Oceanic Trenches

Abstract

Although only recognized in the middle of the last century, oceanic trenches are among the most spectacular structural and morphological features in the deep oceans. Caused by the collision and subduction of tectonic plates and shaped by the interplay of tectonic and sedimentary processes, the morphology of oceanic trenches can be manifold. In this chapter we discriminate between sediment starved trenches, partly sediment filled trenches, and sediment flooded trenches. In sediments starved trenches the tectonic signature is usually well preserved everywhere in the trench, including at the outer slope, the depression, and the inner slope. In contrast, in sediment flooded trenches the outer slope and the trench depression usually correspond to a flat seafloor that results from the deposition of thick sedimentary sequences that overprint all fault scarps. Here, a tectonic signature is only found at the trench inner slope where accretion of trench sediments results in thrust faulting. The remarkable differences in trench morphologies underline that for a comprehensive understanding of the structural evolution of a convergent margin, detailed knowledge on the sedimentary and tectonic history of the adjacent oceanic trench is necessary.