The western Central Luzon arc is apparently a complex zone of volcanism and tectonism. The volcanoes of the northern segment of the arc (the Bataan arc, BA) fall along two semi-parallel lineaments, the Western Bataan Lineament (WBL) and the Eastern Bataan Lineament (EBL). This northern segment is cut off from the southern extension of the arc by a NE-SW "cross arc" zone of volcanism (the Macolod Corridor, MC). The volcanoes of the southern segment of the arc (Mindoro arc, MA) fall along two parallel lineaments, the Western Mindoro Lineament (WML) and the Eastern Mindoro Lineament (EML). Samples collected from the MC, EBL, and MA are alkali (and LIL) enriched compared with the WBL. The enrichment of the EBL is believed to be the result of the release of smaller amounts of hydrous-rich fluids within the mantle below the EBL than below the WBL. This process generated smaller degrees of partial melting below the EBL (as compared to the WBL) which resulted in the higher concentrations of LIL elements in the EBL magmas as compared to the WBL magmas. The alkali and LIL enriched nature of the MC is believed to be the result of small degrees of partial melting during rifting. The enriched nature of the MA is thought to be due to slivers of crustal material from the Palawan-Mindoro Block being incorporated into the mantle during subduction. This region has the highest radiogenic Sr values found in the Philippines. The MC may represent a pull-apart rift zone between the Philippine and West Luzon shear zones and the transform between the Manila and Philippine Trenches.