Nature of the Paleo-Pacific Subduction Along the East Asian Continental Margin in the Mesozoic: Insights From the Sedimentary Record of West Sarawak, Borneo

Abstract

The Mesozoic subduction history of the Paleo-Pacific plate below the East Asian margin remains contentious, in part because the southern part is poorly understood. To address this, we conducted a sediment provenance study to constrain Mesozoic subduction history below West Sarawak, Borneo. A combination of detrital zircon U-Pb geochronology, heavy minerals, trace element, and bulk rock Nd isotope data were used to identify the tectonic events. The overall maturity of mineral assemblages, dominantly felsic sources, abundant Precambrian-aged zircons, and low εNd(0) values (average −13.07) seen in Late Triassic sedimentary rocks suggest a period of inactive subduction near Borneo. Slab shallowing subduction occurred between 200 and 170 Ma based on subdued magmatism and tectonic compression across West Sarawak. From c. 170 to 70 Ma there was widespread magmatism and we interpret the Paleo-Pacific slab steepened. Collectively, we show the Paleo-Pacific plate subduction had variable slab dip histories in Borneo.