Geotechnical, geochemical, and pore pressure data will be collected during a German?led site survey of the Hellenic Subduction Zone in the eastern Mediterranean in support of IODP Proposal 555-Full 3. The aim of this survey and the IODP proposal is to understand the ?intermediate loops? of the subduction factory, which are several tens to hundreds of kilometers behind the toe. The Mediterranean Ridge is a mature zone of collision and provides easy drilling access to deep seated fluid flow processes in an accretionary prism and its buttress. This project will focus on fault-driven fluid release from the frontal and intermediate loop, which will be quantified in situ and calibrated by hydrothermal geotechnical experiments and geochemical analyses of the pore fluids. CAT flow meters will be deployed, in situ pore pressures measured, and gravity cores collected at the outcrops of the faults for geochemical analyses. The geotechnical and geochemical data will be incorporated into a numerical model of fluid flow between the accretionary complex and its hinterland.
Broader impacts: The research will deepen our understanding of the geodynamic and physico-chemical processes along fault zones in the buttress region of an accretionary complex. The data and information from this project will support a highly ranked IODP Proposal and will strengthen international collaborations between IODP scientists. The PI is an early career scientist who will work with educators at the Birch Aquarium at the Scripps Institution of Oceanography in order to disseminate the information generated from this project to a broad non-academic audience.
Mud volcanoes on the active MedRidge accretionary complex On the various mud volcanoes and ridges studied during cruises P410 and P429, 24 gravity cores were taken altogether. The mud domes included Milano and Napoli (which were also drilled during ODP Leg 160 (Emeis et al., 1996) as well as Leipzig, Maidstone, Lich, Bergamo and an unnamed mud ridge in the southern portion of the Olimpi field area. During P410, five CAT meters (fluid flow rate monitoring instruments) were deployed. Four instruments were deployed on mud volcanoes (2 Milano, 2 Napoli) while the fifth was placed at the potential outcrop of the backthrust fault separating the "modern" MedRidge from the Inner Ridge. During P429 all were recovered successfully. In general, the group of features sampled can be broadly divided into active and dormant ones based on the observations in the sediment plus additional data (T data from MTLs, pore pressure from CPTu, physical properties and pore water geochemistry, and results from former studies). We suggest that the recently active features include Milano, Napoli, Leipzig and Bergamo whereas the mud ridge, Lich and Maidstone are dormant. To assess fluid flow rates, the CAT sample coils were subsampled at ~1 day increments and analyzed on an ICP-OES for fluid and tracer composition. All samples were found to consist entirely of tracer. This is the condition when the instrument functions properly and is well sealed to the sea floor, but there is no flow of fluid through the instrument. Our conclusion is that there was no fluid flow across the sediment/water interface at all sites during the time of the deployment. Previous results from ODP drilling at Milano and Napoli mud volcanoes suggested that Napoli was currently active and that Milano was dormant. These new results suggest that, on the contrary, Milano has been very recently active and that Leipzig and Bergamo are also active. Temperature gradients of over 1.5 degC/m at Milano in the top few meters of sediment can only have been produced by a very recent episode of hot mud expulsion. Similarly, extreme depletions of Cl and Mg in the top meter suggest very little time has passed for diffusion with bottom water. Cl profiles are concave down, which would normally suggest advection, are in contrast to the linear temperature gradients, the lack of measured flow at the monitoring sites, the lack of significant shell fragments in the cores, and the complete lack of visible indicators (carbonates, clams, mussels and other chemosynthetic fauna, or microbial mats) of flow during the video surveys. The traditional modeling of pore fluid profiles to determine flow rates assumes that the profile is steady state. This would not be the case where there is relatively recent mud expulsion. An alternative explanation for the concave profiles is that they are in a transition from a homogeneous vertical profile to a linear diffusional profile. This would occur if a fresh flow of mud was emplaced and diffusion between the upper mud and the bottom water was underway. Since we have collocated cores and temperature profiles, we should be able to model the conduction/diffusion at most of the sites to determine when the flows were emplaced and the distribution may help refine where the conduits were. Our observations indicate that at the active mud volcanoes, flow may be restricted to mud flow rather than fluid flow. We have similar observations at mud volcanoes on the Nile Delta and in the Kumano Basin which may suggest that this may be somewhat universal. We tend to see seeps, focused fluid flow, in places where there is hard rock, typically fractured carbonate, or where there is thin sediment cover over rock. This provides a medium for channelized fluid flow. The active MV environment may often be too much of a soft sediment environment for conduits to form. It is not completely clear cut, however, since Mound 11 off Costa Rica is clearly a carbonate mound (chemoherm) but off to one side of it was a small soft sediment feature that clearly had a fresh mud flow on it.
