TECTONICS, METAMORPHISM, AND THE PROBLEMS OF EVOLUTION OF THE OLONDO GREENSTONE-BELT

Based on the correlation of data compiled from both published and original sources, the authors attempted to consider the tectonic and metamorphic evolution of the Olondo greenstone belt, which is regarded as the most typical and the best studied belt in the Aldan Shield. Data on the geologic structure, metamorphic conditions, and tectonic setting are presented. The tectonic relationships of the sequences both within the belt and with surrounding tonalite-trondhjemite gneisses are shown to be complicated and ambiguous, which makes it difficult to reconstruct the initial position of the metavolcanic and metasedimentary sequences. Metamorphic and isotopic data, when taken separately, are unable to help elucidate the primary relationships of the rocks; however, a comprehensive study allows us to propose an adequate model. Nevertheless, the conclusions drawn from this study are not straightforward. A new approach to the problem of reconstructing the primary nature and evolution of the Archean greenstone belts, including those in the Aldan Shield, is proposed on the basis of this investigation.