Crystallization of AlPO4-SiO2 solid solutions from granitic melt and implications for P-rich melt inclusions in pegmatitic quartz
Crystallization of AlPO4-SiO2 solid solutions from granitic melt and implications for P-rich melt inclusions in pegmatitic quartz
复制标题
花岗岩熔体中 AlPO4-SiO2 固溶体的结晶及其对伟晶质石英中富磷熔体包裹体的影响
DOI：
10.2138/am-2003-11-1213
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发表时间：
2003
影响因子：
3.1
通讯作者：
R. Wirth
中科院分区：
文献类型：
--
作者：
I. Veksler;R. Thomas;R. Wirth
摘要 正磷酸铝（AlPO4）与鳞石英、方英石和石英具有同构多晶型。柏林石是相当于 α-石英的低温形式。我们报道了从合成的富磷过铝花岗岩熔体中结晶出来的柏林石-石英固溶体，其成分与伟晶岩中发现的最易挥发的硅酸盐熔体包裹体相似。结晶是在 450-700 °C 和 0.1-0.2 GPa H2O 压力的冷封压力容器中进行的实验中发生的。在这些条件下，菱镁矿-石英互溶度在固溶线的磷酸盐一侧限制为 5-7 mol% SiO2，在富二氧化硅一侧限制为最大 1 mol% AlPO4。互溶度似乎随着温度的降低而降低。在低 T 温度下，柏林石英固溶体的晶体强烈分区，并在富磷相和富硅相之间表现出复杂的共生。通过电子显微探针、透射电子显微镜和拉曼光谱对它们进行了研究。根据我们的新实验结果，之前报道的一些天然石英熔体包裹体的磷极度富集可以解释为含有柏林石的主体的包埋后污染。
Abstract Aluminum orthoposphate (AlPO4) has polymorphs isostructural with tridymite, cristobalite, and quartz. Berlinite is the low-temperature form that corresponds to α-quartz. We report berlinite-quartz solid solutions to crystallize from a synthetic P-rich peraluminous granitic melt, similar in composition to the most volatile-rich silicate melt inclusions found in pegmatites. The crystallization took place in experiments performed in cold-seal pressure vessels at 450-700 °C and 0.1-0.2 GPa H2O pressure. At these conditions, the berlinite-quartz mutual solubility is limited to 5-7 mol% SiO2 on the phosphate side of the solvus and to the maximum of 1 mol% AlPO4 on the silica-rich side. The mutual solubility appears to decrease with falling temperature. At low T the crystals of berlinitequartz solid solutions are strongly zoned and show complex intergrowths between the P-rich and silica-rich phases. They were studied by electron microprobe, transmission electron microscopy, and Raman spectroscopy. In the light of our new experimental results, the extreme P enrichment reported earlier for some natural quartz-hosted melt inclusions may be explained as a post-entrapment contamination by the berlinite-bearing host.