Hot spring hydrochemistry of the Rio Grande rift in northern New Mexico reveals a distal geochemical connection between Valles Caldera and Ojo Caliente

Abstract

Warm and hot springs occur within and on both sides of the Rio Grande rift (RGR) of northern New Mexico. Springs on the western side of the RGR are along the Ojo Caliente fault zone, which intersects the Embudo fault transfer zone that extends northeast of the Valles Caldera. Springs on the eastern side occur along north-south rift-bounding faults near Taos, NM. We compared spring water geochemical data from the western and eastern sides of the RGR to discover spring water origins. Included in our discussion was spring chemistry of the Valles Caldera located to the southwest of our study area. The Valles Caldera is a significant feature because it had major rhyolite eruptions 1.65 and 1.26 Ma, continued rhyolite eruptions until ~30 ka, and an active magmatically-driven geothermal system. The latest volcanic events in the Taos Plateau were basalt flows occurring about ~ 2 Ma. Our spring chemistry findings showed elevated levels of geothermal input in the western spring group, with the greatest input in Ojo Caliente spring waters. The elevated geothermal tracers include CO2, Li, B, Na, Cl, HCO3, Cext, He, Sr, mantle-like δ13C-CO2 values (−3.5 to −6.8‰), radiogenic basement-like 87Sr/86Sr ratios (0.747), and mantle-derived 3He (up to 4.8%) in the presence of highly elevated crustal 4He. Eastern springs had fewer magmatic inputs including tracers listed above and notably lower 87Sr/86Sr ratios ranging from 0.708 to 0.713. Nevertheless, eastern springs contain endogenic carbon and helium isotope values showing up to 4% mantle-derived helium. We interpret the elevated tracer results discovered in Ojo Caliente spring waters as distal influences of the Valles geothermal system, which is about 60 km away. The most conclusive evidence for these results stem from significant contributions of magmatically-derived volatiles including CO2, He, and their isotopes. With evidence of far-traveled water and volatiles, we concluded that the RGR transfer zone fault systems provide conduits for long-distance migration of deep fluids and gases that mix with meteoric water in the shallow subsurface.