Doctoral Leaflet

It seems a bit of Vaudeville is still lingering around the Academe…

THE GRADUATE SCHOOL
of
THE UNIVERSITY OF COLORADO AT BOULDER

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DISSERTATION DEFENSE
of

Zane A. Selvans

FOR THE DEGREE
DOCTOR OF PHILOSOPHY

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Date/Time: 2:30pm, Friday, 20th November, 2009
Bldg./Rm: Benson Earth Sciences (BESC) 380

Examining Committee Members:

• Karl Mueller
• John Wahr
• Robert Pappalardo
• Bruce Jakosky
• John Spencer

OUTLINE OF STUDIES

Major Field: Geological Sciences

BIOGRAPHICAL NOTES

A descendant of Dust Bowl migrants, Zane grew up near Fresno in California’s San Joaquin Valley. He left as soon as humanly possible, and got his BS in Computer Science at the Caltech in Pasadena. After a brief stint working in Silicon Valley (which unfortunately did not result in any kind of dot-com stock option fortune), he returned to Caltech via sea kayak to work with Mars Global Surveyor data, mapping Mars’ south polar layered deposits. While he has been a student at CU Boulder since the fall of 2002 you may not have seen much of him lately, because in early 2006 his wife and advisor both moved to Caltech/JPL, and like a long period comet, he slid back down into that place’s deep potential well to be with them. Next year, Zane intends to spend a lot of time on his bicycle.

THESIS

Time, Tides and Tectonics on Icy Satellites
Faculty Advisor: Karl Mueller

ABSTRACT

In the outer solar system, we cannot directly use the radiometric dating techniques widely applied in terrestrial geology. We also lack the detailed understanding of the correspondence between crater size-frequency distributions and absolute ages that the radiometric dating of lunar samples has given us in the inner solar system. Additionally, many geologically interesting surfaces on the icy satellites are insufficiently cratered to allow us to infer precise relative ages. Thus it is desirable to find other ways to construct geological chronologies that function well in the outer solar system. In this work I develop two techniques.

The first compares the linear tectonic features covering Jupiter’s moon Europa to modeled tensile fractures resulting from tidal stresses due to the non-synchronous rotation (NSR) of the satellite’s decoupled, icy, lithospheric shell. The amount of shell rotation required to align a feature with the stress field resulting from NSR is used as a proxy for time. This translation is potentially convolved with a phase lag between the tidal potential and the stresses it induces, resulting from the shell’s partially viscous response to the NSR forcing. The geography of individual lineaments is found to be no more consistent with NSR stresses than chance would predict, however, the ensemble of global lineaments displays a non-uniform apparent rate of lineament formation throughout the time period recorded by the surface. This non-uniformity may be explained either by steady state fracture formation, activity, quiescence and erasure, or by a transient episode of tectonics.

The second technique encodes the myriad superposition relationships evident between Europa’s tectonic features as a directed graph enabling algorithmic analysis. The observed superposition relationships are generally insufficient to construct complete stratigraphic stacks, but we can calculate the degree to which they corroborate or contradict another hypothesized order of formation. We find that they tend to corroborate the hypothesis that the lineaments are tensile fractures due to NSR stresses.

Together these results offer cautious support for the idea that Europa’s shell rotates independently of its silicate interior, and demonstrate techniques useful in comparing tectonic features on other icy satellites to hypothesized mechanisms of formation.