Noble gases in presolar diamonds 11: Component abundances reflect thermal processing

Transcription

1 Meteoritics 29, (1994). Q MeteOntiCd Society, Printed in USA Noble gases in presolar diamonds 11: Component abundances reflect thermal processing GARY R. Hussl ROY S. LEWIS Enrico Fermi Institute, University of Chicago, 564 S. Ellis Ave., Chicago, Illinois 6637, USA lcurrent address: Division of Geological and Planetary Sciences, 17-25, California Institute of Technology, Pasadena, California , USA (Received I992 August 19; accepted in revised form I994 June I 7) Abstract-Using the isotopic compositions derived in Huss and Lewis, 1994a (Paper I), abundances of the P3, HL, and P6 noble-gas components were determined for 15 diamond separates from primitive chondrites of 8 chondrite classes. Within a meteorite class, the relative abundances of these components correlate with the petrologic subtype of the host meteorite, indicating that metamorphism is primarily responsible for the variations. Relative abundances of P3, HL, and P6 among diamond samples can be understood in terms of thermal processing of a single mixture of diamonds like those now found in CI and CM2 chondrites. With relatively gentle heating, primitive diamonds first lose their low-temperature P3 gases and a "labile" fiaction of the HL component. Mass loss associated with release of these components produces an increase in the HL and P6 content of the remaining diamond relative to unprocessed diamond. Higher temperatures initiate destruction of the main HL carrier, while the HL content of the surviving diamonds remains essentially constant. At the same time, the P6 carrier begins to preferentially lose light noble gases. Meteorites that have experienced metamorphic temperatures 265 OC have lost essentially all of their presolar diamond through chemical reactions with surrounding minerals. The P3 abundance seems to be a function only of the maximum temperature experienced by the diamonds and thus is independent of the nature of the surrounding environment. If all classes inherited the same mixture of primitive diamonds, then P3 abundances would tie together the metamorphic scales in different meteorite classes. However, if the P3 abundance indicates a higher temperature than do other thermometers applicable to the host meteorite, then the P3 abundance may contain information about heating prior to accretion. Diamonds in the least metamorphosed EH, CV, and CO chondrites seem to carry a record of pre-accretionary thermal processing. INTRODUCTION Presolar diamond and Sic are present in the most primitive members of all classes of chondrites (Alexander et al., 199; Huss, 199; Huss and Lewis, 1994b). Presolar graphite, Tic, and A123 have also been found in acid residues from primitive chondrites (Amari et al., 199; Bernatowicz et al., 1991; Hutcheon et al., 1994; Huss et al., 1994; Nittler et al., 1993, 1994). See also reviews by Anders and Zinner (1993) and Ott (1993). Presolar grains are sited in the fine-grained matrices of primitive chondrites, and their abundances within a class are governed primarily by the metamorphic history of the host meteorite (Alexander et al., 199; Huss, 199; Huss and Lewis, 1994b). Small differences in initial matrix-normalized abundances between classes may have been inherited from the accretion disk (Huss and Lewis, 1994b). In the companion paper (Huss and Lewis, 1994a, hereafter, Paper I), we show that presolar diamonds contain three main noblegas components whose abundances vary significantly between diamond samples. They are: HL, the isotopically "exotic" component characterized by Xe enriched in light and heavy isotopes which is released from diamonds at high temperature; P3, the isotopically "normal" component released during pyrolysis at low temperatures; and P6, an apparently "normal" component released at a slightly higher temperature than HL (Table 1). (In this paper, a "normal isotopic composition" is one that is similar enough to the "solar system composition" that an exotic origin cannot be clearly demonstrated on isotopic grounds alone.) In this paper, we show that, like the abundances of presolar grains in meteorites, the abundances of noble-gas components in diamonds correlate with metamovhic grade. The properties of chondritic meteorites were established through a combination of physical and thermal processing in the accretion disk and thermal metamorphism and/or aqueous alteration on the meteorite parent bodies (e.g., Dodd, 1981). For example, CI chondrites like Orgueil are thought to be chemically representative of the material from which the Solar System formed (Anders and Grevesse, 1989), but their mineralogy was produced by aqueous alteration in the parent body (McSween, 1979). The CM2 chondrites are roughly equal mixtures of chondrules and refractory inclusions formed at high temperature in the accretion disk, and chemically primitive, aqueously altered matrix (McSween, 1979). Other classes (e.g., orrlmary, enstatite, CV, CO chondrites) consist primarily of chondrules and other hightemperature objects and 14% fine-grained matrix. These chondrites differ compositionally from CI chondrites in ways that can be understood in terms of accretion-disk processing (e.g., Larimer and Wasson, 1988a,b; Palme et al., 1988; Lipschutz and Woolum, 1988). Thermal metamorphism has been the primary agent of secondary alteration in these meteorites, and most have been metamorphosed severely enough to produce chemical equilibration and large-scale recrystallization (Dodd, 1981). Even the primitive type 3 chondrites (Van Schuss and Wood, 1967) have experienced some parent-body processing (McSween, 1977a,b; Huss et al., 1981). Relative scales of metamorphic intensity have been established for all classes of type 3 chondrites, the most widely used being the thermoluminescence (TL) sensitivity scales for type 3 ordinary and C3 chondrites (Sears et al., 1991a,b). It has been difficult to place absolute temperatures on these metamorphic scales because type 3 chondrites are aggregates of material from various sources that are grossly out of equilibrium. It has also been difficult to correlate the timdtemperature conditions experienced by different classes of meteorites because of compositional and mineralogical differences inherited from the accretion disk. For example, there is no TLsensitivity scale for enstatite chondrites. In this paper, we suggest that the P3 noble-gas component in diamonds, which varies by more than a factor of 1 between samples, may provide a thermometer that is independent of the chemical composition of the surroundings. Such a P3-abundance thermometer would help calibrate the relative levels of metamorphism experienced by different meteorite classes and could provide information on the temperatures experienced by each class prior to accretion. MJiTHODS OF STUDY Chemical Processing and Noble-gas Mass Spectrometry Diamond separates were prepared fiom 14 meteorites as part of a broader study of the abundances of presolar grains in primitive meteorites. The meteorite samples and chemical procedures are documented in Huss and Lewis (1994b). Noble-gas measurements were carried out using stepped pyrolysis on 81 1

2 812 Huss and Lewis Table 1: Isotopic compositions of noble-gas components in diamond separates1 Component Erie u 22Ne Component %e?!ar!?al 22Ne 4He 36Ar 36Ar Ne-P (57).29 (1) P3 <.135 (1).19 (1) - Ne-A2 (GHL + P6)' 8.5 (57).36 (1) HL.17 (1).227 (3) GO Ne-E - I Air 13 Cosmo. Ne.825 (25).888 (38) Air Ne 9.8 (8).29 (3) EKt 8 2 J Q J Q Component * 84Kr 84Kr 84Kr 84Kr 84Kr Kr-P3.65 (1).399 (4) ~ (5) (6) Kr-HL.43 (1).38 (1) ~ (1).363 (18) Kr-P (8) ~ (1).313 (3) Kr-S.211 (31) =.417(19).119 (5).254 (24) Air Kr (12).234 (6).218 (6).338 (6).188 (4) 296. (5) Xe-P3.451 (6).44 (4).86 (2) 1.42 (4).1591 (2).8232 (1).377 (1) ~.31 Xe-HL.842 (9).589 (8).95 (6) 1,56 (2).1544 (3).8442 (13).6361 (13) ~.7 Xe-P6 438 (25).444 (28).89 (2) (8).166 (11).8214 (47).3291 (5) ~.31 Xe-S9 o.33 (19).2159 (14).118 (11).4826 (42).186 (12).222 (53) E.34 Air Xe lo.358 (2).$3 (2).714 (21).9832 (35).1515 (5).7878 (25).3882 (11).3298 (8) Compositions of P3. HL. and P6 from Huss and Lewis (1994a) Ne-A2 and He-HL are pseudo-components consisting of HL and P6. If Ne-E in diamond separates is from small Sic. then it contains small quantities of 2Ne and 21Ne, but the amounts are too small to affect the results of our calculations. From Huss and Lewis (1994b). The exact composition is not important for these samples because they contain so little cosmogenic Ne. Eberhart eta/. (1965). Nier (195b). Average of compositions derived for two smallest Sic size fractions by Lewis et a/. (1994). Eugster et a/. (1967). The composition as measured on their Atlas-CH4 spectrometer is a better match to air Kr as measured on CAS-1 than their preferred value or other commonly used compositions (see Lewis et a/., 1994) Theoretical Xe-S end-member comvosition derived bv Lewis et a/. (1994) lo Nier(195a) our high-sensitivity, noble-gas mass spectrometer, CAS-1. Measurement procedures are detailed in Paper I and in Lewis et al. (1994). Determining Abundances of Noble-gas Components Compositions for the noble-gas components in diamond separates, derived in Paper I, are given in Table 1. With these compositions, it is relatively straightforward to determine the contribution of each component to a measured composition. Stepped pyrolysis improves the precision of this deconvolution by enriching different components in dflerent steps. Helium was resolved into two components, He-P3 and He-HL (Table 1). Helium-P6 was not considered because its composition is unknown. Thus, our He-HL probably also contains He-P6. Helium resolutions were not done for the lowest-temperature steps, which are dominated by cosmogenic He, or for the highest-temperature steps where uncertainties are very large. These steps have little of the total He, so ignoring them should not affect the conclusions of this paper. For larger high-temperature steps where 3He/4He is greater than.17, all He was assigned to the HL component, but this should not affect the fmal conclusions either. Neon was resolved using Ne-A2, a pseudo-component consisting of Ne-HL and Ne-P6 that dominates diamond separates (Paper I), and sets of two of the following components: Ne-P3, Ne-E, cosmogenic Ne, and air Ne (Table 1). Each set of three components defines a triangle in 3-isotope space, but much of the space falls within more than one triangle (Fig. 1). Therefore, independent constraints are required to resolve Ne data uniquely into components. Air Ne was permitted only in the lowest-temperature steps. Neon-E, believed to reside in tiny SIC grains, was excluded for low-temperature steps. These constraints define which triangle (Fig. 1) is applicable to a particular measurement. The components defining the triangle should dominate the sample, but others could still be present. Thus calculated results (Appendix I) are limits on the true abundances. Since Ne-M lies within the triangle defined by Ne-P3, Ne-E, and cosmogenic Ne (Fig. l), some of the calculated Ne-A2 could be a mixture of these components. The Ne-A2 abundances are thus upper limits,and calculated amounts of Ne-P3, Ne-E, and cosmogenic Ne are lower limits. However, the limits on Ne-P3 and Ne-A2, the components of primary interest, are quite tight because we know a priori that Ne-E and cosmogenic Ne are not abundant in these samples. For a few low-temperature steps where air Ne may be present, the data points fall within two small triangles (inset Fig. 1). In these cases, the first extraction step was resolved using air Ne and subsequent steps with Ne-P3. For these few steps, which have little of the total gas, all amounts are upper limits. Because of an apparent systematic dieerence in Ne results obtained immediately after replacing the filament in the mass spectrometer (Paper I), slightly different compositions for Ne-P3 and Ne-A2 (P3: 2NeWNe = f..53, zlne/zzne =.29 f,1; A2: 2oNePNe = f.53, 21NePNe =.36 f.1) were used to resolve data for Bishunpur, Mezo Madaras, Tieschitz, hoville, and Kainsaz. Errors for Ne measurements and end-member compositions were propagated following Rees (1984). No additional error has been assigned to cover uncertainties associated with obtaining only limits on actual amounts of each component. Nor has an uncertainty been assigned based on the use of the Ne- A2 pseudo-component rather than Ne-HL and Ne-P6. However, the conistency of the Ne-M (and He-HL) systematics compared to those of heavy gases (see section on "Relative Abundances of Noble-gas Components") indicates that these unquantifiable uncertainties do not affect the conclusions of this paper. Because Ar has only one useful ratio, Ar data could only be resolved between "planetary" Ar (using Ar-P3) and Ar-HL (Table l), with 4ArP6Ar used to account for air. Again, because of the high Ar count rates, there appears to be a systematic difference between data collected before and after installation of the new spectrometer filament. Data for Bishunpur, Mezo Madaras, Tieschitz, Leoville, and Kainsaz were resolved using: 36Arp8Ar (P3) =.189, 36ArPAr (HL) =.226. The Ar-P3 and Ar-M components apparently have similar 38ArP6Ar (Paper I), so additional information is necessary to partition "planetary" Ar between these components. w o n and Xe resolutions (described below) provide that information. The G-P3/Kr-P6 and Xe-P3/Xe-P6 ratios are similar in high-temperature steps, suggesting that

