Volatiles and Fluids in Subduction Zones

Material input and tectonic behavior during plate subduction

This subproject aims at understanding the interplay between active tectonic processes and fluid flow at convergent margins and incoming oceanic lithosphere using a multidisciplinary approach. A major objective is to contribute to quantify processes of material (mass and fluids) transfer between subducting and overriding plates along the plate boundary. A second main goal is to study deformational processes during bending of oceanic lithosphere at trenches.
The interplay between active tectonic processes and fluid flow will be studied at erosional and accretional convergent margins. Processes at erosional margins will concentrate along the Middle America Trench. Between 2004 and 2006 we will finalize the study of the segment of Costa Rica and Nicaragua extending the work to El Salvador and Guatemala to a total of > 1200 km of the margin (Figure A1-1). From 2006 to 2008 we will initiate the study of a classic accretionary margin along the central Chile trench (Figure A1-2).

Fig. A1-1: Bathymetric and TOBI and DTS-1 sidescan sonar coverage at the Middle American continental margin.

In addition, we will study the bending-related deformation of the incoming oceanic lithosphere subducting at those two trenches. This type of deformation leads to a profound transformation of the chemical and mechanical properties of the incoming oceanic plate by currently poorly understood and quantified processes.

Fig. A1-2: Bathymetric and TOBI and DTS-1 sidescan sonar coverage at the Middle American continental margin.

To study the interplay between tectonics and fluid flow we will use a wide range of geophysical and geological methods. Multibeam bathymetry and side-scan sonar mapping of the seafloor and high-resolution subbottom profiler images will provide a detailed picture of the neotectonic structure and fluid-flow related features of continental margins and incoming oceanic plates. We intend to obtain the most possible complete inventory of fluid-flow related features along the margins. These include mud diapirs, carbonate patches, slump scars and deeply rooted active faults. We will collect ground-truthing data with deep-towed video cameras to characterize the different types of fluid-related extrusive manifestations and search for active fluid manifestations. In addition, we will study the distribution and types of slumps and slides and their failure mechanisms.
Furthermore, using deep-penetrating seismic reflection data that image the margin structure from the plate boundary to the seafloor, the tectonic fabric and fluid-flow related features mapped along the seafloor can be related to processes dominant in the subduction zone (e.g. subduction accretion or erosion). The combination of surface data and sub-surface seismic images will provide the 3-D structure of the margins, helping to quantify long-term material transfer between subducting and overriding plates related to subduction erosion and accretion. Calculation of erosional and accretional rates will contribute to quantify material fluxes budgets at the subduction zone.
In oceanic plates, seafloor mapping and seismic data provide evidence for deformation during plate bending. Side-scan sonar studies can potentially define zones where fluid outflow associated to bending-related faulting may be active at the seafloor of the incoming plate. In addition, we will characterize the sediment cover of the oceanic plate and the evolution of bending-related faulting. The study of the structure of the oceanic plate is also fundamental to understand the interaction of subducting and overriding plates, the tectonics of the forearc, and the input deep in the subduction zone into the area of melt generation.