www.sciencemag.org/cgi/content/full/1128865/dc1 Supporting Online Material for Oxygen Isotope Variation in Stony-Iron Meteorites R. C. Greenwood,* I. A. Franchi, A. Jambon, J. A. Barrat, T. H. Burbine *To whom correspondence should be addressed. E-mail: r.c.greenwood@open.ac.uk This PDF file includes: Materials and Methods Figs. S1 and S2 Table S1 References Published 24 August 2006 on Science Express DOI: 10.1126/science.1128865
Supporting Online Material Methods Oxygen isotope analyses were carried out using an infrared laser-assisted fluorination system (S1). All analyses were undertaken on replicate 1-2 mg aliquots taken from homogenised whole-rock powders (minimum size 50 mg). To maximise yields and decrease the risk of cross-contamination, mesosiderite samples were fused in vacuum to form a glass bead prior to fluorination. O 2 was liberated by heating samples using an infrared CO 2 laser (10.6µm) in the presence of 210 torr of BrF 5. After fluorination, the O 2 released was purified by passing it through two cryogenic nitrogen traps and over a bed of heated KBr. O 2 was analysed using a Micromass Prism III dual inlet mass spectrometer. System precision (1σ), based on replicate analyses of international (NBS- 28 quartz, UWG-2 garnet) and internal standards, is approximately ±0.04 for δ 17 O; ±0.08 for δ 18 O; ±0.024 for 17 O (S1). Quoted precision (1σ) for individual meteorite samples analysed in this study is based on replicate analysis. Details of samples studied Olivine from the following main-group pallasites was analyzed in this study: Admire, Brenham, Esquel, Finmarken, Fukang, Giroux, Imilac, Krasnojarrsk, Marjalahti, Molong, Springwater, Thiel Mountains. For the mesosiderites homogenised whole rock powders were fused prior to fluorination in order to maximise sample yields. Mesosiderites analyzed were: Barea, Clover Springs, Crab Orchard, Dong Ujimqin Qi, Eltanin, Emery, Estherville, Lamont, Lowicz, Mincy, Morristown, Mount Padbury, NWA 1951, Patwar, Pinaroo, Vaca Muerta, Veramin.
The pallasite group The pallasite group is currently divided into three types: (i) the main-group pallasites with 43 members, (ii) the Eagle Station grouplet with 3 members and (iii) the pyroxenepallasite grouplet with 2 members (S2, S3) The samples investigated in this study are all from the main-group. Textural variation in main-group pallasites Main-group pallasites display diverse textures, with olivine, as cm-sized polycrystalline masses, angular crystal fragments or rounded grains, enclosed by varying proportions of metal. It is generally accepted that angular olivines are the primary texture of main-group pallasites. The less common rounded-grain texture is believed to have formed where overlying dunitic mantle was pushed by buoyancy into the underlying molten core (S4, S5). Comparison of the results obtained in this study with previous oxygen isotope investigations of main-group pallasites and mesosiderites While the results presented here for the mesosiderites are broadly in agreement with earlier studies (S6), our mean 17 O value for the main-group pallasites is 0.1 less negative than these previously published results (S6). There is no simple explanation for this discrepancy. Analysis of both mesosiderites and main-group pallasites were interspersed with terrestrial samples as part of an interlaboratory comparison of the TFL, with good agreement being obtained by both participating laboratories (S7). Results on international and internal standards run throughout the course of this work have given
consistent and reproducible results; hence we have a high degree of confidence in the pallasite and mesosiderite data presented here. Compared with previous laser fluorination analyses of the HEDs by us (S8) the main-group pallasites and mesosiderites show slightly greater degrees of scatter. This presumably reflects the fact that the HED data was obtained exclusively on meteorite falls, whereas the vast majority of available pallasite and mesosiderite samples are finds and hence more susceptible to terrestrial weathering.. Oxygen isotopic variation in the mesosiderites Mesosiderites show only limited compositional control on oxygen isotope variation, so that the relatively basaltic class A types span the full range of δ 18 O values (Fig. S1). The more orthopyroxene-rich class B mesosiderites have generally lower δ 18 O values than the class A examples. This situation is somewhat similar to that seen in HEDs where there is clear evidence of mineralogical control, with diogenites having lower δ 18 O than