气候变化领域集成服务门户(CCPortal): The geophysical recognition of a vapor-cored geothermal system in divergent plate tectonics: The Alalobeda (Alalobad) field, Ethiopia

CCPortal

DOI	10.1016/j.tecto.2021.228933
	The geophysical recognition of a vapor-cored geothermal system in divergent plate tectonics: The Alalobeda (Alalobad) field, Ethiopia
	Rizzello D.; Armadillo E.; Pasqua C.; Pisani P.; Balsotti R.; Kebede S.; Mengiste A.; Kebede Y.; Hailegiorgis G.; Mengesha K.
发表日期	2021
ISSN	00401951
卷号	813
英文摘要	We show the results of a geophysical survey carried out in the Alalobeda (Alalobad) geothermal field (Afar, Ethiopia). The site is located on the western margin of the NW-SW Tendaho Graben, at the intersection with the NNE-SSW Main Ethiopian Rift. The survey included 121 Magnetotelluric (MT) and Time Domain Electromagnetics (TDEM) soundings, and 300 gravity records. We applied 3D MT and gravity inversion to target a previously inferred high-T (220 °C) near neutral pH liquid-dominated chloride reservoir. Geophysical modelling identified the graben basin structure, with normal fault stepping in the Afar Stratoid basalts (2485 kg/m3), underlying a low-density (2035 kg/m3) and conductive (1 Ohm m) sedimentary cover. Along the graben shoulder, a density anomaly (+200 kg/m3) suggests a propylitization zone corresponding to the reservoir, underlying the typical conductive clay cap updomings and downdomings of high-T geothermal systems. A major conductive plume, without an appreciable gravity signature, occurs in the graben shoulder. Integration with the geochemical results allows to interpret it as a vapor-cored system. The hot spring water CO2, H2S and Cl content indicates the contamination of magmatic gases into the reservoir that produce fluid acidification while ascending from a deep source. The local bulk resistivity (10 Ohm m) is explainable by assuming conductive permeating acid fluids (10 S/m), an enhanced porosity (20%) and a significant gas saturation (20%). The absence of an appreciable density increase is also justified by the hypothesised porosity and the gas fraction. Since the acidic fluids are neutralised by interaction with the host rock, the sampled waters are nearly pH-neutral. Our results suggest the first occurrence of a vapor-cored system in divergent plate tectonics, such as the Tendaho Graben sector of the Afar rift zone. © 2021 Elsevier B.V.
关键词	3D geophysical modelling Afar Geothermics Gravity Magnetotellurics Vapor-core
英文关键词	Chlorine compounds; Geothermal fields; Groundwater; Hot springs; Hydrogen sulfide; Plates (structural components); Porosity; Surveys; Tectonics; Density anomalies; Geophysical modelling; Geophysical surveys; Geothermal systems; Gravity inversions; Main Ethiopian Rift; Sedimentary covers; Time domain electromagnetics; Geophysics; electrical resistivity; electromagnetic survey; geothermal system; magnetotelluric method; plate tectonics; three-dimensional modeling; Afar; Ethiopia; Tendaho Graben
语种	英语
来源期刊	Tectonophysics
文献类型	期刊论文
条目标识符	http://gcip.llas.ac.cn/handle/2XKMVOVA/208059
作者单位	Tellus sas, Via Pozzetto 2, Sassello, Italy; Dipartimento di Scienze della Terra, dell'Ambiente e della Vita - DISTAV, University of Genova, C.so Europa 26, Genova, Italy; ELC-Electroconsult, Via Marostica, 1, Milano, Italy; Geological Survey of Ethiopia, P.O. Box 2032, Addis Ababa, Ethiopia
推荐引用方式 GB/T 7714	Rizzello D.,Armadillo E.,Pasqua C.,et al. The geophysical recognition of a vapor-cored geothermal system in divergent plate tectonics: The Alalobeda (Alalobad) field, Ethiopia[J],2021,813.
APA	Rizzello D..,Armadillo E..,Pasqua C..,Pisani P..,Balsotti R..,...&Mengesha K..(2021).The geophysical recognition of a vapor-cored geothermal system in divergent plate tectonics: The Alalobeda (Alalobad) field, Ethiopia.Tectonophysics,813.
MLA	Rizzello D.,et al."The geophysical recognition of a vapor-cored geothermal system in divergent plate tectonics: The Alalobeda (Alalobad) field, Ethiopia".Tectonophysics 813(2021).