Determining subduction-zone fluid composition using a tourmaline mineral probe

V.J. van Hinsberg, G. Franz, B.J. Wood
2017 Geochemical Perspectives Letters  
doi: 10.7185/geochemlet.1719 Subduction zones are the sites where crustal materials are recycled into the mantle. In response to increasing pressures and temperatures during this process, hydrated minerals break down and release solute-bearing fluids and, above ~750 ˚C, form hydrous melts. Magmas generated by interaction of these melts and fluids with the mantle have a characteristic arc elemental signature. Here, a zoned refractory tourmaline grain, formed during Alpine subduction and uplift,
more » ... uction and uplift, was used to reconstruct the compositions of the fluids involved in element transfer. The reconstructed compositions confirm that slab-released fluids carry the arc-signature, and suggest that mineral-fluid element partitioning controls their compositions. However, these fluids are calculated to be dilute. To reconcile this with higher element-to-water ratios required for arc magmas, a two-stage arc-magma genesis model is favoured where fluids imprint their compositional signature progressively on a slab mélange that is subsequently transferred to, and interacts with the mantle to generate arc magmas.
doi:10.7185/geochemlet.1719 fatcat:vap5iunh2rdu3inbwaczcbdhfe