Thermal expansivity and high-pressure sound velocities of natural topaz and implications for seismic velocities and H2O and fluorine recycling in subduction zones
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引用次数: 0
Abstract
Topaz is an important mineral formed in deeply subducted sediments and might be a major carrier of both H2O and fluorine into the Earth’s interior. To better understand the seismic velocities and H2O and fluorine recycling in subduction zones, we determined the thermal expansivity of a natural topaz (Al1.93(1)Si1.06(1)O4(OH)0.48(3)F1.52(3), space group pbnm) up to 1073 K using high-temperature powder X-ray diffraction. No phase transition or decomposition was observed within the investigated temperature range. The volume thermal expansion coefficient is 2.24(1) × 10–5 K−1, and the ratio of the axial thermal expansion coefficients α0(a):α0(b):α0(c) is 1.15:1:1.32 at 300 K. We also investigated its compressional (P) and shear (S) wave velocities up to 13.6 GPa at room temperature using ultrasonic interferometry in a multi-anvil apparatus. The adiabatic bulk modulus (Ks) and shear modulus (G) of topaz and their pressure derivatives are KS0 = 151(1) GPa, KS′ = 4.9(1), G0 = 109.4(10) GPa, and G′ = 1.8(1), respectively, by fitting the velocities and density data to finite strain equations. The density and velocity profiles of the topaz were calculated under the upper mantle P–T conditions. Our results reveal that topaz is prone to subduction which drives H2O and fluorine to migrate to the deep Earth. Meanwhile, topaz also has unusually high VP and VS, and low VP/VS ratio relative to common upper mantle phases and the preliminary reference Earth model (PREM, Dziewonski and Anderson, Phys Earth Planet Inter 25:297–356, 1981), which may be diagnostic seismic properties in subducted slabs.
期刊介绍:
Physics and Chemistry of Minerals is an international journal devoted to publishing articles and short communications of physical or chemical studies on minerals or solids related to minerals. The aim of the journal is to support competent interdisciplinary work in mineralogy and physics or chemistry. Particular emphasis is placed on applications of modern techniques or new theories and models to interpret atomic structures and physical or chemical properties of minerals. Some subjects of interest are:
-Relationships between atomic structure and crystalline state (structures of various states, crystal energies, crystal growth, thermodynamic studies, phase transformations, solid solution, exsolution phenomena, etc.)
-General solid state spectroscopy (ultraviolet, visible, infrared, Raman, ESCA, luminescence, X-ray, electron paramagnetic resonance, nuclear magnetic resonance, gamma ray resonance, etc.)
-Experimental and theoretical analysis of chemical bonding in minerals (application of crystal field, molecular orbital, band theories, etc.)
-Physical properties (magnetic, mechanical, electric, optical, thermodynamic, etc.)
-Relations between thermal expansion, compressibility, elastic constants, and fundamental properties of atomic structure, particularly as applied to geophysical problems
-Electron microscopy in support of physical and chemical studies
-Computational methods in the study of the structure and properties of minerals
-Mineral surfaces (experimental methods, structure and properties)