5320

OXYGEN AND MAGNESIUM ISOTOPIC COMPOSITIONS OF ASTEROID 25143 ITOKAWA RETURNED BY THE HAYABUSA MISSION

H. Yurimoto¹, K. Abe¹, M. Abe², M. Ebihara³, A. Fujimura², M. Hashiguchi¹, K. Hashizume⁴, T. R. Ireland⁵, S. Itoh¹, J. Katayama¹, C. Kato¹, J. Kawaguchi², N. Kawasaki¹, F. Kitajima⁶, S. Kobayashi¹, T. Meike¹, T. Mukai², K. Nagao⁷, T. Nakamura⁸, H. Naraoka⁶, T. Noguchi⁹, R. Okazaki⁶, C. Park¹, N. Sakamoto¹, Y. Seto¹⁰, M. Takei¹, A. Tsuchiyama⁴, M. Uesugi², S. Wakaki¹, T. Yada², K. Yamamoto¹, M. Yoshikawa² and M. E. Zolensky¹¹. ¹Hokkaido University. E-mail: yuri@ep.sci.hokudai.ac.jp. ²JAXA-ISAS. ³Tokyo Metropolitan University. ⁴Osaka University. ⁵The Australian National University. ⁶Kyushu University. ⁷The University of Tokyo. ⁸Tohoku University. ⁹Ibaraki University. ¹⁰Kobe University. ¹¹NASA Johnson Space Center.

**Introduction:** The asteroid Itokawa is classified as an S-type asteroid and inferred, based upon reflectance spectrometry, to consist of materials similar to primitive achondrites or ordinary chondrites [1, 2]. In order to unequivocally establish the connection between asteroids and meteorites, determination of oxygen isotopic composition of asteroidal material is absolutely imperative. For example, primitive achondrites and ordinary chondrites are clearly distinguishable by their oxygen isotopic compositions [3]. This is an updated report of the oxygen isotopic composition from the preliminary report [4] and the first report of the magnesium isotopic composition of Itokawa.

**Experiments:** Each grain was mounted at the center of an epoxy disk and the surface was polished under the processes established for the preliminary examination. The samples were gold-coated to a thickness of 60 nm.

Oxygen and magnesium isotope compositions have been investigated by the Hokudai isotope microscope system [5]. A Cs⁺ primary beam of 20 keV and O⁻ of 23 keV was focused to a spot of approximately 10 µm on the surface of the sample for O and Mg isotope analyses, respectively. Secondary ions were collected simultaneously in Faraday cups or in electron multipliers corresponding to the secondary ion intensities using a Cameca multi-collection system. Terrestrial standards of the corresponding minerals were used for normalization.

**Results and Discussion:** All oxygen isotopic compositions of the minerals from Itokawa plot on the upper side of terrestrial materials on an oxygen three-isotope diagram and are distributed parallel to the terrestrial mass fractionation line. The $\Delta^{17}\text{O}_{\text{SMOW}}$ for Itokawa is 1.46‰ ± 0.41 (2σ) for olivine, 1.57‰ ± 0.62 (2σ) for orthopyroxene, and 1.15‰ ± 0.51 (2σ) for plagioclase. The mean $\Delta^{17}\text{O}_{\text{SMOW}}$ for minerals from Itokawa, 1.39‰ ± 0.36 (2σ), coincide with those of LL or L chondrites, but not with those of H chondrites.

We have observed no $\delta^{26}\text{Mg}$-excesses for olivine, orthopyroxene and plagioclase from Itokawa in 2σ confidence of the analytical precisions. The initial $^{26}\text{Al}/^{27}\text{Al}$ ratio is calculated to be 3 ± 8 (2σ) × 10⁻⁸ and the initial $\delta^{26}\text{Mg}$ is to be 0.01 ± 0.02‰, which coincide with those of equilibrated chondrites.

**References:** [1] Abell P. A. et al. 2007. *Meteoritics & Planetary Science* 42:2165–2177. [2] Abe M. et al. 2006. *Science* 312:1334–1338. [3] Clayton, R. N. 2005. In *Meteorites, Comets, and Planets, Treatise on Geochemistry*, vol. 1. Amsterdam: Elsevier. pp. 129–142. [4] Yurimoto H. et al. 2011. Abstract #1755. 42nd Lunar and Planetary Science Conference. [5] Yurimoto H. et al. 2003. *Applied Surface Science* 203–204, 793–797.

