Radiocarbon Dating of Silica Sinter and Postglacial Hydrothermal Activity in the El Tatio Geyser Field

The El Tatio geothermal field in the Chilean Altiplano contains hydrothermal silica sinter deposits overlaying glacial and volcanic units, providing an opportunity to constrain the timing of deglaciation and volcanic activity in an area with sparse absolute chronologies. We obtained 51 new radiocarbon ages and delta C-13 values on the organic material trapped in these sinter deposits. Based on the delta C-13 values, we exclude 29 samples for possible contamination with bacterial mats that incorporate old carbon. We infer that hydrothermal activity initiated similar to 27 ka ago and has been nearly continuous ever since. The ages of the oldest sinter deposits coincide with ages of moraines that stabilized after the most recent deglaciation. Whereas late Pleistocene sinters are broadly distributed in the field, Holocene deposits are found around active hydrothermal features. Although recent volcanism is absent in the vicinity of El Tatio, persistent hydrothermal discharge implies a long-lived magmatic heat source.National Science Foundation (NSF) EAR1724986 Comisión Nacional de Investigación Científica y Tecnológica (CONICYT) CONICYT FONDEF 15090013 "Centro de Excelencia en Geotermia de Los Andes," CEGA FONDECYT Postdoctoral Grant (Comisión Nacional de Investigación Científica y Tecnológica) 3170007 ICM grant "Millennium Nucleus for Metal Tracing Along Subduction" United States Geological Survey USGS Geothermal Energy Projec

Environmental controls on silica sinter formation revealed by radiocarbon dating

Silica sinter deposits overlying geothermal fields are reliable records of environmental, geochemical, and biological changes through time. Therefore, determining the absolute ages of formation of these deposits is fundamental to constrain the timing and evolution of processes that have shaped silica precipitation on the Earth's surface. We performed 14C dating of organic matter trapped within silica sinter deposits from the high-altitude El Tatio geyser field in the Chilean Altiplano. Radiocarbon ages of stratigraphically controlled samples retrieved from four well-preserved paleosinter mounds range from 10,840 ± 30 to 230 ± 35 yr B.P., indicating that the El Tatio system has had active discharge of silica-rich chloride springs over at least the past 10,000 years that has resulted in the formation of extensive sinter deposits. These ages are used to determine the silica precipitation rate at El Tatio, which was calculated to be between 0.14 and 2.57 kg/yr/m2. These values are among the highest precipitation rates in geothermal systems for which data are available, and are consistent with in situ silica precipitation experiments at El Tatio (0.84-2.92 kg/yr/m2). Our results indicate that the extreme environmental conditions of the arid Chilean Altiplano, i.e., high evaporation and cooling rate of thermal waters and significant daily temperature oscillations, play a key role in the construction and preservation of silica sinter deposits

Depositional evolution of an extinct sinter mound from source to outflow, El Tatio, Chile

Siliceous sinter deposits from El Tatio, Chile, preserve a wide variety of depositional environments and biosignatures, from high-temperature (~85 °C) vent-proximal facies to distal deposits dominated by silicified microbial mats. Four cores were drilled into an El Tatio sinster mound and associated distal apron to investigate changes in hydrothermal environments over geologic timescales. Sedimentary and geochemical analysis of multiple sinter cores records the initiation and accretion of diverse depositional features still observed today in El Tatio. Facies adjacent to hydrothermal vents are dominated by laminated sinter crusts on the steep margins of a high-temperature pool, with sparse microbial preservation. Outer margins of the same pool contain extensive sinter columns up to ten centimeters in length, precipitated during repeated cycles of pool overflow and subsequent evaporation. Low-relief hydrothermal pools also form minor deposits within distal debris aprons, and analogous pools are still active close to sampling locations. Debris aprons are dominated by palisade, tufted, and arborescent microbial fabrics, with distinct mat textures revealing well preserved microfossils. Surficial deposits in all cores feature detrital-rich and microbially-influenced sinters overlying higher-temperature facies, indicating a relative decrease in hydrothermal activity over time. Geochemical proxies for hydrothermal fluids and detrital input match depositional interpretations based on sedimentary structures. 14C ages from core deposits extend the mound's history by 11,000 years, recording at least three thousand years of sinter deposition on top of glacial sandstones (13,337–10,232 y. cal. BP). Importantly, this work provides a detailed depositional model unavailable through surficial sedimentology alone