The Cretaceous granitic rocks, the Kitazaki Tonalite and Shikanoshima Granodiorite, and veneer Oligocene sedimentary rocks, the Tsuyazaki Formation, are distributed in the Watari Peninsula, Fukuoka Prefecture. There are mineral veins composed by calcite and zeolites in those rocks. Rb-Sr, and fission track geochronological analyses were carried out for granitic rocks, in order to determine the cooling process of granitic rocks and timing of hydrothermal activity. Biotite and felsic fraction separated from the Kitazaki Tonalite and Shikanoshima Granodiorite give Rb-Sr isochron age of 108.6 ± 2.5 Ma and 107.0 ± 0.7 Ma, respectively. Fission track ages from the Kitazaki Tonalite are 97 Ma (titanite), 89-88 Ma (zircon), 14 Ma (apatite). Fission track ages from the Shikanoshima Granodiorite are 95 Ma (titanite), 87-84 Ma (zircon), 15 Ma (apatite). Fission track ages of apatite from granitic rocks are younger than the Tsuyazaki Formation, which suggests a thermal event at about 15 Ma to reset the fission track apatite age. The homogenization temperature of fluid inclusions in calcite are 89-111 °C (Kitazaki Tonalite), 95-118 °C (Shikanoshima Granodiorite) and 85-91 °C (Tsuyazaki Formation). Sr isotopic compositions of calcite and zeolites in granitic rocks and Tsuyazaki Formation are overlap with one another. These data suggest that vein minerals in granitic rocks and zeolites and calcite in the IC Member of the Tsuyazaki Formation were formed by a series of hydrothermal activity at about 15 Ma.
The dusty blue jadeitites from the Kotaki River, Niigata Prefecture, Japan have been analyzed by transmission electron microscopy (TEM) and electron probe microanalyzer (EPMA). The dendritic texture which is made up of omphacite and concentrates minor element such as diopside and acmite components, is found in blue area. The dendritic texture has subgrain boundaries and cell structures where dislocations are tangled up. The concentration of trace elements and the existence of many dislocations in dendritic texture indicate that omphacites are formed by the Cottrell atmosphere.
Study of rock texture will surely make a breakthrough in the elucidation of the evolution process of planets. This report presents two examples showing methodologies for the study of rock texture in planetary materials. The first example is the study of pallasites. Rounded texture of olivine grains was reproduced through annealing experiments and rounding kinetics was characterized. The result shows that small scale rounding of olivine in pallasites such as Eagle Station requires a rapid cooling after olivine-metal mixing. The second example is the study of polymict eucrites. The results from detailed observation of their texture show the individual origin of pyroxene fragments and suggest that the polymict breccias were generated by gathering locally ordinary eucrites and cumulate eucrites. In future planetary exploration, observation of rock texture will serve as indispensable technology.