(1941- ) Swiss Mineralogist (Textural Analysis)
The Earth has a very strong magnetic field compared with the other terrestrial planets. The reason given has always been that the interaction of the solid and liquid core produces a self-exciting dynamo created by the spinning of the Earth. The details of this interaction, however, have never really been explained. One piece of evidence that adds to this investigation is the stark difference in seismic wave velocity depending upon the direction that they pass through the solid core. They travel much faster parallel to the poles than through the equator. New research by Hans-Rudolf Wenk and his associates appears to be quickly leading to a solution to this fundamental question. Wenk has done experimental work on iron at high pressures and temperatures, which forms hexagonal crystals. These crystals appear to have aligned parallel to the poles through processes of dynamic recrystallization. An example of this work is Wenk’s paper “Plastic Deformation of Iron in the Earth’s Core.”
This work on the core is a natural progression of the research of Wenk on convection in the Earth’s mantle. The upper mantle undergoes thermally induced convective circulation. However, the upper mantle is primarily solid with only small pockets of liquid at the plate margins. The circulation is therefore accomplished dominantly through dynamic recrystallization processes or crystal plasticity. The movement of structural defects on the atomic level throughout the mineral crystal lattice causes shape changes and the alignment of crystals to produce a preferred orientation. Seismic waves travel at different speeds depending upon which direction they travel through the crystal. Seismic waves in the upper mantle travel 10 percent faster perpendicular to mid-ocean ridges than parallel to them as a result of this alignment. Seismologists can map the fabric of the upper mantle using seismic velocities otherwise known as teleseismic imaging.
The scale difference between these Earth scale processes and the minute sizes of the samples that Hans-Rudolf Wenk typically analyzes makes it almost incredible that they could have any bearing on each other. Wenk studies the crys-tallographic alignment of minerals and other materials and the atomic scale processes that produce them. His true expertise is therefore better called textural analysis and he is arguably the foremost expert. He has studied these alignment processes in minerals such as calcite, dolomite, mica, staurolite, and olivine, in rocks such as quartzite, mylonite, eclogite, and opal in chert, and even in mollusk shells, ice, bones, and calcified tendons, and wires, nickel plating, and hexagonal metals. It requires the most sophisticated of analytical equipment to attempt such research. Wenk utilizes a variety of equipment in this analysis including pulsed neutron sources, high-resolution transmission electron microscopy (HRTEM), three-dimensional transmission electron microscopy (3DTEM), synchotron X-ray diffraction, X-ray goniometry, neutron diffraction, and scanning electron microscopy (SEM), among others. Modeling of the processes involved in these alignments involves sophisticated processes and typically supercomputers. Wenk has produced a software package for this application called BEARTEX. He has also written several books on this work including Texture and Anisotropy. Preferred Orientation in Polycrystals and their Effect on Material Properties and An Introduction to Modern Textural Analysis.
Hans-Rudolf Wenk was born on October 25, 1941, in Zurich, Switzerland, where he spent his youth. He attended the University of Basel, Switzerland, where he earned a bachelor of arts degree in geology in 1963. He completed his graduate studies at the University of Zurich, Switzerland, where he earned his Ph.D. in crystallography in 1965. In 1966-1967, Wenk was a research geophysicist at the University of California at Los Angeles under david t. griggs. In 1967, he joined the faculty at the University of California at Berkeley, where he remains today. Hans-Rudolf Wenk married Julia Wehhausen in 1970. He has been a visiting researcher or professor 17 times at such schools as the Universities of Frankfurt, Hamburg, and Kiel in Germany; the Universities of Grenoble, Lyon, and Metz, in France; Nanjing University, China; University of Hiroshima, Japan; and University of Perugia, Italy, among others. Wenk is a seasoned mountaineer and technical mountain climber in his spare time.
Hans-Rudolf Wenk is amid a very productive career having been an author of more than 300 papers in international journals, professional volumes, and governmental reports. Many of these papers set new benchmarks in the study of textu-ral analysis of rocks as well as Earth mantle and core processes. He is also an author or editor of four books and volumes and of an American Geophysical Union-sponsored videotape on anisotropic mantle convection entitled Texturing of Rocks in the Earth’s Mantle. A Convection Model Based on Polycrystal Plasticity. His book Electron Microscopy in Mineralogy is quite popular. In recognition of his contributions to geology, Hans-Rudolf Wenk has received several honors and awards. He has received two Von Hum-boldt Senior Research Awards and a Humboldt Research Fellowship from the Humboldt Society, and the Berndt Mathias Scholarship from Los Alamos National Laboratory.
Most of the service that Wenk has performed has been with the American Geophysical Union and societies involved in material science. He has also served on committees for the Mineralogical Society of America.
