Tectonics of the Papua New Guinea region and implication on geothermal energy

Ampana, Suame 2026. Tectonics of the Papua New Guinea region and implication on geothermal energy. PhD Thesis, Cardiff University. Item availability restricted.

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Abstract

Two contemporary problems of plate tectonics are investigated in this thesis; i) the mechanics of backarc basin formation and evolution and ii) the nature of stress fields in subducted slabs at intraslab depths (d > 60 km). Additionally, the thesis also investigates structures controlling geothermal activity in an arc setting. Papua New Guinea region in the southwest Pacific is chosen to investigate these problems due to its tectonically suitable location. The region, being a site of Australia-Pacific plate convergence, has resulted in formation of a mosaic of small plates. Within this setting, the Bismarck Sea plate, the Solomon slab and the central New Britain arc are targeted to examine these problems. GPS velocity derived geodetic strain-rates, earthquake moment tensor derived seismic strain rates and tectonic stress field inverted from earthquake focal mechanisms of the region are used to test the existing mechanisms for the Bismarck Sea basin; none of them fit the observations adequately. A ‘collision-docking’ model, a ‘non-subduction’ mechanism suggested in this study that entails some aspect of intraplate deformation, provides a better fit to the observed data. In this model, the extensional tectonics of the Bismarck Sea is driven by the Finisterre collision in the southwest margin and docking of Ontong Java Plateau in the eastern margin of the Papua New Guinea region. Collision-docking driven extrusion of the eastern Bismarck Sea commenced the opening of the Manus spreading centre since ~3.5 Ma. The inferred direction of spreading, the orientation of the transform faults, and the higher subduction rates seen in the eastern New Britain Trench are all consistent with the proposed collision-docking model. Based on the intermediate (51 to 300 km depth) to deep (> 300 km depth) stress field inferred from earthquake focal mechanisms, slab seismicity, depth and morphology, nine distinct slab sectors are identified in the Solomon slab. Of the six slab sectors with deep seismicity, one sector (S3) is consistent with the Isacks & Molnar’s (1971) intermediate downdip compression – deep down dip compression (IC-DC) classification while three sectors (S4, S7 and S8) are consistent with intermediate downdip extension – deep depth compression (IE-DC) classification. Two sectors (S5 and S9) with deep seismicity showing IE-DC stress fields are exceptions to Isacks and Molnar classification that predicts IC-DC stress fields. These exceptions are associated with significant slab bending in the upper mantle and are interpreted to indicate interaction of the slabs with high density phase transitions in the upper mantle transition zone. Tensional stress fields seen in the two sectors are induced by slab bending. The three sectors without deep seismicity all show intermediate compressional stress fields, in contrast to expected tensional stress field, are interpreted to indicate these slab sectors are supported from below. In all, five exceptions to Isacks and Molnar classifications have been identified in the Solomon slab which generally indicates that the stress distribution in the slab shows high variability due to variable slab geometry and mantle heterogeneities. Structural controls on geothermal activity in the central New Britain arc are analysed based on trends observed from i) lineaments, ii) land surface temperatures, iii) Fry data and iv) earthquake focal mechanisms. These data sets show northwest and northeast structures in the Willaumez Peninsula & Kimbe, Hoskins-Kasiloli and Silanga subareas. High heat flow is also seen in these subareas. Based on these observations, conjugate strike-slip systems are interpreted beneath these subareas, which provide structural controls on geothermal and volcanic activity. High vertical permeability is expected in such setting, as evidenced by abundant geothermal activity, making the prospects of power generation more favourable. These structures can be activated or reactivated as strike-slip faults in the prevailing east-west compression.

Item Type:	Thesis (PhD)
Date Type:	Completion
Status:	Unpublished
Schools:	Schools > Earth and Environmental Sciences
Date of First Compliant Deposit:	23 July 2026
Last Modified:	24 Jul 2026 08:17
URI:	https://orca.cardiff.ac.uk/id/eprint/188192

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