO, per-haps as low as 7 wt%. The existence of magnesian reservoirs is also shown by the presence of highly forsteritic olivine grains (up to Fo94) in basin-derived impact melts. Thus, the lunar mantle is likely to be heterogeneous, with a portion having low FeO (down to 7 wt%) and another having higher FeO (up to 18 wt%), and probably with gradations in between. It would require 90% of the lunar mantle to have low FeO to result in the Moon having the same FeO as the Earth.

Some open questions: Volcanic glass deposits are richer in many volatile elements by factors of 10-100 compared to other lunar samples. The orange glass has primitive Pb isotopic com-position, has chondritic initial W isotopic composition, and has a significantly lower 57Fe/54Fe ratio than other lunar materials. The magnesian sources and volatile rich reservoirs indicate (i) that the Moon did not accrete homogeneously and was not homogenized subsequently, or (ii) is compositionally stratified, perhaps signal-ing the base of the lunar magma ocean.


JSC-1 AS THE LUNAR SOIL SIMULANT OF CHOICE. Lawrence A. Taylor, Eddy Hill, Yang Liu, James M.D. Day Planetary Geosciences Institute, Dept. Earth Planet. Sci, Univ. of Tennessee, Knoxville, TN 37996. E-mail: [email protected]

Introduction: Lunar simulant, JSC-1 was prepared from a welded tuff that was mined, crushed and sized in northern Ari-zona. As the initial supply of 27 tons is now dwindling, new pro-duction has commenced. Here, we review the chemical, minera-logical and geotechnical characteristics of JSC-1, some of which have been described previously [2-4]. While other lunar soil simulants have been produced (e.g., [5]), they were not standard-ized and results from tests performed on them may not be equiva-lent.

Composition, mineralogy, geotechnical properties: The welded tuff used to manufacture JSC-1 was selected for its glass content (~50%) and because it approximated the geotechnical properties of lunar soil. It was not chosen for its chemistry. The chemical composition of JSC-1 consists of 10 wt.% FeO, ap-proximately halfway between the FeO content of Mare (15 wt.%) and Highland soil (5 wt.%). It approximates that of an Apollo 14 soil (14163) and is atypical of that of the major portion of the lunar surface. Therefore, JSC-1 may not be the best simulant, where chemistry and mineralogy are of prime importance. JSC-1 consists predominantly of olivine, pyroxene, plagioclase and ox-ide minerals welded by silicate glass. When crushed, glassy fragments have a similar appearance to the agglutinates of lunar soil. It is the glassy, friable nature of this simulant that imparts the necessary geotechnical properties to simulate lunar soil. Il-menite, with a considerable Fe3+ content, substantial intergrown magnetite and chromite make up the oxide mineral inventory of JSC-1. Importantly, the magnetite and magnetite component in the oxide are the cause of the magnetic susceptibility of JSC-1, making it similar to lunar soil [6]. Loose packed JSC-1 soil (~40% relative density, RD [4]) has similar strength and defor-mation characteristics to lunar soil [7]. However, medium packed JSC-1 simulant (60% RD) differs from lunar soil [7]. Tests are necessary if the planned landing site on the Moon has a different relative density.

Considerations for Oxygen Production: The process of hydrogen reduction involves the breaking of Fe-O bonds. The Fe-O bonds of a phase are a function of the structure in the phase. For example, the Fe-O bonds in an ordered silicate min-eral are stronger than a glass of the same composition. There-fore, hydrogen reduction of a Fe-bearing glass will occur signifi-cantly faster than a Fe-bearing silicate mineral. The Fe-O bonds of oxide minerals (e.g., ilmenite; ulvöspinel; chromite) are weaker still than glass. In a feedstock containing silicate and ox-ide minerals and silicate glass, the kinetics of hydrogen reduction are: Oxide Minerals >> Silicate Glass > Silicate Minerals. The majority of FeO in JSC-1 is present as Fe-bearing oxide minerals, mainly titaniferous magnetite, making JSC-1 good for simulation of oxygen production through H-reduction.

References: [1] McKay D.S. and Blasic J.D. (1991) LPI Tech Report 91-04, 83pp; [2] McKay et al. (1994) Space IV, ASCE, 857-866; [3] Hill E. et al. 68th Met. Soc. Meeting Abs [4] Klosky et. al. (1996) Space V, ASCE, 680-688; [5] Weiblen et al. (1990) Space II, ASCE, 428-435; [6] Taylor et al. (2005) 1st Space Explor. Conf., AIAA. [7] Carrier et al. (1991) In: Lunar Sourcebook, Heiken et al. (Eds.), Cambridge University Press, New York, 475-594



THE MOON: A TAYLOR PERSPECTIVE. L. A. Taylor1, S. R. Taylor2, and G.J. Taylor3. 1Univ. of Tennessee. E-mail: [email protected]. 2Lunar and Planetary Inst. 3HIGP, Univ. of Hawaii.

Introduction: This Symposium offers us the combined

opportunity to address four unresolved problems in lunar science: crustal structure and composition, core size and composition, bulk lunar composition, and the reality of the cataclysm at 3.9 Gy.

Crust: The thickness of the highland crust was traditionally set at 60 km (10% of lunar volume), from the Nakamura interpretation of the seismic data in the 1970’s. Recent re-evaluations of the seismic data suggest an overall thickness of 45-52 km. A 60 km thick crust implies an Al2O3 content of up to 6% and a corresponding enrichment over solar nebula (CI) values for the other refractory elements. However, a thinner crust obviates this problem to some degree. There is, however, considerable uncertainty in the average Al2O3 content of the crust.

Core: Data from the Lunar Prospector magnetometer have refined the estimate of core radius to 340 km but the evidence for a metallic core remains enigmatic. The siderophile elements are depleted in the Moon in accordance with their metal-silicate distribution coefficients, consistent with their removal into a metallic core. Although this is evidence of metal segregation, perhaps it occurred in precursor bodies before the Moon formed. In the planetesimal hypothesis, the terrestrial planets gradually accreted from a swarm of smaller bodies many of which had themselves melted and differentiated into iron cores and silicate mantles. In the giant impact hypothesis, one such Mars-sized body that had formed from many precursors, impacted the Earth. The upshot is that the depletion of siderophile elements now observed in the Moon might have occurred in any or all of these earlier bodies.

Bulk Composition: Water and volatile elements are clearly depleted in the Moon compared to Earth. FeO is enriched in the Moon (13 wt% cf 8 wt% in Earth bulk silicate), although the small size of the metallic lunar core indicates that the Moon is depleted in total Fe. The Moon might be enriched in refractory elements compared to Earth. Do these features reflect the composition of the moon-forming projectile? Or are they caused by the giant impact event itself? Or a combination? The major depletion of water and volatile elements might have happened before the giant impact. There is a general depletion in the inner solar system of volatile elements such as K, relative to the abundance of refractory elements such as U for Venus, Earth, Mars and many classes of meteorites. Thus the planetesimals (including the lunar-forming impactor) that accreted to form the four inner planets may have been volatile depleted and dry.

Cataclysm: The question of whether the lunar heavy bombardment around 3.8 to 4.0 b.y. represents a spike (or cataclysm) or the tail end of accretion remains unresolved, although dynamicists have devised interesting mechanisms to explain it. The compositions and ages of impact melts from Apollo 15, 16, and 17 and lunar meteorites indicate that several individual impact events have been dated. However, we cannot associate a chemically and chronologically homogeneous group of impact melts with a specific impact basin. The question is solvable by dating impact melts from specific impact basins, such as South Pole-Aitken basin.



THE MOON: A RETROSPECTIVE VIEW S. Ross Taylor Australian National University, Canberra and Lu-nar and Planetary Institute, Houston, Texas. e-mail: [email protected]

Before spacecraft exploration, facts about the Moon were restricted to information about the lunar orbit, angular momen-tum and density. The lunar highlands were thought to be granite or ash-flows. The maria were thought to be sediments or dust, and possibly only a few million years old. The large circular cra-ters were thought to be calderas [1] The rilles were taken as evi-dence that there had been running water on the lunar surface.

The patterns on the lunar surface were thought [2] to be a 'lunar grid' due to tectonic stress. It was widely held that tektites came from the Moon [3]. Others [4] maintained that the Moon was essentially a primitive undifferentiated object. Harold Urey, visiting Oxford in 1956, gave a series of lectures about the Moon and tektites that ignited my interest in this whole subject.

The handful of Apollo data from the sample return in July, 1969 swept away centuries of speculations: a striking demonstra-tion of the power of scientific investigation. The maria were ba-saltic lavas, not dust. The lunar highlands were anorthosite, not granite, the highland plains were ejecta sheets from large basin impacts, not volcanics, and the 'lunar grid' was an artifact of the overlapping basin ejecta. Tektites came from the Earth [5]. The craters were all formed by impacts.

Probably the whole Moon had melted, soon after accretion [6]. The highland crust had crystallised and floated on this 'magma ocean'. The interior had crystallised by about 4.4 billion years into a zoned sequence of cumulate minerals. KREEP was shown to be derived from the final few percent of residual melt from this magma ocean [7]. The bulk Moon was bone-dry, de-pleted in volatile and siderophile elements and apparently en-riched in refractory elements. No pre-Apollo theories of lunar origin survived but a coherent model for forming the Moon ap-peared [8].

The Clementine and Lunar Prospector missions have added materially to our knowledge and understanding of the Moon [9] and have established the importance of the South Pole-Aitken basin, while three crustal terranes: South Pole-Aitken, Feld-spathic Highlands and Procellarum-KREEP [10] have been established. In summary, the lunar missions are a striking demon-stration of the power of scientific methods and enquiry

References: [1] Green, J. [1970] JGR, 76, 5719 [2] Fielder, G. [1961] Structure of the Moon’s Surface [3] Chapman, D. R. [1963] JGR 68, 4305 [4] Urey, H.C. [1952] The Planets [5] Tay-lor, S. R. [1973] Earth Sci Rev 9, 101 [6] Wood, J. [1970] PLC 1, 965 [7] Taylor, S. R. [1975] Lunar Science: A Post-Apollo View [8] Cameron, A.G.W. and Ward, W. [1976] LPSC VII, 120 [9] Zuber, M et al. [1997] JGR 102, 1591 [10] Jolliff, B. et al [2000] JGR 105, 4197.



