Paleomagnetic data from the Philippine Sea Plate and their tectonic significance

Abstract

New paleomagnetic data from Guam and Saipan have been obtained and are used, in conjunction with previously published results from around the Philippine Sea plate, to interpret the origin and history of the Philippine Sea plate. A lower Miocene direction (I=3.5°, D=54.5°, a95=17.4°, k=20.3) and a middle Oligocene direction (I=5.3°, D=68.4°, a95=12.8°, k=52.4) have been obtained from the Palau Islands. Only one reliable result, a middle Oligocene direction (I=15.1°, D=66.1°, a95=11.1°, k=20.1), has been obtained from Guam. Many characteristic remanent magnetic directions have been obtained from the lower Eocene Facpi Formation; however, the results are too scattered (k=4.5) to be considered reliable. Two reliable directions have been obtained from Saipan: a middle Miocene result (I=30.7°, D=28.1°, a95=8.4°, k=64.6), and a lower Eocene result (I=−12.0°, D=43.0°, a95=12.5°, k=16.0). Two lower Eocene results from Chichijima (I=9.5°, D=105.3°, a95=12.6°, k=6.1) and Anijima (I=−0.8°, D=91.7°, a95=16.9°, k=4.9) are the reliable results from the Bonin islands. There are two end‐member interpretations for these data: (1) small scale local rotation of blocks along the plate margin, or (2) rotation of the Philippine Sea plate as a whole. To distinguish between these interpretations, we reconstructed the East Philippine Sea province back to its prerifting configuration. The rotation caused by deformation can be estimated by comparing the paleomagnetism of Guam, Saipan, and the Bonin islands to Palau. Prior to reconstruction, the older declination values are scattered. Closing the marginal basins reduces the declination scatter, and all of the islands show increasing clockwise deflection with time. This suggests that the Philippine Sea plate has rotated up to 80° clockwise and moved northward around 20° since the Eocene, and deformational rotation is a second‐order feature. The finite pole of rotation of the Philippine Sea plate relative to Eurasia must be somewhere near the southeast comer of the plate, because this is the only location that is compatible with both the change in orientation and paleolatitude for the plate. These data cannot distinguish between a backarc origin or trapped crust origin for the West Philippine Sea province. The existing models require major modification to be consistent with the paleomagnetic data.

Evolution of the boundary between the Philippine Sea Plate and Australia: palaeomagnetic evidence from eastern Indonesia

“…The results indicate about 10 ° of northward translation since the Early Miocene. This is similar to estimates from palaeomagnetic studies elsewhere in the Philippine Sea Plate (Louden, 1977;Keating and Herrero, 1980;Kinoshita, 1980;Bleil, 1981;Kodama et al, 1983;Hirooka et al, 1985;Haston and Fuller, 1991;Haston et al, 1992;Koyama et al, 1992).…”

“…Evidence for northward movement of about 15-20 ° of the Philippine Sea Plate has been widely accepted (see review by Haston and Fuller, 1991) but the suggestions of major rotation of the plate have proved more controversial. Interpretations of major (50-100 °) clockwise rotations of the entire plate have been based on the magnetic anomaly skewness in the West Philippine Basin (Louden, 1977;Shih, 1980) and palaeomagnetic data from the eastern margin of the plate (Kodama et al, 1983;Haston and Fuller, 1991;Koyama et al, 1992) but have been disputed for a number of reasons. These include the low resolution provided by anomaly skewness studies, conflict with interpretations based on Shikoku Basin seamount data (Vaquier and Uyeda, 1967) and possibility of local tectonic effects due to subduction at the eastem plate edge (Larson et al, 1975;McCabe and Uyeda, 1983).…”

Paleomagnetic Evidence for Northward Drift and Clockwise Rotation of the Izu-Bonin Forearc since the Early Oligocene

“…Koyama (1989) and Haston and Fuller (1991) reported no significant deflection in paleomagnetic declination from the Izu Peninsula and Saipan Island since 5 Ma. The three Miocene data from Palau, Saipan, and the Leg 126 forearc sites show smaller deflections than the other Eocene-Oligocene data in the same site, respectively.…”

Magnetic and Gravity Field Analyses of Izu-Ogasawara (Bonin) Arc and Their Tectonic Implications.

“…On the other hand, the Titisima block underlying Titisima island shows clockwise deflected magnetization. These differences may pose a question on the entire clockwise rotation of the Izu-Ogasawara arc (Haston and Fuller, 1991).…”

“…The zones C2, and C3 correspond to the topographic highs of the Ogasawara ridge. The Ogasawara ridge is supposed to be subject to clockwise rotation (Haston and Fuller, 1991), however, the good correlation between topography and magnetic basement is recognized for the topographic highs lying the Haha sima islands (C3). These high correlation zones are significant to consider the tectonic framework of the Izu-Ogasawara arc.…”