Compressibility of molten “green glass” and crystal-liquid density crossovers in low-Ti lunar magma
- 作者：Smith ; J. R. ; Agee ; C. B.
- 刊名：Geochimica et Cosmochimica Acta
- 出版年：1997
- 期刊代码：27_00167037
- 类别：ear
- 出版时间：May, 1997
- 卷：61
- 期：10
- 页码：2139-2145
- 文件大小：645 K
摘要
Density measurements of molten Apollo 15 “green glass” have been performed in the pressure range 0.5-3.5 GPa using the floating and sinking sphres technique in piston-cylinder and multi-anvil devices. A density crossover with equilibrium orthopyroxene is predicted for green glass at 3.5 GPa, or g align=center border=0 SRC=/images/glyphs/BQ1.GIF>800 km depth in the lunar interior. Equilibrium olivine should be neutrally buoyant in molten green glass at a pressure slightly greater (5 GPa) than the lunar core value of g align=center border=0 SRC=/images/glyphs/BQ1.GIF>4.7 GPa. At the olivine-orthopyroxene cotectic (g align=center border=0 SRC=/images/glyphs/BQ1.GIF>2.0 GPa), molten green glass is less dense than both crystalline phases. Thus, the results are consistent with models that propose generation and buoyant rise of green glass magma from the depth of the olivine-orthopyroxene cotectic in the lunar interior. Molten green glass has a compression curve slope of 0.093 g/cc/GPa, along the liquidus, in the pressure range investigated. The values of the Birch-Murnaghan isothermal bulk modulus (K) and the pressure derivative of the bulk modulus (K′) at 1645°C are described by the relationship K(GPa) = 19.5 / (1 - (0.25 - 0.063K ′)). Combining this relationship with a calculated isothermal bulk modulus value of 18 GPa, derived from 1-atm ultrasonic measurements, gives K′ = 5.3 for molten green glass.