The group at the University of Bern is specialized in microanalysis of major and trace elements, as well as isotopes in metamorphic rocks. Within this group, Professor Daniela Rubatto is developing new methods to analyse oxygen isotopes at the microscale using the SwissSIMS ion microprobe facility located at the University of Lausanne. Oxygen is a main constituent of minerals and aqueous fluids and thus variations in the isotopic composition of oxygen in mineral zones can be used to trace the passage of aqueous fluids in rocks. When this information is combined with mineral chemical zoning and age, it serves to reconstruct P-T-time-fluid paths of deep processes.
Mineral-aqueous fluid interactions in the two main reservoirs of the Earth’s crust, namely the continental and the oceanic crust, are targeted using a series of key minerals. This approach requires development or improvement of protocols and standards for the in-situ, microscale analysis of oxygen isotopes in minerals such as garnet, micas, quartz, zircon, monazite and apatite.
Measurements of oxygen isotopes is combined with trace element analysis to investigate elemental traces for fluid-mineral interaction, and with age determinations at the micro- or mineral-scale in order to establish the timing of fluid circulation. The analytical approach is flanked by modelling of the evolution of oxygen isotope compositions in minerals and fluids by classical forward modelling packages (collaboration with Dr. Pierre Lanari).
Initial results show that fluid alteration at the mineral scale is a common feature in a variety of rock types recovered from subduction zones, thus recording fluid flow at depth of 50–100km. These results also indicate that fluids during subduction can either be concentrated in narrow shear zones or be pervasively distributed at a km scale. Distinguishing between these two fluid regimes is fundamental to reconstruct the dynamics of subduction.
