上部マントルの電気伝導度構造とマグマ起源

概要

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The electrical conductivity of basalt magma is a few orders of magnitude higher than that of solid peridotite. This experimental fact implies a close relationship between a highly conducting layer and basalt magma existing in some form in the mantle and crust, most probably in a form of partial melting. Observations of electric and magnetic field variations have disclosed the electrical conductivity structure in the crust and upper mantle, and highly conducting layers, characterized by a conductivity of 0.1 S/m or so, have been found in ocean regions and at some active areas in continents. These layers can be interpreted most reasonably as indicating partial melting zones, but the possibility may not be ruled out that high conductivity is realized at a temperature slightly below the solidus. The order-disorder mechanism at such a temperature is considered to be responsible for the high conductivity. In active regions such as spreading, lifting, and subducting zones, high conductivity layers are likely to be associated with basalt magma prevailing in partial melting zones. The lower crust in some regions is conductive because of water trapped there. In active areas such as Tohoku and the Rio Grande rift zone, the process of magma ascent to the upper crust seems to be related to the formation of a conductive zone, although this problem has yet to be challenged.
特定非営利活動法人日本火山学会の論文
1988-10-31