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

Faculty Advisor

Date

2005

Keywords

Martian meteorites, shock metamorphism, fractal analysis, crystal size distribution

Abstract (summary)

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.

Publication Information

Walton, E. L., Spray, J. G., & Bartoschewitz, R. R. (2005). A new Martian meteorite from Oman: Mineralogy, petrology, and shock metamorphism of olivine-phyric basaltic shergottite Sayh al Uhaymir 150. Meteoritics & Planetary Science, 40(8), 1195-1214. doi: 10.1111/j.1945-5100.2005.tb00184.x

Notes

Item Type

Article

Language

English

Rights

All Rights Reserved