大気圧下,85°Cおよび90°CでNaOH溶液との反応により黒曜石からスメクタイトと沸石が生成した。スメクタイトと種々の沸石の生成条件は火山ガラスの量 (g) と溶液中のNaOHの量 (g) の比によって決定される。スメクタイトは(火山ガラスの重量 (g)/NaOH (g)×1/40)の値が1と2の間の条件の時によく生成した。スメクタイトは溶液と黒曜石の表面の直接の反応で生成し,徐々に内部にまでスメクタイトが生成するのに対して,沸石類は溶解した溶液の中にまず沸石の核が形成され,それが成長していくと考えられる。

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Fine lamellar textures with chemical contrast are found in anisotropic grandite garnet from the skarn at the Kamaishi mine, Iwate Prefecture. The lamellae are charaterized by enrichment of iron; i. e., the compositional difference between lamellae and matrix amounts to 5 to 10 mole % in andradite molecules. In the sections sliced normal to (110) faces of garnet, the development of lamellae showing orientation parallel to (111) nearly normal to the growth zoning paralell to (110) face. Furthermore, the fine compositional bands (parallel to (110) growth zoning) are observed cutting the (111) lamellae clearly.
The data cannot confirm that formation of lamellae normal to (110) occurs in subsolidus or not. However, the compositional band parallel to (110) is obviously results of subsolidus decomposition.

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伊豆-小笠原弧南部からマリアナ弧北部にかけての火山フロントにはアルカリ岩の火山活動がおきている。これら島弧の火山フロントに沿ったソレアイト～アルカリ岩の主成分元素,微量元素,希土類元素, ⁸⁷Sr/⁸⁶Sr, ¹⁴³Nd/¹⁴⁴Ndの組成変化はアルカリ岩が他の火山岩に比べてLILEに富み, Sr比が高く, Nd比が低く, HFSEの量がほぼ同じであることを示す。このようなアルカリ岩の地球化学的特徴を調和させるためには雲母やアパタイトを含む交代作用を受けたマントルから分離したLILEに富む流体相が,よりHFSEなどに枯渇したマントルに付加し,この汚染されたマントルが部分溶融することでアルカリマグマが生じたとするモデルが最も適切である。

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The middle Miocene Takakusayama Formation distributed in the southwestern part of the South Fossa Magna mainly consists of lavas, hyaloclastites of alkali basalt, trachybasalt and trachyandesite and intrusives of alkali dolerite and gabbro, and trachyte. The Formation is divided into the lower, middle and upper members. The lower member is mainly trachybasalts, the middle is trachyandesites and the upper is alkali basalts.
SiO₂ contents ranges from 47.38 to 63.95%. As SiO₂ versus some oxide and minor element contents shows linear relation from the rocks of lower to middle member, trachybasalts of the lower member and trachyandesites of the middle member are products of fractional crystallization of the same magma.
Based on TiO₂ contents (1.7-2.5%) and K₂O/TiO₂ ratios (0.4-0.6), the Takakusayama alkali basaltic rocks are different from the island-arc alkali basalt of NE Japan. On the MnO/TiO₂/P₂O₅ and Zr/Y/Nb diagrams, most of alkali basalts are plotted in OIA and WPA fields, respectively, therefore, the alkali basalts are not the island-arc type alkali basalt, but are oceanic island alkali basalt within plate. This is also shown from the patterns of the MORB-normalized spidergram.
Sr and Nd isotopic ratios range from 0.70332 to 0.70338 and from 0.513000 to 0.513059, respectively. On the εNd-⁸⁷Sr/⁸⁶Sr diagram, most of the alkali rocks lie near lower limit of N-MORB and near the field of depleted Hawaiian alkali basalts.
From the above data, it is suggested that the Takakusayama alkali rocks have been derived from depleted mantle source similar to that of alkali rocks of oceanic island such as Hawaiian island.

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