摘要
宁镇山脉岩浆演化到晚期花岗岩时,稀土元素丰度明显降低,出现一种与大多数情况相反的规律,它揭示了花岗岩类中的一个较普遍的问题,即存在着双模式;。其机理为上地幔不均匀性和部分熔融程度差异所致。并认为花岗岩类稀土元素的演化多样性与成因类型复杂性有关。
As the magmatic evolution reaches to the late granite period in Nanjing—Zhengjiang mountains, the content of rare earth element in granite are remarkablly decreased reflecting a reversed law com- pared to the most phenomena.It has revealed a quite common problem in granite in China,i.e the ex- istence of“bimodality”.The reason is inhomogeneons upper mantle and differential melting.The paper studies the relationships between rare earth element contents and the contens of SiO_2,CaO,P_2O_5 and the significances of apatite,Kd value of each kind of minerals,La/Sm-La,Sm/Nd,geological behavior of Eu,fractionation of heavey and light rare earth elements,variation of total content of rare earth ele- ment and the constitutional model of rare earth elements. The paper concluded that the varity of rare earth element evolution of granite is closely related to the complexity of genetic type of granite.The reason for the decrease of rare earth element contents from basic to acidic rocks is considered to bc increased melting degree.The initial melting magma is an- desire.Then,as the molten mass goes up with the temperature increased,the melting magma becomes dacite and rhyolite.The genetic type of granite in Nanjing—Zhengjiang mountains belongs to transi- tional crustal syntexis magma(I—type)which is in accordence with the model of rare earth element evolution.
出处
《江苏地质》
1991年第4期193-199,共7页
Jiangsu Geology
