The Sadowa Igneous Complex, Eastern Papua New Guinea: Ophiolite or Not?

Abstract

Milsom and Smith (1975) suggested the Sadowa Igneous Complex (SIC) could represent a fragment of oceanic crust that has been thrust into its present position. Pigram and Symond (1991) suggested another contemporaneous spreading center north of the Coral sea. The SIC floored that basin between the continental fragments of the Eastern, Papuan and proto-Owen Stanley terranes (Fig. 1). The late Cretaceous to Eocene SIC is mainly composed of gabbro, dolerite, basaltic conglomerate, breccia, lower (with pelagic clasts) and upper volcanic rocks (interbedded and overlained by volcaniclastic graywackes) and a few serpentinites, serpentinized dunites, clinopyroxenites and plagiogranites. The SIC is conformably overlain by pelagic sediments and is cut by reverse or normal faults. It was obducted onto the Owen Stanley metamorphics during the Late Eocene to Middle Oligocene to form the Eastern Papuan Composite Terran (EPCT) after the emplacement of the Papuan Ultramafic Belt (Pigram and Davies, 1987). Subsequently tectonism could be expected to have reversed the southward subduction to northward subduction from the Port Moresby trench (Hamilton, 1979). During the Miocene the EPCT collided with Eastern and Papuan Plateaus (Pigram and Davies, 1987). The Astrolabe agglomerate contains subduction