THEORETICAL MODELING OF ECLOGITE UPLIFT

Studies of eclogites by means of traditional petrological methods prov ide information on the temperature and pressure of merely the main met amorphic episodes. The pressure differences between these episodes oft en attain 10 kbar and more. This paper presents a new approach that ma kes it possible to restore the P-T-t metamorphic conditions between th e main events. This approach is illustrated by the example of the well -studied eclogites of the Greater Caucasus. According to geothermobaro metric data, the rocks were uplifted approximately 35 km at high tempe ratures. The process was modeled along predetermined P-T-t trajectorie s, each of which was then assessed by the kinetic parameters of the di ffusion homogenization of progressively zoned garnet grains. Additiona lly, cooling rates of the metamorphic system were determined independe ntly by modeling the Fe-Mg interdiffusion at the contacts of coexistin g garnet and omphacite. As follows from the calculations, the eclogite s rapidly cooled (with cooling rates of similar to lower 1500 degrees C/m.y.) from 700 to 600 degrees C during the onset of uplift. The late r subisothermal uplift proceeded at the high rate of approximately 7 m m/year. The specific features of the P-T-t uplift evolution of the roc ks account for the good preservation of the eclogitic mineral assembla ge and provide important information on the tectonic mechanisms of the eclogite exhumation.