Palaeomagnetic constraints on terrane tectonics: Highlands and Sepik regions, Papua New Guinea

Abstract

Tectonic development of the northern margin of the Australian plate in the Eastern Indonesia-New Guinea-SW Pacific region has been governed for the last 43 Ma by interaction of three major plates (Fig.1): the west-north-westward moving Pacific plate, the northward moving Australian plate, and minor movement of the Southeastern Asia plate toward the southeast. Current movement rates are 10.2, 7.8 and 0.4 cm/yr respectively, with a resultant Australian-Pacific convergence rate of 12.6 cm/yr (Moore, 1982). This high rate of oblique convergence is taken up largely in a highly active and structurally complex buffer zone with rapid development of microplates. This Tonga-Sulawesi megashear region may represent a present-day analog of the Mesozoic development of terrane accretion along the North American Cordillera (Silver and Smith, 1983). For the New Guinea segment of this megashear, Pigram and Davies (1987) identified more than 32 terranes of oceanic, continental or composite affinity. Palaeomagnetic control on terrane movement of mainland New Guinea is restricted to the Bird's Head region of Irian Jaya (Giddings et al., 1993), and the North Sepik and Highland regions of Papua New Guinea. Results from the latter two regions are here discussed.