5358

CHEMISTRY OF CARBONACEOUS CHONDRITE MATRICES: PARENT-BODY ALTERATION AND CHONDRULE-MATRIX COMPLEMENTARITY

B. Zanda¹,², M. Humayun³, J.-A. Barrat⁴, M. Bourot-Denise¹ and R. H. Hewins¹,². ¹MNHN & CNRS, 61 rue Buffon, 75005 Paris, France (zanda@mnhn.fr). ²Department of Earth & Planet. Sci., Rutgers University, Piscataway, NJ, USA. ³Department of Earth, Ocean & Atmospheric Science and National High Magnetic Field Laboratory, FSU, Tallahassee, FL 32310, USA. ⁴Université Européenne de Bretagne, CNRS UMR 6538, U.B.O-I.U.E.M., Place Copernic, 29280 Plouzané, France.

**Introduction:** The contribution of chondrite matrices to the volatile element budget and the Mg/Si of the bulk rocks is fundamental. Bland et al. [1] showed LA-ICP-MS volatile element abundances of CC matrices to be related to those of the bulk rocks, suggesting a "complementarity" with their adjoining high T fractions. [2] also advocates "complementarity" based on the Mg/Si of these components determined by EMP. However, [3, 4] argued that these relationships were due to parent body alteration. Here we present new data to support this conclusion.

**Method:** We selected a suite of carbonaceous chondrites with varying degrees of alteration [5, 6], including CI chondrites [7] and the Paris CM breccia, which contains significantly different lithologies [4]. Bulk chemical analyses were conducted both at UBO by ICP-MS and ICP-AES after wet chemistry, and at NHMFL by an in-situ rastering with LA-ICP-MS. In-situ analyses of matrices were performed both by EMP and LA-ICP-MS.

**Results and Discussion:** Bulk analyses conducted by the two methods are reproducible and consistent [7]. In particular, they show the bulk compositions of the less altered and more altered zones of Paris to be indistinguishable. On the other hand, in-situ analyses of the matrix differ significantly: matrix in the less altered zones has a CI composition, while that of the more altered zones has lost S and chalcophiles and gained Fe and siderophiles [4]. EMP data for other CM matrices indicate that their S/Si decreases with the extent of parent-body alteration, in agreement with the above results. Matrix compositions thus vary with alteration although the bulk rocks remain isochemical. This suggests local exchange between matrices and high temperature fractions, and a CI composition for the matrices at the time of accretion.

**Conclusion:** These results contradict pre-accretion complementarity between matrix and the high T fraction as advocated by [1, 2] and support the two-component model of Anders [8]. They allow these components to be formed independently and accrete in varying proportions to generate the range of bulk CC compositions. It is thus possible that high T components formed near the Sun were transported over large distances and mixed with matrix in colder regions of the disk, which would explain their presence in cometary materials.

**References:** [1] Bland P. et al. 2005. *Proceedings of National Academic Sciences* 102:13755–13760. [2] Hezel D. and Palme H. 2010. *Earth and Planetary Science Letters* 294:85–93. [3] Zanda B. et al. 2009. Abstract #5280. *Meteoritics & Planetary Science*, vol. 44, suppl. [4] Zanda et al. 2011. Abstract #2040. *Lunar and Planetary Sciences*. [5] Browning et al. 1996. *Geochimica et Cosmochimica Acta* 60:2621–2633. [6] Rubin et al. 2007. *Geochimica et Cosmochimica Acta* 71:2361–2382. [7] Barrat et al. 2011. This conference. [8] Anders E. 1964. *Space Science Review* 3:583–714.
THE STARDUST INVESTIGATION INTO THE CR2 CHONDRITE GRV 021710

X. Zhao¹, C. Floss², F. J. Stadermann², Y. Lin¹ and M. Bose². ¹Laboratory of Earth's Deep Interior, Institute of Geology and Geophysics, Chinese Academy of Sciences, Beijing 100029, China. E-mail: xzhao@mail.iggcas.ac.cn. ²Laboratory for Space Sciences and Physics Department, Washington University, St. Louis, MO 63130, USA.

**Introduction:** Abundant presolar grains have been identified in CR3 chondrites [1, 2], but studies of CR2 chondrites so far have not shown very high abundances of presolar material [3-5]. We are investigating the presolar grain abundance of GRV 021710, which is a very fresh CR2 chondrite collected from Grove Mountains, East Antarctica [6].

