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Updated: Jun 18, 2025

Simulation of Early Earth Hydrothermal Chimneys in a Thermal Gradient Environment
Published on: February 27, 2021
Pristine helium from the Karoo mantle plume within the shallow asthenosphere beneath Patagonia
Tiago Jalowitzki1, Hirochika Sumino2, Rommulo V Conceição3
1Programa de Pós-graduação em Geologia, Instituto de Geociências, Universidade de Brasília (UnB), Brasília, Brazil. jalowitzki@unb.br.
Abstract:
Mantle xenoliths usually represent fragments derived from the depleted and degassed lithospheric mantle with 3He/4He isotope ratios (6 ± 1 RA) lower than those of mid-ocean ridge basalts (8 ± 1 RA). Otherwise, basalts from oceanic islands related to hotspots often have high 3He/4He ratios (>10 RA), suggesting a deep and pristine undegassed mantle source. Here we present a striking high-3He/4He component (up to 27.68 RA) recorded by spinel-facies mantle xenoliths from Patagonia. Remarkably, the highest ratios were found in a long-lived trans-lithospheric suture zone related to the Carboniferous-Permian collision of two continental blocks: the Deseado and the North Patagonian massifs. The mantle xenoliths with notably high-3He/4He ratios are inferred to be fragments of the shallow asthenosphere rising through the eroded and rejuvenated thin lithosphere. The pristine helium component is derived from the western margin of the Karoo mantle plume, related to the initial stages of the Gondwana fragmentation.
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