Model study of the formation of deformation-induced structures of subduction type in block-structured media. Ice cover of Lake Baikal as a model medium

Abstract

The field investigations carried out recently have shown that an effective model medium for studying geotectonic processes can be the ice cover of Lake Baikal, which is a classical example of hierarchically organized block-structured media. Many significant deformation mechanisms of the block-structured ice cover can be compared to the mechanisms known in geodynamics, such as spreading, subduction, pull-apart and other ones. The present paper contains the results of studying dynamic processes of formation and evolution of one of the mentioned deformation-induced structures in the Baikal ice cover, namely, an underride zone that can be considered as a subduction zone analog. It is shown that these processes can be induced by dynamic relaxation events related either to the formation of new interfaces (fragmentation of blocks) or to the activation of the existing but earlier inactive cracks. A supposition is made that fragmentation accompanied by releasing a large amount of elastic energy can be one of possible mechanisms of forming compression impulse, which is considered to be necessary for initiation of subduction in the lithosphere. The processes of forming underride and subduction zones are compared and their qualitative similarity is revealed. After examining the structure of contact between ice plates in the underride zone the conclusion was made that formation of the deformation-induced structure under consideration allows reducing the compression resistance of the plate boundary by orders of magnitude. This suggests that structures of subduction type make for an effective mechanism of realization of high inelastic deformations in block-structured media without noticeable stress growth.