Extensional and vertical tectonics in the New Guinea islands: Implications for island arc evolution

The New Guinea islands region, Southwest Pacific, lies at the frontier of the Australian and Pacific plates and many morphotectonic features are typical of other Western Pacific island arcs. Field geological observations indicate current tectonic models are deficient in key aspects and, from a broader perspective, synthesis of these observations cautions the carte blanche application of plate tectonic theory in similar tectonic provinces. Models generally only account for the last 3.5 Myr (Bismarck Sea opening) of evolution of parts of the region and little is known of Early Tertiary tectonic evolution since the Upper Eocene. The present disposition of slabs of formerly extensive Miocene platform carbonate suggests that New Ireland and New Britain have undergone little more than gentle tilting and uniform uplift, despite location in tectonically dynamic areas, adjacent the New Britain Trench and/or separation by a plate boundary. Major structural corridors present throughout the region have gone unrecognized. They are oblique to existing morphotectonic features, have played a controlling role in localizing igneous activity and mineralization, and have documented long movement histories. Onshore extensional and strike-slip vertical structures in East New Britain show no spatial or genetic relationship to the Bismarck Sea Seismic Lineation (BSSL) and related transforms. High-angle structures predominate throughout the region and indicate major vertical movements of crustal blocks. The nature and timing of movements along many onshore structures indicate that some other major tectonic process has operated (and presently continues) in the New Guinea islands.