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LPI Seminar Series

Effective January 1, 2011, LPI seminars will be held on Fridays.

LPI seminars are held from 3:30–4:30 p.m. in the Lecture Hall at USRA, 3600 Bay Area Boulevard, Houston, Texas. Refreshments are served at 4:30 p.m. For more information, please contact Georgiana Kramer (phone: 281-486-2141; e-mail: kramer@lpi.usra.edu) or Francesca Scipioni (phone: 281-486-2108; e-mail: scipioni@lpi.usra.edu). A map of the Clear Lake area is available here. This schedule is subject to revision.

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See also the Rice University Department of Physics and Astronomy Colloquia and the Department of Earth Science Colloquia pages for other space science talks in the Houston area.

February 2016

Friday, February 19, 2016 - Lecture Hall, 3:30 PM

Nicolas LeCorvec, Lunar and Planetary Institute
Effects of mechanical, rheological and tectonic controls on the formation of giant radial dike systems on Venus: Insights from finite element modeling.
Radial dike systems are intriguing magmato-tectonic features occurring on Venus, Earth and Mars. For such systems to form, massive quantities of magma ascending from the mantle must be redirected laterally at shallow depths within the lithosphere over several hundred kilometers. Observations have shown different patterns from continuous fanning to subswarms of subparallel dikes. As magma ascends towards the surface, accumulation in reservoirs situated at various depths within the lithosphere is often coupled with the growth of a volcanic edifice at the surface. The stability of magma reservoirs, and therefore the generation of magmatic intrusions, is influenced by their shape, their location, the tectonic environment and the mechanical and rheological properties of the lithosphere. Based on previous work investigating the role of flexure on the stability of magma reservoirs, we developed new models to test: 1- the role of a mechanically-layered lithosphere; 2- the role of extensional stresses; and 3- the ellipticity of magmatic reservoirs on the formation of these radial dike systems. To explore these scenarios, we used the COMSOL Multiphysics finite element package allowing us to develop: 1- 2D axisymmetric elastic models made of mantle and crustal components; 2- 3D elastic models in which an extensional stress was applied; and 3- elliptical magmatic reservoirs embedded within 2D axisymmetric elastoplastic models. Different tectonic environments were studied: lithostatic, upward flexure due to uplift consistent with a plume-derived origin and downward flexure due to the load of a volcanic edifice. Mechanical layering within the lithosphere impacts the location of failure along a magmatic reservoir and the type of magmatic intrusions. We observe that shallow magma reservoirs in an upward flexure environment tend to produce radial dikes. Regional Extensional stresses in 3D tend to focus the location of failure along the magma reservoir, therefore limiting the formation of continuous fanning pattern. Finally, the elliptical shape of a magma reservoir favors continued expansion and increasing ellipticity, because failure at the midsection requires less overpressure as the ellipticity of the reservoir increases. These results highlight new physical and structural controls on the formation of radial dike systems on Venus. Specifically, we can infer 1- potential crust/mantle ratios within the Venusian lithosphere; 2- the extensional stress regime linked to the formation of specific radial dike systems; and 3- the mechanisms of magma chamber growth linked to the formation of calderae observed in conjunction with radial dike systems on Venus.
Friday, February 26, 2016 - Lecture Hall, 3:30 PM

Peter James, Lamont-Doherty Earth Observatory at Columbia University
Crustal structure of the South-Pole Aitken Basin from GRAIL and LOLA
The Moon's South Pole-Aitken basin (SPA) is the largest confirmed impact basin on the Moon, and it delineates one of the ~4 major lunar terranes. The gravity and topography data from GRAIL and LOLA respectively provide an opportunity to study the structure the crust and mantle under SPA. Long-wavelength gravity and topography are sensitive to the uppermost several hundred kilometers of the lunar interior, and are consequently sensitive to mass heterogeneities in the lunar mantle. Short wavelength gravity and topography data primarily reveal the bulk densities of the crust. Remote sensing instruments such as the Moon Mineralogy Mapper have detected the presence of anorthosites, pyroxenes, and olivines in various parts of the basin, but ambiguities remain: it is not known whether surface compositions are representative of the crust as a whole, and absolute abundances of mafic components are poorly constrained. By correcting for the distribution of porosity in the lunar crust, I use gravity and topography to estimate the grain densities of various crustal features in SPA. In particular, the rings and peak-rings of basins superimposed on SPA offer an opportunity to sample compositions of materials that originated deep within SPA’s impact melt sheet.

March 2016

Friday, March 4, 2016 - Lecture Hall, 3:30 PM

Nicolle Zellner, Albion College

April 2016

Friday, April 8, 2016 - Lecture Hall, 3:30 PM

Julie Stopar, Arizona State University
Friday, April 15, 2016 - Lecture Hall, 3:30 PM

Silvia Protopapa, University of Maryland
Friday, April 22, 2016 - Lecture Hall, 3:30 PM

Dominique Weis, University of British Columbia
Friday, April 29, 2016 - Lecture Hall, 3:30 PM

Andrew Rivkin, Johns Hopkins University Applied Physics Laboratory


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