A geochemical reconnaissance of the Alid volcanic center and geothermal system, Danakil depression, Eritrea

Geological and geochemical studies indicate that a high-temperature geother mal system underlies the Alid volcanic center in the northern Danakil depre ssion of Eritrea. Alid is a very late-Pleistocene structural dome formed by shallow intrusion of rhyolitic magma, some of which vented as lavas and py roclastic flows. Fumaroles and boiling pools distributed widely over an are a of similar to 10 km(2) on the northern half of Alid suggest that an activ e hydrothermal system underlies much of that part of the mountain. Geotherm ometers indicate that the fumarolic gases are derived from a geothermal sys tem with temperatures >225 degrees C, The isotopic composition of condensed fumarolic steam is consistent with these temperatures and implies that the source water is derived primarily from either lowland meteoric waters or f ossil Red Sea water, or both. Some gases vented from the system (CO2, H2S a nd He) are largely magmatic in origin. Permeability beneath the volcanic ce nter may be high, given the amount of intrusion-related deformation and the active normal faulting within the Danakil depression. Published by Elsevie r Science Ltd on behalf of CNR. All rights reserved.