岩石鉱物科学
Online ISSN : 1349-7979
Print ISSN : 1345-630X
42 巻 , 5 号
September
選択された号の論文の6件中1~6を表示しています
原著論文
  • 髙橋 奈津子, 永嶌 真理子
    2013 年 42 巻 5 号 p. 211-220
    発行日: 2013年
    公開日: 2013/11/16
    ジャーナル フリー
      Occurrence, assemblages and chemical compositions of zeolite and associated amygdale minerals in Otsu alkali basalt from Mukatsuku Peninsula, Nagato, Yamaguchi, Japan, were studied to find formation process of amygdale minerals. Cavities with amygdale zeolite and associated minerals distribute in the Otsu alkali basalt near Cape Kawashiri at about 25 m level (outcrops O4, L1 and L2) and at 45 m level (outcrops O1 and O2) from the bottom of the Otsu alkali basalt. Chabazite-Na occurs in cavities of all outcrops. Phillipsite-Ca, levyne-Ca and erionite occur only in cavities of upper level outcrop O2, whereas they do not occur in the cavities of lower level O4, L1 and L2 outcrops. The erionite grows as the epitaxial crystal on the surface of levyne-Ca. Heulandite-Ca occurs only in L2 outcrop. Calcite is a common amygdale mineral. Barite and quartz occur in cavities of the lower level outcrops. Chabazite-Ca occurs rarely as inclusions in chabazite-Na in the cavity of outcrop O4. In the cavities of outcrops O2, O4 and L2, crystallization trends from the wall to center are phillipsite-Ca to chabazite-Na, chabazite-Ca to chabazite-Na, and heulandite-Ca to chabazite-Na, respectively, whereas, in the cavities of the outcrops O1 and L1, only chabazite-Na occurs. Zeolites formed in early stage tend to rich in divalent exchangeable cations, such as Ca and Mg, and Si. In contrast, zeolites crystallized in the later stage tend to be low in Si and high in monovalent cations. The zeolites and assemblages of amygdale minerals at lower 25 m level outcrops suggest higher crystallization temperature than those at higher outcrops.
特集号「マントル起源物質解読:知りたいこと,読めること,読みたいこと」その5
総説
  • 田村 明弘, 森下 知晃, 荒井 章司
    2013 年 42 巻 5 号 p. 221-231
    発行日: 2013年
    公開日: 2013/11/16
    ジャーナル フリー
      Abyssal peridotite is widely accepted as residual mantle material after partial melting and melt extracted beneath mid-ocean ridge, and is contributed to understanding of magmatism forming oceanic lithosphere. Peridotite samples from the oceanic core complex of the ridge-transform intersection corner high recently provide new insight of upper mantle material inhomogeneity in terms of degree of melting and further melt-related processes. Compiling data of Cr# [Cr/(Cr+Al) atomic ratio] of spinel and clinopyroxene REE compositions of abyssal peridotite from the slow- and ultraslow-spreading mid-ocean ridges, accumulated since 1980s, demonstrate that depleted peridotites are dominantly collected from the oceanic core complex and abyssal plane at shallower depth (<2500 m below sea level), contrasting to relatively fertile peridotite from the transform wall at deeper part of the fracture zone. Various enrichment of clinopyroxene REE compositions in such depleted peridotite reflects that the melt is involved in or after the partial melting stage. The compiling data suggest that the compositional variation of abyssal peridotite is dependent on the mid-ocean ridge structure and that the inhomogeneity of upper mantle material is recognized in regional scale, contrasting to the global-scale inhomogeneity already discussed in previous abyssal peridotite studies. Drilled core peridotite samples from the Atlantis Massif, Mid-Atlantic Ridge 30°N are good example to reveal that the melt penetration into residual peridotite is an important role for creating inhomogeneity of rock-sample scale on the oceanic core complex formation.
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