福州闽侯长安闪长岩岩体的地球化学特征及其地质意义

Geochemical Characteristics of Changan Diorite in Minhou of Fuzhou and Its Geological Significance

为了解长安闪长岩岩体的形成与福州地区中生代岩浆活动的关系,对长安闪长岩岩体进行了岩相学和岩石地球化学特征研究,并与福州复式岩体进行了对比。发现长安闪长岩体呈岩株状分布于福州盆地西边缘,岩体的矿物组成主要为中性长石、角闪石、黑云母、石英,在岩体边缘具有少量的辉石。岩石地球化学特征为:(1)主量元素中SiO2为52.79%～58.89%,平均54.94%;碱度AR一般为1.4～1.9,平均为1.50,属钙碱性的范围;(2)微量元素具有富Rb、Ba、Th、U、K、Pb,而低Nb、Ta的特点;(3)稀土元素∑REE为119.327～169.148,平均143.273;LREE/HREE为8.550～11.672,平均9.435;δEu0.679～1.005,平均0.871,稀土分配模式为明显右倾典线,没有明显的Eu异常或仅具弱的负Eu异常。这些特征显示本区的闪长岩为中性偏基性部分的闪长岩,是福州复式岩体演化早期阶段的产物。

In order to understand the relationship between Changan diorite and the Mesozoic magmatism in the Fuzhou area, the petrography and petrogeochemistry of Changan diorite has been studied. The results show that the Changan diorite is located at the western edge of the Fuzhou basin and has the characteristics of general diorites. The minerals are made of neutral plagioclase, amphibole, biotite, quartz and a small amount of pyroxene at the edge of Changan diorite body. The value of SiO2 is between 52.79 ~ 58.89% with average 54.94%. The AR value is between 1.4 - 1.9% with average 1.5 which indicates that the diorite is belongs to the calc-alkaline series. The trace elements are rich in Rb, Ba, Th, U, K, Pb and low in Nb and Ta. The value of ∑YREE is between 1. 5119. 327 - 169. 148 with average 143. 273. The value of LREE/HREE is 8. 550 - ll. 67 and 9. 435 on average. The value of δEu is between 0. 679 - 1. 005 and 0. 871 on average implying that the fractionation of light rare-earth elements from high rare-earth elements is obvious. Negative Eu anomalies are few. The pattern of REE is a right incline line. These characteristics show that the Changan diorite is intrmediate or has a tendency to be basic in rock property, probably resulted from the early evolution of the Fuzhou complex massif.