摘要
This study presents high-precision analyses of stable potassium(K)isotope ratio using the recently-developed,collision-cell multi-collector inductively coupled plasma mass spectrometry(CC-MC-ICP-MS,Nu Sapphire).The accuracy of our analyses is confirmed by measuring well-characterized geostandards(including rocks and seawater).Our results are consistent with literature values and a precision of 0.04‰(2SD)has been achieved based on multiple measurements of BCR-2 geostandard over a six-month period.We also evaluate factors that may lead to artificial isotope fractionations,including the mismatches in K concentration and acid molarity between samples and bracketing standards,as well as potential matrices.As the K adsorption capacity of AGW50-X8(200-400 mesh)is reduced with an increasing amount of matrix elements,less than 150µg K was loaded during the column chemistry.To evaluate the potential use of K isotopes as an archive of paleo seawater composition,δ^(41)K values of an international seawater standard(IAPSO),a Mn-nodule(NOD-P-1),and two iron formation standards(FeR-2 and FeR-4)are reported.The δ^(41)K value of IAPSO is consistent with other seawater samples reported previously,further substantiating a homogeneous K isotopic distribution in modern global oceans.The K isotopes in Mn-nodule(NOD-P-1:−0.121±0.013‰)and iron formation samples(FeR-2:−0.538±0.009‰;FeR-4:−0.401±0.008‰)seem to be an effective tracer of their formation genesis and compositional changes of ancient seawater.Our results suggest that high-precision measurements of stable K isotopes can be routinely obtained and open up a large variety of geological applications,such as continental weathering,hydrothermal circulation and alteration of oceanic crust.
基金
financially supported by the Experimental Technology Innovation Fund of the Institute of Geology and Geophysics,Chinese Academy of Sciences(Grant No.TEC 202103)
the Youth Innovation Promotion Association,Chinese Academy of Sciences。
