VARIATIONS OF DEFORMATION AND EMPLACEMENT TYPES IN ACCRETIONARY PRISMS: COMPARISON BETWEEN THE FRANCISCAN AND JAPANESE ON LAND AND SUBMERSIBLE EXAMPLES

Some decades of studies on world accretionary prisms and fold-and-thrust belts of convergent margins gave us the total comprehension on the major elements of the development of the prisms, what the difference of deformation and emplacement types are discussed. Large structures of prisms were divided into five different modes, such as 1) chaotic deposits including so-called ocean plate stratigraphy mélange, 2) tightly (isoclinally) folded thin-bedded turbidites (or transposed structures), 3) broadly folded thick-bedded turbidites, 4) mud-pressurized injection bodies (diapirs or broken formations), and 5) sandy and pebbly liquefied chaotic injection bodies. Metamorphic and igneous rock blocks are included in either cases except for 2) and 3). As for minor structures of sandstone and mudstone in prisms, we reached a certain conclusion that not only the role of pore-fluid pressure but stress-strain frequency (strain rate) and mud-pressure during or just after sedimentation, at burial and exhumation stages. Pore fluid and mud-pressures are mainly dependent upon permeability and response of exerted stress frequency either by sudden (by earthquake shake) or slow tectonic rate. We compared these different modes between examples of on-land Franciscan and Japanese examples (Miura-Boso and Shimanto), and drilling or submersible observation from Barbados and the Nankai prism and Japan trench. What we have seen in on-land examples of any styles of deformation have similar or equivalent phenomena to submarine ones that we saw from the submersibles, particularly in the present Nankai accretionary prism and Japan trench. The Franciscan mélange cases would be also explained by these lines of consideration. Such comparative studies might give the modern significance on mélanges and any other types of deformation, including various types of subduction breccias.