a regularly repeating form of occurrence of rocks in the earth’s crust. In the broad sense, the term “tectonic structure” is applied to various parts of the earth’s crust that are formed by the combination of a number of different smaller structural forms. The most important characteristics for the classification of tectonic structures are scale, morphology, and genesis.
A distinction is made between fundamental structural forms and tectonic structures of magmatic bodies. Fundamental structural forms include layers, folds, joints, and faults (for example, steep faults, slips, overthrusts, and overthrust nappes). Examples of tectonic structures of magmatic bodies are dikes, sills, laccoliths, and batholiths. Such structures of magmatic origin may have structural features of smaller, even microscopic, size.
Regular complexes of fundamental structural forms make up tectonic structures of higher orders. For example, folds are grouped in the compound structural forms called anticlinoria and synclinoria, which in turn form fold systems. Structures found in cratons include syneclises, anteclises, and aulacogens. The largest tectonic structures of the earth’s crust have roots in the upper mantle and are called abyssal, or hypogene, structures. Important examples are cratons and oceanic, geosynclinal, and orogenic mobile belts (seeGEOSYNCLINAL SYSTEM and OROGEN); these structures make up the continental and oceanic segments of the lithosphere. Other abyssal structures include abyssal fractures and rifts. Abyssal structures whose development occurs primarily in the crust are called crustal structures. The formation of tectonic structures is influenced by movements having a certain direction and history (kinematics) of development (see) and by forces that cause tectonic deformations and reflect the dynamics of the process.
Fundamental tectonic structures are studied in structural geology. The microscopic tectonic structures of magmatic bodies are investigated by the methods of microstructural analysis (seePETROTECTONICS). Large-scale complexes of fundamental tectonic structures are studied in geotectonics (see).
REFERENCESAzhgirei, G. D. Strukturnaia geologiia [2nd ed.]. Moscow, 1966.
Metody izucheniia tektonicheskikh struktur, fascs. 1–2. Moscow, 1960–61.
Khain, V. E. Obshchaia geotektonika, 2nd ed. Moscow, 1973.
Belousov, V. V. Osnovy geotektoniki. Moscow, 1975.
Belousov, V. V. Strukturnaia geologiia, 2nd ed. Moscow, 1971.
Sander, B. Einführung in die Gefügekunde der geologischen Körper, vols. 1–2. Vienna, 1948–50.
G. D. AZHGIREI