The MARGINS initiative was conceived in its first working form in 1988. Then, as now, its orientation was towards scientifically driven, process oriented and interdisciplinary studies of active processes that cross the shoreline along continental margins. An initial objective was to construct a way to tackle first-order, fundamental research questions of Earth Sciences, the solution of which would advance significantly the science in a single, concerted step. Not surprisingly, then, the mission statement of the MARGINS Program is “to understand the complex interplay of processes that govern continental margin evolution globally." Members of the steering committee generated proposals to host five open NSF-sponsored workshops between 1988 and 1993, in order to engage the community and to define the scope of the overall research initiative, and determine how best (and most efficiently) to focus MARGINS research on scientific questions. The proceedings of a workshop sponsored by the National Research Council (NRC) in Irvine, California, defined, outlined and presented the MARGINS concept: the report was entitled “MARGINS: A research initiative for interdisciplinary studies of processes attending lithospheric extension and convergence." The crucial message of this workshop was the following:
“The outcome of the workshop indicates widespread support and enthusiasm for a new direction in margins research that would focus on interdisciplinary studies of the fundamental processes of margin evolution. Interdisciplinary studies, as a new direction, are demonstrated by the working group reports, which show a remarkable similarity in focus despite the wide diversity of topics addressed and the degree of separation usually present between investigators from different disciplines. Many of the scientific problems that were identified, and their suggested solutions, were common to several working group topics. These similarities define a commonality of direction that belies traditional boundaries based on discipline, geography, or methodology. The principal reason for these similarities is that fluid flow, magmatism, and sedimentation, are not unique to either divergent or convergent margins. Instead, they are fundamental global processes that control the ways in which continents grow and deform with time.
"The MARGINS Initiative is proposed as a means of nurturing this new direction. The primary scientific objective of the initiative will be to develop programs aimed at understanding the processes that control the initiation and evolution of continental margins.”
With these words, the founding philosophy of the MARGINS program was established.
The original MARGINS science plan was published in 1996 by the MARGINS Planning Office, then at the Department of Geology and Geophysics, Rice University, Texas. The original MARGINS science plan outlined a program of multidisciplinary investigations (including theory, observation, and experiment) to be carried out in a complementary fashion in order to advance our understanding of the processes controlling continental margin evolution and development, at a quantitative level. The proposed approach was process-oriented because similar processes occur at all active continental margins, regardless of the exact kinematics of the setting (i.e., convergent, divergent, or transform). A few key processes were identified as important in controlling the evolution of all margins. As such, these were envisioned as the targets for MARGINS investigations. It was proposed that efforts be concentrated in a few optimal locations where the processes are active and where theory, observations, and experiments could be synergistically combined to address one or more of the problems identified as key to understanding margin evolution.
The scientific objectives of the MARGINS program build on a large body of continuing research that has, and is, being conducted using core funding from NSF and other agencies. Achieving the MARGINS objectives requires an experimental approach that includes: developing multidisciplinary case studies, focusing on active systems, studying whole systems (implying an amphibious approach with research spanning the shoreline), establishing scaling relations, including comparative global studies, and establishing event response strategies.
Five general areas of investigation were identified by community workshops and outlined in the original MARGINS Science Plan (1996): 1) the low-strength paradox of lithospheric deformation, i.e., what are the stresses and fluid flow conditions on active faults and how are these related to laboratory observations of the strength of rocks? Under what circumstances can the entire lithosphere rupture?; 2) Strain partitioning during deformation, and in particular, vertical strain partitioning, i.e., is the lower crust of a sufficiently different rheology than the upper crust such that it can accommodate a different strain pattern at depth than that is visible at the surface?; 3) Magma genesis and recycling, that is, can we develop a theory that can explain the chemical, temporal and spatial aspects of melt production and migration?; 4) How is the stratigraphy of geological events preserved?; 5) What are the effects of fluids and fluid fluxes on rock geochemistry, lithospheric rheology, and volcanism? These general questions are applicable to all types of margins. The 1996 science plan did not identify exact locations where these studies would take place—this would be done via a series of NSF-supported community workshops that presented and assessed suitable locales (focus sites) to best address and investigate the various research objectives. However, the science plan did suggest some notional experiments as models that were considered crucial to the success of the MARGINS program.
