中国蓝片岩中闪石族矿物的研究

STUDY OF AMPHIBOLES FROM BLUESCHISTS IN CHINA

本文对中国篮片岩中间石族矿物进行了综合研究,可将它们分为三个亚族:碱性问石亚族;钠钙闪石亚族;钙质闪石亚族。碱性闪石亚族再按Fe 、Mg、Al的比值,后二者按Si的含量划分为矿物种。编制了闪石成分分类图。碱性闪石的光学性质、红外吸收光谱和x射线衍射数据,与其它两个亚族有明显差异,但各亚族内特征基本相似。利用多色性和延性特征鉴别碱性问石各矿物种较为准确,并发现青铝闪石的多色性公式应为Ng-紫色、Nm-深蓝色、Np-浅黄色,与前人描述不一致。

The studies of the compositions, optical properties, infra-red spectrum and X-ray diffraction of amphiboles in major blueschist belts of China indicate that the phiboles in the blueschists are chemically classified into three subgroups. Alkati phibole subgroup is principal component, and mainly crossite and magnesian riebecki-tessodiun-calcium subgroup, mainly winchite and calcium subgroup, mainly actinolite.The analyses of chemical compositions of studied 331 amphiboles from blue-schists show it is possible to subdivide the amphiboles using Na/Na + Ca, Na/Na + Ca>0.68 for alkali amphibole one; 0.68>Na/Na +Ca>0.4 for sodium-calcium am-phibole one and Na/Na + Ca<0.4 for calcium amphibole one. Each subgroup, in which alkali one depends on the relation of Mg/Mg + Fe2 and Fe3+/Fe3+AlⅥsodium-calcium one on Si ionic numbers, can be further classified. As shown in Fig.l.On the relations above, a simple and convenient classification diagram has been charted. In the diagram, except some glaucophanes, the names of other amphiboles are consistent with the classification criteria by International Mineral Society(1978).The optical observations prove that the pleochroic formula for the crossites differs from those, such as Ng = dark blue, Nm = violet described in somebooks of optical mineralogy. In fact, Ng is violet and Nm dark blue on our observation.Simple girdle textures in the amphiboles from glaucophane schists have been universally observed.The study of the compositions indicates that the composition changes between alkali amphibole-sodium calcium amphibole-calcium amphibole may be a continuous scries.The form of alkali amphiboles is close associated with plate underthrusting belts, representing a low-temperature and high-pressure environment.The form temperature for the most alkali amphiboles in china ranges from 350 -450℃,and pressure, 0.5-0.9 GPa. Most of them are related to the basic volcanic rocks, but some appearing in quautz schists and marbles show that host rock composition is not a crucial factor to their formation.