Abstract
On the basis of geological, petrographical and geochronological data, Cretaceous to Paleogene felsic to intermediate igneous rocks extensively developed in the Chugoku and Shikoku districts were divided into four episodic stages of volcano-plutonism. The igneous rocks comprising each stage are as follows; 1st stage) volcanics of the Ryoke Belt and Cretaceous volcanic rocks-Ryoke and Hiroshima Intrusives developed mainly in the Ryoke and San'yo Belts, 2 nd stage) latest Cretaceous to early Paleogene volcanics-Imbi Intrusives, 3 rd stage) volcanics of Takayama age-Namariyama Intrusives (Eocene), and 4 th stage) volcanics and intrusives of Tamagawa age (Oligocene). The last three are distributed in the San'in zone. Based on spatial and temporal distribution of igneous rocks of each stage, it is suggested that location of magmatism during the Late Cretaceous to Paleogene did not migrate from the Pacific Ocean side, but contracted gradually with time to the Japan Sea side.
