The spectral characteristics and remote detection of lunar Mg-spinel: A case study of Tycho Crater

Abstract

Mg-spinel is often regarded as a specific deep-seated lunar mineral excavated onto the surface by giant impacts. The investigations of spinel would provide key compositional information of lunar lower crust or even mantle, thus is meaningful for the study of lunar petrogenesis and crustal evolution. This work overviews the recent progresses of lunar Mg-spinels studies by both remote sensing and laboratory methods. Based on radiative transfer model, a series of mixtures of spinel and other mafic minerals are built, from which we find a quadratic correlation between logarithm spinel content and band ratio parameters. A spinel-pyroxene mixture model is established to quantify the spinel content based on this correlation. We apply this model to the spinel-pyroxene spectra detected by Moon Mineralogy Mapper (M3) data for Tycho Crater, yielding a result that the spinel content only takes up 5.4vol%– 6.4vol% out of the spinel-pyroxene mixture. This result is consistent with those from lunar sample studies. We also find that these kinds of spinel-pyroxene mixtures occur without any olivine observed, indicating that they may be originated from the lower crust, while the olivine mineral detected around the wall of Tycho Crater may be originated from shallow plutonic magma intrusion.