Isotopic and Geochemical Investigations of Meteorites

FINAL REPORT FOR NASA GRANT #NAG510425 200 1-2005

ISOTOPIC AND GEOCHEMICAL INVESTIGATIONS OF METEORITES

PI: RICHARD J. WALKER

Department of Geology University of Maryland College Park, MD 208742 Results of Work: 2001-2005. our previous work, the attainment of low, reproducible Re chemical processing blanks FINAL REPORT permitted us to make precise Re-Os isotopic measurements for the highest-Ni, lowest-Re Overview of work. IIAB and IIIAB endmembers. The primary goals of our research The Re-Os isochron ages for the over the past four years are to constrain the complete suites of IIAB and IIIAB irons are timing of certain early planetary 4530f50 Ma and 45 17+32 Ma, respectively, accretioddifferentiation events, and to and are similar to previously reported Re-Os constrain the proportions and provenance of ages for the lower-Ni endmembers of these materials involved in these processes. This two groups (e.g. Shen et al., 1996; Smoliar work was achieved via the analysis and et al., 1996; Chen et al., 2002). The results interpretation of long- and short-lived isotope for both systems are consistent with initial systems, and the study of certain trace crystallization of both asteroidal cores elements. Our research targeted these goals within several tens of Ma of the origin of the primarily via the application of the I8'Re- solar system. The results for the most i870s, 190Pt-'860s,~&Tc-~~Ru and ?'c-%u highly-evolved irons in both groups are isotopic systems, and the consistent with, but do not require, complete determinatiordmodeling of abundances of the crystallization during the same time frame as highly siderophile elements (HSE; including the initiation of crystallization. Re, Os, Ir, Ru, Pd, Pt, and maybe Tc). The The first high-precision Pt-Os specific events we examined include the isochrons for IIAB (Fig. 1) and IIIAB irons segregation and crystallization histones of were produced. The Pt-Os isochron ages for asteroidal cores, the accretion and the IIAB and IIIAB irons, calculated using metamorphic histories of chondrites and the current best estimate of the h for '%Pt chondrite components, and the accretionary (Begemann et ai., 2001), are 4323 k 80 Ma and differentiation histories of Mars and the and 4325 k 26 Ma respectively. The Re-Os Moon. The results of the proposed research and Pt-Os ages do not overlap within the have: I) provided us with a better uncertainties. The younger apparent ages understanding of the metal segregation and recorded by the Pt-Os system may reflect crystallization histories/pathways in iron much later system closure of the most meteorite parent bodies, 2) provided improved evolved irons from each group, either as a constraints on the behavior of HSE during result of Pt diffusion or late-stage nebular condensation through chrondrite crystallization. A more likely possibility is formation and subsequent alteration, 3) that the decay constant used in the age provided important constraints on the HSE calculations is incorrect. The slope from the budgets of lunar and Martian mantles, and 4) Pt-Os isochron was combined with the age examined the magnitude of early solar system from the Re-Os isochron for the IIIAB irons isotopic heterogeneities in the transition to calculate a revised value of 1.4 I5 x 1 O-'' element Mo. The results/progress of six major a-l for the I9'Pt decay constant (Cook et ai., studies advanced during this hnding cycle are in review). reviewed as follows. The trace element and isotopic compositions of these suites reflect the 1. 'x7Re-'"70s& 'ui'Pt-'x60sIsotopic and HSE crystal-liquid fractionation processes Abundance Studies of Iron Meteorites. involved, and time of crystallization of the In order to examine the asteroidal cores these suites sample. As crystallization histories of two major previously noted for iron meteorite groups asteroidal cores. the '87Re-'870sand lwPt- and experimental systems. solid metal-liquid I86 Os systematics of 13 IIAB and 18 IIIAB metal bulk distribution coefficients (D's) for iron meteorites were analyzed. In contrast to both IIAB and IIlAB systems show