3 Noble gases in presolar diamonds II. 813 p3 and P6 have similar Krlxe. If both Arlxe and Krlxe are similar for P3 and p6, an assumption supported by the rough similarity of these ratios in most trapped meteoritic components, then the proportions of P3 and P6 derived from nmd Xe can be applied to partition the "planetary" Ar in the same steps. Errors for P3 and P6 abundances include, in addition to measurement errors and uncertainties for end member compositions, an estimate of the uncertainty in assigning proportions of Ar-P3 and Ar-P6 in high-temperature steps. For Kr and Xe, proportions of components for each temperature step were determined by mixing the compositions in Table 1 in varying amounts using the spreadsheet program, Microsof@ Excel. Proportions of each component were varied to minimize the differences between calculated and measured compositions (also see Huss and Lewis, 1994b). This method is superior to a graphical method using 3-isotope plots because it simultaneously accounts for all isotopes, allows more than three components to be mixed, handles possible mass fractionation, and d i e s the influence of statistical fluctuations affecting a single isotope. Air Kr and Xe were permitted only in lowtemperature steps. Negative abundances were not permitted. Linear mass fractionation of Kr and Xe was permitted for P3 and HL. Because mass fractionation of "normal" Kr looks like the addition of Kr-HL, fractionation was almost never required for Kr. Mass fractionation of "normal" Xe is distinct from the addition of any of the components in Table 1. The degree of apparent mass fractionation (depleting the light isotopes) for the total Xe ranges ffom zero for most temperature steps up to.9o/damu in the Indarch 91 OC step. However, better matches were often obtained by assigning the fractionation to a single component. Mass fiactionation for steps extracted at 44 OC was assigned to Xe-P3. In such steps, the Xe-P3 abundance was generally less than 1% of the amount in Orgueil diamonds, and the calculated mass fractionation ranged up to 24Ydamu in most samples and up to 7 %/mu in Indarch 91 OC (Appendix 111). Xenon-HL also appears to be depleted in light isotopes ffom.1-.5ydamu in very high-temperature steps from most samples and in intermediate-temperature steps from Indarch diamonds. Some Kr and Xe isotopes were given less weight than others when matching compositions. In low-temperature steps, lzsxe and 12%e often include varying amounts of re-trapped gas (Paper I), so measured ratios were treated as upper limits to true ratios. Among the other six Xe ratios, mismatches that exceeded the 1- measurement uncertainty occurred 1-2% of the time, consistent with expectations. Mismatches were most frequent in samples from the most metamorphosed meteorites (e.g., Qingzhen, Indarch) and tended to appear in the same isotopes in the same temperature ranges, suggesting that additional isotopic components might be present. However, the data are not sufficiently precise to characterize these possible components. Among Kr isotopes, 7% data were not considered reliable because of large corrections for isobaric interferences. Krypton-SO often included a contribution 1 8 a, z cu 6 N. t cu 4 2 n I.o 21Ne/22Ne FIG. 1. Three-isotope plot of Ne components in presolar diamonds. The inset expands the upper left comer. Measurements within any of the triangles can be represented by mixtures of the compositions at its comers. If Ne-A2 is constrained to be present, a measurement not containing air Ne can be resolved as one ofthree combinations of three components (shaded triangles). Iffour (or more) components are present, some of the calculated Ne-A2 would be a mixture of three other components. Thus, the calculated Ne-A2 abundance is an upper limit and abundances of other components are lower limits. For presolar diamonds, where Ne-A2 dominates and Ne-E and cosmogenic Ne are known to be trace components, the calculated limits closely approximate the actual abundances. 5 from isobaric interferences not handled by the blank correction, particularly in data collected &er installation of the new filament (Paper I). In these samples, 8OKr/84Kr was not used in matching. Among the three consistently reliable ratios, mismatches occurred 5-13% of the time. The lower mismatch rate reflects larger measurement uncertainties for Kr and smaller isotopic dif erences between Kr components. In reality, Kr components are less well-resolved than those of Ne and Xe. The uncertainties for Kr and Xe results reported in Table 2 include uncertainties assigned to end-member compositions and an estimate of the degree of flexibility in proportions that still produce a match within measurement errors. Orgueil, Semarkona, and Bishunpur diamonds are rich in Ar-P3 and Kr-P3 and exhibit an apparent low-temperature release of Ar-HL and Kr-HL that is not seen in Xe or in Ar and Kr from P3-depleted samples (Fig. 2). These releases are most likely artifacts of the inability of the deconvolution calculation to distinguish mass fractionation of Ar-P3 and Kr-P3 from the addition of HL. In most samples, the Xe-P3 released between 8 OC and 12 OC seems to be depleted in light isotopes, with inferred mass fractionation reaching 2-3Ydamu in steps containing 51% ofthe Xe-P3 in Orgueil diamonds (Appendix 111). The low-temperature Ar-HL and Kr-HL peaks in Orgueil, Semarkona, and Bishunpur diamonds contain about 2% of the Ar-P3 and Kr-P3 present in the samples and can be accounted for by mass fractionation of P3 gases of.2-.4ydamu. Since the low-temperature Ar-HL and Kr-HL in Orgueil, Semarkona, and Bishunpur are almost certainly artifacts, these gases were reassigned to the P3 component when preparing Figs. 6 and 8 (see below) and Table 3. This reassignment makes no discemable difference in relative P3 abundance (Figs. 3,6, S), but it decreases the calculated Ar-HL and Kr-HL for Orgueil, Semarkona, and Bishunpur by 2-21%, 15-16%, and 24%, respectively. The trends discussed below do not depend on the details of the deconvolution calculations. The uncertainties listed in the Appendices and in Table 2 are a good indication of the reliability of the relative abundances of HL and Ar-P3, Kr-P3, and Xe-P3. Changes in the compositions used for end members would effect all samples in the same way and would not change the trends reported below. The listed errors do not address problems with initial assumptions, such as the possible presence of additional components or the inability to handle the general case of isotopic mass fractionation, but there is no evidence in the data for the presence of unidentified components at the abundance of those included in the calculation. The largest calculational artifact, which was corrected for as described above, would not have changed the basic interpretations if it had gone unrecognized. Relative abundances of P6 and He-P3 and Ne-P3 have somewhat larger uncertainties than those of HL and heavy P3 gases, but they are probably reliable within stated uncertainties. Abundances of the trace components Kr-S and Xe-S are biased toward high values since negative abundances were not permitted. RELEASE CHARACTERISTICS AND RELATIVE ABUNDANCES OF NOBLE-GAS COMPONENTS IN DIAMOND SEPARATES Results of component resolutions for the 14 diamond samples reported in Paper I and for Ne and Xe data from the Murray CE diamond-rich separate measured by Tang and Anders (1 988) are given by temperature step in Appendixes I-IU and are summarized in Table 2. Two uncertainties are listed in Table 2. Uncertainty A is from the deconvolution calculation and is suitable for comparing components within a sample, while B includes a 2% relative uncertainty in the absolute gas contents and should be used when comparing samples. Listed errors do not include the 1% systematic uncertainty in the absolute gas contents (Paper I), which is appropriate for comparisons between laboratories, or any uncertainties due to incorrect choice of components. Release CharacteFistics of Noble-gas Components in Presolar Diamonds Figure 2 shows gas-release curves for the three most important noble-gas components in the Orgueil diamond separate. In Orgueil, 9% of the P3 gases are released below 1 "C. Peak releases of Ar-P3, Kr-P3, and Xe-P3 occur at 49 "C, and the release patterns are very similar. Abundances of He-P3 and Ne-P3 have large errors (Appendix I) and are difficult to interpret. The HL gases are released above 1 OC and the peak releases for Ne, Ar, Kr, and

