Evolution of Arc‐Continent Collision in the Southeastern Margin of the South China Sea: Insight From the Isugod Basin in Central‐Southern Palawan.

The evolution of arc‐continent collision between the Palawan microcontinental block and the Cagayan Ridge in the southeastern margin of the South China Sea (SCS) is vital to understand how this collision correlated with seafloor spreading of the SCS. To address the evolution of arc‐continent collision, we studied the biostratigraphy and provenance of syn‐collisional sediments in the Isugod Basin in central‐southern Palawan. Microfossil analysis indicates a Late Miocene age (11.5–5.6 Ma) for the Isugod and Alfonso XIII Formations and rapid subsidence during initiation of the basin which may have been triggered by local extensional collapse of the wedge in response to forearc uplift. Multidisciplinary provenance analysis reveals that the Isugod and Alfonso XIII Formations were derived from the Middle Eocene–lower Oligocene Panas‐Pandian Formation on the Palawan wedge and the Late Eocene Central Palawan Ophiolite. These results suggest the emergence of both the orogenic wedge and obducted forearc ophiolite at ∼11.5 Ma, implying collision onset before ∼11.5 Ma. The collision initiation in Palawan could be better constrained to ∼18 Ma, based on the drowning of the Nido carbonate platform in the foreland. Therefore, the gravitational collapse of the Palawan wedge and the subsidence/formation of the Isugod Basin might reflect a significant uplift pulse in the hinterland of the wedge beginning within 13.4–11.5 Ma in the late stage of collision. It indicates that although compression originated from spreading of the SCS had ceased at 16–15 Ma, arc‐continent collision in Palawan did not stop and was sustained by compression from the upper plate afterward. Plain Language Summary: The Palawan microcontinental block is a continental fragment separated from the South China margin along with the seafloor spreading of the South China Sea (SCS). It finally collided with the Cagayan Ridge volcanic arc because of southward subduction of the Proto‐SCS. Therefore, precisely constraining the evolution of arc‐continent collision could help us to understand its association with the ending of the SCS spreading. To constrain the evolution of arc‐continent collision, we determined the depositional age and source of syn‐collisional sediments in the Isugod Basin in central‐southern Palawan. Our results shows that the Isugod Basin sediments were deposited during the Late Miocene (11.5–5.6 Ma) following local gravitational collapse of the Palawan orogenic wedge driven by uplift and oversteepening. Isugod Basin sediments were eroded from both the orogenic wedge and obducted forearc ophiolite that were uplifted and exposed subaerially, indicating collision began before ∼11.5 Ma. As the onset of collision could be constrained to ∼18 Ma, we propose a significant uplift pulse in the hinterland of the wedge began at 13.4–11.5 Ma in the late stage of collision. This further indicates that arc‐continent collision in Palawan did not stop although compression derived from spreading of the SCS had ceased at 16–15 Ma. Key Points: Sediments in the Isugod Basin were deposited at 11.5–5.6 Ma following local gravitational collapse of the Palawan wedge driven by upliftThe Isugod Basin sediments were supplied by erosion of the Palawan wedge and obducted forearc ophiolite exposed subaerially since ∼11.5 MaOnset of Palawan arc‐continent collision at ∼18 Ma followed by a significant uplift pulse in the Palawan wedge beginning within 13.4–11.5 Ma [ABSTRACT FROM AUTHOR]