Analogue Modelling of the Papua New Guinea Fold and Thrust Belt

In the PNG Fold Belt the jungle-covered mountains limit data acquisition so that the internal geometry and evolution of the large anticlines are poorly understood. It is postulated that the anticlines formed above old normal faults in basement, which has been tested by analogue modelling and 3D computerized X-ray tomographic scanning. Layers of corundum, sand, silicone and sand/silicone mixes were used to represent the PNG stratigraphy of 2 km of molasse, 1 km of carbonate, 1 km of mudstone, 500m of sandstone and shale reservoirs and 0.5-3 km of syn-rift clastics. The thicknesses, strengths and velocities of deformation were all scaled appropriately and erosion/deposition was modelled by adding or removing ‘molasse’. It was found that the carbonate deformation was often detached from that of the underlying reservoirs and that the structural style was critically dependent upon the strength of the intervening mudstone and of the basal detachment. Structural style was also strongly correlated to deformation rate, in that slower convergence rates yielded a single large fold, whereas optimum rates yielded more realistic detachment folds. It was observed that the development of an overturned detachment fold was greatly enhanced when the basement fault was first partially inverted.