Ocean Floor Formation in the Zones of the Continental Margin Tectonic Plates Bending: a Case Study of the Abyssal Trenches Student assignment on course ’Continental Margin Tectonics and Marine Geodynamics’ Ocean University of China, College of Marine Geo-sciences China, Qingdao Lemenkova Polina July 10, 2018 Abstract Current report on the course “Continental Margin Tectonics and Marine Geodynamics” is intended to highlight the problem of the ocean trench formation of ocean seafloor geomorphological structure in the zones of the continental margin tectonic plates bending. A case study of this essay is morphology of the abyssal ocean trenches and how we can measure and analyze the structure of the ocean floor in the least reachable locations of the world ocean. The report consists of five chapters. The introduction chapter is aimed at understanding the structure of the main geomorphological elements of the continental margin tectonics, as well as the basics of the marine geology are summarized. The second chapter is focused on the studies of the trench morphology, classification and problems of their arising in the tectonic plates. The seabed of the world ocean mid-ocean ridges, transform faults and their relationship with riſt valleys, volcanic structures, deep-water basins, are reviewed in this chapter. The third chapter is focused on the methods of studying and surveying ocean seafloor. It also concerns the basic information on the history of the ocean studies, research methods and instruments. The special part describes the ocean floor sampling: dredging and drilling as examples of the geological analysis methods, structure of passive and active outskirts. Moreover, an attention is paid to the application of the echo sounder devices: their history, types of sounders, as well as adjacent areas of mainland and islands. The basic concepts of the modern geology and geodynamics (tectonic plates subduction, spreading, transform fault, etc.) formed as a result of the study of the margin tectonics of the ocean floor are discussed and reviewed. 1 Introduction The bathymetry of the ocean floor reflects plate tectonics processes, including trench movement, deformation and bending which is associated with mantle convection at the global scale. There are three classified types of the continental tectonic plate boundaries producing a unique type of the seafloor bathymetry. Thus, the ridge axes represent a place in the system where the upwelling magma encounters cold seawater. Hydrothermal cooling of magma at the ridge axes causes recycling of the entire volume of the ocean and provides nutrients for biological communities on the trench. Ocean trenches, being the deepest point of the Earth have particular features in the process of trench morphology formation, changes and nearby located plate bending. The global plate tectonics movements shaping the seafloor bathymetry can be described as follows. The seafloor spreading creates an axial riſt and corrugated hills. Spreading ridges are formed by nearby faults where the most destructive earthquakes occur. Subduction of the cooled plate into the mantle causes creation of the deep ocean trenches and here, as a consequence, the major earthquakes and tsunamis originate. The plates act as giant radiators of the heat cooling, thickening, and gradually subsiding by progressing from ridge to trench. In such a way, tectonic plates form the large-scale pattern of the system 1