The mineral and fluid chemistry of high pressure serpentinite dehydration

Serpentinites are the main water carrying rocks that can potentially transport considerable amounts of water (through subduction) to mantle depths. The processes of hydration at the ocean floor and the metamorphic reactions upon subduction are accompanied by mobilisation and trapping of trace elements as well as their redistribution among the metamorphic minerals and fluids.

During subduction, the serpentine low-P minerals are transformed to the high-P serpentine mineral antigorite. Further subduction leads to a continuous breakdown of antigorite. The reaction atg = ol + opx + chl + H2O transforms the atg-serpentinites to chl-harzburgites. The H2O liberated at this reaction forms an aqueous fluid of which numerous inclusions are entrapped in the spinifex-like olivine of the chl-harzburgite. (This fluid is considered to be responsible for the melting in the mantle beneath the volcanic arcs). We aim to better understand the chemical budget of both the serpentinites and the harzburgites as well as the chemistry of the antigorite breakdown-fluid.

At the Cerro del Almirez, a mountain in an ultramafic body of the Betic Cordillera in southern Spain, these tow rock types crop out next to each other. At the moment we are working on samples from this well described location.