The Manokwari Trough and the western end of the New Guinea Trench

Abstract

The New Guinea Trench is a sparsely surveyed seafloor depression which runs parallel to the north coast of New Guinea for a distance of some 700 km. Its western end lies about 600 km east of the Philippine Trench; the intervening region is occupied by a complex series of north trending ridges and troughs, of which the Ayu Trough and the Tobi and Mapia ridges are the most prominent. It has been suggested and is now widely accepted that the trench marks a site of subduction, but the degree of present‐day activity is disputed. The western termination has recently been defined by combined single‐channel seismic and long range sidescan sonar surveys as lying at the ridge system which culminates in Mapia Island. The trench contains as much as 1 km of flat‐lying undisturbed sediments within the area surveyed, and the southern slopes are extensively channeled, suggesting a lack of recent deformation. The same survey has also shown that for a distance of some 400 km west of the western end of the trench, the north coast of New Guinea is flanked, at a distance of only a few tens of kilometers, by a deep trough. The sonar imagery of this “Manokwari Trough” suggests recent convergence as well as transcurrent movement. Both the existence of this trough and the abrupt termination of the New Guinea Trench are consequences of the seafloor spreading which took place in the Ayu Trough after subduction had ceased at the trench.