Cenozoic motion of the Philippine Sea Plate: Palaeomagnetic evidence from eastern Indonesia

Abstract

The history of motion of the Philippine Sea Plate is poorly known because it is isolated from the oceanic ridge system. Interpretation of palaeomagnetic results from the plate has been controversial because declination data have been obtained only from the eastern margin where subduction-related tectonic processes may have caused local rather than plate-wide rotations. New palaeomagnetic data relevant to the problem have been obtained from 34 sites north of the Sorong Fault and 29 sites within the Sorong Fault system. These sites record southward movement during the Eocene and northward movement during the Neogene. Sites within the Sorong Fault system record both counterclockwise and clockwise rotations interpreted as the result of Neogene block movements at the southern boundary of the Philippine Sea Plate. North of the Sorong Fault, all sites record clockwise declinations. Neogene rocks have small deflections consistent with rotation about the present-day Eurasia-Philippine Sea Plate pole. Oligocene-middle Eocene rocks show consistent clockwise declination deflections of-40 ø . Declinations of lower Eocene rocks indicate -90 ø of clockwise rotation. We propose that the entire area north of the Sorong Fault in east Indonesia has always been part of the Philippine Sea Plate and that the whole plate has rotated clockwise in a discontinuous manner by approximately 90 ø since the early Eocene. The new data from north of the Sorong Fault provide a basis for determining rotation poles which satisfy all the palaeomagnetic data from the Philippine Sea Plate and permit its reconstruction. 1117 1120 HALL ET AL.: CENOZOIC MOTION OF THE PHILIPPINE SEA PLATE Australia and the Pacific. The Sorong Fault has its type locality in the northern Bird's Head region of New Guinea [Visser and Hermes, 1962; Dow and Sukamto, 1984]. We use the term Sorong Fault Zone for an area including the region from the Bird's Head to east Sulawesi. Geology of the Sorong Fault Zone This geological summary is based on fieldwork carried out by London University and GRDC geologists [Hall et al., 1988a, b; Nichols and Hall, 1991; Charlton et al., 1991; Hall et al., 1991; Hall et al. , 1995a, R. Hall et al., unpublished results, 1995]. The Sorong Fault system juxtaposes continental, arc, and ophiolitic rocks (Figures 2 and 3). Australian continental crust is present on the islands of Obi and Bacan within the Sorong Fault system [Hamilton, 1979; Ali and Hall, 1995]. High-grade metamorphic rocks of probable Palaeozoic or greater age are exposed on Bacan and Obi, and lower and middle Jurassic sedimentary rocks, 165-188, 1975.

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

“…At ~ 25 Ma the Philippine Sea Plate began rotating clockwise about a pole located near to 15°N and 160°E. The computed poles of rotation for the Philippine Sea Plate indicate no significant convergence between the Philippine Sea Plate and Australia after 25 Ma, suggesting the existence of a strike-slip boundary (Hall et al, 1995a). The lack of convergence is also consistent with the absence of major Neogene volcanic activity in northern Irian Jaya (Pieters et al, 1983;Dow and Sukamto, 1984).…”

“…Arc activity in the Sorong Fault Zone region continued until the earliest Miocene when collision between the south-facing Philippine Sea Plate arc and the Australian continental margin occurred. The boundary between the Philippine Sea and Australian plates then became a transform boundary with the initiation of the left-lateral Sorong Fault (Hall et al, 1995a). Fragments of Australian and Philippine Sea Plate origin have a common stratigraphic history during the Neogene and there was no significant volcanic activity at the Australian-Philippine Sea boundary.…”

Southeast Asia's changing palaeogeography

“…Before the Eocene the location of the Halmahera Arc is not well known. At 45 Ma it was at equatorial latitudes (Hall et al 1995a) far out in the western Pacific on the southern margin of the Philippine Sea Plate. Between 45 and 25 Ma the Philippines -Halmahera Arc developed above a north-dipping subduction zone where there was subduction of Indian -Australian lithosphere north of Australia as Australia moved north (Hall 1996, 2002, Hall & Spakman 2002).…”

Philippine Sea Plate inception, evolution, and consumption with special emphasis on the early stages of Izu-Bonin-Mariana subduction

“…5, Hall et al 1995a,b,c). For many years, interpretation of paleomagnetic results has been controversial because declination data have been obtained only from the eastern margin, where subductionrelated tectonic processes may have caused local, rather than plate-wide, rotations (Hall et al 1995c). Based on ODP site 1201, drilled ∼100 km west of the KPR and ∼450 km north of the CBF rift, Richter and Ali (2015) produced new data on the PSP drift since the Middle Eocene.…”