Identification of Volcanic Geothermal Systems Based on Integrated Study of Volcanostratigraphy, Structural Geology, and Fluid Geochemistry in Southern Ngada Field, Indonesia

Abstract

Southern Ngada is one of the areas that shows occurrence of volcanic geothermal potential in East Nusa Tenggara. The spreading volcanoes in the study area raised a hypothesis that the Southern Ngada Geothermal Field consists of several geothermal systems. The spreading volcanoes showed the presence of at least three volcanoes and manifestation clusters, which are Nage, Keli-Bena, and Wolo Puti Clusters. This research aimed to identify the number, type, and characteristics of geothermal systems in Southern Ngada Geothermal Field. The identification is conducted through the integration of geomorphology, volcanostratigraphy, structural geology, and geochemistry of fluid manifestation. The determination of geothermal system in Southern Ngada Geothermal Field is important to identify the field characteristics and reduce exploration risks. The Southern Ngada Field constitutes of the pre-caldera, post-caldera, and recent volcanism products. The study area is intensively deformed through strike slip faults and resembled Riedel Shear patterns. Fluid manifestation geochemistry in the study area showed various type of waters, which consists of Cl-SO4, SO4, and SO4-HCO3 waters with meteoric water mixing. The solfatara is associated with active magmatic gases due to boiling of reservoir beneath cinder cones. The fluid mixing processes are explained furthermore in Schoeller diagram plot. The integration of analyses showed the presence of Nage, Keli-Bena, and Wolo Puti Geothermal Systems with each different volcanostratigraphy, structural setting, and fluid mixing processes. The Nage System is associated with inferred heat source beneath the Nage Caldera and eastern part master and antithetic fault. The Keli-Bena System is associated with inferred heat source beneath Bena Crater and western antithetic fault. The Wolo Puti System is associated with inferred heat source beneath cinder cone volcanoes and northern extensional structures.