Publications

Despite two decades of hydrocarbon exploration along the south margin of the western Irian Jaya Fold Belt, major questions regarding gross thrust belt architecture and the extent of deep-seated inversion structures remain unanswered. Apatite fission track (AFT) analyses indicate two recent cooling events related to tectonic uplift. A 20 Ma date correspmds to regional metamorphism recorded in northern Papua New Guinea, whilst a 4 Ma date can be correlated to collision of the Adelbert and Finisterre Arcs with New Guinea and subsequent deformation across the island. These ages provide important constraints on the timing of structures and allow for broad comparisons with similar AFT dates from along strike in PNG.Structurally, the identification from gravity and surface geology of NE-SW trending lineaments, at a high angle to the trend of the thrust belt, is a key feature in interpreting the regional deformation. Such lineaments may be deep-seated basement structures (continental transforms) that controlled structure and facies distribution during Mesozoic passive margin rifting and during Tertiary crustal shortening and collision. From the PNG border in the east to the Weyland overthrust in the west, lateral changes in the Late Permian to Middle Jurassic sequence indicate a marked transition from granites and high-grade metamorphics to widespread clastic graben-fill deposits. This transition from a relatively strong sequence in the east to a rifted, relatively weak sequence to the west corresponds to a change in the trend in the thrust belt from WNW to E-W at approximately 139", E. This suggests that pre-existing extensional faults exerted both a strong influence on the initiation of basement inversion, and that they may have acted as lateral ramps to compartmentalize inverted blocks and separate them from areas of thinskinned thrusting.