| Silicate melts are dominant phases in the Earth’s interior. As the important carriers of mass and heat in the crust and mantle, silicate melts may played an import role in the early evolution of Earth. Knowledge of the elastic properties and pressure-density relation of silicate melts at high temperature and high pressure conditions are essential to understanding the dynamic process and chemical evolutions of the Earth interior. North China Craton is the most important tectonic element of the lithosphere structures of China continent and attracted considerable attention over the last decades, due to a dramatic change form Paleozoic cratonic mantle to a Cenozonic oceanic lithospheric mantle. Experienced strong magmatic activity,tectonic deformation, and structure development, North China Craton has became a excellent place to study internal mechanism of crust-mantle interaction.The basalt melt from Feixian, west of Shandong,studied in this paper, contains the characteristics of asthenosphere and lithosphere mantle in the east of North China Craton. As the typical representative of the places damaged strongest, It can reflect the results of dramatic change in lithosphere mantle. Therefore, Knowledge of the properties of basalt melt at high temperature and high pressure is central important to better assess their role in geodynamical and geochemical evolution and understand the dynamic and transport properties of melts in mantle.In this thesis, Brillouin scattering spectroscopy combined with diamond anvil cell have been employed to investigated the sound velocities, elastic parameters, and densities of basalt glass at high temperature and pressure. The main study result are listed as follow:1. The results of the brillouin measurement under high temperature and high pressure reveal pronounced changes in the slope of the pressure dependence of both Vp and Vs at about 10 GPa. In addition, higher temperature may lead to a slightly advance of the changes in slope, Which suggest that the basalt glass may undergoes significant structural modification in this region.2. Different structural states with marked changes in elastic parameters. For example, at 380 K, both the bulk and shear moduli increase with increasing pressure at low pressure(p < 10 GPa), with the pressure derivative of elastic moduli,(?KS/?P)T = 2.6,(?μ/?P)T = 0.6.Theintermediate-pressure(10<P<15 GPa) structural state is characterized by extremely high rates of increases of both bulk and shear moduli(?KS/?P)T = 10.6,(?μ/?P)T = 2.4,whereas more moderated values are displayed in the high pressure regime(P>15 GPa).3. The compressibility and Poisson ratio undergo a distinct discontinuity near 10 GPa as well as acoustic velocities and elastic moduli with increase pressure. It is notable that there is a significant increase in compressibility with the phase transition that the glass assess a different compressional mechanism.4. The density calculated in the experiment indicate that, the density increases smoothly without singularities upon compression over the investigated pressure range. The discontinue in elastic moduli and compressibility, but apparently not in density, is in accord with the characteristics of a second-order phase transition. Si-O distances increase and bond angle decrease with increasing pressure. The fraction of highly coordinated Si or/and Al conformed at about 10 GPa. In addition, [5,6]Si,[5,6]Al more prone to form at high temperature. This structural responses to temperature suggest that phase change advanced at higher temperature. Thus it can be seen, the degree of polymerization of silicate melt strong affects their transport and dynamic and transport properties under extreme condition.5. The density derived form in situ Brilouin spectroscopy under high temperature and high pressure contrast with PREM and MORB indicate that our basalt melt at the base of upper mantle has a low density. Our results show that the basalt melt may need very low water content(<2.69wt%) at the base of the upper mantle. |
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