Informal weekly presentations by UTIG students and researchers. Bring your lunch!

Speaker: Andrew Gase, Graduate Research Assistant, UTIG

Click to watch the seminar online.

Speaker: William Moore, Hampton University

Host: Thorsten Becker

Title: Venus: How Heat Pipes Closed the Window on Plate Tectonics

Abstract: Venus, like the smaller terrestrial bodies but unlike Earth, exhibits single-plate, rigid lid tectonics and a surface dominated by voluminous plains-forming volcanism. The absence of plate tectonics on Venus has long been a puzzle, since buoyancy forces should be quite similar to Earth. One major difference between the two planets is the surface temperature, which is 430 degrees C hotter on Venus. Venus’ surface is nearly twice as close to the melting point of rocks as Earth’s. For any terrestrial planet, the difference between the surface temperature and the solidus determines the maximum amount of heat that can be transported without melting the mantle. If the heat production exceeds this level, melt will be produced and erupt at the surface, carrying the excess heat in what is known as the heat-pipe mode of planetary heat transfer. This means that a planet with a higher surface temperature, will sustain significant volcanism at lower heat production rates, since sub-solidus convection is less efficient. As planets cool from a hot state and gradually lose heat producing elements, a planet with an elevated surface temperature takes longer to exit the heat-pipe mode from a given initial heat production rate, and this exit takes place at a lower heat production rate. Since heat-pipe volcanism suppresses lithospheric stresses (through the capping of temperatures and flattening of isotherms by the solidus), any opportunity to initiate plate tectonics therefore takes place later and at lower heat production rates and lower lithospheric stress on a planet with a higher surface temperature. If those stresses are insufficient to break the lithosphere, rigid-lid evolution results. This hypothesis explains a number of features of Venusian geology that previously have been explained by strongly non-monotonic behavior which is difficult to reconcile with evolution from a hot initial state. Instead, the extensive plains volcanism, the apparently thick lithosphere, the uniform crater distribution, and the relatively old age of elevated crust are all explained by the rapid cessation of heat pipe volcanism approximately 1 billion years ago, a delay of about 2 billion years (roughly one half life of mantle heat sources) relative to Earth. Venus’ extended childhood has therefore caused it to miss its window of opportunity to undergo plate tectonics and it is now stably trapped in the rigid lid state. 

Informal weekly presentations by UTIG students and researchers. Bring your lunch!

This week: Stefano Nerozzi presents his PhD defense talk!
"Reconstructing the early emplacement of the north polar cap of Mars"

Speaker: Stefano Nerozzi, Graduate Research Assistant, UTIG

Click to watch the seminar online.

Speaker: Amy Clement, University of Miami

Host: Yuko Okumura

Informal weekly presentations by UTIG students and researchers. Bring your lunch!

Speaker: Doug Foster, Senior Research Scientist, UTIG

Click to watch the seminar online.

Speaker: Anne Becel, Lamont-Doherty Earth Observatory

Host: Shuoshuo Han

Title: Connections between along-strike variations in seismic structure and earthquake behavior at the Alaska Peninsula subduction zone

Abstract: Subduction zones worldwide exhibit striking variations in seismic activity and slip behavior along strike and down dip, and many factors have been invoked to explain this variability. The subduction zone off the Alaska Peninsula is characterized by marked changes in seismic behavior, earthquake rupture history and geodetic coupling over relatively small along-strike distances, making it an ideal location to examine controls on seismo- and tsunami-genesis.

Marine seismic reflection and refraction data acquired across this subduction zone with the R/V Marcus Langseth reveal substantial along-strike variations in structure and properties of the incoming oceanic lithosphere as well as differences in thickness and pore-fluid pressure within the subducting sediment layer. We propose the amount of water and sediment delivered into the subduction zone on the incoming plate are influencing seismic behavior throughout this system. Seismic data also reveal major downdip changes in seismic reflection character of the megathrust interpreted as a broadening of the deformation zone at depth and thought to represent a gradual transition from conditionally stable and stable-sliding regions. Last, seismic data show a structural architecture favorable to the generation of tsunami in one of the subduction zone segments that needs to be taken into account when considering hazards for this region.    

Informal weekly presentations by UTIG students and researchers. Bring your lunch!

Speaker: Mark Cloos, Professor, Department of Geological Sciences, Jackson School of Geosciences, The University of Texas at Austin