New Mexico Geological Society Annual Spring Meeting — Abstracts

Large-volume travertine deposits in the southeastern Colorado Plateau of New Mexico and Arizona, USA, occur along the Jemez lineament and Rio Grande rift. These groundwater discharge deposits reflect the vent locations for mantle-derived CO₂, which was conveyed by deeply-sourced hydrothermal fluid input into springs. U-series dating of stratigraphic sections shows that major aggradation and large-volume (2.5 km³) deposition took place across the region episodically at 700-500 ka, 350-200 ka, and 100-40 ka. To explore possible tectonic and paleohydrologic controls on the episodicity of travertine formation, we document overlap of these pulses with timing of regional basaltic volcanism and show an association of travertine deposits with underlying low-velocity mantle that could supply the excess CO₂. We use basalt paleosurfaces to calculate rates of landscape denudation, and find that travertine platforms developed on local topographic highs which required artesian head and fault conduits. We conclude that the travertine platforms and apparent episodicity represent conditions when fault conduits, high hydraulic head, and high CO₂ flux within confined aquifer systems were all favorable for facilitating large-volume travertine formation. By analogy to the active Springerville-St. Johns CO₂-gas field, the large volumes and similar platform geometries of travertine occurrences in our study are interpreted to represent extinct CO₂-gas reservoirs that were vents for degassing of mantle volatiles into the near-surface system.