Accessory phases as petrogenetic tools
Accessory phases are excellent recorders of geological processes and are the main hosts for a wide range of trace elements. Therefore, the presence of such phases severely affects differentiation and partial melting trends in rocks. Special emphasis will be placed on the behaviour of rutile, zircon, monazite and allanite in a wide range of rock types. Recently developed trace element thermometers have shown the potential to obtain formation temperatures from accessory phases. However, these experimental results still need to be tested rigorously in magmatic and high-temperature metamorphic rocks. We plan to use a variety of well characterised magmatic and high temperature metamorphic settings to test the viability of these trace element thermometers and to search for potentially new systems that are sensitive to pressure, temperature and fluid composition.
Accessory phases are widely used for dating magmatic and metamorphic processes and can be used for the in-situ investigation of isotope systems such as Sm-Nd and Lu-Hf. Robust age data (in situ Th-Pb, U-Pb isotope analysis) can now be obtained for specific conditions along the PTDt-evolution of samples, in particular for individual HP-stages of metamorphic growth. We are refining and applying analytical techniques that allow age data to be linked to mineral assemblages in individual samples and to their regional structural context. This involves improving local thermobarometry, trace element analysis (notably of REE), and isotopic (U-Pb and Th-Pb) analysis. We are making use of our LA-ICP-MS lab in Bern and of the capabilities of the Cameca 1280HR ion probe at the Swiss-SIMS facility.