Tracking subduction dehydration and fluid-rock interaction in high-pressure metamorphic phengite using boron isotopes.

Phengite 300px Boron (B) isotopes have great potential to track water cycling and fluid-rock interaction in metamorphic rocks from subduction zone settings. By investigating the boron concentrations and B isotope compositions of white mica, the major mineral host for boron, from a suite of well-characterised high-pressure metamorphic rocks, we will test the hypothesis that deeply subducted metamorphic rocks reflect dehydration in the down-going plate with increasing temperatures in their B contents and B isotope signatures. The effects of subsequent fluid-rock interaction during exhumation will be evaluated in chemically overprinted samples that exhibit step-like compositional zoning in white mica.