The Muro pyroclastic flow deposit (MPFD), distributed in the central part of the Kii peninsula southwest Japan, is composed of rhyolitic welded tuff, representing a single cooling unit. Though the MPFD is a remarkable gigantic igneous unit with the volume of ∼100 km3, its source region is still in dispute. To discuss the problem, bulk rock chemical composition of MPFD were determined by XRF and LA-ICP-MS. The samples used in this study scarcely contain exotic materials. The MPFD welded tuffs indicate rhyolitic compositions with SiO2=74.0-75.5 wt%. They are characterized by LREE enrichments, large Eu negative anomalies (Eu/Eu*=0.30-0.59), and relatively constant chondrite-normalized middle to heavy REE abundances. All the analyzed samples have mole Al2O3/(CaO+Na2O+K2O) ratio higher than 1.1. Garnet is ubiquitously included, and some samples contain cordierite. Some of the rhyolitic rocks in the middle Miocene Setouchi Volcanic Rocks, as found in the lowest horizon of the Nijo Group for example, also have peraluminous bulk rock compositions. However, they are discriminated from MPFD by whole rock chemical compositions, in particular depletion in HREE. Actually, major and trace element compositions of MPFD are very close to those of the middle Miocene S-type granitoids in the Outer Zone of southwest Japan. These facts strongly suggest that MPFD was derived from an S-type felsic igneous body in the Outer Zone, travelling more than 20 km.
K-Ar ages of six hornblendes and two biotites were determined for the igneous rocks in the area around Senmaya and Kesennuma, southern Kitakami Mountains. The Niitsuki Formation, mainly composed of andesitic-basaltic volcanic rocks, is exposed in the eastern part. The Orikabe Plutonic Complex, characterized by quartz monzodiorite and granodiorite, intrudes into the Niitsuki Formation, and is intruded by porphyrite dike swarms in the northern part. The Senmaya Tonalitic Pluton, mainly composed of homogeneous tonalite, is widely exposed in the western part. Hornblende ages from andesitic fragments of the Niitsuki Formation, a granodiorite of the Orikabe Plutonic Complex, and a hornblende porphyrite dike are 121, 120 and 107 Ma, respectively. Hornblende and biotite ages for the Senmaya Tonalitic Pluton range from 105 to 108 Ma and from 109 to 112 Ma, respectively. The hornblende ages for the Niitsuki Formation and the Orikabe Plutonic Complex imply their close relationship, and they are typical K-Ar ages for Cretaceous volcanic and plutonic rocks in the Kitakami Mountains. On the other hand, the hornblende and biotite ages for the Senmaya Tonalitic Pluton and porphyrite dikes are the youngest among the plutonic rocks in the Kitakami Mountains, indicating they are the products of the later igneous activity. The obtained K-Ar ages in this area imply a shift of plutonic activity to the western continental side after the main plutonism in the Kitakami Mountains in the Early Cretaceous.
Some kinds of colored pigments are used for painting of figures and geometric patterns on the decorated chamber walls of mounded tombs in Kyushu. Green pigment collected from four tombs in Fukuoka Prefecture, some of which has been considered as glauconite, was examined by a Gandolfi camera, and newly identified as celadonite. The source of this mineral for the pigment should be pursued hereafter. The present study has made clear that this type of experimental approach will be effectively applied to the archaeological research of the pigments.