Average iron isotopic compositions of the upper continental crust:constrained by loess from the Chinese Loess Plateau

Iron isotopic composition of the upper continental crust（UCC） is critical for understanding Fe mobilization and migration through the Earth. Because rocks exposed at Earth's surface have heterogeneous δ56Fe, finegrained clastic sediments can be used to estimate the average composition of UCC. In this study, we report δ56Fe of loess-paleosol sequences from Yimaguan, Chinese Loess Plateau（CLP）, to constrain the average Fe isotopic composition of UCC. The loess-paleosol sequences in this area formed in glacial-interglacial cycles and are characterized by varying degrees of weathering. Our data show that the loess-paleosol layers have extremely homogeneous Fe isotopic compositions with δ56Fe ranging from 0.06‰ to 0.12‰, regardless of variations in the major element composition and weathering intensity. Our study indicates that since Fe isotopes are not significantly fractionated during loess deposition, the loess can be regarded as representative of UCC. It follows that the average δ56Fe of UCC is 0.09‰± 0.03‰（2SD）, consistent with previous estimates based on igneous rock data.