Mg-spinel lithology: A new rock type on the lunar farside

Abstract

[1] High-resolution compositional data from Moon Mineralogy Mapper (M 3 ) for the Moscoviense region on the lunar farside reveal three unusual, but distinctive, rock types along the inner basin ring. These are designated "OOS" since they are dominated by high concentrations of orthopyroxene, olivine, and Mg-rich spinel, respectively. The OOS occur as small areas, each a few kilometers in size, that are widely separated within the highly feldspathic setting of the basin rim. Although the abundance of plagioclase is not well constrained within the OOS, the mafic mineral content is exceptionally high, and two of the rock types could approach pyroxenite and harzburgite in composition. The third is a new rock type identified on the Moon that is dominated by Mg-rich spinel with no other mafic minerals detectable (<5% pyroxene, olivine). All OOS surfaces are old and undisturbed since basin formation. They are effectively invisible in image data and are only recognized by their distinctive composition identified spectroscopically. The origin of these unusual lithologies appears to be linked to one or more magmatic intrusions into the lower crust, perhaps near the crust-mantle interface. Processes such as fractional crystallization and gravity settling within such intrusions may provide a mechanism for concentrating the mafic components within zones several kilometers in dimension. The OOS are embedded within highly anorthositic material from the lunar crust; they may thus be near contemporaneous with crustal products from the cooling magma ocean.

Active moon: evidences from Chandrayaan-1 and the proposed Indian missions

“…However, it was always found to be associated with mafic minerals. The M 3 data with high spectral resolution and wide spectral coverage identified sites showing Mg-spinel anorthosite (devoid of olivines and pyroxenes and having FeO < 5 wt%) along the rings of Moscoviense basin on the far side of the Moon [54]. These were also found in the central peak of Theophilus crater along the ring of Nectaris basin [55,56].…”

A Survey of Geologic Resources

“…Large concentrations of the mineral spinel have been reported in the inner ring of the Moscoviense Basin by Pieters et al (2010). It was detected using the M 3 instrument aboard Chandrayaan-1.…”

“…; Taylor and Carrier, 1993). Sunshine et al (2010) determined that the spectral signature of two portions of Sinus Aestuum, measured by the Moon Mineralogy Mapper (M 3 ), match the mineral chromite. The chromite mineral signature is dominant in the spectra, although there may be minor amounts of other minerals such as plagioclase, pyroxene, and olivine associated with these deposits, thus physical sampling is required to completely characterize the deposits.…”

Si-Disordering in MgAl2O4-Spinel under High P-T Conditions, with Implications for Si-Mg Disorder in Mg2SiO4-Ringwoodite

“…Coincidently, our synthesizing experiments at 4 GPa and 1500 to 1550 • C (Table 1) plot rather near the P-T locus defined by those heating-up experiments at T ≥ 500 • C (Figure 5a), suggesting that, with a short-distance extrapolation, the x values of the MgAl 2 O 4 -Sp from our experiments at 4 GPa could be accurately estimated. Using the equation shown in Figure 5b, the derived x values are from 0.70 (15) to 0.73 (15); therefore, the true x values should be close to 0.667 (random Mg-Al distribution). In addition, the x values of our synthetic MgAl 2 O 4 -Sp at 5 and 6 GPa should also be~0.667 due to the even higher experimental P and T (Figure 5a).…”