4 Table 2: Abundances of noble gas components in diamond separates listed by amount of reference isotope. 4He =Ne =Ar WKr 1%e Meteorite (1-4 d g) (lo-a W ) (1 fl cc/s) (1-8 Cdg) (lo-8cc/g) (Classification) He-P He-HL Ne-P3 Ne-A2 Ne-E Ne-Cos &-P3 Ar-HL Ar-P6 Kr-P3 Kr-HL Kr-P6 Kr-S Xe-P3 Xe-HL Xe-P6 Xe-S Orgueil P) Mway CE (W) ; Semarkona W.) A1 B1 Bishunpur (LL3.1) A B Ragland (LL3.5) ; M. Madaras -3.5) ; ALHA77214 (L3.5) A B Tieschitz (H3.6) A B Qingzhen (EW A lndarch B (EH3-4) A B Leoville (CV3) A B Vigarano (cm) ; Allende (W 2 Kainsaz (mn) A B Uncertainty Acomes from the deconvolution CalWhtiOn. Uncertainly B also includes the % variability in the pipette and the uncertainty in the weight of the measured sample. Measured by Tang and Anders (1988). Xe, XeP3. XeHL, and XeP3 abundances are -2% higher than in Orgueil, suggesting a difference in the way Xe content was determined. WP3 was not among the three hest Ne components in Oingzhen because low-temperature gas was measured in one step. Error estimates cover probable Ne-P3 abundance , oo , I P x E v)

5 Noble gases in presolar diamonds II. 815 Xe occur at 142 "C. The largest He-HL release occurs at 15 "C, with a secondary peak at 142 "C. The 15 "C He-HL is seen only in Orgueil and Semarkona diamonds (Fig. 4) and seems to belong to a labile subcomponent, while the 142 "C He-HL belongs to the fraction containing most of the heavier HL gases. As discussed in Paper I, the almost identical peak-release temperatures for Ar-P3, Kr-P3 and Xe-P3 and for the retentively sited He-HL, Ne-HL, Ar- HL, Kr-HL, and Xe-HL indicate that these components are released through chemical reaction or structural reordering of the diamonds rather than by diffision. Component P6 is released at a slightly higher temperature than HL, with the peak Xe-P6 release occurring one step later than the peak HL release. For Ar-P6 and Kr-P6, the peak release is in the same step as the peak HL release, but the following step releases almost as much P6 gas. The almost-onestep difference between the temperatures of peak release for Xe-P6 and those for Ar-P6 and Kr-P6 suggests that P6 gases are released in part by difision. The P3 component in diamonds is apparently trapped in sites with a range of thermal resistance. This is shown by the increase in peak P3-release temperature from Orgueil (49 "C) to Semarkona ( "C) to Bishunpur (91 "C) as total P3 abundance decreases (Fig. 3). This pattern indicates that the same mixture of diamonds was acquired by each meteorite but that the most easily released P3 gases have been lost from Semarkona and Bishunpur diamonds. Mezo Madaras has lost almost all of its P3 gases (Fig. 3). The increase in P3-release temperature and decrease in P3 abundance correlates with petrologic type among ordinary chondrites (Fig. 3), indicating that metamorphism is responsible for the loss of P3 gases. Gas-release curves for the HL component, with peak releases for all gases between 12 C and 16 OC, are remarkably similar in all diamond samples (Figs. 2, 4, 5; Appendixes I-III) in spite of significant differences in thermal history and the wide variation in diamond abundances in the host meteorites (Huss, 199; HUSS and Lewis, 1994b). There are second-order differences in release characteristics, however. The "C release of He-HL in Orgueil and Semarkona diamonds is not seen in Bishunpur and Indarch (Fig. 4) or any other sample in this study. The temperatures of peak release of Ne-A2, Ar-HL, Kr-HL, and Xe-HL are also lower in Orgueil and Semarkona diamonds compared to those from Bishunpur and Indarch (Fig. 5) and other diamond samples. These observations suggest that a "labile" subcomponent rich in light noble gases is present in Orgueil and Semarkona diamonds but not in other samples and indicate an increase in degree of thermal processing from Orgueil to Semarkona to Bishunpur and Indarch.. a I! I I-?? Temperature OC I FIG. 2. Gas-release curves for the P3, HL, and P6 components in Orgueil diamonds. Data are normalized to OC so that areas under the histograms accurately represent the gas amounts. Neon through Xe are shown with split scales so smaller components can be seen. For example, the three largest xe steps should be referenced to the top half ofthe left vertical scale and other steps to the lower left and right scales. Component P3 is released below 1 "C with a peak at 49 OC and has much less He and Ne relative to heavy gases than does HL, which is released above 1 OC. Peak release of all five HL gases occurs in the 142 O C step, indicating that diffusion is not important in their liberation. The large He-HL release at 15 "c is from the "labile" HL subcomponent, which is He-rich and is lost on mild heating. Xenon-P6 is released about one step later than Ar-P6 and Kr-P6, suggesting that diffusion plays a role in P6 release. Argon-HL and Kr-HL show a minor release peak at 68 OC which is not seen in Xe-HL. These low-temperature Ar-HL and Kr-HL peaks appear only in P3-rich samples and are artifacts of the deconvolution calculation (see text).

6 816 Huss and Lewis Relative Abundances of Noble-gas Components in Presolar Diamonds Figure 6 shows the abundances for the P3, HL, and P6 noblegas components in diamond separates normalized to the abundances in Orgueil diamonds. Relative to Orgueil diamonds, all samples except Murray CE are depleted in P3 gases; many are severely depleted (Fig. 6a). Among samples from LL, EH, and CV chondrites, P3 abundances decrease with increasing petrologic type of the host meteorite, as determined from TL sensitivity and other measures of metamorphic alteration (McSween, 1977b; Huss et al., 1981; Anders and Zadnik, 1985; Sears et al., 1991a; Symes et al., 1993). The correlation between loss of low-temperature P3 gas and several indicators of metamorphism again suggest that P3 abundance is a function of the temperature experienced by the diamonds. Orgueil, Murray, Semarkona, and Bishunpur, meteorites whose diamonds contain the highest abundances of P3 gases, have all experienced aqueous alteration, the degree of which roughly correlates with the P3 abundance. This correlation could imply that P3 gases were trapped in the surface layers of diamonds during aqueous alteration. However, this is unlikely because the isotopic compositions of P3 gases differ significantly fiom those of P1 gases (Paper I), which are -1OOx more abundant in meteorites and would 81 likely have been the source of any retrapped gases. The correlation of aqueous alteration in a meteorite with high P3 abundances in its diamonds probably reflects a low accretion temperature, which would have allowed aqueous fluids (as ices) to be incorporated into the parent body while preserving the P3 gases in the diamonds. Higher accretion temperatures may have resulted in partial loss of P3 gases from the diamonds, producing different pre-metamorphic diamonds in the various meteorite classes. In contrast to the abundances of P3 gases, which vary by more than a factor of 1 across the suite of samples, abundances of HL. and P6 gases vary by factors of and 2-3 respectively (Fig. 6). In addition, the abundances of HL and P6 gases (except He- HL) generally increase with the loss of P3, indicating that release of P3 gas is accompanied by destruction of diamond, at least some of which is not directly associated with the P3 component (Paper I). Mass loss, by itself, would increase the abundance of all five HL and P6 gases by a constant factor, but this is not observed (Figs. 6b, c). At least two additional factors are required to explain the HL and P6 abundance trends (Figs. 6b, c). The dominant factor controlling the relative abundances of the five HL gases (Fig. 6b) is the presence of a "labile" HL. subcomponent in diamonds from Orgueil, Murray, and to a lesser extent, Semarkona. More than half of the He-HL. in Orgueil and Semarkona diamonds is released by -11 "C (Fig. 4) and can be assigned to this subcomponent. Other samples have a factor of two less He-HL and release their gases at around 14 "C. The heavier gases also have a "labile" fraction. Its removal increases the median release temperature of heavier gases by -12 "C (e.g., Fig. 5). Loss of "labile" HL. also decreases the elemental ratios of the Orgueil (CI) 'I Semarkona (LL3.) I Bishunpur (LL3.1) P I 2 E. E Bishunpur (LL3.1) d Temperature OC FIG. 3. Comparison of Xe-P3 release curves for Orgueil, Semarkona, Bishunpur, and Mezo Madaras diamonds. As Xe-P3 abundance decreases fiom Orgueil to Semarkona to Bishunpur, the temperature of peak Xe-P3 release increases, indicating that Semarkona and Bishunpur contain only the remnants of an original Orgueil-like Xe-P3 component. The same pattem is observed for the Ar-P3 and Kr-P3 (see Appendixes). More-metamorphosed diamonds, like those &om Me26 Madaras, release only trace amounts of Xe-P3. The secondary, high-temperature release in the Orgueil, Semarkona, and Bishunpur samples generally correlates with total Xe-P3 abundance. and probably consists of a mixture of the most retentively sited Xe-P3 and low-temperature Xe-P3 retrapped during earlier pyrolysis steps. This gas is released along with HL gases when the bulk of the diamond is destroyed during pyrolysis. lndarch (EH4) Temperature O c FIG. 4. Release curves for He-HL in Orgueil, Semarkona, Bishunpur, and Indarch diamonds. All diamond samples release approximately the same amount of He-HL between 11 "C and 15 "C, but Orgueil and Semarkona contain an additional He-HL subcomponent released at 7-11 OC. The presence of this subcomponent correlates with a lower median release temperature for heavier gases (Fig. 5).

