On genesis and dynamics of deep trenches

Abstract

Deep sea trenches are gigantic troughs of the earthcrust which both spatially and possibly genetically are in close connection with island arcs. Analysis of data on geomorphology, geology and geophysics shows that deep trenches come into being as rather shallow troughs and later on pass various stages as follows: a) very deep troughs with thin sediment cover; b) deep troughs with thick sediments at the bottom; c) troughs nearly completely filled with sediments. Later the sedimentary mantle within the trench may be folded and an inversion takes place-formation of folded rodge instead of the trough (e. g. Timor and Barbados). Thus deep trench in the course of its evolution passes the same stages as geosynclinal trough. At the time of the trench closing a new trench is usually formed at an adjacent part of the earthcrust, thus a lateral migration of the trench occurs (e. g. Timor trench). In some cases the deep trench increases its length (e. g. Aleutian trench). Deep drilling data from Japanese and Aleutian trenches do not confirm hypothesis of the trenches formation due to subduction. Some other hypotheses are discussed.