HR: 1340h
AN: P13D-1553    [Abstracts]
TI: Spatial and Compositional Variations of Olivine in Terra Tyrrhena, Mars
AU: * Koeppen, W C
EM: koeppen@higp.hawaii.edu
AF: University of Hawaii at Manoa, Hawaii Institute for Geophysics and Planetology, 1680 East- West Road, POST 504, Honolulu, HI 96822,
AU: Hamilton, V E
EM: hamilton@higp.hawaii.edu
AF: University of Hawaii at Manoa, Hawaii Institute for Geophysics and Planetology, 1680 East- West Road, POST 504, Honolulu, HI 96822,
AB: Global modeling of thermal and VIS/NIR spectra of the Martian highlands reveal that many materials contain 10 - 20% olivine that spans a relatively large range of Mg/Fe contents (forsterite numbers 100 - 35). We examine the olivine-bearing locales in Terra Tyrrhena using TES-derived mineralogies, spectral variation maps made from THEMIS IR images, THEMIS and MOC visible images, MOLA topographic profiles, and geologic maps. Basaltic materials containing up to 20% forsteritic olivine (>Fo₈₅) are exposed in knobs and craters near the Hellas rim (71E, 24S); the stratigraphic layer is >550 meters thick and may represent very thick, olivine- bearing flows or the base of an exhumed pluton. Mg-rich (Fo₇₀) olivine is ubiquitous throughout Terra Tyrrhena, but locally high abundances occur in crater ejecta and alluvial fans that spill into craters. This suggests that Mg-rich olivine is a common component of the Martian crust that is in situ primarily in the subsurface, and this composition of olivine is commonly brought to the surface by exhumation via craters. Olivine-bearing materials with intermediate compositions (Fo₅₀) are distributed within flat-lying intercrater flows that embay eroded ridges and knobs. The flows appear younger relative to the Noachian terrain, though they have also been subsequently eroded. Intermediate compositions predominantly occur closer to Syrtis Major, but also appear in small locations near the Hellas rim. Fe-rich olivine (<Fo₄₀) is uncommon in Terra Tyrrhena and is confined to flat-floored craters that are filled with lava or sediments. Fe-rich olivine also commonly occurs in conjunction with more Mg-rich olivine compositions and may represent the spectral modeling of intermediate compositions, zoning within olivine, or Fe-rich groundmass in the basalts of Terra Tyrrhena. Our results suggest that many Mg-rich compositions of olivine occurring in Terra Tyrrhena today may have formed very early in the Noachian and survived weathering during early wet periods by residing in the subsurface. Intermediate and Fe-rich compositions are in place, younger (late Noachian or later), and may have never seen water at the Martian surface.
DE: 5410 Composition (1060, 3672)
DE: 5464 Remote sensing
DE: 5470 Surface materials and properties
DE: 6225 Mars
SC: Planetary Sciences [P]
MN: 2007 Fall Meeting