7 Noble gases in presolar diamonds II. 817 HL component (Table 3). This shows that the "labile" subcomponent is significantly enriched in light noble gases relative to retentively sited HL. The combined loss of "labile" HL gases and the P3 component causes a decrease in He-HL abundance and produces the spread in the apparent enrichment factors of the other HL gases (Fig. 6). Early loss of He-HL-rich "labile" gas does not seem to result from diffusion. A simple diffusion model predicts increasing levels of elemental fractionation with increasing temperature. However, once "labile" HL gases are removed, the elemental ratios of HL remain remarkably constant in samples that have experienced a wide range of temperatures (Table 3). Only in diamonds from hdarch and Allende, the most severely heated samples, is there a noticeable decrease in He-HL/Xe-HL ratio relative to other "labile"-gas-poor samples (Table 3). The spread in P6 enrichment factors (Fig. 6c) has a different cause. Initially Ar-P6, Kr-P6, and Xe-P6 abundances increase by roughly the same amount with P3 loss, and the elemental ratios N 2 L '.. lndarch (EH4) Med. T. = 1443' C Med. T. = 1398' C Bishunpur (LL3.1) Med. T. = 1443' C d '. Temperature OC L r- - 1 FIG. 5. Release curves for Xe-HL in Orgueil, Semarkona, Bishunpur, and Indarch diamonds. All diamond samples release essentially the same amount of Xe-HL (and other HL gases) between 11 "C and 15 'C in spite of significant differences in the thermal history of the host meteorite. Median release temperatures for Xe-HL are given in each panel and are shown by Vertical lines. Orgueil and Semarkona, the meteorites with the low-temperature He-HL sub-component (Fig. 4), have lower median release temperatures than the other samples in the study, suggesting the presence of a "labile" HL ftaction in the most primitive diamond separates. remain approximately constant (e.g., Semarkona, Bishunpur, Mezo Madaras; Fig. 6c and Table 3). With further P3 loss (it?., more heating), the lighter gases are increasingly depleted relative to Xe (e.g., Ragland, ALHA77214, Qingzhen, Allende, Indarch; Fig. 6c and Table 3). This suggests that light gases are lost from the P6 carrier by diffusion at high temperatures. The tendency of Ar-P6 and Kr-P6 to be released ahead of Xe-P6 during pyrolysis (Fig. 2; Appendixes I-UI) also indicates that component P6 is subject to diffusive losses. The lower ratios of Ne-A2 (the pseudo-component consisting of Ne-HL + Ne-P6; Paper I) to Xe-HL in Qingzhen and Indarch diamonds (Table 3) probably reflect depletion of Ne-P6 rather than Ne-HL. The N abundance varies by a factor of seven among diamond samples (Russell et al., 1991, 1992; Fisenko et al., 1992). Russell et al. (1991) interpreted these data in terms of intrinsic differences in the diamond population inherited by each meteorite. These authors argued that metamorphism could not explain the differences because there was no isotopic evidence of diffusive loss of N from diamond samples. However, since the noble gases are not lost via diffusion (see above), this argument is not convincing. Fisenko et al. (1992) provided a solution by suggesting that diamond crystals with the highest N content (up to 16 atoms/grain) are more susceptible to destruction due to higher numbers of structural defects. Nitrogen-abundance differences, summarized in Table 4, can be naturally interpreted in terms of metamorphism. High N abundances are found in diamonds from Orgueil, the CM2 chondrites, and primitive LL chondrites (Table 4), samples which also have high P3 abundances. In contrast, Inman (LL3.4), Tieschitz (H3.6), and Indarch (E4), have low abundances of both N and P3. Nitrogen in diamonds seems to be more thermally resistant than P3 noble gases. Diamonds from Krymka (LL3.1) and Adrar 3 (-LL3.3) have higher N abundances than diamonds from Orgueil or CM2 chondrites (Table 4), suggesting that the N carrier has been enriched along with HL and P6 due to destruction of the most reactive diamond. The lower N abundance in diamonds from Inman, Tieschitz, and Indarch, indicates that much of the N is less tightly bound than HL or P6. The fact that significant N remains in Indarch diamonds suggests that at least some is very retentively sited. The abundance trends discussed above are consistent with a model in which samples of a single diamond mixture have been subjected to various degrees of thermal processing. Figure 7 is a schematic representation of the sequential loss of diamond components. Diamonds recovered from Orgueil (CI) and Murray (CM2) most closely approximate the starting material. The P3 gases and their carrier are lost in stages beginning with mild heating like that seen by Semarkona. A slightly higher temperature, like that experienced by Bishunpur diamonds, removes >8O% of the P3 gases and the "labile" HL component and their carriers. With increasing temperature, more P3 gases and the N-rich diamond are lost. Higher temperatures initiate destruction of the main HL carrier, without changing the HL content of the remaining diamonds. The P6 component begins to lose light gases, and some of its carrier is destroyed. At temperatures sufficient to cause elemental fractionation in the main HL component, only -25% of the original diamond remains (cf: abundances in Huss and Lewis, ). Diamonds from Indarch (EH4) apparently experienced thermal processing of an intensity (and duration?) not seen by other

8 818 Huss and Lewis P 1 I 5.1 e -.- W 3 F.1 3 P.- N 2.1 L C c M e ma % 2 5 e c.- B C W C Q 5 z '3 E.4- rn C.- c?! c C 8 C 8.. I 1 : I : FIG. 6. Abundances of P3, HL, and P6 in diamond separates, normalized to the abundances in Orgueil diamonds, are shown, arranged by compositional group and by decreasing P3 content within a group. Due to large errors (Table 2), He-P3 and Ne-P3 are not plotted, and Ar-HL and Kr-HL abundances for Orgueil, Semarkona, and Bishunpur have been adjusted for an artifact of the calculation (see section "Determining Abundances of Noble-gas Components"). The Ne-A2 pseudo-component is plotted in (b). Classifications of the host meteorites are given at the top of the diagram. (There is no widely accepted numerical scale for petrologic subtype among CV3 chondrites.) The P3 content (a) decreases with increasing petrologic subtype, reflecting the degree of metamorphic heating experienced by the host meteorite (note logarithmic scale). Abundances of both HL (b) and P6 (c) increase with loss of P3. For HL, this trend is partially obscured by the presence of "labile" HL gases in Orgueil and samples. Indarch diamonds have the lowest P3 abundance, the highest HL and P6 abundances, the most elementally fractionated HL and P6 components, and high median release temperatures for HL noble gases (Figs. 5 and 6, Tables 2 and 3, Appendixes I-III). In addition, only Indarch diamonds exhibit isotopic fractionation in Kr and Xe (.2-.3%/amu depleting the light isotopes) in gas-poor steps on the low-temperature side of the HL release peak (91, 112, and 1285 "C steps; Appendixes II and III). The 1285 "C step also has the highest 38Ar/36Ar observed in this study (Paper I). It is likely that, except for the reduced composition of Indarch, thermal processing of this intensity would have destroyed the diamonds. Apparently, Xe-P6 survives thermal processing better than any other diamond component. If Xe-P6 survives unaltered, one can estimate how much Orgueil-like diamond was processed to produce the diamonds now present in other meteorites. For example, from Orgueil (CI) to Semarkona (LL3.) to Krymka (LL3.1) to Bishunpur (LL3. l), the matrix-normalized diamond abundance decreases while the matrix-normalized Xe-P6 abundance remains nearly constant: 1436 f 56,1134 f 69, 18 f 82, 91 f 55 ppm, and.19~.1,.2f.1,.2f.3,.2f.2~ lo-locc/g meteorite, respectively (Huss and Lewis, 1994b). The nearly constant Xe-P6 abundance indicates that these four meteorites originally had the same abundance of Orgueil-like diamonds and that the lower diamond abundances in Semarkona, Krymka, and Bishunpur reflect metamorphic destruction of the less-resistant diamond. Table 5 shows the abundances of Xe-P3, Xe-HL, and Xe-P6 from Table 2 for Orgueil diamonds, for "average P3-depleted" diamonds (Ragland, ALHA77214, Tieschitz, Qingzhen), and for Indarch diamonds, along with the same data normalized to the Orgueil Xe-P6 abundance. The Xe-P6 normalization suggests that 75% of the original Xe and 5% of the original diamonds were lost to make "average P3-depleted" diamonds, implying that Ragland, ALHA77214, etc., or their parent materials, originally had twice as many diamonds as are now present. For Indarch diamonds, >8O% of the Xe and -7% of the mass were lost, implying that the original abundance of Orgueil-like diamonds in Indarch was at least 3.2~ the current abundance of Indarch diamonds. If Xe-P6 was lost or its carrier destroyed at temperatures experienced by these samples, then the original abundances of Orgueil-like diamonds were even higher (for additional discussion, see Huss and Lewis, 1994b). P3 GASES IN DIAMONDS AS TRACERS OF THERMAL PROCESSING We have shown above that within a meteorite class the P3 content of presolar diamonds correlates with various measures of metamorphic grade for the host meteorite. This correlation indicates that metamorphism is primarily responsible for the factor Semarkona. Because the "labile" HL gas is relatively enriched in light gases compared to the retentively sited fraction, its presence in Orgueil diamonds results in lower apparent enrichment factors for light gases in other samples. Loss of the "labile" HL carrier is also largely responsible for the difference in enrichment factors between Xe-HL (-1.5) and Xe-P6 (-2.). Only in Indarch and Allende, the most P3-depleted samples, is there evidence for preferential loss of He-HL (c). However, preferential loss of light gases is responsible for most of the spread in relative abundance of Ar-P6, Kr-P6, and Xe-P6 among the samples (c). (Murray CE, measured by Tang and Anders, 1988, is enriched relative to Orgueil diamonds by roughly 2% in total Xe, Xe-P3, Xe-HL and Xe-P6, suggesting a systematic difference in the way Xe content was determined.)

