Geochronology of Cretaceous to Paleogene Igneous Rocks Along a North–South Traverse in the Western Kinki Region, Southwest Japan

ABSTRACT New zircon U–Pb ages are presented for Cretaceous to Paleogene volcanic and granitic rocks of Awaji Island in the Ryoke Belt, Arima area in the San'yo Belt, and Izushi–Kasumi areas in the San'in Belt. These areas are located on a transect across southwest Japan from the Median Tectonic Line to the Sea of Japan. So this is the first report of the zircon U–Pb ages of the volcano‐plutonic complexes aligned across the Japan arc. The obtained U–Pb ages of the Sennan Rhyolite, foliated granite, and massive granite, all in the Ryoke Belt, are 94.0, 89.3–84.1, and 84.3 Ma, respectively. Those of the volcanic rocks of the Arima Group, Rokko Granite, and Nunobiki Granodiorite in the San'yo Belt are 79.9–74.1, 79.6–77.6, and 76.5 Ma, respectively. The volcanic rocks of the Yadagawa Group and Yadagawa Granite of the Izushi–Kasumi areas in the San'in Belt gave the ages of 68.2–64.9 and 64.0 Ma, respectively. The development of foliation and deformation of the foliated granite and the subsequent intrusion of massive granite on Awaji Island occurred at ca. 84 Ma. The volcanic rocks in the Arima and Yadagawa groups have been correlated to surrounding volcanic rocks based on lithological similarities, but the new U–Pb ages reveal that they each represent separate volcanic events. The durations of volcanic and plutonic activity, based on the zircon U–Pb ages, are 94–83 Ma for Awaji Island, 82–74 Ma for the Arima area, and 68–62 Ma for the Izushi–Kasumi areas, indicating a younging in the magmatic activity from south to north. The volcanic activity preceded the plutonic activity in all of the study areas.