Abstract

Results from the French-Japanese Kaiko exploration program of the Japan Trench and complementary data are used to propose a model of subduction of seamounts. Examples in two seamount chains, one at the junction between the Japan and Kuril trenches and the other in the southern part of the Japan Trench off Inubo Cape, illustrate the stages of subduction. The Japan Trench margin evolved as a homogeneous wedge of deformable, noncohesive Coulomb material during seamount subduction. This is illustrated by the subduction of the Daiichi Kashima seamount in the southern Japan Trench. Our model predicts that the first consequence of seamount subduction is a compressive thickening of the toe of the wedge above the advancing flank of the seamount because of the oversteepening of the rigid base of the wedge; this agrees with our observations in the Daiichi Kashima area. This thickening shifts landward across the wedge with the advancing flank of the seamount. Erosion dominates the wedge above the trailing flank of the seamount because of the corresponding understeepening of the rigid base of the wedge. A reentrant of the toe of the wedge is thus created; it is largest when the oceanic flank of the seamount coincides with the base of the landward slope. At this time, the trench axis will probably have an abnormally large amount of sediments, as illustrated at the junction between the Japan and Kuril trenches. After the subduction of the seamount, the edge of the wedge should progressively move back to its initial location. Frontal accretion is absent or very limited.

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