Mathematics – Logic
Scientific paper
Dec 2009
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2009agufm.p23b1248i&link_type=abstract
American Geophysical Union, Fall Meeting 2009, abstract #P23B-1248
Mathematics
Logic
[5410] Planetary Sciences: Solid Surface Planets / Composition, [6250] Planetary Sciences: Solar System Objects / Moon
Scientific paper
The Moon Mineralogy Mapper (M3) is a guest instrument on Chandrayaan-1, India’s first mission to the Moon. M3 is an imaging spectrometer covering the wavelength range of 430 nm - 3000 nm, and was designed to map the mineralogy of the lunar surface. The high spectral resolution of M3 enables the diagnostic absorption features of lunar minerals to be identified clearly, while the high spatial resolution of M3 allows the identification and mapping of distinct lithologic units. Olivine is an important mineral with which to interpret the petrologic evolution of igneous rocks. The composition of olivine (Mg#) is used to indicate the degree of evolution of the source magma from which a sample crystallized. Visible to near-infrared reflectance spectroscopy is sensitive to the Mg# of olivine, as the diagnostic olivine absorption features shift in response to changing major element abundances (Mg and Fe) content. These changes in diagnostic absorption features can be detected by modeling the individual absorption bands with the Modified Gaussian Model (MGM). Spectra of lunar olivines differ from spectra of their terrestrial and synthetic counterparts due to the inclusions of Cr-spinel common to lunar olivines; however, analysis of lunar olivine mineral separates in terrestrial laboratories and modeling of the resulting reflectance spectra have been able to unravel the chromite effects on the olivine spectrum. Previous efforts at remote compositional analysis of lunar olivine have been limited by spectral resolution and coverage or by spatial resolution. However, the spatial and spectral resolution provided by M3 enable olivine composition to be determined remotely in a spatial context. We are in the process of identifying olivine-bearing lithologies on the lunar farside and analyzing the olivine composition with the modified MGM approach. Initial compositional analyses have been completed for a crater on the rim of the Moscoviense basin that appears to be largely dominated by olivine and relatively free from other optically active mafic phases such as pyroxene. Significant occurrences of other rocks dominated optically by olivine (e.g., troctolites) have been identified elsewhere around the basin. Olivine-dominated rocks in the lunar sample collection almost certainly formed through secondary magmatic processes following crystallization of the lunar magma ocean (the so-called “Mg-suite”). It is possible that similar processes produced the olivine-dominated lithologies around Moscoviense, although the scale of the intrusion required would likely be quite large. It is also possible that the Moscoviense impact event scattered locally-occurring olivine-rich rocks over the broad area observed. Preliminary compositional analysis results range from ~Fo50 to ~Fo75, broadly consistent with olivine compositions found in analyses of feldspathic lunar meteorites (likely to originate from the Feldspathic Highlands Terrane on the farside), as well as with olivines found in Apollo 16 troctolites.
Clark Roger Nelson
Head James W.
Isaacson Peter
Klima Rachel
Petro Noah E.
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