Pulsed fluid release from subducting slabs caused by a scale-invariant dehydration process

Abstract

The chemical composition of a rock has a first-order effect on the onset and duration of rock dehydration. We present a multiscale dataset of chemical heterogeneities found in a low-temperature serpentinite from the Mirdita ophiolite in Albania, and we explore the effects of such heterogeneities on slab dehydration during subduction. The dataset consists of chemical and geological mappings from the micron to the meter scale, spanning five orders of magnitude. At each scale, we investigate the interplay of metamorphic reactions as well as porosity and fluid production through thermodynamic modeling along a slab Moho P-T path typical for subducting plates. Notably, our results show that chemical heterogeneities are preserved, regardless of the observation scale, even in the case of local homogenization by events such as the lizardite-antigorite transition. Consequently, scale-invariant patterns of porosity evolution and fluid production along the P-T path emerge, with characteristic peaks for each dehydration reaction. As such, the dehydration behavior on the slab scale seems to be controlled by the processes on the millimeter scale, whereby resulting peaks correspond to pulsed slab fluid release localized in space and time at each scale, along the strike and along the dip of the subducting plate.