摘要
辽宁宽甸、河北汉诺坝和福建明溪碱性玄武岩中的普通辉石和石榴石巨晶MgO、FeO、CaO含量的变化呈现了矿物的结晶分异趋势。从高温到低温晶出辉石的REE分馏程度不断增高,石榴石REE分馏程度不断降低,即两种巨晶中的LREE不断增加,而HREE逐渐减少,矿物的稀土模式曲线出现交叉现象。 用宽甸和汉诺坝任一层玄武岩作为液相与巨晶所计算的REE分配系数D_(矿物)^(REE)-玄武岩值,均与实验值相近,因而它不能旁证载体玄武岩就是巨晶的母岩浆。辉石晶出后残余岩浆比例Ⅰ值计算表明,母岩浆体可能是一个相对体积不太大的、主元素和REE成分不断变化的相对独立的地质体。
Reported in this paper are the major elements and rare-earth elements (REE) of Al-au-gite and garnet megacrysts in alkali basalts from Kuandian, Liaoning Province, Hannuoba, Hebei Province and Mingxi, Fujian Province. MgO, CaO and FeO in the megacrysts from Kuandian and Mingxi show a tendency of crystal differentiation. LREE tend to increase while HREE to decrease from high-temperature megacrysts to lowtemperature ones, i. e., he REE fractionation degree of Al-augites increases while that of garnets decreases, leading to the appearance of cross REE patterns. By using any layer of basalt from Hannuoba as a liquid phase, all the calculated DREE mineral-liquid values are close to the experimental results. It is suggested that the similarity between the calculated DREE mineral-liquid values and the experimental values could not be evident enough to permit us to draw such a conclusion that the host basalt is the primary magma of megacrysts. The primary magma of megacrysts is closely related with the volcanic process of alkali basalts and might be a relatively independent mass small in volume, of which the REE contents varied during the crystallization process.
出处
《地球化学》
CAS
CSCD
北大核心
1991年第2期153-163,共11页
Geochimica
