中国东部玄武岩风化土壤的粘土矿物及碳汇地球化学研究

Characteristics of Clay Minerals and CO_2 Consumption Rates of Weathering Profiles from Cenozoic Basalts in Eastern China

玄武岩风化是大气CO2的一个主要碳汇过程,气候条件是影响玄武岩风化和固碳速率的重要因素。该文选择中国东部不同气候带的新生代玄武岩典型风化剖面,进行了粘土矿物和常量元素分析。结果显示,在内蒙古—海南岛的采样区间内,随着气候条件由干冷向暖湿转化,风化剖面中粘土矿物组合呈现蒙脱石+伊利石+高岭石→蒙脱石+高岭石→高岭石+三水铝石的转变。剖面中土壤元素得失状况也显示出相应的规律,由于存在粉尘输入与风化淋滤作用的综合影响,在干冷的内蒙古地区,粉尘对于Ca,K,Na,Si等元素的输入量大于这些元素的淋失量;在山东地区,Ca,K,Na元素开始快速淋失,大于粉尘的输入量;在苏皖地区,Si元素的淋失量开始小于粉尘输入量;而在湿热的海南地区,风化作用强烈,Si显示出大量淋失的特点,碱性元素几乎全部流失。根据元素的相对得失率和北方粉尘平均组分的校正,初步估算了研究区内玄武岩风化对大气CO2的消耗速率,其数值在5.37～181.00t(km2.a)之间,与Dessert等(2003)的研究结果大致相当。

Basalt weathering acts as a major atmospheric CO/sink. Climate conditions have important effect on basalt weathering and CO2 consumption rate. In this study, typical weathering profiles of Cenozoic basahs from different climatic zones in eastern China were selected to conduct clay mineral analysis and major elements measurement. Results show that as climate changes from dry-cold in the north to humid-hot in the south in the studied region, the assemblages of clay minerals in the profiles transfer as follows： smectite＋ illite＋ kaolinite --, smectite＋ kaolinite --＋ kaolinite＋ gibbsite. Chemical composition of the weathered samples exhibits correspondent concentrations of overlying pare the soils in Shandong and Si is changes. Ca, K, Na and Si in the soils are relatively enriched due to dust input compared to the nt basaltic rocks in Inner Mongolia under dry-cold climate. Ca, K and Na begin to be leached in leached in Jiangsu and Anhui under temperate climate. Si is leached heavily while the alkaline elements are almost lost in soils due to intensive weathering in Hainan under humid-hot climate. According to relative percentage change of elements and normalization using average composition of dust in northern China, CO2 consumption rate from basalt weathering in eastern China can be estimated about 5.37-181.00 t/km2 · yr, which is within the similar range provided by Dessert et al.＇s （2003）.