New Mexico Geological Society Annual Spring Meeting — Abstracts

Input of deeply sourced (endogenic) waters can degrade water quality, contributing significant salinity and trace metals to groundwater, with faults acting as conduits for subsurface fluid flow. Understanding source, movement, and chemistry of groundwater is becoming more significant with changing climate and weather patterns. Systematic sampling was carried out on a series of carbonic warm and hot springs in New Mexico, USA: 1) Tierra Amarilla springs near San Ysidro south of Nacimiento Mountains, 2) Penasco Springs along the Nacimiento fault west of the Nacimiento basement mountain block, and 3) Soda Dam, Jemez, and Indian hot springs in San Diego Canyon along the Jemez River. Multiple hydrochemical tracers were applied to quantitatively evaluate possible flow paths and mixing. The goal is to test three hypotheses for source and transport of waters to these carbonic springs: San Juan basin origin, meteoric flow from the Nacimiento high topography, and/or influence from the Valles Caldera geothermal system of the Jemez Mountains. Multiple geochemical plots show that all three carbonic spring groups are very different than meteoric and sedimentary aquifer waters. The springs are warm to hot (20oC-60oC) and many deposit travertine, pH ranges from 5.38-6.94; conductivities range from 3300-20000µS and PCO2 ranges from -0.94 to 0.93. San Ysidro springs look similar in major ions to Penasco Springs each showing a different range of the same mixing trend. Soda Dam appears to anchor these mixing trends, but itself is part of a broader mixing trend with a Valles Caldera geothermal water end member.

The main tracers that define mixing trends are: major ions, stable isotopes, conservative tracers, temperature, and helium isotope ratios. In all of these tracers, the Tierra Amarilla and Penasco Springs overlap strongly and fall on well-defined mixing trends anchored by geothermal fluids of the Valles system. Stable isotope composition in the San Ysidro and Penasco springs overlap with Soda Dam hot springs and values fall on a mixing line with Valles Caldera geothermal waters. High lithium, boron, and bromine values all show the San Ysidro carbonic springs to have hydrochemical influence from the Jemez hydrothermal system. Similarly, helium isotope data show elevated 3He/4He values consistent with contributions from the Jemez volcanic system. In San Ysidro and Penasco spring groups, plots of high Li and B versus chloride suggest geothermal waters have acquired Cl from other sources, including salt and gypsum of the Paleozoic and Mesozoic rock aquifers. We interpret these carbonic springs to be distal manifestations of fluid circulation along faults with a mixture of Jemez geothermal waters and waters sourced from either/both San Juan Basin aquifers and meteoric sources. Semi-confined fault conduits, especially of the Jemez and Nacimiento fault zones, provide connectivity between carbonic spring systems and help explain geochemical similarities and mixing trends between Valles Caldera, Soda Dam, and Jemez geothermal waters with more distal San Ysidro and Penasco Spring waters. Penasco Spings are interpreted to reflect a component of outflow from the geothermal system that crosses the Nacimiento Mountain basement block along NE- trending faults.