SPRINGS, GASES AND TRAVERTINES OF THE COLORADO PLATEAU: XENOWHIFFS, LINKS TO TECTONISM, AND VIEW OF A DEEPLY-DISSECTED HYDROLOGIC SYSTEM

Active springs and associated travertines are an underutilized record for investigating modern hydrology, as well as a record for understanding how this system has interacted with Quaternary tectonism. The Colorado Plateau provides access to a deeply dissected aquifer system. Spring water chemistry and gas analysis from Grand Canyon and the Rio Grande rift demonstrate that large volumes of travertine are produced from deep saline waters rich in CO2 (60-90 mol %). Spring waters in travertine-forming localities record high He/Ar and He/N2, and 3He/4He ratios of 0.15 Ra suggesting contributions of mantle-derived He and CO2 potentially from nearby coeval volcanic fields. 87Sr/86Sr in central Grand Canyon springs ranges from 0.710 to 0.728, reflecting radiogenic Sr contributed by deeply circulated waters. Both the modern and ancient travertine-depositing springs, and the Colorado River itself, record a mixing of deeply-circulated waters rising along faults (lower world waters) with surface- and ground waters (upper world waters) of the plateau. Travertine occurs where major spring-producing horizons intersect Laramide and Precambrian basement-penetrating faults. U-series dating suggests that major pulses of travertine accumulation seem to correspond with glacial events/ regional wetness, but also permits correlation with volcanic episodes. Some modern spring discharge variations correspond to microseismicity, and patterns of travertine accumulation are associated with modern intrusive magmatic activity in the Rio Grande rift, suggesting that seismicity and volcanism influence the movements of deep water up faults. An integrated look at the influence of lower world waters and gases on the aquifers and surface waters of the Colorado Plateau region has potential for understanding links between asthenospheric upwelling, basaltic magmatism, and movement of fluid and gas along lithosphere-scale fracture systems. Mantle-derived gas is a rapidly moving "xenowhiff", tracing the activity of a dynamic mantle. In addition, the deep inputs may be the important controlling source of salinity and arsenic content in ground water and surface water systems. Travertines offer rich potential to extend these insights to relationships between neotectonics and paleohydrology over the past million years.