长江三峡坝区花岗岩风化壳化学元素迁移特征

Chemical Element Transferring Features of Weathering Granite Regolith in Three Gorges Dam Region

在长江三峡坝区河谷不同地貌部位系统采样的基础上 ,通过 X射线荧光光谱的化学全量分析及各元素迁移率特征值和强度值的详细计算 ,揭示出不同地貌部位各化学元素的迁移规律 :1长期淹没于水下的河床风化壳 ,易溶的 Ca O、Mg O发生相对富集的现象 ,Al2 O3却呈减少的趋势 ;Fe2 O3的富集率最大 ;2季节性被水浸没的河漫滩风化壳 ,还出现了 K2 O、Mg O含量相对富集的现象 ;3谷坡风化壳是典型的北亚热带地带性风化壳 ,处于化学风化早期到中期的过渡阶段。 4在各种地貌的风化壳中 6.5深度是一个特殊的层位 ,K2 O、 Na2 O对抗现象最为明显 ,即 Na2 O相对富集 ,K2 O相对减少。

The exposure of river valley including riverbed as a result of clearing up sediment and regolith on the foundation of dam in the Three Gorges of the Yangtze River in 1999, river valley including riverbed was exposed which offered a good opportunity to research river valley landforms The chemical element transferring features in different valley landform positions are mainly researched in this paper 1 Sample collection:In lower 100 m of dam foundation, 50 samples were collected along NE42 ° trending cross section of river valley, at 3 different elevations (riverbed, flood plain, valley slope) and 6 typical columnar sections 2 Analysis:Based on the X rays fluorescent slice, weathering ratio, chemical element transferring ratio, the coefficient of average dripping and washing, the intensity of weathering were further calculated in detail 3 Conclusions:(1) In various landform positions of the river valley, the process of desilication is not distinct (2) In riverbed weathering granite regolith, easy soluble CaO and MgO are relatively concentrated on the contrary, Al 2O 3 shows a tendency to decrease The concentrated rate of Fe 2O 3 is the greatest in various landform positions of the river valley (3) In flood plain weathering granite regolith, K 2O and MgO contents are relatively concentrated (4) River valley slope weathering granite regolith is a typical northern subtropical weathering regolith, and its chemical weathering degree is in the transitional period from early phase to middle phase (5) In the upper middle layer of vertical columnar section in riverbed and valley slope weathering granite regolith, there is a concentrated layer of easy soluble elements and a leached layer of concentrated elements (6) Element transferring absolute intensity of riverbed weathering granite regolith is the greatest of three landform positions The order of element transferring relative intensity is flood plain weathering granite regolith > riverbed weathering granite regolith > valley slope weathering granite regolith The above mentioned conclusions indicated that, under certain climate conditions, chemical elements are transferred along with landform and water circulation in weathering granite regolith So, in different landform positions, the transferring law of chemicals is different