**Experimental:** We used the Washington University Cameca NanoSIMS for isotopic mapping. Two C and three O isotopes were collected simultaneously. The total area of matrix analyzed was 10,700 µm². Isotopically anomalous grains were analyzed for their elemental compositions using the Auger Nanoprobe.

**Results and Discussion:** A total of 35 O-anomalous grains and 32 C-anomalous grains were found. Nine of the 35 O-anomalous grains are ¹⁸O-rich and belong to Group 4, with likely origins in supernovae [7]. The remaining O-anomalous grains belong to Group 1, with enrichments in ¹⁷O and close to solar ¹⁸O/¹⁶O ratios [7]. Most of the C-anomalous grains (25 out of 32) have ¹²C/¹³C ratios range from 25 to 76, similar to the compositions of mainstream SiC grains [8]. Six C-anomalous grains are ¹³C-depleted, whereas the remaining one has a very low ¹²C/¹³C ratio (¹²C/¹³C = 4) like SiC A+B grains.

Auger elemental results show that 35 O-anomalous grains consist of 33 Fe- and/or Mg-bearing silicates and 2 oxides, with an average grain size of 260 nm. Based on the (Fe + Mg + Ca)/Si ratios, these 33 silicate grains can be classified into five types: olivine-like grains (10), pyroxene-like grains (7), intermediate grains (6), Si-rich (6) and Si-poor (4) grains. Most of these silicate grains are Mg-rich (mg#s: 29-100). The two oxides include one spinel-like grain and one SiO₂ grain. More structural data is needed to confirm the crystallinity of the SiO₂ grain.

Auger spectra and elemental maps of the 32 C-anomalous grains show 15 SiC and 16 carbonaceous grains. The remaining one was sputtered away during the NanoSIMS measurement and could not be located in the Auger Nanoprobe. Except one SiC A+B grain and one probable SiC Y grain, remaining grains are mainstream SiC grains. Most of the carbonaceous grains are dark in secondary electron images, could be graphites or insoluble organic matter.

Based on the total matrix area analyzed and the surface areas of the grains, we can calculate the abundances of O-anomalous and C-anomalous grains to be 174 ± 30 and 203 ± 36 ppm respectively, which are similar to the results from CR3 chondrites [1,2]. We can also calculate an abundances of 165 ± 29 ppm for presolar silicates, 9 ± 6 ppm for presolar oxides, 135 ± 35 ppm for SiC grains and 50 ± 12 for carbonaceous grains.

**References:** [1] Floss C. and Stadermann F. J. 2009. *Geochimica et Cosmochimica Acta* 73:2415-2440. [2] Floss C. and Stadermann F. J. 2009. *The Astrophysical Journal* 697:1242-1255. [3] Nagashima K. et al. 2004. *Nature* 428:921-924. [4] Floss C. and Stadermann F. J. 2005. Abstract #1390. 36th Lunar and Planetary Science Conference. [5] Leitner J. et al. 2011. Abstract #1713. 42nd Lunar and Planetary Science Conference. [6] Miao B. et al. 2007. *Meteoritics & Planetary Science* 42:A106. [7] Nittler L. R. et al. 2008. *The Astrophysical Journal* 682:1450-1478. [8] Zinner E. 2004. In *Meteorites, comets, and planets*. Treatise on Geochemistry, vol. 1 (ed. A. M. Davis), pp. 17-39.

ON THE QUESTION OF INTRINSIC ISOTOPIC HETEROGENEITY WITHIN PRESOLAR GRAINS

E. Zinner¹ and M. Jadhav¹,². ¹Laboratory for Space Sciences and Physics Department, Washington University, St. Louis, MO, USA. E-mail: ekz@wustl.edu. ²Institute of Geophysics and Planetology, University of Hawaii, Honolulu, HI 96822, USA.

**Introduction:** Detection of isotopic heterogeneity at the time of grain formation could provide information on the astrophysical environment where presolar grains formed. Isotopic heterogeneity has been found in many cases but has been generally attributed to contamination [1, Fig. 8] or isotopic equilibration [2]. Strictly speaking, isotopic contamination or equilibration is always a possibility if only two isotopes have been measured and the resulting ratios in a given grain are not both larger and smaller than solar. But even measurements of 3-isotope system cannot unequivocally identify isotopic heterogeneity. An example is the O-isotopic measurements inside of a TEM slice of a low-density graphite grain from Murchison [2]. Because the ¹⁷O/¹⁶O ratios are close to solar, the large variations in ¹⁸O/¹⁶O can still be explained by isotopic equilibration. The situation is similar for Fe-rich subgrains within a SiC X grain that show differences in the ⁵⁷Fe/⁵⁶Fe ratios but solar ⁵⁴Fe/⁵⁶Fe ratios [3]. These considerations can be extended to apparent variations in inferred ²⁶Al/²⁷Al ratios in X grains that can be explained by contamination with Al [4, 5].

