GEOCHEMICAL STUDY OF THE ALID HYDROTHERMAL SYSTEM, DANAKIL DEPRESSION, ERITREA

Abstract

Detailed geological studies indicate that a relatively young, large, shallow, and still hot magmatic heat source is probably present beneath the Alid volcanic center in the northern Danakil Depression of Eritrea. Fumaroles and boiling pools are distributed widely on the north half of Alid, suggesting that an active hydrothermal system underlies much of that part of the mountain. The area of high convective heat flow covers at least 10 square kilometers. Gas geothermometers indicate likely reservoir temperatures in the range 250?C - 325?C. The isotopic composition of condensed fumarolic steam is consistent with 220-300?C boiling of groundwaters that may have come from various sources, including local lowland rain, fossil Red Sea water, or conceivably, highland rain water that evaporated significantly before percolating underground. Some gases in the reservoir fluid, particularly C02, H2, and H2S may be derived, directly or indirectly, from a silicic intrusion that very likely exists beneath Alid.