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structural geology[′strək·chə·rəl jē′äl·ə·jē]
the branch of tectonics that studies the fundamental forms of occurrence of rocks in the earth’s crust and the origin of these forms. The term “structure” is understood in structural geology to mean the spatial arrangement of rocks and of bedding irregularities resulting primarily from diastro-phism. The principal task of structural geology is to investigate the external appearance (morphology) of structural forms, the kinematic processes of the displacement of matter that lead to the formation of structures, and the dynamic conditions (the arrangement and nature of the applied forces causing deformation) involved.
The structural forms studied by structural geology include layers, folds, joints, discontinuities with displacement (faults, such as steep faults, slips, overthrusts, and overthrust nappes), and bodies of magmatic origin. In addition to tectonic structural forms arising as a result of endogenic processes, there also exist sedimentary structures formed during sedimentation in exogenic processes and gravity structures resulting from the action of the force of gravity (for example, subaqueous slump structures). Structural geology arose and developed in close association with the practical problems of mineral exploration, prospecting, and mining.
Structural geology originated in the 19th century. Pioneering workers in Canada and the USA were C. R. Van Hise, C. Leith, B. Willis, and R. Willis; these geologists investigated tectonic fractures, folds, and cleavage. In Russia, N. A. Golovkinskii studied the formation of layers on the Eastern European Platform, and A. P. Karpinskii and V. A. Obruchev studied the structure of ore deposits in the Altai, Saian, and Ural mountain regions. In Western Europe, A. Heim, M. Bertrand, and E. Argand studied folds and overthrusts in the Alps. Important contributions to the development of structural geology have been made by a number of Soviet geologists, including N. S. Shatskii and A. L. Ianshin (platforms), I. M. Gubkin (oil-bearing structures), V. V. Belousov (the role of radial tectonic forces), and A. V. Peive and V. E. Khain (deep faults and horizontal movements in the formation of folds and fractures).
Structural geology is closely connected with such other areas of geological knowledge as geological surveying, geomorphology, stratigraphy, lithology, petrography, hydrogeology, engineering geology, mineralogy, prospecting, and mining. The data of structural geology are important for the development of the theory of geotectonics. Structural geology uses the method of historical analysis to investigate regularities in the formation of structures. In order to understand the origin of structural forms, extensive use is made of the physical methods of studying rock deformation that are considered in the theory of elasticity, the theory of plasticity, and the theory of strength; tectonophysical simulation is also used, and experimentally produced forms are studied. The investigation of very small structures constitutes a special branch of structural geology (called petrotectonics, or structural petrology), because petrographic structures and textures also reflect tectonic deformations of rocks.
REFERENCESWillis, B., and R. Willis. Strukturnaia geologiia. Baku, 1932. (Translated from English.)
De Sitter, L. U. Strukturnaia geologiia. Moscow, 1960. (Translated from English.)
Azhgirei, G. D. Strukturnaia geologiia. Moscow, 1966.
Belousov, V. V. Strukturnaia geologiia, 2nd ed. Moscow, 1971.
G. D. AZHGIREI