The geology and geochronology of Al Wahbah maar crater, Harrat Kishb, Saudi Arabia

Abstract

Al Wahbah is a large (~2.2 km diameter, ~250 m deep) maar crater in the Harrat Kishb volcanic field in western Saudi Arabia. It cuts Proterozoic basement rocks and two Quaternary basanite lava flows, and is rimmed with an eroded tuff ring of debris from the phreatomagmatic explosion that generated the crater. A scoria cone on the northern wall of the crater was dissected by the explosion and exposes a dolerite plug that was intruded immediately prior to crater formation. The dolerite plug yields a 40 Ar/ 39 Ar age of 1.147 ± 0.004 Ma. This is the best possible estimate of the time Al Wahbah crater formed. It is a few tens of thousand years younger than the age of the lower and upper basalt flows, 1.261 ± 0.021 Ma and 1.178 ± 0.007 Ma respectively. A dolerite dyke exposed within the basement in the wall of the crater is dated at 1.886 ± 0.008 Ma. This is the most precise age so far determined for the initiation of basaltic volcanism of Harrat Kishb, and confirms that it is significantly younger than the other post-rift volcanic provinces in the region. This study provides constrains the timing of humid climatic conditions in the region and suggests that the Quaternary basaltic volcanism that stretches the length of the western side of the Arabian peninsula may prove to be useful for establishing palaeoclimatic conditions.

Geoheritage values of one of the largest maar craters in the Arabian Peninsula: the Al Wahbah Crater and other volcanoes (Harrat Kishb, Saudi Arabia)

“…Along the crater wall localized lava spatter deposits overly lava flows, indicating that prior to crater formation Hawaiian lava fountaining occurred along the vents that likely followed a fissure alignment of roughly NW-SE. Recently obtained Ar/Ar geochronology has also confirmed that the pre-maar scoria cone (1.147 +/-0.004 Ma) is slightly younger than the underlying lava flow sheets (1.261 +/-0.021 Ma -1,178 +/-0.007 Ma) [38]. This new geochronology gives the formation of Al Wahbah maar the minimum age of 1.147 +/-0.004 Ma and clearly separates it from the uppermost pre-maar lava flow emplacement period [38].…”

“…Recently obtained Ar/Ar geochronology has also confirmed that the pre-maar scoria cone (1.147 +/-0.004 Ma) is slightly younger than the underlying lava flow sheets (1.261 +/-0.021 Ma -1,178 +/-0.007 Ma) [38]. This new geochronology gives the formation of Al Wahbah maar the minimum age of 1.147 +/-0.004 Ma and clearly separates it from the uppermost pre-maar lava flow emplacement period [38]. While the chronological order of events seems to be correct, the geological evidence demonstrates that the uppermost part of the pre-maar lava flow units is in close genetic relationship with the pre-maar scoria cone.…”

Niche for high abundant extremophilic microbial communities in an ancient crater

“…Although this unique geotope resulted in different geological components in terms of time and age, the age of the crater is still not known. However, as per the calculation of age using the yield 40 Ar/ 39 Ar, dolerite plug of 1.147 ± 0.004 Ma, lower basalt flows, 1.261 ± 0.021 Ma and upper basalt flows 1.178 ± 0.007 Ma (AbdelWahab et al 2014). But age of 1.147 ± 0.004 Ma is the best estimation time of Al Wahbah crater formed.…”

“…Al Wahbah Mountain is 1105 m above sea level. Very few geological studies on Al Wahbah crater have been conducted (Grainger 1996;Moufti et al 2013;AbdelWahab et al 2014); however, all of them agreed that the crater was formed by explosive eruptions or volcanic explosions as a result of the interaction between magma and groundwater. Continuous volcanic eruptions resulted in phreatic activities that led to deposition of rocks, lava and debris around the crater and created multiple lava flows, the tuff ring, tephra ring, basement, dolerite plug, scoria cones and wall.…”

“…But age of 1.147 ± 0.004 Ma is the best estimation time of Al Wahbah crater formed. The present study focused on the flat floored crater that hosts an ephemeral lake (Grainger 1996;Moufti et al 2013;AbdelWahab et al 2014). This location is occasionally exposed to heavy rainfall (32 mm max.…”