An Experimental Study of the Basalt-Garnet Granulite-Eclogite Transition

The recrystallization of a tholeiitic basalt to garnet granulite and to eclogite has been experimentally examined at temperatures ranging from 800°C up to the solidus of the rock. In addition, the solidus of tholeiitic basalt has been redetermined. The slope of the boundary separating the field of garnet granulite frpm that of basalt is P kb = 0.014 T°C - 5.4 kb. The boundary separating the field of garnet granulite from the field of eclogite has the equation P kb = 0.020 T°C + 4.0 kb. The equation of the newly determined solidus of tholeiitic basalt is T = 6.0 P kb + 1105°C. Curves relating the densities of the mineral assemblages to temperatures and pressures of formation are shown. One relatively abrupt change in density occurs as basalt recrystallizes to garnet granulite, and a second relatively sharp density increase occurs as garnet granulite is recrystallized to eclogite.