9:15 AM - 9:30 AM
[S1-02] Post-entrapment density modification of fluid inclusions by elastic deformation: Implications for fluid inclusion geobarometry of peridotites
Keywords:Fluid inclusion, Geobarometry, Equation of state, Elastic deformation, Raman spectroscopy
Changes in fluid inclusion (FI) density (ρinc) due to elastic deformation of the host mineral have long been recognized as a possible source of systematic error in the estimation of trapping pressures by FI geobarometry (e.g., Ermakov 1950), but it has been difficult to accurately assess the effect of elastic deformation on ρinc. However, recent improvements in elastic geobarometry theory (e.g., Angel et al. 2014; 2017) and equations of state of host minerals (e.g., Angel et al. 2018; Hagiwara et al. 2022) have allowed us to accurately assess the uncertainty that elastic deformation brings to FI geobarometry. Here, we evaluate the influence of elastic deformation on the estimation of the depth provenance by FI geobarometry, using peridotites as examples, and propose a correction method.
We show that, due to elastic deformation, the measured ρinc of FI trapped under typical P-T conditions of spinel-lherzolites are about 0–3% greater than the density at the P-T conditions of entrapment. Therefore, unless the effects of elastic deformation are corrected, trapping pressures will be slightly overestimated. Our results also demonstrate that differences in the elastic properties of the host minerals do not play any role in the widely reported mineral species dependence of measured ρinc (i.e., spinel > opx ~ cpx > olivine) in peridotites. Furthermore, it was also demonstrated that fluid density change by laser heating (Hagiwara et al. 2021a; 2021b) and cation ordering of spinel (Hagiwara et al. 2022) cannot explain this mineral species dependence. These results mean that ρinc of FIs in olivine, orthopyroxene, and clinopyroxene are reduced by factors other than elastic deformation because it is unlikely that any mechanism other than elastic deformation or cation ordering can increase the ρinc. Therefore, Ptrap estimated using the FIs in spinel should be closer to the true entrapment pressures than those obtained from FIs in olivine, orthopyroxene, and clinopyroxene.
References
Angel et al. (2014) Am Mineral, 99, 2146-2149; Angel et al. (2017) Am Mineral, 102, 1957-1960; Angel et al. (2018) Phys Chem Miner, 45, 95-113; Ermakov (1950) University of Kharkov Press, 460 pp.; Hagiwara et al. (2021a) J. Raman Spectros. 52, 1744–1757; Hagiwara et al. (2021b) Chem. Geol. 559, 119928; Hagiwara et al. (2022) Contrib. Min. Petrol. 177
We show that, due to elastic deformation, the measured ρinc of FI trapped under typical P-T conditions of spinel-lherzolites are about 0–3% greater than the density at the P-T conditions of entrapment. Therefore, unless the effects of elastic deformation are corrected, trapping pressures will be slightly overestimated. Our results also demonstrate that differences in the elastic properties of the host minerals do not play any role in the widely reported mineral species dependence of measured ρinc (i.e., spinel > opx ~ cpx > olivine) in peridotites. Furthermore, it was also demonstrated that fluid density change by laser heating (Hagiwara et al. 2021a; 2021b) and cation ordering of spinel (Hagiwara et al. 2022) cannot explain this mineral species dependence. These results mean that ρinc of FIs in olivine, orthopyroxene, and clinopyroxene are reduced by factors other than elastic deformation because it is unlikely that any mechanism other than elastic deformation or cation ordering can increase the ρinc. Therefore, Ptrap estimated using the FIs in spinel should be closer to the true entrapment pressures than those obtained from FIs in olivine, orthopyroxene, and clinopyroxene.
References
Angel et al. (2014) Am Mineral, 99, 2146-2149; Angel et al. (2017) Am Mineral, 102, 1957-1960; Angel et al. (2018) Phys Chem Miner, 45, 95-113; Ermakov (1950) University of Kharkov Press, 460 pp.; Hagiwara et al. (2021a) J. Raman Spectros. 52, 1744–1757; Hagiwara et al. (2021b) Chem. Geol. 559, 119928; Hagiwara et al. (2022) Contrib. Min. Petrol. 177