U-SERIES DATING, GEOCHEMISTRY, AND GEOMORPHIC STUDIES OF TRAVERTINES AND SPRINGS OF THE SPRINGERVILLE AREA, EAST-CENTRAL ARIZONA, AND TECTONIC IMPLICATIONS

High CO₂ springs and related travertine deposits of the Springerville area in Arizona provide an exceptional field laboratory for understanding travertine-depositing spring systems. U-series dating of travertines provides the opportunity to unravel paleohydrologic and neotectonic histories near the southeastern edge of the Colorado Plateau.

Seventy travertine mounds covering >33 km² are clustered near the Little Colorado River (LCR) and along fault lineaments overlying the Springerville-St. Johns Dome, a faulted asymmetric anticline trapping a large natural CO₂ reservoir. This travertine and CO₂ system is bounded on the west by the Springerville volcanic field, active until 308 ka, and on the east by the Red Hill-Quemado volcanic field, active until 71 ka.

Precise new U/Th dates indicate that travertine deposition began >350 ka, overlapping with waning volcanic activity in the adjoining fields, and is still ongoing. Synchronous outflow occurred from springs at different elevations above the river, reflecting an unresolved combination of fluctuations in hydraulic head, gas pressure in the CO₂ reservoir, paleoseismicity, and partitioning dynamics of traps within the stacked CO₂ reservoir system. One major travertine mound accumulated >20 m of layered travertine from sustained outflow of CO₂-charged spring waters between 73 and 48 ka with a deposition rate of 0.94 m/ka.

Major times of accumulation at 350-300, 280-200, and 100-36 ka are interpreted to represent wetter paleohydrologic intervals. Hiatuses of ~25-60 ka in the travertine rock record correlate both with warm interglacial peaks in paleoclimate records and with the most recent volcanic episodes in the adjoining volcanic fields. Thus, the apparent ~70 ka cyclicity of travertine deposition may be due to a combination of increased climatically-modulated groundwater recharge during wet/glacial times and over-pressuring of the CO₂/groundwater system due to the periodic influx of magmatically sourced fluids. Dated travertines and basalts associated with elevated LCR gravel terraces in the region provide constraints on river incision and landscape denudation. Basalt incision points indicate a long-term rate of 40-50 m/Ma. U-series dates on travertine indicate incision rates of 100-150 m/Ma from 350-100 ka, increasing to 320 m/Ma in the last 100 ka.