Project Kaiko : Introduction
Résumé
The Kaiko project was a French-Japanese cooperative scientific effort to investigate the structures and geodynamic processes in the deep trenches surrounding the Japanese islands. Seabeam mapping, as well as detailed geophysical investigation of eight selected areas in the Nankai, Suruga and Sagami Troughs and in the Japan Trench, including the trench triple junction, were performed in 1984. Twenty-seven manned dives, to a maximum depth of 6000 m, were made over five of these areas at carefully selected sites in 1985. The main results of the project are presented in this special issue together with a set of coloured bathymetric maps and block diagrams. They illustrate a great diversity of tectonic styles, from the turbidite-filled trenches of the Shikoku Basin with a well developed accretionary prism, to the much deeper Japan Trench with widespread evidence for large-scale slumping and erosion over the inner wall. Special insight has been gained into the processes involved in the subduction of seamounts and of volcanic ridges. Benthic communities, associated with chemosynthetic processes, were discovered at several locations during manned dives in the Nankai Trough as well as in the Japan Trench. They thus appear to be a common feature of deep-sea trenches. Thermal, geochemical and biogeochemical measurements, coupled with tectonic observations, indicate that they are related to overpressure fluid advections along zones of active surface deformation.