Exploring the Mineralogical Diversity of Hed Meteorites with Microimaging Vswir Spectroscopy

Introduction: We used visible-short wavelength infrared (VSWIR) imaging spectroscopy to survey the spectral diversity of the howardite, eucrite, and diogenite (HED) meteorite suite at 80-μm/pixel spatial scale. This group of meteorites is widely believed to originate from the asteroid Vesta. Our goal in this work is to contribute to understanding the petrologic diversity of the HED suite and the evolution of Vesta by (1) resolving spectral end members – i.e., spectra of the mineral constituents of Vesta— for use in interpretation of infrared remote sensing data from the Dawn spacecraft, (2) locating rare phases that can be examined using detailed analytical techniques, and (3) nondestructively and rapidly classifying large numbers of meteorites, including estimating their modal mineralogy within a petrographic context. Here we focus on results from (1). Methods: We analyzed 11 howardite, 8 eucrite, and 9 diogenite fragments using JPL’s Ultra-Compact Imaging Spectrometer (UCIS) (Fig. 1) [1]. In microimaging mode, UCIS collects spectra from samples at 81 μm/pixel across 213 discrete wavelengths from 0.5 – 2.5 μm. Meteorite samples were provided by the ASU Center for Meteorite Studies, the Caltech mineral collection, Y. Liu, and G. Rossman. An initial assessment of sample spectral diversity was performed both manually and with a variety of near-automated techniques available in the ENVI software package [2]. These techniques included using a minimum-noise fraction (MNF) transformation to reduce random spectral noise, N-dimensional visualization to locate spectral endmembers within a scene, spectral angle mapping to classify an image using given endmembers, and spectral parameter mapping. Spectral diversity: We identify four major classes of materials based on VSWIR absorptions that identify pyroxenes, olivines, Fe-bearing feldspars, and glassbearing/featureless materials (Fig. 2). These identifications were validated in select spots in samples NWA 1769 (both fragments), and NWA 6920 using SEM/EDS point analyses. Pyroxene: Pyroxene is characterized by a pair of broad absorptions centered near 1 and 2 μm caused by Fe in the M1 and M2 sites of the pyroxene crystal structure and referred to as band 1 (B1) and band 2 (BII) (Fig. 2). Most pixels showed pyroxene spectral