In the late 1990s, the MARGINS steering committee began to further organize the program and to detail the science plan. At the same time, well-organized groups in the community had been planning major research themes, such as the detailed petrological plumbing of subduction systems and the factors governing the nucleation of seismogenic earthquakes, which could be integrated into the general MARGINS science plan. Thus, the general science plan acquired a number of first-order research initiatives, the philosophies of which required the same multidisciplinary, coordinated and focused study of active systems advanced by the MARGINS science plan. These four initiatives were: Rupturing of the Continental Lithosphere (RCL) and the birth of an ocean; Subduction Factory (SubFac), SEIZE, the Seismogenic Zone Experiment, and Source-to-Sink (S2S).
This publication, a collection of the recently updated science plans of each of the MARGINS Initiatives, is the result of an immense amount of work by the community, champions within each initiative to organize workshops and finalize their respective science plans, the MARGINS Steering Committee, individuals who worked with their communities to create executive summary documents, and the MARGINS Office. Particular thanks go to Dr. Olaf Svenningsen, who developed the graphic design and layout for the entire book, redrafted innumerable figures, revamped sections of text, and spent an eternity looking for missing references. The fact that this book exists at all is in large part due to his determination and enthusiasm.
These science plans should be viewed as dynamic documents, reflecting increasing knowledge and an evolving scientific community. One fundamental objective of MARGINS has already been attained—the building of a community of scientists who are well-informed across a broad range of disciplines and sub-disciplines not related to their own. This was achieved by way of many interdisciplinary workshops, theoretical institutes, symposia, AGU town meetings, and professional meetings fostered by the MARGINS program. With the community now so engaged, there needs to be a commensurate awareness within NSF of this “community collaborative spirit” in addition to a marked increase in the MARGINS budget (with contributions from NSF-OCE, NSF-ODP and NSF-EAR) in order for the program to address the research objectives outlined in the science plans over the lifespan of the program.
We will begin this science plan introduction with a detailed account of the RCL science plan, as MARGINS had its origins in attempting to study, characterize, and understand the deformation of the continental lithosphere. The evolution of the MARGINS program since 1988 saw dramatic changes in content and focus, augmenting RCL with SEIZE, SubFac and S2S, while retaining its original strategy. Further, the intense discussions, interactions, and “pain” experienced by RCL in extracting a consensus from the community in terms of research objectives and focus sites is common to all the initiatives; what we learned from RCL occurred in each and every initiative in its early days of planning.
A fundamental and accepted aspect of the MARGINS program revolves around the axiom to focus on active and “complete” systems. MARGINS concentrates on active systems because it becomes tractable to characterize the boundary conditions and the initial physical and chemical states of materials in the system.
Furthermore, one or more of its characteristics may have changed during the active-passive transition, with paleo-conditions being potentially difficult to infer from the rock record. The “complete” system approach is deemed critical because of the need to study the margin as a large, complex, interactive dynamic system.
The RCL science plan was the outcome of an NSF-sponsored Theoretical and Experimental Workshop on “Rheology and deformation of the lithosphere at continental margins” in January, 2000. The purpose of the workshop was to review the status of the fundamental objectives defined in the initial science plan and to select focus sites for the investigation of faulting, strain partitioning, and magma emplacement at sites of active continental rifting, where there is a transition to initial seafloor spreading.
For the RCL initiative, the main goals have evolved into:
1) To understand the driving forces of rift initiation and continuation,
2) To determine the controls on the locus of rifting, and to understand the conditions of initial rifting in different environments,
3) To characterize the rift as a thermo-mechanical system (rheological flow laws, and the role of brittle failure, including low-angle normal faults),
4) To determine the scale of deformation of the lower crust during the rifting process,
5) To quantify the transfer of heat into and within the lithosphere during rifting,
6) To understand the distribution of the extensional (and transcurrent) strain with depth, in map view, and in time,
7) To understand the controls on rift architecture,
8) To determine the role of fluids and volatiles during rifting,
9) To understand the timing, kinematics, and rheology of the transition from continental extension to seafloor spreading,
10) To determine the composition and origin of transitional crust formed during the process of completely rifting a continent.
