5:15 PM - 6:45 PM
[SIT14-P13] Deformation-induced Crystallographic Preferred Orientation of δ-AlOOH at High Pressure and High Temperature
Keywords:δ-AlOOH, Deformation, Crystal preferred orientation, Seismic anisotropy
Understanding the rheological properties of hydrous phases under extreme conditions is pivotal for elucidating the mechanical behavior of subducting slabs and the associated seismic anisotropy within the Earth's mantle transition zone and lower mantle. Unlike other hydrous minerals, which decompose in the lower mantle, δ-AlOOH, the high-pressure polymorph of diaspore, forms a solid solution with phase H and can coexist with bridgmanite or post-perovskite, remaining stable up to conditions at the core-mantle boundary. It is characterized by an orthorhombic crystal structure with high elastic anisotropy. This study focuses on the rheological behavior of δ-AlOOH under high-pressure and high-temperature conditions, a key hydrous mineral believed to play a significant role in the water cycle and seismic phenomena of subducting lithospheric plates into the lower mantle.
We synthesized polycrystalline samples of δ-AlOOH and subjected them to well-controlled uniaxial deformation experiments at 20 GPa and 1000 °C, conditions representative of the mantle transition zone and the uppermost lower mantle. Our findings reveal that δ-AlOOH develops a pronounced (010) texture perpendicular to the compression direction, as confirmed by in-situ synchrotron X-ray diffraction observation.
Our findings suggest that δ-AlOOH can develop a significant anisotropic fabric under mantle conditions, which could contribute to the ubiquitously observed seismic anisotropy in these regions near subducting slabs. The observed crystallographic preferred orientation (CPO) and consequent elastic anisotropy are helpful for our understanding of the mantle's dynamic processes, including the flow patterns and deformation mechanisms in the transition zone and lower mantle. This study not only sheds some light on the role of water-bearing minerals in the deep Earth but also enhances our understanding of the contributions of hydrous mineral physics to seismic anisotropy, offering insights into the interpretation of seismic observations for mantle dynamics.
We synthesized polycrystalline samples of δ-AlOOH and subjected them to well-controlled uniaxial deformation experiments at 20 GPa and 1000 °C, conditions representative of the mantle transition zone and the uppermost lower mantle. Our findings reveal that δ-AlOOH develops a pronounced (010) texture perpendicular to the compression direction, as confirmed by in-situ synchrotron X-ray diffraction observation.
Our findings suggest that δ-AlOOH can develop a significant anisotropic fabric under mantle conditions, which could contribute to the ubiquitously observed seismic anisotropy in these regions near subducting slabs. The observed crystallographic preferred orientation (CPO) and consequent elastic anisotropy are helpful for our understanding of the mantle's dynamic processes, including the flow patterns and deformation mechanisms in the transition zone and lower mantle. This study not only sheds some light on the role of water-bearing minerals in the deep Earth but also enhances our understanding of the contributions of hydrous mineral physics to seismic anisotropy, offering insights into the interpretation of seismic observations for mantle dynamics.