IN-SITU U-Pb DATING OF PHOSPHATES IN LUNAR BASALTIC BRECCIA ELEPHANT MORAINE 87521 K. Terada1,2 and Y. Sano3, 1Department of Earth and Planetary Systems Science, Hiroshima University, Higashi-Hiroshima 739-8526, JAPAN ([email protected]), 2MIRAGE Project Center, Hiroshima University, Higashi-Hiroshima 739-8526, JAPAN, 3Center for Advanced Marine Research, Ocean Re-search Institute, The University of Tokyo, Nakano-ku 164-8639, JAPAN.

Introduction: The lunar meteorites have been valuable

sources for understanding the origin and evolution of the Moon, as they could potentially provide a new insight into the thermal history of unexplored regions of the Moon. For example, the pre-dominance of low-Ti and Very-Low-Ti (VLT) basaltic materials in the lunar meteorites contrasts with the scarcity of VLT basalts among lunar samples returned by the six Apollo and three LUNA missions [1-2]. In spite of their scientific interests, chronological studies of brecciated lunar meteorites have proved to be difficult, since they are mixtures of materials with different origins. In this paper, we report the in-situ U-Pb dating of phosphates in the brecciated lunar meteorite Elephant Moraine 87521 (hereafter abbreviated as EET 87521), which are classified into VLT basalt [3-6], and then compare with those of EET 96008 which are con-sidered to be paired, using the Sensitive High Resolution Ion Mi-croProbe (SHRIMP) installed at Hiroshima University, JAPAN [7-9].

Results and Discussion: Three analyses of whitlockite and five analyses of apatites indicate a total Pb/U isochron age of 3531 ± 110 Ma (95% confidence limit), consistent with those of EET 96008 (3569 ± 100 Ma [10]) and slightly older the K-Ar gas retention age in the range 3.0-3.4 Ga based on the bulk analysis [11,12]. This age discrepancy may be due to radiogenic 40Ar loss related to the shock event.

It is noted that these phosphate ages are quite distinct from previous chronological studies on VLT mare basalt of 3.2-3.3Ga for LUNA 24 [13], extending the VLT magmatism 0.2 Ga prior to the known. Taking into account of the recent radiometric ages of VLT lunar meteorite “Northwest Africa 773”(2.91 Ga [14,15]), the VLT basalt activity appears to have been continuous and/or intermittent during the time span of 6~7x108 years.

References: [1] Lindstrom M. M. et al. (1991) AMR 4, 12-32. [2] Warren P. H. and Kallemeyn G. W. (1991) AMR 4, 91-117. [3] Delaney, J. S. (1989) Nature 342, 889-890. [4] Warren P. H. and Kallemeyn G. W. (1989) GCA 53, 3323-3330. [5] Takeda H. et al. (1992) LPS XXII, 355-364. [6] Arai T. et al. (1996) M&PS 31, 877-892. [7] Sano Y. et al. (2000) M&PS 35, 341-346. [8] Terada K., Monde T. and Sano Y. (2003) M&PS 38, 1697-1703. [9] Terada K. and Sano Y. (2004) M&PS 39, 2033-2041. [10] Anand M. et al. (2003) GCA 67, 3499-3518. [11] Vogt S. et al. (1993). GCA 57: 3793-3799. [12] Nyquist L. E. et al. (2001). Radiometric chronology of the Moon and Mars, chapter 55, pp. 1325-1376. [13] Eugster O. et al. (1996) M&PS 31: 299-304. [14] Fernandes V. A. et al. (2003) M&PS 38: 555-564. [15] Borg L. E. et al. (2004) Nature 432: 209-211


DISCOVERY OF A NEW STREWN FIELD OF DISTAL EJECTA IN THE SOUTHERN PARANA BASIN AT THE PERMIAN TRIASSIC BOUNDARY. J.M.Théry, 9 Jardin Gabrieli, 37000 Tours. [email protected]. E. Dransart and M. Baron (EMTT): 69300 Francheville, France [email protected]

Introduction: More than 1200 km south from the impact

related ejecta from the impact crater of Araguainha, a new strewn field of distal ejecta has recently been discovered in the State of Rio Grande do Sul at PTB [1,2] Samples were collected in 1998 with Pr. Stocke da Rosa (Univ. of Santa Maria, RS). Laboratory studies were carried out during the last years on five samples: Nb 1A RS, 1C RS, 5RS, 9RS and 10 RS. They were scattered over an elongated ellipsoidal area 170 to 350 km in size to Acegua, at the border with Uruguay, from Rosario do Sul in the west, to Cachoeira do Sul (RS) eastward.

Results: The newly studied samples are impactites, in particular sample Nb 9RS, collected at 17 km from Cachoeira do Sul. This sample is assumed to be ejecta from an impact related crater located much more eastwards, probably in Africa. The matrix is fluidal: shocked quartz and other minerals are fractured with angular cracks as in a breccia. Grains of potassium aluminosilicates are also shocked and surrounded by a rim of shocked quartz or silica. The loss of birefringence of the quartz under polarized light points to diaplectic glass but without the characteristics of suevite. Small microspherules of aluminosilicates of Fe and Cr are present. They are magnetic and formed from molten material at high temperature (more than 1200o), probably from a meteorite immediately upon entering the earth’s atmosphere. According to EMTT, based on MEB and EDS spectra, a rapid cooling followed, indicated by dendritic features of solidification with octahedral structures. In addition the results of XRF analyses showing 300,9 ppm Zr, 15,6 ppm Ga and 24,8 ppm Ni, confirm the importance of above information. Sample 10 RS, collected 2 km more to the north in the Santa Maria Formation (L.Triassic) [1,3,4] showed also PDF’s during laboratory investigations. Along route 290, about 30 km east of Rosario do Sul, two samples were collected in a fine-grained red sandstone, 50 cm apart on either side of a crenulated horizontal bed. A detailed electron microscopy examination of sample 1C RS showed grains of an iron aluminosilicate with PDF’s and angular pulverized triangular quartz fragments similar to the ones we found at Montividiu (GO) in the basal part of the lower Triassic. We observed the same quartz fragments in sample 5 RS. XRF analyses showed 6,8 ppm Sr, 135 ppm Zr, 7,9 ppm Ga and 1,6 ppm Ni. Much higher results were obtained in sample 1A RS, representing the top most part of the Permian, namely: 18,1 ppm Sr, 212,3 ppm Zr, 10,1 ppm Ga and 4,7 ppm Ni. Compared with sample 9 RS, sample 1A RS is certainly closer to the candidate crater in the east along the long axis of the ellipsoidal area.

Discussion: According to Echauren et al. (2004) impactites representing fragments from Araguainha (MT,GO) have been ejected up to 238 km from the impact centre [5]. Therefore the most likely candidate crater could not have been Araghuainha but was probably located in the Huab Basin in Namibia at the Permian Triassic boundary. This area was probably only some hundred kilometres separated from Cachoeira do Sul in Permian times following the collision of the Rio do Plata and Kalahari cratons in Precambrian times. Candidate craters are believed to exist there where sequences of late Permian are present in outcrops [6].

References: [1] Schultz, E.L. (2005), in Koutsoukos, E.A.M. Edit. Springer. [2] Crosta, A.P. et al. (1981), Rev. Bras. do Geosc., v 23, n 3, 224-233. [3]Carraro,C.C. et al.(1974) Mapa Geologico do Rio Grande do Sul UFRGS, [4] Lavina, E.L. (1991). Tese Doutorado; Instituto de Geosci., UFRGS. [5] Echauren et al.(2005) Meteoritics and Planetary Sci. 39,Suppl., A35 [6]. Faure, K and Cole, D. (1999). Pal., Pal., Pal. 152, 189-213.


HYPERVELOCITY IMPACT EXPERIMENTS OF IRON PROJECTILES ON DRY AND WATER-BEARING SAND-STONES. K. Thoma1, T. Behner1, T. Kenkmann2, D. Stöffler2, R. T. Schmitt2, S. Mayr3 and the MEMIN-Team,: 1EMI-Freiburg, Germany. [email protected]. 2Humboldt-University Berlin. 3 Technical-University Berlin.

Introduction: To analyze strength dominated cratering

processes on an experimental scale the interdisciplinary project MEMIN was recently established. The rationale of this project is to fully describe and constrain impact cratering processes by re-cording petrographic-petrophysical properties and physical pa-rameters of the projectile and target before, during, and after a hypervelocity impact. The objective is to better understand proc-esses of crater damage, the role of fluids, the nature of geophysi-cal anomalies of craters, and to create a well documented data base that can be used to validate numerical simulations of impact cratering.

Experiments: Two vertical impact experiments (2808, 2809) were carried out using a two-stage light gas gun. The main axis of the gun was horizontal. Spherical steel projectiles of 1 cm diameter (4.1 g) were impacted on blocks (1.0 x 1.0 x 0.5 m) of sandstone (“Seeberger Sandstein”) enclosed in a steel frame. The target material has an average grain size of 0.17 mm and ~18 % porosity. One of the blocks was put in a water basin for four month and reached a water saturation of 44 vol.% (2809). The strength and elastic modulus is 62.4 +/- 2.8 MPa and 14.8 +/- 1.4 GPa for the dry sandstone (2808) and 47.0 +/- 3.7 MPa and 12.1 +/- 1.0 GPa for a fully water saturated equivalent. The blocks were positioned vertically to simulate a vertical impact on flat lying sediments. Ejecta catchers consisted of fiber boards that were placed 56 cm above the target surface. A high speed camera recorded the excavation in 12 photographs and gauges recorded shock pressure at the rear surface and the sidewall of the blocks.

