西藏阿里西部八面体假像透辉石、透闪石和绿泥石的化学标型特征

阿里西部超镁铁岩带八面体假像透辉石具有富钙贫铝的化学特点和降温降压的晶胞参数。八面体假像绿泥石具有富硅贫铝和贫铁的特点,它们都与地壳浅成热水产物的透辉石和绿泥石的化学特征完全不同。而它们可能是超镁铁岩由地幔上升侵位的早期所形成的热水交代产物。本文讨论了由尖晶橄榄石向八面体假像硅酸盐矿物转变的交代反应。

Chemical Typomorphic Characteristics of Pseudomorphic Octahedral Diopside,Tremolite and Chlorite in Western Ali,Tibet

The pseudomorphic octahedral chlorite and serpentine in chromitite of western Ali, Tibet were previously discussed by the authors (1983). Recently, they have found pseudomorphic octahedral diopside, tremolite, and chlorite in serpentinized harzburgite of the same area. The Ca-rich and Al-poor characteristics of octahedral diopside suggest a metasomatic reaction under the condition of lowering temperature and pressure. This is consistent with the characters of cell parameters of octahedral diopside. The Si-rich and Al-poor features of octahedral chlorite are similar to conditions of octahedral diopside, but are completely different from the chemical characters of hypabyssal hydrothermal chlorite. The octahedral diopside is also obviously distinct from diopside of hypabyssal altered ultramafite in chemical composition. The chemical fratures of these two octahedral silicates may be attributed to hydrothermal metasomatism during the early stage uplifting and emplacement of the mantle rock. The reactions of ringwoodite-octahedral diopside-octahedral tremolite and ringwoodite-octahedral serpentine-octahedral chlorite are dealt with in this paper.