Parental magma signatures recorded in hybrid zones

Abstract

Mixing of magmas has been argued as a process to account the intermediate composition of magmatic systems. The coalescence of magmas of contrasted compositions in composite magma chambers is fact observed in fossil magma chambers or plutons and is also deduced from lava sequences in volcanic successions. Nevertheless, it remains unclear if this process can produce magma with an intermediate composition. Hybrid zones, addressed in this study, can be divided into mono- and poly-compositional types according to textural and compositional differences, respectively. We propose magma splitting as mechanism able to segregate two submagmatic systems with so contrasting textures. The trigger for the compositional and textural splitting is the second boiling segregating a water-saturated melt (coarsegrained end member; low liquidus magma, LLM) from the solid residue (fine-grained end member; high liquidus magma, HLM) by means of gas-driven filter pressing (Langmuir, 1989). The most favorable scenario for the magma splitting effectiveness is the subvolcanic environment since the second boiling can be suddenly reached and the textures are preserved by quenching. Hybrid zones are used as a proxy of parental magmas quenched at the level of emplacement. The hybrid zones are now considered as key outcrops to determinate the parental composition linking the HLM and LLM end-members of the calcalkaline magmas and to stablish an innovative protocol to study these magmatic suites.