Results: The projectiles reached a speed of 5338 ms-1 (2808) and 5269 ms-1 (2809), respectively. The resulting craters have average diameters of 23.8 cm (2808) and 28.7 cm (2809) and depths of 5.5 cm (2808) and 4.8 cm (2809), respectively. The catchers collected only a subordinate amount of the ejecta. Ejected material was partly recovered from a console below the sandstone block and amounts to 178 g (2808) and 301 g (2809), respectively. The ejecta comprises a wide spectrum of fragment sizes from <160 µm to >3 cm. The size distribution has a maxi-mum in the interval 160-310 µm corresponding to the initial grain size of the sandstone, and in the interval >2,5 cm. The latter fragments are spall fragments. In experiment 2808 2.84 g of the projectile (69%) stuck in the catcher, but in exp. 2809 no larger projectile remnants were found. The mean ejecta velocity per-pendicular to the target surface decreases from 2.3-2.4 kms-1 after 0-20 µs to 0.2-0.3 kms-1 after 230-470 µsec.

Discussion: The analysis of the experiments is not com-pleted yet. However, our first and preliminary inspection shows that the presence of fluids seems to have influenced the cratering process. A wider spall zone, a shallower crater depth, the lack of projectile remnants, and a smaller amount of shocked ejecta char-acterize the wet target compared to the dry sandstone.

Further members of the MEMIN-Team: U. Yaramanci, H. Burkhardt (TU-Berlin), A. Deutsch, (WWU Münster), C. Grosse (IWB-Stuttgart), F. Langenhorst (Univ. Jena), G. Dresen (GFZ-Potsdam).


NEPHELINE FORMATION IN CHONDRULES IN CO3 CHONDRITES: RELATIONSHIP TO PARENT-BODY PROCESSES. K. Tomeoka and D. Itoh. Department of Earth and Planetary Sci-ences, Faculty of Science, Kobe University, Nada, Kobe 657-8501, Japan. E-mail: [email protected].

Introduction: Sodium is volatile and mobile in aqueous ac-

tivity and thus serves as a sensitive indicator of secondary proc-esses that chondrites may have experienced. Chondrules in CV3 chondrites contain Na-rich nepheline [e.g. 1, 2]. Previous studies [e.g. 1] revealed that nepheline in chondrules formed by replac-ing primary mesostasis glass and plagioclase. However, it has been controversial whether the Na-metasomatism occurred by reaction with the gas in the solar nebula before accretion [e.g. 1] or by reaction that took place on the meteorite parent body [e.g. 2].

Chondrules in CO3 chondrites also contain nepheline [e.g. 3], although much less work has been done on it compared to the counterparts in CV3 chondrites. We have studied the mineralogy and petrology of mesostases of 783 type-I chondrules in seven CO3 chondrites that range in petrologic subtype from 3.0 to 3.7.

Results: Chondrule mesostases in the CO chondrite of sub-type 3.0 consist mainly of primary glass and plagioclase, whereas chondrule mesostases in the CO chondrites of higher subtypes (3.2-3.7) contain various amounts of nepheline as a secondary alteration product of glass and plagioclase. The nephelinization has proceeded preferentially from the outer margins of chon-drules toward the inside. Although the degree of nephelinization differs widely among chondrules in each of the metamorphosed chondrites, our modal analyses and bulk chemical analyses of individual mesostases indicate that the amounts of nepheline in chondrules systematically increase with increasing petrologic subtype of the host chondrites. Nepheline also has a tendency to increase in grain size with increasing petrologic subtype.

Discussion: From these results, we conclude that nepheline in chondrules in the CO3 chondrites has formed largely as a re-sult of effects related to heating on the meteorite parent body. We suggest that nepheline formed initially as hydrous nepheline un-der the presence of aqueous fluids and was subsequently dehy-drated after exhaustion of aqueous fluids. The degree of hydro-thermal activity must have increased with increasing degree of heating, and thus, chondrules in more thermally metamorphosed chondrites produced larger amounts of nepheline. The aqueous alteration probably occurred under the presence of relatively small amounts of aqueous fluids, and thus aqueous fluids did not infiltrate the meteorite parent body extensively and the alteration ceased shortly after heating, due to exhaustion of fluids. These imply that CO3 chondrites have gone through three-stage altera-tion processes on their parent body: (1) low-grade aqueous altera-tion, (2) thermal dehydration, and (3) thermal diffusive exchange of atoms without the aid of fluids.

References: [1] Ikeda Y. and Kimura M. 1995. Proceedings of the NIPR Symposium on Antarctic Meteorites 8:97-122. [2] Krot A. N. et al. 1997. Meteoritics & Planetary Science 32:31-49. [3] Jones R.H. and Brearley A.J. 1994. 25th Lunar and Plane-tary Science Conference. pp. 641-642.


ANALYTICAL TRANSMISSION ELECTRON MICROSCOPY OF EXPERIMENTALLY SHOCKED MURCHISON CM CHONDRITE N. Tomioka1, K. Tomeoka1, K. Nakamura2, 1Department of Earth and Planetary Sciences, Kobe University, Kobe 657-8501, Japan, 2 NASA, JSC, Houston, Texas, 77058, USA. E-mail: [email protected]

Introduction: A large fraction of dust particles falling to the

Earth’s surface has characteristics related to hydrated, porous meteorites [e.g.1]. It has been widely believed that hydrated, po-rous meteorites are so friable that they are mostly broken up into dust particles during atmospheric passage [2]. Recent shock ex-periments of Allende CV and Murchison CM chondrites suggest that hydrated asteroids will readily be explosively dispersed by impacts and produce dust particles at a much higher rate than anhydrous asteroids [3]. However, the effects of heating in shocked Murchison remain to be more studied. Here we report the results of ATEM study of the matrix of Murchison CM chon-drite experimentally shocked at 10, 21, 30, 36 and 49 GPa [4].

Results and Discussion: In the samples shocked at 10 and 21 GPa, Si-rich glass is the dominant phase. It contains numerous grains (< 0.2 µm) of Fe-oxide and Fe-sulfide. In places, coarse grains (0.7-5.5 µm) of serpentine are embedded in Si-rich glass. Tochilinite is absent. The Si-rich glass with Fe-oxide and Fe-sulfide grains may be breakdown products of serpentine and to-chilinite. In the sample shocked at 36 GPa, Si-rich glass with numerous vesicles (< 0.5 µm) is the dominant phase. It contains grains of Fe-oxide and Fe-sulfide and minor amounts of olivine and low-Ca pyroxene (< 2 µm). Serpentine is absent. The sample shocked at 49 GPa contains abundant olivine grains and a lesser amount of low-Ca pyroxene grains. Si-rich glass occurs in inter-stices of olivine and low-Ca pyroxene grains. The effects of heat-ing on dust particles such as alteration and melting have previ-ously been mainly ascribed to aerodynamic drag during atmos-pheric entry [e.g.1]. Previous workers conducted flash heating experiments of the CI and CM chondrites to simulate the effects of atmospheric entry of hydrated interplanetary dust [5,6]. In the CI samples heated at > 800 °C, phyllosilicates were mostly de-composed, and the dominant phases are olivine and pyroxene with interstitial Si-rich glass [5]. The mineralogy and texture of the heated CI samples are similar to those of the matrix of Mur-chison shocked at 49 GPa presently studied. If hydrated asteroids are among the main sources of dust particles falling to the Earth, the heating effects of extraterrestrial impacts on dust particles may be overprinted on those of atmospheric entry. Therefore, we believe that the thermal history of dust particles needs to be fur-ther re-evaluated.

References: [1] Nakamura T. et al. 2001. Geochimica et Cosmochimica Acta 65: 4385-4397. [2] Baldwin B. and Sheaffer Y. 1971. Journal of Geophysical Research. 76: 4653-4668. [3] Tomeoka K. et al. 2003. Nature 423: 60-62. [4] Tomeoka K. et al. 1999. Geochimica et Cosmochimica Acta 63: 3683-3703. [5] Greshake A. et al. 1998. Meteoritics & Planetary Science. 33: 267-290. [6] Toppani A. et al. 2001. Meteoritics & Planetary Science 36: 1377-1396.


ION PROBE ANALYSIS OF CATION CONCENTRATION PROFILES IN PALLASITE OLIVINE. T. Tomiyama1 and G. R. Huss1 HIGP, University of Hawai`i at Manoa, Honolulu, HI 96822. [email protected]

Introduction: Pallasites consists primarily of comparable vol-umes of olivines and Fe-Ni metal, and may have formed at the core-mantle boundary of highly differentiated asteroids [1,2]. Pallasite olivines exhibit compositional gradients from core to rim [3-5] that can be interpreted as diffusion profiles. Miyamoto et al. [3,4] calculated cooling rates of a few to tens of degrees per year from 1100 to 600 oC based on these profiles. Such fast cooling rates are in conflict with those estimated for lower temperatures from Fe-Ni metallography (~1 oC/Myr) [6]. In order to better un-derstand pallasite cooling history, we obtained precise chemical concentration profiles of the pallasite olivine and performed nu-merical calculations of cation diffusion in olivines.

Experimental: A ~1 cm olivine with grain boundaries perpen-dicular to the cut surface was selected in the Esquel pallasite. Chemical concentration profiles for major and minor elements were obtained by electron microprobe and profiles for trace ele-ments were obtained using the Cameca IMS 6f at Arizona State University. Elements measured by ion probe were Al, Ca, Mg, Ti, V, Cr, Mn, Fe, Co and Ni. Theoretical diffusion profiles were ob-tained by numerical step-wise calculations. Diffusion coefficients and oxygen fugacity are from the literature [7-9].

