九州-四国の四万十帯の低角ナップ構造

In the Shimanto Terrane of Kyushu, the Cretaceous Morotsuka Group is thrust toward SE over the Cretaceous Makimine Group and Paleogene Kitagawa Group along the Tsukabaru Thrust. The Makimine and Kitagawa Groups are phyllite-dominated strata, and are thrust toward SE over the Paleogene Hyuga Group along the Nobeoka Thrust. The Tsukabaru and Nobeoka Thrusts are nearly horizontal as a whole, and form giant nappes and some klippen.
In east Shikoku, the Cretaceous Mugi Formation is thrust over the Paleogene Murotohanto Group along the Aki Tectonic Line, which is correlative with the Nobeoka Thrust of Kyushu. The Aki Tectonic Line, which is originally low-angle thrust, probably became high-angle by later folding.
In west Shikoku, phyllitic strata do not occur near the boundary between the Cretaceous Lower Shimanto Group and Paleogene Murotohanto Group. However, the Miocene Takatsukiyama Granitic Rocks, intruding the Lower Shimanto Group, have many xenoliths of politic schists and phyllites. These metamorphic rocks might be correlative with the phyllites over the Nobeoka Thrust of Kyushu. This suggests the occurrence of the Aki Tectonic Line underneath the phyllites. The low-angle nappe structures may be the fundamental structures of the Shimanto Terranein Shikoku, too.