鸭绿江端元粒度分级样品常量元素控制因素分析及物源识别

Provenance and controlling factors of major elements in graded components of sediments from the Yalu River

对鸭绿江河口表层沉积物陆源组分进行了水动力敏感粒度分级,以消弱"粒度效应"对沉积物地球化学组成的影响。通过多元统计方法,对不同粒级样品内常量元素含量特征、控制因素、源区特征等内容进行了探讨,并与全样测试结果进行对比分析。结果表明:源区化学风化程度是控制常量元素分布的主要因素,"粒度效应"和表生环境下的自生作用对常量元素的分布也有一定的控制作用,但"粒度效应"主要控制8μm以下样品内元素分布;源区目前处于以斜长石风化为主的中等化学风化程度阶段,风化产物未遭受钾交代影响;Al2O3、Fe2O3、MgO、MnO、TiO2、P2O5六种元素在>63μm、32~63μm和8~32μm 3个粒级内含量相近,8μm以下样品随粒级减小元素含量显著增加,CaO、Na2O两种元素在各粒级内含量分布特征与上述6种元素相反,高K2O含量且未受"粒度效应"控制,可作为鸭绿江端元的指示性元素。根据流域岩性特征分析,>2μm粒级样品可能主要来自鸭绿江中下游地区变质基底和花岗质侵入体的风化产物;而<2μm粒级样品则可能主要来自鸭绿江上游地区基性侵入体的风化产物。此外,对比分析还表明,全样测试结果仅相当于分粒级样品的均值水平,极大地掩盖了不同粒级内元素地球化学特征的差异性和规律性。因此,在利用全样地球化学特征进行物源示踪时需综合考虑。

Terrigenous surface sediments taken from the Yalu River estuary were separated into grades in order to reduce the control of grain size on sediment geochemistry.With the statistical method for multivariate,major elements content,controlling factors and provenance characteristics of samples were discussed grade by grade in this paper,compared with the original testing data for bulk samples.The results show that the chemical weathering intensity in the provenance is the major factor controlling the distribution patterns of major elements.Grain size and authigenesis also play certain roles in control over the distribution patterns of elements in the samples smaller than 8μm.The provenance is now suffering from moderate chemical weathering characterized by the weathering of plagioclase and never affected by potassium replacement.The differences in Al2O3、Fe2O3、MgO、MnO、TiO2、P2O5 contents in the fractions>63μm、32~63μm and 8~32μm are rather small,but increased significantly in the fraction smaller than 8μm.The contents of CaO and Na2O in each fraction are opposite to those of the above six elements,suggesting the consistency of lithology of provenance rocks.The K2O,which can be used as an indicative element,remains high in each grain fraction.According to the lithologic characteristics of provenance,the components>2μm are mainly coming from metamorphic basement and granitic intrusive rocks at the middle and lower reaches,while the components<2μm are mainly from the weathering products of basic intrusive rocks from the upper reach.Comparative analysis also suggests that the original bulk sample test results are close to the average of graded samples.As the result,the differences and change trend of geochemical characteristics between grades are hard to be observed.Therefore,integrated consideration is required in case the original geochemical data of bulk samples are used to trace the provenance.