New Mexico Geological Society Annual Spring Meeting — Abstracts

Both groundwater and surface water are important sources for many metropolitan and agricultural communities along the Rio Grande corridor. Both high salinity and trace element concentrations are regionally important in impairing water quality. Although these waters are dominated volumetrically by meteoritic sources, recent research has revealed the widespread presence of volumetrically small, but geochemically important deep fluid sources. These "endogenic" waters have been associated with springs issuing along rift-bounding faults in central New Mexico. This study reports new geochemical data from springs and groundwaters in a cross-rift transect located in the Sevilleta National Wildlife Refuge and evaluates contributions from endogenic fluids. This transect extends from the Colorado Plateau on the west to the Great Plains on the east and includes springs along deep rift-bounding faults. This transect is also strategically located at the intersection of the Albuquerque and Socorro basins: a structurally complex zone that appears to coincide with longitudinal changes in the Rio Grande surface water as reported in previous research.

Results indicate the interaction of three distinct hydrochemical facies: the first is a NaCl/SO₄ composition which consisted of the San Acacia pools, Rio Salado Springs, and the Rio Salado. The second, with a mixed cation-HCO₃ rich composition, consisted of the San Lorenzo Springs. The third, with a Ca/Mg-Cl/SO₄ composition, consisted of Cibola and Milagro Springs. We interpret these results in light of other regional groundwater surveys and evaluate mixing models to explain the observed variations. Ongoing trace element analysis will allow for further testing of hydrologic mixing models.