The Mindanao collision zone: a soft collision event within a continuous Neogene strike-slip setting

Abstract

Two volcanic belts are presently juxtaposed on Mindanao Island in the southern Philippines. Southward, the collision is still active in the Molucca Sea which is commonly regarded as a region of doubly verging subduction, plunging eastward below the Halmahera arc and westward below the Sangihe arc. In the Molluca Sea, tectonic features related to the incipient collision appear only in the very thick sediments of the basin, and the morphology of the parallel Halmahera, Talaud and Sangihe ridges is closely controlled by recent N-S strike-slip faults. Among these faults, the Philippine Fault is a neotectonic feature crosscutting the Agusan-Davao Basin which seals tectonic events not younger than Eocene. In addition, the Central Cordillera shows strong similarities with the Pacific Cordillera for both stratigraphy and tectonic evolution, and several indications favour a Eurasian margin affinity for the Daguma Range (Southern and Eastern Kudarat Plateau that may be part of the Sangihe arc, as inferred for the Zamboanga Peninsula and the Northern Arm of Sulawesi. Thus the island of Mindanao can be divided into two composite terranes, the western one (northward extension of the Sangihe arc) being restricted to the Kudarat Plateau and the Zamboanga Peninsula. The apparent continuation of the Sangihe arc into the Central Cordillera of Mindanao is thus the result of post collision tectonics. The portion of the suture where the collision is completed curves westward north of the southern peninsula and extends beneath the sediments of the Cotabato Basin or the volcanic plateaus of the Lanao-Misamis-Bukidnon Highlands. In the northern part, the contact is linear and suggests, together with the absence of compressional deformation, a docking of the eastern oceanic terrane (Philippine Mobile Belt-Halmahera arc) against the western continental terrane (Zamboanga-Daguma) in a strike-slip environment. Prior to Early Pliocene, the eastern and the western terranes were subject to different tectonic regimes with direction of extension perpendicular to the present one. From Late Pliocene to present, both terranes are affected by NNE and E-W compression.