Transportation of beryllium with H₂O at high pressures: Implication for magma genesis in subduction zones

Abstract

The degree of transportation of beryllium with H2O is measured under the upper mantle P/T conditions in order to examine the incorporation of 10Be in subduction zone magmas. 5.4±0.3% of original beryllium in the starting serpentinite is extracted with H2O from the system through the dehydration reaction of serpentine at 850°C and 1.5 GPa. It follows that the partial melting of oceanic lithosphere including 10Be‐rich sediment layer is not necessarily required for inclusion of the isotope in island‐arc lavas. We suggest that the dehydration processes in the subducted slab and mantle wedge materials dragged downward by the slab subduction govern the concentration of 10Be in arc lavas.

Implications of the serpentine phase transition on the behaviour of beryllium and lithium–boron of subducted ultramafic rocks

“…Fiorentini and Beresford, 2008), or that Li within clinopyroxene and olivine are in disequilibrium (Seitz and Woodland, 2000). For Be, this is in-line with the experimental data of Tatsumi and Isoyama (1988) at 1.5 GPa and 850°C, where peridotite loses up to 5% of the initial Be mass. Such an extraction process potentially increases the Be concentration within the mantle wedge.…”

“…Bebout et al, 1993;Ryan et al, 1996;Bouvier et al, 2008). However, Be shows some mobile behaviour under high T and P (850°C and 1.5 GPa) as suggested by Tatsumi and Isoyama (1988). They showed that a max.…”

“…On the other hand limited Be mobility at Implications of the serpentine phase transition on the behaviour of beryllium and lithium-boron of subducted ultramafic rocks 1259 Line missing high-grade metamorphism was suggested by Domanik et al (1993), in-line with the experiments of Tatsumi and Isoyama (1988). We infer that Be concentrations within mantle minerals are following a two-stage process: (A) at low T and P and common fluid compositions, any phase transformation related to serpentinization keeps the Be content of minerals stable suggesting limited mobility of Be during low-temperature alteration.…”

“…We infer that Be concentrations within mantle minerals are following a two-stage process: (A) at low T and P and common fluid compositions, any phase transformation related to serpentinization keeps the Be content of minerals stable suggesting limited mobility of Be during low-temperature alteration. (B) At high-temperature (850-900°C) and pressure (1.5-2.0 GPa), such as in the experiments of Tatsumi and Isoyama (1988) and Brenan et al (1998), Be displays some mobile behaviour and can therefore be slightly enriched within the mantle wedge.…”

Subduction dynamics at the middle America trench : new constraints from swath bathymetry, multichannel seismic data, and 10BE

“…Solid-fluid parition coefficients for beryllium are consistently at least two orders of magnitude larger than partition coefficients for boron at 900°C and 2.0 GPa (Brenan et aI., 1998b). Experiments on serpentinite at 850°C and 1.5 GPa showed that only small amounts of beryllum were liberated with H20 during dehydration (Tatsumi and Isoyama, 1988).…”