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Abstract In this study, we demonstrate that it is possible to fit the resilience at the high temperature limit using only the atomic mean square displacement determined from cryogenic temperature single crystal diffraction data. Our method introduces the Debye phonon model, under which the atomic mean square displacement displays quantum behavior at cryogenic temperatures and deviates from a linear temperature dependence. From the resilience of Si extrapolated from cryogenic temperature X‐ray diffraction data, one can calculate the Si isotope fractionation using our recently developed force constants approach. We applied our method to epidote and coesite, which are common minerals in ultra‐high pressure metamorphic rocks, and our predicted Si isotope fractionation lnαSi30/28are consistent with mass spectroscopy observations of Δ30Si in Dabie eclogite and Alps whiteschist. Our results indicate that the geofluid involved in the fluid‐rock interaction in Dabie and Alps orogens doesn't significantly alter the Si‐isotope composition of ultrahigh pressure metamorphism. Our manuscript presents a novel experimental methodology to determine the high‐temperature resilience and equilibrium isotope fractionation factors of silicon in minerals, which can be applied to the metastable upper mantle silicates that are non‐quenchable at high temperatures and room pressure.
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Equilibrium Silicon Isotope Fractionation in Eclogites and Granites Constrained by Single Crystal X‐Ray Diffraction and the Force Constants Approach
Abstract Using our recently developed X‐ray diffraction basedforce constantsapproach, we have determined the equilibrium Si isotope fractionation between omphacite/garnet, quartz/kyanite, and quartz/zircon at temperatures relevant to the petrogenesis. We find that Na strongly affects the Si isotope fractionation between omphacite and garnet. Our results have suggested that the omphacite and garnet in eclogite collected in the Dabie Mountain, as well as the kyanite and its host quartz veins, are isotopically in equilibrium, which further suggests that the Dabie Mountain eclogites and its host veins underwent the same high pressure‐temperature condition during their formation. The Si isotope fractionation determined by our methods, together with published mass spectroscopy measurements, DFT‐CIPW calculations and sigmoid fitting on various felsic granites, have suggested that the Si isotope fraction between zircon and whole rock “saturates” at ∼0.45‰ at 1000 K when the SiO2content in the granite is above ∼70 wt%.
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- PAR ID:
- 10585113
- Publisher / Repository:
- AGU
- Date Published:
- Journal Name:
- Geophysical Research Letters
- Volume:
- 52
- Issue:
- 8
- ISSN:
- 0094-8276
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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- Free Publicly Accessible Full Text
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Accepted Manuscript
- Journal Article:
- https://doi.org/10.1029/2023GL107954
