ExTerra: Evolution of arc crust

  Kimpton Hotel Monaco
700 F Street NW, Washington, DC 20004
Athens Room
 icon-calendar Sunday December 9, 2018, 8:00 AM – 12:15 PM

Registrations are now closed. Questions should be directed to the GeoPRISMS Office at info (at) geoprisms.org

 icon-chevron-right Participant list (last update 12/06/18)

 icon-chevron-right Agenda (last update 12/05/18)


Stacia Gordon (University of Nevada-Reno) and Alicia Cruz-Uribe (University of Maine)


Inspired by the success of convergent margin research funded through GeoPRISMS and discussions generated at ExTerra meetings, this workshop will gather together researchers with expertise in all aspects of the arc system on the Sunday preceding the AGU Fall Meeting in Washington, DC. The goal is to gather a broad group of geoscientists that use a variety of different approaches (field, experimental, petrological, geochemical, geochronological, seismic, numerical modeling) applied to different parts of the arc (the subducting plate, mantle, magma plumbing system, supracrustal rocks). The group will discuss what the major questions are that still surround the evolution of arc crust and what tools and methods will best answer these questions. The meeting will also serve to provide a space where early career researchers can network with more senior personnel, and where scientists from a variety of subdisciplines who work on different arc sections around the world can compare and contrast observations. In addition, this gathering of the  arc crust community will make a plan for future convergent margin research, specifically on arc crust. It is important to establish new goals and questions concerning arc crust before GeoPRISMS has fully ended to keep the momentum that this program established.

The format of the workshop will include a keynote lecture given by Oliver Jagoutz (MIT), followed by breakout groups on different areas of scientific interest within the broader arc system: 1) subduction/mantle influences, 2) plutonic plumbing system/magma storage, 3) volcanic components, and 4) supracrustal (metamorphic) components. One proposed outcome of the workshop will be for multiple groups to develop collaborative proposals to NSF EAR programs for research and field forums/institutes, which could then be leveraged for the submission of a larger proposal.

8-8:45 | Social Hour (Coffee, pastries, registration)

8:45-9 | Welcome & Introduction (GeoPRISMS Office Chair Demian Saffer and Mini-Workshop Conveners Stacia Gordon and Alicia Cruz-Uribe)

9-9:45 | Keynote (Oliver Jagoutz) (30 minute talk, 15 minutes for questions/discussion)

9:45-10:45 | Breakout discussions (4 groups)

  • What are the outstanding questions that can be addressed?
  • How can we better integrate field studies with experimental and modeling approaches?
  • What data and meta-data do we need to collect and store?
  • How can we make data and samples accessible to all?

10:45-11 | Coffee break

11-12 | Group reports/group discussion

12-12:15 | Wrap Up

ExTerra: Evolution of Arc Crust
Sunday December 9th, 2018, AGU Fall Meeting, Washington D.C.

Workshop Leaders: Stacia Gordon (University of Nevada-Reno), Alicia Cruz-Uribe (University of Maine)

