Gas Emissions and Subsurface Architecture of Fault-Controlled Geothermal Systems: A Case Study of the North Abaya Geothermal Area
Gas Emissions and Subsurface Architecture of Fault-Controlled Geothermal Systems: A Case Study of the North Abaya Geothermal Area
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断层控制的地热系统的气体排放和地下结构：北阿巴亚地热区的案例研究
DOI：
10.1029/2022gc010822
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发表时间：
2023
期刊：
影响因子：
--
通讯作者：
Hutchison W
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文献类型：
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作者：
Hutchison W
东非拥有大量未开发的地热能储备。勘探主要集中在地质上年轻（<1 Ma）的硅火山口，然而有许多地热潜力的地点与活火山没有明确的联系。人们对这些系统的起源和架构知之甚少。在这里，我们将遥感和实地观测相结合，研究了位于埃塞俄比亚主裂谷Abaya湖北部的断层控制的地热作用。土壤气体co2和温度测量用于检查可渗透通道，并显示沿一个约110米高的断层升高，该断层标志着阿巴亚地堑的西部边缘。在多个相交的断层形成楔形主机结构的地方，地温特别高。这说明深穿透地堑边界断裂和近地表断裂相交控制着热液流体和气体的上升。沿地堑断裂的co2排放总量为~ 300 t d−1；这一数值与硅质破火山口火山的二氧化碳排放总量相当。喷气孔气体δ13C值为−6.4‰~−3.8‰，空气校正3he /4He值为3.84 ~ 4.11 ra，表明喷气孔气体来源于上地幔和地壳氦的混合。虽然我们的北阿巴亚地热系统模型需要深部侵入热源，但我们没有发现火山不动或沿地堑断裂的近期火山活动的地面变形证据。这代表了相对于通常承载这些资源的活性硅火山口的一个关键优势，并表明断层控制的地热系统为地热勘探提供了可行的前景。
East Africa hosts significant reserves of untapped geothermal energy. Exploration has focused on geologically young (<1 Ma) silicic calderas, yet there are many sites of geothermal potential where there is no clear link to an active volcano. The origin and architecture of these systems are poorly understood. Here, we combine remote sensing and field observations to investigate a fault‐controlled geothermal play located north of Lake Abaya in the Main Ethiopian Rift. Soil gas CO2and temperature surveys were used to examine permeable pathways and showed elevated values along a ∼110 m high fault, which marks the western edge of the Abaya graben. Ground temperatures are particularly elevated where multiple intersecting faults form a wedged horst structure. This illustrates that both deep penetrating graben bounding faults and near‐surface fault intersections control the ascent of hydrothermal fluids and gases. Total CO2emissions along the graben fault are ∼300 t d−1; a value comparable to the total CO2emission from silicic caldera volcanoes. Fumarole gases show δ13C of −6.4‰ to −3.8‰ and air‐corrected3He/4He values of 3.84–4.11RA, indicating a magmatic source originating from an admixture of upper mantle and crustal helium. Although our model of the North Abaya geothermal system requires a deep intrusive heat source, we find no ground deformation evidence for volcanic unrest or recent volcanism along the graben fault. This represents a key advantage over the active silicic calderas that typically host these resources and suggests that fault‐controlled geothermal systems offer viable prospects for geothermal exploration.