摘要
自然界绿柱石存在三个类质同象系列．即“八面体”绿柱石（c/a=0．991～0．996）·“正常”绿往石（c/a=0．997～0．998）和“四面体”绿柱石（c／a=0．999～1．003）。绿柱石矿物精细结构研究表明，二公阳离子置换八面体中Al，Li置换四面体中Be，而碱离子被绿柱石通道所容纳，用于补偿低价阳离子置换Al八面体和Be四面体引起的电价不足。伟晶岩绿柱石通常含有＞1．6Wt％的通道水，而包裹体中流体仅为0．15Wt％左右。室温下绿柱石通道中存在Ⅰ型和Ⅱ型H2O，其H-H矢量分别垂直和平行于c轴。由于高温脱水（T＞800℃）过程绿柱石通道水氢同位素无明显分馏效应，因此通道水代表绿柱石矿物形成时的原生水。现有的研究表明．绿往石通道水δD和流体包裹体水δD具有显著差异。利用绿柱石通道水测定岩浆水的氢同位素组成．可避免流体包裹体测定δD值因多个世代包裹体污染而引起地质含义的不确定性。无疑，它将是一种了解岩浆-热液过渡阶段性质、定量示踪伟晶岩挥发分演化（主要H2O）以及伟晶岩成因等的强有力工具。
There are three isomorphous series of beryl in nature, that is'octahedral' beryl (c/a= 0. 991 - 0. 996 ). 'tetrahedral' beryl (c/a = 0. 999 - 1. 003 ) and 'normal' beryl (c/a = 0. 997 -0. 998). The refinements of beryl structure suggest that divalent canons substitute for Al in octahedral slies and Li for Be in tetrahedral ones, while alkali canons are accommodated by the channel of beryl to balance the deficiency of positive charges resulting from the replacement of octahedral Al and tetrahedral Be by canons of lower valence. Normally. there are more than 1. 6 wt % H2O in the channel of Pegmatitic beryl and only approx. 0. 15 wt % in .fluid inclusion. There exist two types of H2O in channel of heryl at room-temperature: type-I H2O and type-II H2O. with the vector of H-H perpendicular and parallel to the c axis. Because isotope fractionation is minimal during high-temperature dehydration (T>800℃ ), H2O released from the structural channel of beryl represents the original water of the mineral formation. Previous investigations indicated that the are some differences in hydrogen isotopic composition between H2O in the channel and that in fluid inclusion. Therefore,it is of spedal advantage to use H2O In the channel of beryl to measure the hydrogen isotopic composition of magmatic water since the analysis of inclusion fluid is usually affected by contamination from inclusions of multi-generations. As such, it provides a powerful tool to understand the properties of magmatic/hydrothermal transition and to trace quantitatively the volatile evolution and genesis of pegmatite.
出处
《矿物学报》
CAS
CSCD
北大核心
1999年第3期370-378,共9页
Acta Mineralogica Sinica
基金
国家杰出青年科学基金!49625304
国家攀登计划预选!95-预-39
关键词
伟晶岩
绿柱石
矿物
通道水
氢同位素示踪
beryl
mineralogy
H_2O in channel
hydrogen isotopic composition
