多硅白云母中Fe^（2＋）的高压有序效应

Fe￣(2+) ORDER RESULTING FROM HIGH METAMORPHIC PRESSURE IN PHENGITE

２１个多硅白云母来自４个低温高压变质带。用电子探针、Ｘ射线粉末衍射及穆斯堡尔谱测定其化学成分、ｂ０值及Ｆｅ２＋占位。建立Ｆｅ２＋（Ｍ１）／Ｆｅ２＋（Ｍ２）对ｂ０值相关图，发现Ｆｅ２＋在八面体晶位有序化并解释其有序机理。

amples of phengite used for present work were collected from 4 low-temperature and high-pressure metamorphic belts in China. The chemical compositions, b0value and Fe2+ site occupancy have been measured by means of electron microprobe,X-ray powder diffraction and Mossbauer spectrometer. The ratio, R=Fe2+ (M1)/Fe2+(M2), is used to describe Fe2+ order degree in phengite. b0 vs R diagram has been established, in which there are 3 regions corresponding to low-, medium- and highpressure. This is a new geobarometric indicator. Mechanism of Fe2+ order at M2 site of phengite have been discussed. Progress of Fe2+ order at M2 site of phengite is suggested: high metamorphic pressure→Tschermarks substitution → (1) Si4+ replace tetrahedral Al3+, more Si enter phengite structure, (2) (Mg, Fe) replace Al3+ at M2site, which results in Fe2+ order at M2.