Philippine Sea Plate motion history: Eocene-Recent record from ODP Site 1201, central West Philippine Basin

Abstract

Ocean Drilling Program Site 1201 (19°17.8′N, 135°5.9′E) was drilled in the West Philippine Basin, about 100 km west of the inactive Palau-Kyushu Ridge and 450 km north of the extinct “Central Basin Fault” spreading center. A 509-m long Eocene to Miocene sedimentary sequence overlying middle Eocene (Chron C21n, ∼47 Ma) basalts was recovered. Using paleomagnetism, this site provides an excellent opportunity to deduce the paleolatitude and motion history of the central Philippine Sea Plate throughout the last 45–50 m.y. Although plate motion models for the Philippine Sea Plate are now fairly well established, data gaps exist both in time and geographical spread. The sediments at Site 1201 consist of a lower sequence of volcaniclastic turbidites sourced from the Palau-Kyushu Ridge and an upper succession of late Oligocene to early Pliocene red deep-sea clays. Paleolatitudes derived from the sedimentary sequence support the model of northward movement of the plate since the Eocene. Analysis of 37 basaltic basement samples indicates that this part of the plate lay ∼7.1°(+5.4°,−5.2°)S in the middle Eocene. The rate of movement shows slowing of the plate between 50 and 20 Ma, with a minimum of plate movement at 20 Ma. An attempt to extract a rotational component of the plate using the present-day field overprint from the azimuthally unoriented drill cores suggests a clockwise motion compatible with existing models.