9 I Noble gases in presolar diamonds II. 819 Table 3 Elemental ratios in noble gas components from interstellar diamonds from data in Table 2 Diamond ~--- He-P3 Ne-P3 Ar-P3 Kr-P3 - Ar-P6 Kr-P6 - He-HL Ne-A2 ~ Ar-HL _ Kr-HL _ sample Xe-P3 Xe-P3 Xe-P3 Xe-P3 Xe-P6 Xe-P6 Xe-HL Xe-HL Xe-HL Xe-HL ~ Orgueil 52, , Murray 'CE' 12, , Semarkona 82, * 21, Bishunpur 14, , Ragland Mezo 14, 18 Madaras 8, 66 ALHA Tieschitz 33, 11 11, 36 Qingzhen lndarch 6, 14 3, 7 Leoville 17, 35 7, 2 Vigarano 1, 9 11, 77 Allende 4,56,3 3 2,88, 934 Kainsaz 22, 38 37g , 48 2, 4 12, 49 14, , 52 1, , 51 1, , ,.3 125, 49 12, 3 145, 49 11, 4 79, 49 17, 7 11, , , Best estimates for pure components Primitive 67, , , , Processed 12, , Measured by Tang and Anders (1988) Ratios corrected for low-temperature Ar-HL and Kr-HL thought to be artifacts of the deconvolution calculation (see text) Low-temperature gas measured in a single step Ne-P3 was not amono the three laraest Ne components in Qingzhen Error estimate covers probable Ne-P3 content: of >lo difference in P3 abundance between samples (Table 2). The P3 gases are released over a range of temperatures (Fig. 3), apparently via structural reorganization of the surface layers of diamond crystals (Paper I). Although the HL-release temperature is -25 OC lower in chromic-acid-etched bulk-meteorite residues than in purified diamond samples, P3-release temperatures are essentially the same (Appendixes I-III; Paper I; Huss and Lewis, 1994b), implying that P3 release does not depend significantly on the nature of the surroundings. This should not be too surprising since P3 release occurs at temperatures below those required for most chemical reactions to proceed efficiently. Once P3 gases are lost, they cannot be reacquired because there is apparently no reservoir of P3 gases in the Solar System other than diamonds. These characteristics indicate that P3 abundance in diamonds is a function only of the maximum temperature experienced by the diamonds and, therefore, provides a thermometer that is independent of the composition of the surroundings. A thermometer that is independent of composition would allow direct comparison of the maximum temperatures experienced by different classes of primitive chondrites and permit cross calibration of various scales of petrologic type. The P3 abundances could provide this thermometer, provided that each meteorite class inherited the same mixture of presolar diamonds from the accretion disk. A complication is that P3 abundances provide no way to distinguish between metamorphic and nebular heating. Thus, a meteorite that originally acquired diamonds with little P3 gas will appear to be metamorphosed when in fact it is not. On the other hand, if independent evidence can be used to show that such a meteorite has not been metamorphosed, then the P3 abundance would provide information about heating in the nebula. The P3 abundances for the diamond samples in this study are plotted as the sum of Kr-P3 and Xe-P3 vs. meteorite class in Fig. 8. It is difficult to calibrate the P3 abundance thermometer to absolute temperatures because mineral thermometers, which assume chemical equilibrium, cannot be used in unequilibrated chondrites. Fortunately, other types of temperature information are available, particularly for CI, CM2, and ordinary chondrites. Trace-element abundances and isotopes indicate that Orgueil (CI), Murray (CM2), and Murchison (CM2), whose diamonds apparently contain their full complement of P3 gases, have experienced temperatures of "C (Anders et af., 1973; Clayton and Mayeda, 1984). Alexander et al. (1989) estimated an upper limit of 25 OC for the temperature reached during the matrix alteration experienced by Semarkona, whose diamonds have lost about half of their P3 gases (Table 2). Rambaldi and Wasson (1981) used Ni content in matrix metal to estimate metamorphic temperatures of 3-35 "C for Bishunpur, whose diamonds have lost more than 8% of their P3 gases. Sears et al. (1991a) suggest that petrologic type 3.5 corre-

10 82 Huss and Lewis : Table 4: Nitrogen abundances (ppm) in presolar diamonds.' Meteorite Two-component C/N plateau mixing 2 values 3 Orgueil CI 7,56i45 7,9 f 24 Cold Bokkeveld CM2 8,35 f 1,29 12,5 f 2, Murchison CM2 8,19 f 2,9 ALH 831 CM2 9,22 f 1,3 11, f 1,3 Krymka LL3.1 9,6 f? Adrar 3 LL ,6 f? 17,7 f? lnman LL , f 82 Tieschitz H3.6 2,2 f 51 lndarch EH3-4 4,21 f 56 Allende CV3 3,2 f 1,7 3,77 f 15 1 From Russell ef a/. (1991; 1992); Fisenko et a/. (1992). 2 Two component mixing of diamonds (815N = -345%) and air (615N = ). 3 Based on measured C and N making up 656% of the gas released in relatively constant proportions (see Russell eta/., 1991). 4 From TL sensitivity adjusted for weathering following Sears eta/. (1982). sponds to the orderldisorder transition in feldspars, which occurs at 5-6 "C. Wlotzka (1985, 1987) used a Cr-spinellolivine thermometer to estimate equilibration temperatures for Dhajala (H3.Q Study Butte (-H3.7), and Clovis #1 (H3.7) in the range of 6-7 "c. Tieschitz is too unequilibrated for this method (Wlotzka, 1987). Comparing these temperatures with the P3 concentrations of the ordinary chondrites (excluding Mezo Madaras and Tieschitz for reasons discussed below) gives the temperature scale on the right side of Fig. 8. Uncertainties range fiom -5 "C at the low end to -1 OC at the high end of the temperature scale. Among the ordinary chondrites in Fig. 8, Mezo Madaras and Tieschitz exhibit some discordance between petrologic subtype and P3 abundance. Mezo Madaras is a breccia (Binns, 1968) that contains material of different metamorphic grades (Sears et al., 1991a). The TL sensitivity of our piece of Mezo Madaras was.2 ; f.4 corresponding to type 3.5 (P. Benoit, pers. comm.), while the P3 abundance in Mezo Madaras diamonds indicates type The presence of a small, high-grade clast would be enough to shift the bulk TL sensitivity to a higher value (higher indicated type) due to the exponential dependence of TL sensitivity on metamorphic grade. Tieschitz (type 3.6, Sears et al., 1991a) contains an unusual feldspathic "white matrix" (Christophe-Michel-Levy, 1976) that may bias the TL sensitivity to a higher value. Another measure of metamorphism in primitive ordinary chondrites is the spread in composition of matrix olivines (Huss et al., 1981). : Matrix olivines o in Tieschitz have a distribution more like those in Chainpur (LL3.4) or Sharps (H3.4) than that in Khohar (L3.6) (Huss et al., 1981). Tieschitz also retains at least one-third of its original diamonds. These data and the P3 abundance in Tieschitz diamonds (Fig. 8) indicate that Tieschitz is type 3.4, not 3.6. The P3 Table 5: Xe abundances (18 cdg) for three levels of thermal processing. Xe-P3 Xe-HL Xe-P6 Sum Orgueil P3 depleted diamonds' lndarch Normalized to Xe-P6 abundance in Orgueil Orgueil ~ P3 depleted diamonds' lndarch d Average of abundances for Ragland, ALHA77214, Tieschitz, and Qingzhen (Table 2). o o abundance in diamonds should not be affected by the presence of either high-grade clasts or "white matrix" and thus should provide a better estimate of petrologic type for these meteorites. Qingzhen is one of the most primitive EH3 chondrites, as indicated by its texture and mineral chemistry (prinz et al., 1984; Keil, 1989). The P3 abundance suggests that Qingzhen diamonds experienced a temperature 25 "C, corresponding to type -3.5 ordinary chondrites. Without an independent calibration of the degree of metamorphism in Qingzhen, it is impossible to tell whether the diamonds were heated before or after accretion. However, a metamorphic temperature of 25 C for Qingzhen would imply either that the EH parent body was much hotter than those of other chondrite types, or that the truly primitive EH chondrites have not yet been recovered. If, on the other hand, Qingzhen diamonds record heating prior to accretion, such as the heating that produced an EH composition out of bulk solar-system material (e.g., Huss and Lewis, 1994b), then such high.-.c 5 loo 5 7\ ) C - 1 a, 5 c g o o l l 5 UI He-HL Xe-HL Xe-P6 F Increasing Temperature FIG. 7. Schematic representation of the sequential loss of components h m presolar diamonds during thermal processing. The left edge of the diagram represents the starting material, believed to be diamonds like those in Orgueil (CI) or Murray (CM2). As diamonds experience increasingly higher temperatures, noble-gas components, N, and their carriers are lost. Although all components exhibit a range of thermal resistance, a sequence of relative thermal resistance can be defined P3 < "labile" HL < "labile" N < retentively sited HL < lighter P6 gases < heavier P6 gases. I

