碳酸岩岩浆演化的指示性矿物—环带金云母——以山东西部雪野碳酸岩为例

山东西部莱芜－淄博地区的中生代雪野碳酸岩中发育有大量罕见的反环带云母，云母的电子探针分析表明，云母斑晶的核心为黑云母，过渡带和边缘是金云母，基质中云母为金云母，核心黑云母与过渡带的金云母界限清晰，成分突变以及核心黑云母的溶蚀结构表明，核心黑云母和过渡带与边缘带金云母不是同一岩浆体系结晶的产物，核心黑云母可能是碳酸岩岩浆捕获的外来黑云母，过渡带与边缘带金云母同基质中金云母具有相似的化学成分，从过渡带到边缘带，金云母的Mg(Mg Fe)逐渐降低，反映了碳酸岩岩浆的不断结晶演化过程，TiO2的不断降低，一方面是由于岩浆的分异结晶，另一方面则是岩浆上升期间去气作用导致岩浆内CO2／H2O值降低所致。云母斑晶从过渡带向边缘带Al2O3含量逐渐减少，表明碳酸岩浆自过渡带云母结晶后没有富Al的圈岩物质加入。

Undex mineral: zoned phlogopite for evolution of carbonatitic magma: an example from the Xueye carbonatite in western Shandong.

The composition of phlogopite presented as phenocrysts and groundmass in Xueye carbonatite was determined by electron microprobe analysis. The cores of the phenocrysts are all biotite with their Mg/(Mg + Fe) ratios less than 0. 66, the compositions of the mantle and rim of the phenocrysts are similar to those of phlogopites occurred as groundmass. The abrupt change of compositon between core and mantle and the resorption of core implied that the core and the outer parts of phenocrysts were not crystallized from the same carbonatitic magma, the core biotite is likely exotic biotite entrapped during the ascending of the carbonatitic magma. The resemblance in composition of the mantle and rims of the phenocrysts and the phlogopite in groundmass indicates that the outer part of the phenocrysts and the groundmass were crystallized from carbonatitic magma. In phenocryst phlogopite, Mg/(Mg + Fe) ratio and TiO2 content gradually reduced from mantle to rim which reflected the crystallizing process and the decreasing of CO2/H2O ratio in the magma caused by degassing. The gradually decreasing of A12O3 from mantle to rim indicated no Al-rich wallrock added into the carbonatitic magma.