In the Kabato district, central Hokkaido, the Aoyama Basalt which represents a volcanic on-land product of the early phase of Cenozoic magmatism, is locally exposed. The basaltic lava flows unconformably cover the Eocene Kabato Formation and are overlain by the Middle Miocene Ponsubetsu Formation showing an angular unconformable relationship. The Aoyama Basalt consisting of basalt and basaltic andesite belongs to the tholeiitic rock series. The patterns of MORB-normalized incompatible elements show that the Aoyama Basalt is enriched not only in LIL elements but also relatively in HFS elements, being similar to those of some island arc tholeiites from NE Japan Arc and active continental margin rocks. The abundance of the incompatible elements is higher than the island arc tholeiites. The Aoyama Basalt has higher ⁸⁷Sr/ ⁸⁶Sr and lower ¹⁴³Nd/ ¹⁴⁴Nd ratios, which are distinguishable from the Pliocene volcanic rocks in the same region. In comparison with the NE Japan Arc magma and the Pliocene magma in the same region, the source mantle and the relationship to the spreading of the Japan Sea basin were disscussed.

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The late Pleistocene air fall pyroclastics, distributed around Ontake volcano, are composed of rhyolitic to andesitic pumice and scoria. The air fall pyroclastic deposits are divided into three formations: the Osakada Loam (OLF), the Lower Hata Loam (LHF), and the Upper Hata Loam (UHF) Formations, in ascending order on the basis of obvious unconformity and/or intercalation of paleosoil. These observations show a repose of volcanic activity between the Formations. Members, divided by weathering surfaces, are OLF I, OLF II, LHF I, LHF II, UHF I, UHF II, and UHF III, in ascending order. The degree of weathering, which is somewhat weaker than that of the paleosoil between the Formations, will imply a 'short repose' of volcanic activity. The OLF contains 9 beds of pumice fall erupted from Ontake volcano. The main phenocrysts associated with salic pumice (Pm-1 A, -1 B, --2 A) are of plagioclase (An 50-40), biotite, hornblende, orthopyroxene (En 60-45), magnetite (Tc=430-450℃: Curie Temp.), ilmenite, and rare apatite and zircon. The dacite pumice (Pm-2 B, -3 A, 3 B, -3 C, -3 D) are composed of the minerals plagioclase (An 55-45), hypersthene (En 68-65), augite (En 41 Fs 15 Wo 44), magnetite(Tc:=400℃), ilmenite, hornblende, apatite, and zircon. The mineral assemblage and the chemical compositions of the minerals systematically change from aci dic to rather basic following to the order of eruptions : from Pm-1 A to -2 B and -3 C to 3 D, respectively. An abrupt increase of magma temperature and compositional change from acidic to basic may take place between Pm-2 B and -3 A. Ol-bearing and Ol-free andesitic scoria are the prevailing component of the LHF and the UHF. The Ol-free scoria contains plagioclase, hypersthene (En 73-68), augite (En 40-45 Fs 12-21, Wo 39-48), and magnetite (Tc=220-270℃) as phenocrystic minerals. Plagioclase, olivine (Fo 75-70), augite (En 40-45 Fs 12-21 Wo 48-39), orthopyroxene (En 76-70'En65-60), and magnetite (Tc=180-290℃), are of constituent phenocrystic minerals of Ol-bearing and esite scoria rarely associated with hornblende and apatite. Pyroxene crystals having broad compositional range associated with Mg-rich olivine show complex zoning pattern in the Ol-bearing andesitic scoria. Plagioclase containing dusty inclusion is abundant phenocryst of the scoria. These petrographic features of the Ol-bearing andesitic scoria will suggest disequilibrium relationship between minerals [Sakuyama (1979)]. The LHF II consists of Ol-free scoria, the remaining Members are composed of Ol-bearing scoria. Therefore, it is assumed that the two types of andesitic magma concurrently were active in the latter half of the late Pleistocene beneath Ontake volcano.

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Miocene fromations widely overlie the Mesozoic formation, ultramafic rocks and Cretaceous granite in the Minakami area, northern part of Gunma Prefecture. This series is divided into the following six formations, in ascending order: Okura Formation (300 m in thickness), Awazawa Formation (550 m), Gokan Formation (260-2600 m), AkayaFormation (200 m+), Mitsumineyama Formation (350 m) and Tone Welded Tuff (200 m). The Gokan Formation unconformably overlies the underlying formations. The Mitsumineyama Formation and Tone Welded Tuff unconformably cover the Gokan and the Akaya Formations. Late Cenozoic tectonic evolution in this area is summarized as follows. In the Early Miocene, a large amount of basalt erupted on land. Many dykes of basalt show NE-SW trendingσ_<H-max>. In the earliest Middle Miocene, felsic pyroclastics deposited in shallow seas. The feeder dykes of the andestie-rhyolite show NE-SW trending σ_<H-max>. In the early Middle Miocene (15-14 Ma), mud deposited in lower middle bathyal environment. In the latest Middle Miocene (11 Ma), dacitic pyroclastics deposited on land and no more major geologic deformation have not occurred since then.

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The Tokai Group, one of the representative Pliocene-Pleistocene sequence in the Second Setouchi Sedimentary Basin, is widely distributed around Ise Bay and composed of lacustrine and fluvial deposits such as gravels, sands and muds with many intercalations of volcanic ash layers. The volcanic ash layers of the Tokai Group in Chita, Kameyama, Yokkaichi and Inabe areas are petrographically investigated, and the following results are obtained. 1) Petrographic characteristics of each ash layer are summarized in Table 1. 2) On the basis of the tephrostratigraphic, lithologic and petrographic data of the volcanic ash layers, the Tokai, Kobiwako and Osaka Groups are correlated with each other as shown in Fig. 4. The Otani vocanic ash layer of the Tokoname Formation in Chita area is correlated with the Akogi volcanic ash layer of the Kusuhara Formation in Kameyama area. The Iwamori volcanic ash layer of the Kameyama Formation is correlated with the Ichinohara volcanic ash layer of the Kono Formation in Inabe area and also the Masugi volcanic ash layer of the Kobiwako Group around Lake Biwa. The Chomyoji E volcanic ash layer of the Kameyama Formation may be correlated with the Minamidani-1 volcanic ash layer of the Ichinohara Formation in Inabe area, the Sagami I volcanic ash layer of the Kobiwako Group and the Habutaki I volcanic ash layer of the Osaka Group around Osaka Bay. The Nagasawaand Koyashiro volcanic ash layers of the Sakuramura Formation in Kameyama area can be correlated with the Komazuki and Mushono volcanic ash layers of the Kobiwako Group respectively. The Kawashima n volcanic ash layer of the Hachioji Formation in Yokkaichi area is correlated with the Bando-1 volcanic ash layer of the Ichinohara Formation in Inabe. The Karegawa volcanic ash layer of the Oizumi Formation in Inabe area, which is the most useful marker bed in the Tokai Group, is correlated with the Gokenjaya volcanic ash layer of the Kobiwako Group and the Fukuda volcanic ash layer of the Osaka Group. The Tara volcanic ash layer of the Oizumi Formation is correlated with the Pink volcanic ash layer of the Osaka Group.

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