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ABSTRACT: Northern Papua New Guinea: Structure and Sedimentation in a Modern Arc-Continent Collision

Lon Abbott, Eli Silver

Northern Papua New Guinea and the Solomon Sea are the site of a modern, oblique, arc-continent collision, which is progressing from northwest to southeast. By combining offshore seismic data from the Solomon Sea with geologic mapping in the Markham Valley area of northern Papua New Guinea we are predicting the outcome of this collision. The Huon Gulf is the present site of initial collision. Seismic profiles show this area is dominated by thin thrust sheets. Onshore, the bulk of the uplifted accretionary wedge is a melange with exotic blocks of a variety of lithologies. Structurally below the melange lies the Leron Formation, composed of thick, channelized sandstone and conglomerate. It dips north at approximately 40° and is cut by several thrust faults with associat d folds.

Limestone blocks within the melange are reported to be 2 Ma, and Beryllium 10 anomalies from Bismarck arc volcanoes suggest that initial collision of the Finisterre block (375 km northwest of the present collision point) began no earlier than 3 Ma. This implies the collision is propagating laterally at about 125 km/m.y.. Large outcrops of basalt and gabbro within the melange suggest that segments of oceanic crust were incorporated into the accretionary wedge.

Modern sedimentation within the collision zone grades from fluvial sediments in the Markham Valley to deep-water turbidites ponded behind a structural ridge near the point of incipient collision. The Markham submarine canyon occupies the collision front here, and efficiently erodes the accretionary wedge. This setting may serve as a modern analog for deposition of much of the Leron Formation, which exhibits tremendous sediment reworking.

AAPG Search and Discovery Article #91003©1990 AAPG Annual Convention, San Francisco, California, June 3-6, 1990