Abstract

The fold belt of western Papua New Guinea provides a good example of large-scale detachment tectonics. Orogenic deformation occurred during mid- to late-Pliocene times and involved a Mesozoic and Tertiary sedimentary section deposited in a major structural downwarp known as the “Papuan Basin.” Prior to Pliocene times, the basin was affected by epeirogenic warping only. The pattern of the detachment is related to the configuration of two large basement uplifts aligned west-northwest en echelon to the central spine of the island. These uplifts are anticlinal in form, and the sedimentary cover is not subject to significant faulting. Movement was southwest, away from a rupture zone associated with the northeastward uplift, and the slide front can be traced around the east-southeast-plunging nose of the southwestern uplift. The width of the slide belt is up to 75 mi and its length exceeds 250 mi. Transport at the slide front is generally less than 5,000 ft and foreshortening within the belt is accommodated on subsidiary faulting. Substantial uplift has occurred throughout the fold belt and continued after the thrust movements had ceased, with consequent modification to the dip of the glide planes and the structural form.

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