**Results:** The best candidate for a grain with intrinsic isotopic heterogeneity is ORG1f3m-25 from the high density graphite fraction (2.02-2.04 g cm⁻³) from Orgueil [6]. This 5 µm large grain has ¹²C/¹³C = 486, δ²⁹Si = -55‰, δ³⁰Si = -30‰, normal N, O, and Mg, but large anomalies in Ca (δ⁴²Ca = -69‰, δ⁴³Ca = 487‰, δ⁴⁴Ca = 1193‰) and Ti (δ⁴⁶Ti = -792‰, δ⁴⁷Ti = -122‰, δ⁴⁹Ti = 1802‰, δ⁵⁰Ti = 5300‰). Large variations in the Ti signal during grain analysis indicate the presence of Ti-rich subgrains (TiC). However, while the ⁴⁹Ti/⁴⁸Ti and ⁵⁰Ti/⁴⁸Ti ratios are fairly uniform throughout the graphite grain, the ⁴⁷Ti/⁴⁸Ti ratio shows large variations (Fig. 1). While the fact that δ⁴⁴Ca > δ⁴³Ca and the association of the largest ⁴⁴Ca excesses with the highest ⁴⁸Ti/⁴⁰Ca ratios (in the middle of Ti-rich subgrain 2) indicate that some ⁴⁴Ca is from ⁴⁴Ti decay, Ti-rich subgrain 1 seems to have no or only little radiogenic ⁴⁴Ca, but a ⁴⁷Ti excess comparable to that in subgrain 2.

**References:** [1] Zinner E. et al. 1995. *Meteoritics* 30:209-226. [2] Stadermann F. J. et al. 2005. *Geochimica et Cosmochimica Acta* 69:177-188. [3] Marhas K. K. et al. 2008. *The Astrophysical Journal* 689:622-645. [4] Lin Y. et al. 2010. *The Astrophysical Journal* 709:1157-1173. [5] Zinner E. et al. 2011. Abstract #1070. 42nd Lunar and Planetary Science Conference. [6] Jadhav M. et al. 2006. *New Astronomical Review* 50:591-595.

<figure><img src="image_40.png" /></figure>
5375

## LITHOPHILE TRACE ELEMENTS IN MAGMATIC IRON METEORITES

J. Zipfel¹, M. Chaussidon², C. Rollion-Bard², H. Palme¹ and A. Pack³. ¹Senckenberg Forschungsinstitut Frankfurt, Senckenberganlage 25,D-60325 Frankfurt, Germany. E-mail: jzipfel@senckenberg.de. ²CRPG-Nancy Université-CNRS, UPR2300, BP 20, 54501 Vandoeuvre-lès-Nancy, France. ³Geowissenschaftliches Zentrum, Universität Göttingen, D-37077 Göttingen, Germany.

**Introduction:** The chemical composition of iron meteorites reflects the conditions and processes under which they formed, such as condensation, oxidation and fractional crystallization. Magmatic irons are characterized by steep trends of Ir versus Ni consistent with formation by fractional crystallization. Assuming that magmatic irons formed in the cores of molten asteroids in the presence of coexisting silicates we expect lithophile trace elements, e.g., Si to be dissolved in metal melts in concentrations of the order of 10–100 ppm [1]. Earlier work has shown that concentrations of Si are extremely low in all groups of iron meteorites, magmatic and non-magmatic. Concentrations around approximately 0.12 ppm apparently reflecting low temperature processes rather than high temperature metal/silicate melt equilibrium [1]. We have started systematic analyses of lithophile elements, Si and Al, as well as Cr and P in IVB, IVA and IIIB iron meteorites.

**Analyses:** Trace concentrations of Si, Al, Cr and P were analyzed with a Cameca ims1280 HR2 at the CRPG in Nancy at high mass resolution (M/AM approximately 7000). Sensitivity factors for all elements were calculated relative to the intensity of ⁵⁶Fe and based on intensities in known standards from the Bundesanstalt für Rohstoffe (BAM). The spot size was about 20 µm allowing to separate between Ni-rich and low-Ni lamellae if Widmanstätten patterns were wide enough.

