Geophysics and Tectonics Seminar - spring-2015

April 10, 2015
noon - 1 p.m.
Geology 3814

Presented By:

• Alex Patthoff - JPL

Fissures near the south pole of Saturn’s icy moon Enceladus are observed to be erupting jets of water, which illustrates that the small moon is presently geologically active. Farther to the north, ridges, fractures, and relaxed crater topography preserve evidence for a surprisingly complex history of recent tectonic and thermal activity on the small moon. Here we demonstrate that the regions near the south pole, and along the leading and trailing hemispheres are each morphologically distinct, suggesting unique tectonic deformation events for each area. Previous researchers have demonstrated that some terrains appear to have experienced more ductile deformation, pointing to a significant amount of heat flux generated in the interior of the moon. We show that some ridged terrains, particularly on the leading and trailing hemispheres, preserve a history of apparent brittle deformation that accommodated significant contraction. This analysis of the ridge terrains seeks to constrain the recent and long-term tectonic history of Enceladus.

April 17, 2015
noon - 1 p.m.
Geology 3814

Presented By:

• Vicki Hansen - University of Minnesota, Duluth

We are undertaking a detailed structural analysis of a targeted portion of an Aphrodite fracture zone in order to understand the architectural evolution through time and space and, ultimately, to construct thermal models in order to gain insight into possible mechanisms of heat transfer on Venus. The target area (15S-20S/110E-124E), characterized by extreme density of faults and pit chains, encompasses over 700,000 km2. It is part of an extensive fracture zone that overlaps with focused coronae chains to the east,and splits into regional splays to the west,cutting highland crustal plateaus. Hybrid tectono-volcanic structures,change along strike from en echelon fractures, fractures, pit-­?chains, graben, leaky dikes, and canali. Widths range from 1 to >5 km; lengths exceed several 100 km; structure spacing ranges from 10’s of km to lineament overlapping, intersecting, or coalescing. Hybrid structures, which play a key role in transferring material to/from depth, both predate and postdate surface deposits.The fracture zone domain is the youngest regional domain in Aphrodite Terra, and extends ~2000 km in width and over 6000 km in length. The hybrid structures likely play a significant role in cooling reflecting contemporary mechanisms/processes.

May 1, 2015
noon - 1 p.m.
Geology 3814

Presented By:

• Krishan Khurana - UCLA

Theoretical models of tidal dissipation in Io’s interior have provided support for a global subsurface melt layer. The extremely high temperature of the lava erupting on Io’s surface also hints at an extremely hot interior consistent with an internal magma ocean. However, the only direct evidence of a subsurface magma ocean in Io is provided by the electromagnetic induction response observed by Galileo (Khurana et al. 2011, Science, 332, 1186).

Using Jupiter’s rotating magnetic field as a sounding signal, Khurana et al. (2011) analyzed the response of Io observed during four different flybys of Io by the spacecraft Galileo, and showed that the magnetic field response is global, variable and in sync with the time varying field of Jupiter. Modeling of this signature shows that the induction response from a completely solid mantle model is inadequate to explain the magnetometer observations. However, a layer of asthenosphere > 50 km in thickness with a rock melt fraction ? 20% is adequate to accurately model the observed magnetic field.

In this presentation, after summarizing our current knowledge of Io’s interior from Galileo’s induction measurements, I will outline a scheme to further infer properties of Io’s interior, especially its internal temperature profile, by marrying the principles of thermodynamics with those of electromagnetism. In particular, we would obtain guidance on stable mineral phases and their physical properties (such as density, melt state and electrical conductivity) from thermodynamic principles whereas how the resulting internal conductivity profile affects the magnetic environment around Io from electromagnetic theory. I will also explore how induction measurements could be obtained at multiple frequencies from a future mission and be used to constrain both the location and the thickness of the magma ocean.

Finally, I will explore the consequences of the global magma ocean of Io on its physical properties such as the current sites of tidal energy dissipation, the absence of an internal magnetic field and a lack of plate tectonics on its surface.

May 15, 2015
noon - 1 p.m.
Geology 3814

Presented By:

• Leslie Rogers - Caltech

Sub-Neptune, super-Earth-size exoplanets are a new planet class. Though absent from the Solar System, they are found by microlensing, radial velocity, and transit surveys to be common around distant stars. The nature of planets in this regime is not known; terrestrial super-Earths, mini-Neptunes with hydrogen-helium gas layers, and water-worlds with several tens of percent water by mass are all a-priori plausible compositions. Disentangling the contributions from each of these scenarios to the population of observed planets is a critical missing link in our understanding of planet formation, evolution, and interior structure. I will review individual highlights from the diverse complement of sub-Neptune-size planets discovered to date, and present statistical analyses constraining the nature and origins of short-period rocky planets. With the suite of space-based exoplanet transit surveys on the horizon (K2, TESS, CHEOPS and PLATO) and the continuing development of ground-based spectrographs (e.g., MAROON-X, Keck SHREK, EXPRES, SPIRou, Carmenes, HPF, ESPRESSO, G-CLEF), the pace of exoplanet discovery and characterization is poised to continue accelerating. I will conclude by describing pathways forward to identify bulk composition trends in the growing census of known exoplanets and to connect these composition trends back to distinct planet formation pathways.

May 29, 2015
noon - 1 p.m.
Geology 3814

Presented By:

• Pål Brekke - Norwegian Space Centre

Seminar Description coming soon.