Given the MARGINS strategy to concentrate on both active and complete extensional systems, for the RCL initiative there are actually only a handful of potential candidate sites around the world, such as the Gulf of Aden/Gulf of Tadjura (Arabia-Somalia), the Gulf of California/Salton Sea (Mexico/USA), Red Sea/Gulf of Suez (Arabia-Nubia), and the western Woodlark Basin (Papua New Guinea). In order to assess each region, Focus Site Criteria were devised representing essential, desirable, and logistic characteristics required of the study regions. The sites were evaluated in terms of their scientific merits with some consideration given to political feasibility and the likelihood of partnership with scientists from other countries. Two of the sites (the Gulf of California and Northern and Central Red Sea) were selected by the community, one to represent rifting in old cratonic lithosphere (the Red Sea) and the other to represent rifting in young orogenic lithosphere (the Gulf of California). In addition, these two rifts have different degrees of obliquity: the Red Sea is a nearly orthogonal rift whereas the Gulf of California is highly oblique. In October 2000 and March 2001, NSF-sponsored workshops specifically focused on the more detailed science questions for each of the focus sites. Most importantly, these workshops were designed so that investigators who had not worked previously in the focus sites could familiarize themselves with the current status of research efforts in the region, thereby allowing then to explore what scientific opportunities exist and to learn what studies have already been undertaken.
Although it has been only two proposal cycles since RCL proposals have been funded within the MARGINS program, certain aspects of the proposed studies have already been accomplished, due in part to projects that were underway but funded outside the MARGINS program itself. The RCL science plan has been updated to reflect these studies and reviews the latest information on observational findings from the two focus sites, as well as the latest thinking on these issues coming from both laboratory and theoretical studies. Unfortunately, political and military instabilities in the Middle East and judicial issues stemming from active seismic-source experiments and the Marine Mammals Protection Act has slowed our ability to work in the RCL focus sites.
Subduction of oceanic plates causes earthquakes, tsunamis, and explosive volcanism, together with changes in the composition of the mantle, including its abundance of volatile and heat-producing elements. Subduction also gives rise to beneficial products, such as ore deposits, geothermal energy, and the ground we live on. Thus, subduction is one of the Earth’s most important dynamic processes. It also is one of the least well understood because of the limited accessibility, the complexity, and the immense length-scales of subduction zones. The goal of the Subduction Factory Initiative is to focus research on two contrasting subduction zones to address fundamental questions about how this process works. The community-selected focus sites are the Izu-Bonin-Marianas and Nicaragua-Costa Rica subduction systems.
The “Subduction Factory” recycles raw materials from the subducting lithosphere to the surface and deep Earth. SubFac aims to study this recycling process by imaging subduction zones with a variety of techniques and quantifying fluxes of subducted materials through the mantle to the surface in the form of melts, aqueous fluids and gases. Embedded within this approach are essential links to the thermal and viscosity structure of the slab and mantle wedge, the nature of mantle flow through the wedge, and the timescales of magma generation and transport.
Three fundamental science themes are addressed by this initiative:
1) How do forcing functions such as convergence rate, age of the subducting plate, sediment dynamics, and upper plate thickness influence the production of magma and fluid from the Subduction Factory?
2) How do subducted volatiles (mostly H2O and CO2) impact biological, physical, and chemical processes from the trench to the volcanic arc and back-arc as well as the deep mantle?
3) What is the mass balance of chemical species and material across the Subduction Factory, and how does this balance affect continental growth and evolution?
Ongoing projects funded by NSF and contributing to SubFac combine mapping of the incoming plate and fore-arc slope with both active and passive seismic experiments to image structures and composition of the upper plate, mantle wedge, and subducting slab. Heat flow measurements and GPS deformation rate estimates are being combined with other geophysical data to constrain the physical operation of the subduction system. Riserless drilling continues to provide samples of the input material seaward of the trench and output material in the forearc (e.g., fluids, possibly accreted sediments and hydrated forearc mantle) and arc (fluids, gases, extrusive and intrusive rocks). With the recent launching of the Japanese riser drill ship, Chikyu, deeper holes into the incoming crust and upper plate will more thoroughly chart the inputs and outputs of the system. A record of volcanic evolution and fluxes on the upper plate will also be provided by on-land drilling into the arc. On-land and offshore boreholes will be exploited to sample fluid outputs from the system.
