Robert S Coe

TitleProfessor Emeritus
DivisionPhysical & Biological Sciences
DepartmentPBSci-Earth & Planetary Sciences Department
Web Site Website
OfficeEarth & Marine Sciences A202
Campus Mail StopEarth and Planetary Sciences
Robert S Coe

Research Interests

Rob Coe is a geophysicist whose primary research involves the application of paleomagnetism to a broad spectrum of problems:

* Tectonics, on scales ranging from structural geology to ancient configurations of plates and continents;

* Magnetostratigraphy, especially regarding paleoclimatology and paleoceanography;

* Geodynamo, as revealed by the behavior of Earth's magnetic field through geologic time and by numerical simulations.

A major component of the paleomagnetic research effort of Coe and his research group has concerned tectonic problems. In the western U.S. they have been studying how right-lateral, plate-boundary shear has rotated crustal blocks about vertical axes, first in the Coast Range of southwestern Washington and currently in the Coso Range of eastern California. In Alaska their research demonstrated counterclockwise oroclinal bending of Central and Western Alaska and clarified the kinematics of terrane accretion along the southern Alaska margin during the Late Mesozoic and Early Tertiary. In China their work over the past 20 years includes significant advances defining the extent of the North China Block through time and determining the collision and suturing of South China, North China and Siberia. Their study in Papua New Guinea concerning the kinematics of accretion of the Finisterre Mountains terrane, a Miocene volcanic arc that is in the process of colliding right now with the Australian continental block, revealed a decrease in paleomagnetic declination anomalies along the arc, implying a relative rotation rate of eight degrees per million years that is in good agreement with the instantaneous rate from GPS geodesy. The plate tectonic model that best fits these data entails a highly oblique collision in early stages with the Finisterre arc converging along a left-lateral suture, gradually changing to the nearly orthogonal convergence observed today. Currently they are extending their tectonic studies of southeast Asia northward into southern Siberia and Kazakhstan in an attempt to better decipher the timing and effects of the collision with the North China-Mongolia block. In this project they are also examining the southward extent of volcanism that is coeval with the huge outpouring of Siberian Traps flood basalt at the end of the Permian, using both paleomagnetic and geochemical approaches. Support for new graduate students to work on aspects of these problems is available now.

Coe, his students, and collaborators have been studying of the past behavior of the geomagnetic field, that is, secular variation, excursions, and polarity reversals, in order to gain insight into the processes in the core that give rise to the magnetic field. Indications of extremely fast field variations recorded by basalt flows at Steens Mountain, Oregon, during a Miocene field reversal have generated much interest in the community. If they prove real, they have significant implications for fluid velocities in the core, functioning of the geodynamo, and, as an aside, the mean conductivity of the mantle. If they are artifacts, they signal a virtually invisible remagnetization mechanism that paleomagnetists must strive to understand and guard against. They have also found thick volcanic sections on the Hawaiian islands of Kauai, Oahu, and Maui to be fruitful sources of information about reversals. Similarly, the group has been studying the record of magnetic field variations in outcrops and long cores of sediment from ancient and present-day Great Basin lakes in California and Nevada and from both windblown and fluvial deposits in China. An important facet of this research is to assess the fidelity with which these sediments record the magnetic field. Finally, in collaboration with Gary Glatzmaier, who is conducting 3-D numerical computer simulations of the geodynamo, they are using paleomagnetic field behavior to evaluate the simulations and better constrain the conditions deep in the earth that control how the field is generated.

A long-term interest is how to determine the intensity of the ancient geomagnetic field. One motivation for this research is that long-term intensity may be correlated with stability of the field, and thus might shed light on the cause of the Cretaceous normal superchron, a 40 million year period of no reversals, and on reversals in general. Another motivation is the idea that convection or other processes in the lower mantle may modulate dynamo action in the core. If so, variation of ancient field intensity could carry information about the convective state of the lower mantle, and thus also about those manifestations of the earth's tectonic cycle that occur on a similar time scale, such as hot spot activity, global heat flow, mean plate velocities, and true polar wander. A novel apparatus for carrying out paleointensity experiments has been constructed and is in operation, and a program to determine field intensity in Cretaceous and Tertiary time is underway.

Biography, Education and Training

B.A., Harvard University

M.S., Ph.D., University of California, Berkeley

Postdoctoral, Australian National University

Teaching Interests

Physics in the Earth & Planetary Sciences

Paleomagnetism (ES117)

Earth Potential Fields

Topics in Geophysics

The Dynamic Earth (ES110C)

Great Papers (ES206)

The Yellowstone Hotspot (ES290C)