We examined time and spatial distributions of sedimentary facies surrounding the spit sediments in the bay-mouth portion of the Paleo-Okutokyo Bay by using sedimentary facies and radiocarbon dates obtained from two sediment cores (MZ and SZ cores) from the eastern margin of the Tokyo Lowland. Latest Pleistocene to Holocene incised-valley fills (the Chuseki-so) which unconformably overlie Middle to Late Pleistocene deposits Shimosa Group) consist of braided river, meandering river, estuary, spit and delta sediments in MZ core in ascending order. The Chuseki-so consists of delta sediments in SZ core. MZ and SZ cores yields radiocarbon dates ranging from 13150 to 3160 cal BP and from 3930 to 730 cal BP, respectively. Sand shoal sediments constituting part of the spit sediments in MZ core forms a sand body which elongates northeastward from the spit sediments. nd this sand body seems to have deposited in a bay-mouth channel which existed behind the spit between 4500 nd 3500 cal BP.
Late Cretaceous granitoids of central area in the Abukuma terrain were analyzed by polarized XRF method and compared with the Ryoke granitoids of Chubu district. The Abukuma granitoids are mostly composed of hornblende and/or biotite granodiorite to granite and less in amount of muscovite-biotite granites, and are higher in Na2O and Al2O3, lower in K2O, Rb, Pb and Ba than the Ryoke granitoids on the Harker diagrams. The Abukuma granitoids appear to be generated within the continental crust of inmatured island-arcs, having mafic magmas and heat from the upper mantle. The Abukuma granitoids are generally reduced type accepting sedimentary carbon from the continental crust, similarly to the Ryoke granitoids, but an intermediate series occurs in the eastern-end zone. Zone II granitoids, which are rich in CaO and poor in K2O and lithophile components such as Rb, Pb, Y, Ce and La, have weak signature of high Sr/Y ratio for adakite. An adakitic magma may have brought up from the subducting slab, but extremely modified within the continental crust.
High susceptibility bands of about a few meters were shown at contact zones between ilmeniteseries granite and andesite of Miocene volcanic conduits in northern part of Ehime Prefecture, southwest Japan. A profile of susceptibilities across the Senohana volcanic conduit in Nakajima, Matsuyama City clearly shows high susceptibility bands. Thirty-nine andesite and contacted granite samples were obtained from 11 sites of the Miocene volcanic conduits. Susceptibility, natural remnant magnetization and density were measured of 42 samples. Thermomagnetic and hysteresis measurements were carried out 15 samples of them. Natural remanent magnetization and susceptibility of marginal parts of volcanic conduits tend to be stronger than those of the inner part. Hysteresis parameters suggest that magnetites of marginal parts are smaller than those of inner parts. The granite in contact with andesites exceptionally had high susceptibility and natural remnant magnetization, although ilmenite-series granite had quite low susceptibility and natural remanent magnetization. A lot of fine magnetites were recognized in the granite in contact with andesite by microscope observation. They seem to be formed from biotites in the granite by contact metamorphism with intrusion of volcanic conduits.
Fission track dating was performed for the Murasho granite porphyry in the Outer Zone of Kyushu, Southwest Japan. A zircon fission track age was determined to be 14.3 ± 0.5Ma(1σ). This result is similar to those reported for the zircon fission track ages of the felsic rocks of Outer Zone of Kyushu.
Kogajajima, composed of hornblende andesite and dacite lavas, is a small volcanic island 0.5 by 1 km in diameter and is at the summit of a seamount 5 by 10 km in diameter and more than 800 m high. The eastern half of the island is hydrothermally altered. Several active fumalores and hot springs were recognized in our survey in 2005 and 2006. In addition to the young K-Ar age suggesting late Pleistocene in age, the fumarolic activities implies that the volcano is still active in recent years.