2 Os>Re>>Pt>l, during the initial stages of The short-lived 98T~-98R~(tx between 4 core crystallization (e.g. Pernicka and and -10 Ma), *Tc-~~Ru(tx = 0.21 Ma) Wasson, 1987; Jones and Drake, 1983; chronometers were studied because they Morgan et al., 1995). The latter stages of may yield important information on the crystallization for each core are generally relative chronology of processes that characterized by D's for Re>Os>>Pt. The affected metal phases in the early solar relative partitioning behaviors of these system. These include volatility-related elements are much more complex in the processes, such as condensation and IIIAB core relative to the IIAB core. evaporation, metal-silicate segregation in asteroids, early core crystallization and aqueous alteration. Furthermore, the proof of extant *Tc in the solar system would also constrain the time interval between production of the nuclide and injection of s- -10 process isotopes into the protosolar cloud. Previous studies of the Tc-Ru systems 0.126 reported positive deviations for 98R~in iron 0.125 meteorites relative to a terrestrial standard, a small positive deviation for *Ru in 0.124 chondritic metal, but normal compositions for calcium-aluminum-rich inclusions 0.123 (CAIs) from chondrites. Our Ru isotopic data for group IIAB 0.122 irons (Negrillos, Bennett County, Coahuila, 0.121 Filomena, Old Woman) and IIIAB irons (Casas Grandes, Costilla Peak), and the 0.120 chondrites Allende (CV3) and Allegan (H5) indicate that the abundances of 98R~and 0.119 " '... " '' '.. ''". 99 Ru in these meteorites overlap with the 0.0 0.2 0.4 0.6 0.8 1.0 terrestrial values at the k0.8 and kO.3 E levels (parts in 1O,OOO), respectively (Figs. 2-3). Lack of heterogeneities of 98R~and 99 Ru among the iron meteorites is not Fig. 1. 1wPt-1860sisochron for group IIAB surprising in light of a recent experimental iron meteorites (Cook et al., in review). study that shows that crystal- liquid Open triangles-Cape York suite. Solid fractionation of metal changes the Tc/Ru triangles-low Ni. Triangles with crosses- (and Tc/Mo) ratio by substantially less than high Ni. A is the per mil deviation from the a factor of 2 (Lazar et al., in review). Using IlAB isochron. these constraints and solar system initial abundances of *Tc derived from This work was largely the result of astrophysical models, evolution models for the Masters Thesis work of D.L. Cook (now the *Tc-*Ru chronometer can produce a Ph.D. candidate at the University of barely resolvable deviations in *Ru (0.3 E) Chicago) and was recently published (Cook only if these fractionation events occurred et al., 2004). It was done in collaboration during collapse of the molecular cloud that with M.F. Horan at the Carnegie Institution formed our solar system (

3 individual analyses. Uncertainties are 20, (in-run).

3. Scale of isotopic heterogeneity between inner solar system bodies.

Recent Mo isotopic studies on meteorites reported evidence for differences in isotopic compositions for whole rocks of some primitive (Yin et al., 2002; Dauphas et al., 2002a, b) and differentiated meteorites (Qi-Lu and Masuda, 2000; Dauphas et al., 2002a), relative to terrestrial materials. Relative enrichments of r- and p-process isotopes of up to 3-4 E units (E unit = parts in NAB Iron 1 04) over s-process dominated isotopes are - the most prominent features. Certain types 0 -1 of presolar grains show enrichments in s- .-E process isotopes (Nicolussi et al., 1998). If I, the reported variability in r- and p-process 4 isotope enrichments reflects the true isotopic E characteristics of the whole rocks, the .--0 u, -1 implications are quite profound. It would suggest the presence of large scale Mo w 0 8ennetlCo 0 Coaiwta isotopic heterogeneity within the solar 8 Old Woman accretion disk with likely collateral effects for other elements. Because similar effects are not apparent from our Ru isotope work, nor from Zr isotopic studies of meteorites Fig. 2. Ru isotopic composition of IIAB iron (Schonbachler et al., 2002), we examined meteorites. Data are means of multiple the Mo isotopic composition of iron analyses. Uncertainties are 20,. Grey area meteorites, chondrites and CAls using indicates *20, uncertainty of multiple (n = negative thermal ionization mass 4-6) standard runs. spectrometry. 2[ I I1 With the exception of '"Mo, the Mo isotopic composition of the bulk meteorites and CAIs we analyzed overlap with terrestrial Mo within *I E unit, when normalized to 92M0P8M0(Figs. 4-5). 'ooMo - is the only Mo isotope outside the mass range used for normalization, and hence, may yield the least precise results. Our -UMD Aldrich Ru I results on IIAB iron meteorites and the w . A Nlends(CV3) 1 . v Allegan (HS) Allende whole rock show no evidence for -2 1 enrichments in p- or r-process isotopes, relative to pure s-process 96~~.In contrast, two CAIs from Allende show patterns that bear a similarity to the whole rock patterns Fig. 3. Ru isotopic composition of the for Allende reported by Yin et al. (2002) chondrites Allende and Allegan. Data are and Dauphas et al. (2002a), and patterns of Allende leachates and residues (Dauphas et could reflect heterogeneity of Allende on the al., 2002b). cm-scale, since it appears that some of its components, such as CAIs, show isotopic IlAB Iron - Terrestrial MO 0 Negrillos n=5 heterogeneity (Fig. 6, see also Yin et al., Bennett Co n=5 Meteorites 0 Old Woman n=4 2002; Dauphas et al., 2002b).

