在西伍德拉克海盆,海底扩张直接延伸到巴布亚—新几内亚大陆地壳,已不局限于弧后构造。由于印度—澳大利亚板块和太平洋板块在南太平洋会聚,导致这里的小板块发生扭转。沿西伍德拉克扩张轴,火山岩循序而变。开始是洋中脊常见的玄武岩,继而变为地球化学成分与弧后区相类似的玄武质安山岩,并兼有过碱性流纹岩。 In the West Woodlark Basin, the seabed expansion extends directly to the Papua-New Guinea continental crust, and is no longer limited to the post-arc structure. As a result of the convergence of the Indo-Australian plates and the Pacific plates in the South Pacific, the small plates here are reversed. Along the Westwood Drake expansion axis, volcanic rocks change in sequence. Beginning with basalts that are common to mid-ocean ridges, they turn into basaltic andesite with similar geochemical composition to the backarc zone, with over-basal rhyolite.