**Samples:** We analyzed two to eight spots in Ni-rich or Ni-poor areas in the IVB iron Hoba, IVA-an iron Steinbach, one IC iron Bendego and three IIIB irons Turtle River, Grant and Acuña. Trace concentrations of Si and Al are highest in metal of Hoba (Si = 0.75 ppm and Al = 0.05 ppm) and Steinbach (Si = 0.25 ppm and Al = 0.02 ppm), respectively. Concentrations in metal of the IIIBAB are identical and extremely low with Si = 0.04 ppm and Al = 0.007 ppm. The aluminum concentration in Bendego is slightly higher with Al = 0.013 ppm while Si is as low (Si = 0.04 ppm) as in IIIBAB irons. No difference in concentrations of these two elements between Ni-rich and Ni-poor metal was observed. P and Cr concentrations are high and variable in Hoba (P = 4100–7300 ppm, Cr = 180–475 ppm in Hoba) and low in Steinbach, Bendego and all IIIB irons. In addition, there is a clear anticorrelation of P with Cr; kamacite being high in Cr and low in P and taenite being low in Cr and high in P.

**Conclusion:** Our results confirm previous studies [1] that Si concentrations in iron meteorites are significantly lower than expected from metal/silicate melt equilibria. This is also confirmed by low Al concentrations. Apparently lithophile elements do not reflect the high temperature history of iron meteorites. Concentrations of Cr and P are lower than bulk metal INAA data [e.g., 2]. This indicates that bulk analyses may be dominated by inclusions rich in such elements.

**References:** [1] Pack A. et al. 2011. *Meteoritics & Planetary Science*, in revision. [2] Wasson J. 1999. *Geochimica et Cosmochimica Acta* 63:2875–2889.

5181

## HOW REPRESENTATIVE OF AN ASTEROID'S MINERALOGY ARE SAMPLES FROM ITS PONDED DEPOSITS?

M. E. Zolensky¹, W. Cribbs², L. Le³ and D. K. Ross³. ¹NASA Johnson Space Center, Houston, TX 77058, USA. ²University of Houston, Clear Lake, TX 77058, USA. ³Jacobs ESCG, Houston, TX 77058, USA. E-mail: michael.e.zolensky@nasa.gov.

**Introduction:** An unexpected observation of asteroid 433 Eros by the NEAR mission was the ponded deposits [1, 2]. Hayabusa recently returned to Earth with dust from the surface of a ponded deposit on asteroid Itokawa [3–5]. Thus the nature of asteroid ponds is of considerable interest. While ponded deposits should initially be global samples, various asteroid surface processes can modify them. Thus, how representative of a bulk asteroid is a sample from a ponded deposit?

**Pond Samples:** Compared to the bulk asteroid, ponds are distinctly bluer, and depleted in S and Fe, possibly due to loss of species by settling or sputtering [1, 2, 6]. We have previously proposed that we have meteoritic samples of ponds from at least one asteroid, the parent body of Vigarano (CV3) [7, 8]. There are clasts found in Vigarano which consist nearly entirely of fine-grained olivine, of a composition that is identical to that of the host meteorite. The most distinctive features of these clasts are cross-bedded, arcuate bands which contain a high proportion of the finest-grained, iron-rich olivine. The relatively fine-grained bands are located at the bottom of each bed. Given that the Vigarano clast mineralogies are consistent with what we already know about ponds on Eros, we think these crossbeds formed from impact-induced seismic shaking. On a suitably small, airless body, this process can result in grain-size separation with fine-grained materials “percolating” through a coarse matrix to the bottom [9] which is exactly what we observe in the Vigarano clasts. Thus the mineralogy of a sampled pond varies according to where in the pond's vertical column the sampling is made.

We have recently found another clast we believe to be from a ponded deposit. The clast is in the SAH 98328 L4 chondrite, and is a porous agglomeration of anhedral to euhedral crystals of olivine (Fa21–29, peak at Fa25–26), low Ca pyroxene (Fs17–35, no peak), plagioclase, troilite, metal and minor phases. The host meteorite has the same mineralogy and mineral compositions, except that the host has a narrower range of olivine and pyroxene compositions. Unlike the Vigarano clast there is no mineralogical layering in the SAH clast, which would suggest that this clast derives from within a single pond layer.

**Implications for Sampling Missions:** How representative are sample return missions that sample only smooth, flat, pond deposits? The smallest asteroids have low G, and so settling may be minimized. Largest asteroids have sufficient mass to prevent ponds from forming. The midrange is where the setting effects are most pronounced, and mineralogical differentiation will be greatest. The implication of these results will be discussed.

