LARGE-VOLUME QUATERNARY TRAVERTINE DEPOSITS IN THE RIO GRANDE RIFT AND JEMEZ LINEAMENT, NEW MEXICO AND ARIZONA: IMPLICATIONS FOR PALEOCLIMATE, LANDSCAPE EVOLUTION, AND NEOTECTONICS

New Mexico and Arizona host several large-volume (0.2-0.9 km³) travertine deposits with surface areas of 10 - 40 km² and thicknesses ranging from 5 to more than 60 m. They are present both along the NE-trending Jemez lineament and NS-trending Rio Grande rift and record natural CO₂ leakage related to Quaternary magmatic CO₂ degassing. U-series data show that travertine deposition overlapped temporally from place to place. High volume deposition was not steady, but occurred episodically at 36-100 ka, 200-380 ka, and 520-660 ka. Stable isotope analyses from the travertines overlap substantially, exhibiting high δ¹³C values, +2.0‰ to +8.3‰, and δ¹⁸O values that range between -13.5‰ to -4‰. High δ¹³C values are interpreted to be caused by rapid CO₂ degassing while the range of δ¹⁸O values is interpreted to represent changing water temperatures and mixing trends of groundwater. Times of high accumulation rates are interpreted as times of high groundwater flow and hence as a proxy for regional paleohydrology/paleoclimate control, while the primary control on the spatial localization of large-volume travertine is high tectonic CO₂ flux in areas of mantle upwelling, crustal magma chambers, and fault conduits. Large-volume travertine occurrences are important indicators of the extent of past natural CO₂ leakage that can inform carbon sequestration models. By analogy to the active Springerville CO₂ gas field in Arizona, the large volumes and similar platform geometries of the travertine occurrences in New Mexico are interpreted to record extinct or dormant CO₂ fields. Travertine platforms now occupy positions high in the landscape (inverted topography) and also provide data on the scales and timing of regional landscape evolution. Erosion rates measured from travertine-capped mesas reveal differential denudation across the study areas and may have implications for Quaternary uplift associated with the Jemez lineament.