Results: Lithophile and siderophile elements show zoning at the edges of olivine grains. Al, Ca, Ti, V, Cr, Co and Ni abun-dances decrease at the grain edges, Mn show a slight increase, and Fe and Mg are essentially flat. These trends confirm observations by [3,5]. In the interiors of the grains, lithophile elements show sharp downward excursions from the expected flat profiles. These excursions may reflect cracks or inclusions in the olivine.

Discussion: In this abstract, we discuss Ca and Cr, which ex-hibit steep gradients at grain boundaries. If we suppose that olivine was initially homogeneous at a temperature of 1100 oC and cooled at a constant rate with a constant grain boundary condition [3], cooling rates of 10-100 oC/yr and 0.1-1 oC/yr are obtained for Ca and Cr, respectively. A similar result for Ca was obtained by [3]. The disagreement between our Ca and Cr cooling rates shows that our model is too simple. The observed profile for Ca has a signifi-cantly steeper gradient than the theoretical diffusion profile. This may reflect a change in the boundary condition, which has a huge influence on the shape of diffusion profile. Changes in boundary conditions can result from nucleation of new phases, a change in oxygen fugacity, or the temperature dependence of partition coeffi-cients. Our suite of elements ranges from highly lithophile to siderophile and should permit us to sort out changes in oxygen fu-gacity. Growth of phosphates or chromite during cooling could also change the boundary condition. Although the olivines carry a record of pallasite cooling history, the factors discussed above (and others) must be better understood in order to read that record.

References: [1] Buseck P. R. (1977) GCA 41, 711-140. [2] Dodd (1981) Meteorites, Cambridge Univ. Press, 368 pp. [3] Mi-yamoto M. (1997) JGR 102, 21,613-21,618. [4] Miyamoto M. et al. (2004) MAPS 39, A70. [5] Hsu W. (2003) MAPS 38, 1217-1241. [6] Buseck P. R. and Goldstein J. I. (1969) GSA Bull. 80, 2141-2158. [7] Jurewicz A. J. G. and Watson E. B. (1988) Contrib. Min-eral. Petrol. 99, 186-281. [8] Ito M. et al. (2004) LPSC XXXV #1324. [9] Brett R. and Sato M. (1984) GCA 48, 111-120. Sup-ported by NASA grant #NNG05GG48G.


MARTIAN RAYED CRATERS: IMPLICATIONS FOR MARTIAN METEORITE SOURCE REGIONS. L. L. Torna-bene1*, H. Y. McSween Jr.1, J. E. Moersch1, J. L. Piatek1, K. A. Milam1 A. S. McEwen2 and P. R. Christensen3, 1University of Tennessee, Knoxville, Tennessee 37996-1410, USA, 2University of Arizona, Tucson, Arizona 85721, USA, 3Arizona State University, Tempe, Arizona 85287–6305, USA.

Introduction: Four definitive large (km-sized) rayed craters have been recently been identified on Mars along with three prob-able ones [1-2]. These four craters are similar to the Martian rayed crater Zunil (D=10.1 km) [3-5] with rays that are most easily rec-ognized by a thermophysical contrast in THEMIS nighttime and daytime thermal infrared images from the Mars Odyssey Thermal Infrared Imaging System (THEMIS) [1-2].

These craters are presently thought to be the best candidate source craters for the Martian Meteorites (MMs) [1, 5]. This hy-pothesis is based on observations of rayed craters and the MMs, models of ray formation and MM delivery, inferences from the MM collection with respect to the source region(s) and our current knowledge of the Martian surface.

Crater parameters from current MM delivery models: Oblique impacts may be required to both generate crater rays on Mars, and to effectively eject materials from the Martian gravity field [6-9]. Models suggest that moderately oblique (30-45º) im-pacts generate the highest ratio of spallation volume to impactor volume [6]. Four of the five definitive rayed craters and all three “probable” rayed craters exhibit a “forbidden zone” or asymmetric ejecta patterns - evidence of moderately oblique impact events [2].

The diameters of rayed craters are also consistent with recent MM delivery models. Six of the eight craters we describe have di-ameters that are within or above the minimum size estimated for MM source craters (~2.5-3 km) [6, 10].

Geographic bias: Five of the eight craters described here are found within the volcanic plains of Elysium. The other three ap-pear in volcanic plains of similar thermophysical properties else-where on Mars. This geographic distribution suggests certain types of geologic terrain favor the formation and/or preservation of rayed craters. The composition, age, and physical properties of these ter-rains may be related to properties of the MMs measured in the laboratory.

Age bias: Crystallization ages for most MMs range from 175 Ma to 1.3 Ga and ejection ages range from 0.7 to 20 Ma [11]. Both suggest these meteorites originate from recent impacts on an Ama-zonian surface. Elysium is one of the youngest surfaces on Mars [5] with Martian rayed craters presumably being amongst the youngest craters on the surface of Mars for their size class (<10 km) [2-5]. Zunil’s age suggest that it may be as young as 4-10 Ma, consistent with MM ejection ages [5]. If the other rayed craters are comparably young, then the 4 new rayed craters are also consistent with the MM ejection ages.

References: [1] Tornabene et al. (2003), Mars Crater Consor-tium 7, Abstract # 0710. [2] Tornabene et al. (submitted) JGR-E. [3] McEwen et al. (2003) LPSC XXXIV, Abstract #2040. [4] McEwen A. S. (2003) 6th Int’l. conf. Mars, Abstract #3268. [5] McEwen et al. (submitted) Icarus. [6] Artemieva and Ivanov (2004), Icarus, 71,84-101. [7] Nyquist, L. E. (1983) , JGR, 88, A785-A798. [8] Nyquist, L. E. (1984), JGR, 89, B631-B640. [9] O’Keefe and Ahrens (1986), Science, 234, 346-349. [10] Head et al. (2001), Science, 298, 1752-1756. [11] Nyquist et al. (2001), Space Sci. Rev., 105-164.


BULK COMPOSITION AND ORIGIN OF A GABBRONORITE GRANULITE CLAST IN LUNAR METEORITE ALHA81005. A.H. Treiman1, A.K. Maloy1,2., C.K. Shearer Jr.3 1Lunar and Planetary Institute, Houston TX 77058. <treiman_lpi.usra.edu>. 2Dept. Earth Sciences, Rice University, Houston TX. 3Institute of Meteoritics, University of New Mexico, Albuquerque NM

An improved chemical composition for a granulite clast in lu-

nar meteorite ALHA81005 [1,2] is basaltic with ~1% TiO2 and a flat REE pattern at ~13xCI. Its composition is consistent with VLT basalt, but is not identical to Apollo or Luna VLT samples.

Introduction: Most lunar meteorites must be from sites outside those visited by Apollo and Luna landers, and so can provide cru-cial additional data on the rock types and compositions of the lunar crust. To enlarge knowledge of lunar highland rock types (and the Moon’s early history), we are analyzing granulite clasts from lunar highland meteorites.

Methods: Major and minor elements in constituent minerals are by EMP at Johnson Space Center. Trace elements (REE, Ni, Th, etc) are by SIMS, using the Cameca ims 4f at the University of New Mexico. For minerals with grains too small for SIMS analyses (e.g., phosphate), trace element abundances are calculated from mineral/mineral partition coefficients. Mineral proportions are clas-classified from element X-ray maps, with mulitspectral remote sensing codes.

Clast 2: The clast consists of equant grains, 10-100µm across, of chemically homogeneous plagioclase (42.5%), opx (31%), cpx (23%), chromite (0.5%), ilmenite (1.5%), and rare Ca-phosphate. Opx-cpx thermometry gives ~1100°C, like other lunar granulites [3]. The bulk composition (right) is basaltic.

Interpretation: Clast 2 is like VLT basalt in having a basaltic composition (Table) with TiO2~1% (14xCI), and relatively low REE abundances (~13xCI) in a Ca and Al are high relative to known VLT brepresent admixture of an anorthositic compobasalt (24109) is similar (REE and Ti at ~10xmore ferroan (Mg*=36) than Clast 2. A15 greeA17 VLT (78526) are more similar in Mg*, bdances are only 2-5xCI [4]. A17 glass 70295Mg* and flat REE at ~10xCI, but has a strong Clast 2 is similar to known VLT, but noALHA81005 contains a few fragments of VLTnot known if they are chemically similar to Clafrom a highland site near a VLT-bearing marVLT composition and those of its magnesiasource cannot be near the Apollo or Luna sites

References: [1] Goodrich C.A. et al. 1984[2] Maloy A.K. & Treiman A.H. 2004. AbstPlanet. Sci. Conf. [3] Cushing J.A. et al. 1999.[4] BVSP, 1981. Basaltic Volcanism on the Pergamon. [5] Taylor S.R. 1982. Planetary Scspective. LPI. [6] Shearer C.K. et al. 1991. EPSTreiman A.H. & Drake M.J. 1983. GRL 10, A.K. et al. 2005. MaPS 40, this volume.


