ModInc: Modelling the decompression of Ultra-High-Pressure Host-Inclusion systems

• Applicant: Professor Dr. Thibault Duretz
• Subject Area: Mineralogy, Petrology and Geochemistry ; Geology ; Geophysics
• Term: since 2025
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 559027825

Minerals may host inclusions of different chemical and mechanical properties. Host-Inclusion Systems (HIS) can record precious information on the geological history of tectonics units and are thus of geodynamic significance. In particular, in Ultra-High-Pressure (UHP) units, HIS may feature high grade mineral phases, witnessing extreme thermo-barometric conditions. In addition, deformation of host minerals may reflect the tectonic processes that govern decompression. The ModInc project aims at (1) predicting the occurrence of deformation structures in HIS under quasi-static and dynamic unloading conditions, (2) identifying the factors that control the preservation of UHP phases, and (3) providing independent estimates of decompression rates of UHP units. First, the decompression of HIS will be modelled using three-dimensional (3D) non-linear thermo-mechanical models. In particular, the role of loading rates, yielding modes, creep models, mechanical anisotropy of hosts, phase transitions and kinetics will be quantified. This study will allow to identify the conditions that lead to both garnet yielding and partial coesite preservation. The numerical model results will be compared with natural HIS (garnet, kyanite hosts) sampled in UHP domains (Alps, Norway). An interactive interface for HIS decompression modelling will be published. This will enhance the accessibility to and visibility of the outcomes of ModInc. Second, synthetic Pressure-Temperature-time (PTt) paths will be extracted from thermo-mechanical models of subduction and collision. The PTt paths will be used as input to model HIS decompression. This will further allow identifying which geodynamic scenario best explains the formation of structures observed in natural samples. By confronting HIS-scale and lithosphere-scale models to geological observations, ModInc will provide new insights into the physical processes at play in subduction-collision zones.

• DFG Programme: Research Grants