Table 1 and Table S1-S2
Description
Table 1 Iron isotopic compositions of whole-rock samples, amphibole separates and geostandards (‰). Table S1 Table S1 Whole-rock major (wt.%) and trace (ppm) element compositions of the Milin samples. Table S2 Table S2 Major compositions ofamphiboles from the Milin samples determined by EPMA (wt.%) and corresponding temperatures.
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Iron isotope analysis of whole rocks and separate minerals were conducted at the Wuhan Sample Solution Analytical Technology Co., Ltd, China. Approximately 50 mg of sample powders was weighed into in-house PTFE-lined steel bombs and dissolved by step-wise acid digestion. Fe was purified by a single column ion-exchange chromatography using Bio-Rad strong anion resin AG-MP-1M following the method described by Liu et al. (2014). Briefly, samples were loaded onto the pre-cleaned column. Then, a large volume of 8 M HCl was used to completely remove the matrices. Quantitatively recovery of Fe was achieved by rinsing of 16 ml 0.5 M HCl. The obtained Fe recovery is >99% based on the elution curve test of geological rock standards. The total procedural blanks are typically no more than 10 ng based on long-term monitoring, which are considered negligible. The Fe fractions were dried and dissolved in HNO3 and H2O2 to eliminate the possible effects from organic materials. Iron isotopic ratios were measured using the Neptune plus MC-ICP-MS. Samples were introduced at a concentration of 1.5 ppm in 2% HNO3 using wet plasma method combine with a highly sensitive Jet+X cone setting, yield a typical 20V signal for 56Fe beam. Standard-sample bracketing (SSB) method was used in order to correct for instrumental mass fractionation. Fe isotopic data are reported in standard notation in per mil relative to standard reference material IRMM-014: δiFe=[(iFe/54Fe)sample/ (iFe/54Fe) IRMM-014-1]×1000, where i= 56 or 57. The long-term external reproducibility for δ56Fe measurements is better than ±0.05 ‰ (2SD) based on repeated analyses of natural samples and synthetic solutions. Three international rock standards (BCR-2, BHVO-2, GSP-2) were analyzed along with samples for Fe isotopes in this study. The obtained results well agree with reported δ56Fe value from previous studies (Li et al., 2019; Liu et al., 2014).