Large‐scale folding in the Asemi‐gawa region of the Sanbagawa Belt, southwest Japan

Abstract

AbstractThe Sanbagawa Belt generally shows higher metamorphic grade at higher structural levels. This inversion can be interpreted as reflecting an original inverted thermal structure typical of subduction zone environments. However, repetitions in the distribution of the metamorphic zones seen in central Shikoku, Japan, clearly show the original thermal structure has been affected by deformation after the peak of metamorphism. This repetition has been attributed to both the action of tectonic discontinuities and regional folding. It is important to distinguish between these two interpretations to determine the extent to which the original subduction zone sequence is preserved. Analyses of lithological and structural data reveal the presence of a large‐scale post‐metamorphic fold in the central part of the highest grade region. This folding has an axis that coincides with the thermal axis implied by the distribution of the metamorphic zonation, suggesting the repetition of metamorphic zones in this area can be accounted for by folding without the need for major discontinuities.