The Bataan Volcanic Arc Complex comprises the Central Luzon segment of the Luzon volcanic arc. This segment is separated from the Northern Luzon segment by the northwest trending Umingan-Lingayen branch of the Philippine Fault that separates the Central Luzon Basin from the Caraballo Range and Central Cordillera. To the south, this segment is separated from the Southern Luzon segment by the “Macolod Corridor” of Defant and others (1988), a northeast-trending swath of volcanic centers transverse to the general direction of the arc. Within the Central Luzon segment, two distinct belts of volcanic centers are recognized. The western belt includes Pinatubo, Negron, Cuadrado, Bitnung, Balakibok, Santa Rita, Natib, Samat, Mariveles, and Limay, among others. These have been extruded through the Zambales ophiolite terrane. The eastern belt - consisting of Balungao, Amorong, Cuyapo and Arayat - lie along the axis of the Central Luzon Basin upon which a thick pile of Tertiary sedimentary rocks have been laid. It is not known whether the Central Luzon Basin is floored by the Zambales ophiolite. Offshore, farther to the west, is the Manila Trench which defines the structure along which the South China Plate is being subducted beneath the Luzon arc of the Philippine Sea Plate. A general younging of the volcanic centers from west to east is noted by De Boer and others (1980), with the western belt dating back to more than 4 Ma (Mariveles Complex) and even up to 8 Ma (Mt. Pinatubo) and the eastern belt giving a range of 1.59 Ma (Mt. Cuyapo) to 0.53 Ma (Mt. Arayat). Bau and Knittel (1993) assign a range of 7 Ma to Present for the western belt and 1.7 Ma to 0.1 Ma for the eastern belt. This suggests that volcanism was initiated in the west and progressed eastward with the subducting slab, which could have induced partial melting of the mantle during its descent. Defant and others (1988) estimate that the eastern and western belts are approximately 100-120 km and 180-200 km, above the Wadati-Benioff zone, respectively, whereas Bau and Knittel (1993) reckon that the eastern belt is 180 km above the subducting slab. The main characteristics of the eastern and western volcanic belts are tabulated below.