Structure and tectonics of the Manila trench system, Western Luzon, Philippines

The Manila Trench subduction zone is an active convergent plate margin between the South China Sea and the northern Philippines. The Manila Trench is associated with an east-dipping Benioff zone beneath Luzon, a well-developed forearc basin system and a volcanic arc. The Luzon Trough forearc basin system contains up to 4.5 km of Cenozoic sediments. Trench strata are folded and faulted at the base of the trench slope. The major décollement at the Manila Trench usually forms near the unconformity separating the pelagic from the turbidite sediments in the trench. The accretion of turbidite sediments deposited in the Manila Trench has resulted in the upbuilding of an accretionary prism which forms the seaward margin of the forearc basin system. The uplifted Zambales ophiolite and its offshore extension form the landward side of the forearc basin. Uplift of the forearc basins is confined to a narrow zone near the intersection of the relict spreading center within the South China Sea plate. The forearc north of Lingayan Gulf is disrupted by active, northerly trending fault systems that extend offshore from the Luzon Central Valley and from the southern Cordillera Central. The Early Miocene uplift and tilting of the Zambales ophiolite may mark the beginning of subduction at the Manila Trench. We infer that the long-term average convergence rate across the Manila Trench has been about 1 cm/yr and may be slowing in the north due to the collision of Taiwan with Eurasia.