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Meteor 54, Fluid and Subduction Costa Rica, 06.07. - 11.10.2002

The RV METEOR M 54 cruise addresses basic objectives of and is of central importance to the "Sonderforschungsbereich" SFB 574. The title of the SFB is: Volatiles and Fluids in Subduction Zones: Climate Feedback and Trigger Mechanisms for Natural Disasters. Its main objective is to understand the budget, reactions, and recycling of volatile elements in subduction zones, and their role in climate forcing. In this way the SFB addresses the long- and short-term development of the Earth´s climate, the geochemical evolution of the hydrosphere and atmosphere, and the causes of natural disasters. These processes are all connected with the return flow and impact of volatiles and fluids from subduction zones. The multi-disciplinary analysis of the volatile phases (water, carbon, sulfur and halogens) and their complex effects on the exosphere, is an ambitious undertaking, and one of the highest priority objectives of modern geoscience. The major volatile input into subduction zones are the sediments, the alteration products of the oceanic crust, and the trench-fill from down-slope mass wasting. The output is via fluid venting at the deformation front, by gas hydrate dissociation, and volcanic eruptions at the fore-arc. Inside the subduction zone the incoming material is transformed, mobilized or fractionated into different volatile reservoirs and phases. These phases are either ejected into the exosphere through the upper plate, accreted to the leading edge of the continental plate, or are transported into the lower mantle. The tectonic style of subduction, the structure of the margin wedge, and the properties and configuration of the down-going plate all exert a first order control on volatile budget,it's transformation, and return pathway.

Figure 1 The area of investigation off Costa Rica/Nicaragua.


The area of investigation off Costa Rica/Nicaragua is well suited for such an undertaking because of small-scale change of characteristic features influencing volatile cycling; i.e. the composition and age of the incoming oceanic crust, the morphology of continental slope, and the accretionary tectonic style. Equally important are the composition of the volcanic rocks on land as well as in submarine outcrops to trace the history of volcanic emissions.The basic data for these investigations aboard RV METEOR at the fore-arc off Central America are geophysical surveys, drill-hole information, multibeam and side-scan sonar surveys as well as video-guided sea floor observations obtained earlier. Accordingly, the M 54 expedition is divided into three legs using different methodologies.

Figure 2 The first leg of the Meteor 54 expediton.

During the second leg, M 54/2, sediment coring, heat flux measurements, and dredging are the main activities. The sampling will be done along pre-selected profiles (Fig.3). Sediment cores are used to investigate diagenetic processes, determine the physical properties of sediments, and to reconstruct the history of explosive volcanisms based on ash layers. Focus of the heat flow profiles is the thermal structure of the lithospheric plate in order to constrain the seismogenic zone. Additionally, the thermal anomalies at and around fluid conduits and slump features will be measured.

Figure 3 The second leg of the Meteor 54 expediton.


During the first leg, M 54/1 (Fig.2)high-resolution seismic profiles are acquired in order to obtain the geometry and thickness of the incoming sediment packages. Special attention is given to the distribution of gas hydrates as evident in the BSR, which is linked to upward fluid flow. In combination of different geophysical methods, applied to small-scale selected areas, the quantification of physical properties of the sediments and their pore fluids will be attempted.

Figure 4 Potential sampling targets in the northern working area during leg 3.


During the third leg, M 54/3, the focus is on identification and sampling of sites influenced by venting of methane-rich fluids. Chemoautotrophic benthic communities and carbonate chimneys, crust and other authigenic mineral precipitates will be obtained. TV-guided deep-sea instrumentation will be deployed in order to quantify the amount of fluids released from the seafloor and the turnover of methane in the sediment as well as at the seafloor and in the water column. Radiogenic and stable isotope will be used along with trace element pattern to ascertain source depth and residence time of fluids. The main geological features which so far have shown signs of fluid venting are carbonate mounds, subducted seamount scarps and submarine land slides. These features will be the main targets during leg M54/3 (Fig. 4-7).


Figure 5 Potential sampling targets in the southern working area during leg 3.

Figure 6 OFOS and TV-Grab locations on Mound Culebra done during SO163.

Figure 7 Potential sampling targets in the Jaco Scarp area during leg 3.

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