0 '1 Allende CAls - Terrestrial Mo A 3659-8 (n.2) . A 3529-41-6 (F3) 0

-1

-2] 92 94 95 96 97 98 100 I

Fig. 4. Isotopic composition of Mo in IIAB iron meteorites, normalized to terrestrial Mo 92 94 95 96 97 98 100 measured at UMD and displayed as -2 p p s,r s s,r s,r r deviations in E units. Data are means of multiple analyses. Uncertainties are 20,. Fig. 6. Mo isotopic composition of CAls from Allende. Data are means of multiple - Terrestrial Mo Chondrites Allende (CV3) n=2 analyses. Uncertainties are 20,~. 3 0 Forest Vale (H4) n=4 Because of these unresolved issues it is I/difficult to assess whether or not the existing Mo isotope data indicate large-scale isotopic heterogeneity in the inner solar system. While our new Mo data are consistent with existing Zr isotopic data, new Ru isotopic data by Chen et al. (2003) may hint at a small deficit of the pure s-process IwRu -2 92 94 95 96 97 98 100 isotope in some differentiated meteorites and in Allende. This in turn may indicate Fig. 5. Mo isotopic composition of large-scale isotopic heterogeneity in the chondrites Allende (CV3) and Forest Vale inner solar system. (H4). Data are means of multiple analyses. Uncertainties are 20,. 4. 's7Re-'s70s and HSE Systematics of Chondrites The reason why some research groups During this funding period we find isotopic heterogeneity in the same completed long-term studies of the Is7Re- groups of iron meteorites (Qi-Lu and IS7Os isotopic, and HSE elemental Masuda, 2000; Dauphas et ai., 2002a), and systematics of bulk chondrites (Walker et others don't (Yin et al., 2002, Becker and al., 2002a; Horan et al., 2003). For the Re- Walker, 2003) remains unresolved. The Os work, a suite of 47 carbonaceous, different results obtained for whole rocks of enstatite and ordinary chondrites were Allende by different groups could simply examined. We discovered significant reflect a sample digestion issue (teflon differences in the '87Re/'S80sand '870s/'880s beakers vs. Carius tube). Alternatively, it ratios of carbonaceous chondrites compared with ordinary and enstatite chondrites. The

5 average '87Re/'880s for carbonaceous Department of Terrestrial Magnetism. As chondrites is 0.39220.015 (excluding the with the Re/Os ratio, there are significant anomalous CK chondrite, Karoonda), differences in relative HSE abundances compared to 0.42220.025 and 0.421+0.013 between the 3 main chondrite groups (Horan for ordinary and enstatite chondrites (lo et al., 2003). Of greatest note is the standard deviations). These ratios recast into distinctly higher average PdIr present in elemental Re/Os ratios are: 0.08 14+0.003 1, some enstatite chondrites relative to 0.087620.0052 and 0.0874+0.0027, ordinary and carbonaceous chondrites (Fig. respectively. Correspondingly, the 8). The fractionations of the HSE are '870s/'880s ratios of carbonaceous presumably the result of both high chondrites average 0.1262+0.0006 temperature nebular and secondary (excluding Karoonda), while ordinary and processes, such as impact events. enstatite chondrites average 0.1283*0.00 17 and 0.1281* 0.0004, respectively (lo standard deviations). The results indicate that the Re/Os ratios of meteorites within 0 Carbonaceous each group are, in general, quite uniform. A Enstatite The minimal overlap between the isotopic compositions of ordinary and enstatite 0.130 chondrites versus carbonaceous chondrites indicates long-term differences in Re/Os for these materials, most likely reflecting chemical fractionation early in solar system 0.125 history. A majority of the chondrites do not plot within analytical uncertainties of a 4.56 Cia reference isochron (Fig. 7a-b). Most of the 0.120 deviations from the isochron are consistent 0.30 0.35 0.40 0.45 0.50 with minor, relatively-recent redistribution of Re, and/or Os on a scale of mm to cm. Some instances of the redistribution may be 10 attributed to terrestrial weathering, others A are most likely the result of aqueous 0 alteration or shock events on the parent body within the past 2-3 Ga. -10 The i870s/'880s ratio of Earth's 0.30 0.35 0.40 0.45 0.50 primitive upper mantle has been estimated to be 0.1296+8 (Meisel et al., 2001). If this '87Rel'880s composition was set via addition of a late veneer of planetesimals following core Fig. 7. a. '87Re/1880sversus 1870s/i880sfor all formation, the composition suggests the bulk chondrites analyzed by this study. veneer was dominated by materials that had Shown for reference is the 4.557 Ga group Re/Os ratios most similar to ordinary and IllAB iron meteorite isochron reported by enstatite chondrites. Smoliar et al. (1 996). b. ls7Re/1880sversus In order to examine the behavior of the A for all bulk chondrites analyzed by this HSE in chondrites further, we generated study. A is the per mil deviation of a sample high-precision HSE patterns for a broad from the IIlAB iron isochron of Smoliar et al. sampling of ordinary, enstatite and (1996). These results were published in carbonaceous chondrites. This work was Walker et al. (2002a). done in collaboration with M.F. Horan at the Carnegie Institution of Washington,