**Acknowledgment:** We thank the Muséum National d'Histoire Naturelle (Paris) for the loan of the section of SAH 98328.

**References:** [1] Cheng et al. 2002. *Meteoritics & Planetary Science* 37:1095–1106. [2] Veverka et al. 2001. *Science* 292:484–488. [3] Tsuchiyama et al. 2011. *Science*, in press. [4] Nakamura et al. 2011. *Science*, in press. [5] Noguchi et al. 2011. *Science*, in press. [6] Trombka et al. 2001. *Meteoritics & Planetary Science* 36:1605–1616. [7] Zolensky et al. 2002. 33rd Lunar and Planetary Science Conference. [8] Zolensky et al. 2004. 35th Lunar and Planetary Science Conference. [9] Horz and Schaal. 1981. *Icarus* 46:337–353.
## AUTHENTIC REPLICAS OF CHONDRITES FOR BASIC EDUCATION PROGRAMS

M. E. Zucolotto¹. ¹Museu Nacional/UFRJ, RJ, Brazil. E-mail: mezucolotto@globo.com.

As very few meteorites are found by geologist one of the purpose of our divulgation program "Is there an ET in your backyard?" is to teach people to identify meteorites. A proper way for identify meteorites requires a study of a large variety of samples. Indeed meteorites are not abundantly available for loan to schools or astronomy clubs and only few museums have a representative collection for public exhibition.

The meteorites on displays at museum are many times polished and etched and the meteorites are not found like this in the country so that it is need show them as they are real find. Many students of geology or astronomy never picked up a meteorite.

The reproduction of meteorite masses before cutting was done since the XIX century whether for exhibitions or for study, is show to be very important for activities of any meteorite divulgation program.

The ability to recognize a possible meteorite in the country will require some degree of familiarity with their general appearance.

To make a replica of the meteorite before cutting it can preserve most of the important features of this appearance, but replica are not quite equal to real object.

To account for postulations of private and public schools, as well as the request of the community in general, there were developed at the Seção de Meteoritica/DGP Museu Nacional Rio de Janeiro a didactic kit of authentic replica of meteorites for loan to the schools, astronomy clubs and museums pretend to promote the elementary education in Meteoritics at the schools with the objective to develop strategies, that allow the recognition of meteorites.

Particularly the molding technique has achieved a notable advance, which was made possible due to the development of new products such as silicone. There are several articles describing how molds and casts are made but very few present the steps that precede the realization of the mold.

The basic technique for molding three-dimensional meteorites. When the mold is made of two or more parts it is necessary to separate each part of the surface through the application of clay (or plastiline) around the meteorite, according to a previously established molding plan.

Here we present a variation of the classical technique using resin, cement, sand and iron fillings to make a real authentic replica of a chondrite that can compose a meteorite kit for schools and small museums.

## VARRE-SAI (L5) – A RECENT METEORITE FALL FROM BRAZIL

M. E. Zucolotto², L. L. Antonello¹, R. B. Scorzelli¹, M. E. Varela³, D. E. Magnelli³, P. Munayco¹, E. dos Santos¹ and I. P. Ludka⁴. ¹Centro Brasileiro de Pesquisas Fisicas (CBPF/MCT), Brazil. ²Museu Nacional/UFRJ, RJ, Brazil. ³ICATE- CONICET, San Juan, Argentina. ⁴IGEO/UFRJ, RJ, Brazil. E-mail: mezucolotto@globo.com.

A bright fireball was observed at noon, on June 19, 2010, north of Rio de Janeiro and south of Espirito Santo state (Brazil). After detonations a whistling sound of the stone falling was perceived by a farmer, about 17 km from Varre-Sai (RJ) and 8 km from Guaçui (ES). Due to the meteorite divulgation program sponsored by Faperj and CNPq on Brazilian schools, the Museu Nacional was contacted. At least five masses (total ~2.5 kg) were recovered in the next days at both states. The name Varre-Sai was proposed to the NomCom as the first piece was recovered in the RJ State. Most of the stones are fusion crusted with the exposed interior surfaces light gray with few dark shock veins.

Three thin polished and etched sections from a slice of 35 g on deposit at MNRJ were investigated by optical and scanning electron microscope, microprobe and Mössbauer spectroscopy.

