Donna M. Jurdy Professor Ph.D., University of Michigan, 1974 847-491-7163 donna@earth.northwestern.edu Personal page here.

Research Interests
Plate tectonics, past plate motions and polar wander, driving forces and stress. Active tectonics on Venus and Mars.

Research Projects

Our research on Venus utilizes the topographic and radar data returned by the Magellan project. Michael Stefanick and I have focused our investigation on the distribution of coronae and craters. Coronae - unique to Venus - are circular features from 100-2600 km in diameter with raised interiors, surrounded by an annulus and peripheral moat and have been compared with hotspots or diapirs on Earth. We find that the distribution of Venus coronae and craters are related to chasmata which are thought to be extensional zones. Coronae are almost twice as dense near chasms as a random set of the same size. Of the various types of coronae, the radial-concentric and volcanic are even more highly concentrated near chasms, whereas the concentric-caldera type are absent near the chasms. The distribution of craters can indicate locations of tectonic activing on Venus' surface. Craters, to the first order, are randomly the distributed, although when we compare distribution with random sets we note a deficit of about 40-50 craters close to the chasms. Also, the tectonized and embayed craters tend to be near the rift zones and their distribution closely resembles that of the coronae. This suggests that the volcano-tectonic process creating coronae may be the same one destroying craters. Graduate student John DeLaughter and I are using concentric caldera coronae and radial concentric coronae as age end-members in the model of corona formation and evolution. From the number of impact craters near these structures and the degree of modification, we attempt to infer the stress field and volcanism associated with corona formation.

My research on driving forces for the plates is being extended back through the Phanerozoic; for much of the earlier times no seafloor remains and reconstructions are made entirely from paleomagnetic data and geological constraints. With Chris Scotese, we modeled the opening and closing of the ocean between Laurentia and Gondwana 560-400 Ma to test dynamical models by comparing the observed rates of motion for a model for the forces acting on a single plate with a hypothesized set of boundaries. In the late Precambrian Laurentia rifted away from Gondwana: by the earliest Cambrian it was near 40°S; by Late Cambrian and Ordovician it had moved to the equator; then during the Silurian and Devonian Laurentia reversed direction and collided with Gondwana at 40°S. In a model of the forces acting on the plates, slab pull, ridge push, and trench suction are assumed to balance plate drag. We find that only certain ranges of ridge-push and trench parameters can model both the opening and subsequent closing of the ocean, and that these forces are adequate to account for the observed opening and closing of oceans. Over the last 600 m.y., averaged plate speeds show considerable variation; Gondwana's speed oscillates from 20 to 60 km/m.y. over a long timescale (200-400 m.y.) with considerable noise superposed.

We have begun to consider the possibility tectonics on other solar system bodies. Ganymede is, perhaps, the only other body in the solar system to hint at activity like plate tectonics. The detailed multiple imaging of Ganymede planned for the probe Galileo may give us the opportunity to model plate tectonics. We will attempt a kinematic plate reconstruction similar to those done for terrestrial plate tectonics followed by a torque balance model analogous to our models for Earth. We are looking at Voyager maps of the body to devise a preliminary plate model using plates of 100 km thick ice sliding over a layer of mush. Features on its surface have a superficial resemblance to mountains, fault zones and wrinkle ridges on Earth and from these stress indicators might be inferred. A comparison of forces driving the plates on Ganymede to those on Earth will be made.

Three-Dimensional Images

Southeast Asia Bathymetry

Venus Chasmata and Coronae