GEOCHEMISTRY AND GEOCHRONOLOGY OF LARGE-VOLUME QUATERNARY TRAVERTINE DEPOSITS OF THE SOUTHEASTERN COLORADO PLATEAU: IMPLICATIONS FOR PALEOHYDROLOGIC AND PALEOTECTONIC CONTROLS ON TRAVERTINE FORMATION AND TRAVERTINE FACIES

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 represent places of persistent and significant mantle CO₂ degassing in high discharge spring systems and are found along faults and above magmatic systems. U-series dating shows that large volumes (2.5 km³) of travertine formed episodically at 700-500 ka, 350-200 ka, and 100-40 ka. Episodes of travertine deposition overlap with episodes of magmatic activity suggesting that high CO₂ flux takes place during basaltic magmatism and associated high seismicity such as exemplified by the Springerville volcanic field in Arizona and the modern Socorro magma body system in New Mexico. Times of high accumulation rates reflect increased recharge and high hydraulic head (paleohydrology) as well as times of high CO₂ flux (paleotectonics) in confined aquifer systems. The paleohydrologic conditions control depositional environments of travertine, e. g. spring mound, step-pool, marsh, and, consequently, travertine facies which affect the geochemical and stable isotopic composition of the travertine. Stable oxygen and carbon isotope analyses of the different travertine deposits overlap substantially exhibiting δ¹⁸O values that range between -14‰ to -3.8‰, and δ¹³C values that range from -4.9‰ to 9.8‰. Preliminary results of rare earth element (REE) and trace element analyses show characteristic REE signatures for different areas and similar trends for trace elements throughout the region, with high (> 1000 mg/kg) concentrations of Fe, Mg, Mn, Na, and Sr. REE analysis allows identifying the source of the groundwater, e. g. shallow or deeply derived water, and recharge area. Mg/Ca and Sr/Ca ratios reveal groundwater residence times and seasonal recharge fluctuations while concentrations of Mg and Sr/Ba ratios are used to estimate paleo-water temperatures. We infer that episodes of high head resulted from an interplay of wet climate, high hydrothermal pressure, and high CO₂ flux, as filtered through complex artesian aquifer systems. A simple correspondence of travertine accumulations episodes to glacial and interglacial cycles is not observed in our dataset.