黄河和长江沉积角闪石亲石元素地球化学特征对比与物源辨识

Comparison of Geochemical Characteristics of Lithophile Elements of Amphibole: Identification of estuarine sediment provenance, Huanghe River and Changjiang River

为辨识黄河和长江入海沉积物中角闪石的物源差异,对采自黄河口段、长江口段以及废黄河口和苏北沿岸,共26个样点、38组粒度粗细不同的碎屑角闪石进行了矿物元素地球化学测试,获得了这些角闪石群体的50种常量和微量元素含量值。结果表明:不同粒级测量的同源角闪石元素含量除少数大离子活泼元素相对偏差较大之外,大部分元素含量差异性较小,说明来自黄河与长江角闪石的物源属性具有各自较一致共性,粒度效应不明显。两个河口的群体角闪石地球化学具有高Ca、Mg和低Na、K特征,大离子亲石微量元素Sr、Ba、Rb、Pb、Th、U元素与占据角闪石结构的A和B位的K、Na、Ca等常量元素类质同象广泛,这些大离子微量元素在同源样品内波动变异较大,在异源样品间具有中等至较大的均值差异。高场强亲石元素如Zr、Hf、Sc、Y、REE、Nb、Ta等,在角闪石结构中与占据C位的Fe、Mg、Al、Ti、Mn等常量元素之间进行复杂的类质同象替代,它们的含量相对稳定,同源样品内部变异较小,异源样品之间多种元素含量及其元素间的比值显示出较大的差异性,尤其是Be、Y、Zr、Hf和Sm含量以及Zr/Sc、Zr/Rb、Zr/Nb、Zr/Y、Y/Hf、K/Nb、Sc/Hf、Y/Nb、Rb/Hf等比值在黄河和长江角闪石中呈现集团式显著差异,可作为物源识别指标。多组元素比值散点图有明显定性识别河源矿物的功能,采用化学质量平衡法源解析,利用多种高场强微量元素含量值和最小二乘法计算,可实现物源的定量评估。

Samples from 26 locations on the Huanghe River Estuary,the Changjiang River Estuary,the abandoned Huanghe River Estuary and the northern Jiangsu coast were analyzed to identify the provenances of amphibole in sediments from the Huanghe and Changjiang Rivers. Thirty-eight groups of different-size detrital amphibole particles were tested by element geochemistry(ICP-OES and ICP-MS). Fifty major and trace element contents were obtained for every amphibole group. The results show homologous amphibole element content for the different particle sizes. Except for the relatively large deviation of a few large ion-active elements,most of the element content differences are relatively small. This indicates that the provenances of the amphiboles from the Huanghe River and Changjiang River have individual characteristics in common. The collective geochemistry of amphibole from the two estuaries showed high Ca,Mg,low Na,K content. The large-ion lithophile elements occupy the A and B sites of the amphibole structure,and the constant elements K,Na,Ca and trace elements Sr,Ba,Rb,Pb,Th,U etc. are closely related,and have a wide range of isomorphism. These large-ion trace elements fluctuate greatly in the homologous samples,with medium to large average differences between heterogeneous samples. The high-field-strength profile elements(e.g.,Zr,Hf,Sc,Y,REE,Nb,Ta,etc.)have undergone complex isomorphic substitution in the structure of the amphibole;the constant elements(e.g.,Fe,Mg,Al,Ti and Mn)occupy the C sites. Their content is relatively stable,with only small internal variation in homologous samples. In heterogeneous samples the content of various elements and the ratio between elements differ greatly,especially the contents of Be,Y,Zr,Hf and Sm,and the ratios of Zr/Sc,Zr/Rb,Zr/Nb,Zr/Y,Y/Hf,K/Nb,Sc/Hf,Y/Nb and Rb/Hf. These show significant group differences in the amphiboles from the Huanghe River and from the Changjiang River,which is useful for indicating provenance. Scatter plots of the ratios between multiple-group elements act to qualitatively identify source minerals,and multiple high field-strength trace element content allows a quantitative assessment of the provenance by using chemical mass balance source analysis and a least-squares algorithm.