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The Rio Grande rift has active volcanism and faulting providing a field laboratory for examining links between mantle degassing and faults as conduits for fluids and volatiles. CO2 flux measurements were taken at 6 sites in the northwestern Albuquerque basin and Valles caldera. All sites progress to the southwest from the caldera, down the riftrelated Jemez fault network, to intersect with the Nacimiento fault. The instrument used to measure CO2 flux was an EGM-4 CO2 gas analyzer (PP systems) with an accumulation chamber. Individual diffuse and spring measurements (n) were obtained from each site at approximately 50 m spacing or less. Carbonic springs at Penasco Springs (n=41) and San Ysidro (n=261), and the carbonate-cemented Sand Hill fault (n=42), were targeted. The Sand Hill fault had the smallest maximum flux (8 g/m²d). The other two sites are approximately equal distance between the Sand Hill fault and caldera sites. Our work suggests these sites reflect intersections of the Nacimiento fault with NE trending faults that connect to the Jemez fault network. The maximum diffuse flux recorded at San Ysidro (434 g/m²d) and Penasco Springs (25 g/m²d) are high, especially along the fault near springs. Maximum diffuse flux measurements of Alamo Canyon (20,906 g/m²d), Sulphur Springs (2,400 g/m²d), and Soda Dam (1,888 g/m²d) at the Valles caldera geothermal sites (n=63, 59, and 92, respectively) are comparable to Yellowstone geothermal systems. Results indicate fault networks allow for volatile transport consistent with the geological occurrence of carbonate accumulations (travertines and cements) along the same structures. [ABSTRACT FROM AUTHOR]

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 CO 2 , Li, B, Na, Cl, HCO 3 , C ext , He, Sr, mantle-like δ13C-CO 2 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 CO 2 , 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. • Trace Valles Caldera geothermal fluids and gases found in Ojo Caliente spring water via deep advection system. • Sufficient permeability for fluid and gas migration demonstrated along the Embudo and Ojo Caliente faults. • Faulting provides significant migration pathways in areas of extension, crustal thinning, and high geothermal gradient. • Regional mantle degassing is shown along the Jemez lineament. [ABSTRACT FROM AUTHOR]