Geology of the Shortland Basin Region, Central Solomons Trough

Detailed Description

Bruns, T.R., Vedder, J.G., and Cooper, A.K., 1989, Geology of the Shortland Basin region, central Solomons Trough, Solomon Islands--review and new findings, in Vedder, J.G., and Bruns, T.R., eds., Geology and offshore resources of Pacific island arcs—Solomon Islands and Bougainville, Papua New Guinea Regions: Houston, Texas, Circum-Pacific Council for Energy and Mineral Resources, Earth Science Series, v. 12, p. 125-144.

Geology of the Shortland Basin Region, Central Solomons Trough, Solomon Islands—Review and New Findings

ABSTRACT

Multichannel seismic-reflection data acquired during 1982 in the Solomon Islands over the Shortland basin region were used to establish a preliminary framework for the seismic stratigraphy, structure, and tectonic history of the basin. Four seismic-stratigraphic units, A through D from oldest to youngest, were identified; these units form distinct sedimentary wedges that can be correlated with geologic units and tectonic events on the surrounding islands. Basin development was largely driven by vertical tectonics on the northeastern and southwestern flanks of the basin. These vertical movements were in turn controlled by tectonic events associated with the subduction and arc-reversal history of the Solomon Islands region.

Additional seismic-reflection data acquired during 1984 resulted in new findings as follows:

  1. A basement half graben with as much as 6 krn of relief is present in the center of the basin. Unit B strata, of inferred late Oligocene and Miocene age, thicken into and fill the half graben and onlap against the bounding faults. The half graben may have developed as a pullapart basin or by block rotation in a strike-slip fault or oblique subduction system. Development of the half graben is coincident with and may have been caused by entry of the Ontong Java Plateau into the early Tertiary subduction zone.
  2. The maximum sediment thickness in the basin is over 7 krn, which is greater than previously reported. Subsidiary depocenters are present beneath Vella Ridge and west of Mono Island, where sediment thicknesses are as much as 3 and 2 km, respectively.
  3. We find no obvious connection between Shortland basin and Bougainville basin on the southwestern side of Bougainville because a basement high apparently separates the two basins. The thick sedimentary section in the axial part of Shortland basin could extend northwestward beneath the volcanic rocks of southern Bougainville; however, the basin strata thin toward the island, and the basin may end near or beneath the island.
  4. Refraction data confirm that a thick basin fill of interbedded volcaniclastic and volcanic rocks is present beneath the New Georgia wedge region. This observation corrects an erroneous interpretation of thin fill that was based on shallow acoustic basement on seismic-reflection data.

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