Geochemical examination has been carried out for the slags obtained in the Yodhawewa area, Mantai district, northwestern Sri Lanka. Mantai was well-prospered port town trading across the Indian sea from protohistoric time. There occur numerous slags in the Yodhawewa archaeological sites, of which bulk iron contents show variation from 1.42 to 20.59 wt%. Slags of relatively lower iron contents, less than 10 wt% show luster and are transparent revealed from observation of thin section. The colors of these samples are highly variable range from light green to dark gray, some with hues of red. Some glassy slags have flow texture. Noteworthy is an occurrence of olivine in the slags with higher contents of iron. Olivine crystals show various morphologies, namely, almost euhedral (0.5–1.0 mm in size), fletching and acicular, which might be related to cooling mode. Electron probe microanalysis of olivine demonstrates that they are fayalite in composition. Fayalite in the slags is associated with glass, leucite and wstite. The phase equilibrium examination of olivine and glass contained in the crystal evidence that crystallization temperature of olivine was estimated to be over 1100°C. Leucite forms fine-scale intergrowth with fayalite, suggesting its crystallization at the fayalite-leucite eutectic temperature of ~1128°C. Present result would be the first report to estimate smelting temperature of ancients handling considerably hot firing in the furnace.

The upper Cenozoic sedimentary basin of the northern Fossa Magna was generated during 16.5-15.5 Ma with the eruption of submarine volcanics > 5 km thick, converting a previous land area to a bathyal basin. The eruption of the thick volcanics suggests the existence of an extraordinal thick partial melting zone in the lower crust to upper mantle at that time. In such a setting it is speculated that the gravity loading by overburden squeezed out and upwelled a large amount of magma from the partial melting zone. The upper crust thus seems to have subsided in compensation for the volume loss of the magma extraction in depths and to have generated the sedimentary basin on the surface.

abstraThe early to Middle Miocene Uchimura Formation, which consists of normal marine sedimentary members and volcanic sedimentary members, is widely distributed in the Takeshi Mountains of the northern Fossa Magna region, In an early stage of the northern Fossa magna, these clastic sediments has accumulated in the Uchimura Basin with a large-scale interfingering relationship. Normal clastic sediments has mainly supplied from the south to southwest basement area, On the other hand, volcanic materials has supplied from the Uchimura submarine volcano which actively erupted in the basin. The Uchimura Formation is important implications as one of the structural and historical processes associated with the formation of the Fossa Magna. ct

The uppermost part of the Neogene sequences in the Chichibu Basin, called the Chichibumachi and Yokozemachi Groups, are distributed in the southeastern corner of the basin, in contact with the basement rocks of the Sanbagawa metamorphic and the northern Chichibu belts. The compositions of sandstones and conglomerates of the groups, as well as the occurrence of derived fossils of the Cretaceous age, indicate the existence of the lost Cretaceous system of the Sanchu Graben that supplied a large number of clasts to the southeast side of the Chichibu Basin during the deposition of the two groups.

The Nagano Basin is one of the Quaternary Inland Sedimentary Basins in the northern part of the Fossa Magna region. It is approximately 40 km long and 10 km short in the northeast-southwest direction. A group of reverse faults called the West Nagano Basin Fault Zone (WNBF) cause subsidence of the basin and uplift of the mountains to the west. The Chikuma River, together with the Saigawa River and other rivers, supplied large amounts of clastic sediments to the Nagano Basin and formed fans and lowlands consisting of natural levee and backmarsh. In this study, the distribution and stratigraphy of the Flood-plain deposit were clarified based on about 1,900 newly collected boring data throughout the Nagano Basin. The backmarsh deposits consist of the clay layer I and II and organic soil layers, and the natural levee deposits consist of the sand layer I and II . Of these, the clay layer I with N value of 4 or less and the sand layer I with N value of 10 or less were classified as soft ground. The clay layer I is distributed mainly in the western part of the Nagano Basin and the Entoku lowland, while the sand layer I is distributed mainly in the Chikuma and Okada River basins. This study found that the distribution of damages caused by the Zenkoji Earthquake and the subsequent two earthquakes of magnitude of about 6 in the Nagano Basin overlapped with the distribution of soft ground.

Major and trace elements analysis and rare earth elements (REE) analysis were conducted on tuffites from the Wakino Subgroup, Kanmon Group in the eastern part of northern Kyushu, and from the Jinju Formation, Sindong Group, Gyeongsang Supergroup in the southeastern part of Korean Peninsula. Tuffite samples from the Wakino Subgroup in the Murasaki and Kuro Rivers area indicate lower Cr, Nb, Ni, Th and Zr contents, higher Sr contents and some higher V contents than that of Mt.Uibon-san area in the Korean Peninsula. Tuffites show the patterns rich in light REE, poor and flat in heavy REE. Altough tuffites from the Yakiyama River area show positive and negative Eu anomaly, tuffites from the Murasaki and Kuro Rivers area and Mt. Uibon-san area show negative Eu anomaly. We proposed four discrimination triangle diagrams: Cr-V-Rb diagram, Sr-V-10Th diagram, Ga-Th-Pb diagram, 10Ni-10Th-Sr diagram, and discrimination total REE variation diagram for source region of tuffite. Stone tools from the Kifune Shrine are plotted in the Wakino Subgroup field in those discrimination diagrams.

A characteristic pyroclastic dyke consisting of tuff and tuffite was found at south of Lake Biwa, central Japan. It intrudes into the Jurassic sedimentary rocks of the Tamba Belt along the Sagami River, Otsu City, Shiga Prefecture. The dyke is considered to be one of pyroclastic dykes at the latest stage of Late Cretaceous igneous activities forming the Biwako cauldron. The occurrence and lithology of the dyke are reported.