Earth's Deep Mantle: Structure, Composition, and Evolution
Published by the American Geophysical Union as part of theGeophysical Monograph Series, Volume 160.
Expanding our knowledge here requires input from a range ofgeoscience disciplines, including seismology, geodynamics, mineralphysics, and mantle petrology and chemistry. At the same time, withbetter data sets and faster computers, seismologists are producingmore detailed models of 3-D variations in the propagation speed ofdifferent types of seismic waves; new instrumentation and access tostate-of-the-art community facilities such as synchrotrons haveenabled mineral physicists to measure rock and mineral propertiesat ever larger pressures and temperatures; new generations of massspectrometers are allowing geo-chemists to quantify minuteconcentrations of diagnostic isotopes; and with supercomputersgeodynamicists are making increasingly realistic simulations ofdynamic processes at conditions not attainable in analogueexperiments. But many questions persist. What causes the lateralvariations in seismic wavespeed that we can image with mountingaccuracy? How reliable are extrapolations of laboratorymeasurements on simple materials over many orders of magnitude ofpressure and temperature? What are the effects of volatiles andminor elements on rock and mineral properties under extremephysical conditions? Can ab initio calculations help us understandmaterial behavior in conditions that are still out of reach oflaboratory measurement? What was the early evolution of our planetand to what extent does it still influence present-day dynamics?And how well do we know such first-order issues as the average bulkcomposition of Earth?