Chemically analysed lavas from Bagana, an active andesitic volcano on Bougainville Island, can be assigned to one of three age groups - pre-1943, 1943-53, or 1959-75. Lavas of the oldest group are chemically the most fractionated, whereas those of the 1943-53 group are the most mafic. The rocks of the youngest group, although intermediate in degree of fractionation have K2O, Rb, and Ba abundances similar to, or lower than, the rocks of the 1943-53 group. The three groups appear to represent distinct batches of magma that were successively erupted from Bagana, possibly from a high-level reservoir that was periodically emptied and refilled. The andesites are regarded as fractionates of mantle-derived mafic magmas. Most of the crystal fractionation probably took place during ascent from the mantle source region, and before entry into the reservoir beneath the volcano. An average chemical composition of the analysed Bagana andesites has major-element values close to those of the mean for more than 800 analysed late Cainozoic volcanic rocks from Papua New Guinea, and is proposed as a reference andesite composition for comparative studies.

Geochemical data are presented for a sequence of spilitic pillow basalts (Tumu River basalts) associated with peridotites and gabbros of the Marum ophiolite complex in northern mainland Papua New Guinea. The basalts are strongly differentiated from relatively magnesian types (Mg-value = 70) to ferrobasalts (Mg-value = 30) characterised by high levels of Fe, Ti, Zr, Nb, Y. The Tumu River basalts are enriched in large ion lithophile elements such as REE, Zr, Hf, Nb, P2O5, and compare with tholeiites from oceanic islands. Major and trace elements suggest extensive fractionation involving olivine, pyroxene, and plagioclase, followed by pyroxene, plagioclase, titanomagnetite, and ilmenite. Trace-element plots are used to examine fractionation processes and to estimate abundances in the parent magma. The calculated initial concentrations are compared with abundances and abundance ratios in least fractionated enriched and depleted tholeiites. The abundances in the parent magma are used to calculate source abundances for large (20-30%) degrees of partial melting. The levels range from 2-3 times chrondites for HREE, Ti, Y, Zr, Sc, and P2O5, to 3.5-5.5 times for LREE, and are similar to those inferred for other LREE-enriched tholeiites from both oceanic and continental areas. The chemistry of the basalts therefore reflects the mantle-source composition rather than a particular tectonic setting within an ocean basin.

Consolidated Maritime Boundaries between Australia and Papua New Guinea Diagram AU/PNG-07 Refer to GeoCat 73168 Treaty text and coordinates can be found at: http://www.austlii.edu.au/au/other/dfat/treaties/1985/4.html

Protected Zone under Article 10 (1) and Annex 9 of the Treaty between Australia and the Independent State of Papua New Guinea concerning Sovereignty and Maritime Boundaries in the area between the two Countries, including the area known as Torres Strait, and Related Matters (1978) Diagram AU/PNG-05 Refer to GeoCat 73165 Treaty text and coordinates can be found at http://www.austlii.edu.au/au/other/dfat/treaties/1985/4.html

Territorial sea boundaries as established under Article 3 (4) and Annex 3 of the Treaty between Australia and the Independent State of Papua New Guinea concerning Sovereignty and Maritime Boundaries in the area between the two Countries, including the area known as Torres Strait, and Related Matters (1978) Diagram AU/PNG-13

The Kuta Formation is mainly a limestone deposit which crops out on the flanks of the Kubor Anticline in the Central Highlands of Papua New Guinea. It has been variously regarded as Cainozoic, Permian and Permo-Triassic in age, but is now positively dated as late Norian or Rhaetian (Late Triassic) on the basic of conodonts, molluscs and brachiopods. The Kuta Formation is thus the youngest known Triassic formation in Papua New Guinea. Interpretation of the local stratigraphy is simplified by this dating. It is now apparent that the marine Triassic sedimentation in Papua New Guinea commenced no later than the Anisian (Middle Triassic) and continued, probably uninterrupted, until Rhaetian time. The fossils identified and described include the conodont Misikella posthernsteini Kozur and Mock, 1974, the ammonite Arcestes (Arcestes) cf. sundaicus, Welter, 1914, and some bivalves. The brachiopods Clavigera, Zugmeyerella, Sinucosta, Robinsonella, ?Hagabirhynchia are equally important in dating the assemblage, but will be described in detail separately. All the more closely identified fossils have a Tethyan Provincial aspect except Clavigera which was previously known only from New Zealand and New Caledonia.

Interpretation of seismic refraction data from the southwestern coast of the Papuan Peninsula and the northwest Coral Sea gives consistent results using several inversion techniques. Sediments over the Papuan Plateau are 5 km thick; to the west and northwest they thicken to 10 km along the axes of the Moresby and southern Aure Troughs. Farther out into the Coral Sea, over the Eastern Plateau, they are 1 to 2 km thick. Beneath the sediments, a layer with a P-wave velocity of 6.07 km s^-1 was inferred over the region. It is underlain along the southern coastline of the peninsula by a lower crustal layer with a velocity of 6.9 km s^-1, which is probably also present under the Eastern Plateau. We cannot say whether the lower crustal layer also occurs offshore under the Moresby Trough, but it is not present under the Aure Trough in the north. Intervals where the velocity increases with depth are likely in the lower crust (> 17 km) under the peninsula, but we have insufficient data to say if they are present offshore. The Moho is 27 to 29 km deep along the southwestern coast of the peninsula. It shallows to 19 km under the Moresby Trough and deepens to 25 km under the Eastern Plateau. The crust is therefore continental under the Papuan Peninsula and Eastern Plateau and, excluding the sediments, oceanic under the Moresby Trough. We have examined several tectonic models for the region that imply different stress patterns at the time of formation of the Moresby Trough. We favour one in which northern Australia, the Eastern and Papuan Plateaus and the Papuan Peninsula once formed a continuous, continental crust. With the opening of the Coral Sea Basin, crustal thinning extended northwards along the axis of the Moresby Trough, probably into the Aure Trough. This model implies a regional tensional stress pattern at the time of formation.

Geoscience Australia`s involvement in Papua New Guinea mapping includes managing the production of maps for select urban areas as part of a MOU between Department of Defence and PNG. In addition, Geoscience Australia distributes some (now aging) 1:100,000 scale maps produced by the Department of Defence for much of Papua New Guinea. At this scale 1cm on the map represents 1km on the ground. Each map covers a minimum area of 0.5 degrees longitude by 0.5 degrees latitude or about 54 kilometres by 54 kilometres. The contour interval is 20 metres. Many maps are supplemented by hill shading.

Geoscience Australia`s involvement in Papua New Guinea mapping includes managing the production of maps for select urban areas as part of a MOU between Department of Defence and PNG. In addition, Geoscience Australia distributes some (now aging) 1:100,000 scale maps produced by the Department of Defence for much of Papua New Guinea. At this scale 1cm on the map represents 1km on the ground. Each map covers a minimum area of 0.5 degrees longitude by 0.5 degrees latitude or about 54 kilometres by 54 kilometres. The contour interval is 20 metres. Many maps are supplemented by hill shading.

At this scale 1cm on the map represents 1km on the ground. Each map covers a minimum area of 0.5 degrees longitude by 0.5 degrees latitude or about 54 kilometres by 54 kilometres. The contour interval is 20 metres. Many maps are supplemented by hill shading.