Abstract
A Jurassic accretionary complex within the Northern Chichibu Belt, Yanadani area, western Shikoku, is divided into three distinct geologic units (units I, II, and III) based on the constituent rocks and geologic structure. Unit I is characterized by pelitic mélange containing blocks of greenstone, chert, limestone, and terrigenous clastic rocks. Unit II consists mainly of psammitic and pelitic phyllites, and Unit III consists of large blocks of greenstone-limestone complex with alternating beds of sandstone, mudstone, and pelitic mélange. The contacts between the units are northward-dipping faults. Here, we propose a method of analyzing grading structure, and there by younging direction, which involves grain-size measurements under the microscope. The younging directions of coherent sequences and pillow lava were determined at 63 localities. These data reveal consistent younging directions within large-scale blocks, demonstrating that the strata of Units I and II, and the terrigenous clastic rocks of Unit III are overturned, younging to the south. In contrast, the greenstone-limestone complex within Unit III is not overturned, and youngs to the north. This large-scale overturned structure within the Northern Chichibu Belt is interpreted to represent a large-scale overturned fold.
