ROBUST AND RELIABLE: A MODERN U-TH DATING METHODOLOGY FOR SILICEOUS SINTERS

Hydrothermal systems are vital to the crustal transport of heat used for geothermal energy and thus, understanding their long-term evolution is important for resource characterization. Meteoric water has been shown to be a main source of hydrothermal fluid, therefore, climate acts as one of the primary controls on the evolution of these systems. Although current active systems have been dated to the Pleistocene/Holocene, modern high resolution dating techniques for sinters are lacking, and there is no reliable measure for their longevity or evolution over time. ¹⁴C dating of bacterial mats is commonly used but can suffer from old carbon reservoir effects. High temperature (>170℃) hydrothermal systems are commonly marked by deposits of micro-laminated siliceous sinter, which have the potential for dating using U-Th disequilibrium. While U-Th dating was utilized in several previous studies, it was not applied systematically. A refined dating methodology can offer more reliable ages and provide insights into how climatic impacts to the hydrological cycle are reflected in sinter deposits. For this project, we use U-Th dating via TIMS analysis, which provides a detailed chronology and requires less material than ¹⁴C, meaning finer layers can be sampled. Samples were collected at two sites: the El Tatio Geyser Field in the Atacama Desert of northern Chile, and Casa Diablo Hot Springs, situated on the southwest edge of the Long Valley Caldera resurgent dome. While the climatic history of Long Valley has been well studied, the hydrothermal history is less constrained; the last major U-Th dating effort for sinters at Long Valley was over 30 years ago. By comparing existing ¹⁴C dates with U-Th results, El Tatio serves as an independent constraint for testing this methodology, with certain sampling characteristics, such as high fluorescence and low porosity, providing promising initial results. Preliminary data from El Tatio shows that U-Th ages are consistently younger than our ¹⁴C ages, suggesting ¹⁴C could be a maximum age due to the influence of old carbon. Going forward, this methodology will be applied to samples from Casa Diablo to deepen our understanding of the evolution of the hydrothermal system from the Pleistocene to the present.