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- Title
Mantle Flow Induced by the Interplay of Downgoing Slabs Revealed by Seismic Anisotropy Beneath the Sula Block in Eastern Indonesia.
- Authors
Cao, Lingmin; Lü, ChuanChuan; He, Xiaobo; Rawlinson, Nicholas; Hao, Tianyao; Widiyantoro, Sri; Supendi, Pepen; Zhao, Liang; Yuan, Huaiyu; Zhao, Minghui; Qiu, Xuelin; Rafie, Muhammad Taufiq; Alfian, Alfian; Sahara, David Prambudi
- Abstract
The North Sulawesi subduction zone is characterized by southward subduction of the Celebes Sea slab to a depth of ∼250 km, mainly overlying the Sangihe slab that subducts west from the Molucca Sea and penetrates the mantle transition zone. The palaeo‐subducted Sula slab dips northward and partially underlies both the Sangihe and Celebes Sea slabs. Adjacent subduction zones with horizontal overlapping subducting slabs in the upper mantle have unclear dynamic interactions. An extensive strike‐slip fault forms the western boundary of the active North Sulawesi subduction zone, providing an ideal setting to study mantle flow between overlapping slabs. We use local S‐wave and teleseismic S and SK(K)S waveform splitting analysis to measure seismic anisotropy in the northern Sulawesi region. Our observations reveal typical mantle wedge corner flow within the Sangihe subduction system. In the Gulf of Tomini, the observed trench‐oblique fast‐axis orientations above the Celebes Sea slab are likely a consequence of the interaction between two subducting slabs. The southernmost measurement with an E–W‐trending fast direction in the mantle wedge might be related to the subduction of the Sula slab. Furthermore, fault‐parallel fast‐axis orientations of anisotropy near the southern segment of the Palu‐Koro fault are attributed to large‐scale shearing across this lithospheric‐scale strike‐slip fault system. Overall, our observations suggest that the strain caused by lithospheric and asthenospheric deformation is mainly confined within the microplate, displaying a restricted flow pattern and localized effects due to the size of the plate boundaries, such as the Palu‐Koro fault. Plain Language Summary: North Sulawesi is bordered by the Makassar Strait, Celebes Sea, Molucca Sea, and Gulf of Tomini and hosts the Palu‐Koro fault. The region hosts two active subduction zones: the smaller, southward dipping North Sulawesi subduction zone and the larger westward dipping Sangihe subducting slab. Another fossilized submerged slab –Sula slab lies beneath both the Celebes Sea and Sangihe slabs to the south. Thus, it is an ideal area to investigate how the interaction between neighboring subduction zones can affect the upper‐mantle deformation and whether a strike‐slip fault could contribute to the mantle dynamics. We use shear‐wave splitting analysis to measure seismic anisotropy to reveal the lithospheric deformation and upper mantle flow patterns of this interactive area. Our results show that the Celebes Sea slab controls mantle wedge dynamics in the North Sulawesi subduction zone, and the interaction between the Celebes Sea and Sangihe slabs occurs where two slabs entirely overlap. The strike‐slip fault at the western boundary only appears to have a local influence on the regional strain field in western Sulawesi. Key Points: We employ shear‐wave splitting analysis to characterize the seismic anisotropy to infer upper‐mantle deformation in north SulawesiWe find evidence for slab‐slab dynamic interactions and constrain their influencing spatial rangeThe Palu‐Koro fault marks the west limit of lithospheric deformation imposed by the complex subduction system
- Subjects
SULAWESI (Indonesia); SEISMIC anisotropy; SLABS (Structural geology); SUBDUCTION; SUBDUCTION zones; WAVE analysis; ANISOTROPY
- Publication
Journal of Geophysical Research. Solid Earth, 2024, Vol 129, Issue 5, p1
- ISSN
2169-9313
- Publication type
Article
- DOI
10.1029/2023JB028110