Comparison of carbon isotope variations in grain size fractions of presolar diamonds separated from three meteorites (Efremovka, Boriskino and Krymka) suggest that diamond from various parts of solar nebular have had diffrent C isotope signature

Fisenko, A. V.

Pillinger, C. T.

Semjonova, L. F.

Verchovsky, A. B

Wright, I. P.

English

Open Research Online (The Open University)

Open Research OnlineThe Open University’s repository of research publicationsand other research outputsPresolar diamonds in Krymka: C, N and Xe isotopedata from grain-size separates and comparison withother meteoritesConference or Workshop ItemHow to cite:Verchovsky, A. B; Fisenko, A. V.; Semjonova, L. F.; Wright, I. P. and Pillinger, C. T. (2004). Presolar diamonds inKrymka: C, N and Xe isotope data from grain-size separates and comparison with other meteorites. In: 35th Lunarand Planetary Science Conference, 15-19 Mar 2004, Houston, Texas, USA.For guidance on citations see FAQs.c© [not recorded]Version: [not recorded]Link(s) to article on publisher’s website:http://www.lpi.usra.edu/meetings/lpsc2004/pdf/1673.pdfCopyright and Moral Rights for the articles on this site are retained by the individual authors and/or other copyrightowners. For more information on Open Research Online’s data policy on reuse of materials please consult the policiespage.oro.open.ac.ukPRESOLAR DIAMONDS IN KRYMKA: C, N AND Xe ISOTOPE DATA FROM GRAIN-SIZE SEPARATES AND COMPARISON WITH OTHER METEOROTES.  A. B. Verchovsky1, A. V. Fisenko2, L. F. Semjonova2,  I. P. Wright1 and C. T. Pillinger1, a.verchovsky@open.ac.uk,1The Open University, Walton Hall, Milton Keynes MK7 6AA, UK 2Vernadsky Institute of Geochemistry and Analytical Chemistry RAS, Moscow, Russia.   Introduction:  In this study we present the first results from an investigation of C, N and Xe isotopic compositions in a new set of grain-size fractions of presolar diamonds separated from the Krymka (LL3.1) ordinary chondrite. This is the third meteorite which we have analysed in this way; Efremovka (CV3) and Boriskino (CM2) have been analysed previously [1, 2] and are quite different from Krymka in terms of their parent body composition and metamorphic history. Comparison of isotopic data allow us to investi-gate how metamorphism on different parent bod-ies has affected the diamonds and gaseous com-ponent trapped within them. In addition we can asses whether there are any differences in dia-mond populations sampled by these bodies. In contrast to similar studies of bulk diamond frac-tions [3, 4], grain-size separation allows a more detailed and specific investigation due to better resolution of the components present in the dia-monds. Experimental technique: Presolar diamonds have been separated from the bulk Krymka sam-ple using standard techniques (i.e.[5]). Colloidal diamonds then were treated to ultracentrifugation in the way we have described before [1]. Four grain-size fractions were obtained in two sequen-tial ultracentrifugations allowing us to deduce a relative sequence of grain sizes in the fractions. All the fractions, along with the unseparated bulk diamond sample, were analysed for C, N and no-ble gas isotopes using two static machines de-scribed earlier [1, 6].  Results: In a similar way to all results ob-tained so far for grain-size fractions of presolar diamonds [1, 2], the new samples show a clear systematic dependence of all the noble gas con-centrations and isotopic compositions on grain size. For instance, Xe concentrations very by a factor of 4 and 136Xe/132Xe ratio by 12% between the coarsest and the finest fractions. Similarly, way C and N isotopic compositions show signifi-cant systematic variations with grain size from -18 to -39‰ and from -210 to -320‰ respectively.  