SiO2 46.8 TiO2 1.0 Al2O3 16.1 Cr2O3 0.27 FeO 12.3 MnO 0.20 MgO 8.56 CaO 13.9 Na2O 0.21 K2O 0.03 P2O5 0.004Sum 99.4

flat pattern [4,5]. Its asalts, which could nent. Luna 24 VLT CI) [4], but is much n glass (15426) and ut their REE abun-,26 has comparable Eu deficit [6]. Thus, t identical to any. basalt [7], but it is

st 2. ALHA81005 is e [7]; based on this n granulites [8], its (see [8]). . JGR 89, C87-C94. r. #1159. 35th Lun. MaPS 34, 185-195. Terrestrial Planets. ience: A Lunar Per-L 102, 134-147. [7]

783-786. [8] Maloy

THE ORBIT OF VILLALBETO DE LA PEÑA: AN L6 CHONDRITE DELIVERED BY THE 3:1 RESONANCE. J.M. Trigo-Rodríguez1, J. Borovička2, P. Spurný2, J.L. Ortiz3, J.A. Docobo4, A. J. Castro-Tirado3 and J. Llorca5,6. 1 Institute of Geophysics & Planetary Physics, UCLA, CA 90095-1567 USA. E-mail: [email protected]. 2 Astronomical Institute of the Czech Academy of Sciences, Ondrejov Observatory. 3 Instituto As-trofísica de Andalucía (CSIC). 4 Observatorio Astronómico Ramon Maria Aller, Universidade de Santiago de Compostela. 5 Departament Química Inorgànica, Universitat de Barcelona. 6

Institut d’Estudis Espacials de Catalunya. Introduction: An absolute magnitude -18±1 superbolide

overflew Leon and Palencia provinces (Spain) on Jan. 4, 2004. The energy released during its entry deduced from video, seismic and infrasound data, together with information on the recovery of 32 meteorite fragments ranging from 11 g to 1.4 kg, strewn field, classification, isotopic analysis, and petrography have been re-cently published [1]. Fortunately, eyewitnesses obtained one video record and two direct pictures of the fireball. Additional pictures were taken of a 25±1 km smoky trail lasting for ~35 min. From these records we have obtained the atmospheric tra-jectory of this fireball and its heliocentric orbit [2]. Villalbeto de la Peña is the ninth meteorite with a known orbit.

Procedure: We made stellar calibrations for the video and three photographic records showing horizon details from the dif-ferent locations where the fireball was recorded, following the procedures of [3]. From these images we obtained the astrometric positions of the stars and the apparent coordinates of common objects present in the original pictures. By using them, we deter-mined the azimuth and elevation of the fireball. The Moon was recorded on the video and in one of the pictures, and used for the refinement of the calibration. Finally, the fireball’s trajectory was reconstructed with an accuracy of ~200 meters. The velocity of the fireball was measured from 86 video frames, covering a height from 32.8 to 22.2 km and a time interval of 1.70 s with a resolution of 0.02 s. A dynamic model was built and compared to the fireball light curve in order to estimate the initial velocity. Taking all uncertainties into account, the estimated initial veloc-ity is 16.9±0.4 km s–1. A modeled initial mass of 600±200 kg is in agreement with other methods [1] showing that no severe fragmentation occurred in the early part of the trajectory.

Results: Like all previously determined orbits of meteorites, the L6 ordinary chondrite Villalbeto de la Peña came from the main asteroid belt (a=2.3±0.2 AU, e=0.63±0.04, i=0.0±0.2º). From the orbital elements of meteorite progenitor bodies, it seems that bodies with semimajor axes of ~2.5 and eccentricities of ~0.6 are probably delivered to the Earth by the 3:1 main jovian resonance [4, 5]. The same mechanism explains the deliv-ery of Příbram, Neuschwanstein and Park Forest. These studies of the Villalbeto de la Peña bolide as well as the analysis of the meteorite itself have converted this meteorite fall into one of the best-documented in history.

References: [1] Llorca J. et al. 2005. Meteoritics & Plane-tary Science, in press. [2] Trigo-Rodríguez J.M. et al. 2005. Me-teoritics & Planetary Science, submitted. [3] Borovička et al. 2003. Meteoritics & Planetary Science 32: 975-987. [4] Wisdom J. 1985. Nature 315: 731-733. [5] Wisdom J. 1985. Icarus 63: 272-289.


IN-SITU OBSERVATION OF HYPERVELOCITY PARTICLES CAPTURED IN A SILICA AEROGEL COLLECTOR USING SYNCHROTRON-BASED MICRO-RADIOGRAPHY. A. Tsuchiyama1, K. Uesugi2, T. Nakano3, H. Yano4, K. Okudaira4,5 and T. Noguchi6. 1Department of Earth and Space Science, Graduate School of Science, Osaka University. E-mail: [email protected]. 2JASRI/SPring-8, 3AIST/JSC, 4JAXA/ISAS, 5Sokendai University, 6Ibaraki University.

Introduction: In January 2006, the Stardust mission will re-

turn cometary and perhaps interstellar dust particles, which are captured in silica aerogel collectors. Several techniques for ex-traction and analysis of hypervelocity impact samples have been developed (e.g., [1, 2]). However, techniques for in-situ observa-tion of particles in aerogel collectors, which will give information about fragmentation of projectiles, remain primitive. Here, we report an in-situ observation technique with high spatial resolu-tion for hypervelocity impact tracks in silica aerogel collectors using synchrotron-based X-ray micro-radiography.

Experiments: A sample used in the present study is a labora-tory simulant (Fe-rich hydrous silicate (cronstedtite) projectiles at about 4 km/sec [3]). The sample was observed at beamline BL47XU of SPring-8 using a micro-tomography system (SP-µCT [4]). Transmitted images of the sample were obtained at X-ray energies of 10 keV and just above and below the Fe K-absorption energy (7.124 and 7.098 keV, respectively). Each image has 2000x1312 matrix (0.940 x 0.617 mm2: 0.47 µm pixel size). Re-fraction contrasts were enhanced by taking 40 mm distance be-tween the sample and the X-ray detector to observe aerogel sur-faces together with absorption contrasts for the particles. Succes-sive eleven images were arranged to make a tiled image for the sample. A stereograph was made from two sets of tiled images separated by 5 degrees.

Results and discussion: The transmitted images were con-verted to the images expressed by transmittance: t = I/I0 = exp[-∫µds], where I and I0 are the intensities of the transmitted and incident X-ray beams, µ is the linear attenuation coefficient of the sample and s is the coordinate along the X-ray beam path. In the transmittance images, we can recognize particles (2-30 µm) by absorption contrast. Aerogel surfaces and a part of impact track are recognized by refraction contrast. Subtraction of the transmit-tance at 7.124 keV from that at 7.098 keV gives Fe distribution images. The refraction contrast was completely disappeared and only the absorption difference due to Fe was seen. Some particles recognized in the transmitted images do not contain any Fe, sug-gesting that they are not cronstedtite but contaminants or molten silica grains. 3-D distribution of the aerogel surfaces and the par-ticles was also seen. The results show the applicability of this technique to the Stardust samples. The effective spatial resolution of ~2 µm in the present experiments will improve to ~1 µm or less if a new X-ray detector with 0.2 µm pixel size is used.

References: [1] Westphal A. J. et al. 2004. Meteoritics & Planetary Science 39:1375-1386. [2] Graham G. A. et al. 2004. Meteoritics & Planetary Science 39:1461-1473. [3] Okudaira K. et al. 2004. Advances in Space Research, 34:2299-2304. [4] Ue-sugi K. et al. 2001. Nuclear Instruments & Methods in Physics Research A, 467-468, 853-856.


LA-ICP-MS AND EMPA ANALYSIS OF MELT ROCK PARTICLES FROM THE YAXCOPOIL-1 BOREHOLE, CHICXULUB IMPACT STRUCTURE, MEXICO. M. G. Tuchscherer1, U. W. Reimold1, R. L. Gibson1, and C. Koeberl2, 1ICRG, School of Geosciences, University of the Wit-watersrand, Private Bag 3, P.O. Wits, 2050 Johannesburg, South Africa, 2Department of Geological Sciences, University of Vienna, Althanstrasse 14, A-1090 Vienna, Austria.

Introduction: Melt rock particles from impactites of the

Yaxcopoil-1 (Yax-1) core [1] have been analyzed by conven-tional electron microprobe analysis (EMPA) and LA-ICP-MS. This was done in order to document their compositional diver-sity, determine precursor phases (minerals or protoliths), com-pare these findings with previous results [e.g., 2,3,4], and discuss the various processes that affected the melts after cratering, namely hydrothermal (immediately post-impact) and seawater-related (since impact) alteration.

Results and discussion: Melt rock particles are of highly heterogeneous compositions at the 3 µm scale (EMPA) and slightly less so at the 100 µm scale (ablation pit scale). Numerous mixtures between components characterised by TiO2, MgO + FeOtot, CaO, and Na2O + K2O exist, which makes the classifica-tion of melt particles very difficult and is linked to the high dis-equilibrium conditions related to the impactite formation.

Mafic melt rock particles are all volatile rich (low EMPA to-tals) and register strong K-overprint. Other particles, mostly but not exclusively from the upper part of the section are CaO and Na2O depleted. Some melt particles of 55-60 wt% SiO2 yielded good EMPA totals and chemically correspond non-stoichiometric feldspathic compositions of ca. An33Ab32Or35, An04Ab03Or93, but with up to 8 wt% FeOtot. We also found compositions corre-sponding to stoichiometric plagioclase of An49Ab47Or4, which indicates single mineral melting and admixture of different melts to form larger melt particles.

Trace elements, especially immobile elements such as Sc or Zr, provide a further means to constrain potential melt precursor compositions. Currently known target rock types include granite and granodiorite/granitic gneiss, clastic sedimentary rocks (quartzite, sandstone, siltstone), and shale [5]. From isotopic work by [6] and our own chemical analuysis a mafic (amphibo-lite or gabbroic) component is also required. Sc/Zr ratios of all analyzed melt particles fall the ratios for granitic gneiss/granodiorite and clastic sedimentary rocks. More mobile elements, such as Ba, Rb, and Sr, do not provide further con-straints due to their relationship to the secondary overprint on the impactites. Chondrite normalized REE patterns are distinctly dif-ferent from melt particle to particle, which we relate to various combinations of target rocks and/or melting of individual or combinations of minerals.

Conclusions: Yax-1 melt rock particles are products of min-eral melting, melt mixture, and secondary alteration. Our initial LA-ICP-MS study has shown that immobile element ratios may be effective in discriminating compositions of different melts. References: [1] Dressler et al. 2003. EOS Trans. AGU 84:125-130. [2] Ames et al. 2004. MAPS 39: 1145-1167. [3] Hecht et al. 2004. MAPS 39:1169-1186. [4] Tuchscherer et al. 2004. MAPS 39: 899-930. [5] Tuchscherer et al. 2005. MAPS, in press.


