Methods for Medium-Scale Tectonic Mapping of Deep Ocean Areas

In our overview, we describe the evolution of methods and approaches for medium-scale tectonic mapping of deep ocean areas at scales from 1 : 1 000 000 to 1 : 15 000 000 and smaller, which is a synthesis of data on the structure of the bottom and a theoretical geodynamic model that interprets the genesis of the observed structures. Changes in the content of map legends are shown depending on the instrumental level of research and theory of tectogenesis to the level developed for land tectonics. Until 1970, the development of tectonic ocean mapping followed the path of direct convergence of the composition of map legends with their land counterparts, since data were interpreted based on fixism theory. When the ideas of mobilism were formed in the theory, the content of ocean maps acquired tectonic elements that differ from land, peculiar only to oceans. By 1970, extensive geological and geophysical data and their interpretation based on plate tectonics finally resulted in a specific tectonic legend for oceans. Tectonic maps were constructed with a new set of legend elements for all oceans, which were part of general tectonic maps of the framing of continents. The age gradation of the oceanic basement was created, based on the indexation of linear magnetic anomalies and the primary classification of younger intraplate structures overprinted on the basement. The use of satellite altimetry data, which has dense and uniform coverage at medium scales, gave new impetus for mapping the ocean floor and basement structures, even in areas where they are overdraped by sedimentary cover and are not highlighted in the ocean floor relief. This led to new-generation maps with a no less reliable topographic basis than spatially nonuniform echosounding. At the end of the 1980s, there began a fundamentally new stage of accumulation of instrumental measurement data and attempts to rationally adapt them into a theoretical geodynamic model. In the structure of oceanic crust, previously unknown tectonic elements were identified that had not been recorded during nonuniform shipboard surveys. New tectonic elements, established according to modern data, received a rational geodynamic interpretation using plate tectonics theory, assuming the block and tectonically stratified structure of moving plates. New tectonic maps and reference data are so saturated with information that it is necessary to move from small scales to 1 : 10 000 000 to display the details of the topographic bases on which they were interpreted. In our review, we address the unsolved problems that currently arise in compiling medium-scale tectonic maps of deep ocean areas, which are the structural features of intraplate deformation and magmatic structures.