Abstract
The Oharai Formation is studied to elucidate the provenance of clastic materials. Metamorphic rocks and sedimentary rocks are commonly found as pebbles in the Oharai Formation. The lithofacies of these rocks are closely akin to those in the Tsukuba-Yamizo belts. Metamorphic grades of the pebbles range from low to middle parts of the biotite zone of the Ryoke metamorphic belt. The K-Ar age of biotite from a coarsegrained biotite schist is determined to be 99.6 Ma. The K-Ar ages for two granitic pebbles are 64 Ma and 73 Ma. The provenance of the pebbles is considered to be a terrain located at the east or south of the Tsukuba-Yamizo mountains.
