南京娘娘山碱性岩中REE丰度及其在矿物中的分配系数

从具强烈成分分带的娘娘山碱性火山杂岩中分选出7个全岩。2个基质和8个单矿物,测定了REE含量,验证了矿物学和化学成分研究的结论,即岩浆房内主岩浆体顶部存在一个演化程度较高的粗面——响岩质岩浆层。LREE和HREE与其它不相容元素(如Rb、Zr等)在此岩浆层中强烈富集,而Eu则与Sr、Ba、Sc以及相容元素一样强烈亏损,MREE也显示中等程度的亏损。表明分离结晶是该成分梯度产生的主要原因。

REE ABUNDANCE AND DISTRIBUTION COEFFICIENT IN ALKALINE ROCKS FROM NIANGNIANG-SHAN, NANJING

Seven rock samples, two matrix samples and eight minerals selected or separated from Niangniang-Shan alkaline volcanic complex with strong compositional zontion were analyzed on REE contents by ICP. The obtained data suggest that there was a highly fraction ated phonolitic magma "cap" covered the dominant volumn of magma (with relative mafic composition) within Niangniang-Shan magma chamber. The similar conclusion also obtained studing from mineralogy and chemical component. Similar to other incompatible elements(e.g. Zr. Rb), LREE and HREE strong enriched in the upper part of the magma chamber, but Eu, as Sr. Ba. Sc and compatible elements, strong depleted in the roof zone. MREE also show a middle depletion within the "cap" of the chamber. The data of REE distribution cefficients of minerals prove that crystal fractionation was the main mechanism caused the compositional gradient and zonation. But different minerals had different effects on different parts of magma chamber, the fractionation of pyroxene, hauyne (within second subcycle magma chamber) as well as leucite (within first sub-cycle magma chamber) were very importante to the formation of the "cap" over the magma chamber, but the mechanism of formation of the compositional gradient within the " cap" mainly was the fractionation of sanidine, plagioclass and biotite.