KREEPy lunar meteorite Dhofar 287A: A new lunar mare basalt

Abstract

287B) is attached on the side. Dho 287A is only the fourth crystalline mare basalt meteorite found on Earth to date and is the subject of the present study. The basalt consists mainly of phenocrysts of olivine and pyroxene set in a finer-grained matrix, which is composed of elongated pyroxene and plagioclase crystals radiating from a common nucleii. The majority of olivine and pyroxene grains are zoned, from core to rim, in terms of Fe and Mg. Accessory minerals include ilmenite, chromite, ulvöspinel, troilite, and FeNi metal. Chromite is invariably mantled by ulvöspinel. This rock is unusually rich in late-stage mesostasis, composed largely of fayalite, Si-K-Ba-rich glass, fluorapatite, and whitlockite. In texture and mineralogy, Dho 287A is a low-Ti mare basalt, with similarities to Apollo 12 (A-12) and Apollo 15 (A-15) basalts. However, all plagioclase is now present as maskelynite, and its composition is atypical for known low-Ti mare basalts. The Fe to Mn ratios of olivine and pyroxene, the presence of FeNi metal, and the bulk-rock oxygen isotopic ratios, along with several other petrological features, are evidence for the lunar origin for this meteorite. Whole-rock composition further confirms the similarity of Dho 287A with A-12 and A-15 samples but requires possible KREEP assimilation to account for its rare-earth-element (REE) contents. Cooling-rate estimates, based on Fo zonation in olivine, yield values of 0.2-0.8°C/hr for the lava, typical for the center of a 10-20 m thick flow. The recalculated major-element concentrations, after removing 10-15% modal olivine, are comparable to typical A-15 mare basalts. Crystallization modeling of the recalculated Dho 287A bulk-composition yields a reasonable fit between predicted and observed mineral abundances and compositions.

Lunar regolith breccia Dhofar 287B: A record of lunar volcanism

“…Minor quantities of chromite, ilmenite, apatite, silica, FeNi metal, and troilite are also present. Rare fragments of a fayalite + K-rich glass mesostasis, described in Dho 287A (Anand et al 2003a), occur as well.…”

“…Mineral chemistries from the Dho 287A basalt (Anand et al 2003a) are shown in Figs. 3-10 for comparison.…”

“…The main portion (95%) of the stone is a mare basalt (Dhofar 287A); a minor, adjacent portion (~5%) is a regolith breccia (Dhofar 287B). Taylor et al (2001) and Anand et al (2003a) have reported petrology, mineralogy, and chemistry of the Dho 287A basalt. Anand et al (2003a) have demonstrated that Dho 287A is a low-Ti, olivine cumulate, mare basalt, which is highly enriched in late-stage mesostasis.…”

“…Taylor et al (2001) and Anand et al (2003a) have reported petrology, mineralogy, and chemistry of the Dho 287A basalt. Anand et al (2003a) have demonstrated that Dho 287A is a low-Ti, olivine cumulate, mare basalt, which is highly enriched in late-stage mesostasis. Isotopic studies of Sm-Nd and Rb-Sr (Shih et al 2002) have indicated that Dho 287A basalt is of hybrid origin and has an age of 3.46 ± 0.03 Ga.…”

Petrography, mineralogy, and geochemistry of lunar meteorite Sayh al Uhaymir 300

“…Variation in Fo content for olivine in lithic clasts and fragments in SaU 300. (Semenova et al 2000;Anand et al 2002;Nazarov et al 2002;Cahill et al 2004;Takeda et al 2006). These rocks may simply be breccias containing a mixture of both FAN and HMS rocks or represent pristine crustal lithologies (Cahill et al 2004).…”