This article includes the following topics : 1. Introduction. 2. Relation between the Chichibu and Mongolian Geosynclines. 3. The Yangtze Basin in Central and South China. 4. Southeast Asia. 5. Eastern Australia. 6. Biogeography of Eastern Asia and the Western Pacific Areas. 7. Southern, Western and Northern Parts of Asia. 8. Arctic, Eastern Pacific and Andine Areas. 9. Silurian Biogeography in view point of Trilobita. 10. Recent References. The faunal analysis of trilobites is carried out on the levels of genus and family. As result, the Arctic region, Mongolian, Chichibu, Tethyan and the Burma-Thai-Malaysian geosynclines, the Yangtze basin and Australian, Arctic, western North American and South American regions are distinguished. Endemic genera of these regions are listed. The Silurian trilobites of Eastern Asia clarified that the Oriental Meterogen which consists of the Koreo-Chinese land, Yangtze basin and Indosinian Island was embraced by the Mongolian, Chichibu and Tethyan geosynclines from the Pacific side.
Several Holocene former shorelines are observable in the southern part of the Boso Peninsula, southern Kanto, central Japan. They are considered to have emerged by co-seismic uplifts, and their height distribution must indicate the accumulated amount of seismic vertical crustal movements of 1703 (Genroku) and 1923 (Taisho) types. In this study, the mean recurrence time of the 1923 type earthquake is estimated on the basis of the most fitted combination of the two type movements to the height distribution of the N-surface shoreline, i.e. the raised shoreline formed at the culmination stage of the sea level in the middle Holocene (ca. 6, 200 years BP). The data of 36 localities (Fig. 2) on HN, HG and hT (Table 1) has been used to find the most fitted combination of the 1703 and 1923 type movements, where HN is the height of the N-surface shoreline, HG is the height of the Genroku shoreline i.e. the raised shoreline which emerged in 1703 coseismically, and hT is the geodetically measured co-seismic uplift amount at the 1923 earthquake. The relationship between the three variables are as follows : HN=2.8HG+2.6hT+5.8 The high value of the multiple regression coefficient of 0.911 of the equation indicates that the main Holocene crustal movements in the southern part of the Boso Peninsula have been the 1703 and 1923 type seismic crustal movements undoubtedly. The equation also shows that the sum of the sea level drop amount and the place-independent uplift amount afer the emergence of the N-surface shoreline is approximately six meters. Apart from the two types of the seismic crustal movements, fault displacement is likely to have been playing a certain role for the Holocene crustal movement. Two possible models, models A and B, of the seismic vertical crustal movement has been adopted in this study. Model A is the case that the 1703 and 1923 type seismic crustal movements occur independently (Fig. la). Model B is the case that only an event of several events is of 1703 type and the other events are of 1923 type (Fig. 1b). It is known that the mean recurrence time of the 1703 type earthquake has been around 2, 000 years during the past 6, 200 years. Observed value of mean annual uplift amount for the recent 32 years at the Mera Tide Observatory (Loc. 19) has been -0.0019 meters. Based on these data, the mean recurrence time of the 1923 type earthquake has been calculated to meet the above-mentioned regression equation. The resultant values are 890 years in the case of model A and 610 years in the case of model B. The interseismic recovery ratios have been also calculated. The recovery ratio of the 1703 type movement (dG) is 0.44 in both cases of model A and B, and that of the 1923 type movement (dT) is 0.37 in the case of model A and 0.39 in the case of model B. The result of model B is presumably more harmonious with the geomorphologically deduced Holocene shoreline shift history. It is likely that the data have included certain errors. The calculation has been based on very simple models. Moreover, some unconfirmed assumptions, such as the 1703 and 1923 events are the typical representatives of the 1703 and 1923 type earthquakes, respectively, have been used for the calculation. Therefore discussion in detail is not so meaningful. In this study, it can be concluded that the mean recurrence time of the 1923 type earthquake has been estimated as several hundred years to one thousand and several hundred years.
