The geology of north and central Malaita, Solomon Islands: the thickest and most accessible part of the world’s largest (Ontong Java) ocean plateau
Published:January 01, 2004
Michael G. Petterson, 2004. "The geology of north and central Malaita, Solomon Islands: the thickest and most accessible part of the world’s largest (Ontong Java) ocean plateau", Origin and Evolution of the Ontong Java Plateau, J. Godfrey Fitton, John J. Mahoney, Paul J. Wallace, Andrew D. Saunders
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This paper presents the most complete results yet published of geological surveys in Malaita, north of latitude 9°05′S between 1990 and 1995. The geology of Malaita reflects its position as an obducted part of the Alaska-size Ontong Java Plateau (OJP). The geology comprises a monolithological Cretaceous basalt basement sequence up to 3–4 km thick, termed the Malaita Volcanic Group (MVG), conformably overlain by a 1–2 km-thick Cretaceous–Pliocene pelagic sedimentary cover sequence. Cretaceous–Pliocene pelagic sedimentation was punctuated by alkaline basalt volcanism during the Eocene and by intrusion of alnöites during the Oligocene. Basement and cover sequences were both deformed by an intense, but short, middle Pliocene event. A number of localized, Upper Pliocene–Pleistocene, shallow-marine–subaerial, predominantly clastic formations overlie the middle Pliocene unconformity surface. The MVG comprises a monotonous sequence of pillowed and non-pillowed tholeiitic basalt lavas and sills with a predominant clinopyroxene–plagioclase–glass–opaques ± olivine mineralogy. The basaltic plateau morphology of the MVG is reflected in the presence of trap-like topographic features exposed in numerous river sections. Remarkably little sediment is present between basalt flows (most interlava contacts are basalt–basalt), indicating high to very high effusion rates. When present, inter-lava sediment is laminated pelagic chert or limestone, millimetres to centimetres thick, reflecting emplacement of the basalt in deep water (near or below the calcite compensation depth). Gabbro intrusions, dolerite dykes and an unusual spherulitic dolerite facies are locally present. The deep-water eruptive environment of the MVG probably was defined by the accumulation of voluminous eruptions from a multi-centred, submarine, possibly fissure-fed, volcanic source. The Malaitan cover sequence largely comprises a series of foraminifera-rich, pelagic calcilutites and calcisiltites with chert and, in the younger formations, arc-derived mudstone interbeds at various stratigraphic levels.
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Origin and Evolution of the Ontong Java Plateau
The Cretaceous submarine Ontong Java Plateau, in the western Pacific Ocean, is the most volumnous of the world’s large igneous provinces (LIPs), and represents the largest known magmatic event on Earth. LIPs are the products of basaltic volcanism on a scale and at an effusion rate not seen on Earth at the present time, and their formation may have had significant effects on the Earth's climate and biosphere. The currently favoured explanation for LIP formation is the rapid decompression and melting of anomalously hot mantle in the heads of newly ascended mantle plumes. This volume summarizes the results of research aimed principally at testing the plume-head hypothesis for the formation of the Ontong Java Plateau, and presents the results of integrated studies following recent basement drilling on the plateau by the Ocean Drilling Program. Nineteen papers cover topics as diverse as petrology, geochemistry, tectonics, volcanology, paleomagnatism and biostratigraphy.