The Helium and Carbon Isotope Characteristics of the Andean Convergent Margin

Subduction zones represent the interface between Earth’s interior (crust and mantle) exterior (atmosphere oceans), where carbon other volatile elements are actively cycled Earth reservoirs by plate tectonics. Helium is a sensitive tracer of sources can be used to deconvolute mantle crustal in arcs; however it not thought recycled into subduction processes. In contrast, readily recycled, mostly form carbon-rich sediments, thus understand delivery via subduction. Further, chemically-reactive isotope fractionation determine main processes controlling movements within arc systems. Here, we report helium abundance data for 42 deeply-sourced fluid gas samples from Central Volcanic Zone (CVZ) Southern (SVZ) Andean Convergent Margin (ACM). Data assess influence parameters (e.g., thickness, inputs, convergence rate) on composition volatiles surface volcanic emissions. He isotopes CVZ backarc range 0.1 2.6 R A ( n = 23), with highest values Puna lowest Sub-Andean foreland fold-and-thrust belt. Atmosphere-corrected SVZ 0.7 5.0 19). Taken together, these reveal clear southeastward increase 3 He/ 4 He, (in SVZ) falling below nominal associated pure upper (8 ± 1 ), approaching mean value gases (5.4 1.9 ). Notably, found CVZ, suggesting more significant inputs (i.e., assimilation He) budget. The thickness (up 70 km) significantly larger than SVZ, just ∼40 km. We suggest that exerts primary control extent fluid-crust interaction, as rise through ACM. also 11) sites δ 13 C varies −15.3‰ −1.2‰ [vs. Vienna Pee Dee Belemnite (VPDB)] CO 2 / vary over two orders magnitude (6.9 × 10 8 –1.7 11 ratios reported 13) −17.2‰ −4.1‰. four (4.7 7 12 Low consistent removal calcite precipitation dissolution) shallow hydrothermal Carbon modeling suggests occurs at temperatures coincident temperature limit life (122°C), biology may play role C-He systematics arc-related