Field and analytical studies of the arc system focus on the mass fluxes of constituents through the Subduction Factory by measuring chemical compositions of lavas, melt inclusions, and gases. Laboratory studies provide element partitioning relationships, phase equilibria, and calibrations for rheological and seismological properties. A wide array of in situ observatories and multiple re-occupation campaigns, coupled with a strategy for rapidly responding to major events, round out the data collection strategy. These diverse field and lab measurements are being integrated with physico-chemical models for subduction, fluid flow, melting and melt flow. Phenomena predicted from geodynamic models are guiding the data acquisition efforts, and the data collected will provide constraints for future generations of models. In this way, modeling and observations will complement and motivate each other.
The Central American and Izu-Bonin-Mariana (IBM) subduction zones were chosen as focus sites for these studies. These sites provide ample volcanic and seismic activity, accessibility to input and output samples for geochemical analyses, along-strike variations in forcing functions, cross-arc and historical perspectives, and minimal upper plate contamination of magmas. Central America features variations in forcing functions along-strike from Nicaragua to Costa Rica, including the age and surface morphology of the subducting plate and the variation in the quantity of sediment transported to depth. These are matched by sympathetic chemical gradients in the volcanic output, which allows the mass-flux through the system to be thoroughly examined. Extensive carbonate subduction and extremely volatile element-rich eruptions enable investigation of the carbon and water cycles through subduction zones. High-fidelity tracer studies in Recent to Miocene igneous rocks will constrain a mass balance of chemical constituents through the arc with time. Many of the Subduction Factory objectives link naturally with those of the SEIZE science plan in Central America. The IBM margin is an excellent complement to Central America. The oldest and presumably coldest crust on the planet subducts beneath the IBM with relatively little, and carbonate-absent, sediment. Active back-arc volcanism allows output to be accessed across strike and through time, and provides a framework with which to test the effects of back-arc flow on subduction dynamics. Vigorous fluid venting from trench to rear-arc provides samples for studying volatile cycling across the entire margin.
The Seismogenic Zone Experiment (SEIZE) was developed to study the shallow subduction plate interface that is locked and accumulates elastic strain, periodically released in large or great earthquakes, often tsunamigenic. Considerable progress has been achieved on many of the underlying objectives of the Seismogenic Zone Experiment, which sets the foundations for future work. As of March 2003, 10 programs (consisting of multiple proposals) have been funded directly by MARGINS, of which approximately seven are mostly complete. The MARGINS program has stimulated considerable interest in the US science community as demonstrated by MARGINS-related science funded by Earth and Ocean Sciences core programs and internationally, principally with German, Japanese, Costa Rican, and Nicaraguan scientists engaging in complementary work. The focus sites, Nankai and Central America (Nicaragua-Costa Rica) complement each other, with shallow seismogenic zones, possibly reachable by riser drilling, in both areas. Central America is characterized by basement topography and sediment thickness that vary greatly along strike, with “patchy” seamount distribution, possibly related to patchy locking. Characteristic earthquakes tend to be smaller in magnitude (M~7-7.5) with a limited slip distribution, possibly controlled by bathymetry; slow tsunamigenic earthquakes have occurred off Nicaragua. Nankai is characterized by larger magnitude (M~8-8.5) earthquakes, with relatively uniform fault properties and only small lateral changes; large areas are fully locked most of the time.
A major accomplishment at this point has been the construction of a functioning community of scientists across major sub-disciplines of Earth Sciences. This community, by way of several workshops, theoretical institutes, symposia and professional meetings, most fostered by the MARGINS program, now share a common understanding of the complexity of the earthquake cycle, share a common vocabulary, and have been developing a clearer and sharper focus on the most important issues as reflected in the revised SEIZE science plan. There is a much greater appreciation of the theoretical, experimental, and modeling contributions and of critical observations, including their limitations, necessary to test and foster our understanding of seismogenesis. The IODP drilling community, which overlaps substantially with MARGINS-SEIZE, are using these developments to hone deep drilling objectives for the Japanese riser ship, Chikyu, in Costa Rica and Nankai, with fault targeted drilling, sampling and monitoring possible as early as 2007.
