Sub-arc Mantle Heterogeneity of the Northern Luzon Volcanic Arc: Mineral and Whole Rock Compositional Variability in Mantle Xenoliths from Lutao Island.

This article focuses on the characterization of mantle xenoliths from the island of Lutao to understand the nature and evolution of the sub-arc lithospheric mantle beneath the northern Luzon volcanic arc. The xenoliths, primarily spinel harzburgites with minor lherzolite and olivine orthopyroxenite, exhibit mineral and whole rock compositions similar to abyssal peridotites but show geochemical and isotopic evidence of modification by fluids or melts derived from subducted South China Sea sediments. Pyroxene thermometry indicates elevated equilibrium temperatures (>1000 °C) relative to other northern Luzon arc regions, which, along with geochemical signatures of the host mafic volcanic rocks, suggest that the xenoliths were entrained during a post-collisional intra-arc rifting event rather than typical subduction-related melting. The study concludes that the Lutao xenoliths represent a sub-arc lithospheric mantle source modified by subduction processes and subsequently affected by extensional tectonics following the collision between the Luzon arc and the Eurasian margin.