冀北与角闪石岩相关铁钛磷灰岩的特征及成因--磷灰石矿物化学的证据

Occurrence and Genesis of Hornblendite-Associated Nelsonite in Northern Hebei Province,China:Evidence from Apatite Geochemistry

铁钛磷灰岩在超基性岩中很少发育,笔者野外工作发现冀北铁马哈叭沁超基性岩杂岩体的角闪石岩中发育少量团块状铁钛磷灰岩。本研究选择岩浆演化不同阶段的辉石角闪石岩、角闪石岩和铁钛磷灰岩中的磷灰石进行了电子探针和LA-ICP-MS激光探针分析,对比分析了磷灰石矿物主微量元素特征。不同岩石类型中磷灰石微量元素蛛网图形态十分相似,但铁钛磷灰岩中磷灰石的F、U、Th、Sr、∑REE含量明显更高,连续变化的趋势与岩体岩相序列相符,表明在岩浆演化的晚期阶段,随着分异程度的增强,角闪石岩母岩浆中的Fe-Ti-P组分逐渐富集并达到饱和,从而在角闪石岩中发育团块状的铁钛磷灰岩。

Occurrences of nelsonites associated with ultramafic rocks are very rare.Recently,small concentrations of nelsonites were discovered in close association with Fe-Ti-P hornblendites from the Tiemahabaqin clinopyroxenite-hornblendite complex,Northern Hebei Province,China.In order to gain information about the genesis of the nelsonites,this study presents major and trace element data of the apatites from rocks that formed at different stages of magmatic evolution including clinopyroxene hornblendites,hornblendites and nelsonites.Spider diagrams of apatites form different rock types are very similar in shape.However,trace element compositions such as F,U,Th,Sr and ΣREE of apatites from the nelsonites are significantly higher than those from the clinopyroxene hornblendites and hornblendites and exhibit a continuous trend.It is indicated that the nelsonites were separated at the latest stage of magmatic evolution when Fe-Ti-P components were saturated in the parent magma of the hornblendites.