Rock magnetic results from Ocean Drilling Program Leg 192: implications for Ontong Java Plateau emplacement and tectonics of the Pacific
Published:January 01, 2004
Xixi Zhao, Maria Antretter, Peter Riisager, Stuart Hall, 2004. "Rock magnetic results from Ocean Drilling Program Leg 192: implications for Ontong Java Plateau emplacement and tectonics of the Pacific", Origin and Evolution of the Ontong Java Plateau, J. Godfrey Fitton, John J. Mahoney, Paul J. Wallace, Andrew D. Saunders
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A rock magnetic study has been performed on rock samples recovered at Ocean Drilling Program Leg 192 sites on the Ontong Java Plateau in the western Pacific. Igneous rocks from the five Leg 192 sites displayed variable rock magnetic properties. The differences in the rock magnetic properties are a function of mineralogy and alteration. Titanomagnetite and titanomaghemite are present in the Ontong Java rocks. Samples with titanomagnetite exhibit Verwey transitions in the vicinity of 120K. Low-temperature curves for samples with multiple magnetic phases do not clearly show the Verwey transition. The inversion of titanomaghemite to a strongly magnetized magnetite is shown by the irreversible thermomagnetic-cooling curve. Despite the geographically widespread locations of the drill sites, variations in rock magnetic properties closely resemble each other, consistent with the fundamental results of the leg that the basement rocks were derived from homogeneous Kwaimbaita-type magma with a single age of approximately 120 Ma. The rock magnetic investigation provides constraints to evaluate the fidelity of the natural magnetic memory in the basalt rocks and corroborates the palaeomagnetic palaeolatitudes determinations for the Ontong Java Plateau. The generally good quality of rock magnetic data exhibited by Leg 192 rocks supports the inference that the characteristic directions of magnetization isolated from the Cretaceous Ontong Java Plateau sites were acquired near the onset of the Cretaceous Long Normal Superchron about 120 Ma. The portion of the Pacific plate containing the Leg 192 sites was in the southern hemisphere during the mid-Cretaceous volcanism.
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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.