Constraints on Mapping Source Regions of Martian Meteorites and the Distribution of Pyroxene on Mars: Ir Microspectroscopy of Pyroxene in Shergottites

Introduction: The surface mineralogy of Mars is constrained by spectral and chemical data from orbiters and landers. One technique for determining lithologies is thermal emission spec-troscopy. Virtually the entire surface of Mars has been mapped using either the TES [1] or THEMIS [2] instruments and the Mini-TES has made in situ measurements [e.g. 3]. These data have been used to try and find source regions of Martian meteor-ites[e.g. 4]. Other studies have shown that pigeonite is the dominant low-Ca pyroxene in Mars [5,6]. Pigeonite is important in shergottites and on the surface of mars. At present, there is only one pigeonite spectrum in the ASU spectral library [7]. Microspectroscopy [e.g., 8] allows expansion of databases to include minerals for which it is difficult to obtain physical separates , but which are accessible in meteorite thin sections. Preliminary spectral measurements [9,10] using an infrared microscope attached to a benchtop FT-IR examined chips or thick sections of meteorites or terrestrial rocks. Using a similar system, we measured Martian meteorite pyroxene in thin section [11]. Samples and Analytical Techniques: Bi-directional reflec-tance spectra from 2.5 to 14 µm of pyroxenes in thin sections of Zagami and Los Angeles were acquired using a Perkin Elmer AutoIMAGE FT-IR microscope attached to the SpectrumOne FT-IR spectrometer (aperture = 25 µm; spectral resolution = 4cm