大陆地壳风化亏损的碳循环限定  

Carbon Cycle Restrained Quantification of Weathering Depletion in Making Continental Crust

作　　者：杨瑞钰 李高军 陈骏[1] YANG Ruiyu;LI Gaojun;CHEN Jun(Key Laboratory of Surficial Geochemistry of Ministry of Eductation,Nanjing University,Nanjing 210023,Jiangsu,China)

机构地区：[1]南京大学表生地球化学教育部重点实验室,江苏南京210023

出　　处：《地球科学与环境学报》2018年第2期155-161,共7页Journal of Earth Sciences and Environment

基　　金：国家自然科学基金项目(41730101)

摘　　要：大陆地壳安山质成分的形成原因一直是学界关注的问题。地表风化作用可将易溶元素自大陆地壳淋滤至海洋进入洋壳,并随俯冲作用返回地幔,因此,风化作用可能是安山质大陆地壳的形成原因之一。但是风化作用在大陆地壳成分演化过程中的实际贡献难以量化。大陆风化通量受控于地幔CO_2排气作用,基于碳循环可以间接计算大陆地壳风化亏损。采用Hofmann地幔两阶段熔融模型限定大陆地壳原始组成,通过大陆沉积CaCO_3的总量以及大陆地壳风化过程中Mn、Fe、Mg、Na、P、Li及Sr等7种元素含量与Ca含量的比值计算各易溶元素的风化通量。结果表明,这7种元素的大陆风化通量恰好匹配大陆地壳中各自的风化亏损量,风化作用在大陆地壳成分演化过程中具有重要影响。The cause leading to the andesitic composition of the continental crust is enigmatic.Soluble elements are leached out by chemical weathering from continents to oceans,and return to mantle through subduction,hence,continental weathering may be one possible explanation for the formation of andesitic continental crust.However,the contribution of weathering process remains difficult to be quantitatively constrained.As continental weathering is primarily controlled by p(CO 2),the deficit of continental weathering can be indirectly calculated by carbon cycle restraint.The two-stage mantle melting model proposed by Hofmann was used to constrain the primary composition of the continental crust;specifically,based on total continental calcite in sediments,and Mn,Fe,Mg,Na,P,Li,Sr corresponding to their molar ratios with Ca in weathering process following the elemental mass balance,the weathering fluxes were calculated.The results show that the depletion of the above 7 elements is consistent with their fluxes during weathering process,suggesting chemical weathering may have major impacts on the compositional evolution of the continental crust.

关 键 词：元素地球化学 大陆地壳 大陆风化 碳循环 元素平衡 易溶元素 地幔熔融 安山质成分 

分 类 号：P595[天文地球—地球化学] P591.1[天文地球—地质学]