Dissected hydrologic system at the Grand Canyon: Interaction between deeply derived fluids and plateau aquifer waters in modern springs and travertine

Abstract

Geochemical study of water and gas discharging from the deeply incised aquifer system at the Grand Canyon, Arizona, provides a paradigm for understanding complex groundwater mixing phenomena, and Quaternary travertines deposited from cool springs provide a paleohydrologic record of this mixing. Geochemical data show that springs have marked compositional variability: those associated with active travertine accumulations (deeply derived endogenic waters) are more saline, richer in CO 2 , and elevated in 87 Sr/ 86 Sr relative to springs derived dominantly from surface recharge of plateau aquifers (epigenic waters). Endogenic waters and associated travertine are preferentially located along basement-penetrating faults. We propose a model whereby deeply derived fluids are conveyed upward via both magmatism and seismicity. Our model is supported by: (1) gas analyses from spring waters with high He/Ar and He/N 2 and 3 He/ 4 He ratios indicating the presence of mantle-derived He; (2) large volumes of travertine and CO 2-rich gases in springs recording high CO 2 fluxes; and (3) 87 Sr/ 86 Sr in these springs that indicate circulation of waters through Precambrian basement. Geochemical trends are explained by mixing of epigenic waters of the Colorado Plateau aquifers with different endogenic end-member waters in different tectonic subprovinces. Endogenic waters are volumetrically minor but have significant effects on water chemistry. They are an important and largely unrecognized component of the hydrogeochemistry and neotectonics of the southwestern United States.

Using fossil spring deposits in the Death Valley region, USA to evaluate palaeoflowpaths

“…However, the contribution of deep, upwelling fluids rich in dissolved CO 2 and radiogenic 87 Sr/ 86 Sr ratios from interaction deep within basement rocks cannot be entirely discounted (e.g. Crossey et al, 2006;Liu et al, 2003) and may mask the overall contribution of regional groundwater, or even local recharge if sufficient water-rock interaction occurred.…”

“…This regional component may include endogenic waters with high P CO 2 values commonly associated with upwelling along faults and carbonate deposition (e.g. Crossey et al, 2006;Liu et al, 2003).…”

Evaluation of groundwater residence time in a high mountain aquifer system (Sacramento Mountains, USA): insights gained from use of multiple environmental tracers

“…The regional aquifer system merges downgradient and provides recharge through underflow with the artesian aquifer in the Roswell Artesian Basin conducting studies of groundwater residence time using tritium-helium methodology. Elevated 3 He/ 4 He ratios in groundwater samples indicate that those waters may contain a significant percentage of mantle-derived helium-3, thereby invalidating tritium-helium dates (Newell et al 2005;Crossey et al 2006;Solomon et al 2010). Analyses obtained from this study provide ratios of 3 He/ 4 He in water samples compared to ratios of 3 He/ 4 He in the atmosphere (R/Ra).…”

Evolution of fault permeability during episodic fluid circulation: Evidence for the effects of fluid–rock interactions from travertine studies (Utah–USA)

“…Travertine is a term used to qualify carbonate precipitations under near ambient conditions in continental areas (Crossey et al, 2006;De Filippis et al, 2011Pentecost, 2005). In the study zone, modern travertines are currently formed by CO 2 bubbling springs and geysers.…”