Alexandre, A.

Folco, L.

Franchi, I. A.

Gattacceca, J.

Greenwood, R. C.

Rochette, P.

Sonzoghi, C.

Suavet, C.

English

Open Research Online (The Open University)

Open Research OnlineThe Open University’s repository of research publicationsand other research outputsOxygen isotope ratios of large cosmic spherules:Carbonaceous and ordinary chondrite parent bodiesConference or Workshop ItemHow to cite:Suavet, C.; Alexandre, A.; Franchi, I. A.; Gattacceca, J.; Sonzoghi, C.; Greenwood, R. C.; Folco, L. andRochette, P. (2009). Oxygen isotope ratios of large cosmic spherules: Carbonaceous and ordinary chondrite parentbodies. In: 40th Lunar and Planetary Science Conference, 23-27 Mar 2009, Houston, Texas.For guidance on citations see FAQs.c© 2009 The AuthorsVersion: Accepted ManuscriptLink(s) to article on publisher’s website:http://www.lpi.usra.edu/meetings/lpsc2009/Copyright 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.ukOXYGEN ISOTOPE RATIOS OF LARGE COSMIC SPHERULES: CARBONACEOUS AND ORDINARY CHONDRITE PARENT BODIES.  C. Suavet1, A. Alexandre1, I. A. Franchi2, J. Gattacceca1, C. Sonzogni1, L. Folco3,  R.  C.  Greenwood2 and  P.  Rochette1,  1CEREGE,  Aix-Marseille  Université,  CNRS,  France (suavet@cerege.fr),  2PSSRI,  Open University,  United Kingdom,  3Museo Nazionale  dell’Antartide,  Università  di Siena, Italy.Introduction:  Based  on  petrographic  and  ion probe investigation of small micrometeorites (150–250 µm),  previous  studies  (e.g.  [1])  have  concluded that 99% of  them should  come from carbonaceous,  pos-sibly  cometary  parent  bodies  (CM/CR  related).  Our oxygen isotope measurements of 33 large (>500 µm) silicate type cosmic spherules (CS), using IR-laser flu-orination/mass spectrometry, indicate that 30% of the CS are above the terrestrial  fractionation line (TFL), i.e. are unrelated to carbonaceous chondrites but rather to ordinary and R chondrites.Samples and Methods:  Thirty three silicate CS from the Transantarctic Mountains collection [2] were selected  for  this  study.  Their  masses  range  from 262 µg to 877 µg after the weathered rim was leached out  using  diluted  HCl.  SEM images  of  the  samples were  taken,  non  destructive  chemical  analyses  were made  with  a  X-Ray  Fluorescence  microscope,  and magnetic  properties  were  measured,  at  CEREGE, France. SEM images (Figure 1) allowed to distinguish between  barred  olivine  (BO,  23  CS),  porphyritic olivine (PO, 3 CS) and glassy (7 CS) textures [3]. This proportion is similar to that of large collections (e.g. [4]),  assuming that cryptocrystalline and BO textures are merged.Measurements of δ18O and δ17O were carried out on 28  spherules  at  the  Stable  Isotopes  Laboratory  of CEREGE,  France.  Molecular  oxygen  was  extracted using the IR-laser fluorination technique [5-6] and the three oxygen isotopic composition was measured with a  dual  inlet  mass  spectrometer. The  gas  was  passed through a –114°C slush to refreeze potential interfering gases before being sent to the mass-spectrometer.  In order to get sufficient 34/32 and 33/32 signals (2-3 V), the oxygen from <0.3 mg standards and all CS samples was concentrated in the mass spectrometer in an auto-cooled 800 µL microvolume filled with silica gel and directly connected to the dual-inlet  system. δ18O and δ17O values of the reference gaz were fixed through the analysis of NBS28. The oxygen isotope results are ex-pressed in ‰ relative to V-SMOW. Measured δ18O and δ17O  values of the samples were corrected on a daily basis  using  a  1.5mg  quartz  laboratory  standard “Boulangé” (∆17O=0.006, SD=0.034, n=37). Replicate analyses  of  1.5mg  NBS28  (∆17O=–0.004‰,  SD= 0.055‰, n=11),  San  Carlos  olivine (∆17O=–0.024‰, SD=0.031‰, n=18) and UWG-2 [7] (∆17O=–0.004‰, SD=0.055‰,  n=8)  were  made  during  the  analyzing period.Figure  1: Back-scattered  electron  images.  