Temperature and co-crystallization effects on Zr isotopes
Abstract
We undertook Zr isotope measurements on zircon, titanite, biotite, amphibole, and whole rocks from the La Posta pluton (Peninsular Ranges, southern California) together with trace element analyses and U-Pb age measurements to understand the controls on Zr isotope fractionation in igneous rocks, including temperature, crystallization sequence, and kinetic effects. We find large (>0.6‰) Zr isotope fractionations (expressed as δ⁹⁴/⁹⁰Zr) between titanite and zircon forming at approximately the same temperature. Using equilibrium fractionation factors calculated from ionic and ab initio models, we infer the controls on Zr isotope evolution to include the relative order in which phases appear on the liquidus, with titanite fractionation resulting in isotopically lighter melt and zircon fractionation resulting in isotopically heavier melt. While these models of Zr fractionation can explain δ⁹⁴/⁹⁰Zr variations in zircon of up to ∼1.5‰, crystallization order, temperature and presence of co-crystallizing phases do not explain all aspects of the intracrystalline Zr isotopic distribution in zircons in the La Posta pluton or the large range of Zr isotopic values among zircons (>2‰). Without additional constraints, such as knowledge of co-crystallizing phases and a better understand of the true causes of Zr isotope fractionation, Zr isotopes in zircon remains an ambiguous proxy of magmatic evolution.
Additional Information
© 2023 Elsevier Ltd. We thank Mary Reid, Paolo Sossi, and Paul Savage for their helpful reviews which greatly improved this manuscript, Ed Young for help with the ionic model, and Ming-Chang Liu and Andreas Hertwig for assistance with the ion probe. This work was supported by a UCLA Dissertation Year Fellowship and a Geological Society of America student research grant to H.M.K., NSF-EAR 2131632 and 2131643 grants to M.I-M., and by NSF grants EAR-1824002 and MGG-2054892, a Packard Fellowship and Caltech start-up funds to F.L.H.T. The ion microprobe laboratory at UCLA is partially funded by grant EAR-1734856 from NSF's Instrumentation and Facilities program. The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.Attached Files
Supplemental Material - 1-s2.0-S001670372300217X-mmc1.pdf
Supplemental Material - 1-s2.0-S001670372300217X-mmc2.xlsx
Files
Name | Size | Download all |
---|---|---|
md5:24536f7b294274d7484eac55afb3deac
|
358.0 kB | Preview Download |
md5:e710522feafbabc0c88167c7d6af0cb1
|
552.2 kB | Download |
Additional details
- Eprint ID
- 122173
- Resolver ID
- CaltechAUTHORS:20230706-731611100.5
- UCLA
- Geological Society of America
- EAR-2131632
- NSF
- EAR-2131643
- NSF
- EAR-1824002
- NSF
- OCE-2054892
- NSF
- David and Lucile Packard Foundation
- Caltech
- EAR-1734856
- NSF
- Created
-
2023-07-07Created from EPrint's datestamp field
- Updated
-
2023-07-07Created from EPrint's last_modified field
- Caltech groups
- Division of Geological and Planetary Sciences