广平花岗岩风化壳稀土元素的地球化学特征及意义

Rare Earth Elements Characteristics and Significance of Guangping Granite Weathering Crust

钦杭成矿带南段广平花岗岩为晚侏罗世黑云母花岗岩,对其风化壳中残积层和全风化层进行了稀土元素分析。结果表明,两者ΣREE(包括Y)含量为387.67×10-6~953.22×10-6,平均608.76×10-6;轻稀土元素(LREE)中等-强富集,LREE/HREE=2.08~6.70,平均为3.43。残积层稀土总量为387.67×10-6~626.71×10-6,平均512.46×10-6;LREE强烈富集,LREE/HREE=3.75~6.70,平均4.94;Ce弱-中等负异常。相比之下,全风化层稀土总量为452.41×10-6~953.22×10-6,平均为640.86×10-6;LREE中等富集,LREE/HREE=2.08~4.75,平均为2.97;Ce表现为强烈负异常。两者均具有中等Eu异常。岩体风化程度不同,其稀土总量及配分模式差异明显,且具有一定规律。多元统计学结果显示,该岩体风化壳稀土元素可分为两类,Ce元素特征与其他元素明显不同。

Guangping granite is late Jurassic biotite granite,which is located in Qinzhou-Hangzhou metallogenic belt. The results of the rare earth elements of eluvium and fully weathered horizons show that the content of total rare earth elements(including Y) is from 387. 67×10-6 to 953. 22×10-6(average of 608. 76×10-6),with weak-moderate enrichment of LREE. The ratio of LREE/HREE is 2. 08 ~ 6. 70,with an average of 3. 43. Eluvium and fully weathered horizons have different rare earth distribution patterns. For eluvium,the content of total rare earth is from 387. 67 × 10-6 to 626. 71 × 10-6(average of 512. 46×10-6),the ratio of LREE/HREE is 3. 75 ~ 6. 70,with an average of 4. 94. The samples have a very intense enrichment of LREE and weak-moderate negative Ce anomalies. For fully weathered horizon,the content of total rare earth is from 452. 41×10-6 to 953. 22×10-6(average of 640. 86×10-6),the ratio of LREE/HREE is 2. 08~4. 75,with an average of 2. 97. There is a moderate enrichment of LREE in the fully weathered horizon and a strong negative anomaly for Ce. Both of them have a moderate negative anomaly in Eu. The difference of weathering degrees determines their distinct ∑REE contents and REE distribution patterns. Multivariate statistical results show that the rare earth elements of Guangpinggranite weathering crust can divided into two types. Ce has an obviously different characteristics with other rare earth elements.