In the southern part of the Hidaka belt, andalusite-sillimanite type metamorphic rocks, tonalites and gabbros are widely exposed. To clarify tectono-thermal evolution of the belt, K-Ar ages of 43 biotite and 5 hornblende separated from metapelites, amphibolites, tonalites and gabbro were determined. These ages are divided into two groups according to their distribution area, the group of 35-29 Ma (biotite age) is in the northeastern part and that of 19-17 Ma (biotite age) is in the southwestern part. Cooling rates of the older and younger groups are estimated using biotite and hornblende K-Ar ages to have been about 120 °C/Ma and about 23 °C/Ma, respectively. The rocks of the younger group had been strongly mylonitized under ductile deformation during their uplifting. It is estimated that narrow transitional zone or fault, which separates the K-Ar ages into two groups, would exist along the mountain ridge of NW-SE direction in the studied area.
     On the basis of these K-Ar ages with geological and petrological studies which have been already published, the tectono-thermal evolution of the study area can be divided into four stages: (1) stage of the regional metamorphism and anatexis (60-41 Ma), (2) stage of emplacement of tonalite body formed by anatexis and subsequent contact metamorphism by the tonalite intrusions (ca. 40 Ma), (3) stage of upthrusting and mylonization of lower crustal rocks (36-17 Ma), and (4) stage of uplifting and cooling of these rocks.

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平木カオリン鉱床（兵庫県加東郡社町）は，白亜紀末の流紋岩質火山砕屑岩中に胚胎する。層状鉱床である。鉱山及びその周辺では，層序的に下位より上位へ，流紋岩溶岩，これと整合的に流紋岩質平木非溶結凝灰岩（=鉱床胚胎層準），木層と不整合に流紋岩質平木溶結凝灰岩が重なっている。非溶結凝灰岩層は，選択的に強い変質作用を受けた結果，ほぼ全域にわたってカオリナイト—石英帯（厚さ約100 m）となっている。上記3層準の岩石試料中の主成分及び微量成分についてXRF法により分析した結果，これらはすべてアルカリに乏しい過アルミナ質であり，且つ鉱床は単一のprecursor（=平木非溶結凝灰岩）の変質により生じたものであることが明らかとなった。物質移動についての計算結果は，次のことを示している:（1）カオリナイト—石英帯（鉱化帯）では，30∼40wt% SiO₂の添加， Na₂O， K₂O， CaO， Fe₂O₃及びMnOの溶脱，（2）絹雲母“帯”ではFe₂0₃とK₂O，緑泥石“帯”ではFe₂O₃が局所的に濃集，（3）微量成分の巾ではZrとNbが最もimmobileである。

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1770k/6 GPaで合成したLiGaSi₂O₆単斜輝石と，同結晶を1073 K/1気圧および1123 k/1気圧でアニールしたもの，計3種の結晶構造を，単結晶x線データをもとに精密化した。これらはLiAlSi₂O₆スポジュメンと同型であり，アニール処理が進むと共に平均Ga-O1距離は増加し， Ga-O1-Ga角は減少する。これらの事実は，6配位席を占めるGaに，電子状態の異なる2種類のGaが，存在することを示唆する。また，1770 k/6 GPaで合成したLiGaSi₂O₆単斜輝石の固体ガリウム-69 NMRスペクトルと，アニール処理したLiGaSi₂O₆のNMRスペクトルとを比較したところ，6配位席を占めるGaには，電子状態の異なる2種類のGaが，存在することが確かめられた。

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Hydrous mineral inclusions in chromian spinel were commonly found in chromitite from the Yanomine complex, one of the dunite-harzburgite complexes in the Sangun zone of the central Chugoku district, southwest Japan. Hydrous minerals are Na-phlogopite and pargasite, both of which are relatively high in Ti. Similar inclusions were also found in spinel in dunite from the Yufune complex and in troctolite from the Ashidachi complex. Chromitite pods which are relatively large-scale from the Tari-Misaka complex have no hydrous mineral inclusions in chromian spinel. Existence of hydrous mineral only as inclusions in chromian spinel may indicate a melt which is enriched with incompatible elements played an important role during precipitation of chromian soinel in the Yanomine comolex.

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