On Sunday, December 9th, 34 scientists from a variety of institutions from the US and abroad gathered in Washington, D.C. prior to the start of the fall AGU Meeting to discuss arc systems and, in particular, the major questions that still surround the evolution of arc crust and the tools and methods that will best answer these questions. With the nearing end of GeoPRISMS, the workshop built upon the energy of this program and the discussions and questions that it has opened. In addition to GeoPRISMS, the workshop was also motivated by ExTerra, a group within the Geoscience community that studies Exhumed Terranes. The ExTerra community has had multiple workshops on exhumed terranes in general, and scientific questions concerning what can be learned from exhumed crustal arc sections have been included within the overall ExTerra framework. In addition, a 2016 ExTerra White Paper laid out a broad array of research themes linked to exhumed terranes. This GeoPRIMS workshop was intended to take the ExTerra White Paper one-step further by having a focused workshop for the part of the ExTerra community particularly interested in arc systems.
To start the workshop, GeoPRISMS Chair Demian Shaffer gave a brief introduction to familiarize the attendees with the GeoPRISMS program. Sarah Penniston-Dorland and Maureen Feineman, lead organizers of ExTerra and PIs on a ExTerra Field Institute and Research Endeavor grant, summarized the goals of the ExTerra program and the recent success in obtaining funding for a highly collaborative, multiple PI project through the NSF PIRE program. Subsequently, workshop leaders Stacia Gordon and Alicia Cruz-Uribe presented 1) overview ideas of all the different parts of the arc system (from the subducting plate to the volcanic components) that combined provide critical details on the evolution of arc crust; and 2) some of the major questions concerning arc systems that had been included in past white papers. Finally, to stimulate ideas and lead into group discussions, Oliver Jagoutz (MIT) and his PhD student, Benjamin Klein, presented a keynote talk on their geochemical, geochronological, and structural results from mainly the Sierra Nevada batholith and the Kohistan Arc, and the knowledge that has been gained about arc crust through these exhumed terranes.

The main goal of the workshop was to create an environment in which there was significant discussion, where all participants felt comfortable sharing their opinions, and to provide a networking opportunity for junior scientists to interact with and meet many senior personnel. To do this, after the introductory activities described above, the attendees divided into four groups based on different areas of scientific interest within the broader arc system. Junior scientists were charged with leading the discussion and recording notes, including Emily Chin (UCSD) for the subduction/mantle interface group; Barbara Ratschbacher (Cal Tech) for the plutonic plumbing system; Martin Jutzeler (U. of Tasmania) for the volcanic components; and Besim Dragovic (Boise State) for the metamorphic components. The workshop leaders provided topics for the groups to discuss, including outstanding scientific questions, what data and samples are needed, etc.

Subsequently, the group leaders gave a summary to the overall group. The subduction/mantle interface group reported that there are still many questions concerning what processes and properties control the stress state of the down going slab and the role of volatiles (other than H2O) in subduction zones. The plutonic group discussed major questions about how magma transport, ascent and emplacement mechanism vary with depth and how is space created during the movement of magma. The volcanic group presented questions on how can we estimate eruption periodicity and the processes controlling eruptions as well as what are the roles of pre-existing crustal thickness and the local stress field on the style and kinds of volcanism. The metamorphic group focused on the arc crustal section and asked what is the distribution of water, and how do oxygen fugacity and the thermal structure change throughout the arc crustal section and through time.

In the larger group, two main topics were discussed after the subgroup leaders gave their summaries: 1) whether or not to have a focus site for arc crust research, and 2) the best way to move forward and promote ExTerra and the arc crust community. In general, it seemed like most were opposed to choosing one field locality, as it is difficult to choose one arc crustal terrane that would be the ‘best’ for answering the questions that the subgroups discussed. In addition, focus sites can sometimes exclude and limit the number of scientists involved in a project. To follow this workshop, the larger group discussed several possibilities of how to proceed in terms of moving forward with writing proposals and securing funding for arc crust research. Most were not in favor of a field institute for the same reasons as the focus site described above. Instead, a larger meeting targeting the arc crust community was proposed as potentially the best mechanism to show NSF and other funding agencies that the arc crust community consists of a large number of scientists that are organized and have specific questions and hypotheses that have implications for a variety of different Geoscience subdisciplines. The group discussed that this next meeting could be a CIDER-type workshop that would involve both faculty and students.

In summary, a large number of graduate students, postdocs, and early career faculty members were in attendance and were able to network with a variety of US and international scientists at all different stages of their career. Feedback from student participants indicated that the opportunity to participate in the workshop, and in many cases meet scientists whom they knew only through reading their papers, was invaluable for them. Many important questions concerning the evolution of arc crust were discussed, and many of the students, postdocs, and junior faculty expressed interest in being involved in future events surrounding arc crust. The workshop leaders will encourage these junior scientists to take the lead on developing proposals and on being part of planning for a CIDER-type workshop.