The Earth's inner dynamics and their surficial manifestations are closely linked to the physical properties of the mantle. Therefore, posing quantitative constraints on these properties is crucial for understanding the dynamic processes that govern the evolution of our planet.

Water influences the physical, transport, and rheological properties of the mantle, and impacts the melting regimes of mantle rocks. Subduction processes may deliver water into the Earth's lower mantle, stored by δ-(Al,Fe)OOH solid solutions within oceanic slabs subducted to those depths. δ-(Al,Fe)OOH is expected to exhibit an important shear wave anisotropy at pressures representative of the lowermost mantle. Therefore, textured δ-(Al,Fe)OOH in subducted slabs may contribute to seismic anomalies observed in the deepest regions on the lower mantle. Yet, to our knowledge, experimental constrains on texture development in δ-(Al,Fe)OOH solid solutions are lacking as no plastic deformation studies have been conducted so far. This lack of experimental observations hinders our ability to seismically detect water subducted and stored in the lower mantle, thereby impacting our insights into the geodynamical and geochemical evolution of our planet.

Here, the deformation behavior of δ-(Al,Fe)OOH has been experimentally investigated by synchrotron X-ray diffraction in radial geometry (r-XRD) using the setup available at the Extreme Conditions Beamline P02.2 at PETRA III/DESY. High-pressure, high-temperature deformation studies were performed through the coupling of r-XRD with resistively-heated diamond-anvil cells. In this contribution, we will describe our experimental results, and discuss our findings regarding the interpretation of geophysical observables with a focus on seismic detectability of bound water in the lower mantle.