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ABSTRACT: Paleomagnetic Evidence from Land-Based and ODP Cores for Clockwise Rotation and Northward Translation of the Philippine Sea Plate

S.M. Cisowski, M. Fuller, Roger B. Haston, M. Koyama

On-land and deep-sea core paleomagnetic data have been collected from around the Philippine Sea plate. Data from the Palau islands suggest 70° of clockwise rotation and northward translation since the mid-Oligocene. We interpret this rotation as a rotation of the West Philippine Sea basin as a whole.

New paleomagnetic data from Guam indicate 70° of clockwise rotation and northward translation since the early Oligocene. Although Eocene results have been previously quoted, the new data suggest that there is no reliable Eocene data from Guam. New data from Saipan suggest 50-60° of clockwise rotation since the Late Eocene and 20° of clockwise rotation since the mid-Miocene, along with northward translation.

During ODP Leg 126, a new technique utilizing the formation microscanner logging tool was employed to obtain orientated drill cores from the Bonin forearc basin. Preliminary results indicate that 70-110° of clockwise rotation has occurred there since the mid-Oligocene. Inclination studies on cores from ODP Legs 125 and 126 along with the on-land paleomagnetic data support 15° of northward translation of the Philippine Sea plate since the mid-Oligocene.

The consistent clockwise rotations found around the Philippine Sea plate suggest that the entire plate, including the Bonin and Mariana arcs, has rotated more than 50° since the mid-Oligocene. The similarity of Oligocene results from the Bonin forearc and Guam suggest that little or no relative rotation has occurred between these two points. This implies that the shape of the Mariana arc is probably not due to rotational deformation.

The northward translation and clockwise rotation of the Philippine Sea plate established oblique subduction along the proto-Philippine margin, which could account for the 600 km of subducted slab beneath the eastern Celebes Sea. This implies the Molucca Sea plate probably is a trapped piece of old Philippine Sea plate, isolated by a seaward jump of subduction.

AAPG Search and Discovery Article #90097©1990 Fifth Circum-Pacific Energy and Mineral Resources Conference, Honolulu, Hawaii, July 29-August 3, 1990