The effects of subsurface boiling and dilution on the isotopic compositions of Yellowstone thermal waters

Abstract

Studies of isotope hydrology of geothermal systems have generally emphasized deep circulation of meteoric water, demonstrated by constancy of deuterium contents, and an ‘oxygen isotope shift’ to higher oxygen 18 contents produced by water‐rock reactions. However, subsurface boiling (in high‐temperature systems) and dilution may cause deuterium (and oxygen 18) contents of hot spring and recharge waters to difference significantly. By using thermodynamic and isotopic fractionation data for water and steam the differences in chloride, oxygen 18, and deuterium between surface and deep thermal waters have been calculated for ‘single‐stage’ (in which steam remains mixed with water and separates near a single temperature) and ‘continuous’ (in which steam is separated as it is formed) steam separation. Although changes in chloride concentration resulting from these processes are nearly identical, isotopic changes differ greatly. Single‐stage steam separation from 250° to 95°C results in increases in Cl, 103 ln Δ18O, and 103 ln ΔD(Δ = [(103 + δsurf)/(103 + δdeep)]) of 1.44 times, 1.75‰, and 9.1‰, respectively, whereas continuous steam separation results in increases of 1.41 times, 1.05‰, and 3.1‰. Because of these effects, deuterium contents of hot springs may be substantially higher than those of recharging waters, and part of the observed oxygen isotope shift may be due to boiling. These calculations have been applied to the deuterium and chloride compositions of hot spring and shallow drill hole waters of Norris, Lower, and Shoshone Geyser basins in Yellowstone National Park, Wyoming. The diverse compositions observed could result from boiling with ‘multiple‐stage’ (intermediate between single‐stage and continuous) steam separation of mixtures of a single deep thermal water (360°C, 310 ppm Cl, and −149‰ δD) with cold dilute (5°C, 2 ppm Cl) meteoric waters differing in deuterium according to locality (Norris, −142‰; Lower, −144‰; and Shoshone, −133‰). The recharge to the deep thermal water must be precipitation remote from the geyser basins or ancient precipitation from a colder period.

Anomalous alkaline sulphate fluids produced in a magmatic hydrothermal system — Savo, Solomon Islands

“…thermometer from Truesdell et al (1977). Error bars for K/Mg and quartz variants are within point size.…”

Time scale of hydrothermal water-rock reactions in Yellowstone National Park based on radium isotopes and radon

“…Studies of the Yellowstone hydrothermal system (Truesdell and Fournier, 1976;Truesdell et al, 1977;Mazor and Thompson, 1982;and Fournier, 1988) have suggested that the thermal water from the various basins originates from the same deep reservoir. This conclusion is based on the similar maximum temperatures determined at depth, similar isotopic composition of the source water, and similar chemistries for certain diagnostic elements of the spring waters.…”

“…Truesdell and Fournier (1976) and Fournier (1989) have suggested that the reservoir is located beneath the caldera at a depth of 3-5 km. Truesdell et al (1977) believe that the primary water has a chloride concentration of 310 ppm. Oxygen and hydrogen isotopes have shown that the majority of the thermal water which surfaces in Yellowstone is of meteoric origin (see Craig, 1963, andTruesdell et al, 1977).…”

“…Truesdell et al (1977) believe that the primary water has a chloride concentration of 310 ppm. Oxygen and hydrogen isotopes have shown that the majority of the thermal water which surfaces in Yellowstone is of meteoric origin (see Craig, 1963, andTruesdell et al, 1977). Based on these data Truesdell et al (1977) suggest that the recharge water is either residual from a colder time (last glacial maximum) or from the Gallatin mountains which lie to the west and the northwest.…”

“…For the ash tuff deposits he reports calcium concentrations between 0.16 wt.% and 0.24 wt.%, sodium between 2.45 wt.% and 2.67 wt.%, and potassium between 3.82 wt.% and 4.14 wt.%. For the purposes of this study, we have assumed a calcium concentration of 0.21 wt.%, sodium of 2.5 wt.%, and potassium of 4.0 wt.% for the rock and a hydrothermal water chloride concentration of 310 ppm, which is the value that Truesdell et al (1977) calculated for the primary thermal water prior to vapor loss. The Wcalculated with these values for the average Norris Geyser Basin water is roughly 250.…”