11 Noble gases in presolar diamonds II metamorphic temperatures are not required. Metamorphism would not be recorded by EH-chondrite diamonds until temperatures higher than those experienced prior to accretion were reached. However, the metamorphism experienced by Indarch (EH4), which has a recrystallized texture, would still be recorded by the diamonds, whose P3 abundance implies a temperature of -65 "C (Fig. 8). The P3 abundances in diamonds from the CV chondrites Leoville, Vigarano, and Allende indicate maximum temperatures of 3-35 "C, -45 "C, and -6 "C, respectively (Fig. 8). Leoville is slightly less metamorphosed than Vigarano, based on Ni content of kamacite (McSween, 1977b), TL sensitivity (3. vs. 3.3; Symes et al., 1993), and presolar grain abundances (Huss and Lewis, 1994b). Both are less metamorphosed than Allende, as indicated by mineral chemistries (McSween, 1977b) and lower diamond and Sic abundances (Huss, 199; Huss and Lewis, 1994b), although the TL classification of Allende is 3.2 (Symes et al., 1993). Leoville has been shocked sufficiently to flatten its chondrules and inclusions, but because the deformation apparently occurred through multiple shocks at low temperature (Nakamura et al., 1993), there has been little effect on the P3 content of its diamonds or the abundances of presolar grains. The P3 abundances imply that the metamorphism experienced by Leoville is comparable to that of a type 3.2 ordinary chondrite. The TL classification of Leoville is type 3., and it is not clear if the difference between the P3 and TL classifications represents a systematic shift in the level of metamorphism experienced by CV and ordinary chondrites or if the diamonds are recording a previous heating event. However, there is some evidence in the P3-release patterns to suggest that & t,,, ~,,,,,,,, 1,.I CI LL L H EH CV CO FIG. 8. Abundances of Kr-P3 + Xe-P3 for the diamond separates in this study are plotted as a function of meteorite group. The host meteorites are identified by abbreviations of their names, and their petrologic classifications are indicated. The approximate and smoothed temperature scale was derived from trace-element, oxygen-isotope, and mineral-transition thermometers for Orgueil and the ordinary chondrites as described in the text. If P3 abundance is a function only of the maximum temperature experienced by the diamonds and all classes acquired the same mixture of diamonds at accretion, then this diagram allows comparison of metamorphic temperature experienced by each class. However, ifthe P3 abundance indicates a metamorphic grade that is clearly too high compared to other indicators, then the diamonds may contain information about thermal processing prior to accretion. (Classification for ordinary chondrites fiom Sears et al., 1991a, except that petrologic types for Ragland and ALHA77214 have been increased by.1 to account for terrestrial weathering; Sears et al., Those for Mezo Madaras and Tieschitz come kom TL measurements of our samples, P. Benoit, unpublished data. Classification for EH chondrites ftom Keil, 1989; for CV3 chondrites from Symes et al., 1993; for Kainsaz kom Sears et al., 1991b.) much of the diamond in Leoville and Vigarano was heated prior to accretion. Releases of P3 from Leoville and Vigarano diamonds (Appendixes 11 and ID), though quite small, peak at -75 "C in patterns more similar to those for Semarkona and Bishunpur than to those fiom Tieschitz and Mezo Madaras, which do not peak in the low-temperature region (Fig. 3). This suggests that the P3 gases may be coming from a small fraction of P3-rich diamonds that was either unheated or heated to no more than -3 C and was mixed with P3-depleted diamond when Leoville and Vigarano accreted. If so, then the temperature indicated by the P3 abundance in diamonds is a lower limit on the nebular temperature experienced by most of the CV diamond and associated material. After accretion, Leoville and Vigarano may have experienced metamorphic temperatures of 2-3 "C, an event that may have been recorded by the P3-rich fraction of the diamonds. The difference in P3 abundance between Leoville and Vigarano may in part be a measure of the mixing ratio between heated and unheated diamond instead of simply metamorphic temperature. If so, then the nebular temperature experienced by most, but not all, of the diamonds in these meteorites and the associated material was >45 oc. Allende diamonds, which have almost no P3 gases, may not have acquired much of the low-temperature component, or may have been metamorphosed sufficiently to remove the P3 gases. The P3 abundance thermometer indicates a temperature for Allende of -6 "C, comparable to that experienced by a type ordinary chondrite (Fig. 8). Mineral chemistry and the abundances of presolar grains also indicate moderate metamorphism (McSween, 197%; Huss and Lewis, 1994b). Calcium-aluminum inclusions in Allende have experienced more secondary alteration than those in Leoville and Vigarano (e.g., Ma et al., 199), although some of this alteration could have taken place prior to accretion (Peck and Wood, 1987). Taken together, these data seem to be inconsistent with the low petrologic type (3.2) indicated by TL (Symes et al., 1993). The Kainsaz CO chondrite has been classified as type 3.2, although various criteria -are somewhat contradictory (Scott and Jones, 199; Sears et al., 1991b). Kainsaz does not exhibit the suite of TL, CL, and mineralogical characteristics found in the most primitive C3 chondrites (Sears et al., 1991b). The P3 abundance suggests that Kainsaz diamonds experienced a temperature of 45 "C (Fig. 8), similar to that experienced by Tieschitz (type 3.4 by P3 abundance) during thermal metamorphism. The TL sensitivity suggests a metamorphic grade of -3.5, but mineral chemistry and volatile abundances suggest type -3.2 (Sears et al., 1991b). Kainsaz diamonds also release their P3 gases in a small peak around 7 "C, indicating that the diamonds are a mixture of highand low-temperature material. The preservation of a lowtemperature P3 release peak implies that metamorphism in the parent body did not reach a temperature much above 3 "C, consistent with type -3.2, and that most, but not all, of the diamond (and associated matrix) was processed to >45 "C prior to accretion. SUMMARY AND CONCLUSIONS In this paper, we have shown that the noble-gas characteristics of presolar diamonds can be understood in terms of thermal processing of a single mixture of diamonds, samples of which seem to be preserved in CI and CM2 chondrites. With relatively gentle heating, the diamonds lose their P3 gases and the "labile" HL fraction along with up to 5% of the most reactive diamond,

12 822 Huss and Lewis resulting in an increase in the HL and P6 content of the surviving diamond compared to unprocessed diamond. At higher temperatures, the main HL carrier begins to disappear and the P6 carrier preferentially loses the light gases. At temperatures that produce elemental fractionation in the HL component (6-65 "C), -75% of the original diamond has been destroyed. Within a meteorite class, the level of thermal processing of diamonds correlates with other measures of metamorphic grade, such as TL. sensitivity, matrix recrystallization and equilibration, and abundances of presolar diamond, Sic, and graphite. The P3 abundance seems to be a function only of the maximum temperature experienced by the diamonds. If all classes inherited the same mixture of primitive diamonds, then P3 abundances would tie together the metamorphic scales in different meteorite classes. When the P3 abundance thermometer is applied to ordinary chondrites, Mezo Madaras and Tieschitz appear to be more primitive (-type 3.4) than their current classifications indicate. If the P3 abundance indicates a higher temperature than do other thermometers applicable to the host meteorite, then the P3 abundance may contain information about heating prior to accretion. Diamonds in the least metamorphosed EH, CV, and CO chondrites seem to carry a record of pre-accretionary processing. Acknowledgments- We thank Jeff Rosenbaum for implementing the calculation of Rees (1984) in our spread sheet and Mary-Eleanor Johnson for editorial help. Helphl discussions with Edward Anders, Ian Hutcheon, and Roger Wiens are gratehlly acknowledged. Detailed reviews were provided by C. T. Pillinger, R. H. Nichols, D. W. G. Sears and an anonymous reviewer. We also thank Paul Benoit of the University of Arkansas for determining TL sensitivities on our samples of Mezo Madaras and Tieschitz. 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13 Noble gases in presolar diamonds II. 823 SCOTT E. R. D. AND JONES R. H. (199) Disentangling nebular and asteroidal features of C3 carbonaceous chondrite meteorites. Geochim. Cosmochim. Acta 54, SEARS D. W. G., GROSSMAN J. N. AND MELCHER C. L. (1982) Chemical and physical studies of type 3 chondrites-i: Metamorphism related studies of Antarctic and other type 3 ordinary chondrites. Geochim. Cosmochim. Acta 46, SEARS D. W. G., HASAN F. A., BATCHELOR J. D. AND LU J. (1991a) Chemical and physical studies of type 3 chondrites--xi: Metamorphism, pairing, and brecciation of ordinary chondrites. Proc. Lunar Planet. Sci. Con$ Zlst, SEARS D. W. G., BATCHELOR D., Lu J. AND KEcx B. D. (1991b) Metamorphism of CO and CO-like chondrites and comparisons with type 3 ordinary chondrites. Proc. NIPR Symp. Antarctic Meteorites 4th SYMES S. J. K., GUJMON R. K., BENOIT P. H. AND SEARS D. w. G. (1993) Thtmnohminescence and metamorphism in CV chondrites (abstract). Meteoritics 28,446. TANG M. AND ~ E R E. S (1988) Isotopic anomalies of Ne, Xe, and C in meteorites. 11. Interstellar diamond and Sic: Carrlers of exotic noble gases. Geochim. Cosmochim. Acta 52, VAN SCHMUS W. R. AND WOOD J. A (1967) A chemical-petrologic classification for the chondritic meteorites. Geochim. Cosmochim. Acta 31, WLOTZKA F. (1985) olivine-spinel and olivine-ilmenite thermometry in chondrites of different petrologic type (abstract). Lunar Planet. Sci. 16, WLOTZKA F. (1987) Equilibration temperatures and cooling rates of chondrites: a new approach (abstract). Meteoritics 22, APPENDIX I Abundances of Helium, Neon, and Argon components from diamond separates calculated as described in "Methods of Study" section. 4He abundances in ccstfvg; 22Ne and 36Ar abundances in 1@* ccstp/g. s may differ from column sums due to roundoff error. Tmp 4He-P 4He-HL 22NeAir 22Ne.p3 22Ne-A2 22Ne.E 22Ne-Cos 36Ar-Ajr 36Ar-P3 36Ar-HL 36Ar-p6 OC Oroueil.~ 'BF' f f.9 3. f.5.4f f22 t t1 f f f f fo fz28 98 f f1 4f1 56 f f f15 45f f35 17f f f f3 178 flfl4 +nr3 n13fo f f t i5r7.16 f f f7.8.9 f f f f f f f f f f.13 3.f.3.25 f.4.1 f ;o.i8 13 f f f15 38 f15.3fo f fm 29 f37.22f f f f152.4f f4 138 f26 21 f38 f f f1.3 l?.?f!.! f.3.25 f.4.7f.38.1f f fo.9 '.'*''' f.2.12 f.3 O.OOO1fo.oo~~.1f f1.3 3.f.8 6.9f12 179f4 435f f fl8 83 f16 3. f f fo f326 1 f2w 529 f161 Semarkona 'AF' f f f15 1 5f f f f32 f2 f5 26f15 17f25 79f 1 75f6 57f5 46f32 Bishunpur 'BF' lf2 3f2 91 7f5 11f f9 25f f15 83f f15 63f f f24 211f24 Ragland 'AF f f f f f fl8 44 f14 6 f9.3 f.4.24f f93.79 f f f f f18 91 f f f f f f f57.12 fo t f f f.97.2 f.53.3 f f f fo f f.3.23 f f f.37.8of f.57.5 f f f f f fl.9.21 f f f5.4.5 f f f8..52 fo.w 41 f29 28 in.3 f f2.9.7 f f f f f f f f.3 3.8f.3.47 f.3.5 f.6 2.3f.3.6 f.3.5 f f f f f f f f f46.34 f f f5.5.8 f I f f f f f f fO.1.23f.25.5 f f9. 63 f f f f.93.1f.31.5f.33.19f.34 f.35 f.34.1 Of.34.12f.35.1f.32.1f.34.13f.34 f.36.8of f f.18.22fO.18.24t.18.1f f.18.22f.18.21f.21 O.8f.18.9f.16.4f f f fm 1387 f f56 47 f19 27 f f61 87 f fm 63.5f f f f f f f f f f f f f f f113.1 f 1.1 fm 39 f54 56 f56 31 f19 65 f f33 38 fw 78 i15 34 f6 3.lf.8 61 f19.7f.9 1.4f i24 26 i13 13 f f5 25 *4 27.6f f f f72 27 f f f f2 58.6f7. 6.6fl.l 762 f19 42 f fea 527 f f f2. 6.5f2. 87 f13

