Tectonic Map

a map that portrays the structure of the earth’s crust and, usually, reflects the primary phases in development of the crust within particular regions or for the earth as a whole. Such maps are made on the basis of geologic maps through the use of geophysical and other data.

Tectonic maps may be divided into structure-contour maps and tectonic maps proper. (This classification is followed by the Soviets; in American usage, structure-contour maps are regarded as a separate type rather than as a subdivision of tectonic maps.) Structure-contour maps indicate the morphology of tectonic structures. By contrast, tectonic maps, in the narrow sense, show, in addition to morphology, (1) the history of the formation of the structures, (2) phases in the structures’ development, and (3) the relationship between magmatism and tectonics. Several types of tectonic maps, in the narrow sense, may be distinguished: standard tectonic maps, paleotectonic maps, maps devoted to a specific topic (for example, tectonic maps of the basement complex of the USSR), and special-purpose maps (for example, seismotectonic maps). Each of these types is subdivided into general maps, which may have a scale of 1:2,000,000 or a smaller scale, and regional maps, whose scales are usually between 1:200,000 and 1:1,000,000.

Small-scale tectonic diagrams, or sketch maps, were the forerunners of tectonic maps. One of the first such diagrams was published by A. Gressly in 1838 and showed the Jura Mountains in France and Switzerland. In the late 19th and early 20th centuries, similar diagrams were made by E. Suess, F. Kossmat, M. Bertrand, E. Argand, G. Haug, H. Stille, and A. P. Karpinskii.

In the USSR, small-scale tectonic diagrams covering the entire country were made in the 1930’s by A. D. Arkhangel’skii, N. S. Shatskii, D. V. Nalivkin, and M. M. Tetiaev. The first general tectonic map of the USA was published in 1944; it was primarily of a structural nature. The tectonic information accumulated in the USSR through geologic mapping was summarized in the Tectonic Map of the USSR and Adjacent Countries, which was published in 1953 on a scale of 1:4,000,000 and in 1956 on a scale of 1:5,000,000 under the editorship of N. S. Shatskii. These maps received wide recognition in the USSR and abroad and served as a model for the International Tectonic Map of Europe (1964) and maps of other continents and countries. The USSR subsequently published a large number of multipage colored general and regional tectonic maps of both the standard and special-purpose types.

General tectonic maps have been produced in the USSR for Eurasia (1966, scale 1:5,000,000), the earth’s polar regions (1969, 1:10,000,000), the Pacific Ocean region (1970, 1:10,000,000), and the tectonics of the Precambrian continents (1972, 1:15,000,000). Similar methods have been used outside the USSR to make and publish tectonic maps of North America (1969, 1:5,000,000), Africa (1968, 1:5,000,000), India (1969, 1:2,000,000), and Australia (1972, 1:5,000,000). The International Geological Congress is sponsoring the preparation of a tectonic map of the world on a scale of 1:15,000,000; the work for the map is being carried out primarily in the USSR.

The fundamental principle underlying the making of tectonic maps since the 1950’s has been that of regionalization according to the time at which a given region of the earth’s crust changed from a geosynclinal (highly mobile) state into a relatively consolidated folded structure. This time is reckoned relative to the age of the primary epoch of folding. Individual phases in the development of geosynclines and the folded systems that emerge from them are shown by identifying structural events, which occur in a definite age succession, possess structural independence, and are usually separated by unconformities. Within the cratons gradated coloring is used to show the variation in the depth of occurrence of the basement and, less frequently, the distribution of individual stratigraphic complexes of the sedimentary mantle. The color corresponds to the age of the craton, that is, the time at which the formation of the basement was completed. Folded complexes of different ages are depicted by a certain color, and the structural stages making up the complexes are shown in shades of this basic color.

Tectonic maps may also be based on the regional, or historical-genetic, principle. This principle is used in the tectonic map of the USSR on a scale of 1:2,500,000 published by T. N. Spizharskii in 1966.

As a result of advances in research on the geology of the oceans and, in particular, through the comparison of ophiolitic groups with the present-day oceanic crust, a new type of tectonic map has become possible. It divides the folded geosynclinal complexes of the continents into formations that correspond to the basic phases of the conversion of oceanic crust into continental crust.

Tectonic maps provide a basis for clarifying the relationships between mineral deposits and types of tectonic structures. Such maps thereby contribute to more accurate predictive evaluations of deposits and to more efficient prospecting.