Tectonics in central Papua and the adjoining part of New Guinea

Detailed stratigraphic and structural analysis has shown that tectonic development in the central Papua region can be divided into three stages. The first stage involved apparent eastward migration of zones of deformation and sedimentation from the Palaeozoic to the late Mesozoic. Pre-Permian, late Palaeozoic to Triassic, and mainly ?Jurassic sediments were thickly deposited in three adjacent belts, with the east-ern ?Jurassic belt probably formed on a floor composed of the rocks now uplifted and exposed in parts of the Papuan Basic-Ultrabasic Belt. Sedimentation may have been controlled by subsidence caused by crustal tension. This eastwards, sedimentary prograding towards an oceanic province was punctuated by phases of deformation and metamorphism before the Permian, in the late Triassic, and in the early Cretaceous, each event being restricted to the wedge of sediment built up just prior to the deformation. The axial parts of the pre-Permian and late Triassic belts of deformation are reflected in the trends of the Erave-Wana Swell and the \Bismarck-Moresby high\" respectively. Early Cretaceous deformation included the initial westerly downthrow of the Owen Stanley Fault which is the western boundary of the Papuan Basic-Ultrabasic Belt. The second stage involved westward migration of zones of late Mesozoic to Middle Miocene deformation and sedimentation across a basement of rocks formed and deformed during the first stage. Cretaceous Eocene early and late Lower Miocene and Middle Miocene deep-water marine sediments were thickly deposited in five adjacent belts parallel to and west of the Owen Stanley Fault each belt overlapping the western margin of the preceding one. The sediments were affected by periodic folding and uplift along trends parallel to the Owen Stanley Fault. The most intense deformation during any one phase occurred within the sedimentary belt formed just before the deformation. Thus fold belts which were the provenance of the deep-water sediments and troughs in which they accumulated were closely related in space and time. Migration in the late Cretaceous and in the late Palaeogene was caused by periodic crustal compression accompanied by metamorphism. Further westward migration was due to phases of compression or to vertical oscillation of crustal blocks with folding produced by surficial gravity spreading. The third stage involved Middle Miocene to Recent deformations and zones of sedimentation trending NNW to west both of which were superimposed on; but mainly oblique to the older tectonic features. The broad anticline and syncline-like warpings of the Eastern Cordillera the Ramu-Markham Depression (an area of Pliocene to Quaternary sedimentation) and the Lakekamu Embayment (Upper Miocene to Quaternary sedimentation) were probably produced by compressive forces directed NE-SW. WNW-trending sinistral transcurrent faults were also moving from the Middle Miocene to the Recent and may have been caused by the same compressive forces. Since there is also evidence of anticlockwise crustal rotations in the area the stress field may have involved an overall sinistral shear couple acting about a vertically oriented intermediate principal stress. Some of the Pleistocene folds in the Lakekamu Embayment could have developed through gravity sliding of rocks off the SW flank of the rising Eastern Cordillera."