Differences in the degree of weathering between Antarctic and non-Antarctic meteorites inferred from infrared diffuse reflectance spectra

Abstract

Infrared diffuse reflectance spectra were measured for Antarctic and non-Antarctic meteorites to compare the degree of terrestrial weathering by using the integrated intensity of absorption bands near 3 μm caused by hydrous minerals and the intensity of absorption bands near 7.4 μm (1350 cm −1) probably caused by hydrous carbonates. Non-Antarctic ordinary chondrite finds usually show large values of the integrated intensity of the 3 μm band, whereas non-Antarctic ordinary chondrite falls show small intensities. Some Antarctic ordinary chondrites are as fresh as non-Antarctic ordinary chondrite falls in the sense of the integrated intensity of the 3 μm band. Some Antarctic eucrites show large values of the integrated intensity of the 3 μm band, although the degree of weathering on the A-B-C scale is reported to be A. Weathering-produced hydrous carbonates seem to be ubiquitous in Antarctic ordinary chondrites, because the spectra of all the Antarctic ordinary chondrites measured show the presence of the 7.4 μm band. Non-Antarctic ordinary chondrite falls show very weak 7.4 μm bands, suggesting only little weatheringproduced hydrous carbonates. Diffuse reflectance spectra were also measured for the mixtures of akaganeite. goethite, artinite, or calcite with the Nuevo Mercurio (H5) ordinary chondrite to examine spectral changes and to compare them with those of meteorites. Absorption bands near 7 μm of diffuse reflectance spectra are sensitive to the presence of carbonates.