云开地块西南缘的庞西垌复式岩体由外而内、 由上而下依次为花岗片麻岩、 片麻状花岗岩和花岗岩, 即由高级变质岩渐变过渡至岩浆岩。 X射线荧光光谱、 等离子体质谱对三类岩石的分析结果表明, 三类岩石皆属于过铝质岩石系列, 造岩组分和微量元素具有渐变过渡的特征。 在花岗片麻岩演化为花岗岩的熔融、 分异过程中, Al2O3, CaO, MgO与TiO2等造岩组分含量逐渐增高, SiO2含量逐渐降低;稀土元素总量整体升高, 稀土元素中轻稀土含量逐渐增高, 而重稀土含量逐渐降低, 显示出轻重稀土分异增强的特征, 在多期演化过程中, 形成了具有亲缘演化基因的庞西垌花岗质岩石系列。 这表明云开地块表变质壳岩石的重熔可能是花岗质岩石的重要成因。 其演化机制可能是, 表壳岩石在发生熔融之后SiO2最先脱离母岩不断熔出, 重稀土可能随着SiO2熔体逐渐向上富集;而Al2O3, CaO, MgO, TiO2以及轻稀土相对SiO2则向下富集。

Pangxidong composite granitoid pluton located in the southwestern margin of Yunkai massif. The metamorphic grade of this pluton increases from outside to inside, that is, banded-augen granitic gneisses, gneissoid granites and granites distribute in order from edge to core. X-Ray Fluorescence Spectroscopy and Plasma Mass Spectrometry are conducted to study the geochemical characteristics of the three types of rocks. The result shows that all the three types of rocks are peraluminous rocks and their contents of main elements and rare earth elements change gradually. From granitic gneisses to granites, the contents of Al2O3, CaO, MgO, TiO2, total rare earth elements and light rare earth elements increase, but the contents of SiO2 and heavy rare earth elements decrease. It is suggested that the phylogenetic relationship exists between granitic gneisses, gneissoid granites and granites during the multi-stage tectonic evolution process. Furthermore, the remelting of metamorphosed supracrustal rocks in Yunkai massif is probably an important cause of granitoid rocks forming. The evolutionary mechanism is probably that SiO2 and heavy rare earth elements were melt out from the protolith and gradually enriched upward, but Al2O3, CaO, MgO, TiO2 and light rare earth elements enriched downward.