EVIDENCE OF ENHANCED SPACE WEATHERING EFFECT BY COEXISTING METALLIC IRON. Y. Ueda1, T. Hiroi2 , S. Sasaki3 and M. Miyamoto1. 1Dept. Earth Planet. Sci., Univ. Tokyo, Hongo, Bunkyo-ku, Tokyo 113-0033, Japan. 2Dept. Geological Sci., Brown Univ., Providence, RI 02912, USA. 3National Astronomical Obs. of Japan, Mitaka, Tokyo 181-8588, Japan. E-mail: [email protected]

Introduction: Space weathering is the characteristic effect

that was found from the lunar regolith samples returned by Apollo missions, and now commonly used as the cumulative ef-fect that causes spectral changes on airless bodies [1]. It is now known to be due to nanophase iron particles inside a thin amor-phous layer on each regolith particle [2]. By the space weather-ing effect, the reflectance spectrum shows characteristic changes such as spectral reddening, absorption band weakening and al-bedo decrease. Since the reflectance spectra of many asteroids have same features, many researchers believed that regolith on the surface of many asteroids should be space-weathered, and the data observed by the spacecraft missions support the idea [3].

Experiment: Olivine from San Carlos (Fo91) was pulverized by a corundum mortar and a pestle, dry-sieved to a <100 µm par-ticle size fraction. A manufacture reagent of metallic iron pow-der of particle size <150 µm was used for mixing with the olivine sample. Two mixture samples were prepared with metallic iron contents of (1) 10 wt% and (2) 20 wt%. We also used (3) pure olivine powder sample for comparison. Many researchers have performed the space weathering simulation experiments using various methods, such as ion implantation [4, 5] and laser irradia-tion [6, 7]. In this report, we used the laser irradiation technique after Yamada et al.’s procedure [7]. Total laser irradiation en-ergy was 30 mJ. After irradiations, reflectance spectra were measured over the wavelength range of 0.3 to 2.5 µm by a UV-Visible-NIR spectrometer located at JAXA.

Result and Discussion: After laser irradiations, the reflec-tance spectra of olivine-metallic iron mixtures changed much more than laser irradiated pure olivine sample in reddening and reduction of absorption bands. To date, olivine is known to be one of the key minerals in studying the space weathering [8]. This experiment suggests that the changes of reflectance spec-trum due to the space weathering are enhanced in the case when metallic iron exists in regolith. Since metallic iron is one of the common minerals in various kinds of meteorites, such as ordi-nary chondrites [9], its existence would be one of the important factors when we treat the space weathering problem.

Conclusion: In our experiment, the existence of metallic iron in olivine is found to be a great contributor to the space weather-ing effect. From this result, there is a possibility that the rate of space weathering is much higher than we estimated, especially on the surface of asteroids that contain metallic iron as a major mineral, such as ordinary chondrite parent bodies.

References: [1] Pieters C. M. et al. 1993. Journal of Geo-physical Research 98:20817-20824. [2] Keller L.P. and McKay, D. S. 1993. Science 261:1305-1307. [3] Chapman C. R. et al. 2002. Icarus 155:104-118. [4] Hapke B. 2002. Journal of Geo-physical Research 106:10039-10074. [5] Strazzulla G. et al. 2005. Icarus 174:31-35. [6] Moroz L. et al. 1996. Icarus 122, 366-382. [7] Yamada M. et al. 1999. Earth Planets Space 51:1255-1265. [8] Hiroi T. et al. 2001. Meteoritics & Planetary Science 36:1587-1596. [9] Rubin A. E. 1997 Meteoritics & Planetary Science 32:231-247.


CHONDRITES FROM THE ATACAMA DESERT E. M. Valenzuela 1, P. A. Bland2, S. S. Russell3, C. Roeschmann1 and D. Morata1. 1Departamento de Geología, Fac. Ciencias Físicas y Matemáticas, Universidad de Chile, Plaza Ercilla 803, Santiago, Chile. E-mail: [email protected]. 2Department of Earth Science and Engineering, Imperial College London, SW7 2AZ, UK. 3Department of Mineralogy, The Natural History Museum, London SW7 5BD, UK.

Introduction: The Atacama Desert in northern Chile, South

America, is one of the driest deserts on Earth [1]. Its age is about 15 Mys and the arid conditions were established around the Middle Miocene [2], with some more humid cycles in the Holocene [3]. Its extreme aridity and the presence of vast ablation surfaces have allowed the preservation of meteorites of unknow terrestrial ages. At present, there are 67 meteorites registered. From this list, 15 are chondrites, collected from three main areas. Recent studies [4, 5, 6] carried out on meteorites from other deserts - Australia, Africa and North America - have shown important relations between their terrestrial age and the weathering stage of their primary mineralogy. These data give some clues on terrestrial processes, that in some cases have been strongly influenced by climatic or geomorphologic conditions at the accumulation sites. In the same way, Atacama Desert chondrites can contribute to the understanding of terrestrial weathering processes acting on meteorites and also on terrestrial surfaces.

Past studies: Until now, most chondrites have not been analysed beyond a basic classification. Only [7] reports a complete petrological and geochemical study from Paposo, a LL ordinary chondrite showing unusually Fe-rich olivines and pyroxenes, (Fa 333 333-Fs27, respectively), an enriched LREE pattern (LaN=3,381, CeN=2,833, normalized to CI) and weathering products as akaganéite, goethite and maghemite.

One of the recovery surfaces, a plain of about 750km2, appears to be a great accumulation site with samples from at least three different falls, inferred from some preliminary terrestrial ages [8]

Present Studies: Some of the studies that will be performed with these chondrites are measurement of 14C and 36Cl terrestrial ages, 57Fe Mössbauer spectroscopy (to quantify the degree of oxidation in samples) and petrologic and geochemical analyses. From terrestrial ages and oxidation-frequency distributions for populations of samples we expect to estimate the ages of some Atacama Desert surfaces, as well as to impose constraints on the effect of climate on rock weathering rates between different sites from the differences in the weathering rate of samples. We also hope to contribute to the understanding of the Atacama Desert paleoclimatic evolution during the last 50 kys, studying the structure in the oxidation–terrestrial age distribution for meteorites from these accumulation sites.

References: [1] Navarro-González R. et al. 2003. Science 302: 1018-1021 [2] Alpers C.N. and Brimhall G.H. 1988. Geological Society of America Bulletin 100:1640-1656. [3] Grosjean M. et al, 2003. Palaeogeography, Palaeoclimatology, Palaeoecology 194:247-258. [4] Bland P.A. et al. 1998. Geochimica et Cosmochimica Acta 62:3169-3184. [5] Bland P.A. et al. 2000. Quaternary Research 53, 131–142. [6] Jull A. J. T. 1995. Lunar and Planetary Institute Technical Report 95-02: 37–38. [7] Valenzuela E.M. et al. 2003. Extended Abstract Volume of the X Congreso Geológico Chileno. [8] Jull A.J.T. 2005. Personal communication.


ZINDER: A NEW PYROXENE-BEARING PALLASITE. D. van Niekerk1. 1Hawaii Institute of Geophysics and Planetology, University of Hawaii, Manoa, Honolulu HI, 96822, USA. E-mail: [email protected].

Introduction: The pyroxene pallasite grouplet is a small and

relatively new group of meteorites [1]. They currently consist of Vermillion, Yamato 8451, Zinder, and Northwest Africa 1911. Zinder is a relatively new pyroxene pallasite that was found in Ni-ger [2]. We are currently studying one thin section of Zinder to characterize its basic mineralogy, major chemistry and trace ele-ments.

Mineralogy and Chemistry: Electron microprobe mapping and scanning electron microscopy indicates that Zinder is predomi-nantly composed of kamacite, olivine, and low-Ca pyroxene. Phos-phate content is negligible, as is chromite. Olivine (Fa11.7) makes up 27% of the modal mineralogy, pyroxene (Fs11.1Wo2.0En86.9) makes up 28%, and kamacite 44% [2]. Electron microprobe data for these phases are presented in tables 1 and 2. Table 1: Representative electron microprobe analyses of oli-vine and pyroxene in Zinder. (Results are in wt%).

Olivine Pyroxene SiO2 39.7 55.8 TiO2 <0.03 0.13 Al2O3 <0.03 0.91 Cr2O3 <0.05 0.78 FeO 11.5 7.6 MgO 48.4 33.3 MnO 0.3 0.33 CaO <0.02 1.05

Table 2. Representative electron microprobe analysis of kamacite in Zinder. (Results are in wt%; b.d.l=below detection limit).

Fe Ni Co Cr Si P S Total 92.4 7.0 0.53 <0.05 b.d.l 0.08 <0.03 100.00

Trace Element Data: In situ trace element analyses of sili-

cates and siderophiles in metal are currently in progress. Discussion: Zinder is the third pyroxene-rich pallasite discov-

ered up to date. It bears the distinction of being the secondmost pyroxene-rich of the four. As with all the pyroxene pallasites, Zinder differs from Main Group pallasites in that pyroxene is a ma-jor, discrete phase instead of only occurring as symplectic inter-growths on olivine margins. The pyroxene in Zinder differs from that of Vermillion, in that augite is not present as inclusions in oli-vine [3]. The Zinder pyroxene that is enclosed in olivine, is of the low-Ca variety. In Y-8451 both low-Ca clinopyroxene and low-Ca orthopyroxene is present [3]. All the low-Ca pyroxene in Zinder is orthopyroxene. Pyroxene in Zinder appears to be enriched in Cr2O3 relative to Vermillion and in TiO2,,Al2O3, Cr2O3, and FeO relative to Y-8451.

