The Woodlark Plate is a small, nearly triangular tectonic block named for the Woodlark region, located immediately east of New Guinea and concentrated in the northern sector of the Woodlark Basin. Its spatial extent overlaps with, but does not encompass, the entire basin, reflecting a localized plate that occupies only the basin’s northern half. The plate resides within a structurally intricate tectonic milieu characterized by closely spaced, interacting faults and boundaries, a complexity that has attracted extensive geological and geophysical study since the plate was first proposed. Recent integration of island-based GPS velocities with high-resolution bathymetric and tectonic mapping of the sea floor has substantially revised earlier conceptions of its size and geometry, demonstrating that the plate is considerably smaller than originally estimated. These geodetic and marine data together have delineated the plate margins and clarified the Woodlark Plate’s role within the regional plate-tectonic framework east of New Guinea.
Tectonics
Recent geophysical and geodetic work has substantially reduced the inferred size of the Woodlark plate: rather than the extensive entity proposed in 2003, it is now best constrained to the northern portion of the Woodlark Basin. GPS, seismicity and other geophysical indicators show the plate interacts in a complex triple-junction network—possibly four active triple junctions, two of which occur along its southern margin with the Australian plate—reflecting a highly segmented and dynamic plate boundary environment.
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Early models that extended the Woodlark plate westward along eastern New Guinea and invoked its subduction beneath the Caroline plate have been superseded. Those former boundary segments are now commonly reassigned to neighboring plates or microplates (notably the Solomon Sea plate and a hypothesized Trobriand microplate) on the basis of ground-station kinematics and seafloor mapping. Oceanographic surveys identified a transform fault along the former eastern margin of the older model, prompting enlargement of the inferred Solomon Sea plate or recognition of additional discrete blocks. Geological and geodetic studies further resolve the region into multiple crustal blocks—distinct Woodlark Basin motion relative to a defined “Trobriand Block” and several eastern New Guinea blocks—allowing up to five discrete kinematic elements, some of which are treated as components of separate microplates in recent interpretations.
The northern boundary of the basin is defined by the Woodlark Rise and the Nubara Transform Fault, which constitutes a firm boundary with the Solomon Sea plate (and would likewise bound a Trobriand microplate if it is active). On the eastern margin the Woodlark lithosphere is being subducted northeastward beneath the New Georgia Islands where it meets the Solomon Sea/Pacific system; this deformation front lacks a classic outer-rise–trench morphology and is expressed by the San Cristobal Trough. The relatively thin, young oceanic crust of the Woodlark Basin remains shallow during subduction, is prone to melting upon interaction with the mantle wedge, and is implicated in generating the prolific arc volcanism of the western Solomon Islands. Subduction at the Trobriand Trough was assumed in early models but has been questioned because of locally low seismicity and measured motions; nonetheless, portions of that trough appear to be actively subducting, and the existence and present-day kinematics of a Trobriand microplate remain subjects of active debate.
The southern margin of the Woodlark plate is an active mid‑ocean ridge that extrudes tholeiitic basalt compositionally similar to MORB. Spreading is oriented principally north–south across an east–west–trending central zone and is segmented by transform faults into five sections, producing uneven extension. Two principal transforms are the Moresby transform in the central basin and the Simbo transform at the eastern end. Spreading rates are markedly asymmetric: about 6.7 cm/yr in the eastern sector versus ~3.8 cm/yr in the western sector. This rate disparity, together with the kinematic offset at the Moresby transform, produces an axial graben in the eastern basin roughly 500 m deeper than the western seafloor and an overall asymmetric basin morphology. The regional spreading geometry and plate motions underwent a major reorientation ca. 450 ka, with a subsequent slowdown in divergence around 200 ka, marking significant Pleistocene changes in the tectonic regime.