TY - JOUR

T1 - Mass-independent Sn isotope fractionation and radiogenic 115Sn in chondrites and terrestrial rocks

AU - Bragagni, Alessandro

AU - Wombacher, Frank

AU - Kirchenbaur, Maria

AU - Braukmüller, Ninja

AU - Münker, Carsten

N1 - Funding Information: We thank the associate editor Zaicong Wang for editorial handling and Zhengbin Deng and two anonymous reviewers for providing comments and criticism that helped significantly to improve the manuscript. We thank Steffen Happel (Triskem) for providing information and material about the TBP resin. We also thank John Molloy (NIST) for information on SRM 3161a and SRM 371. We thank Addi Bischoff (University of Münster), Erik Strub (University of Cologne), Glenn McPherson and Tim McCoy (Smithsonian Institute) for providing chondrite samples. This work benefitted from lively and prolific discussions in the geochemistry group of Cologne (J. Tusch, P. Sprung, B. Elfers, E. Hasenstab, M. Pfeiffer, F. Kurzweil, C. Obert, R.O.C Fonseca). We also want to thank Xueying Wang for helpful information during the development of the analytical procedure. This work was supported by the 397 European Commission through ERC grant No. 669666 “Infant Earth” to CM.

PY - 2023/3/1

Y1 - 2023/3/1

N2 - Tin has ten stable isotopes, providing the opportunity to investigate and discriminate nucleosynthetic isotope anomalies from mass-dependent and mass-independent isotope fractionation. Novel protocols for chemical separation (based on TBP-resin) and MC-ICP-MS analyses are reported here for high precision Sn isotope measurements on terrestrial rocks and chondrites. Relative to the Sn reference standard (NIST SRM 3161a), terrestrial basalts and chondrites show isotope patterns that are consistent with mass-dependent and mass-independent isotope fractionation processes as well as with 115Sn radiogenic ingrowth from 115In. Two different mass-independent isotope effects are identified, namely the nuclear volume (or nuclear field shift) and the magnetic isotope effect. The magnetic isotope effect dominates in the two measured ordinary chondrites, while repeated analyses of the carbonaceous chondrite Murchison (CM2) display a pattern consistent with a nuclear volume effect. Terrestrial basalts show patterns that are compatible with a mixture of nuclear volume and magnetic isotope effects. The ultimate origin of the isotope fractionation is unclear but a fractionation induced during sample preparation seems unlikely because different groups of chondrites show distinctly different patterns, hence pointing towards natural geo/cosmochemical processes. Only the carbonaceous chondrite Murchison (CM2) shows a Sn isotope pattern similar to what expected for nucleosynthetic variations. However, this pattern is better reproduced by nuclear volume effects. Thus, after considering mass-independent and mass-dependent effects, we find no evidence of residual nucleosynthetic anomalies, in agreement with observations for most other elements with similar half-mass condensation temperatures. Most chondrites show a deficit in 115Sn/120Sn (typically −150 to −200 ppm) relative to terrestrial samples, with the exception of one ordinary chondrite that displays an excess of about +250 ppm. The 115Sn/120Sn data correlate with In/Sn, being consistent with the β− decay of 115In over the age of the solar system. This represents the first evidence of the 115In-115Sn decay system in natural samples. The radiogenic 115Sn signature of the BSE derives from a suprachondritic In/SnBSE, which reflects preferential partitioning of Sn into the Earth's core.

AB - Tin has ten stable isotopes, providing the opportunity to investigate and discriminate nucleosynthetic isotope anomalies from mass-dependent and mass-independent isotope fractionation. Novel protocols for chemical separation (based on TBP-resin) and MC-ICP-MS analyses are reported here for high precision Sn isotope measurements on terrestrial rocks and chondrites. Relative to the Sn reference standard (NIST SRM 3161a), terrestrial basalts and chondrites show isotope patterns that are consistent with mass-dependent and mass-independent isotope fractionation processes as well as with 115Sn radiogenic ingrowth from 115In. Two different mass-independent isotope effects are identified, namely the nuclear volume (or nuclear field shift) and the magnetic isotope effect. The magnetic isotope effect dominates in the two measured ordinary chondrites, while repeated analyses of the carbonaceous chondrite Murchison (CM2) display a pattern consistent with a nuclear volume effect. Terrestrial basalts show patterns that are compatible with a mixture of nuclear volume and magnetic isotope effects. The ultimate origin of the isotope fractionation is unclear but a fractionation induced during sample preparation seems unlikely because different groups of chondrites show distinctly different patterns, hence pointing towards natural geo/cosmochemical processes. Only the carbonaceous chondrite Murchison (CM2) shows a Sn isotope pattern similar to what expected for nucleosynthetic variations. However, this pattern is better reproduced by nuclear volume effects. Thus, after considering mass-independent and mass-dependent effects, we find no evidence of residual nucleosynthetic anomalies, in agreement with observations for most other elements with similar half-mass condensation temperatures. Most chondrites show a deficit in 115Sn/120Sn (typically −150 to −200 ppm) relative to terrestrial samples, with the exception of one ordinary chondrite that displays an excess of about +250 ppm. The 115Sn/120Sn data correlate with In/Sn, being consistent with the β− decay of 115In over the age of the solar system. This represents the first evidence of the 115In-115Sn decay system in natural samples. The radiogenic 115Sn signature of the BSE derives from a suprachondritic In/SnBSE, which reflects preferential partitioning of Sn into the Earth's core.

KW - Sn

KW - Mass-independent isotope fractionation

KW - Moderately volatile elements

KW - Nucleosynthetic anomalies

KW - Tin isotopes

UR - http://www.scopus.com/inward/record.url?scp=85146697128&partnerID=8YFLogxK

U2 - 10.1016/j.gca.2023.01.014

DO - 10.1016/j.gca.2023.01.014

M3 - Article

AN - SCOPUS:85146697128

VL - 344

SP - 40

EP - 58

JO - Geochimica et cosmochimica acta

JF - Geochimica et cosmochimica acta

SN - 0016-7037

ER -