Earth and Planetary Sciences ETDs

Publication Date

8-27-2009

Abstract

High CO2 springs and related travertine deposits of the Springerville area of east-central Arizona provide an exceptional field laboratory for understanding travertine-depositing spring systems. U-series dating of travertines provides an opportunity to unravel paleohydrologic and neotectonic histories near the southeastern edge of the Colorado Plateau. This interdisciplinary study combines water and gas chemistry data, travertine morphology and geochronology, analysis of geologic structures, basalt geochronology, and river incision studies to formulate an integrative model for both travertine formation and for landscape evolution of this region. More than 70 individual travertine mounds and large platforms, formed from the coalesced deposits of multiple spring vents, cover a surface area of >33 km2 near Springerville, Arizona. This area is at the intersection of the southeastern edge of the Colorado Plateau with the Jemez lineament, a northeast-trending zone of volcanic activity over the last 4.5 Ma. Travertine deposits occur in clusters 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 Plio-Pleistocene Springerville volcanic field (SPV) which was active until 308 ka and on the east by the late Mio-Pleistocene Red Hill-Quemado volcanic field where volcanic activity continued until as recently as 71 ka. Modern springs adjacent to the CO2 field are actively degassing CO2, have Cexternal values of 50%, concentrations of TDS up to 2538 mg/l, and are currently depositing minor volumes of travertine. 3He/4He ratios from wells in the CO2 field and adjoining springs range up to 0.58 RA, indicating the presence of asthenospheric mantle-derived gases in modern spring waters (up to about 7% of the total helium). To explain the diversity of water chemistry in this small region, we hypothesize that deeply sourced fluids rise along NE- and NW-trending basement-penetrating faults that intersect at the SE end of the dome. These endogenic waters then mix with groundwater producing a complete mixing trend between meteoric and bicarbonate rich, high TDS end members. Precise new U/Th dates indicate that travertine deposition began >350 ka, overlapping with waning volcanic activity in the Springerville and Red Hill-Quemado volcanic fields, and is still ongoing. Major times of accumulation at 350-300, 280-200, and 100-36 ka are interpreted to represent wetter paleohdrologic intervals. Synchronous outflow occurred from springs at different elevations above the LCR (from near river level up to 400 m above the river at ca. 200 ka) 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. The life of one major travertine mound system near the LCR that accumulated >20 m of layered travertine has been bracketed between 73 and 48 ka (25 ka). This mound formed from the sustained outflow of CO2-charged spring waters from a central vent with a deposition rate of 0.94 m/ka. Hiatuses of ~25-60 ka in the travertine rock record correlate with obliquity-forced warm interglacial peaks in the Devils Hole calcite δ18O paleotemperature and global paleoclimate records. Periods of deposition also correlate with the five most recent volcanic episodes in the SPV and Red Hill-Quemado fields. Thus, the apparent ~70 ka cyclicity of travertine deposition appears to 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. Using the base of flows, basalt incision points indicate a long-term rate of 40-50 m/Ma. U-series dates on travertine that cements gravels directly above bedrock straths indicate incision rates of 100-150 m/Ma near Lyman Lake from 350-100 ka, increasing to 320 m/Ma in the last 100 ka.

Degree Name

Earth and Planetary Sciences

Level of Degree

Masters

Department Name

Department of Earth and Planetary Sciences

First Committee Member (Chair)

Karlstrom, Karl E.

Second Committee Member

Crumpler, Larry S.

Language

English

Keywords

Springerville, travertine, U/Th dating

Document Type

Thesis

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