Lithologic, Hydrothermal Alteration and Structural Mapping of Okemesi Folds and Environs Using LandSat 8 OLI and ASTER DEM
Ayo A. Omitogun
University of Ibadan, Nigeria
John O. Ogbole *
National Center for Remote Sensing, Jos, Nigeria
*Author to whom correspondence should be addressed.
Abstract
Structural and tectonic studies of an area, help in the understanding of the magmatism, metallogeny, groundwater, seismicity, geothermal and hydrothermal resources of the region. The Precambrian rocks of Okemesi folds and its environs exhibit multiple deformations, repetitive folding, fracturing and metamorphism. LandSat data have been used widely in mapping lithological and altered rocks in geology. Several Red–Green–Blue colour combination images and specialized band ratios, prepared from Landsat-8 bands coupled with Band ratios derived from image spectra, helped in delineation of altered rocks, lithological units and vegetation. Aerial photographs have limitations because of their dependence on natural east-west solar illumination paths which highlight north-south linear features, perpendicular to the solar illumination; therefore hillshade generated from digital elevation models (DEMs) are an alternative source for identification of lineaments. In this research, a procedure for extracting lineaments from hillshaded ASTER DEM was applied; the results of this study illustrate the effectiveness of extracting lineaments from hillshaded DEMs. The final interpreted lineament map was then produced with a total of about 178 lineaments extracted from the ASTER DEM. The azimuthal distribution indicated that most of the lineaments are trending to NE-SW and NNE-SSW with a few E-W and NNW-SSE directions. These directions are distributed throughout the Okemesi fold axis and on most of the rock complexes.
Keywords: Lithologic, hydrothermal alteration and structural mapping, LandSat 8 OLI and ASTER DEM