HR: 14:05h
AN: S12D-02 INVITED     [PDF]
TI: Mantle Mineralogy and Mineral Physics: Paradigms and Paradoxes
AU: * Duffy, T S
EM: duffy@princeton.edu
AF: Princeton University, Department of Geosciences, Princeton, NJ 08544 United States
AU: Shim, S
EM: sangshim@mit.edu
AF: MIT, Department of Earth, Atmospheric, and Planetary Sciences 77 Massachusetts Avenue, Cambridge, MA 02139 United States
AB: Don Anderson has made important contributions to our understanding of the mineralogy and mineral physics of the earth's mantle and core for more than 4 decades. For example, Don's elucidation of elasticity systematics and his perceptive application of such knowledge to understanding the Earth's mantle has been one of the prime motivations for more than a generation of experimental studies. In this talk, we summarize the current status of laboratory experimentation on the mineralogy of the deep mantle, focusing on the areas of elasticity and phase changes. The connection of mineral physics to seismology, a particular area of interest to Don Anderson, will be emphasized. Recently, the study of elastic properties of mantle and core materials has mushroomed as a result of new experimental capabilities. These include the development of several synchrotron-based tools including, for example, x-ray inelastic scattering and lattice strain anisotropy measurements. These have greatly extended the accessible pressure range and sound velocities have now been reported in iron and other materials to pressures up to 1 MBar. New high-precision studies of compositional variations in garnets, olivines, and high-pressure silicates are placing tight constraints on compositional and structural effects on seismic velocity at upper mantle pressures. In the (Mg,Fe)$_2$SiO$_4$ system, there is now broad agreement among different research groups on the relevant pressure and temperature derivatives of the aggregate elastic moduli. To first order, the results support Anderson's long-standing proposal for an olivine-poor transition zone, although the presence of volatiles and the non-linear nature of the transformation have been used to argue for more olivine-rich compositions. New synchrotron x-ray diffraction capabilities together with advanced laser heating techniques have also led to important developments in understanding of phase relations in the mantle. In the transition zone, new in situ studies have reopened controversy surrounding the location and slope of the post-spinel transition in Mg$_2$SiO$_4$. Phase relations in MgSiO$_3$, SiO$_2$, and CaSiO$_3$ have been carefully explored at deep lower mantle pressures as have some more chemically complex systems. Broadly speaking, these studies have revealed the existence of structurally subtle phase transitions that nevertheless could have important geophysical implications. Minor chemical elements may also have a major effect on physical and chemical properties under deep mantle conditions. A few key advances and some of the outstanding problems will be highlighted.
DE: 1025 Composition of the mantle
DE: 3630 Experimental mineralogy and petrology
DE: 7207 Core and mantle
DE: 8147 Planetary interiors (5430, 5724)
SC: Seismology [S]
MN: 2003 Fall Meeting