Discipline: Ecology Environmental and Earth Sciences
Subcategory: Geosciences and Earth Sciences
Cristian Virrueta - University of California San Diego
This research project focuses on methane-helium relationships (δ13CCH4 and 3He/4He) to elucidate on the complex tectonic and geologic environment of Panama. Panama has three volcanoes active since the Holocene (Baru, El Valle, and La Yeguada) and we target geothermal fluids (fumaroles, hot springs, and other geothermal waters) for their volatile systematics. We aim to understand the methane characteristics of these volcanoes, its origins as biogenic, thermogenic, and abiogenic methane, and its relationship to 3He/4He ratios as a discriminate of methane provenance and its volcanic flux. While samples will be characterized for their general gas chemistry, we obtained isotope data on CH4 and He to derive information of the sources of these volatiles. This will allow us to resolve origins between sedimentary inputs – associated with subduction of sediments in the region, and mantle inputs with/without modification in the crust and/or the geothermal system. Eight geothermal samples were collected following a west-to-east transect across western Panama. The approach adopted involves transfer of the field sample to a laboratory-based vacuum system, carefully avoiding air contamination. An FID gas chromatograph analyzes the hydrocarbon gas chemistry to determine relative abundances. The methane is then isolated from other gaseous constituents within each sample using a TCD gas chromatograph, oxidized to pure CO2, and condensed into a suitable container for transfer to a mass spectrometer for isotope measurement. Across all sampling sites, the 3He/4He isotope data ranges between 1.35 RA and 9.09 RA, with δ13C signatures between -7.9 and -23.9‰. The MORB-like and abiogenic signatures suggests that subduction may play an important role in the creation of the Baru, La Yeguada, and El Valle volcanoes within western Panama. The unusually high 3He/4He ratios with increasing distance from the trench may be explained by the shallowing of the subduction angle and varying crustal thickness. Eastern Panama is devoid of any active volcanism presumably due to the cessation of subduction in that area.
Not SubmittedFunder Acknowledgement(s): Warren College Research Scholarship
Faculty Advisor: David Hilton, drhilton@ucsd.edu