Forearc basin development along Western Luzon, Philippines

Sediment distribution within the Manila Trench exerts a strong influence on the tectonic evolution of the accretionary prism and the forearc basins of this convergent plate margin. Multichannel seismic data show up to 2600 m of turbidite-style sediments overlying a thin pelagic/ hemipelagic sediment layer and oceanic basement in the northern part of the Manila Trench. Manila Trench sedimentation is dominated by turbidite sources at the ends of the trench coupled with transport along the trench axis. In contrast, the forearc basin system of the Manila Trench receives sediment through submarine canyons incised into the West Luzon continental slope. The rate of sediment supply to the forearc basin system is not directly related to the rate of sediment supply to the trench. The size of the accretionary prism varies significantly along strike of the trench and is strongly correlated with the local thickness of turbidite sediments within the trench. More than 200 m of trench turbidites are probably needed to create net uplift of the trench-slope break through accretion. This general relationship may apply to other convergent plate margins. The uplift rate at the trench slope break varies along the trench and is largely independent of variations in the local sediment accumulation rates in the forearc basins. Several different types of forearc morphology are formed along the Manila Trench. The overall seismic stratigraphy of the West Luzon Trough forearc basin is remarkably uniform, with continuous seismic sequences for up to 110 km along strike. The unconformities that bound these seismic sequences result from a complex interplay of relatively long-term (~ 10 + m.y.) uplift of the accretionary prism and relatively short-term (~ 1−5 m.y.) variations in sediment supply to the forearc basin. The latter may be controlled by eustatic sea level changes.