Local Shear Deformations as a Cause of Eclogitization: Evidence from the Gridino Melange Zone, Belomorian Mobile Belt

摘要

The problem of the genesis of eclogites has been a subject of continuous discussion. One very popular concept is that of their generation in subduction zones. Owing to the findings of Archean eclogites in the Gridino melange zone and Salma (central part of the Belomorian mobile belt), these viewpoints have been extended to the Late Archean. At the same time, there are indications that eclogitization cannot be explained by lithostatic loads, which "compelled eclogite-gneiss and eclogite-schist complexes to subside in the deep mantle to a depth of 100 km or more followed by their subsequent hopeless attempts to develop mechanisms of exhumation". Manifestations of local eclogitization indicate that great depths are not required to produce high-pressure metamorphism. These facts have stimulated the development of new models of eclogite formation. In particular, the model of retrograde granu-lite transformations under the influence of fluids penetrating along the shear zones was proposed to explain the local eclogitization in western Norway. Tec-tonophysical modeling showed that it is possible for conditions of high-pressure metamorphism to be met in shear zones at the junction of blocks. Our data confirm the possibility of eclogitization in local shear zones.