Abstract
This paper aims to utilize the ASTER data for lithologic discrimination and to evaluate the panchromatic Landsat data (band 8 with resolution 15m) for automatic lineaments extraction and analysis over the Neoproterozoic basement rocks of Arafat Area, Makkah Al-Mukarama, Western Arabian Shield, Saudi Arabia. Field geology and structural mapping of the basement rocks covering the area around the Holy Arafat revealed the presence of the following main units, arranged based on their field relations from the oldest: diorites, granodiorites (locally sheared) perthitic leucogranites, and post-tectonic granites. With the exception of the variable degrees of shearing exhibited by the granodiorites, the other rock units are generally massive, non-deformed and pervasively jointed. The major structure in the area is a horseshoe or domal-like structure, delineated by the huge mountainous granodioritic chain of Jabal Kabkab, which is remarkably sheared in its outermost zone. In the inner core, isolated very low exposures of perthitic leucogranites, exhibit sharp intrusive contact with Jabal Kabkab granodiorite.
Three different false color composite images of ASTER data (FCC 4, 5 and 7 in RGB image, MNF image and band ratios image) were generated and evaluated for lithological mapping. A false color composite ratios image of ASTER data (6/8:R; 4/8:G and 11/14:B) was generated and used for production of a 1: 100 000 geological map for the study area. Massive sheared granodiorites and diorites have light and dark grey image signatures respectively on the 4/8 band ratio image. Post-tectonic granites and acidic dykes have a dark grey image signature on the 6/8 band ratio image. The alteration products of hornblende, biotite, and plagioclases (chlorite, serricite, and clay minerals) may be responsible for the absorption features near the 1.65 mu m and 2.35 mu m regions. On the TIR band ratio image 11/14 of ASTER data, diorite, granodiorite, and post-tectonic granites have bright, grey, and dark image signatures respectively, which may be attributed to the different response of these units to emissivity.
Throughout this study, panchromatic Landsat band-8 was used for automatic lineaments extraction under User-defined parameters within PCI GeoAnalyst software. The extracted lineament trends are E-W (ENE), N-S (NNW) and NE-SW Constituting 31.4%, 30.0%, and 26.1%, respectively. NW-SE as subordinate direction constitutes 12.5% of the total number of lineaments. Field studies reveal that the most Conspicuous structural fabric elements in the area are faults and a horseshoe structure. The majority of faults exhibit strike-slip sense of shear. They are generally arranged in a radial pattern, although the most prominent trends are: ENE-WSW (to E-W) and NNW-SSE (to N-S). It is suggested that these faults are genetically-related to the forceful emplacement of granodioritic intrusion and the stress trajectories associated with horseshoe- or domal-like structure with circular cross-section.