Repeated eruptions of calc-alkaline magmas in recent 250000 years gave rise to the main body of the Adatara volcano. Geological and stratigraphical reexamination distinguished 37 eruptives. Based on temporal and spatial association, the eruptives were grouped into 7 volcanic units: eastern side first and second units (ES1, ES2); Minowasan unit (MI); summit area unit (SU); northern and southern rims of Numanotaira units (NN, SN); Numajiri unit (NU). Chronological data revealed that the ES1 and MI were developed 0.25-0.20 Ma, the SU was formed around 0.12 Ma, and that probably NN and SN were built up less than 0.1 Ma.
     Bulk chemically, 3 groups were distinguishable; group 1 (ES1, ES2) ejecta are rich in TiO₂ FeO^* Sc, V and Co, poor in MgO, K₂O, Rb, Ba and Zr compared with group 3 (NN, SN, NU), and the group 3 has higher Rb/Ba, Zr/Nb and Rb/Zr than those of group 1. The group 2 (MI) shows similar Rb/Ba, Nb/Zr and Rb/Zr to those of the group1, but displays distinctive trends for Sr, Nb, Sc and V.
     Among the three essential materials (pumice and scoria 1 of the earlier eruptives and scoria 2 of the later member) in the AT2 erupted at 0.12 Ma (SU), the scoria 1 compositionally corresponds to the primitive members of the group 1, and the compositions of scoria 2 come close to the low SiO₂ extension of the trends for the group 3. Further, the correlations accord with their relevant chemical characteristics such as Rb/Ba, Nb/Zr and Rb/Zr, and also compatible element trends.
     The inferred transition of the magma plumbing system is as follows: Two magma systems (groups 1 and 2) had been active about 0.25 to 0.2 Ma. During 80000 years of dormancy, relatively primitive magma had been preserved only in the main system (group 1). Around 0.12 Ma, the third magma system (group 3) came underneath the main system. One felsic and two andesitic magma bodies co-existed at the beginning of the eruption at 0.12Ma, but the andesitic magma of the group 1 exhausted halfway of the eruption, and was completely replaced by the third system. The renewed system has been preserved and active after the eruption of 0.12 Ma to build up SN and NN.

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Acid alteration in the western Izu Peninsula, Shizuoka Prefecture, is distributed widely within Miocene and Pliocene formations, and overlain by Quaternary volcanoes. For the purpose of understanding its origins, we examined the acid alteration and the property of alunite from several locations throughout the district.
     The acid alteration zone consists of acid-leached andesite, vuggy silica and massively silicified rocks, surrounded by advanced and intermediate argillic alterations. They are underlain by district-wide propylitic alteration. The advanced argillic alteration is characterized by an assemblage of pyrophyllite, diaspore and alunite. The alunite has cores rich in Sr and PO₄. Oscillatory zoning of K, Na and Ca in alunite, natroalunite and minamiite is found. δ³⁴S values are +18 to +26 per-mil. The oscillatory zoning is ascribed to the variation in the composition of hydrothermal fluid precipitating the alunite crystals, whereas the increased trend in SO₄/PO₄ from core to margin reflects the chemical evolution of hydrothermal fluid. The mineral assemblage and isotopic data suggest that the acid alteration in Ugusu district was formed from higher temperature fluid, which contained reactive magmatic components, while the acid alteration in Shotsubotoge-Nishina district was formed from lower temperature fluid.

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Ba-rich tweddillite were found from the Kamisugai mine in Sambagawa metamorphic belt, which is embedded in piemontite schist, showing green-schist facies metamorphism. These minerals occur as veinlets or aggregates of fine needle crystals in albite veins cutting braunite-hollandite-piemontite ore, associated with okhotskite and calcite. This mineral is purplish red in color, prismatic crystal up to 1mm in length, reddish brown to yellowish brown in pleochroism and show anomalous interference in thin section. This mineral is strongly zoned with cores richer in Ba than the rims. EPMA analysis for tweddillite with highest Ba content gave the empirical formula : Ca_1.02(Sr_0.63Ba_0.41)_Σ1.04(Mn³⁺_1.67Fe³⁺_0.75Al_0.58)_Σ3.00Si_2.98O_12.5 on the basis of 12.5 oxygens (O₁₂(OH)). Ba cation occupy up to 40% of A2 site and Mn³⁺ + Fe³⁺ / Mn³⁺ + Fe³⁺ + Al value attains up to 81% of M sites. Cell dimensions of Ba-rich tweddillite are a = 8.96(1), b = 5.714(2), c = 10.34(2)Å, β = 114.9(1)°, V = 480(1) ų. These minerals were formed at the low temperature condition during the retrograde Sambagawa metamorphism.

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