Abstract
The proto-South China Sea (proto-SCS) is a fully consumed Mesozoic plate that once existed between the South China-Eurasian margin and Borneo. Remnants of this oceanic domain are believed to be emplaced as ophiolitic lithologies in Palawan and Zambales, Philippines and Borneo. Cretaceous and Eocene ophiolitic lithologies are exposed in the central and southern portions of Palawan island. The Eocene central Palawan Ophiolite (CPO) is composed of mantle peridotites, isotropic and layered gabbros, and massive and pillow lavas. In lieu of a sheeted dike complex, mafic dikes with distinct bake-and-chill margins cut the CPO, from the metamorphic sole to the crustal section. The Cretaceous southern Palawan Ophiolite (SPO) comprises of peridotite and pillow basalt exposures. Isotropic olivine gabbros are mainly preserved as floats. Troctolite and olivine gabbro dikes also cut the peridotites in the SPO.The CPO crustal rocks and mafic dikes have dominantly back-arc basin basalt affinities. The SPO lithologies exhibit ocean island basalt-like signatures with a mafic dike showing island arc basalt-like compositions. A plagiogranite sample from Puerto Princesa indicates an Eocene age (40.01 ± 0.54 Ma) for the CPO. U-Pb dating of olivine gabbro and syenite floats yielded a minimum age of Early Cretaceous (100.73 ± 1.07 and 102.97 ± 1.07 Ma, respectively) for the SPO. This is the first reported radiometric age for the now completely subducted Mesozoic proto-SCS exposed in southern Palawan, which complements existing paleontological dates. Geochemical and geochronological characteristics of the SPO and CPO are similar to those of the Darvel Bay and Telupid Ophiolites in Borneo, which are interpreted to originate from the proto-SCS. The CPO and SPO are thus construed to represent fragments of the proto-SCS emplaced in Palawan. Complex tectonic processes in the region during the Cretaceous to Eocene led to the inception of multiple subduction and rifting events involving the proto-SCS.
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