14 824 Huss and Lewis 22Ne-Air APPENDIX I (Continued) 22~e-p~ 22Ne-A2 22Ne-E 22Ne-Cos Me2 Maws 'AF f2 f2 83 5f5 5t5 15 5f5 35f f1 69f f f f12 212f17 ALHA77214 'AL' Tieschitz 'w f5 5f5 23f1 3f5 5f5 3f5 28f 1 51f5 42f5 35f5 15f f13 25f15 Dimmitt EF Qingzhen 'BF' lndarch 'DF f3 f3 91 f2 11f2 11 t2 18f t5 52f f3 11f f f7 213f8.38 f.48.7 fl f f fo.8.28f f f f.16.27f f f f f.51.26f f f f f.72.18f f14 7 f43 13 f25.41 f.28.2f *I 6 f f52.76 f.52.2f f f f f.39.16f.2 99 f f f f.27 fo f f f f.24.13f f f.3.37 f.5.24 f.5.3f f fO.2.49f.21.39f.25.9f f.8 27 f f59 8. f f f f f f f flll 285 f65.15 f f f f f f fo.ll 3.47f.7.17 f.8.3 f.12.2f t1.3.9 f f ill1 956 f f f f.1.5 fo.ll.41 f f.1.7 f f f.14.6 f f.25 5 f19 45 fll.15 fo.ll 6 f38 69 f22.17 f f1.3.1 f f f1.6.9 f f f f f f f t f f f f fo t f f f f.9.16f f f f f f f f fl f.2.51 f.18.5 f f fl f f f f f f f fl fl.o.52 f f f f f.8 1. f.8.1 f.9 95 f f f f.5.44 f.5.25 fo f f.12.9 f f.2.3 f.19.5 f f.28.4 f.27.5 f f f.47.1 fo f2..6 fl.9.28 f f t f f f f f f.14.7 fo f f fo.1.25f f f f f f f.8.95f f f f4.5.68f f f f6.8.8f f8.6.56f.7 29 f12.51f.71 f32.79f.7 18 f36.77f f f.71 2 f27.6f f17.162%.7 9.f fO f f f72.1 f f.9.2f f2. f.3 35.f2.2 f f1.8.2f.3 f.35 f.31 f.7 f.32 f 6..15f.31 f 8.9 f.27 f 1.1.3f.26.21fO.25.44f.97 f.6 1.2f f12 1.8f f f f14 1.9f6. 17 f f f9 94 ill 44 f12 23 f28 33 f f f6l 32.3f f f f f.5 1.5f f f78 2.5f f f f f f f f f f f f fz? 237 f4 129 f f f f19 3.f f f1. 7.f f f78 4.5f f f f f f fll.7f f38 12 f39 32 f f3 16.4f f Of f f1. 6.fl.l 973 f f5 Leoville 'BF f2 1fz 945 3f5 14f f5 42f f15 9f f15 64f f f22 241f f f.45.9 fo f f f f f3.7.2 f f f1.5.1 f f f f f6 233 f61.33 f f3.5.4 f f f f2.2.7 f f.9.64 f f f.3.22fO.41.1 f f.3.22fO.4.7 f.4 1.6f f f f fl.1.14f.9 64.f6.9.11f f23.6f f3 f f31.6f f13.19fo f39.26f ill.18f f48 O.8fO f3.8.12f.8 1.f1.7.33f f f f f f f6.1 9 f22 9 fll f f12 f29 36 f7 44 f f18 64 f f flol 166 f f f f f1. 9.1f f1. 8.4f f f127

15 ~ ~~~ Noble gases in presolar diamonds II 825 APPENDIX I (Continued) Temp. oc 4He-P 4He-HL z2ne-air 22Ne-P3 22Ne-A2 22Ne-E 22Ne-Cos 36Ar-Air 36Ar-P3 36Ar-HL 36Ar-P6 Vigarano 'BF' 35.4f fl f.63.6f f f f5 f f f f.24.15f f f f5 12f f f t.36 O.OlfO fll 21 ill 945 3f5 31f f f6.1.2 f.46.1f f f6.4 f f1 71f1 33 f f16. f1.2.1f f1 77.5f f1 133 f1 152 f5 95f1 4f5 33 f f f f f.73 f.31.12f.17.11f f38 f55 27 f f f fa 175 f f f f.5 f.17 f9 49.9f6. 89 f f.2.34f.35.4 f.4 f f.8 5.f.7 6.8f f Of f.21 f.16 f f.7 ll.8f f f.24.3f.15.1fo f f.8 1.fl.6 16f17 248f18.4f f fn 3.8 f fo.8.5f f f f81 Allende 'EB' 7 21 f f f f f f f2 f2 51 f46 99 fa.84 f f ill 8.4f f f3 136f3 8 f f144.2 f f.69 f f5 198 f f1 32f1 233 f2 3.8 f f f.69 f f fr) 174 6f f f.5.28 f.5 2.3f.61 f f f f f f fO fl.l 7.4f1. 5.1f f37 175f37 81 f f f f f f f f6 Kainsaz 'BF 32.23f f f.7.3f f f f f f.19.22f f f f2 f2 7.5 f f f.9.32f f f f3 1f3 9.6 f f7.1.1 fo.ll.15f f f f1 46f1 24 f27 11 f27.16 f.41.18f f f ill f1 Elf1 11 f6 265 f61.32 f.95.27f f f15 69 f loflo 61f f f2.7.9 f.44.27f f4 283 f f f fl f f.26.6f f f f f.1.68 fo.1.13 fo.2.27f f f f f.2.1 fo.2.11 f.5 f f fl.l 15.5f f f.5.1 f.8 f.17 f.9 3.9f.6 9.Of1.1 3t18 222f16.23f f f f f f f f f75 Murray CE 6 2 f12 56 f33 25 f fll 49 f33 33 t f f f f f f f24 14 f24.28 f fr) 168 f6 696 f f fo.86 APPENDIX I1 Krypton compositions from mixing calculations described in the section "Methods of Study," and S4Kr abundances for each component calculated from the proportions that produced the listed composition and the 84Kr abundance measured for that temperature step (Kr isotopic ratios x 1; 84Kr amounts in 1-8 ccstp/g). Calculated ratios that differ from measured values by more than twice the measurement error are underlined. s may differ from column sums due to roundoff error. Temp WKr 82Kr 83Kr WKr %-Air WKr-P3 e4kr-hl 84Kr-P6 WK~.S Frat. (%/mu) OC WKr % 84Kr 84Kr 84Kr P3 HL Orgueil 'BF' f t.8 f f f1.3 fo f.36.23f.46 f.2 f f f f.32 f.16 t f t.87 f f f f.3 f.15 f t f t.14 f f f f.54 f f fO f fo fO.14.73f.3.54f.14.6 f fo.1.29fo.1.21 fo.1.3 f f..1.29f.1.1 to.1.1 f.2 f f f f f.116 Semarkona 'AF' f.2.169fo.6.1f.4 fo.oo1 f fo f f.39 fo fo.we fo.o1o 1.12 f fo.1 f.52 fo f f f f f f f f.14.96t f fo.ll.321 f fo f fo.ll 1.42tO f.17.4f f.2 fo.ll f f.9.96 f f f f f f.55.4 fo f.7.5 fo.4 f.8.16 f f.5.11 f.3 f.4.19 f.38

16 826 Huss and Lewis Bishunpur 'BF Ragland 'AF fo.1.78f.2 f.5.93f.21 f.5.964f f f io.ll 2.27 fo i f.59.27f.25.52f.19 f f.5.36f.1.49f.1.25i f f f f f f fO.OO4.82fO i.13 fo.oo1 f.5 f.5 f.19 f fo.ll 1.13 f f.33.53f.6.12 f.25.57f f.49.7 fo.~ f.2 f.2 f.7 f.7 f.7.57 f fo.2.7 f.m.12 f.8 f.6.18 f.3.84 r.1.51r f.26 fo t.6 f.8.86t f f f.5 f.7 f f f f.21 f f f fo.8 f f.8.17f.24 fo.oo1 f.5.43i.1.53f.5 f.3.84 fo.ll.6 f f f f.24 Mezd Madaras 'AF f.3.196i.5 f.3.542f.12 fo.oo1.63f.15.68f.15 io f.28.66f.45.57f.22.13f.7 fo io.34.78f.3 fo.oo1.6 fo.6.78f.6 f.3.6 fo.1.171f.9 fo.4.12 f.2.193f.9 f.8.2 i.2 186f49 496f14 274f49 2 f3 15f65 88f31 259fO65 5 f f f fo.o1l 3.35 f f.28 f f f.45.5 f.3.96f.4.66f.22 f.7.53f.1 f.7 f f f i.21 ALHA77214 'AL' Tieschilz 'AF Dimmitt 'EF fO i.4 f.13.7f.13 f.6 f.3 fo.11 fo.o1.4 fo.o1.166f f.35 f.4.326f.1 f.2.24 f.1 1 f.1.416f f f fo.1 f.14 i.16 io.22.1 f fo.1.11 fo.ll.16 f.24 f i io.24 i f f f fo fo f.3 f f fo.ll.18 fo.o1l.14f.3.52f.1.8 fo.oo1.4f.2.8f.8 fo.oo i f f.23.34f f f.17.34f f f fO.W 1.55 f f f f f f f.13 f.4 fo.o1o fo.11 io.18.82fo fo.1.61 f.14.5 f io f fo.1.21 fo.ll.41 f f f.2.45 f.2 f.2 f.3 f.2.12 i.6.14 f.9.12 fo.o1o.6 f f.12 fo.6.9 f.4 fo.oo1.138 f f f i1.85 f.62 Qingzhen 'BF' f.1 f.1 f.2 f f f.99 fo.12 f.14 f f.45 f.2 1. f f f f f f f f fo.1 fo.1.237f f f f i f f.25.3 f.3.8 f.6.47 f.7.26 f.9.1 f.8.8 f.3 * i.15 lndarch 'DF f.1.56 f.3 io.2.125f.7 fo.oo1.157f f.15 f.17 f.12 f.88 f.86 fo.8 fo.4.23 f.4.7f.2.43 f.13.74f.3.185f.7.2f fo.8.37 f f f f f.7.65f f f.14 f.3 f.6 fo.18 f f.17.9f f.88 f f.8.117f.5.57 f.4.33 f.13.5 f.3.9 f.6 f.7 f.6 fo.oo1.3 f.4.4 f f fo.oo1.9 f.6 f io.19.5

