In the magma with volatile matters highly concentrated, the crystallization of magnetite is distinctly promoted to have an influence on the decrease of the FeO/MgO ratio of the ferro-magnesian silicate minerals (Taneda, 1947, 49, 50).
E.F. Osborn (1959), A. Muan and others certified experimentally the similar influence of volatile matters on fractionating liquid corresponding to magma, and pointed out the differences in the FeO/Fe₂O₃-SiO₂ relation at the different oxygen partial pressure.
The FeO/Fe₂O₃ values for SiO₂ in alkalic rocks are comparatively low, and the trend of variation corresponds to Osborn's crystallization course (FeO/Fe₂O₃-SiO₂ curve) in the FeO-Fe₂O₃-MgO-SiO₂ system (Osborn, 1959) at high oxygen partial pressure, while those of non-alkalic rocks (tholeiitic and calc-alkalic rock ) are comparatively high, corresponding to low oxygen partial pressure. Calc-alkalic rock magmas are assumed to be slightly higher in oxygen pressure than tholeiitic rock magmas. The FeO/Fe₂O₃-H₂O relations of representative rocks also support such an interpretation.
Moreover the PF relations [Pyroxene-Feldspar relations; (Di_??_Hy)-(An_??_(Ab+Or)) and (Di+An)-(Hy+Ab•Or) relations] of various rocks including alkalic, tholeiitic and calc-alkalic rocks are very suggestive for the influence of vapour pressure on the magma production and its consodilation to yield rocks. The PF relations are divided into three types, A, B and C. A Type: Ab+Or and/or Di predominate, B Type: Di/An= Hy/(Ab+Or), and C Type: An and/or Hy predominate. Almost all “alkalic rocks” and small number of “tholeiitic and calc-alkalic rocks” belong to A type, while almost all “tholeiitic and calc-alkalic rocks” and rarely a part of “alkalic rocks” belong to C type. A few“aklalic”, “tholeiitic” and “calc-alkalic” rocks belong to B type.
(1) It seems to be true that the rocks of A Type are derived by some way where crystallization starts and/or predominates in the pyroxene filed of the PIT system and the rocks of C Type are formed largely in the feldsapr field in the same system.
(2) Generally speaking, alkalic rock magmas are produced and crystallized at comparatively high vapour pressure (over 1 K bars approx. to 3-5 K bars) and comparatively low temperature, while non-alkalic rock magmas at low vapour pressure (less than 1K bars approx.) and high temperature (Figs. 6 & 7).
Tholeiitic rock magmas are slightly lower than calc-alkalic rock magmas in vapour pressure.
(3) The basic magmas, involving non-alkalic and alkalic, are produced by partial or almost complete melting of gabbroic rocks corresponding to eclogites or amphibolites, though some of alkalic rock magmas can be, and may be, produced also by partial melting of ultrabasic_??_basic rocks. Although the gabbro-amphibolite-elcogite transformation should be reinvestigated, the magmas with vapour, are formed at various depths related to largely vapour pressure, ranging from 40 to 70Km or more approximately (Fig. 8). The alkalic magmas are produced at shallower depth than the tholeiitic magma.
The granitic-rhyolitic magmas which are formed by the partial_??_complete melting of granitic rocks, can be formed at shallow depths in the granitic crust.

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The Yokokawagawa metamorphic rocks which have long been thought to be northeastern extension of the Sambagawa metamorphic rocks of northern end of Akaishi mountains are studied from the viewpoint of structure as well as metamorphism. They are divided into two zones. The one is so-called spotted schist zone where garnet is stable in pelitic rocks, and porphyloblastic albite is widely developed. The other is so-called non-spotted schist zone where garnet is unstable and no porphryoblastic albite is developed.
The metamorphic grade increases toward west in relation to descending order of stratigraphy. Comparing these rocks with Sambagawa metamorphic rocks of northern Akaishi mountains, structural and metamorphic similarities are found. The lateral displacement of the rocks by the fault of the western margin of the Fossa-Magna is estimated as 12 Km in left lateral sense. The origin of schist pebble in the Neogene formations in the Fossa-Magna region must be sought partly in this area.

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[in Japanese]

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