PARAMETERS OF THE GENERATION OF ABYSSAL T HOLEIITES

Numerical modeling of the partial melting of lherzolitic material perm itted to estimate pressure and temperature of the beginning of generat ion of primitive MORBs from dry peridotites as 1450 degrees C at 27 kb ar. The estimated value of potential temperature is higher than genera lly accepted T-pot for the convecting part of upper mantle. This may i mply the involvement of hot material from deep levels in the ascending fluxes of mantle rocks. The observed levels of the concentration of R EE and shift in Th/U ratio show that the geometry features of drainage zones of partial melts in ascending diapirs result in the increasing contribution of more deep seated melts corresponding to the initial st ages of mantle anatexis in the formation of composite magmas collected in a crustal magmatic chamber.