伊犁盆地昭苏黄土不同粒径和相态稀土元素特征及其物源指示意义

Rare earth elements characteristics in different grain sizes and phases of Zhaosu loess in Yili Basin and their provenance implications

为了探讨伊犁盆地风成沉积物质来源特征,对伊犁地区昭苏黄土剖面代表性样品各个粒级全岩、酸溶组分和残渣组分中的稀土元素进行了分析。结果表明,各个粒级组分全岩样品的稀土总量(∑REE)的变化范围为114.61~178.37μg·g^(-1),剖面中各个粒级组分稀土球粒陨石标准化配分模式呈轻稀土富集,存在明显的Eu负异常,Ce无明显异常。各个粒级组分酸溶残渣稀土特征与上述全岩特征类似。酸溶组分稀土的上部大陆地壳标准化呈现稳定的中稀土富集。随着各组分粒级变粗,酸溶组分稀土占全岩比例呈现先降低后升高的趋势,即从<2μm组分到16~32μm组分比例渐次降低,而后从16~32μm组分到>63μm渐次升高,这主要反映了以西风为代表的远源输送体系和以近地面风为代表的近源输送体系下两种来源的碎屑碳酸盐稀土的混合。本文不同粒径和赋存形态下稀土元素的特征表明了利用风成沉积物稀土元素反映源区物质特征存在一定复杂性。

In order to explore the provenance of aeolian deposits in Yili Basin, rare earth elements（REE） concentrations in three phases of whole-rock, acid soluble, and acid residue in each grain sizefractions of seven representative samples in Zhaosu loess section are analyzed. Whole rock ΣREE ineach grain size fractions range from 114.61-178.37 μg·g^-1, showing light REE enriched chondritenormalizedpatterns with distinct negative Eu anomaly and undetectable Ce anomaly. REE characteristicof acid residues in each grain size fractions resemble those of whole rock phase. Upper continentalcrust normalized REE concentrations of acid soluble phase showed observed middle REE enriched.Along with increasing grain sizes, the proportions of acid soluble phase in whole rock display initialdecreasing and then increasing variations. More specific, those proportions decreased from 〈2 μm to16-32 μm fractions, then increased from 16 - 32 μm to 〉63 μm fractions, which are the mixing resultsof REE in detrital carbonate derived from distant source transported by the westerly and adjacent source transported by the near-surface wind. The REE characteristic in different grain size and phase exhibitsthe complexity of using REE in aeolian deposits to trace provenance change.