6 0 140

0 Carbonaceous 0.135

0.130 (D 0 0.125 g - 0.120 L .I 0.115 z 0 110 02 03 04 05 06 '87RePOs

Fig. 9. Isochron plot of CAI data for Allende 0.124 0.128 0.132 and Leoville. CT = Carius tube data; r = residues from Carius tube digestions; t = combined CT and r data (see Becker et al., 2001 for details). Fields for whole rock Fig. 8. Bulk chondrite Pd/Ir ratios versus samples of carbonaceous, ordinary and I87 OS/'~~OS.Also shown for comparison is enstatite chondrites are shown for the current best estimate for the Earth's comparison. The IIIA iron meteorite primitive upper mantle (PUM) from Meisel isochron from Smoliar et al. (1996) is shown et al. (2001) and Morgan et al. (2001). for comparison.

5. Re-Os isotopic studies of SNC meteorites. As a means of examining the Determining the absolute and distributions of HSE in chondrites and relative abundances of HSE in the Martian determine when the HSE were mobile, we mantle are of great importance. As an have also begun analysis of chondrite example, the abundances of Os we have components including: chondrules, calcium measured in most SNC meteorites lie within, aluminum inclusions (CAIs), matrix and but at the low end of the range of data sulfides (Becker et al., 2001; Walker et al., defined by terrestrial volcanic rocks, and 2002). Most materials examined to date were within the range of terrestrial cumulate rocks from the Allende meteorite. Most CAIs plot (e.g. pyroxenites) (Fig. 10). This may very close to the iron meteorite isochrons and suggest that the abundances of the HSE in display a modest range in '870s/'880s(Fig. the Martian mantle are similar to, or only a 9). CAIs, with highly fractionated REE factor of 2-5 lower than in the terrestrial patterns (Group 11), display a larger range in mantle (Walker et al., 2002b). This, in turn, Re/Os and 1*70s/1880sthan the other CAIs. If may indicate a late accretionary period representative of early condensates, the similar to that experienced by Earth, that limited distribution of 1870sl'880sfor most buffered the abundances of the HSE at much CAIs, except those with Group I1 REE higher levels than what remained in the patterns, indicate a solar system value for silicate Mars immediately subsequent to I87 OS/'~~OSof approximately 0.127. Our core formation. Similar conclusions were work on chondrites has resulted in the reached from the abundances of other HSE, publication of three papers during this most notably Pt (Jones et al., 2003). funding cycle (Becker et al., 2001; Walker et al., 2002a; Horan et al.. 2003).

7 mantle and the implications for the early differentiation history of Mars. We have now examined ten SNC meteorites for Re-Os isotopic compositions. The best estimates of the initial yos values for SNC meteorites indicate a long-term Re OAaa" depletion history for the NC group, with a present day yos value extrapolated to be approximately -3+2. In contrast the S-group 0 A, meteorites were derived from a source with a long-term, slightly suprachondritic Re/Os. This source has evolved to a higher yos (+5&2) than the present-day primitive upper mantle of Earth (+1.6*0.8). The source that a Pyroxenites 0 Gorgona-Curacao generated EETA 79001 had an Os isotopic PUM composition consistent with chondritic Re- 0 SNC Os evolution. Of note, the variations in 0 OIBAvg. 0 MORBAvg. Re/Os of the two apparently endmember mantle sources appear to have been set I I during the earliest differentiation history of Mars. This is indicated by the correlations Fig. 10. Abundances of MgO (wt. %) between initial yos, and &182W, and &{42Nd plotted versus Os (in ppb) for SNC (Fig. 1 1). meteorites. SNCs define a J-shaped pattern similar to terrestrial rocks from the Caribbean plateau (Gorgona-Curacao) and terrestrial pyroxenites. Only ALH 84001 4 plots well below the trend. From Walker et al. (2002b). 0

