Digital classification of the contact metamorphic aureole along the Los Pedroches batholith, south - central Spain, using LANDSAT thematic mapper data

Visible and near-infrared laboratory reflectance spectra of soils sampled over the southern contact metamorphic aureole of the Los Pedroches granodiorite north of Cordoba in the southern-central part of the Iberian Peninsula are characterized in terms of relative albedo, depth, width, asymmetry, and wavelength position of absorption features. A decrease in albedo and relative depth of the Al-OH absorption feature (near 2.2μm), the H20 feature (near 1.9μm), and the OH feature (near 1.4μm) is observed with distance to the contact metamorphic domain. This effect is attributed to spectra quenching related to the absorbing capacity of finely disseminated carbonaceous material in soils which opacity increases with increasing temperature related to metamor-phism. Fe+2 and Fe+3 cause absorption features near l.0μm. 0.55μm, and 0.46 μm and also, a decrease of reflectivity in the 0.8-0.4μm wavelength region. These absorption features, however, are unaffected by the amount of carbonaceous material. Landsat-TM images were used for mapping variations in iron, water, and hydroxyl absorption features over the contact zone using ratio and normalized difTerence images with TM-3:1 for Fe and TM-5:7 for H20. TM-5 was added as blue component in a colour ratio component image mapping the effect of spectral quenching. Ratios enhanced the spectral variability between individual bands resulting in correlation coefficients of the order of (plus or minus) 0-2.