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Originally published in Science Express on 27 July 2006
Science 8 September 2006:
Vol. 313. no. 5792, pp. 1426 - 1428
DOI: 10.1126/science.1128235
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Reports

Volcanism in Response to Plate Flexure

Naoto Hirano,1,2* Eiichi Takahashi,1,3 Junji Yamamoto,1,4 Natsue Abe,3 Stephanie P. Ingle,1,5 Ichiro Kaneoka,6 Takafumi Hirata,1 Jun-Ichi Kimura,7 Teruaki Ishii,8 Yujiro Ogawa,9 Shiki Machida,8 Kiyoshi Suyehiro3

Volcanism on Earth is known to occur in three tectonic settings: divergent plate boundaries (such as mid-ocean ridges), convergent plate boundaries (such as island arcs), and hot spots. We report volcanism on the 135 million-year-old Pacific Plate not belonging to any of these categories. Small alkalic volcanoes form from small percent melts and originate in the asthenosphere, as implied by their trace element geochemistry and noble gas isotopic compositions. We propose that these small volcanoes erupt along lithospheric fractures in response to plate flexure during subduction. Minor extents of asthenospheric melting and the volcanoes' tectonic alignment and age progression in the direction opposite to that of plate motion provide evidence for the presence of a small percent melt in the asthenosphere.

1 Department of Earth and Planetary Sciences, Tokyo Institute of Technology, 2-12-1 Ookayama, Meguro, Tokyo 152–8551, Japan.
2 Scripps Institution of Oceanography, University of California, San Diego, 9500 Gilman Drive, La Jolla, CA, 92093–0225, USA.
3 Japan Agency for Marine-Earth Science and Technology, 2-15 Natsushima, Yokosuka, 237–0061, Japan.
4 Institute for Geothermal Sciences, Kyoto University, Noguchibaru, Beppu 874–0903, Japan.
5 School of Ocean and Earth Science and Technology, University of Hawaii, 1680 East-West Road, Pacific Ocean Sciences and Technology Building 606, Honolulu, HI 96822, USA.
6 Earthquake Research Institute, University of Tokyo, 1-1-1 Yayoi, Bunkyo, Tokyo 113–0032, Japan.
7 Faculty of Science and Engineering, Shimane University, 1060 Nishikawatsu, Matsue 690–8504, Japan.
8 Ocean Research Institute, University of Tokyo, 1-15-1 Minamidai, Nakano, Tokyo 164–8639, Japan.
9 Institute of Geoscience, University of Tsukuba, 1-1-1 Tennodai, Tsukuba 305–8571, Japan.

* To whom correspondence should be addressed. E-mail: nhirano{at}ucsd.edu

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