The Ronda peridotite (Spain): A natural template for seismic anisotropy in subduction wedges

Jacques Précigout (1) , Bjarne S.G. Almqvist (2)

1 ISTO - Institut des Sciences de la Terre d'Orléans - UMR7327
2 Department of Earth Sciences [Uppsala]

The origin of seismic anisotropy in mantle wedges remains elusive. Here we provide documentation of shear wave anisotropy (AVs) inferred from mineral fabric across a lithosphere-scale vestige of deformed mantle wedge in the Ronda peridotite. As predicted for most subduction wedges, this natural case exposes a transition from A-type to B-type olivine fabric that occurs with decreasing temperature and enhanced grain boundary sliding at the expense of dislocation creep. We show that B-type fabric AVs (maximum of 6%) does not support geophysical observations and modeling, which requires 8% AVs. However, an observed transitional olivine fabric (A/B) develops at intermediate temperatures (800–1000°C) and can generate AVs ≥ 8%. We predict that the A/B-type fabric can account for shear wave splitting in contrasting subduction settings, exemplified by the Ryukyu and Honshu subduction wedges. The Ronda peridotite therefore serves as a natural template to decipher the mantle wedge deformation from seismic anisotropy.

Domaines: Tectonique; Volcanologie

Jacques Précigout, Bjarne S.G. Almqvist. The Ronda peridotite (Spain): A natural template for seismic anisotropy in subduction wedges. Geophysical Research Letters, 2014, 41 (24), pp.8752-8758. ⟨10.1002/2014GL062547⟩. ⟨insu-01096459⟩