Accreted terranes in the northern part of the Philippine Archipelago

Abstract

The Philippine Archipelago consists of a complex array of ophiolites, continental fragments and island arc elements that can be identified as accreted terranes, similar to those increasingly recognized as components of orogenic zones. The northern Philippines, including Luzon, Mindoro and nearby smaller islands, can be divided into at least six of these tectonic elements. From west to east across central Luzon there are the Neogene accretionary prism of the West Luzon Arc, the Eocene Zambales ophiolite, the Cretaceous Angat ophiolite, and a late Cretaceous‐early Paleogene volcanic arc built on an older metamorphic basement. This arc terrane is repeated by offset along the Philippine Fault. To the south, the western Luzon terranes are juxtaposed against the metamorphic basement block of Mindoro, which itself is colliding with the North Palawan microcontinental fragment. The ophiolites appear to have originated in back arc basins rather than in oceanic plateaus, and the metamorphic belts have protoliths indicating deformation along active margins, perhaps deep within accretionary prisms. The Philippine terranes are interpreted as fragments that originated within the complex Pacific‐Eurasian plate boundary rather than as intra‐Pacific basin units. These terranes have been assembling at least since the Oligocene by strike‐slip and convergent displacements. Strike‐slip displacement, either along transcurrent faults or as a component of convergence played a very important, if not dominant, role in this assembly. Most terranes identified in the northern Philippine appear to be plate fragments, with attached crust and upper mantle. Their characteristics contrast with those usually interpreted for terranes in the North American Cordillera, where near‐orthogonal convergence and shallow dipping terrane sutures are favored.