A-B, Barred olivine cosmic spherules for which oxygen iso-tope ratios show relationship with carbonaceous chon-drites (A) and ordinary chondrites (B).  C, Porphyritic olivine cosmic spherule. D, Glassy cosmic spherule.Measurements of small masses (0.2–0.7 mg) of quartz and olivine show a systematic negative offset on the value of  δ17O (–0.2‰, SD=0.05‰, n=9). Therefore, a direct +0.2‰ correction was made on the value of δ17O for  CS  samples.  Five  more  BO-PO  spherules  were measured  at  the  Open  University,  UK  following  a different method [8].Results  and  Discussion: As  CS  melt  during  at-mospheric entry, their oxygen isotopic composition is a mixture between primary extraterrestrial components and high  altitude  atmosphere  interaction  (defined  by iron  oxide  spherules  [9-10]  at  δ18O=40–60‰  and 1776.pdf40th Lunar and Planetary Science Conference (2009)∆17O= 0‰).  From the  results,  we  can  distinguish  4 families of extraterrestrial components:– Most BO CS (16/23, or 48% of the total) have ∆17O≈–3  to  –5‰  and  δ18O  in  the  10–30‰  range (similar to values typically obtained by ion microprobe [11]). These values correspond to the atmospheric con-tamination of a parent material with ratios on the car-bonaceous  chondrite  anhydrous  minerals  (CCAM) line, e.g. typical of CO/CV carbonaceous chondrites.– 5 BO CS and 2 glassy CS (21% of the total) have ∆17O  around  –1‰  and  δ18O  in  the  15–35‰  range (similar to values typically obtained by ion microprobe [11-12]).  These  values  could  correspond  to  atmos-pheric contamination of hydrothermally processed car-bonaceous material, e.g. CM/CR parent material.– 2 BO, all 3 PO (Figure 1C), and 3 glassy CS (24 % of the total) have ∆17O≈0.4 to 0.8‰ and δ18O in the 10–20‰ range. These values could correspond to at-mospheric contamination of ordinary chondrite parent material. It is the first time that any evidence has been uncovered  for  ordinary  chondrite  parent  material  for CS.–  Finally,  2  glassy  CS   (6%  of  the  total)  have ∆17O≈+1.8‰ and δ18O≈41‰, which is close to the va-lue found for one glassy CS in a previous study [11]. The only known parent material could be an R chon-drite,  or  the  high  ∆17O  component  observed  in  the magnetites  [13]  and the mesostasis  of  unequilibrated ordinary chondrites [14]. Enrichments in  17O and  18O are  known  for  some  atmospheric  components  and therefore a possible atmospheric effect in these glassy CS with very high  δ18O cannot be entirely ruled out. These  specimens  may  also  be  related  to  two cryptocrystalline  CS with very large  17O enrichments previously reported [11].For the first two families (below the TFL) a posi-tive correlation is found between the value of δ18O and the amount of magnetite determined by magnetic mea-surements. This correlation can be interpreted as a con-trol of both  δ18O value and magnetite formation from primary olivine by the amount of contamination with atmospheric oxygen. The proportion of contamination can be estimated in the 30–70 % range from the  δ18O values of end members (C chondrites and iron oxide spherules).Conclusions:  Oxygen