| Title | A Geological and Geochemical Reconnaissance of the Alid Volcanic Center, Eritrea, East Africa |
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| Authors | Michael A. Clynne, Wendell A. Duffield, Robert O. Fournier, L. Woldegiorgis, Cathy J. Janik, G. Kahsai, Jacob Lowenstern, K. Weldemariam, James G. Smith and T. Tesfai |
| Year | 2005 |
| Conference | World Geothermal Congress |
| Keywords | Alid, Fumaroles, Danakil Depression, Volcanism, Eritrea |
| Abstract | Alid volcanic center is a 700-metre tall mountain in Eritrea, northeast Africa. This mountain straddles the axis of an active crustal spreading center called Danakil Depression. Though volcanism associated with this crustal spreading is predominantly basaltic, centers of silicic volcanism, including Alid, are locally present. Young silicic centers imply the recent intrusion of silicic magma to a relatively shallow depth in the crust and thus a possible shallow potent heat source for a hydrothermal convection system. Boiling temperature fumaroles are common on Alid, and their gas compositions indicate a reservoir temperature of at least 250 degree centigrade. Alid is a 7-km x 5-km structural dome. The domed rocks, in decreasing age are Precambrian schist, a sequence of intercalated sedimentary rocks and basaltic lavas, and a sequence of basaltic and rhyolite lava flows. Doming was likely caused by intrusion of relatively low-density silicic magma into the upper crust. Subsequent to dome formation, a substantial volume of pyroxene rhyolite magma erupted from a vent near the west end of the summit area of the dome. This eruption produced a blanket of rhyolite pumice over most, if not all, of the dome and fed pyroclastic flows that covered part of the Danakil Depression around the base of the dome. The pumice deposits contain abundant inclusions of granophyric, miarolitic pyroxene granite, chemically indistinguishable from the host pumice. This granite likely represents the uppermost part of the magma reservoir, which crystallized just prior to the pumice eruption. The most recent volcanism near Alid was eruption of basalt lava flows from vents on the floor of the Depression, just north and south of the Dome. The history of volcanism and high reservoir temperature indicated by fumarole gases on Alid suggest that a geothermal resource of electrical grade lies beneath the mountain. Though drilling is needed to determine subsurface condition, the process of dome formation and the ongoing crustal spreading probably create and maintain fracture permeability on the hydrothermal system that feeds the Alid fumaroles. |