Mantle Flow Patterns Beneath the Junction of Multiple Subduction Systems Between the Pacific and Tethys Domains, SE Asia: Constraints From SKS‐Wave Splitting Measurements

Abstract

Abstract The region around the Celebes Sea, SE Asia, is evolving within a convergent tectonic environment involving the Pacific plate to the east and the Indian‐Australian plate to the south. It is arguably one of the most tectonically complex regions in the world and serves as an ideal setting to study dynamic interactions between the Pacific and Tethys tectonic domains. The issue of which subducting plate plays a leading role in governing the regional mantle flow is not well understood. Mantle flow can be characterized by seismic anisotropy observations, providing clues for understanding regional tectonics. We conducted SKS‐wave splitting analysis by using data from seven seismic stations located around the Celebes Sea. Our results, when combined with previous observations, suggest the presence of various types of mantle flow in this area, including (a) corner flow in the mantle wedge above the westward‐subducting Molucca Sea (Sangihe) slab, (b) two‐layer anisotropy related to the eastward‐subducting Molucca Sea (Halmahera) slab, (c) deflected flow due to proximity to the Sangihe slab's edges, (d) trench‐normal mantle flow beneath southeastern Borneo due to the subduction of the Indian‐Australian plate, and (e) Northwest Borneo‐Palawan trough‐parallel mantle flow beneath northeastern Borneo. Various types of mantle flow indicate that the dynamic interactions of adjacent subduction zones played crucial roles in influencing the regional upper mantle dynamics between the Tethys and western Pacific domains since the breakup of the Gondwana supercontinent in the Mesozoic.