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Publication Detail
MicroRaman spectroscopy of diamond and graphite in Almahata Sitta and comparison with other ureilites
  • Publication Type:
    Journal article
  • Publication Sub Type:
    Article
  • Authors:
    Ross AJ, Steele A, Fries MD, Kater L, Downes H, Jones AP, Smith CL, Jenniskens PM, Zolensky ME, Shaddad MH
  • Publisher:
    WILEY-BLACKWELL
  • Publication date:
    03/2011
  • Pagination:
    364, 378
  • Journal:
    METEORIT PLANET SCI
  • Volume:
    46
  • Issue:
    3
  • Print ISSN:
    1086-9379
  • Language:
    EN
  • Keywords:
    CHEMICAL-VAPOR-DEPOSITION, X-RAY-DIFFRACTION, RAMAN-SPECTROSCOPY, HEXAGONAL DIAMOND, NOBLE-GAS, GROWTH DIAMONDS, RIES CRATER, THIN-FILMS, ORIGIN, SHOCK
  • Addresses:
    Ross, AJ
    UCL Birkbeck Res Sch Earth Sci
    Ctr Planetary Sci
    London
    WC1E 6BT
    England

    CALTECH
    Jet Prop Lab
    Pasadena
    CA
    91109
    USA

    Univ Glasgow
    Dept Geog & Earth Sci
    Glasgow
    G12 8QQ
    Lanark
    Scotland
Abstract
This work is the first detailed study of carbon phases in the ureilite Almahata Sitta (sample #7). We present microRaman data for diamond and graphite in Almahata Sitta, seven unbrecciated ureilites, and two brecciated ureilites. Diamond in Almahata Sitta was found to be distinct from that in unbrecciated and brecciated ureilites, although diamond in unbrecciated and brecciated ureilites is indistinguishable. Almahata Sitta diamond shows a peak center range of 1318.5-1330.2 cm-1 and a full width at half maximum (FWHM) range of 6.6-17.4 cm-1, representing a shock pressure of at least 60 kbar. The actual peak shock pressure may be higher than this due to postshock annealing, if shock synthesis is the source of ureilite diamonds. Diamond in unbrecciated and brecciated ureilites have peak center wave numbers closer to terrestrial kimberlite diamond, but show a wider range of FWHM than Almahata Sitta. The larger peak shift observed in Almahata Sitta may indicate the presence of lonsdaleite. Alternatively, the lower values in brecciated ureilites may be evidence of an annealing step either following the initial diamond-generating shock or as a consequence of heating during reconsolidation of the breccia. Graphite in Almahata Sitta shows a G-band peak center range of 1569.1-1577.1 cm-1 and a G-band FWHM range of 24.3-41.6 cm-1 representing a formation temperature of 990 +/- 120 degrees C. Amorphous carbon was also found. We examine the different theories for diamond formation in ureilites, such as chemical vapor deposition and shock origin from graphite, and explore explanations for the differences between Almahata Sitta and other ureilites.
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