isotope ratios measurements allowed to relate cosmic spherules to at least 3 distinct parent materials: carbonaceous chondrite material, hy-drothermally processed carbonaceous material, and or-dinary chondrite material. Interestingly, texture is not discriminative for BO spherules, as specimens with si-milar  texture  can  be  related  to  any  parent  material (Figure 1A-B); however, all the so far measured spe-cimens with PO textures are related to ordinary chon-drite parent material. Glassy spherules also have a vari-ety of isotopic signa-tures, as they can be related to hy-drothermally  reprocessed  carbonaceous  material  as well as ordinary chon-drite material; furthermore, part of the specimens have a very high  δ18O and positive ∆17O that could indicate another parent material, or be due to an unknown atmospheric effect. Our finding of 30% of spherules above the TFL, while previous stu-dies by ion probe [1,12] found none (or 6% [11]), may be related to the lower precision of the ion probe (e.g. not allowing to decipher the ordinary chondrite related family from the TFL), and/or to a higher proportion of ordinary chondrite related material in our large (>500 µm)  spherules,  that  may  show an  intermediate  pro-portion  between  meteorites  (80%  above  TFL)  and small micrometeorites (0-6% above TFL).References: [1]  Engrand C.,  Maurette  M. (1998)  Meteoritics  & Planet.  Sci.,  33, 565–580.  [2] Rochette  P.,  Folco L., Suavet C., van Ginneken M., Gattacceca J., Perchiazzi N., Braucher R., and Harvey R. P. (2008)  Proc.  Natl.  Acad. Sci. USA, 105, 18206–18211.  [3] Genge M. J., Engrand C., Gounelle M., Taylor S. (2008) Meteoritics  & Planet. Sci., 43, 497–515. [4] Taylor S., Lever J. H., Harvey R. P. (2000)  Meteoritics & Planet. Sci.,  351, 651–666.  [5]  Alexandre  A.,  Sonzogni  C.  Basile  I., Sylvestre F., Parron C., Meunier J.D., Colin F. (2006) Geochim.  Cosmochim.  Acta,  70,  2827-2835.  [6] Crespin J.,  Alexandre A.,  Sylvestre  F.,  Sonzogni  C., Paillès C., Garreta V. (2008)  Anal. Chem., 80, 2372-2378.  [7]  Valley  J.  W.,  Kitchen  N.,  Kohn  M.  J., Niendorf  C.  R.  Spicuzza  M.  J.  (1995)  Geochim. Cosmochim.  Acta,  59,  5223–5231. [8]  Miller  M.  F., Franchi  I.  A.,  Sexton  A.  S.,  Pillinger  C.  T.  (1999) Rapid  Communications  In  Mass  Spectrometry,  13, 1211-1217. [9] Clayton  R.  N.,  Mayeda  T.  K., Brownlee  D.  E.  (1989)  Earth  Planet.  Sci.  Lett.,  79, 235–240. [10] Engrand C., McKeegan K. D., Leshin L. A.,  Herzog  G.  F.,   Schnabel  C.,  Nyquist  L.  E., Brownlee  D.  E.  (2005)  Geochim.  Cosmochim.  Acta,  69, 5365–5385. [11] Yada T., Nakamura T., Noguchi T.,  Matsumoto  N.,  Kusakabe  M.,  Hiyagon  H., Ushikubo  T.,  Sugiura  N.,  Kojima  H.,  Takaoka  N. (2005)  Geochim.  Cosmochim.  Acta,  69, 5789–5804. [12] Matrajt G., Guan Y., Leshin L., Taylor S., Genge M., Joswiak D.,  Brownlee D.  (2006)  Geochim. Cosmochim.  Acta, 70, 4007–4018. [13] Choi B. G., McKeegan K. D., Krot A. N., Wasson J. T. (1998) Nature, 392, 577-579  [14] Franchi I. A., Baker L., Bridges J. C., Wright I.  P.,  Pillinger  C.  T.  (2000)  Phil.  Trans.  Royal  Soc. Series A, 359, 2019-2034.1776.pdf40th Lunar and Planetary Science Conference (2009)

Oxygen isotope ratios of large cosmic spherules: Carbonaceous and ordinary chondrite parent bodies

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Oxygen isotope ratios of large cosmic spherules: Carbonaceous and ordinary chondrite parent bodies

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