Ancient Os isotope signatures from the Ontong Java Plateau lithosphere: Tracing lithospheric accretion history |
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| Authors: | Akira Ishikawa D Graham Pearson Christopher W Dale |
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| Institution: | 1. Key Laboratory of Mineralogy and Metallogeny, Guangzhou Institute of Geochemistry, Chinese Academy of Sciences, Guangzhou 510640, China;2. University of Chinese Academy of Sciences, Beijing 100039, China;3. Department of Earth Sciences, The University of Hong Kong, Pokfulam Road, Hong Kong, China;4. Guangzhou Marine Geological Survey, Guangzhou 510760, China;5. State Key Laboratory of Isotope Geochemistry, Guangzhou Institute of Geochemistry, Chinese Academy of Sciences, Guangzhou 510640, China;1. State Key Laboratory of Marine Geology, Tongji University, Shanghai 200092, China;2. National High Magnetic Field Laboratory, Department of Earth, Ocean and Atmospheric Science, Florida State University, Tallahassee, FL 32306, USA.;3. Department of Marine Geology and Geophysics, Woods Hole Oceanographic Institution, Woods Hole, MA 02543, USA.;1. GEOMAR Helmholtz Centre for Ocean Research Kiel, Wischhofstr. 1-3, 24148 Kiel, Germany;2. Earth, Environmental and Biological Sciences, Queensland University of Technology, GPO Box 2434, Brisbane, Qld 4001, Australia;3. Department of Natural Sciences, Hawai''i Pacific University, 45-045 Kamehameha Highway, Kaneohe, HI 96744-5297, USA;4. Department of Geology and Geophysics, School of Ocean and Earth Science and Technology, University of Hawaii, Honolulu, HI 96822, USA;5. Pacific Centre for Isotopic and Geochemical Research, Department of Earth and Ocean Sciences, University of British Columbia, 6339 Stores Road, Vancouver, BC V6T 1Z4, Canada;1. Department of Earth Science and Astronomy, The University of Tokyo, 3-8-1 Komaba, Meguro, Tokyo 153-8902, Japan;2. Research and Development Center for Submarine Resources, Japan Agency for Marine-Earth Science and Technology, Yokosuka 237-0061, Japan;3. Department of Solid Earth Geochemistry, Japan Agency for Marine-Earth Science and Technology, Yokosuka 237-0061, Japan;4. Department of Earth Sciences, Durham University, Durham DH1 3LE, UK;5. General and Analytical Chemistry, Montanuniversität, 8700 Leoben, Austria |
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| Abstract: | In order to better understand the nature and formation of oceanic lithosphere beneath the Early Cretaceous Ontong Java Plateau, Re–Os isotopes have been analysed in a suite of peridotite xenoliths from Malaita, Solomon Islands. Geological, thermobarometric and petrological evidence from previous studies reveal that the xenoliths represent virtually the entire thickness of the southern part of subplateau lithospheric mantle (< 120 km). This study demonstrates that vertical Os isotopic variations correlate with compositional variations in a stratified lithosphere. The shallowest plateau lithosphere (< 85 km) is dominated by fertile lherzolites showing a restricted range of 187Os/188Os (0.1222 to 0.1288), consistent with an origin from ~ 160 Ma Pacific lithosphere. In contrast, the basal section of subplateau lithospheric mantle (~ 95–120 km) is enriched in refractory harzburgites with highly unradiogenic 187Os/188Os ratios ranging from 0.1152 to 0.1196, which yield Proterozoic model ages of 0.9–1.7 Ga. Although the whole range of Os isotope compositions of Malaita peridotites is within the variations seen in modern abyssal peridotites, the contrasting isotopic compositions of shallow and deep plateau lithosphere suggest their derivation from different mantle reservoirs. We propose that the subplateau lithosphere forms a genetically unrelated two-layered structure, comprising shallower, typical oceanic lithosphere underpinned by deeper impinged material, which included a component of recycled Proterozoic lithosphere. The impingement of residual but chemically heterogeneous mantle, mechanically coupled to the recently formed, thin lithosphere, may have a bearing on the anomalous initial uplift and late subsidence history of the seismically anomalous plateau root. |
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