摘要
根据文献中列出的５６个产于碳酸岩－碱性岩磷灰石的成分数据，讨论了这些岩浆型磷灰石结构四面体（Ｔ位置）替换特征的标型意义，并定义出四面体替换指数（ＴＳＩ＝（Ｓｉ＋Ｓ＋Ｃ）／Ｐ，单位晶胞原子数百分比），以区别侵入相碳酸岩磷灰石（ＩＡＰ）、喷发相碳酸岩磷灰石（ＥＡＰ）和碱性岩磷灰石（ＡＡＰ）：ＩＡＰ的ＴＳＩ为０～６．９，平均３．６２，仅少量Ｃ进入Ｔ位置；ＥＡＰ的ＴＳＩ极大，为６．３～４８．７，平均１９．２４，大量Ｓｉ，Ｃ进入Ｔ位置；ＡＡＰ有中等的ＴＳＩ值：３．２～１４．０，平均６．５１，以富Ｓ为特征。上述磷灰石Ｔ位置的替换特征反映了其母岩的成分与结晶环境特点。
With the data of composition of 56 apatites from some carbonatitic alkalinic rocks, the Tetrahedral Substitution Index (TSI)is defined (TSI=(Si+S+C)/P,atm%) to distinguish the apatites from intrusive carbonatite (IAP), from extrusive carbonatite (EAP) and from alkaline rocks (AAP). Only a small amout of carbonate enter the T site of IAP, and its TSI is 0￣6.9, with an average of 3.62 from 26 samples; the substitution of a great deal of Si,C for the P of EAP which makes it with the largest TSI: 6.3￣48.7, with an average of 19.24 from 19 samples; The AAP contain much S and has a middle TSI: 3.2￣14.00 from 11 samples, with an average of 6.51. The tetrahedral substitutional differences of these apatites reflect the characteristics of compositional and crystallinal environment of their host rocks.
出处
《矿物岩石》
CAS
CSCD
北大核心
1997年第3期5-10,共6页
Mineralogy and Petrology