References: [1]Boesenberg J. S. et. al. 1995. Meteoritics 30:488-489. [2] Russell S. S. 2003. Meteoritics and Planetary Sci-ence 38:A212. [3] Boesenberg J. S. et al. 2000. Meteoritics and Planetary Science 35:757–769.

Acknowledgement: The sample being studied is on generous loan from Ted Bunch.


WEATHERING FORMS OF ANTARCTIC STONY METEORITE FINDS: TERRESTRIAL WEATHERING BRINGS OUT SUBTLE TEXTURES IN EUCRITES AND HOWARDITES. M. A. Velbel. Dept. of Geological Sciences, Michigan State Uni-versity, East Lansing, MI 48824. E-mail: [email protected].

Introduction: Terrestrial weathering of terrestrial boulders

and outcrops often acts differentially on exposed volumes of rock with different composition, texture, structure and/or fabric. Of-ten (e.g., cross-bedding), it is the enhancement and amplification of such variations by differential weathering that makes such fea-tures visible to the unaided eye (as slight variations in the micro-topography of the weathered surface). The purpose of this pres-entation is to illustrate how terrestrial Antarctic weathering pro-duces weathering forms on Antarctic HED finds, and how such weathering forms reflect the internal textures and structures of Antarctic eucrite breccias and howardites.

Results: Fractured surfaces and polished surfaces show igne-ous textures, and brecciated textures consisting of various proportions of coarse (cm-scale) discernably igneous fragments and fine (mm-/sub-mm-scale) fragments too small to identify reliably with the unaided eye. Some terrestrially weathered Ant-arctic eucrite breccias and howardites show weathering pits breaching the fusion crusts. In general, such weathering pits are typically approximately 1 cm across. More advanced weathering of the meteorite surfaces is associated with more extensive to near-complete removal of fusion crust); some such extensively weathered surfaces exhibit small-(cm-)scale cavernous weather-ing. Where interior textures are exposed by fractures and/or cut surfaces during sample processing, maximum fragment sizes are seen to be approximately 1 cm. Similar cross-sections reveal that surface pits penetrate interiors to depths of ~1 cm.

Discussion: Terrestrially weathered Antarctic eucrite brec-cias and howardites exhibit a nearly-complete surface-modification sequence. The least-weathered meteorites have unmodified and complete fusion crust. At intermediate weather-ing stages, fusion-crusted surfaces are penetrated by pits. The most advanced weathering stages show near-complete destruc-tion/removal of the fusion crust and cavernous weathering of the weathered interior material. At all stages, the width and depth scales of fusion-crust-penetrating pits and the cavernous-weathering pits are the same as the scale of the coarse fragments in the breccia.

All well-developed weathering pits on Antarctic HED mete-orites examined here occur on brecciated meteorites (howardites, and eucrite breccias). The scale and distribution of weathering pits is consistent with the possibility that cm-scale fragments are more vulnerable to Antarctic weathering than are lithologies con-sisting of, for example, smaller fragments encased in shock-melt glass.

Conclusions: Weathering forms of Antarctic HED meteor-ites appear to be associated with primary textural-structural fea-tures of the rocks. Non-brecciated eucrites show no weathering pits. Weathered eucrite breccias and howardites show weather-ing pits with sizes and distributions similar to the sizes and dis-tributions of coarse fragments in the brecciated parent rock prior to weathering. Terrestrial weathering of Antarctic HED meteor-ites highlights textural aspects of the rocks themselves.


AQUEOUS ALTERATION IN QUE93005 (CM2): DIFFERENT ALTERATION SCALES FOR ANTARCTIC AND NON-ANTARCTIC CM CHONDRITES? M. A. Velbel1, E. K. Tonui2 and M. E. Zolensky3. 1Department of Geological Sciences, Michigan State University, East Lansing, MI 48824-1115. E-mail: [email protected]. 2Department of Earth and Space Sciences, UCLA. 3Astromaterials Research & Exploration Science Office, NASA Johnson Space Center.

Introduction: Some phyllosilicates in CM carbonaceous

chondrites formed by aqueous alteration of anhydrous precursor phases (e.g., [1,2]). Broad trends in the compositions of hydrous phyllosilicates are recognized and believed to be related to trends in degree of aqueous alteration [2,3]. This paper reports textural and compositional measures of aqueous alteration in the CM2 chondrite QUE93005 [4], and compares QUE93005 with previ-ously published results for non-Antarctic CM2 falls [2].

Results: QUE93005 (CM2; [4,5]) is not discernibly brecci-ated at thin-section or hand-specimen scales. Chondrules are abundant. Most olivine-bearing objects are subrounded to rounded, and exhibit elliptical to circular cross-sections in thin-section. Most also have fine-grained rims visibly identical to “accretionary” rims noted in carbonaceous chondrites interpreted by some as “primary accretionary rocks” [6]. Olivine composi-tions ranging from Fo77 to Fo99 were observed partially re-placed by serpentine in QUE93005; more fayalitic but unre-placed olivine also occurs [4]. Fayalitic olivine is commonly more extensively replaced than forsteritic olivine [4]. The Min-eralogical Alteration Index (MAI; [2]) of QUE93005 matrix is approximately ~0.7.

Discussion: Alteration of Antarctic CM find QUE93005 shows little correspondence with the CM fall alteration sequence proposed by [2]. QUE 93005 exhibits considerable replacement of olivine by serpentine, although many instances of unreacted olivine survive [4]. QUE 93005 is texturally much more exten-sively altered than Murchison, widely regarded as one of the least altered CM falls [2]. The preliminary MAI for QUE93005 is much higher than that of Murchison, and similar to the MAIs of extensively altered non-Antarctic CM chondrites [2]. How-ever, despite the considerable difference in several measures of the degree of aqueous alteration of olivine between Murchison and QUE 93005, these two CM chondrites have nearly identical whole-rock oxygen isotope compositions [5]. A moderately to extensively altered Antarctic CM find has essentially the same oxygen isotope composition as a minimally altered CM fall. If oxygen isotope composition is associated with the extent of pre-terrestrial aqueous alteration in CM chondrites [2], it appears likely that a given oxygen isotope composition reflects a differ-ent degree of aqueous alteration in Antarctic finds than in non-Antarctic falls.

References: [1] Bunch T.E. and Chang S. (1980) GCA, 44, 1543-1577. [2] Browning L. B. et al. (1996) GCA, 60, 2621-2633. [3] Zolensky M. E. et al. (1993) GCA, 57, 3123-3148. [4] Velbel M. A. et al. (2005) LPSC XXXVI #1840. [5] Clayton R.N. and Mayeda T.K. (1999) GCA, 63, 2089-2104. [6] Metzler K. et al. (1992) GCA, 56, 2873-2897.


POPIGAI FLUIDIZITE DYKES: DATA ON VOLATILES. S. A. Vishnevsky1, N. A. Gibsher1, J. Raitala2, S. G. Simakin3, N. A. Palchik1. 1Institute of Mineralogy & Petrology, Novosibirsk-90, 630090, RUSSIA, <[email protected]>; 2University of Oulu, Oulu, P.O. Box 3000, FI-90014, FINLAND, <[email protected]>; 3Institute of Microelectronics & Infor-matics, Yaroslavl-7, 150007, RUSSIA, <[email protected]>.

Introduction: Earlier, the Popigai impact fluidizites, which

are the first occurrence of so kind in the terrestrial impact struc-tures, were described in [1-4]. New data on their volatiles (both for the bulk rock and separate glass species) are presented below.

Observations: Volatiles were studied by means of gas chro-matography (step-heating extraction at 100-500, 500-700 and 700-800oC) and ion probe (Cameca IMS-4F) analyses.

Data on gas chromatography. Total volatile amount in fluid-izites (6 samples, all data in wt.%) is 2.64 to 4.1, including H2O (1.99-3.77), CO2 (0.12-0.47), CO (0.04-0.11), H2 (0.01-0.05) and CH4 (<0.01 to 0.02); traces of C2H2, C2H4, etc. are also detected; no N2, SO2 and H2S is found. The water extraction dynamics (up to 63-67 rel.% at 100-500oC) is in agreement with smectite alteration of the rocks. Total volatile amount in the host gneisses (4 samples) is lower (0.42 to 1.78 wt.%), including H2O (0.28-1.47 wt.%) and CO2 (0.12-0.26 wt.%). The H2O and CO2 extraction dynamics (up to 89.8 and 92.6 rel.% at 500-800oC) is in agreement with chlorite and carbonate alteration of the rocks.

Ion probe data. 20 analyses of H2O and F were made in indi-vidual fresh glass particles: 14 for type I glasses (the most com-mon homogeneous, H, ones); 3 for type II glasses (fine-banding of type I and K-Na-Ca glasses); 3 for type III glasses (high-silica, HS, and lechatelierite, L, ones). Next volatile amounts (range, R, average value, X, and standard deviation, SD, all data in wt.%) are found: i) type I glasses: H2O 1.76–6.41; 4.69±1.21; F 0.091–0.138; 0.106±0.014; ii) type II glasses: H-bands, H2O 5.22 and 5.97; F 0.124 and 0.144, respectively; K-Na-Ca bands: H2O 8.97; F 0.0008; iii) type III glasses: HS-particles, H2O 2.82 and 3.32; F 0.019 and 0.023, respectively; L: H2O 1.11; F <0.001. SEM- and microprobe data for the glasses show low totals: 92.97–95.55 (type I); 94.26–95.36 (type II, H-bands); 89.67 (type II, K-Na-Ca bands); 96.45–97.06 (type III, HS-bands); 97.86 (type III, L). Based upon volatile amounts, new totals are, respectively: 95.95–101.61; 100.37–100.7; 98.64; 99.29–100.40 and 98.97.

