The Pyroclastic Flows in the Goino Area, Kagoshima City, Kyushu, Japan

Abstract

The three pyroclastic flow deposits are exposed in the Goino area, southern part of Kagoshima City, South Kyushu. They are, in order of superposition, the Goino pyroclastic flow, the Ata pyroclastic flow, and the “Shirasu”. The stratigraphic relation between the former two pyroclastic flows is not clarified by the field survey. It is, however, concluded that the Goino pyroclastic flow is older than the Ata pyroclastic flow because the zircon from the Ata pyroclastic flow is colorless in mass color indicating the middle Pleistocene to the Recent, while that from the Goino pyroclastic flow is dull rose-pink indicating the early to middle Pliocene. The peterographic characters of these three pyroclastic flows are as shown in Table I. The Ata pyroclastic flow in this area is variable in lithological features, but the optical constants for the constituent minerals coincide exactly with those of the flow exposed in the Osumi Peninsula and Makurazaki areas. Throughout the flow deposit, are enclosed many granitic xenoliths derived from the South-Osumi granodiorite. It is consistent with the conclusion that the Ata pyroclastic flow magma is intimately related to the South-Osumi granodiorite constructing the basement of the Ata caldera in chemical composition (S. Taneda et al., 1966). The “Shirasu” exposed in this area, is red to greyish pink in color, about 20 meters in thickness, not consolidated and not welded. It is a primary pyroclastic flow deposit from the Aira caldera volcano in the latest Pleistocene.