| Summary: | 碩士 === 國立成功大學 === 地球科學系碩博士班 === 94 === Water has great influences on the physical properties and chemical reactions of the mantle phases. Phase A is one of the dense hydrous magnesium silicates fromed in the high pressure environment. Structurally and chemically Phase A has been suggested to be related to the serpentine mineral, antigorite in the subduction slabs (Ulmer and Trommsdorff, 1995).
High pressure infrared experiments were carried at beamline U2A, National Synchrotron Light Source. The absorption spectra were collected up to 32 GPa at the ambient temperatures. The wavenumbers (ω) of the lattice vibration modes increase progressively as a function of pressure, but those of the OH bands (3410.9 cm-1 and 3517 cm-1) were decreasing linearly. The slopes (∂ω/∂P) of lattice vibration modes and the OH modes change at pressure of 13 GPa. For the OH modes, the ∆ω (wavenumber difference, ω3517 cm-1 – ω3410.9 cm-1) decreased gradually during the compression and had a minima value at 13 GPa. Above 13 GPa, the ∆ω increases with increasing pressure. All these changes may be taken as evidence for a minor structure change or a compression mechanism in Phase A at pressure greater than 13 GPa. A similar phenomenon was also observed in a previous Raman study (Liu et al. 1997), that the transition pressure was reported to occur above 18 GPa. Furthermore, we did not observe the splitting of the most intense OH band (3517 cm-1), which was reported by Liu et al. (1997). These discrepancies need to be further investigated.
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