Presenter Information

Kendra BunnellFollow

Class

Article

Graduation Year

2017

College

College of Science

Department

Geology Department

Faculty Mentor

Dennis Newell

Presentation Type

Poster Presentation

Abstract

Carbon and oxygen stable isotope ratios in laminated hot-spring travertine veins are sensitive to temperature and groundwater source. In Tibet, an area affected by both monsoonal flow and continental storm tracks, we hypothesize geochemical fluctuations in travertine laminations recording the influence of these climatic processes. In addition to tracking climatic influences, the carbon and oxygen isotope ratios trace the water source and sources of carbon.

A vein within a fault-associated fossil hot spring system in Tibet was sampled in 2012. Stable isotope ratios of carbon and oxygen in each successive lamination were measured using the phosphoric acid method and a ThermoScientific Delta V Advantage isotope ratio mass spectrometer at the USU Stable Isotope Lab. To provide age control for vein growth and the groundwater fluctuation, a subset of the laminations are currently being dated using 238U-230Th disequilibrium methods in the ICMP-MS Lab at the University of Utah.

Results indicate high δ13C values compared to the carbonate host rocks, ranging from 5.2 to 7.7 ‰ vs PDB, fluctuating up to 1.6‰ between successive laminations. The δ18O values are similar to meteoric water, ranging from -24.8 to -17.0‰ vs PDB, fluctuating up to 4.7 ‰ between successive laminations. The oxygen and carbon isotope values show a general positive correlation.

The high δ13C values may indicate metamorphic de-carbonation of the area’s host rocks, with the fractionation in isotope ratios due to degassing and mineralization along flow paths. Thus: 1) oxygen isotope ratios track changes in the groundwater composition due to the meteoric infiltration source; and 2) carbon isotope ratios give information on water-rock interactions. The covariation between the isotopes is attributed to changes in spring water composition as the travertines are precipitated. These findings with forthcoming U-Th ages will provide insight on the climate and tectonic activity of the fault-based system.

Location

North Atrium

Start Date

4-13-2017 3:00 PM

End Date

4-13-2017 4:15 PM

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Apr 13th, 3:00 PM Apr 13th, 4:15 PM

Interpreting Climatic Fluctuations Using the Chronology and Isotope Geochemistry of Tibetan Hot Spring Travertine Deposits

North Atrium

Carbon and oxygen stable isotope ratios in laminated hot-spring travertine veins are sensitive to temperature and groundwater source. In Tibet, an area affected by both monsoonal flow and continental storm tracks, we hypothesize geochemical fluctuations in travertine laminations recording the influence of these climatic processes. In addition to tracking climatic influences, the carbon and oxygen isotope ratios trace the water source and sources of carbon.

A vein within a fault-associated fossil hot spring system in Tibet was sampled in 2012. Stable isotope ratios of carbon and oxygen in each successive lamination were measured using the phosphoric acid method and a ThermoScientific Delta V Advantage isotope ratio mass spectrometer at the USU Stable Isotope Lab. To provide age control for vein growth and the groundwater fluctuation, a subset of the laminations are currently being dated using 238U-230Th disequilibrium methods in the ICMP-MS Lab at the University of Utah.

Results indicate high δ13C values compared to the carbonate host rocks, ranging from 5.2 to 7.7 ‰ vs PDB, fluctuating up to 1.6‰ between successive laminations. The δ18O values are similar to meteoric water, ranging from -24.8 to -17.0‰ vs PDB, fluctuating up to 4.7 ‰ between successive laminations. The oxygen and carbon isotope values show a general positive correlation.

The high δ13C values may indicate metamorphic de-carbonation of the area’s host rocks, with the fractionation in isotope ratios due to degassing and mineralization along flow paths. Thus: 1) oxygen isotope ratios track changes in the groundwater composition due to the meteoric infiltration source; and 2) carbon isotope ratios give information on water-rock interactions. The covariation between the isotopes is attributed to changes in spring water composition as the travertines are precipitated. These findings with forthcoming U-Th ages will provide insight on the climate and tectonic activity of the fault-based system.