The SEIZE initiative was the first to get started, having its roots in a 1995 workshop in Japan, “Dynamics of Lithosphere Convergence,” sponsored by the International Lithosphere Program, followed by an NSF-sponsored workshop in 1997 to flesh out the science plans and identify focus sites. The planning and precursor efforts of SEIZE thus began long before the first direct MARGINS funding in 1999. A great deal of seismic reflection data has been obtained, sufficient to image the entire seismogenic zone beneath Nicaragua, Costa Rica, and Southeastern Japan. Two 3-D reflection surveys have been done off Japan, and one 3-D in Central America. Much geodetic work has been carried out in both regions and we have significantly better understanding of locked vs. slipping zones. The Ocean Drilling Program installed a long-term sea floor observatory sampling deeply sourced fluids within the décollement zone off Costa Rica, to monitor fluid pressures, temperatures, flow rates and compositions and their changes through time. The importance of transient strain events, possibly related to fluid flow, has been recognized. Integration of heat flow data, thermal modeling and laboratory studies has led to a new set of questions about the controls on the updip limit of seismicity at convergent margins.
Recently, a revised science plan was commissioned as part of a SEIZE Theoretical and Experimental Institute in March 2003. The science plan derived from the 1997 meeting focused on the following questions:
A. What is the physical nature of asperities?
B. What are the temporal relationships among stress, strain and pore fluid composition throughout the earthquake cycle?
C. What controls the updip and downdip limits of the seismogenic zone of subduction thrusts?
D. What is the nature of tsunamigenic earthquake zones?
E. What is the role of large thrust earthquakes in mass flux?
Based on work done since, the science plan has been updated with these supplemental questions:
1) What controls the overall distribution of seismic energy release during a subduction zone earthquake (up, down, and sideways). Is there one P-T-X condition that defines the onset and down dip limit, or do they vary with the material properties and fault geometry in the subduction system?
2) What controls the sometimes heterogeneous distribution of locking patterns on the plate interface and subsequent variations of energy release ? Are such “asperities” linked by common physical processes within the fault region or governed by separate, unrelated phenomenon? Do they vary in time, and if so, over what time scale?
3) What controls the rate of propagation and slip rates of earthquakes and the distribution of fast, slow, tsunamigenic, and silent earthquakes in time and space?
4) What is the nature of temporal changes in strain, fluid pressure, and stress during the seismic cycle? Do these change gradually during the seismic cycle or are there transient interseismic phenomena that lead to strain and energy release at various times during the seismic cycle?
5) What are the prediction errors associated with typical mechanical models?
A major goal of the Earth Science community is to provide quantitative explanations and predictions of the effects of perturbations on surface environments and on the geologic record preserved in sedimentary strata of continental margins. In past decades, margins have been investigated piecemeal, by researchers who have tended to focus on a particular segment (from a disciplinary perspective), and eschewed the broader perspective of the margin as an interconnected whole. Recognizing this shortcoming, NSF was instrumental in initiating the MARGINS Source-to-Sink Program which, for the first time, will attempt to understand the functioning of entire margin systems through dedicated observational and community modeling studies.
The Source-to-Sink Initiative seeks to make significant advances in our predictive capability of sediment and solute fluxes across the Earth’s continental margins. Improved predictions of sediment and solute mass from source to sink are needed now because this transfer plays a key role in the cycling of elements such as carbon, in ecosystem change caused by climate change and sea-level rise, and in resource management of soils, wetlands, groundwater, and hydrocarbons. Yet, we are presently unable to anticipate how perturbations in one part of the source to sink system will affect another.
It is for this reason that the S2S science plan calls for an unprecedented coupling of physical and numerical modeling and integrated field studies. A suite of inter-connectable numerical and physical-process models with shifting boundaries is to be constructed to test hypotheses concerning process connections and to predict the behavior of these source to sink systems on time scales ranging from individual events to millions of years. Rates and mechanisms of sediment production, transport, and accumulation will be monitored using high-resolution digital elevation models, new dating and tracer techniques using cosmogenic isotopes and optically stimulated luminescence, and field acoustic and optical velocimeters for measuring sediment velocity and concentration. High-resolution records of sedimentary deposits are to be collected through swath mapping and CHIRP, combined with sediment coring involving logging tools such as GRAPE and FMS. Ultimately, IODP drilling may provide the best test of S2S concepts and working hypotheses as the work continues in the defined focus sites; the Fly River/Gulf of Papua system of Papua-New Guinea and the Waipaoa River system of the North Island, New Zealand.
