Postmelting hydrogen enrichment in the oceanic lithosphere

Veronique Le Roux , Benjamin M Urann , Daniele Brunelli , Enrico Bonatti , Anna Cipriani , Sylvie Demouchy (1) , Brian D Monteleone

1 Géosciences Montpellier

The large range of H 2 O contents recorded in minerals from exhumed mantle rocks has been challenging to interpret, as it often records a combination of melting, metasomatism, and diffusional processes in spatially isolated samples. Here, we determine the temporal variations of H 2 O contents in pyroxenes from a 24-Ma time series of abyssal peridotites exposed along the Vema fracture zone (Atlantic Ocean). The H 2 O contents of pyroxenes correlate with both crustal ages and pyroxene chemistry and increase toward younger and more refractory peridotites. These variations are inconsistent with residual values after melting and opposite to trends often observed in mantle xenoliths. Postmelting hydrogen enrichment occurred by ionic diffusion during cryptic metasomatism of peridotite residues by low-degree, volatile-rich melts and was particularly effective in the most depleted peridotites. The presence of hydrous melts under ridges leads to widespread hydrogen incorporation in the oceanic lithosphere, likely lowering mantle viscosity compared to dry models.

Domaines: Géochimie; Minéralogie; Pétrographie

Veronique Le Roux, Benjamin M Urann, Daniele Brunelli, Enrico Bonatti, Anna Cipriani, et al.. Postmelting hydrogen enrichment in the oceanic lithosphere. Science Advances , 2021, ⟨10.1126/sciadv.abf6071⟩. ⟨hal-03255870⟩