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Arc magmatism and mineralization in North Luzon and its relationship to subduction at the East Luzon and North Manila Trenches

1988; Pergamon Press; Volume: 2; Issue: 2 Linguagem: Inglês

10.1016/0743-9547(88)90011-6

1879-1832

John A. Wolfe,

Geological and Geochemical Analysis

The Tertiary tectonics of North Luzon are complicated by an early thermotectonic regime in the Eocene (40–50 Ma) and the second from 30 to 17 Ma in the Oligocene resulting from subduction in the East Luzon Trench. The second stage coincided with the opening of the South China Sea on the west side of the Philippines. Portions of the western Philippines were translated south from China by the opening of the South China Sea. This includes Mindoro Island, Palawan and the Reed Bank area. No one has presented any evidence that any oceanic crust existed between early Luzon and China prior to opening of the South China Sea. After spreading of the South China Sea ceased, China began to extrude eastward and coupled with the oceanic crust of the South China Sea initiated subduction in the North Manila trench under Luzon at about 17 Ma. Commencing at approximately 15 Ma a graben formed east of the Manila Trench, centered in Baguio City. It contained the volcanic arc which began to develop as the Agno batholith intruded the graben. The graben extends for at least 75 km on the southwest flank of the Cordillera with relayed extensions into the Cordillera. Porphyry copper mineralization developed within the graben from 10 to 8 Ma interrupted by the explosion of a caldera or volcano tectonic depression extending south of Baguio. This graben contains 22 porphyry copper bodies, some of them uneconomic. Described by Gervasio as a "crackle zone", the same zone was described by Fernandez and Damasco as the area most favorable for gold exploration. The second period of mineralization was imposed on the district from 4 to 3 Ma. Gold mineralization in the Baguio district constituted a third phase of mineralization in the Pleistocene. Absence of commercial mineralization in the Cordillera and Sierra Madre correlated with the Paleogene is one of the criteria for distinguishing between the subduction related to the South China Sea and that related to the Philippine Sea on the east. One of the important conclusions of this paper is that the Oligocene phase of subduction on the East Luzon Trench coincided with the opening of the South China Sea and both of these activities ceased when spreading on the South China Sea ceased. The period of mineralization in the graben at Baguio relates to the Manila Trench on the west side of Luzon with igneous activity commencing about 15 Ma.