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Abstract: The Shirakawa ignimbrites were generated by caldera-forming eruptions in the Aizu caldera cluster, northeast Japan, during the Early Pleistocene. They have a total volume of >300km3 dense rock equivalent and consist of the Kumado ignimbrite (1.4Ma) from Ono caldera, the Ashino ignimbrite (1.3Ma) and the Nagurasawa ignimbrite (1.2Ma) from Tonohetsuri caldera, the Nishigo ignimbrite (1.1Ma) from Narioka caldera and the Ten-ei ignimbrite (1.0Ma) from an unknown, concealed caldera. These calderas overlap each other within a 20×20km area in the eastern part of the cluster. The Shirakawa ignimbrites are relatively small in the eruption rate and have sufficient interval times that are longer than the residence times for their magma volume. The individual ignimbrites are composed of 20–40% phenocrysts set in high-silica rhyolite glass and they lack vertical chemical zoning. The SiO2 content of the Kumado, Ashino, Nagurasawa, Nishigo and Ten-ei ignimbrites are 68–70wt.%, 67–70wt.%, 68–69wt.%, 72–74wt.% and 69–70wt.%, respectively. They plot within the medium-K field, but show distinct trends for most major elements at the same SiO2 ranges. Although they all have similar arc-related trace-elements patterns with Nb, Ta and Ti negative anomalies, high LREEs and flat HREEs, they differ in their Zr/Nb, Ba/Th and K/La ratios. Also, isotopic ratios of these pumices from each unit are distinct; 87Sr/86Sr varies from 0.7044 to 0.7047 and 143Nd/144Nd from 0.51271 to 0.51278. These results imply that the ignimbrite sources were renewed with every caldera-forming eruption. Seismic tomography and pre-eruption uplifting of the caldera cluster suggest that a substantial amount of mantle-derived magma was stored within the lower crust and contributed to the evolution of a crustal hot zone. Observed geochemical features also suggest that silicic magmas were generated by the melting of variably assimilated mafic intrusions. To explain the renewal of the Shirakawa magma system, melted materials must have been completely evacuated from a deep-seated source zone by each caldera-forming eruption and different mafic rocks subsequently subsided into the hot zone as raw materials for the next eruption. [Copyright &y& Elsevier]

The author explores the blunders in negotiation of Japan with North Korean government following its abduction of Japanese citizens. He believes that the massive public relations strategy of Japanese government toward its citizens has affected the negotiation process and eventually backfired on the government. He notes that the abductions from Japan by agents of North Korean government happened from 1977 to 1983. He highlights that resolution of the abduction issue was an implausible precondition for the normalization of diplomatic relations.

Abstract: Flare-up of silicic volcanism has occurred in the back arc of NE Japan arc since 0.3 Ma; Sunagohara, Numazawa, Kinunuma, Hiuchigatake and Iiji volcanoes have all grown during this time interval. Although arc front volcanism has continued during the Quaternary period, back-arc volcanism varies in space and time. All ejecta of the back-arc volcanoes are medium-K calc-alkaline rhyolite to dacite in composition and 1 to 10 DRE km3 in volume. The Sr and Nd isotopic ratios of the ejecta vary widely among the individual volcanoes and suggest the origin of the felsic magmas may be generated by anatexis of mafic igneous rocks of the lower crust. Temporal variation in geochemistry of the 5 km3 Numazawa ejecta shows more details of the anatexis. Numazawa volcano erupted the Shibahara pyroclastics at 110 ka, the Mukuresawa lava at 70 ka, the Mizunuma pyroclastics at 45 ka, the Sozan lava at 40 ka, the Maeyama lava at 20 ka, and the Numazawako pyroclastics at 4.6 ka. The time-accumulated volume diagram of Numazawa volcano shows the increase of magma eruption rate through time. All elements of the Numazawa rhyolite to dacite define time-controlled, discontinuous linear trends. SiO2, K2O, Na2O, Rb, Y, Ba, and Nb decrease with the ascending eruption units, whereas MgO, Fe2O3, CaO, Al2O3, TiO2, Sr and V increase. SiO2 contents are variable from 72% in Nm–MK at 71 ka to 66% in Nm–NK at 4.6 ka. The rhyolite to dacite of the Numazawa ejecta are homogeneous with respect to the isotopic ratios. I show that the temporal linear trends for the bulk compositions of the Numazawa rhyolite to dacite are most plausibly caused by increase of batch partial melting at constant bulk distribution coefficient. The calculated patterns of trace-element abundances show that partial melting of high-alumina basaltic igneous rocks in the lower crust can generate the Numazawa rhyolite to dacite. In this case, the degree of partial melting varies from about 20% at 71 ka to about 60% at 20 ka and 4.6 ka. It is plausible that repeated intrusions of mantle-derived melts have gradually increased the ambient temperature of the cooled lower crust since 110 ka. The time-controlled systematic variation in bulk chemical compositions of Numazawa volcano suggests that the systematic felsic to intermediate compositional evolution is not due to shallow level processes but due to eruption of magmas generated in the lower crust with little upper crustal evolution. [Copyright &y& Elsevier]

River incision into bedrock results in the decrease of burial depths, which can be of critical importance, for example, in the safe long-term storage of high-level radioactive waste. For the long-term prediction of river erosion, it is essential to know the rate of incision during the Late Quaternary period. In the Abukuma Mountains on the forearc side of northeast Japan, a low-relief peneplain that was uplifted in the Pliocene period is widely developed. Degradational fluvial terraces that are discontinuously distributed along draining rivers are scattered in the study area. The fluvial sediments were mainly transported from the summit regions as debris flows or hyperconcentrated flows. The terrace deposits are capped by a series of eolian veneers containing key tephra beds. From the oldest to the youngest, these tephra beds are the 150–125 ka Iizuna–Kamitaru tephra, the 135–125 ka Hiuchigatake–Tagashira tephra, the 120 ka Adatara–Dake tephra, the 70–80 ka Bandai–Hayama-2 tephra, the 45 ka Numazawa–Mizunuma tephra and the 42 ka Bandai–Hayama-1 tephra. Using tephrochronological data, the terraces are divided into three groups: higher, middle and lower. The ages of formation of the higher, middle and lower terraces are estimated to be within marine isotope stage (MIS) 6, MIS 5.4–5.2 and MIS 3 to MIS 2, respectively. The incision rate, calculated from the relative height between the terrace surface and present-day valley floor fill, is 1.5–0.8 m/10 000 years in the elevations from 350 to 700 m. The calculated rate does not show significant differences between the higher, middle and lower terraces. All the relative heights decrease with increasing elevation, because the erosional rates of streams in the upper reaches are lower than those in downstream reaches where the discharge rates are higher. This value can be regarded as an estimate of the rate of incision in granitic mountains where there is no volcanic or distinct tectonic activity. [ABSTRACT FROM AUTHOR]