Migrated teleseismic P wave receiver functions reveal intricate post-subduction crust and upper mantle structure of northern Borneo (Sabah), SE Asia

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Borneo is a key piece of the regional tectonic puzzle of southeast Asia and a unique location to study subduction termination, particularly in the north. The tectonic history of Sabah in northern Borneo includes elements of five different subduction events: 1) westward Triassic Palaeo-Pacific (~240-200 Ma); 2) southward Cretaceous Proto-South China Sea (92-86 Ma); 3) southward Late Eocene to Early Miocene (~40-20 Ma) Proto-South China Sea; 4) northwestward Celebes Sea (~17-9 Ma); and 5) southeastward Middle Miocene Sulu Sea (~15-10 Ma) subduction. Anti-clockwise (~45°) rotation of Borneo and Neogene (~23-5 Ma) uplift and subsidence events preceded Late Miocene-Early Pliocene exhumation and emplacement (7.8-7.2 Ma) of the 4095 m high Mt. Kinabalu granite pluton. We utilize the northern Borneo Orogeny Seismic Survey (nBOSS) seismological dataset to calculate teleseismic receiver functions and constrain crust and upper mantle discontinuities beneath Sabah using common conversion point migration imaging. Mid-crustal and Moho discontinuities occur beneath most of Sabah at 22-25 and 30-40 km depth, respectively, but major lateral variations delineate lithospheric boundaries that appear associated with surface ophiolites, Mt. Kinabalu granite, and sedimentary depocenters. We show evidence for an uppermost mantle slab remnant beneath Sabah in the form of a gently westward-dipping, 75-100 km wide, discontinuity at 45-55 km depth, likely composed of oceanic crust, its lithosphere detached, and associated with Celebes Sea subduction. Sabah geology, tectonics, uplift and subsidence are reexamined in light of the new lithosphere images, revealing Sabah and post-subduction tectonics in unprecedented detail.

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