The key scientific issues that, if answered, would produce a quantum leap in our quantitative understanding of geomorphological, hydrological, and geological Earth Systems were identified at two community-wide MARGINS Source-to-Sink Workshops (Lake Quinault and Lake Tahoe) and an AGU MARGINS town meeting. These meetings helped to define the concept of a Community Sediment Modeling Environment. The scientific issues are encapsulated in the following three questions:
1) How do tectonics, climate, sea level fluctuations, and other forcing parameters regulate the production, transfer, and storage of sediments and solutes from their sources to their sinks?
2) What processes initiate erosion and sediment transfer, and how are these processes linked through feedbacks?
3) How do variations in sediment processes and fluxes and longer-term variations such as tectonics and sea level build the stratigraphic record to create a history of global change?
The Source-to-Sink Initiative focuses on two active convergent continental margins that produce large amounts of sediment deposited in adjacent, closed basins, as their focus sites. Following community-wide discussions, the Fly River and adjacent Gulf of Papua (Papua-New Guinea) and the Waipaoa River System on the east coast of New Zealand’s North Island were chosen for focused research. The Fly River and Gulf of Papua constitute one of the few modern examples of a developing foreland basin, and the Waipaoa drainage basin reflects growth of a terrain by volcanism and vertical uplift. The Fly/Gulf System experiences a tropical environment, whereas the Waipaoa is sub-tropical/ temperate. Because of differences in oceanographic environments, the Gulf of Papua possesses both siliciclastic and carbonate sedimentary environments, whereas the Waipaoa margin contains only siliciclastic sediments. The Fly drainage basin (75,000 km2) experiences relatively constant discharge, the main perturbations being linked to ENSO-related droughts, and it is practically unaffected by human activity, although recent mining on the Ok Tedi has provided a sediment spike that can be monitored farther downstream. In contrast, the Waipaoa system (2000 km2) is strongly affected by seasonal variations in discharge and (particularly) by tropical cyclones; and for the past 100 years it has been affected by the impact of European land-use and (to a lesser extent) by dam construction.
At the Fly/GOP focus site, historic measurements along the river are relatively few. Consequently, the community decided that we need first to understand how changes in water discharge and sediment loading impact floodplain and shelf-clinoform sedimentary sinks, and how escaping sediments impact carbonate production by coral/algal communities on the shelf and in deeper water. A dedicated Waipaoa workshop held in Gisborne, Palmerston North and Wellington, New Zealand, helped to hone the research objectives for the Waipaoa focus site. For this focus site, shallow and deep coring of lacustrine and shelf environments along with chronostratigraphic analyses are needed to define the inputs and sedimentary architecture. Geophysical characterization of the shelf needs to be carried out, principally by swath bathymetry and high-resolution seismic profiling, with limited ground-truthing. Monitoring and modeling studies are required to understand the mechanisms of sediment dispersal from Poverty Bay to the open shelf, and the resulting depositional signatures.
In conclusion, the development of MARGINS programs in the US and abroad promotes a changing and challenging approach to research in the Earth Sciences. The MARGINS objective was, and remains, to develop a self-consistent understanding of the processes that are fundamental to margin formation and evolution. The MARGINS approach involves concentration on several study areas targeted for intense, multidisciplinary programs of research in which an ongoing dialogue among field experiment, numerical simulation, and laboratory analysis researchers is fundamental and symbiotic. The various science plans of the MARGINS Program all define methodologies for investigating those processes that fundamentally govern the evolution of margins, which comprise lithospheric deformation, magmatism and mass fluxes, sedimentation, and fluid flow. The goal of the MARGINS Program is to provide a focus for the coordinated, interdisciplinary investigation of these processes that are the foundation of the MARGINS Initiatives.
The need to integrate multiple lines of evidence to better understand complex dynamical systems requires both interdisciplinary approaches and a concentration of resources in areas likely to yield outstanding results. Within the MARGINS framework, implementation workshops, AGU and GSA special sessions and town meetings, and Theoretical and Experimental Institutes provide opportunity for explicitly synthesizing field, observational and analytical studies with theoretical and experimental approaches to frame next-generation studies. This overview shows the commonality of approaches in the four MARGINS initiatives and the frequent transcendence of the processes under study, often irrespective of tectonic setting. A corollary is that progress in one initiative will frequently benefit another.