Helium and carbon isotope systematics in arc-related fumarolic gases and geothermal fluids

BARRY P.; BEKAERT D; CURTICE J; BARTELS C.; HUDAK M; DE MOOR M.; JESSEN G.; GIOVANELLI D.; SCHRENK, M.O.; AGUILERA, F.; AGOSTINA CHIODI; RAMIREZ C.; LLOYD K.

Congreso; AGU Fall Meeting 2022; 2022

Convergent margins represent the interface between Earth’s interior and exterior, where carbon and other volatiles are actively cycled between Earth reservoirs by plate tectonics. Helium is an excellent tracer of mantle inputs and can be used to deconvolute mantle and radiogenic (crustal) volatile pathways in arcs,however it is not thought to be recycled into the mantle by subduction processes. In contrast, carbon is readily recycled, mostly in the form of carbon-rich sediments, and can thus be used to understand volatile delivery via subduction. Further, carbon is chemically-reactive and isotope fractionation can be used to determine the main processes controlling volatile movements within arc systems.Gas and water samples are typically collected at subaerial hot and warm springs, natural gas seeps and fumaroles using standard inverted funnel sampling techniques1-2 or the water-displacement method3.With respect to the former method, gases and fluids are flushed through silicone tubing and into 3/8-inch copper tubes4 and closed on each end, trapping the sample inside of the copper tubing, between the clamps5.Samples are then analyzed by static mass spectrometry for noble gases and on a Picarro for carbon isotopes. In addition to an overview of sampling techniques, data from several recent He-C studies will be presented6-9, demonstrating the utility of combining inert (noble gas) tracers with stable isotopes (e.g., carbon and nitrogen) to understand volatile sources and pathways in fluid and gas samples from convergent margins.