DHOFAR 732


Achondrite, ungrouped
Olivine-orthopyroxenite
(possibly winonaite-related
)
standby for dhofar 732 photo
Found November 15, 2002
19° 24.3' N., 54° 34.7' E.

A single moderately weathered meteorite weighing 17 g was found in the Dhofar region of Oman. Dhofar 732 was classified at the Vernadsky Institute, Russia (S. Demidova) and the Naturhistorisches Museum, Austria (G. Kurat) as an ungrouped achondrite. Dhofar 732 is an olivine orthopyroxenite petrographically similar to the aubrites, diogenites, and the unique martian ALH 84001, but it is unlike any of these orthopyroxenite meteorites in its mineralogical, chemical, and O-isotopic compositions. It is composed of 68 vol% lath-shaped orthopyroxene grains (enstatite, up to 0.8 mm), 16 vol% olivine grains (up to 0.3 mm), and 16 vol% mesostasis (consisting of Ca–Al-rich, Na-poor glass, Cr–Al–Ti-rich clinopyroxene [augite], and silica). Accessory chromite, troilite, and FeNi-metal are also present. The rock contains abundant round voids throughout. The very low Fe/Mn value of orthopyroxene distinguishes Dhofar 732 from diogenites, including Dhofar 700 which was found in the same vicinity on the same day.

Greenwood et al. (2007) report that O-isotope and mineralogical data suggest a possible relationship might exist between Dhofar 732 and winonaites, as it plots along an extension of the trend line of the silicate component of the winonaite–IAB iron complex meteorites (see diagram below).

standby for o-isotopic diagram
Diagram credit: Greenwood et al., Chemie der Erde, vol. 77, p. 23 (2017)
'Melting and differentiation of early-formed asteroids: The perspective from high precision oxygen isotope studies'
(open access: http://dx.doi.org/10.1016/j.chemer.2016.09.005)

However, the low Na content of Dhofar 732 cannot be reconciled with this or any other known meteorite groups. It was suggested by Demidova et al. (2004) that this meteorite could represent a cumulate that was derived from a melt source initially accreted from isolated forsterite and enstatite grains, components which have been identified in some CM and CR chondrites. Indeed, O-isotopic ratios similar to those in Dhofar 732 have been established for CR chondrites as well. The specimen shown above is a small 8 mg partial slice of Dhofar 732. The photo below shows the main mass of this meteorite in situ.

standby for dhofar 732 photo
Photo courtesy of Serge Afanasiev