Li同位素组成对太古宙海水相关的表生环境过程的初步限定

研究试图利用Li同位素地球化学对太古代海水相关的表生环境过程进行初步的限定.通过对来自南非Kaapvaal克拉通的海相碳酸盐岩样品进行Li同位素分析,发现在3.0～2.9 Ga期间形成的碳酸盐岩δ7Li值为～+1‰,而在2.6～2.5 Ga期间,碳酸盐岩δ7Li值达到7‰～10‰.经过反演计算得到对应时代的海水Li同位...

Preliminary Definition of Li Isotope Compositions on Surficial Environmental Processes Associated with Archean Seawater

In this study it attempts to use the Li isotope geochemistry to preliminarily limit the surficial environmental processes associated with Archean seawater. It performed Li isotope analysis on marine carbonate samples from the Kaapvaal craton in South Africa and finds that the carbonate shows light Li compositions of~+1‰ during the period of 3.0-2.9 Ga, and increase of +7‰ to +10‰ during the period of 2.6-2.5 Ga. Through inversion calculation, the Li isotope compositions of seawater in the two periods are~+12‰ and~+ 20‰, respectively, which are significantly lower than modern seawater (~+31‰). However, the δ7Li value of seawater during 2.6-2.5 Ga is more than 8‰ higher than that at 3.0-2.9 Ga. As an effective tracer for continental weathering of silicate rocks, Archean seawater shows relatively low δ7Li values, which indicates that the surficial weathering at that age was dominated by the dissolution of source rocks, and secondary minerals were rarely formed. During 3.0-2.5 Ga, the decrease in the overall temperature of the seawater and the increase in the formation of secondary minerals may jointly lead to an increase in the seawater δ7Li value during Late Archean. The study of Li isotopes of Archean carbonate can effectively invert the Li isotopic composition of paleoseawater, and provide new information for understanding the surficial environmental processes related to the Archean seawater.