The hydrothermal outflow plume of Valles Caldera, New Mexico, and a comparison with other outflow plumes

Abstract

Stratigraphic, temperature gradient, hydrogeochemical, and hydrologic data have been integrated with geologic data from previous studies to show the structural configuration of the Valles caldera hydrothermal ouflow plume. Hydrologic data suggest that 25–50% of the discharge of the Valles outflow is confined to the Jemez fault zone, which predates caldera formation. Thermal gradient data from bores penetrating the plume show that shallow gradients are highest in the vicinity of the Jemez fault zone (up to 190°C/km). Shallow heat flow above the hydrothermal plume is as high as 500 mW m−2 near core hole VC‐1 (Jemez fault zone) to 200 mW m−2 at Fenton Hill (Jemez Plateau). Chemical and isotopic data indicate that two source reservoirs within the caldera (Redondo Creek and Sulphur Springs reservoirs) are parents to mixed fluids flowing in the hydrothermal plume. However, isotopic data, borehole data, basic geology, and inverse relations between temperature and chloride content at major hot springs indicate that no single reservoir fluid and no single diluting fluid are involved in mixing. The Valles caldera hydrothermal plume is structurally dominated by lateral flow through a belt of vertical conduits (Jemez fault zone) that strike away from the source reservoir. Stratigraphically confined flow is present but dispersed over a wide area in relatively impermeable rocks. The Valles configuration is contrasted with the configuration of the hydrothermal plume at Roosevelt Hot Springs, which is dominated by lateral flow through a near‐surface, widespread, permeable aquifer. Data from 12 other representative geothermal systems show that outflow plumes occur in a variety of magmatic and tectonic settings, have varying reservoir compositions, and have different flow characteristics. Although temperature reversals are commonly observed in wells penetrating outflow plumes, reversals are not observed in all plumes. Less information is available on the absolute age of hydrothermal outflow plumes, although the data show that they can be as old as 106 years and display episodic behavior.

The impact of CO2 on shallow groundwater chemistry: observations at a natural analog site and implications for carbon sequestration

“…Studies of the second type are far more common, due in part to the ease of sampling springs or geysers. Studies of CO 2 -charged springs (Glennon 2005;Goff et al 1988;Newell et al 2005;Vuataz et al 1984) provide insight into the dynamics of CO 2 flow and into geochemical processes occurring at depth, but they are not particularly informative about the impact of CO 2 on aquifers, since the CO 2 may not significantly impact a shallow aquifer if it rises along a conduit and rapidly discharges at a spring (Fig. 1a).…”

Evolution of a mineralized geothermal system, Valles Caldera, New Mexico

“…Meteoric precipitation recharges the hydrothermal system, which equilibrates at depths of 2 to 3 km and temperatures approaching 300øC in caldera fill tuffs and precaldera The model in Figure 10 is relatively simple and resembles general models of volcanic-hosted hydrothermal systems presented by Henly and Ellis (1983). Differences between the models occur primarily in the structural setting and direction of lateral flow due to differences in tectonics and hydrogeology (see also Goff et al, 1988). We know, however, that the hydrothermal system is more complex when examined in detail.…”

Sedimentary petrology and authigenic mineral distributions in the Oligocene Creede Formation, Colorado, United States

“…These controls are interpreted to have resulted in extensive lateral flow away from the area of most intense alteration bordering the Creede mineral district. Similar types of lateral-flow systems are identified by reversals in downhole thermal gradients (Goff et al, 1988) in many modern hydrothermal systems, including the Valles caldera and Long Valley caldera systems (Sorey et al, 1991). In both of these systems, hot (>200°C) fluids ascend to near the surface and flow laterally downgradient in porous units and along faults.…”