Scholarly record

THE CHARACTERISTICS OF MICROFRACTURE FORMATION IN A STRESS-DEFORMED GRANITIC MASSIF

PhD Vitali Shekov, Researcher Andrey Ivanov, PhD Oksana Myasnikova

Abstract

Until recently, the effect of various factors, which are due to the stressed state and physical weathering of a massif on the development of microfractures in igneous rocks in elastic-brittle state has been poorly studied. Therefore, the genesis of fractures of various sizes cannot be revealed and the strength of the massif cannot be reliably forecasted. The authors have assessed the conditions and formation pattern of microfractures in rapakivi granites from the Salmi massif, the Fennoscandian Shield, which display a uniform composition without well-defined structural characteristics by the optical study of the orientation characteristics of microfractures in samples collected from the surfaces of bedrock exposures using a certain scheme. The authors have found that fractal characteristics upon the formation of fractures of various sizes are well-defined on all fracturing diagrams, and the structural features of small-scale fractures are affected by larger-scale fractures. This pattern is mainly due to the influence of compression or shearing forces, as shown on fracturing diagrams correlating systems of micro- and macrofractures on various scales. Weathering occurs already along newly-formed fractures and microfractures, depending on mode of occurrence. The complex fracturing pattern of massif zones is illustrated by the variability of the deformation field. This makes the structural parameters of fracturing in the case of single samples less informative and requires the study of spatially selected samples on a small area. Therefore, the scattering of microfracture occurrence values can be statistically considered and the directions of the action of the main stress axes in this zone can be calculated. Such concepts of the interrelations of fractures of various sizes provide the possibility of the more detailed least expensive study of the quantitative indices of massiveness of rocks overlain by a thick bed of rocks of various ages using diamond samplers instead of the removal of detritus from large areas The study of the genesis of microfractures provides information about the strength of rocks from the massif of interest and the possible production of large blocks from the massif, which is important for the forecasting of the arrangement of building stone deposits.

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