Spinel–olivine magnesium isotope thermometry in the mantle and implications for the Mg isotopic composition of Earth

Homogeneous magnesium isotopic composition of seawater: an excellent geostandard for Mg isotope analysis

“…1(C)). This inconsistency may reflect analytical artifacts and/or sample heterogeneity since different labs worked on different San Carlos olivine grains; however, analyses of different aliquots of homogeneous powder made by homogenizing a large amount of San Carlos olivine also yielded different d 26 Mg values, ranging from À0.55 to À0.19 [10,18,23] (Fig. 1(D)), indicating that heterogeneity is not the primary problem.…”

“…[5,9,10,12,13,16,18,[20][21][22][23][24][25] Both debates may reflect the presence of MC-ICP-MS analytical artifacts in high-precision Mg isotopic analyses conducted at different laboratories. [7][8][9]18,20] Analyses of geostandards BCR-1 and BCR-2 in different laboratories yielded significantly different Mg isotopic compositions ( Fig. 1) [5,9,12,13,[20][21][22][23]26] (e.g.…”

“…26 Mg values, [7,[13][14][15]18,[23][24][25][27][28][29] its use also does not test for sample preparation accuracy and reproducibility, since the pure Mg standard needs no sample preparation as is necessary for natural samples. Reliance on this standard for inter-laboratory comparison leaves the Mg isotope science community open to major problems in accuracy assessment and comparability because sample preparation processes, e.g.…”

“…[7,9,11,14,15,17,19] Nevertheless, debate continues regarding: (1) whether the earth has a chondritic Mg isotopic composition or not, [7][8][9]13,18,20] and (2) the accuracy of Mg isotopic compositions reported by different labs for certain geostandards, such as BCR-1, BCR-2 and San Carlos olivine. [5,9,10,12,13,16,18,[20][21][22][23][24][25] Both debates may reflect the presence of MC-ICP-MS analytical artifacts in high-precision Mg isotopic analyses conducted at different laboratories. [7][8][9]18,20] Analyses of geostandards BCR-1 and BCR-2 in different laboratories yielded significantly different Mg isotopic compositions ( Fig.…”

“…[5,6] For example, a precision of AE0.07% ( 26 Mg/ 24 Mg, 2SD) can be routinely achieved for MC-ICP-MS Mg isotopic analysis, [7] which is sufficient to discriminate mass-dependent Mg isotopic variations in natural samples. [6] Recent high-precision Mg isotopic studies have significantly increased our knowledge of Mg isotope geochemistry by documenting the Mg isotopic variations in the mantle and crustal rocks, [5,[7][8][9][10][11][12][13][14][15][16][17][18] and illuminating the processes that may produce these variations, e.g. igneous differentiation, metamorphic dehydration, and continental weathering.…”