Abstract
Al Taif area is located in the central western portion of the Arabian Shield, Saudi Arabia. The area was a part of a geosyncline, in which sediments were deposited, followed by granitic and dioritic intrusions. During the Hijaz orogeny (650-800Ma), the area was subjected to a progressive regional metamorphism to lower amphibolite facies which produced chlorite schists and micaceous quartzofeldspat hic schists. This metamorphism also affected the igneous rocks to produce gneissic granite and metadiorite. The metamorphism was followed by the intrusion of other granitic plutons (490600 Ma). This work aimed to discriminate the lithologic rock units and structural framework of the study area in order to map the geology of Al Taif area. The study area was not subjected previously to detailed geological mapping using the modern image processing techniques. However, it was subjected only to reconnaissance geological mapping. The study area was geologically remapped in this work through image processing techniques of Landsat 7 Enhanced Thematic Mapper (ETM)+ digital data and field verifications. The fusion between multispectral ETM+ data and panchromatic ETM+ band 8 produced a color composite fused image for the study area of scale 1: 50,000. The fused image was delineated the main regional folds, faults, and fractures of the study area. It was also defined and recognized the chlorite schist and the intrudedmonzogranitic rocks. The processed Landsat ratio image and supervised classification map discriminated the most lithologic units of the study area. The results of this work produced detailed and accurate geological map of scale 1: 50,000 for the investigated area.