Sn isotope data for UCC

Stable Sn isotope ratios are emerging as a novel tracer for a wide range of geological processes, however, the Sn isotopic baseline of the upper continental crust (UCC) is not yet well-constrained. Here, we report high-precision Sn isotope data of a wide range of UCC samples, including granites, pegmatites, and sediments, to document the Sn isotopic composition of the UCC. Significant variations in δ122/118Sn3161a (per mil deviation in 122Sn/118Sn relative to NIST 3161a) values are revealed for I-type (δ122/118Sn3161a = 0.025±0.026 to 0.495±0.046‰, N=20) and S-type (δ122/118Sn3161a = 0.156±0.018 to 0.501±0.075‰, N=22) granites. More extreme Sn isotope variability is observed from pegmatites, which have δ122/118Sn3161a of 0.256±0.047 to 0.930±0.049‰ (N=13). The δ122/118Sn3161a of I-type granites decrease with declining TFe2O3 (total Fe as Fe2O3) and MgO contents and are attributed to the segregation of Fe-bearing minerals. The Sn isotope variation of S-type granites likely arises from source heterogeneity. The Sn isotope variability of pegmatites may reflect fluid activities. In contrast, the loess samples display homogeneous δ122/118Sn3161a (0.132±0.034‰ to 0.239±0.020‰, N=20) that show no correlation with the degree of chemical weathering, suggesting that loess is representative of the average Sn isotope composition of the UCC. The δ122/118Sn3161a of modern sediments and sedimentary rocks range from 0.080‰ to 0.490‰ (N=25). The Sn isotope variations of modern sediments and sedimentary rocks may be related to chemical weathering or sediment provenance. Based on the lithology-weighted average δ122/118Sn3161a of UCC samples (41 granites and 45 sediments) in this study, the δ122/118Sn3161a value of the UCC is estimated to be 0.233±0.099‰, providing a reference point for further applications.