Petrographic and geochemical characterization of the crustal section of the Pujada Ophiolite, southeastern Mindanao, Philippines: Insights to the tectonic evolution of the northern Molucca Sea Collision Complex

Abstract

The Molucca Sea Collision Complex (MSCC) preserves the complex interaction between the Eurasian, Philippine Sea and the completely subducted Molucca Sea Plates. Petrological studies of obducted arc and ophiolitic materials in this region thus provide a unique opportunity to elucidate the tectono-magmatic evolution of the area. In this study, we present new petrographic and geochemical data on the crustal section of the Pujada Ophiolite which is extensively exposed in southeastern Mindanao, Philippines. Our work reveals that this ophiolite is a remnant of an oceanic lithosphere with backarc affinity. U-Pb dating of zircons from the isotropic gabbros further constrains the age of the Pujada Ophiolite to Late Cretaceous (90 Ma). This age is consistent with the inferred age of the proto-Molucca Sea Plate based on tectonic reconstructions and tomography. Exposed to the north of the Pujada Ophiolite and separated by a NE-SW trending thrust fault is the Iba Formation. This unit originally purported to be the carapace of the Pujada Ophiolite records an IA (island arc) affinity. The geochemical signature of the Iba Formation suggests derivation from an enriched mantle source affected by slab-derived components related to the East Mindanao-Halmahera Arc. We therefore interpret the Pujada Ophiolite as a trapped fragment of the proto-Molucca Sea Plate that was thrust onto the Halmahera Arc possibly during the waning stages of the collision between the Sangihe and Halmahera Arcs.