Discussion and conclusion: High H2O amounts show its im-portance for the dyke origin (delay of shock pressure release, in-tensive post-impact alteration, etc. [3,4]). Previously (R,X,SD-data for H2O in wt.%), “dry” (0.32–0.98; 0.74±0.19) and “wet” (1.21-3.14; 2.23±0.61) melt rock varieties and globules of impact anatectic glass (4.23–6.93 wt.% of H2O) were known for the Popigai impactites [5]. Recently, based upon low SEM-totals, high H2O amounts were supposed for some Ries glasses [6]. Ear-lier, it was generally assumed that impact glasses are very “dry” (<0.15 wt.% of H2O) [7]. Data by [1-6] and these show impor-tance of H2O in origin and evolution of the impact melts.

Acknowledgement: This study was supported by the RFBR grant #04-05-64127 and by the Finnish Academy grant #207759.

References: [1] Vishnevsky S. A., et al. 2003. Abstract #4034. Lunar & Planetary Institute Contribution #1167. [2] Vishnevsky S. A., et al. 2004. Meteoritics & Planetary Sci-ence 39:A109. [3] Vishnevsky S. A., et al. 2005. Geologia i Geofizika (in press, in Russian). [4] Vishnevsky S. A., et al. 2005. Abstract #1145. Lunar & Planetary Institute Contribution #1734. [5] Vishnevsky S. A. and Montanari A. 1999. Geological Society of America Special Paper 339:19-59. [6] Osinski G. R. 2003. Me-teoritics & Planetary Science 38:1641-1667. [7] Beran A. and Koeberl C. 1997. Meteoritics & Planetary Science 32:211-216.




SIGNIFICANCE OF LOW SILICON CONTENTS IN IRON METEORITES. I. A. Vogel1, A. Pack2, B. Luais2 and H. Pal-me1. 1Institut für Geologie und Mineralogie, Universität zu Köln, 50674 Köln, Germany. E-mail: [email protected]. 2CNRS Centre de Recherches Pétrographiques et Géochimiques, 54501 Vandoeuvre-lès-Nancy, France.

Introduction: Iron meteorites are fragments of asteroidal

cores, that have separated from the mantel silicates by gravita-tional settling of liquid FeNi. During this process some Si parti-tioned into the metal. The Si content in the iron meteorites is thus a sensitive indicator of temperature and oxygen fugacity during metal segregation in small planetesimals.

Si contents in iron meteorites are not well known, they are below the detection limit of most analytical methods. Wai and Wasson [1] give an upper limit of 20 µg/g. Here we used secon-dary ion mass spectrometry (SIMS) to determine Si contents in various iron meteorites.

Analytical: With a Cameca 1270 SIMS spectrometer at the Centre de Recherches Pétrographiques et Géochimiques in Nancy, France the Si contents of the following magmatic and non-magmatic iron meteorites (related group in brackets) were analyzed: Toluca, Landes, Canyon Diablo (group IAB), San Mar-tin, Sao Juliao de Moreira, Walker County, Guadaloupe y caldo (group IIAB), Cape York (group IIIAB), Seeläsgen (group IIICD) Ballinoo, Perryville (group IIC), Mont Dieu, Watson, Miles (group IIE).

Results: The measured Si contents are remarkably low, they lie between 0.1 to 0.3 µg/g. There is no difference between magmatic and non-magmatic groups, average of magmatic irons is 0.25±0.05 µg/g and that of non-magmatic irons is 0.14±0.02 µg/g. Also we did not see a difference in Si between kamacite and taenite in meteorites exhibiting Widmanstätten patterns. Discussion: Si contents of iron meteorites were calculated for different temperatures by assuming equilibrium between eucritic silicates and FeNi, using activity coefficients for Si in FeNi de-termined recently by furnace experiments [2]. Comparison with the measured data shows, that final metal-silicate equilibration in iron meteorites must have occurred at temperatures as low as 1200 °C. This temperature is difficult to reconcile with fractional crystallization of large bodies of molten FeNi that are required to explain the siderophile trace element patterns of iron meteorites. In general, the low contents of Si and also Cr in iron meteorites

chi

require oxidizing conditions during metal formation. Oxidizing conditions alone are not sufficient to produce the low Si-contents measured in this work, low temperates are required in addition.

References: [1] Wai C. M. and Wasson J. T. 1969. Geo-mica et Cosmochimica Acta 33:1465–1471. [2] Vogel I. A.

and Palme H. 2003. Meteoritics & Planetary Science 38: A131


HIGH RESOLUTION 40AR/39AR DATING OF PLAGIOCLASE SEPARATES FROM IAB SILICATE INCLUSIONS – NEW METHODOLOGICAL AND THERMOCHRONOLOGICAL INSIGHTS. N. Vogel1,2 and P.R. Renne1. 1Berkeley Geochronology Center, CA 94709, USA. [email protected]. 2present address: Institute of Physics, Space Research and Planetary Sciences, University of Bern, Switzerland.

Introduction: As inferred from age determinations with

various chronometers, the formation and thermal evolution of the IAB parent body is not yet fully understood [1, 2]. We present Ar-Ar ages of silicate inclusions from Caddo County, Campo del Cielo, Landes, and Ocotillo. In contrast to conventional Ar-Ar dating of whole inclusions we prepared plagioclase separates from individual inclusions to minimize problems, e.g., due to excess 40Ar* or recoil 39ArK. To monitor the influence of grain size and quality on the age, 2-3 plagioclase size fractions and quality grades were analyzed from each inclusion.

Results: The different separates of each inclusion generally span age ranges of which the oldest isochron ages (errors 2σ) are 4540 (11) Ma for Caddo, 4438 (18) Ma and 4433 (17) Ma for 2 Campo inclusions, 4496 (29) Ma and ~470 Ma for 2 Landes in-clusions, and 4416 (17) Ma for Ocotillo. The lower ages of some separates are caused by 40Ar* loss due to parent body metamor-phism, impact events, or terrestrial weathering of the samples.

Discussion: While an influence of the plagioclase quality on the age could not be detected, a clear correlation exists between the average grain size of the different inclusions and their aver-age ages. Within the inclusions this correlation exists for one Campo inclusion and for Ocotillo, but not for Caddo and Lan-des., i.e., here smaller grain size fractions show higher ages. Since this cannot be explained by 39ArK recoil loss, the expected preferential diffusive loss of 40Ar* from smaller grains must to be superposed by another effect. Impact resetting at about 470 Ma ago clearly is the reason for the young age of the second Landes inclusion situated only a few cm apart from old one, underlining the very local influence of such events on a sample.

Conclusions: Our study shows (i) that Ar-Ar age differences between IAB meteorites usually assigned to different burial depths or times of resetting [e.g., 2] might be rather a function of the analyzed plagioclase grain size, (ii) that a significant age range exists within each inclusion depending on grain size and further factors that are yet to be identified, and (iii) that, based on the results of 2 Landes inclusions, the common technique of mix-ing of several inclusions to increase the sample amount might lead to geochronologically meaningless ages. Taking into account a slightly excessive 40K decay constant [2, 3] would increase the oldest Caddo Ar-Ar cooling age by at least ~30 Ma to ~4570 Ma, indistinguishable from the time of forma-tion of the first solids in the solar system. This might support an impact formation of IAB irons in individual melt pools on a still very porous chondritic body [4] rather than models requiring as-teroid wide metamorphism and core formation [5] for which cer-tainly several Ma would have to be allowed before IABs can form and cool through the K-Ar blocking temperature.

References: [1] Mittlefehldt D.W. et al. (1998) Planetary Materials, Vol. 36: 4/1–4/195. [2] Bogard D.D. et al. (2005) MAPS 40: 207-224. [3] Renne P.R. (2000) EPSL 175: 13-26. [4] Wasson and Kallemeyn (2002) GCA 66: 2445-2473. [5] Benedix et al. (2000) MAPS 35: 1127-1141.



DEVELOPMENT AND FIRST TEST RESULTS OF A LOW-VOLUME UV-LASER NOBLE GAS EXTRACTION LINE 1N. Vogel, 1I. Leya, 1H. Lüthi, 1J.A. Whitby. 1Institute of Physics, Space Research and Planetary Sciences, University of Bern, Switzerland. [email protected].

Introduction: We have developed a low-volume noble gas

extraction line connected to a dual-wavelength laser system (New Wave Research®, continuous 10.6 µm or pulsed 1.06 µm radiation) and a MAP 215-50 noble gas mass spectrometer. No-ble gases from individual components of meteorites will be ex-tracted in situ from meteorite sections by UV laser ablation. This technique allows the determination of the noble gas composition of components of previously characterized meteorite sections on a microscopic scale and avoids wasting time and material during sample separation. Several attempts to do in situ noble gas work on meteorites with IR lasers have revealed problems concerning noble gas fractionation and the determination of the degassed sample volumes for He to Xe [e.g., 1, 2]. These problems can be ameliorated by the use of an appropriate laser power density and beam profile, and the use of shorter wavelengths.

Anticipated experiments: At the conference we will present detailed results from the experiments described below: First, a careful determination of noble gas blank levels in the sys-tem and their stability over time will be performed. This is of particular importance when analyzing small gas amounts as will be the case for the in situ gas extraction with the UV laser. Sub-sequently, we will do extensive tests in order to determine and ideally eliminate noble gas fractionation during gas extraction from the sample by UV laser. Therefore, different materials con-taining homogeneously distributed noble gases on a microscopic scale will be selected. On the one hand, total gas extractions by IR laser from small individual samples of these materials will be performed. On the other hand we will analyze noble gases ob-tained by in situ UV laser extraction from aliquots of the materi-als. Comparing the results will provide information about ele-mental and isotopic noble gas fractionation as well as informa-tion about the sample volumes degassed by the UV laser. By ad-aptation of, e.g., the laser shot frequency, the laser energy per shot, or optical parameters we will optimize our UV laser extrac-tion technique.

References: [1] Nakamura T. et al. (1999) Geochimica et Cosmochimica Acta 63:241-255. [2] Okazaki R. (2001) et al. Na-ture 412:795-798.


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