julie

Summary
Subduction Factory Workshop
June 6-9, 1998     La Jolla CA
 The Subduction Factory: The global impact of mass and energy transfer at convergent margins

Overview:  Approximately 65 scientists, representing the wide range of disciplines required for integrated studies of the Subduction Factory, attended the workshop.  About half were invited participants, with half selected (by MARGINS and the workshop organizing committee) from open applications. About 25% of attendees were international participants from Australia, Canada, France, Germany, Japan, New Zealand, the Philippines and the United Kingdom.
The mandate for the workshop was to build/identify community consensus for scientifically and geographically focused interdisciplinary studies at selected margins, to identify the needs of the experimental and theoretical community, and to coordinate and integrate efforts across the subduction zone community. Participants were briefed by e-mail beforehand about the scientific and logistical recommendations and criteria emerging from previous planning efforts.  The first day of the workshop was a series of science talks designed to educate a broad audience about the issues of interest and approaches available across the wealth of disciplines represented.  The next day and a half were spent on focussed group discussion leading to: 1) a subset of scientific themes regarded as first order in importance and tractable now; 2) identification of margins ready for focussed study and/or important for allied studies; and 3) other actions necessary for rapid progress in understanding the subduction factory.
To my mind, one of the best results from this meeting is the strong, although not unanimous, consensus among participants that the MARGINs philosophy is necessary to coordinating and integrating national and international efforts within the broad subduction zone community in order to maximize scientific insight and results. In this context, discussion leaders and  participants did a great job of focussing on achieving the greatest scientific return, and discussion led to a series of recommended actions.

Scientific Themes The group discussed the scientific themes presented in the MARGINs scientific plan, and recognized them as the ultimate destination for subduction factory research.  A subset of topics was recognized as essential for progress now, and increasingly tractable:
- The role of subduction parameters (such as slab and mantle temperature, convergence rate, subduction dynamics and mass transport to depth, physical properties of the decollement) as forcing functions in regulating chemical cycling and crustal growth.
- The volatile cycle through subduction zones and its impact on physical, chemical and biological processes across the entire convergent margin from the trench through the back-arc region, thereby modifying the slab delivered to the deep mantle.
- Paving the way for studies of mass balance and continental growth through approaches such as experimental element partitioning studies; geological, geochemical and seismic studies of middle and lower arc lithosphere.

Recommendations. The workshop endorsed these actions:
- Central America (Nicaragua/Costa Rica) was strongly endorsed for focussed interdisicplinary studies because it allows progress on all three scientific themes. Variations in subduction dynamics and mass transport to depth appear to be matched by sympathetic chemical gradients in the volcanic output; abundant carbonate subduction sets the stage to begin investigating the CO2 cycle; the deeper plutonic section is exposed.  Note that the first of these reasons links Subduction Factory and SEIZE scientific goals into a scientifically integrated package.  In addition, work in Central America can include studies of the volcanic gases and their role in volcanic hazards, climate modification, and mass balance. As an added benefit, the group recognized the potential for synergy with interdisciplinary studies planned and underway in the German marine science community.
- The participants recognized the need for a counterpoint to Central America, specifically in a non-accretionary margin where old, cold slabs are subducting, and back-arc spreading is present.  The Marianas, Izu-Bonin and Tonga margins are all places where key forcing functions are distinctly different from Central America; consensus was elusive, however, in that each margin was better suited for addressing a different scientific theme.  The group recommended a MARGINs workshop at AGU in order to evaluate the scientific and logistical issues necessary for further prioritization.
- Variations in subduction parameters along-strike in the Aleutians (convergence rate and obliquity, plate age, subducted sediment composition and volume, upper plate structure) present a great opportunity to examine forcing functions in regulating the factory.  The opportunity to study continental growth from exposures of deeper arc crust and the hazards presented to US residents and planes flying in US airspace were also recognized as additional reasons for working in the Aleutians.  However, the relatively limited database makes it difficult to formulate the key scientific questions or design a focussed experiment at present.  The group endorsed selected studies of the subducting input and the volcanic and plutonic products of the Aleutians.
- Integrated theoretical and experimental studies are essential for understanding the internal workings of the subduction factory, and for linking observations across the disciplines.  The models are lagging behind the observations.  The workshop participants recommend a Theoretical and Experimental Institute to investigate the internal workings of the subduction factory.
- The participants recognized the international nature of exciting science at convergent margins.  They enthusiastically endorse international cooperation to facilitate MARGINS science in Japan, building on the strong body of science already in place.  More generally, they support the current efforts of the MARGINs office to establish  Inter-Margins with all deliberate speed.  The full workshop report includes workshop presentations of international foci on convergent margins around the world.
- Interdisciplinary studies and international cooperation require free and easy access to a wide array of data.  The workshop strongly recommends interaction between MARGINs and GERM to further the development of a) databases for studies of the Subduction Factory and b) systems for sample curation and distribution.
- Many arcs or arc segments are lacking adequate sample sets, critical pieces of information or adequate data synthesis, necessary to test models developed in regions of focussed study.  The workshop participants recognize the need for, and encourage support of, well-defined studies in critical localities.