Crustal intrusion beneath the Louisville hotspot track |
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| Authors: | E Contreras-Reyes I Grevemeyer AB Watts L Planert ER Flueh C Peirce |
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| Institution: | 1. Department of Solid Earth Geochemistry, Japan Agency for Marine-Earth Science and Technology, Yokosuka 237-0061, Japan;2. Kochi Institute for Core Sample Research, Japan Agency for Marine-Earth Science and Technology, Nankoku 783-8502, Japan;3. Research Institute of Earthquake and Volcano Geology, Geological Survey of Japan, Tsukuba 305-8567, Japan;4. Research and Development Center for Ocean Drilling Science, Japan Agency for Marine-Earth Science and Technology, Yokosuka 237-0061, Japan;5. Graduate School of Engineering, Osaka University, Suita, Osaka 565-0871, Japan;6. Research Institute of Geology and Geoinformation, Geological Survey of Japan, Tsukuba 305-8567, Japan;7. Graduate School of Arts and Sciences, The University of Tokyo, Meguro, Tokyo 153-8902, Japan |
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| Abstract: | We report here the first detailed 2D tomographic image of the crust and upper mantle structure of a Cretaceous seamount that formed during the interaction of the Pacific plate and the Louisville hotspot. Results show that at ～ 1.5 km beneath the seamount summit, the core of the volcanic edifice appears to be dominantly intrusive, with velocities faster than 6.5 km/s. The edifice overlies both high lower crustal (> 7.2–7.6 km/s) and upper mantle (> 8.3 km/s) velocities, suggesting that ultramafic rocks have been intruded as sills rather than underplated beneath the crust. The results suggest that the ratio between the volume of intra-crustal magmatic intrusion and extrusive volcanism is as high as ～ 4.5. In addition, the inversion of Moho reflections shows that the Pacific oceanic crust has been flexed downward by up to ～ 2.5 km beneath the seamount. The flexure can be explained by an elastic plate model in which the seamount emplaced upon oceanic lithosphere that was ～ 10 Myr at the time of loading. Intra-crustal magmatic intrusion may be a feature of hotspot volcanism at young, hot, oceanic lithosphere, whereas, magmatic underplating below a pre-existing Moho may be more likely to occur where a hotspot interacts with oceanic lithosphere that is several tens of millions of years old. |
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