Midway Evaluation - Daniel G. Villarroel

Title of thesis:
Geochemical Characterization of Geothermal Fluids in the Sol de Mañana–Laguna Colorada System, Bolivia

Student:
Daniel G. Villarroel

Doctoral committee:
Dr. Andri Stefánsson, professor at Faculty of Earth Sciences, University of Iceland
Dr. Sæmundur A. Halldórsson, research professor at Institute of Earth Sciences, University of Iceland
Dr. Þráinn Friðriksson, research specialist at Reykjavík Energy

Abstract:
Geothermal fluids in continental volcanic arcs reflect the combined influence of several factors including characterization of meteoric water recharge, magmatic and crustal volatile inputs, and water-rock interaction. The Sol de Mañana–Laguna Colorada geothermal area, on the western margin of the Altiplano–Puna Volcanic Complex (APVC) in the Bolivian Altiplano (22°S), is hosted within exceptionally thick continental crust (>70 km) above the Altiplano–Puna Magma Body (APMB). This setting provides a natural laboratory to assess how crustal thickness and the APMB influence reservoir fluid composition and surface degassing. This study addresses three main questions: (i) the origin and evolution of reservoir fluids; (ii) the relative contributions of magmatic, sedimentary, and crustal sources to the volatile inventory; and (iii) the role of deep upflow in controlling surface degassing along structural pathways. These questions are investigated using a dataset of more than 220 samples, integrating new and published chemical and isotopic data from thermal and non-thermal waters, fumaroles, mud pools, and two-phase well discharges. Analyses include major and trace element chemistry, noble and reactive gas systematics (³He/⁴He, CO₂/³He, δ¹³C–CO₂, S/³He, δ³⁴S–H₂S), water isotopes (δ²H, δ¹⁸O), and soil CO₂ flux measurements. The aim is to quantify how Sol de Mañana differs from regional Central Volcanic Zone (CVZ) averages and to constrain magmatic volatile transfer through thickened continental crust.