Variable-temperature 27Al and 29Si NMR studies of synthetic forsterite and Fe-bearing Dora Maira pyrope garnet: Temperature dependence and mechanisms of paramagnetically shifted peaks
Abstract
We present variable-temperature (VT, 31 to 204 °C) 29Si magic angle spinning NMR (MAS-NMR) spectra of a synthetic forsterite containing dilute paramagnetic impurities and 27Al and 29Si spectra of two iron-bearing natural pyrope garnet specimens from the Dora Maira ultrahigh-pressure metamorphism locality. Previous NMR studies of these materials reported multiple “anomalous” resonances outside the range of expected frequencies. It has been hypothesized that these peaks were caused by interactions between paramagnetic centers and the resonating nuclei. Our VT MAS-NMR study shows a linear relationship between peak position and inverse temperature for the “anomalous” resonances, confirming their assignment as paramagnetic shifts. A detailed analysis of the peaks in the pyropes indicates that the “anomalous” resonances are caused by a combination of the Fermi contact and pseudocontact interactions. The paramagnetic shifts in the 29Si spectra are likely caused by Fe2+ in the first, second, and third nearest dodecahedral sites while those in the 27Al spectra are likely caused by one or two Fe2+ in the first shell dodecahedral site.
© 2015 by Walter de Gruyter Berlin/Boston
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Articles in the same Issue
- Needs and opportunities in mineral evolution research
- Rutile inclusions in quartz crystals record decreasing temperature and pressure during the exhumation of the Su-Lu UHP metamorphic belt in Donghai, East China
- A first-principles study of the phase transition from Holl-I to Holl-II in the composition KAlSi3O8
- Sejkoraite-(Y), a new member of the zippeite group containing trivalent cations from Jáchymov (St. Joachimsthal), Czech Republic: Description and crystal structure refinement
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- The effect of Fe on olivine H2O storage capacity: Consequences for H2O in the martian mantle
- Kinetics of thermal transformation of partially dehydroxylated pyrophyllite
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- Thermoelastic property and high-pressure stability of Fe7C3: Implication for iron-carbide in the Earth’s core
- Yttriaite-(Y): The natural occurrence of Y2O3 from the Bol’shaya Pol’ya River, Subpolar Urals, Russia
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- Letter. High-pressure I2/c-P21/c phase transformation in SrAl2Si2O8 feldspar
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