Advanced strain and mass transfer analysis in crustal-scale oroclinal buckling and detachment folding analogue models

Abstract

Abstract The PIV (particle image velocimetry) method became a standard tool for the calculation of displacement fields in physical geodynamic models. For understanding the deformation dynamics of geodynamic models, in our study, we implemented several post-processing algorithms on the derived displacement field and calculated the velocity and strain(-rate) components, such as the divergence of the velocity field, vorticity and shear strain-rate. In the model of oroclinal buckling, we focused on strain analysis of the upper crust and correlated the shear strain-rate, vorticity and divergence anomalies with visual deformation patterns in the upper crust. The divergence of velocity fields in these models correspond to the pop-up and pop-down belts oriented along the axial trace of the oroclinal bends. High shear strain-rate domains correlate with horizontal, isovolumic shear zones alongside these belts, while vorticity shows rotational trend of fold axial traces of the pop-up and pop-down belts, around orocline inflection. In another series of models, we simulated the development of melt-cored crustal scale detachment folds and employed the same set of parameters to investigate the ductile deformation visible in side-view of the model domain. We developed a method that allows tracing the divergence in subcells locked on target subdomains. We tracked and quantified melt flow between the melt source area at the bottom of the model and progressively developing folds. This mass transfer analysis revealed polyphase fold evolution, where initial fold perturbations quickly amplify as the melt accumulates in the triangular hinge sector below and between the rotating fold limbs. While the early amplification leads to decompression driving the melt into the hinge zone area between the limbs, the fold lock-up stage and continued attenuation of the vertical limbs is associated with melt expulsion from the fold interlimb domain back into the source layer, where it can be transferred laterally to the foreland.