The Kikai caldera volcano located under water in East China Sea is one of the most gigantic calderas in southern Kyushu. At the caldera, a violent eruption occurred from the submarine vent, at ca. 70-80 ka. The eruption is interpreted to have been phreatomagmatic throughout. Each eruptive phase of the eruption sequence generated its own characteristic deposits. The sequence of the events can be summarized as fallows ; (1) a small phreatomagmatic eruption, which generated the fine grained ash including accretionary lapilli, (2) the catastrophic pyroclastic-flow eruption, which formed a large-scale pyroclastic flow (the Nagase pyroclastic flow), two pyroclastic surges (Nishinoomote-1 member : Ns-1, Nishinoomote-3 member : Ns-3), and a wide-spread co-ignimbrite ash fall (Nishinoomote-2 member : Ns-2). The Nagase pyroclastic flow came down from the rim of the caldera, and entered the sea. Then, the flow body, which included a large amount of large pumice blocks and heavy lithic fragments, was disintegrated as gas-particle flow by violent phreatomagmatic explosions, or continued subaqueously as water-supported mass flow. Dilute and fine-particle-rich pyroclastic surges, probably with a density much less than that of water, 1.0 g/cm3, generated off the top or head of subaerial Nagase pyroclastic flow. They could cross on the smooth surface of the sea, becoming water-cooled, vaporish and depleted in large clasts which dropped into the sea. Eventually, the cool and wet pyroclastic surges attacked the islands around the caldera, and deposited as Ns-1 and Ns-3. Ns-2 co-ignimbrite ash fall, composing of glass shards were generated from the upper convective part of the eruption column of the Nagase pyroclastic flow. Included accretionary lapilli indicate that the eruption column was very moisture because of much sea water flash-out subaerially for very violent explosions from the submarine vent. Ns-2 is probably correlated with the Kikai-Tozurahara ash which was found in central Japan more than 500 km off the source.
Neogene volcanogenic sedimentary rocks such as tuffaceous silt stone or silt stone in which fine grained pyrite (probably of biogenic) is commonly observed are easily reacted with water solution (distilled water, NaCl-bearing water, SrCl2 ·6H2O-, CsCl-, Co (OH) 2-, Sr (OH) 2·8H2O- and Co (OH) 2- bearing waters) to form gypsum, celestite, kieserite, bieberite, holotrichite, moorhousite, thenardite, mirabilite and other kinds of sulphate, carbonate and chloride minerals. This interactions between rocks and water solutions should be deeply considered when we are going to keep the so-called Low Lovel Radioactive Waste at relatively shallower part of the earth, because radioactive clement-bearing minerals formed at the earth surface of repositories by the interaction between radioactive waste and groundwater and evaporation would be easily entered into ECOCYCLE even if the repository areas are tightly encircled by the fence made of barbed wire.
Experimental studies have been conducted on the vaporization of silica, forsterite and enstatite at pressures between 10-10 and 10-4 bar and at temperatures between 1350° and 1870°C. The results indicate that silica and forsterite vaporize congruently, whereas enstatite vaporizes incongruently to forsterite and silica-rich vapor. The ' triple point ' where solid, liquid and vapor coexist together lies at about 5×10-6 bar-1600°C, 10-5 bar-1700°C, and 2 × 10-6 bar-1500× for silica, forsterite and enstatite, respectively. These 'triple points' shift to higher pressures with increasing hydrogen in the vapor phase. In the case of enstatite, the, triple point ' lies at about 2×10-2 bar and 1550°C when the H2/MgSiO3 ratio is 104 which is considered to be close to that of the primitive solar nebula. It is suggested that liquid was not stable in most part of the primitive solar nebula and that chondrule melts were not the products of direct condensation of gas. It is most probable that such melts were produced by metastable melting of pre-existing minerals such as olivine and pyroxene. Fractional condensation of the nebular gas would have produced locally silica-enriched residual gas because of the existence of the reaction relation of forsterite and gas to form enstatite. This process is somewhat similar to the fractional crystallization of basaltic magma to produce silica-rich residual liquids. The fractionation would, however, be more efficient in the fractional condensation of gas than in the fractional crystallization of magma.
After a brief retrospect on the developement since middle 1950's of studies on metasomatic process, the paper deals with some recent results of experiments aimed to observe the mechanism of propagation of the metasomatic material tranfer in silicates. It is shown that “relict” minerals often participate in the metasomatic reaction. The situation was demonstrated in natural pyroxene skarn transforming into garnet skarn, by a iteration experiments of alkali feldspars and of rhyolitic rock. It is pointed out that the glass phase in rhyolite remained as glass at experimental temperatures as low as 200°300°C and change its composition by Na-K exchange reaction with aqueous solution. Another experimets showed that the metasomatic reaction propagate to the interior of the crystal through the infiltration of the fluide through cleavage and dislocation lines. The observed reaction rate is about 1000 times greater than that estimated according to a model in which the exotic element is fixed on the surface layer by ion exchange and then by solid state diffusion in the crystal.