Tilting-Axis Anisotropic Tomography and Subduction Dynamics of the Java-Banda Arc

The 180 degrees curvature of the Banda arc at the eastern end of the Java-Banda subduction zone reflects complicated geodynamic processes. A detailed investigation of its anisotropic structure would reveal its subduction dynamics, further resolving the controversial issue on how the highly arcuate Banda arc formed. We apply tilting-axis anisotropic tomography to obtain a high-resolution 3-D anisotropic model beneath the Java-Banda region. Our results show significant differences between Java and Banda in the pattern of anisotropy in both the subducting slab and its surrounding mantle, which reflect two distinctly different deformation modes in the two domains. Our results support the single-slab subduction model for the Banda region. In addition, trench-normal and upright fast-velocity-planes appear in the deep upper mantle, which may indicate material migrations in the big mantle wedge. Fast-velocity-planes in the shallow mantle exhibit a toroidal distribution, reflecting past counter-clockwise rotation and asthenospheric material extrusion. How the great curvature of the Banda arc formed remains in debate. Previous studies have proposed a single slab model and a double slab model for this subduction zone. Seismic anisotropy in the subducting slab and its surrounding mantle could provide clues on which model is correct. In this work, we perform the first tomographic inversion for tilting-axis anisotropy to reveal the 3-D anisotropic structure of the Java-Banda subduction zone. The anisotropic features in the subducted slab and its surrounding mantle revealed by our anisotropic tomography support the single-slab subduction model for the formation of the Banda arc. Significant anisotropic differences exist between Java and Banda in both the mantle and slab Slab subduction is the main cause of seismic anisotropy in the Java-Banda arc Our results support the single slab model for the Banda subduction zone