| Abstract |
The Northern Lake Abaya area located in the southern part urlhe Main I:lhiopian Rill (i1I1{) encloses a variety of manifestations that indicatc the exislelKc ur ccollomically exploitahle geothermal resources. Tertiary volcanic sllcccssion has been dO-1l 1~llliled into the ri n Il( HII and in part is covered by the rin valley lakes such as Lake Abaya. The I()rmatioll or the M I, I{ was accompanied by late Pliocene rift shoulder volcanic activity from ccnters slieh as I Jamula rredolll inantly made lip of trachytic lava. and ri It margin rhyol it ic volcanic complexcs \ h icll produced extensive ignimbrite succession now exposed along the riB eSGlrpll1Cllh. I JlIring 11ll ()uaternary period the extensional axis of the MER became thc loclls ur volcanic alti, it: \ itll a bimodal basalt rhyolite extrusion in the rift: floor. It is evident that shallow crustal magma chambers feeding felsic volcanic complexes such as Duguna Fango. Salwa 1)on: - Ilak{l. Chericho, Kilisa and Donga provide the heat for the hydrothermai system vhich n:i(k ill Pliocene volcanic f()rmations and are capped by Quaternary lacllstrine and volcalloclasliL sediments. Lake Abaya forms a closed drainage basin with adjacent plateau receiving over 1500 mm of average precipitation maintains a stable recharge for the prevailing hydrothermal system. Regional ground water tlow direction in the study area is to the southwest 1()llo\ ill~ Hi/ate River which is the major river draining into the lake and parallel to thL: major;. I SS \: structural tabric orthe ritt which provides secondary permeabilit). Three hydrothermal ticlds exist in the study area, a hydrothermal field around the J)ugun;1 Fango volcanic complex with manifestations at Bilho. tobacco plantation and I )imlll has strong volcanological supportive teatures despite lower in ferred reservoir Iluid geochemica1 geothermomcter temperaturcs. About 40 km to the southwest t\o other hydrothermal fkld (~orttlvest Abaya fault and Bolcho-Northeast Abaya respectj vely) arc located at a lat itlldinal distal1u: of about 20 kms between each other. The northwest Abaya 1~1lI1t hydrothermal !idd vith the most profuse hydrothermal manilestalions prohably derives its heat lrum till: SahvaDore .... Hako and Obitcha volcanic centers to lhe north. This lield despite 110 near h) prominent volcanic features as a heat source discharge mature waters with high!:r Iluid geochemical geothermometer temperatures. A-cross the Chewkare grahen the Bokho and northeast Abaya hydrothermal fields located in a hydrologically most ftlVorahlelocaliotl bctween Bilate and Gidabo rivers show a variety of hydrothermal manifestations indicating the existence of high-enthalpy geothermal reservoir related to the cluster or fCisic volcanic centers such as Chericho, KiJisa, Donga and Wereneha. Fluid geochemical data on hi~h temperature springs also suggests the existence of at least two distinct hydrothermal n:<.,ervuir-., in the study area. I f on the contrary the fluids have the -same ()rigin it Gill he speculated l~lal <til upflow zone of an advective hydrothermal system located tu the north Ilas out n()\ to lhe south at the northern shores of Lake Abaya which is the hydrologic dcpoccnter. Ilov.ever future geoscientif1Jc studies should also evaluate data in light or the model or regionally layered reservoirs (intermediate T overlying a high T reservoir) proposed I()r lhe northern -iLR to cplain the occurrence of both l:-> 65 |