17 Noble gases in presolar diamonds II. 827 Leoville 'BF Vigarano 'BF Allende 'EB' Kainsaz. 'BF f.3.264f.18 f.4.68 f.41 f f f f.64.6 fo.ll 2.31 f f f f.16.73f.15 f f.49 f.2.12ofo.3 f f.2 f f f.13 fo.54 f.185 f.236 f.54 f.5 f.7 fo.o1o f f.31.33f.3.13fo f f f f f f f.13.6f.3.79f f f f f f f fo.ll.655 f f.2.37f.2.55f f.15.33f.17.79f.39 f.81 fo f fo.ll 1.27 f f.b.93f f.16 i f.49 io.oo1 f.5 to.8 fo.o1l.454 f f i f f.5.37 f.8.45f f.31 fo.oo1 fo.2 f.5.5 fo.5.5 f.4 *.6 fo f.16 fo.2.2 io.5 i.5.39 f.29.2 f.5.1 t.3.23 f.5.2 f.3 f.3.7 fo f f.3 f.3 f.2 f.3.85 f.2 fo.7.385f.1.279f.9 M.7 M.2 fo.4.448i *.17 M.O1l M.3 f.5 f fo.ll.2 M.25 M.15 i M M M.1 fo i m.35 M.2 fo.12.73t.2.49m.12 io.4 fo.o1o.83 f f fo.3.47 io.19 f *.3 f f.5 io.oo1.831 fo t i f f f.25.4f f.2 f.9 f f.35.59f.2.65 f.3.1 3f f f fO fo.ll 3.21 f f f.5.54 f fo.1 fo.oo1 f.5 f.7.19fo.55.38k f.z 1.51 f f f.2.36f f f.6.17 f.6.5 f.3.19 f.2.2 fo.3.15 t.5 f.13.4 f.15.3 io.2 f.6 f.3.13 f.21 APPENDIX I11 Xenon compositions from mixing calculations described in section "Methods of Study," and I3*Xe abundances for each component calculated from the propottions that produced the listed composition and the l32xe abundance measured for that temperature step {Xe isotopic ratios x 1, 332Xe amounts in 1-8 ccstp/d. Calculated ratios that differ from measured values bv more than twice the measurement emor are underlined. s mav differ from column sums due to 131xg 132xe 134~~ 136~~ -- 13%e 132~e P3 HL fo.o1.97 f.35 f f.51 f f f f.4.58 f f.8.79f.5.51 f.3.3f.1.15f.1 f f.67.23f.2.189f f fo f f fo f.9.15f.5.5ofo.2.81 f f.32.6 fo.2.29 fo.29 f.23 f.7 f.3.5 f.3.3 f.5.7 f t.52 f.2.871f.52 f.85.95f.5.21 fo.6.12fo.1.12~ f.1.13f f.7.52 fo.44

18 828 Huss and Lewis Semarkona 'AP Bishonpur BP Ragland 'W MezOMadaras 'AF ALHA77214 'AL' Tieschitz 'W Dimmin 'EF Qingzhen BP f.9.37f.9 fo fO.37 f f f fO f f f f.17.4oof f.3.45 f fo.oo1.55fo.1 f.3.363f.5 f.2.369f f f f f f f.11.7f.3.91 fo.3 fo f.6.8 f.m2.141 i.3.25f.9.319f f i f f i f f fo.1 f.1 i.4.4 f.7 t f f i.2.7f f f.3 f.9 fo.1 f.4 f.3 i.8 f.18 fo.o1o f.7 fo.oo1 f f.4 f f.3.5 f.2.119f.2.4 fo.ocn.397f.1 f.9 f.4.571f.9 f.15.3 i f.23 f.23.9 f f.67.69f f f f.86 fo f f f.7.376fo.5.93f.5.8 f.2.244i.3 f.3,1 fo.oo fo.ll 2.26 f f.24.2 fo.1.336f fO.36 f.3 fo.5.258f f.32 f.5 f.5 2. f.7 f fo f.67 f.27 f f.61 f.12.96f f f.16.5 f f.3.229f.2.51 f.3 f.6.2 f.13.7 fo f f.9.5 f.3 f.9.132f.7 f.8.249f.6 f.3.26f f.5.269f f fo.41 f.44 f.12 f.6.19 f.2 f f.7.55f.2.4 f.4.144f.2.4 fo.1.245f.4.8ofo.1.2 fo f.5.56f.1 fo.oo f.11 f.9 f f.21 f.16.8 f f.63.26f.42.5 fo io f.9 f f.3.627f.25.7 fo.5.6f.9.145fo.7 fo.1.171f.3.12f.2 f f fo.1.26 f.22.6 f.45.67f f.17 f.3 f f f.7 f.24.6 fo.9 2. f f f.12 f.23 f f fO.58 f.11 fo.7.599f.8.129f.7.3 fo.oo1 f.3.275f.4.49f.3 fo.1.6f f f f.13.9 fo.28 f.9.126f.9.18f f.8 f.2.165f.3 fo.4.224f.8.13 f.12.23f.21 fo io f.37 f.34 fo.2 f.15.32f.4.18f f.7 i.92.67f.4 t f.9 io f.37.86f.48 fo.45 i.46.76f f.6 f f.92.53f.4.12 f.3.15t.3.558f f f f f f f f fO f fo f.4 fo.oo2 fo.4.97 f.6.299f f f f fo f f f f f fo.8 fo.oo1 fo.oo1 f f.5.5 f f.12.3 f f f.17 fo.1.8 f.8 f.2.56 fo f.9.76f.8 f f.49 f f fO.W.43f fo f i.57 fo.o1l 4.774f i.58.6 fo f r f.5.582f.9.37f.7.6 fo.oo f fo.ll.71 f.21

19 ~ Noble gases in presolar diamonds II idarch ~DFF Leoville 'BF' ' Vigarano 'BF' Allende 'EB Kainsaz 32 51, 'RP Murray CF f.4.47f.1 f.2.88f.2 f.3.94f.2.12 f.1 f.2 f.8 f.32 f.37 fo.18 f.7.7f.w f.5.25 f.5.36f.2.1 1f.4 f.5.328fo.6 f.4.536f f f.9.32 f f f f.8.24 f.2.9f.1.36f fo.1.91 fo.oo1.2 f.3.279f.3.5 f.7.411f.5 fo.oo1.3 fo.oo f.5.44f.1.2 fo.oo f.8.63f.2.4 fo.oo f.3.139iO.8.2 f fo.ll.747f f f f f f.16.5f f.4.472f.8.181f.7.51 fo.oo f.7.147fo.w.3 fo.oo f f.8.18 f.33.87f.6.6 f f.5 fo.oo1.29ofo.8.2 f.2.316f.8 f.2.2 f.2.635f.1 f.2.1 fo f.31 f.13.8 f fo.ll.637f.73 f f f.65 f f.16.48f.13.2 f.3.35f.5.72f.4 fo.1.228f.4.42f.3 f f fo.1.15 f.25.22f.4.32f.2.67f.2.8f.2.65f.6.232fo.w.351 f.7 fo.oo1 f.4.443f.8.425f.1 f.4 fo.2.258f.5.479f.8 f.4 fo.oo1.171f f.2 f.12.3 f f f.82 f f f fo f.8 f.16 f f f.23 f.4.41k.2.162fo.3.8f.2.6f.4 f.1.91f.1.18f.1 i.m.25f.1.89f.1.5f.1 f f fo f fo.1.23 f.21 f.8.118fo.og4.734f.12.9f.17 f.8.76f f.23.76f.17 f.3 f f f.111 f.22 fo fo.ll 1.346f.88 f.17 f f f.25.2 fo f.ow.276f.5.7f.4 fo.oo1 fo.o1l.27 f f f.15.3 f.29.6f.1.89 fo.oo1 fo.oo1.138f.2 f.3.416f.7.253f.5.245f.1.28f.19 f.33 f.45.43f.9 f.3 fo.oo fo.6.32f.3.47f f.7.29f t f f f fO t.8.6 f.3.9 f o.ooo4.3 fo.oo1 fo.1.2 fo.oo1 f.3.8 fo.3 f.5.7 f f.14 f f.91.9 fo f.17 f.3.9f.6 fo.oo1.21 f.3.31 f.2 f f f.9.3 fo f2..26 f f fo.23.36f.72 f.14.7 f f.7 2.3f.8 f.19 f f f f f f fO f.34.5 f f.1.167f.8.13f.4.44 f.w 41.2 f f fo f.68.15