一种稀土参数图解新方法:以内蒙古拜仁达坝-维拉斯托闪长岩成因研究为例

A Novelty Method of REE Parameter Diagrams:A Case Study of Petrogenesis of Bairendaba-Weilasituo Dioritoids in Inner Mongolia

稀土元素的示踪作用在地质学、地球化学研究中具有重要意义,稀土参数图解可以揭示岩石的形成机理、条件和成因分类,追踪各种复杂地质作用的演化历史。利用稀土元素参数REE与SiO_(2)、REE与LREE/HREE、δEu与LREE/HREE图解,在内蒙古拜仁达坝-维拉斯托铅锌银多金属矿区从偏基性端元向偏酸性端元演化的闪长岩类野外岩相学观察和室内测试的基础上,发现其全岩稀土参数之间的相关关系,进而结合岩石地球化学数据、稀土参数图解新方法与微量元素聚类分析,判别其闪长岩的成因和岩浆源区。结果显示,拜仁达坝赋矿的闪长岩具有高硅、富钠及较高MgO和Al_(2)O_(3)含量的特征,属钙碱性系列,显示地幔岩浆分异与下地壳熔融岩浆混合的特点;拜仁达坝-维拉斯托闪长岩LREE/HREE-REE和δEu-LREE/HREE曲线显示,稀土高值组端元分别呈负相关和正相关关系,负Eu异常明显,相对富集Rb、Th、U、K等大离子亲石元素,亏损Nb、Ta、Sr、P、Ti等高场强元素,而稀土低值组端元反之。上述特征表明,拜仁达坝-维拉斯托闪长岩为一套活动大陆边缘幔源为主、壳幔混合成因的钙碱性岩浆岩系列。实例研究初步证实,提出的稀土参数图解新方法是有效的,具有较强的普适性,适合在常规的地质科研中完善并推广。

REE parameter diagrams are important tracers for geochemical and geological studies which show potential for the rapid determination of petrogenesis and magma source.By using REE and SiO_(2),LREE and LREE/HREE,δEu and LREE/HREE diagrams of dioritoids,we investigate the correlation among REE parameters taking the Bairendaba-Weilasituo dioritoids as an example.Through field petrological observation and whole-rock geochemical data,new REE parameter diagrams and REE R-type cluster analysis,this paper studied the petrogenesis and magma source.The results show that the Bairendaba-Weilasituo dioritoids have high SiO_(2),Na_(2)O,MgO,and Al_(2)O_(3) contents,and belong to the calc-alkaline series,indicating the mixing source of magma from both the mantle and the lower crust.The high-REE values of the Bairendaba-Weilasituo dioritoids respectively show negative correlation and positive correlation between LREE/HREE-REE andδEu-LREE/HREE,and show obviously negative Eu anomaly.They are enriched in Rb,Th,U,and K,and depleted in Nb,Ta,Sr,P,and Ti,whereas the low-REE values show absolutely contrary characteristics.We concluded that this suite of calc-alkaline dioritoids were originated from the mantle substance dominated by hybrid crust-mantle mixing magma associated with an active continental margin.The developed method can be used for estimating petrogenesis and magma source in Bairendaba-Weilasituo calc-alkaline dioritoids refe-rence materials.This empirical method shows great potential for the rapid determination of petrogenesis and magma source in large batches of samples commonly analyzed for mineral exploration and REE geochemistry studies.