LITHOLOGIC CONSTRAINTS ON THE HYDROLOGICAL PARAMETERS OF REGIONAL AQUIFERS IN THE IBB PROVINCE, WEST-CENTRAL REGION OF YEMEN (MIDDLE EAST)

The lithology of the Ibb Province Yemen (Middle East) consists of Precambrian gneissic bedrocks with post-tectonic intrusions of granite and granodiorite. The overall topography is dominated by extensive volcanic extrusions that randomly surround Ibb Province with minimal Mesozoic sedimentary outcrops. According to the Yemen Geological Survey and Mineral Resource Board (YGSMRB), the origin and age of such extrusive bodies that manifest on the surface as dikes, lava flows, and small (currently passive) cinder-cone volcanoes are of Cenozoic age associated with the rifting episode of the Arabian Peninsula and subsequent opening of the Red Sea. The overall aerial extension of the volcanic extrusions diminishes further east towards Hammam-Damt (Al’Dali Province) with a noticeable shift in magma composition from basaltic to rhyolitic. The regional aquifer, a vital source of drinking water, seems to possess similar hydrogeological properties across the Province. However, physical surveys of watersheds, stream patterns, passive pumping stations, and active freshwater wells suggest that unlike rhyolitic rocks, Basaltic rocks are non-vesicular type, dense and having no apparent hydraulic conductivity and in view of these unique lithological characteristics, do not promote groundwater recharge. Also considering extensional geomorphic control on the drainage pattern, it is possible that investigated drainages are fault or structure-controlled and provide a significant constraint on groundwater flow. Therefore, an assessment of such a geomorphological disadvantage was conducted by correlating with terrain geomorphology, bedrock composition, stream patterns, and hydrologic conductivity observed in water wells.