From Indosinian to Yanshanian tectonic events recorded in the Palawan Continental Block, Philippines: New constraints from zircon U-Pb-Hf isotopes

Southeast Asia records a prolonged and complex tectonic history from the Permian to the Cenozoic, marked by the accretion of continental fragments, subduction-related magmatism, and repeated reorganization of plate boundaries. Within this framework, the Palawan Continental Block (PCB) contains one of the most complete records of Mesozoic–Cenozoic continental margin evolution in the western Philippines and records key evidence of pre-Cenozoic tectonic events. However, the genetic relationships among its internal tectonic blocks remain unresolved. This study utilizes zircon U–Pb geochronology and Hf isotopic data from Paleozoic to Cenozoic strata extending from northern Palawan to Mindoro Island to constrain the timing, provenance, and tectonic affinity of rocks forming the PCB.

Igneous and detrital zircons from the Mindoro Metamorphics define a coherent Middle to Late Permian age population (270–254 Ma) with uniformly low Th/U ratios (<0.1), indicating a major Permian tectonothermal event related to the Indosinian orogeny. Jurassic strata from northwest Panay yield distinct unimodal age peaks at ~252 Ma (Early Triassic) and ~174 Ma (Middle Jurassic). The Middle Jurassic population overlaps with unimodal Early to Middle Jurassic age peaks (189–182 Ma) from strata on Busuanga Island, recording the development of Yanshanian arc magmatism along the South China continental margin. The recognition of both Permian-Triassic Indosinian (ca. 255-202 Ma) and Jurassic-Cretaceous Yanshanian (ca. 200-100 Ma) tectono-magmatic signatures, characteristic of the South China margin, establishes a direct temporal and genetic link between the tectonic evolution of the PCB and that of southern China. Moreover, the comparable detrital zircon age spectra and Hf isotopic signatures of the Permian-Eocene strata from Palawan and Mindoro indicate derivation from a common continental source, supporting the interpretation of the PCB as a single continental fragment rather than a collage of discrete accreted terranes.