Oriented feldspar-feldspathoid intergrowths in rocks of the Khibiny massif: genetic implications
Oriented feldspar-feldspathoid intergrowths in rocks of the Khibiny massif: genetic implications
复制标题
希比内地块岩石中定向长石-长石共生体：遗传意义
DOI：
--
复制
发表时间：
2012
影响因子：
1.8
通讯作者：
N. V. Trubkin
中科院分区：
文献类型：
--
作者：
O. Ageeva;R. Abart;G. Habler;Boris Ye. Borutzky;N. V. Trubkin
含有大量长石-霞石和长石-方钾硅石显微或层状共生包裹体的碱长石异质巨晶是希比内地块的亮长石的特征。基于使用 4 轴通用平台的光学研究和使用电子背散射衍射的晶体取向成像，确定了共生相之间严格的晶体取向关系。最常观察到的取向关系是方钾硅石和霞石 [001] 方向与碱长石主体的 [010] 方向平行，并且长石 [100] 方向与碱长石的 [100]-、[101]- 和 [001] 方向一致。共生域内存在残渣霞石、碱长石连续取代霞石前体以及相关的长石-长石共生体的形成表明，霞石是由长石云辉石发育而来的，其中霞石是主要的长英质相。从钾和二氧化硅的大量引入以及钠的去除来确定硅镁石向菱镁石转变的交代性质。高温下发生交代作用；希比内地块巨大的磷灰石矿床似乎与这一交代事件有关。
Poikilitic megacrysts of alkali feldspar with abundant inclusions of feldspar-nepheline and feldspar-kalsilite micrographic or lamellar intergrowths are characteristic for the rischorrites of the Khibiny massif. Strict crystallographic orientation relations were identified among the intergrowth phases based on optical investigation using a 4-axes universal stage and crystal orientation imaging using electron back scatter diffraction. The most frequently observed orientation relation is the parallel orientation of the kalsilite and nepheline [001] directions with the [010] direction of the alkali feldspar host and concomitant coincidence of the feldspathoid [100] directions with the [100]-, [101]- and [001] directions of the alkali feldspar. The presence of relic nepheline within intergrowth domains and the successive replacement of precursor nepheline by alkali feldspar and associated formation of feldspar-feldspathoid intergrowth suggest development of the rischorrites from feldspar urtites, in which nepheline is the dominant felsic phase. The metasomatic nature of the transformation of urtites to rischorrites is identified from massive introduction of potassium and silica and removal of sodium. Metasomatism occurred at high temperature; the gigantic apatite deposits of the Khibiny massif seem to be related to this metasomatic event.