强烈风化条件下玄武岩发育土壤的元素地球化学特征

海南岛地处热带,晚第三纪以来喷发的玄武岩上广泛发育铁铝土。土壤剖面的常量元素、微量元素、化学风化指标及元素迁移率的研究表明:(1)土壤Al2O3、Fe2O3、SiO2和TiO2元素富集,水溶型元素强烈淋失,高CIA值和低ba值均显示其经历强烈的化学风化作用;(2)元素含量和元素迁移率的计算结果显示,温带难迁移的Ti、Zr、Hf和Nb等元素在高温多雨的热带环境下也会发生强烈的淋失,究其原因主要受湿热环境下高有机质含量和强酸性条件影响;(3)Fe、Al、Cu和Ni等元素的迁移则反映了基岩发育土壤自下而上的风化渐进特征;(4)表层土壤K、Na和Sr元素的强烈富集则与大气沉降有关。

Mobilization and Redistribution of Elements in Soils Developed from Extremely Weathered Basalts on the Hainan Island

The Hainan Island is located in a tropical zone and most of the ferralsol profiles that developed on Neogene basalt in this region have undergone extensive weathering.Major,trace and organic elements of a laterite profile were reported to investigate elements mobilization and redistribution in tropical regions.The results indicate that SiO2,Al2O3 and Fe2O3 are the dominant chemical components,CaO,Na2O,MgO and K2O concentrations are extremely low and CIA and CIW values are high for all soil samples.These results suggest that the profile has undergone extremely strong weathering.The strongly acidic environment and organic matter(OM) can remarkably improve the transfer of insoluble elements.As for the general conservative elements during incipient chemical weathering,such as Ti,Zr,Hf and Nb,the removals are up to 30%~40% in the upper profile;and Fe,Al,Cu and Ni are removed from the upper profile,transferred downwards,and then precipitated in the lower profile.In addition,atmospheric inputs,including sea salt aerosol and dust,have a profound effect on the budgets of elements that are susceptible to leaching-induced losses(e.g.K,Na and Sr).The overall elemental behaviors in this profile suggest that organic matter and atmospheric inputs play a very important role in the mobilization and redistribution of elements during extreme weathering in tropical regions.