Home – Home – Jornals – Russian Geology and Geophysics 2006 number 1

A model for free-convective flows in the asthenosphere beneath the ocean has been derived. The thermophysical model for the asthenosphere beneath a mid-oceanic ridge is a horizontal layer being heated from the side (in the vicinity of the ridge axis) and cooled from above, with the sole adiabatic. Laboratory modeling yielded velocity and temperature fields in the horizontal layer in the boundary-layer regime. Requirements for the correct determination of the velocity and temperature fields in the asthenosphere have been defined from the results of thermophysical modeling. The asthenosphere viscosity and maximum temperature difference in the asthenosphere in the vicinity of the MOR axis have been estimated. Velocity and temperature fields in the asthenosphere layer have been obtained under slow-spreading conditions. Stability fields of the main deep-seated parageneses and a zone of partial melting in the asthenosphere have been established on the basis of the experimental field of temperature and streamlines, using the velocity field obtained by laboratory modeling and experimental state diagram of peridotite. The width of the partial-melting zone could average 5-7 km (on the one side of the ridge), and its depth, about 80 km. Depthward, the gabbroid associations grades into spinel peridotites, which in turn give way to garnet peridotites. At depths of more than 400 km olivine grades into ringwoodite.