--> ABSTRACT: The Trobriand Basin, SE Papua New Guinea, as a Supradetachment Basin and Its Implications for the Crustal Dynamics of Highly Extended Terranes, by S. J. Friedmann; #91021 (2010)

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The Trobriand Basin, SE Papua New Guinea, as a Supradetachment Basin and Its Implications for the Crustal Dynamics of Highly Extended Terranes

FRIEDMANN, S. JULIO

The Trobriand basin, SE Papua New Guinea, formed above a low-angle normal fault system exposed in the D'Entrecasteaux Islands metamorphic core-complex. Uplift and deformation of the core-complex and its boundary fault system began 3-4 Ma, and associated metamorphism is as young as 0.9 Ma. This system shows evidence of current low-angle seismicity, which suggests the system as a whole is still active. Stratigraphic data comes from industry seismic lines, exploration well cores and logs, and observation of modern topography and depositional environments.

Basin deposition began 3.5-4 Ma in a near marine system above a low-relief unconformity (no local topography during early deposition). The basin filled with 4000 ft of Plio-Pleistocene strata; a lower package comprising 2000 ft of shale, conglomerates, and lignites, and an upper package of 1000-2000 ft of limestone capped by the modern carbonate system. All units were deposited at or near sea, and the modern zone of maximum subsidence is approx. 30 km from the range front faults. Basin topography is flat and shallow (< 100 m water depth). In contrast, footwall topography is high, with approx. 2.5 km of relief. Breccia bodies containing clasts of eclogite and amphibolite, which crop out in the footwall, were found in core of the lowest package near the basin center, suggesting that footwall topography was high at the basin's inception and that gravel rapidly accumulated 30 km into the basin. The basin is uncut internally by major faults, which suggests that the deformation forming the Islands and basin occurred chiefly along the primary boundary fault system, characterized by hangingwall translation and footwall uplift. This closely matches the model for a Phase I supradetachment basin, and implies active footwall uplift with a relatively passive upper plate. 

AAPG Search and Discovery Article #91021©1997 AAPG Annual Convention, Dallas, Texas.