Discussion:  All the chemical and isotopic similarities suggest that diamonds in meteorites of different groups are basically the same in terms of their origin. Their all contain three components of noble gases (P3, HL and P6 [7]) implanted likely with different energies into the same or similar (in grain-size distribution) diamond populations which have been more or less completely mixed in the solar nebula and uniformly distributed be-tween different parent bodies in the early Solar System. Nebular processing, thermal metamor-phism and aqueous alterations on the parent bod-ies affect the noble gas system in the diamonds mostly by removing the least resistant low tem-perature P3 component such that its concentration in diamonds is a function of metamorphic grade [3]. Applying such a criterion to diamonds from the three meteorites considered herein (Fig. 1) shows that Krymka is the most processed meteor-ite as its diamonds have the lowest relative abun-dance of the P3 component. The least processed material is represented by Boriskino with the highest relative abundance of P3 gases. Efre-movka has an intermediate position closer to Krymka than to Boriskino. The curves shown in Figure 1 can be regarded as mixing lines between a pure HL composition with 136Xe/132Xe≈ 0.7, (equivalent for all the meteorites) and that repre-senting the P3/HL mixing ratio, which is different for each meteorite. The reason for the variations of C and N iso-topic compositions with grain size of diamonds is less well understood. From figs 2 and 3 it can be seen that for diamonds from each meteorite two end-members can be identified which seem to be different in each case. At least this is definitely true for the end-members with relatively heavier composition. It appears that the higher the proc-essing experienced by meteorite, the heavier the isotopic composition of the end-member for both C and N. One of the reasons for the observation could be that thermal metamorphism destroys diamond of  certain isotopic compositions. A more attractive explanation, however, is that the Lunar and Planetary Science XXXV (2004) 1673.pdfdifference in the compositions of the heavy end-members is associated, not with meteorite proc-essing, but rather with meteorite type, i.e. with its chemical composition. In this case we can specu-late that material accreted from different parts of the solar nebula contained diamonds with differ-ent C isotopic compositions. If so, then most of the diamonds with the heavy end-member iso-topic compositions are not associated with Xe-HL since there is no correlation between Xe-HL iso-topic composition and the type of meteorites (Fig. 1). As a hypothesis to explore further we propose that these isotopically heavy diamonds (i. e. with δ13C≈  -14, -23 and -30‰ and δ15N≈  -180, -210 and -225‰ respectively) could have a Solar Sys-tem origin [8]. Obviously such a proposal will require further work to substantiate.  References [1] Verchovsky A. B. at  al. (1998) Science 281, 1165-1168. [2] Verchovsky A. B. et al. (1999) LPSC XXX, abstr. 1746. [3] Huss G. R and Lewis R. S. (1994) Meteoritics, 29, 811-829. [4] Huss G. R. et al. (2003) GCA 67, 4823-4848. [5] Amari S. et al. (1994) GCA 58, 459-470. [6] Wright I. P. and Pillinger C. T. (1989) US Geol. Bull. 7890, 9-34. [7] Huss G. R and Lewis R. S. (1994) Meteoritics, 29, 794-810. [8] Dai Z. R. et al. (2002) Nature 418, 157-159.  0.350.40.450.50.550.60.650.70.750 5 10-7 1 10-6 1.5 10-6136 Xe/132 Xe132Xe/C, cc/gBoriskinoEfremovkaKrymka Figure 1. Correlation between Xe concentrations and isotopic compositions in grain-size fractions of presolar diamonds from different meteorites.   -40-35-30-25-20-150 5 10-7 1 10-6 1.5 10-6BoriskinoEfremovkaKrymka132Xe/C, cc/gδ13 C,‰ Figure 2. C-Xe three-isotope diagram. Carbon end-members isotopic compositions of the two-components mixtures are different in different meteorites.  -350-300-250-200-1500 100 5 10-5 1 10-4 1.5 10-4 2 10-4 2.5 10-4 3 10-4δ15 N,‰132Xe/N, cc/gBoriskinoEfremovkaKrymka Figure 3. The same as in Figure 2 for N-Xe sys-tem.  Lunar and Planetary Science XXXV (2004) 1673.pdf

Presolar diamonds in Krymka: C, N and Xe isotope data from grain-size separates and comparison with other meteorites

http://oro.open.ac.uk/8763/1/Presolar_diamonds_in_Krymka.pdf

Presolar diamonds in Krymka: C, N and Xe isotope data from grain-size separates and comparison with other meteorites

Abstract

Similar works

Full text

Available Versions

Open Research Online (The Open University)