Fluorite particles inducing butterfly aggregates of incipient microperthite in alkali feldspar from a syenite, the Patagonian Andes, southern Chile
Fluorite particles inducing butterfly aggregates of incipient microperthite in alkali feldspar from a syenite, the Patagonian Andes, southern Chile
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萤石颗粒诱导智利南部巴塔哥尼亚安第斯山脉正长石中碱长石中早期微长石的蝴蝶聚集体
DOI：
10.2138/am-2002-1013
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发表时间：
2002
影响因子：
3.1
通讯作者：
A. Sugaki
中科院分区：
文献类型：
--
作者：
S. Nakano;J. Akai;A. Sugaki
摘要智利南部巴塔哥尼亚安第斯山脉的正长岩中发现的碱长石颗粒，体积成分约为Or40 Ab59 An0.5，在光学显微镜下观察时由两部分组成：透明部分和浑浊部分。颗粒内部是两部分的混合物，而边缘主要是浑浊的。显微镜下几乎没有微孔的透明部分是隐纹长石，而混浊部分是微纹长石。微条纹长石为斑块型，浑浊是由于大量的微孔，这些微孔呈多边形，直径一般小于1 mm。斑片状微条纹长石是原生隐条纹长石经热液反应粗化而形成的。微条纹长石形成的初始阶段被记录为具有对角伸长的富OR长石和富AB长石分离成具有“蝴蝶”形状的聚集体。微条纹长石的每个蝶形集合体的长度通常小于10 mm。电子探针和透射电镜分析表明，蝶形聚集体的中心通常被直径约为1mm的圆形萤石颗粒占据。萤石颗粒可能是在流体阶段形成的。微条纹长石的形成可能是在热液阶段沿着与萤石颗粒的界面沿着蝴蝶聚集体开始的。蝴蝶状集合体进一步变粗，变为斑块状微条纹长石。萤石颗粒形成的时间和过程对长石显微结构的演化和氟在碱性火成岩中的行为有重要的影响。
Abstract Alkali feldspar grains found in a syenite from the Patagonian Andes, southern Chile, have bulk compositions of about Or40Ab59An0.5, and consist of two parts when viewed under an optical microscope: a clear part and a turbid part. Grain interiors are mixtures of the two parts, whereas the rims are mainly turbid. The microscopically clear part, which is almost free of micropores, is cryptoperthitic, whereas the turbid part is microperthitic. The microperthite is of the patch type, and the turbidity is due to abundant micropores that are polygonal and generally less than 1 mm in diameter. The patch microperthite has been formed by coarsening of primary cryptoperthite by hydrothermal reactions. An incipient stage of the microperthite formation is recorded as the segregation of the Or-rich feldspar with diagonal elongation and Ab-rich feldspar into aggregates that have a “butterfly” shape. Each butterfly aggregate of microperthite is generally less than 10 mm in length. The centers of the butterfly aggregates are usually occupied by round fluorite particles about 1 mm in diameter, which were identified by EPMA and TEM analyses. The fluorite particles may have been formed at the fluid stage. The microperthite formation may have started as butterfly aggregates along the interfaces with the fluorite particles at the hydrothermal stage. The butterfly aggregates have changed to patch microperthite with further coarsening. The timing and process of the formation of the fluorite particles are important in relation to the evolution of feldspar microtextures, and the behavior of fluorine in alkaline igneous rocks.