Report to KITP on 2006 Summer Program in Geophysics in the framework of CIDER (Cooperative Institute for Deep Earth Research), on “The Transition Zone”. Santa Barbara, July 16- Aug 4, 2006.
prepared by Barbara Romanowicz, Berkeley Seismological Laboratory and Department of Earth and Planetary Science, UC Berkeley
This summer program is the second CIDER program held at KITP, following a successful program in the summer of 2004. The primary goal of CIDER is to provide opportunities for cross-education among the different disciplines in Geosciences which together can help advance our understanding of the dynamics of the earth's interior and the driving mechanisms of plate tectonics (see http://www.deep-earth.org for a more detailed description of the goals of CIDER).
The term “Transition Zone” refers to the earth's deep upper mantle (400-700 km depth) where elastic properties are known to vary rapidly with depth, and which includes a series of sharp mineral phase transitions with increasing pressure. Understanding the three dimensional structure and dynamics of the transition zone is key to resolving some currently vivid debates such as whole mantle versus layered convection, stagnation of subducting slabs in the upper mantle and “flushing” events, style of mixing of compositional heterogeneity, the possible presence of water reservoirs and the role of water in mantle dynamics.
The organizers of the 2006 summer program were: Adam Dziewonski (Harvard), Stan Hart (Woods Hole Oceanographic Institution), Louise Kellogg (U.C. Davis) and Barbara Romanowicz (U.C. Berkeley). This three week program consisted of two overlapping parts: a “tutorial part” which lasted the first two weeks, and a “workshop part” which was initiated during the second week and fully developed during the third and last week.
The “tutorial part” of the program involved, every morning, two one hour lectures by senior members of the geosciences community followed by a 30 mn discussion. The 15 participating lecturers (see appendix) were chosen to represent the four main disciplines (seismology, geodynamics, mineral physics and geochemistry). The program was designed to provide a general and critical background on the tools and state of knowledge in each discipline, focused around the specific theme of the workshop. Each afternoon featured a “hands-on” tutorial in successively different disciplines, which involved computer simulations, examination of various databases, and data interpretation. The program is available on the web in the KITP archive as well as on the CIDER webpage at http://www.deep-earth.org/summer06.html.
The participants were 35 advanced graduate students and post-doc's selected upon credentials and also to represent a balance between the disciplines. Their list is given as appendix. 25 (?) of the participants and 6 of the instructors) stayed on for the workshop part of the program, and were joined in the second week by 6? additional senior participants.
During the second week of the program, the participants were solicited to establish a list of multidisciplinary timely research themes concerning the “transition zone” that we thought could be realistically advanced during the third week given the range of expertise among the participants. A two hour discussion was devoted to describing and selecting the themes. Five themes survived by Thursday night, but two of the groups later joined forces to obtain a better balance of expertise.
A senior member of the community was assigned as coordinator for each of the groups. The selected themes were (groups D and E fused into group E):
A) “Slabs in the Transition Zone” (coordinator A. Dziewonski)
B) “Seismic Velocity gradients across the Transition Zone” (coordinator B. Romanowicz)
C) “Mantle Potential temperature” (coordinator C.T. Lee)
E) “Mixing- aka Progress towards Chaos” (coordinators S. Hart and L. Kellogg)
Each
group met on Friday afternoon of the second week to get organized.
The entire third week was devoted to activities within individual
groups, with a plenary session at 2pm every afternoon to compare
notes on the progress of each group. On the last afternoon of the
workshop, formal presentations were made of the results of these
activities. These presentations are posted on the CIDER website at
http://www.deep-earth.org/2006/workshop.html.
The work of two of the groups will be presented in three posters and
two oral talks which will be given in the upcoming American
Geophysical Union meeting in San Francisco (Dec 11-15):
U11A-08 “Transition Zone as a Boundary Layer” *A M Dziewonski, V Lekic, B Kustowski, B A Romanowicz
U21A MCW Level 2 “Seismic Velocity Gradients Across the Transition Zone” C Escalante, F Cammarano, *N De Koker, A Piazzoni, Y Wang, F Marone, C Dalton, B Romanowicz
U21A MCW Level 2 “Seismic Constraints on Slab Interaction With the Transition Zone” *V Lekic, C Reif, A M Dziewonski, A Sheehan, J van Summeren
V33D-08
“The thermal state of the Earth”
C. T. Lee, A.
Courtier, R. Halama, M. Jackson, A. M. Larson, J. Lawrence, Z. Wang,
J. Warren, R. Workman, M. Hirschmann, S. Hart, L. Stixrude, C.
Lithgow-Bertelloni, W. P Chen
U21A-
Quantifying Mixing and Scales of Heterogeneity in 2-D
Numerical
Models of Chaotic Mantle Mixing
AU: * Harris, A C, J.
Naliboff, J. Prytulak, E. Vanacore, K. M. Cooper, S. Hart and L.
Kellogg
In addition to the activities described above, during week 2 and 3, 15mn presentations by volunteering post-docs and graduate students were worked into the afternoon program (see http://www.deep.earth.org/2006/workshop.html).
Also, Professor Louise Kellogg gave the monday noon KITP lecture which generated a lot of interest among the participants of the “Brain” summer program held at KITP at the same time as ours.
We believe this program was very productive. First, the lecture and tutorial part of the program is unique in the field: no individual institution in the US has sufficient breadth in expertise either at the faculty level or at the graduate student and post-doc level to be able to bring together the kind of critical mass we can assemble during the CIDER summer programs and with which we can begin to educate the next generations of geoscientists in a truly multidisciplinary manner. Second, the workshop part demonstrated once again the power of across-disciplinary interactions that can develop over an extended time-period in the KITP framework – some notable results that came out of the workshop and have continued to be developed since are:
the benchmarking of different mineral physics approaches to computing the elastic profiles in the upper mantle, the realization that large uncertainties result from different computational assumptions and the choice of different experimental constraints, but that in any case, the standard “pyrolite” composition does not match the seismological observation (group B)
Documenting that most global seismological models of the mantle present increased heterogeneity at the bottom of the transition zone, which may indicate a significant accumulation of slabs “ponding” on top of the 670 km discontinuity (group A)
Four independent determinations of mantle potential temperatures: 1) thermobarometry of primary magma compositions of mid-ocean ridge basalts (MORBs) and ocean island basalts (OIBs); 2) globally-averaged transition zone thickness from SS precursors and receiver functions, 3) comparisons between melting models and the average thickness of oceanic crust, and 4) the bathymetry of ridge axes. Thermobarometry of MORBs constrain the sub-ridge potential temperature to be 1370 ± 50°C, and the other methods give results falling within this range. In contrast, the potential temperature of hotspot (plume) basalts is at least 130°C hotter.A consensus reached in a multidisciplinary way on the potential temperature beneath ridges (1300-1400o C) and a conclusion that hotspots are hotter by at least 100o C than ridges.
Evaluations of the program by the junior participants (grad students and post-docs are
given as appendix “CIDER_evaluations.doc). These evaluations were collected anonymously.
Acknowledgments
Support for this program's participants was provided through a grant to U.C. Berkeley from the NSF Geosciences Directorate (CSEDI Program, PI Romanowicz). KITP provided on-site infrastructure support.