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Davis, A.S., Gray, L.B., Clague, D.A. and Hein, J.R. (2002). The Line Islands revisited: New Ar-40/Ar-39 geochronologic evidence for episodes of volcanism due to lithospheric extension. Geochemistry, Geophysics, Geosystems 3: |
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[1] New Ar-40/Ar-39 ages of mineral separates and whole rock samples from nine volcanic edifices in the northern Line Islands region, between latitudes 20degreesN and 6degreesN, are incompatible with single or multiple hot spot models. Instead, two major episodes of volcanism, each lasting similar to5 Ma and separated by similar to8 Ma, occurred synchronously over long distances, not just along the main chain but also at nonaligned edifices. Volcanism during the older episode (81-86 Ma) extended over a distance of at least 1200 km along the eastern part of the complex seamount chain. Volcanism during the younger episode (68-73 Ma) was concentrated in the western part of the chain and may have extended over a distance of >4000 km. Chemical analyses of 68 samples represent a compositionally diverse suite, including tholeiitic, transitional, and alkalic basalt, strongly alkalic basanite and nephelinite, and alkalic differentiates ranging from hawaiite to trachyte. The most diverse assemblage of rocks was recovered from a cross-trending seamount chain south of Johnston Atoll. Although compositions of rocks from the two volcanic episodes overlap, compositions from the younger episode generally are more alkalic and include a larger proportion of highly differentiated compositions. None of the samples from the older episode, but many from the younger one, contain hydrous mineral phases such as amphibole and biotite. Extensive coeval volcanism along major segments of the chain is compatible with decompressional melting of heterogeneous mantle due to diffuse lithospheric extension along pre-existing zones of weakness. Episodes of volcanism are probably related to broad upwarping of the Superswell region in the eastern South Pacific, where these lavas originated. |
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| BACKGROUND DATA FILES |
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Abstract |
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Appendix A: Sampling & Analytical Techniques: A1. Geochemistry |
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Appendix A: Sampling & Analytical Techniques: A2. Geochronology |
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Appendix A: Sampling & Analytical Techniques: A3. Data Reduction |
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Appendix B: Description of Volcanic Rocks B.1. Seamount Near 20¿n, 171 |
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Appendix B: Description of Volcanic Rocks B2. Johnston Atoll |
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Appendix B: Description of Volcanic Rocks B3. Keli Ridge |
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Appendix B: Description of Volcanic Rocks B4. Seamount 14¿n, 170¿w |
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Appendix B: Description of Volcanic Rocks B5. Guyot at 9¿n, 165¿w |
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Appendix B: Description of Volcanic Rocks B6. S.p. Lee Guyot |
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Appendix B: Description of Volcanic Rocks B7. Kingman Reef Area |
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Appendix B: Description of Volcanic Rocks B8. Horizon Guyot |
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Appendix B: Description of Volcanic Rocks B9. Karin Ridge |
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Appendix B: Description of Volcanic Rocks B10. Seamount at 10¿n, 162¿w |
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Appendix: Table B1 |
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Table 1 |
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Table 1b |
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Table 2a |
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Table 2b |
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Sampling & Analytical Methods |
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Sampling & Analytical Techniques: Geochemistry |
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Sampling & Analytical Techniques: Geochronology |
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Sampling & Analytical Techniques: Data Reduction |
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Keywords
central pacific, line islands, mesozoic volcanism, geochronology, igneous petrology, trace elements, 1035 geochemistry, geochronology, 3640 mineralogy and petrology, igneous petrology, 3670 mineralogy and petrology, minor and trace element composition, 9609 information related to geologic time, mesozoic, hot-spot hypothesis, ferromanganese crusts, isotope geochemistry, central pacific, mantle, age, seamounts, plate, earth, dynamics |
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Publisher
American Geophysical Union
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