Summary Subduction Factory Workshop
June 6-9, 1998 in 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
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
- 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.