BASEMENT SLIVERS WITHIN THE NEW BRITAIN ACCRETIONARY WEDGE - IMPLICATIONS FOR THE EMPLACEMENT OF SOME OPHIOLITIC SLIVERS

Using multichannel seismic data from the western Solomon Sea we have imaged several 2.5 to 3-km-thick oceanic basement slivers within the New Britain accretionary wedge which may serve as a modern analogue for the detachment of some ophiolitic slivers. The most recently accreted basement sliver is located just over 5 km from the thrust front. An approximate area balance indicates the subjacent section of the downgoing plate from which this sliver originated is between 11 km and 15 km arcward of its present position. Though we have not imaged the basement ramp, sedimentary strata beneath the basement sliver pinch out between 9 and 12 km from its seaward edge, suggesting that detachment occurred in that vicinity. Normal faults reactivated in response to the flexural bending of the downgoing oceanic plate are a prominent feature of this region. Significantly, almost all basement normal faults near the recently accreted basement sliver, including those imaged beneath the toe of the wedge, dip arcward. Based on these data, we suggest that small (1-3 km thick) basement slivers are decoupled along favorably oriented, preexisting zones of weakness formed by normal fault detachments within the oceanic basement.