Narsarsukite: a new occurrence in peralkaline trachyte, south Greenland
Narsarsukite: a new occurrence in peralkaline trachyte, south Greenland
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Narsarsukite：格陵兰岛南部过碱性粗面岩中的新发现
作者：
B. Upton;R. Macdonald;P. G. Hill;B. Jefferies;C. Ford
前寒武纪岩墙群中的一个坚硬的、球粒状的过碱性粗面岩岩墙主要由钠长石和霓石组成。其中，纳沙苏石的自形晶体Na 2（Ti，Fe）Si 4 O 10（F）以短棱柱平行于c伸长的形式出现。这将它们与所有先前描述的具有扁平习性的narsarsukites区分开来。存在的次要相包括云母、磷灰石、石英、透闪石、诺钙石和硅酸钍。介绍了纳萨尔苏石、霓石、钠长石、黑云母、磷灰石、梳状磷钙石、诺钙石和硅酸钍的探针分析。从矿物学和地球化学的角度来看，含那霸岩脉不太可能是该地区幔源玄武岩-粗面岩-comendite岩浆的分异。该岩墙与低海拔出露的一条石英石英长岩墙共线，表明含钠砂苏铁岩墙是由石英闪长岩基底与来自下地壳石英长岩的挥发性碱性溶液之间的反应生成的一种变质长岩。
Summary A flinty, spherulitic dyke of peralkaiine trachyte in a Precambrian dyke-swarm consists mainly of albite and aegirine. Within this, euhedral crystals of narsarsukite, Na2(Ti,Fe)Si4O10(F), occur as short prisms elongate parallel to c. This distinguishes them from all previously described narsarsukites, which have tabular habits. Minor phases present include micas, apatite, quartz, pectolite, nordite, and a thorium silicate. Probe analyses are presented for narsarsukite, aegirine, aibite, biotite, apatite, pectolite, nordite, and the thorium silicate. On mineralogical and geochemical grounds it is unlikely that the narsarsukite-bearing dyke is a differentiate of supposedly mantle-derived basalt-trachyte-comendite magmas in the region. The dyke is colinear with a comendite dyke exposed at lower altitude and it is suggested that the narsarsukite- bearing dyke developed as a rhcomorphic fenite generated by reaction between quartz diorite basement and fugitive alkaline solutions from the subjacent comendite.