Boron recycling across the Subduction Factory: Insights from SIMS measurements of metasomatized mantle xenoliths from Kamchatka arc
Abstract
There is no direct observation of element transfer through the subarc mantle. A novel approach to constrain element mobility in the mantle wedge is by studying metasomatized mantle xenoliths erupted by arc volcanoes. Here, we present boron contents and δ11B of hydrous vein minerals, phlogopite and amphibole, in ultramafic mantle xenoliths from the Avachinsky and Shiveluch volcanoes in Kamchatka. They provide evidence of fluid/melt flow originating from dehydration/melting of the subducting plate. New SIMS measurements reveal that B in phlogopite and amphibole is extremely low and range from 0.3 to 3.1 μg g-1 and from 0.2 to 6.4 μg g-1, respectively. The δ11B of phlogopite and amphibole are highly variable and range from -16.6 to - 0.5‰ (± 1.4) and from -12.1 to + 0.9‰ (± 1.6), respectively. The unexpectedly low B contents and highly variable but isotopically light δ11B ratios of the metasomatic minerals may reflect sluggish slab dehydration under the arc front volcanoes. The well-documented and very large B outfluxes in the shallow parts of subduction zones1 seem to be in stark contrast with the deep (100-150km) slab derived fluids as recorded in the hydrous minerals we studied. References: 1. De Hoog, C.J. & Savov, I.P., 2018. Boron Isotopes as a Tracer of Subduction Zone Processes. In: Marschall H., Foster G. (eds) Boron Isotopes. Advances in Isotope Geochemistry. Springer Cham, 217-247.
- Publication:
-
EGU General Assembly Conference Abstracts
- Pub Date:
- April 2018
- Bibcode:
- 2018EGUGA..2016155T