A UNIQUE RECORD OF P-T HISTORY OF HIGH-GRADE POLYMETAMORPHISM

Abstract

Precambrian granulite complexes repeatedly affected by high-temperature polymetamorphism (HTM) retain records of thermal and dynamic history of both events. Repeated high-grade metamorphism should apparently create a new isotopic system that determines the age of rock, whereas the older mineral assemblage should be replaced by a new one that fits the younger thermodynamic parameters, the more so as the repeated metamorphism is realized along ductile deformation zones . However, the relicts of the first event are retained within these zones, and the age difference of the events may reach hundreds of million years. Hence, the repeated HTM occurred rapidly, and the complete reequilibration of minerals was not achieved.