THE ELEMENTAL TRANSPORT FEATURES OF RED EARTH FROM TX-SECTION AND ITS PALEO-CLIMATIC IMPLICATIONS
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摘要: 金衢盆地汤溪红土剖面主量元素地球化学特征研究揭示:(1)主量元素组成以SiO2、Fe2O3、Al2O3为主,K、Na、Ca、Mg等易溶组成含量很低。SiO2含量的平均值略低于UCC均值,Fe2O3、Al2O3含量则略高于UCC均值,符合亚热带地区风化成土中硅酸盐矿物大量转化为黏土矿物的脱硅富铝化过程的特征。(2)汤溪红土化学风化强烈,全岩样品的CIA指数(化学蚀变指数)高达89.10%~89.68%,ba (风化淋溶指数)系数为0.19~0.21。烧失量LOI与SiO2/Al2O3、SiO2/R2O3、CIA、ba系数之间均存在线性相关,对红土脱硅富铝和化学淋蚀程度具有一定指示意义。LOI值越大,脱硅富铝程度越强。(3) SiO2/Al2O3和SiO2/R2O3较好地指示了TX剖面从网纹红土至均质红土风化强度渐弱的趋势,TiO2-Al2O3、TiO2-Fe2O3、TiO2-SiO2、Al2O3-K2O等元素对协变分析也得出了同样的结论,网纹红土风化程度较均质红土更强。(4)以Zr为参比的元素剖面迁移特征表明,Fe2O3、Al2O3沿剖面向下呈相对富集态势,SiO2则相反,呈亏损态势;Na、P沿剖面均呈迁出特征,K、Mg、Ca呈波动式迁出,个别层段有轻微富集;Mn沿剖面向下呈亏损态势,与铁呈反向变化;Ti相对于Zr的迁移虽有波动但迁移量最小。τj,w系数总体上也反映TX剖面从上至下脱硅富铝化程度增强的趋势。Abstract: Red earth is an important carrier to record paleo-climatic and paleo-environmental evolution. The major element compositions from TX red earth section in Jinhua-Quzhou basin show that (1) SiO2,Fe2O3 and Al2O3 are dominated chemical components for all samples, the average content of SiO2 is lower than that of UCC, those of Fe2O3 and Al2O3 are both higher than that of UCC, and K, Na, Ca, Mg, and P are very low. So, TX-section has typical desilica-allitization features. (2) High CIA value and low Ba value both indicated stronger chemical weathering of TX-section, and its loss ignition(LOI) is linear related to CIA, Ba, SiO2/Al2O3, and SiO2/R2O3. To some degree, LOI may be regarded as an indicator for desilica-allitization of TX red earth. The higher LOI is, the stronger desilica-allitization. (3) SiO2/Al2O3 and SiO2/R2O3 indicate the trend of chemical weathering of TX-section:the degree of weathering increasing down-section, and being further confirmed by TiO2-Al2O3,TiO2-Fe2O3,TiO2-SiO2, and Al2O3-K2O distributions, from which we can see that chemical weathering degree of plinthitic red earth was stronger than that of typical red earth. (4) Using Zr as calculation strain, mass-balance equations were applied to geochemical analyses to show that Si moves out and Fe and Al are enriched in the plinthitic red earth unit. The τj,w coefficient also responded to the trend of weathering weakening upward.
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Key words:
- Quaternary red earth /
- major elements /
- elemental transport /
- Jinhua-Quzhou basin
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