The rate of water loss from olivine-hosted melt inclusions
- 364 Downloads
Diffusive water loss from olivine-hosted melt inclusions has been reported previously. This process must be considered when interpreting melt inclusion data. This study measured the rate of water loss from olivine-hosted melt inclusions during heating-stage experiments to test a previous diffusive reequilibration model and the hydrogen diffusion mechanism that controls the rate. Olivine-hosted melt inclusions were heated to a constant temperature in reduced Ar gas in a heating stage for a few hours, and unpolarized Fourier transform infrared spectra were repeatedly measured through the inclusions. Water loss occurred rapidly in the experiments. Within a few hours, the water absorbance at 3,500 cm−1 wavenumber decreased by half. The observed water loss rate can be explained by the diffusive reequilibration model and hydrogen diffusion in olivine coupled with metal vacancy. The beginning of water loss was different in the low- and high-temperature experiments. At low temperatures (1,423 and 1,437 K), water loss did not occur in the initial 1 or 2 h. At high temperatures (1,471–1,561 K), water loss began immediately. The initial time period without water loss at low temperatures may be explained by a hydrogen fugacity barrier in the host olivine. At low temperatures, the internal pressure may be lower than the equilibrium pressure of melt inclusion and olivine, causing lower hydrogen fugacity in the melt inclusion than in the olivine, which will delay the water loss from the melt inclusion. The tested model and diffusivity were used to estimate the rate of water loss during homogenization experiments and magma eruption and cooling. For 1-h homogenization experiment, the model shows that large inclusions (50 μm radius) in large olivines (500 μm radius) are robust against water loss, while large or small inclusions (50–10 μm radius) in small olivines (150 μm radius) may suffer 30–100% water loss. For natural samples, the correlation between water concentration and melt inclusion and olivine sizes may be helpful to infer the initial water concentration, degree of diffusive reequilibration, and magma cooling rate.
KeywordsMelt inclusion Olivine Water concentration Diffusive reequilibration rate
Y. Chen thanks Dr. E.F. Rose-Koga for borrowing her heating stage. Discussion with Dr. G.A. Gaetani, K. Koga, N. Bolfan-Casanova and many other colleagues at LMV was very beneficial. The authors thank two anonymous reviewers for their insightful and constructive reviews, and Dr. Danyushevsky LV and an anonymous reviewer for their comments to an earlier version of this manuscript. This project is funded by the Agence Nationale de la Recherche (grant no. ANR-07-BLAN-0130-01).
- Cottrell E, Spiegelman M, Langmuir CH (2002) Consequences of diffusive reequilibration for the interpretation of melt inclusions. Geochem Geophys Geosyst 3. doi: 10.1029/2001GC000205.
- Gaetani GA, O’Leary JA, Shimizu N (2009) Mechanisms and timescales for reequilibration of water in olivine-hosted melt inclusions. Eos Trans AGU 90(Fall Meet Suppl).Google Scholar
- Hier-Majumder S, Anderson IM, Kohlstedt DL (2005) Influence of protons on Fe-Mg interdiffusion in olivine. J Geophys Res 110. doi: 10.1029/2004JB003292.
- Koga K, Hauri E, Hirschmann M, Bell D (2003) Hydrogen concentration analyses using SIMS and FTIR: comparison and calibration for nominally anhydrous minerals. Geochem Geophys Geosyst 4. doi: 10.1029/2002GC000378.
- Lemaire C, Kohn SC, Brooker R (2003) The effect of the silica activity on the incorporation mechanisms of water in synthetic forsterite: a polarized spectroscopic study. Contrib Mineral Petrol 147:48–57Google Scholar
- Mukasa SB, Stefano C, Leeman WP, Shimizu N (2009) Exceptionally high water, other volatile and LILE concentrations in olivine-hosted melt inclusions from the Yellowstone hotspot and Columbia River flood basalts. Eos Trans AGU 90(Fall Meet Suppl).Google Scholar
- Qin Z, Lu F, Anderson AT (1992) Diffusive reequilibration of melt and fluid inclusions. Am Mineral 77:565–576Google Scholar
- Roedder E (1979) Origin and significance of magmatic inclusions. Bull Mineral 102:487–510Google Scholar
- Sobolev AV, Barsukov VL, Nevsorov VN, Slutsky AB (1980) The formation conditions of the high-magnesian olivines from the monomineralic fraction of Luna 24 regolith. In: Proceedings of the 11th lunar science conference, pp 105–116Google Scholar
- Sobolev AV, Clocchiatti R, Dhamelincourt P (1983) Les variations de la température, de la composition des magmas et de l’estimation de la pression partielle d’eau pendant la cristallisation de l’olivine dans les océanites du Piton de la Fournaise (Réunion, éruption de 1966). C R Acad Sci Paris 296:275–280Google Scholar
- Zhang Y, Xu Z, Zhu M, Wang H (2007) Silicate melt properties and volcanic eruptions. Rev Geophys 45:RG4004. doi: 10.1029/2006RG000216.