17:15 〜 18:30
[SVC29-P06] Tectonic controlled and hydrothermal alterations of geothermal reservoirs in El Salvador
キーワード：水熱、ミネラル変質、地熱貯留層、マグマ
A comparative study of magma-hydrothermal activities of main geothermal fields (Ahuachapán, Berlín, San Vicente, and Chinameca) was carried out in El Salvador/ Central America, where significant relationships were identified between volcanism and geothermal activities.
All geothermal fields are located north and/or northwest flank of the volcanic complex inside ESFZ (El Salvador Fault Zone). Geothermal reservoirs are controlled by fault system, which direction is mainly N-S, NE-SW, NW-SE, and E-W. The reservoirs are developed in the intersected area of those faults.
Most of the reservoir are developed in the San Salvador Cuscatlán and Bálsamo formation of Pliocene-Holocene in age.
The top depths of geothermal reservoirs are ranging from 600 to 2000 m. Ahuachapán is relatively shallow (below 600 to 1500 m, thickness around 800 to 1200 m), and Berlín (below 1500 m, thickness around 600 to 1000 m ). Geothermal reservoirs of San Vicente and Chinameca were estimated around 1100 to 1400 m in depth. The temperatures of the reservoirs in the different geothermal fields range from 200 to 300°C.
The mineral alteration facies in the four fields have a very similar distribution (Fig. 1), and Propylitic, Phyllitic-Propylitic, Phyllitic zones correspond to the geothermal reservoir. In the different facies, key minerals are Argillitic: Low-temperature clays like Smectites (Montmorillonite, Saponite); Argillitic-Phyllitic: Chloritic clays (mixed-layer clay minerals) like Corrensite; Phyllitic: Chlorite; Phyllitic-Propylitic: Incipient epidote or in very low percentages. Propylitic: key mineral: epidote. Other minerals are also present in each facie. In the shallow zone, the Argillic alteration is dominant and is in the range of temperatures of 50oC-120oC, the Argillic-Phyllitic mineral alteration is found in the temperature range of 100oC-180oC, Phyllitic-Propylitic mineral alteration type is found in the temperature range of 200oC-260oC and in the deepest zone, the Propylitic type mineral alteration is dominant, found it at temperatures ranging from 250oC to temperatures around 300oC.
The chemical composition of trace elements of volcanic rocks in El Salvador shows a subduction setting through Miocene to the present. The Miocene-Pliocene volcanoes located northward of ESFZ were similar to the back-arc setting. A wide range of mineral assemblages of volcanic rocks was observed (Mainly from the series calc-alkaline from basalts to rhyolites), however, it is rare to contain quartz.
In the case of Quaternary volcanoes distributed inside ESFZ (and parallel to the Middle America Trench), the magma chamber was presumed to be slightly shallower, and variation of geochemical behaviors may show that El Salvador is located as a transition zone of the subduction system of the Cocos Plate between Guatemala and Nicaragua
All geothermal fields are located north and/or northwest flank of the volcanic complex inside ESFZ (El Salvador Fault Zone). Geothermal reservoirs are controlled by fault system, which direction is mainly N-S, NE-SW, NW-SE, and E-W. The reservoirs are developed in the intersected area of those faults.
Most of the reservoir are developed in the San Salvador Cuscatlán and Bálsamo formation of Pliocene-Holocene in age.
The top depths of geothermal reservoirs are ranging from 600 to 2000 m. Ahuachapán is relatively shallow (below 600 to 1500 m, thickness around 800 to 1200 m), and Berlín (below 1500 m, thickness around 600 to 1000 m ). Geothermal reservoirs of San Vicente and Chinameca were estimated around 1100 to 1400 m in depth. The temperatures of the reservoirs in the different geothermal fields range from 200 to 300°C.
The mineral alteration facies in the four fields have a very similar distribution (Fig. 1), and Propylitic, Phyllitic-Propylitic, Phyllitic zones correspond to the geothermal reservoir. In the different facies, key minerals are Argillitic: Low-temperature clays like Smectites (Montmorillonite, Saponite); Argillitic-Phyllitic: Chloritic clays (mixed-layer clay minerals) like Corrensite; Phyllitic: Chlorite; Phyllitic-Propylitic: Incipient epidote or in very low percentages. Propylitic: key mineral: epidote. Other minerals are also present in each facie. In the shallow zone, the Argillic alteration is dominant and is in the range of temperatures of 50oC-120oC, the Argillic-Phyllitic mineral alteration is found in the temperature range of 100oC-180oC, Phyllitic-Propylitic mineral alteration type is found in the temperature range of 200oC-260oC and in the deepest zone, the Propylitic type mineral alteration is dominant, found it at temperatures ranging from 250oC to temperatures around 300oC.
The chemical composition of trace elements of volcanic rocks in El Salvador shows a subduction setting through Miocene to the present. The Miocene-Pliocene volcanoes located northward of ESFZ were similar to the back-arc setting. A wide range of mineral assemblages of volcanic rocks was observed (Mainly from the series calc-alkaline from basalts to rhyolites), however, it is rare to contain quartz.
In the case of Quaternary volcanoes distributed inside ESFZ (and parallel to the Middle America Trench), the magma chamber was presumed to be slightly shallower, and variation of geochemical behaviors may show that El Salvador is located as a transition zone of the subduction system of the Cocos Plate between Guatemala and Nicaragua