Variations in the short-lived systems -4 of i82Hf-'82Wand i46Sm-'J'Nd in the SNC meteorites indicate an early isolation of, and -8 subsequent inefficient mixing between, Nakhla 1 mantle reservoirs in Mars (Lee and Halliday, 12 chasT 1997; Harper et al., 1995). Thus, early r differentiation histories may be preserved in 1.0 -0.5 0.0 0.5 1.0 1.5 other isotopic systems in these meteorites as well. The Re-Os isotopic systematics of Martian meteorites can provide valuable information on what chemical processes affected the Martian mantle, particularly Fig. 11. yos versus EIJ?yd plot for SNC with regard to the relative abundances of meteorites. Os data are from Brandon et al. highly siderophile elements (HSE), (2000) and Walker et al. (2002b). Nd data including core formation, late veneer are from Harper et al. (1 995) and L. Nyquist addition, and early melting. Towards that (pers. comm.). end we are studying the Re-Os isotopic systematics of the SNC meteorites to Although the SNC meteorites crystallized at different times, extrapolations determine which, if any, of these processes to any one time during the last 2 Ga would affected the HSE budget of the Martian not cause major shifts in the relations,

8 because of the presumed, nearly chondritic abundances of these glasses are dominated Re/Os of the sources. The negative by a meteoritic contaminant. Mixing correlation between yos and El42Nd is calculations indicate that even very minor especially interesting because both systems amounts of a meteoritic contaminant have likely reflect early melt depletion (Nd and strongly affected the HSE concentrations Re removal). Conversely, the S meteorites and Os isotopic compositions of most are consistent with derivation from a melt glasses (Fig. 13). enriched (Re and Nd addition) reservoir, possibly even a relict of an early magma ocean. EETA 79001 (lithology A) is either derived from a mixed source, or alternatively, a primitive, un-differentiated source. Initial results of this work were published in Brandon et al. (2000).

6. HSE Systematics of the Lunar Interior. As with Mars, the absolute and relative abundances of the HSE present in the lunar mantle may provide unique insights to the formation and late accretionary history of not only the Moon, but also Earth. Determining the HSE content of the lunar mantle, however, Re Os Ir Ru Pt Pd has proven difficult, because no bona fide Figure 12. CI chondrite normalized HSE mantle rocks have been collected from the plot for orange glasses 74220 and 74001. moon. Primitive materials, such as picritic Note that one of the glass fractions has quite glasses are potentially the most diagnostic low Os and a highly fractionated pattern. materials we have for constraining HSE abundances in the lunar interior (e.g. Ringwood, 1992; Righter et al., 2000). Consequently, we have begun to determine \ Os isotopic compositions and Re, Os, Ir, Ru, 0.30 \A Indigenous ? Pt and Pd concentration data for green and orange glasses. This work is being done in 006 0.001 % z collaboration with M.F. Horan at the \ Carnegie Institution of Washington, l-6 0.20 Department of Terrestrial Magnetism, and z C. Shearer and J. Papike at the University of Chondritic New Mexico. As with previous studies 0.15 0.01% utilizing neutron activation analysis, we are 0.1% : examining different size fractions of the 0.10 -""' ' . """' ' ' """' glass spherules to assess the role of surface 10 100 IO00 condensation in the generation of the HSE abundances. Absolute and relative abundances of HSE in green and orange glasses are highly Figure 13. Mixing calculations suggest that variable (Fig. 12). Some fractions of orange all orange glasses analyzed contain some glass we have examined are characterized by proportion of a chondritic contaminant. One highly fractionated HSE patterns with major sample, with quite radiogenic '870sl'880s depletions in Os and Ir. In contrast, some may approach the composition of the fractions (particularly of green glass) are indigenous orange glass component. relatively flat, indicating that the HSE

