A new Martian meteorite from Oman: Mineralogy, petrology, and shock metamorphism of olivine-phyric basaltic shergottite Sayh al Uhaymir 150

Authors: Walton, E.L.; Spray, J.G.; Bartoschewitz, R.

Source: Meteoritics & Planetary Science, Volume 40, Issue 8, Pages 1123-1272 (August 2005) , pp. 1195-1214(20)

Publisher: Arizona Board of Regents (University of Arizona)

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Abstract:

The Sayh al Uhaymir (SaU) 150 meteorite was found on a gravel plateau, 43.3 km south of Ghaba, Oman, on October 8, 2002. Oxygen isotope (δ17O 2.78; δ18O 4.74), CRE age (∼1.3 Ma), and noble gas studies confirm its Martian origin. SaU 150 is classified as an olivine-phyric basalt, having a porphyritic texture with olivine macrocrysts set in a finer-grained matrix of pigeonite and interstitial maskelynite, with minor augite, spinel, ilmenite, merrillite, pyrrhotite, pentlandite, and secondary (terrestrial) calcite and iron oxides. The bulk rock composition, in particular mg (68) [molar Mg/(Mg + Fe) × 100], Fe/Mn (37.9), and Na/Al (0.22), are characteristic of Martian meteorites.

Based on mineral compositions, cooling rates determined from crystal morphology, and crystal size distribution, it is deduced that the parent magma formed in a steady-state growth regime (magma chamber) that cooled at <2 °C/hr. Subsequent eruption as a thick lava flow or hypabyssal intrusion entrained a small fraction of xenocrystic olivine and gave rise to a magmatic foliation, with slow cooling allowing for near homogenization of igneous minerals.

SaU 150 experienced an equilibration shock pressure of 33–45 GPa in a single impact event. Post-shock heat gave rise to localized melting (∼11 vol%). Larger volume melts remained fluid after pressure release and crystallized dendritic olivine and pyroxene with fractal dimensions of 1.80–1.89 and 1.89–1.95, respectively, at −ΔT >70–365 °C.

SaU 150 is essentially identical to SaU 005/094, all representing samples of the same fall that are similar to, but distinct from, the DaG shergottites.

Document Type: Research article

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