Characterization of the Angat Ophiolite: New insights from bulk major and trace element geochemistry and petrographic analysis

Abstract

The Angat Ophiolitic Complex, located north-northeast of Manila, Luzon is perhaps one of Luzon’s most fundamental suspect terranes. The definite age of the ophiolite is not well-established, with various authors having different claims. Encarnacion et al. (1993) conducted a U-Pb age dating for the Angat wherein the Angat Ophiolite was found to have an Early Middle Eocene age (48 Ma), close to the ZOC age - leading to the assumption that the two ophiolites are related and underlie most of Central Luzon. Hence, this paper aims to collect samples from the Eocene and Cretaceous Angat Ophiolite for petrographic and geochemical analyses, identify the relationship between the separated basalt units from the basalts in the main ophiolite body, and compare the geochemistry of the Eocene and Cretaceous units of the Angat Ophiolite with the other well-known ophiolites from the literature. Field investigations were conducted in five important localities wherein 15 samples were obtained. The results highlighted that the major mineral phases in the samples collected are plagioclase and augite, with some samples having hornblende and olivine. All samples appear to have undergone low-grade greenschist facies metamorphism, which may be attributed to hydrothermal alteration. Chloritization of pyroxene minerals is also evident, along with the hydrothermal alteration products of plagioclase and pyroxenes. The relationship between the EAO, MOC, and separated basalt patch in Marilaque Highway is identified. The Coto Block of the Zambales Ophiolite and the Angat Ophiolite may be related and formed over a mantle initially enriched by a subduction component.