The meteorite has a poor defined chondritic texture. The discernible chondrules have sub-spherical, ellipsoidal or irregular shapes with variable amounts of metal and/or sulfide. Their apparent diameter range in size from 350 µm to 2.2 mm (mean size of ~800 µm). Clearly visible are large radial pyroxene (RP) (~1.8 mm) and barred olivine (BO) (~2.2 mm) types with the porphyritic ones (mean size 800 µm) being the more abundants. Chondrules are imbedded in a recrystallized matrix, being sometimes difficult to discern chondrule fragments from dispersed crystals of the matrix. The later is composed by anhedral silicates crystals (~80 µm) and fresh glass.

The essential minerals are the ferromagnesian olivine and pyroxene; the accessories are plagioclase (almost transformed into maskelinite) and the opaque minerals sulfides and Fe-Ni metal. Olivine crystals have undulatory to mosaic extinctions, and are fractured with PDFs occurring in larger grains. Pyroxenes and olivine exhibit similar features. Plagioclase grains are mainly <50 µm in size, mostly with undulatory extinction. Opaque minerals are represented by troilite and metal phases. Kamacite and taenite can develop plessitic texture. The troilite show a slight polygonization and undulatory extinction and taenite grains are zoned or with martensitic interior. The kamacite occurs as single crystals with many displaying the shock-hatched ε structure, although some recrystallized polycrystalline grains occur near the heat affected zone close to fusion crust.

Microprobe analysis yielded olivine (Fa₀.₂₅, Fo₀.₇₅) and low-Ca pyroxene (Fs₂₁.₆₆, En₇₆.₄₈ Wo 1.₄₉). Mössbauer analysis of the bulk exhibit troilite, olivine and pyroxene; and Fe-Ni metal in the magnetic fraction.

The poorly delineated chondritic texture, the occurrence of very little clinopyroxene grain and the plagioclase size indicates petrologic type 5. The presence of planar fractures in olivine and mosaicism indicates that the chondrite is weakly shocked (S4 [2, 3]). The degree of weathering is W0.

**References:** [1] Brearley A. J. and Jones R. H. 1988. In *Planetary Materials*, edited by J. Papike. pp. 3-1-3-398. [2] Stöffler et al. 1991. *Geochimica et Cosmochimica Acta* 55:3845-3867. [3] Bischoff A. and Stöffler D. 1992. *European Journal of Mineral* 4:707-755.
## MECHANICAL DISASSEMBLING AND TESSELLATION REASSEMBLING, TOOLS FOR UNDERSTANDING THE WIDMANSTÄTTEN STRUCTURE

M. E. Zucolotto¹, O. Grillo¹ and L. L. Antonello², H.S. Amorim³. ¹Museu Nacional/UFRJ, ³IF/UFRJ, RJ, Brazil. ²CBPF/ MCT, RJ, Brazil. E-mail: mezucolotto@globo.com.

Although the Widmanstätten structure has been studied for more than two centuries with many mechanism been proposed to explain this pattern, there is still much about this transformation that is not well understood. The EBSD and use of orientation mapping techniques applied to meteorites [1–3] has proved very useful in better understanding of its crystallographic interrelations.

The three-dimensional (3-D) microstructural analyses provides a new insights into the widmanstätten pattern transformations not aboarded previously by any two-dimensional (2-D) techniques.

Tessellations or tilling, the repeating arrangements of crystallographic solids, combined with the X-ray crystallography techniques in special electron backscatter diffraction (EBSD) is a very powerful tool for three-dimensional characterization of the materials. The tessellation can help on understand of the intricate arrangement of bars, needles, plates and lath shapes lamellae of widmanstätten pattern on meteorites.

A recently arrived sample for identification at Museu Nacional/UFRJ, found in Descoberto, MG, probably another mass of São João Nepomuceno, an anomalous IVA silicate rich iron, exhibits near the surface plates so loose that can easily be disassembled and broken into interpenetrating triangle plates, acute rhombic prisms and tetrahedrons in steady of the expected octahedrons.

The sample has been studied by stereo and metallographic microscope, electron microprobe, crystallographic macrotexture optical goniometer and microtexture by x-ray diffraction and EBSD.

The Kepler's *Stella Octangula* (an octahedron with a tetrahedron on every face) in a cubic unitcell, which is also a compound of two tetrahedras from the fcc cubic alternating vertices is the cell observed in steady of expected octahedral fcc cubic cell. These structure could also been present in the high-pressure phases in the closest packing cubic or hexahedral cells.

The goal of the use of tessellation is to link the observed 3-D morphology and crystallography compared with other techniques concerning 3-D in 2-D observations, providing new insights into the widmanstätten formation mechanism.