I I 9 Horan M.F., Walker R.J., Morgan J.W., In those samples with the most Grossman J.N. and Rubin A. (2003) Highly fractionated HSE patterns, Os and Ir siderophile elements in chondrites. Chem. concentrations are quite low, and even Pt Geol. 196,5-20. and Pd concentrations are a factor of 6-8 lower than abundances for terrestrial Becker H. and Walker R.J. (2003) The Yc- volcanic rocks with similar MgO. This may 98 Ru and 99T~-99R~chronometers: new results indicate that the lunar mantle source of at on iron meteorites and chondrites. Chem. least the orange glasses had bulk HSE Geol. 196,43-56. abundances substantially lower than the terrestrial (or evidently the Martian) mantle. Becker H. and Walker R.J. (2003) Efficient This, in turn, may suggest that a significant mixing of the solar nebula from uniform Mo portion of the late veneer added to the Earth- isotopic composition of meteorites. Nature Moon system occurred subsequent to the 425, 152-155. formation of the lunar crust at 4.2-4.5 Ga. Results of this work were recently published Lazar G.C., Walker D. and Walker R.J. (Walker et al., 2004). (2004) Experimental partitioning of Tc, Mo, Ru and Re between solid and liquid during PUBLICATIONS (2001- 2005) crystallization in Fe-Ni-S. Geochim. Cosmochim. Acta 68,643-652. Becker H., Walker R.J., MacPherson G.J., Morgan J.W. and Grossman J.N. (2001) Cook D.L. Walker R.J., Horan M.F., Wasson Rhenium-osmium systematics of calcium- J.T. and Morgan J.W. (2004) Pt-Re-Os aluminum-rich inclusions in carbonaceous systematics of group IIAB and IIIAB iron chondrites. Geochim. Cosmochim. Acta 65, meteorites. Geochim. Cosmochim. Acta 68, 3379-3390. 1413-143 1.

Morgan J. W., Walker R.J., Brandon A.D. and Gelinas A., Kring D.A., Zurcher L., Urmtia- Horan M.F. (2001) Siderophile elements in Fucugauchi J., 0. Morton and Walker R.J. Earth’s upper mantle and lunar breccias: Data (2004) Osmium isotope constraints on the synthesis suggests manifestations of the same proportion of bolide component in late influx. Meteoritics and Planetary Science Chicxulub impact melt rocks. Meteoritics 36, 1257-1275. Planet. Sci.39, 1003- 1 008.

Becker H., Dalpe C. and Walker R.J. (2002) Walker R. J., Horan M.F., Shearer C.K. and High precision Ru isotopic measurements by Papike J.J. (2004) Depletion of highly multi-collector ICP-MS. The Analyst 127, siderophile elements in the lunar mantle: 775-780. evidence for prolonged late accretion. Earth Planet. Sei. Lett. 224,399-41 3. Walker R.J., Horan M.F., Morgan J.W., Becker H., Grossman J.N. and Rubin A. Pietruszka A.J., Walker R.J. and Candela P.A. (2002) Comparative 187Re-1870ssystematics Determination of mass dependent of chondrites: Implications regarding early molybdenum isotopic variations by MC-ICP- solar system processes. Geochim. MS: an evaluation of matrix effects. Chem. Cosmochim. Acta 66,4I 87-420 1. Geol., in review.

10 Geology Building U N IV E RS ITY OF University of Maryland College Park, Maryland 20742-42 1 1 R/IARyTm USA DEPARTMENT OF GEOLOGY 301.405.4089 TEL 301.314.9661 FAX www.geol.umd.edu

August 8,2005

Dr. D. Lindstrom NASA Headquarters, Code SR Washington, D. C. 20546

Dear Dave,

Please find enclosed a copy of the final report for my NASA Cosmochemistry grant NAG5 10425, which was active from 2001 to 2005. Please note that there is a list of publications resulting from this grant on the last page. If you have any questions regarding this research, please feel free to contact me at 301-405-4089. Thanks for the support.

Sincerely,

Richard J. Walker Professor of Geology

cc. Brad Poston

12 Geology Building U N I VERS ITY OF University of Maryland College Park, Maryland 20742-42 1 1 mnm USA DEPARTMENT OF GEOLOGY 301.405.4089TEL 301.314.9661 FAX www.geol.umd.edu

August 8,2005

Mr. Brad Poston Contracting Officer NASA/Goddard Space Flight Center Code 2 10.G Greenbelt, MD 20771

Dear Mr. Poston,

Sincerely,

Richard J. Walker Professor of Geology

C.C. D. Lindstrom