Global tectonic significance of the Solomon Islands and Ontong Java Plateau convergent zone

Abstract

Oceanic plateaus, areas of anomalously thick oceanic crust, cover about 3% of the Earth's seafloor and are thought to mark the surface location of mantle plume “heads”. Hotspot tracks represent continuing magmatism associated with the remaining plume conduit or “tail”. It is presently controversial whether voluminous and mafic oceanic plateau lithosphere is eventually accreted at subduction zones, and, therefore: (1) influences the eventual composition of continental crust and; (2) is responsible for significantly higher rates of continental growth than growth only by accretion of island arcs. The Ontong Java Plateau (OJP) of the southwestern Pacific Ocean is the largest and thickest oceanic plateau on Earth and the largest plateau currently converging on an island arc (Solomon Islands). For this reason, this convergent zone is a key area for understanding the fate of large and thick plateaus on reaching subduction zones. This volume consists of a series of four papers that summarize the results of joint US–Japan marine geophysical studies in 1995 and 1998 of the Solomon Islands–Ontong Java Plateau convergent zone. Marine geophysical data include single and multi-channel seismic reflection, ocean-bottom seismometer (OBS) refraction, gravity, magnetic, sidescan sonar, and earthquake studies. Objectives of this introductory paper include: (1) review of the significance of oceanic plateaus as potential contributors to continental crust; (2) review of the current theories on the fate of oceanic plateaus at subduction zones; (3) establish the present-day and Neogene tectonic setting of the Solomon Islands–Ontong Java Plateau convergent zone; (4) discuss the controversial sequence and timing of tectonic events surrounding Ontong Java Plateau–Solomon arc convergence; (5) present a series of tectonic reconstructions for the period 20 Ma (early Miocene) to the present-day in support of our proposed timing of major tectonic events affecting the Ontong Java Plateau–Solomon Islands convergent zone; and (6) compare the structural and deformational pattern observed in the Solomon Islands to ancient oceanic plateaus preserved in Precambrian and Phanerozoic orogenic belts. Our main conclusion of this study is that 80% of the crustal thickness of the Ontong Java Plateau is subducted beneath the Solomon island arc; only the uppermost basaltic and sedimentary part of the crust (∼7 km) is preserved on the overriding plate by subduction–accretion processes. This observation is consistent with the observed imbricate structural style of plateaus and seamount chains preserved in both Precambrian and Phanerozoic orogenic belts.