Craig H. Jones
Ph.D. Massachusetts Institute of Technology, 1987
Associate Professor, Geological Sciences
E-mail: cjones@cires.colorado.edu
Office: ESCI (Benson) 440C
Phone: 303-492-6994
Web: Prof. Jones
Research Interests
Jones’s research focus on the deformation of continents with a special interest in the western United States.
Current Research: Tectonics of Foundering Lithosphere, Sierra Nevada, CA
In contrast with oceanic tectonics, continental tectonics are diffuse and occur in places and with styles not easily anticipated from plate kinematics. One potential cause is the antibuoyant mantle lithosphere under continents and the potential that it could detach and sink into the mantle. The Sierra Nevada of California might overlie lithosphere that foundered in the past 10 million years. Jones and colleagues at CUBoulder and several other universities are analyzing data from the Sierra to understand the dynamics of this process.
Heidi Reeg, a CIRES graduate student, has constructed a tomographic image of the Sierran upper mantle and crust. All project scientists met in November 2008 to discuss early results and to plan on publications. A special issue of Geosphere will house many of the papers from this project. CIRES graduate student Will Levandowski has worked from several datasets—tomography, images of the Moho from collaborators at the University of Arizona, surface topography, and recent subsidence—to estimate the density variations required in the mantle.
Cutaway views of the Sierra Nevada from the west and southwest, showing observed variations in P-wave speed and pre-experiment hypotheses for Sierran structure.
The removal of mantle lithosphere may drive enigmatic deformation in continents, but hypotheses for the impacts of such an event were largely based on theory. Previous geophysical data allowed for two possibilities in the Sierra: that only some of the dense layer was removed from part of the range, leaving explanation for most of the elevation of the Sierra to another cause (A in the figure) or that uplift of the range was caused by convective removal of a dense layer at the base of the crust (B in the figure). Inversion of the arrival times of P-waves from distant earthquakes were used to image variations in seismic wavespeed under the Sierra and much of surrounding California (top panel), revealing elements of both ideas. To the right (south), lowspeed material (oranges) appears under the southern Sierra to the northeast of the high wavespeed “drip” under the San Joaquin Valley, consistent with case A. Far to the north, high-wavespeed material with a subducting slab is also tied to shallow high-wavespeed material under the Sierra, suggesting some Sierran material being entrained with the downgoing slab, as in B. (The bulk of the slab does not show up in this section, owing to coverage from available seismometers). The analysis of density variations indicates that the high-wavespeed bodies (in blue) are denser than if the seismic variation was solely due to temperature. This indicates that some or all of the garnetrich lithologies are still present under the Sierran foothills and in the “drip” seen at the right of the image, indicating that the process is still underway.
Publications
Click here for a complete list of published works »
Dr. Jones is a professor at the University of Colorado at Boulder.
