NANOSCALE VISION OF HIGH-PRESSURE MINERAL REACTIONS: FROM SUBDUCTING SLABS TO PLANETARY IMPACTS (Invited Presentation)

Peter Buseck was a professor at ASU in the late 1970s when high-resolution transmission electron microscopy (HRTEM) and image simulation were being developed there for investigating the lattice-scale structure of materials. With the help of scientists like Sumio Iijima, Dave Veblen and others, Peter pioneered the use of HRTEM imaging and analytical electron microscopy in mineralogy. Over the years, Peter supported many students and post docs to explore minerals at the nanoscale with the powerful techniques being developed at ASU. I was fortunate to be one of those students.

An important application of TEM-related techniques is the study of solid-state mineral reactions. The mechanisms by which olivine and enstatite transforms to their high-pressure polymorphs are important for understanding mantle dynamics and the generation of deep focus earthquakes. The depth to which metastable olivine and enstatite survive in the cold cores of old subducting lithosphere is determined by reaction kinetics and thermal history of the subduction zone. The use of TEM, combined with Multi-anvil experiments, has elucidated transformation mechanisms and kinetics for olivine transformations. These data, combined with thermo-kinetic modelling, have provided important constraints on the depth to which olivine can persist metastably and the origin of deep focus earthquakes.

Nearly all natural examples of deep-mantle minerals occur in shock-melt veins in highly shocked meteorites. The formation mechanisms and conditions of these minerals have been controversial. TEM, combined with FESEM and Raman spectroscopy has played a vital role in understanding the transformation reactions that occur during shock. Some of the same mechanisms that occur in laboratory experiments over minutes to hours, also occur in shocked meteorites over periods of tens to hundreds of milliseconds.

Aberration corrected TEM/STEM and new detector technologies are providing even more powerful tools for atomic-resolution characterization of minerals. Throughout his career of research in mineralogy and microscopy, Peter Buseck has sharpened our vision of minerals at the nanoscale.