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Simulation of the Planetary Interior Differentiation Processes in the Laboratory
Published on: November 15, 2013
Slab melting versus slab dehydration in subduction-zone magmatism
Kenji Mibe1, Tatsuhiko Kawamoto, Kyoko N Matsukage
1Earthquake Research Institute, University of Tokyo, Yayoi, Tokyo 113-0032, Japan. mibe@eri.u-tokyo.ac.jp
Abstract:
The second critical endpoint in the basalt-H(2)O system was directly determined by a high-pressure and high-temperature X-ray radiography technique. We found that the second critical endpoint occurs at around 3.4 GPa and 770 °C (corresponding to a depth of approximately 100 km in a subducting slab), which is much shallower than the previously estimated conditions. Our results indicate that the melting temperature of the subducting oceanic crust can no longer be defined beyond this critical condition and that the fluid released from subducting oceanic crust at depths greater than 100 km under volcanic arcs is supercritical fluid rather than aqueous fluid and/or hydrous melts. The position of the second critical endpoint explains why there is a limitation to the slab depth at which adakitic magmas are produced, as well as the origin of across-arc geochemical variations of trace elements in volcanic rocks in subduction zones.
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