Pristine helium from the Karoo mantle plume within the shallow asthenosphere beneath Patagonia

Tiago Jalowitzki; Hirochika Sumino; Rommulo V Conceição; Manuel E Schilling; Gustavo W Bertotto; Andrés Tassara; Fernanda Gervasoni; Yuji Orihashi; Keisuke Nagao; Marcelo Peres Rocha; Rodrigo Antonio de Freitas Rodrigues

doi:10.1038/s41467-024-50773-4

Pristine helium from the Karoo mantle plume within the shallow asthenosphere beneath Patagonia

Nat Commun. 2024 Jul 30;15(1):6402. doi: 10.1038/s41467-024-50773-4.

Authors

Affiliations

¹ Programa de Pós-graduação em Geologia, Instituto de Geociências, Universidade de Brasília (UnB), Brasília, Brazil. [email protected].
² Research Center for Advanced Science and Technology, University of Tokyo, Tokyo, Japan.
³ Programa de Pós-graduação em Geociências, Instituto de Geociências, Universidade Federal do Rio Grande do Sul (UFRGS), Porto Alegre, Brazil.
⁴ Instituto de Ciencias de la Tierra, Facultad de Ciencias, Universidad Austral de Chile, Valdivia, Chile.
⁵ INCITAP, CONICET - Universidad Nacional de La Pampa, Santa Rosa, Argentina.
⁶ Departamento de Ciencias de la Tierra, Universidad de Concepción, Concepción, Chile.
⁷ Centro de Engenharias, Universidade Federal de Pelotas (UFPel), Pelotas, Brazil.
⁸ Department of Earth and Environmental Sciences, Hirosaki University, Hirosaki, Japan.
⁹ Division of Polar Earth-System Sciences, KOPRI (Korea Polar Research Institute), Yeonsu-gu, South Korea.
¹⁰ Programa de Pós-graduação em Geologia, Instituto de Geociências, Universidade de Brasília (UnB), Brasília, Brazil.
¹¹ Research School of Earth Science, Australian National University, Canberra, ACT, 0200, Australia.

Abstract

Mantle xenoliths usually represent fragments derived from the depleted and degassed lithospheric mantle with ³He/⁴He isotope ratios (6 ± 1 R_A) lower than those of mid-ocean ridge basalts (8 ± 1 R_A). Otherwise, basalts from oceanic islands related to hotspots often have high ³He/⁴He ratios (>10 R_A), suggesting a deep and pristine undegassed mantle source. Here we present a striking high-³He/⁴He component (up to 27.68 R_A) 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.