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- Title
Layered Mantle Flow Field Associated With Plate Kinematics and Slab Modulation Underneath the Horseshoe‐Shaped Banda Arc‐Islands.
- Authors
Li, Sijia; Kong, Fansheng; Liu, Kelly H.; Gao, Stephen S.
- Abstract
The Banda arc‐continent collision zone signifies one of the most seismically active and tectonically intricate zones. The high convergence rate across the region, coupled with the exceptionally arcuate arc and subducted slab, makes it an ideal locale for investigating interactions between plate (slab) kinematics and plastic flow in the asthenosphere, which can be diagnosed by seismic anisotropy from shear wave splitting analyses. In total, 206 pairs of splitting measurements using teleseismic SKS, SKKS, and PKS, along with 43 pairs using local S phases, are obtained by utilizing broadband seismic data from five permanent seismic stations. To reduce the ambiguity in determining the origin of anisotropy leading to the teleseismic splittings, which lack vertical resolution, crustal anisotropy is constrained according to the sinusoidal moveout of converted S phases at the Moho using receiver functions. A layered anisotropic structure based on joint analyses of the anisotropy measurements characterizing different depth layers suggests the presence of trench‐parallel flow both in the mantle wedge and the sub‐slab region. The northeastward motion of the slab, entrained by the fast‐moving Australian Plate, deflects asthenospheric materials. The modulation results in trench‐parallel plastic mantle flows and leads to the steepening of the southern portion of the asymmetric spoon‐shaped Banda slab. In the shallower part of the sub‐slab region, the northeastward Australian Plate motion produces simple shear in the transitional layer between the rigid lithosphere and the viscous asthenosphere. The shear deformation induces seismic anisotropy with resulting fast orientations in accordance with the plate motion direction. Plain Language Summary: The Banda region represents a nascent arc‐continent collision with the Australian continental lithosphere. The volcanic arc and non‐volcanic arc‐islands display a unique horseshoe shape. The subducted slab is anomalously bent 180°, leading to a spoon‐shaped morphology with a steeper southern portion. The role of the kinematics of the Australian Plate and this bent slab in shaping the asthenosphere is not clear. This study uses seismic anisotropy measured using data recorded over 14 years by five broadband seismic stations on the non‐volcanic arc‐islands to explore this intriguing problem. Results suggest that the northeastward movement of the Australian Plate makes asthenospheric materials flow along the depth contour of the slab, steepening the Banda slab's southern part. In the sub‐slab region, the upper portion follows the movement direction of the Australian Plate, while the deeper part is influenced more by slab deflection, directing asthenospheric flow. Key Points: Mantle flow field associated with the spoon‐shaped Banda slab is investigated using seismic azimuthal anisotropy measurementsObservations can be explained by trench‐parallel flow both in the mantle wedge and the sub‐slab regionNortheastward movement of the slab relative to the asthenosphere induces the two flow systems and leads to steepening of the southern slab
- Subjects
SEISMIC anisotropy; SLABS (Structural geology); LITHOSPHERE; ISLAND arcs; KINEMATICS
- Publication
Journal of Geophysical Research. Solid Earth, 2024, Vol 129, Issue 3, p1
- ISSN
2169-9313
- Publication type
Article
- DOI
10.1029/2023JB027694