the basaltic eucrites (S8). However, the most orthopyroxene-rich sample analysed, the class C mesosiderite Dong Ujimqin Qi has an intermediate δ 18 O value. Mesosiderites are highly brecciated and so that the poorly defined compositional correlation is to be expected. This is illustrated by the analyses of individual clasts separated from the Vaca Muerta mesosiderite (Fig. S2). These display a very wide variation in δ 18 O. Four of the clasts plot close to the mean 17 O value of the mesosiderites, whereas as one (VM1) plots well away from it. One possibility is that clast VM1 represents silicate material from the metal-rich projectile that impacted to form the mesosiderites However, it is more likely that like the HED ploymict breccias the messoderites contain a range on non-indigenous
clasts. Thus, carbonaceous chondrite fragments are found in the howardite Bholghatti, and ordinary chondrite-like material in the polymict eucrite Pasamonte (S8). References S1. M. F. Miller, M.F, I. A. Franchi, Sexton A. S. Pillenger C.T., Rapid Commun. Mass Spectrom. 13, 1211 (1999). S2. D. W. Mittlefehldt, T. J. McCoy, C. A. Goodrich, A. Kracher, Planetary Materials J.J. Papike Ed. (Min. Soc. Am. Reviews in Mineralogy 36), 4-1-195 (1998). S3. Meteoritical Buletin Database http://tin.er.usgs.gov/meteor/ S4. E. R. D. Scott, G.J. Taylor. Lunar Planet. Sci. Conf. 21, 1119 (1990). S5. J. T. Wasson, B-G. Choi. Geochim. Cosmochim. Acta 16. 3079 (2003). S6. R. N. Clayton, T. K. Mayeda Geochim. Cosmochim. Acta 60, 1999 (1996). S7. D. Rumble, M. F. Miller, I.A. Franchi, R.C. Greenwood, Lunar Planet Sci. XXXV11, #1416 2006) S8 R. C. Greenwood, I. A. Franchi, A. Jambon, P. C. Buchanan, Nature 435, 916 (2005). S9. M. F. Miller, Geochim. Cosmochim. Acta 66, 1881 (2002)
Figure captions Figure. S1 Oxygen isotope variation in mesosiderites showing compositional classes. Symbols: Filled sqares are mesosiderites, open circles are pallasites. Dashed lines show the mean 17 O values for the pallasites and mesosiderites obtained in this study. Figure S2. Oxygen isotope variation in clasts from the Vaca Muerta mesosiderite. Symbols: filled diamonds, with error bars (1σ), are clasts from Vaca Muerts mesosiderite. Open squares other analysed mesosiderites, open circles pallasite analyses. Dashed lines show the mean 17 O values for the pallasites and mesosiderites obtained in this study.
Table S1. Oxygen isotope analyses of mesosiderites and main-group pallasites. Sample reference N Lithology Find? δ 17 O SMOW 1σ δ 18 O SMOW 1σ 17 O 1σ PALLASITES Brenham 4 Anomalous Find 1.242 0.072 2.726 0.160-0.187 0.023 Marjalahti 4 Main Group Fall 1.374 0.098 2.951 0.185-0.173 0.033 Molong 3 Main Group Find 1.420 0.038 3.079 0.064-0.194 0.005 Esquel 3 Main Group Find 1.358 0.095 2.942 0.155-0.185 0.013 Springwater 3 Ungrouped Find 1.481 0.005 3.159 0.010-0.175 0.007 Admire 3 Main Group Find 1.343 0.074 2.929 0.157-0.193 0.017 Fukang 2 Main Group Find 1.182 0.067 2.570 0.094-0.165 0.018 Giroux 3 Main Group Find 1.283 0.178 2.817 0.352-0.194 0.009 Thiel Mountains 4 Main Group Find 1.390 0.186 2.986 0.376-0.175 0.015 Imilac 3 Main Group Find 1.370 0.064 2.957 0.164-0.181 0.025 Krasnojarsk 3 Main Group Find 1.390 0.168 2.990 0.359-0.178 0.022 Finmarken 2 Main Group Find 1.290 0.196 2.826 0.353-0.192 0.011 Pallasaite average 1.343 0.082 2.911 0.158-0.183 0.009 MESOSIDERITES Vaca Muerta 1 Mes-A1 Find 1.814 0.203 3.934 0.321-0.248 0.037 2 ELTANIN-Maskelinite 2 Mes Find 1.984 0.022 4.243 0.043-0.239 0.000 ELTANIN-Breccia 1 Mes Find 1.941 4.156-0.237 NWA 1951 2 Mes-C Find 1.854 0.107 3.999 0.127-0.241 0.040 Dong Ujimqin Qi 5 Mes Fall 1.585 0.089 3.506 0.149-0.252 0.021 Estherville 3 Mes-A3/4 Fall 1.568 0.024 3.469 0.049-0.250 0.009 Lowicz 2 Mes-A3 Fall 1.615 0.032 3.534 0.063-0.237 0.001 Veramin 2 Mes-B2 Fall 1.645 0.055 3.634 0.109-0.260 0.002 Patwar 3 Mes-A1 Fall 1.990 0.204 4.303 0.407-0.265 0.011 Barea 2 Mes-A1 Fall 1.607 0.001 3.509 0.001-0.233 0.000 Mount Padbury 3 Mes-A1 Find 1.678 0.021 3.694 0.040-0.258 0.005 Morristown 2 Mes-A3 Find 1.889 0.029 4.046 0.120-0.231 0.034 Pinaroo 2 Mes-A4 Find 2.055 0.024 4.406 0.045-0.254 0.001 Emery 2 Mes-A3 Find 1.530 0.081 3.384 0.157-0.244 0.002 Clover Springs 3 Mes-A3 Find 2.064 0.227 4.395 0.452-0.239 0.036 Crab Orchard 2 Mes-A1 Find 1.710 0.011 3.747 0.077-0.254 0.029 Mincy 2 Mes-B4 Find 1.573 0.059 3.453 0.122-0.238 0.005 Lamont 2 Mes Find 1.751 0.053 3.782 0.076-0.232 0.013 Mesosiderite average 1.769 0.182 3.844 0.349-0.245 0.010 17 O = 1000 ln (1+ (δ 17 O/1000)) λ1000 ln (1+ ( δ 18 O/1000)) where λ = 0.5247 (S9)