Résumé
Accessory minerals such as zircon, apatite, rutile or titanite are widely used as powerful thermochronological tools in order to constrain the timing and/or thermal evolution (cooling) of magmatic and/or metamorphic events. In this study, we use these minerals not only as radiochronometers but also as petrogenetic tracers of processes and sources for various petrographic rocks outcropping in a fossil arc crustal section in Pakistan. To reach such a goal, we used a variety of different geochemical tracers (titanium thermometry, trace elements, Sr-Nd-Pb isotopes…) on accessory minerals from which we obtained geochronological constraints. A previous geochemical conventional study (major and trace elements combined with isotopes) allowed us to propose a multi-stagecomplex evolution for the intra-oceanic Kohistan arc [1]. Datings of accessory minerals extracted from different lithologies from the crustal section of the arc allow putting precise temporal constraints for the geodynamical evolution of this section, i.e. both for the volcanic arc s.s. building (from ∼110Ma to ∼98My) and for major underplating events occurring during the section evolution at ∼98My, ∼91My and ∼85My. Major and trace elements have been measured « in situ » by EPMA or LA-ICPMS on these accessory minerals either in thick sections or included in epoxy mounts. Isotopes have been measured « in situ » by LA-ICPMS method or by the microdrill technique followed by chemical separation of isotopes and MC-ICPMS analyses. In order to assess the geochemical responses of accessory minerals investigated, we discuss and compare our results to those obtained on wholerocks and pyroxenes separated from different lithologies (gabbros, diorites, granites…) and analyzed for the same elements.