Thermal infrared emission spectroscopy of titanium-enriched pyroxenes

Abstract

Pyroxenes are useful indicators of igneous processes and may be identified in geologic materials in the laboratory or remotely through the use of spectroscopic analysis. Studies of the thermal infrared (vibrational) spectra of many compositions in the pyroxene solid solution series (quadrilateral orthopyroxene and clinopyroxene, and some nonquadrilateral compositions) have shown that spectral absorption features shift in wavelength position, vary in number, and change shape as a function of pyroxene silicate structure and cation substitution. These spectral variations can be used to identify the approximate composition(s) of pyroxenes in the thermal infrared emission spectra of rocks. Here I demonstrate that the spectra of Ti-rich calcic clinopyroxenes also have thermal infrared spectral characteristics that distinguish them from typical quadrilateral compositions via a comparison to the spectrum of Angra dos Reis, a meteorite dominated by Ti-enriched clinopyroxene. The distinctive spectral character of Ti-rich pyroxenes may permit their identification not only in laboratory mineral and rock samples but also in thermal infrared remote sensing data, providing additional chemical information about igneous lithologies.