The tessellation of a tetrahedron is formed by tetra hedrons plus rhombohedrons (a combination of tetrahedra and octahedra). In a tetrahedral site the interstitial is in the center of a tetrahedra formed by four lattice atoms. Three atoms, touching each other, are in plane; the fourth atom sits in the symmetrical position on top.

It is therefore of interest to raise the question of whether the crystallographic data gathered in the (taenite + kamacite) region on the one hand and the plessite regions on the other can improve our understanding of the transformation mechanisms that govern the formation of these microstructures.

**References:** [1] Zucolotto M. E. and Pinto A. L. 2000. *Meteoritics & Planetary Science* 35:A180. [2] Nolze G. and Geist V. 2004. *Crystallographic Research and Technology* 39:343–352. [3] Goldstein J. I. and Michael J. R. 2006. *Meteoritics & Planetary Science* 41:553–570.

## NEW INSIGHTS INTO THE STRONTIUM CONTAMINATION OF METEORITES

F. J. Zurfluh¹, B. A. Hofmann², E. Gnos³, U. Eggenberger¹, I. M. Villa¹,⁴, N. D. Greber¹,² and A. J. T. Jull⁵. ¹Institut für Geologie, Universität Bern. E-mail: florian.zurfluh@geo.unibe.ch. ²Naturhistorisches Museum der Burgergemeinde Bern. ³Muséum d'histoire naturelle de la Ville de Genève. ⁴Università di Milano Bicocca, Milano, Italy. ⁵NSF Arizona AMS Laboratory, The University of Arizona, Tucson, AZ 85721, USA.

**Introduction:** Since the discovery of meteorites in hot deserts, studies on their weathering and contamination have become important to understand the terrestrial overprint of these samples. One of the early recognized features is the continuous uptake of Ba and Sr of meteorites in hot deserts [e.g., 1–4]. Our studies focus on the quantification of the contamination patterns and on the determination of the source of contaminants and their correlation with terrestrial ages.

**Methods:** Meteorites found during the joint Omani-Swiss meteorite search project are routinely classified by standard procedures. Some selected samples (covering all weathering degrees and all LL chondrites) were dated by ¹⁴C [e.g., 5]. Currently, the elemental concentrations of all samples (excluding samples from large strewn fields) are systematically analyzed by handheld XRF (HHXRF) with special focus on Ba and Sr contamination. Three L chondrites from selected sites representing three distinct typical geographical provenances of meteorites were analyzed for their ⁸⁷Sr/⁸⁰Sr isotopic ratio. Strontium isotopes were measured on aqueous and acidic leaches from meteorites and corresponding soil samples.

**Results:** The terrestrial age pattern of Omani meteorites is characterized by an abundance peak at 20 ka and a lack of young (<10 ka) meteorites. The correlation of terrestrial age and weathering degree with Ba and Sr contamination is obvious. An estimation of the terrestrial age of meteorites by a combination of HHXRF measurements, weathering degree, geographical find location and physical weathering signatures such as fragmentation and wind ablation will likely be possible. Strontium isotope ratios of corresponding meteorite-soil pairs obtained by leaching with water are very similar, but characteristic for each of the three locations. Acidic leaches from meteorites are also similar to the former, while the leachates of soil samples with strong acid are less radiogenic, probably because leaching with strong acid taps Sr reservoirs that are insoluble in rainwater.

**Discussion:** Based on our observations there is strong evidence that the source of Sr contamination is the local soil and not sea spray, since the strontium isotope ratio of Miocene and recent ocean-water is significantly more radiogenic [6]. By measuring the contamination pattern (Ba and Sr concentration, Sr isotopes and alteration mineralogy) of meteorites it is possible to trace back the find location, to some extent even within the homogeneous Omani desert.

**References:** [1] Gibson E. K. and Bogard D. D. 1978. *Meteoritics* 13:277–289. [2] Stelzner T. et al. 1999. *Meteoritics & Planetary Science* 34:787–794. [3] Al-Kathiri A. F. et al. 2005. *Meteoritics & Planetary Science* 40:1215–1239. [4] Lee M. R. and Bland P. A. 2004. *Geochimica et Cosmochimica Acta* 68:893–916. [5] Jull T. 2006. In *Meteorites and the early solar system II*, eds. D. S. Lauretta and H. Y. McSween pp. 889–905. [6] Palmer M. R. and Elderfield H. 1985. *Nature* 314:526–528.