Meeting

Hydrothermal energy transfer and the ocean carbon cycling

N. Le Bris, UPMC - CNRS, France

East Pacific Rise 15.4°N: A geochemical approach at very small spatial and temporal scale in a hotspot-ridge context.

Electrical conductivity (or its reciprocal resistivity) is sensitive to temperature, component, and phase of materials, and the degree and form of interconnection of material in matrix for two or more materials’ system.

The Stalemate Fracture Zone (FZ) is a 500 km long SE-NW trending transverse ridge between the northernmost late-Cretaceous Emperor Seamounts and the Aleutian Trench. Sampling at the Stalemate FZ and the fossil Kula-Pacific Rift valley was carried out during the R/V SONNE cruise SO201 Leg 1b in 2009 in frame of Russian-German project KALMAR. We present in this work results on mineralogical composition of mantle peridotite dredged at the station DR37 from the northernmost  part of the Stalemate FZ on border with Aleutian Trench.

Chemical and isotopic compositions of mid ocean ridge basalts (MORBs) are relatively homogeneous when compared with the basalts from other tectonic settings, e.g., ocean islands and arcs. Nevertheless, their variations indicate that the source mantle beneath MORs should be heterogeneous and the melt generation and coalescence processes are complex. I here present an overview of such the melting processes of peridotite beneath MORs.

InterRidge-Japan community conducted an interdisciplinary research project TAIGA, Trans-crustal Advection and In-situ biogeochemical processes of Global sub-seafloor Aquifer, from 2009 to 2013. The flows and chemical compositions of subseafloor fluid are regulated by tectonics, and are modified by the host rocks. During 5 years project, we selected three integrated study sites of different tectonic settings and carried out multi-disciplinary studies.

The Okinawa Trough is a back-arc basin behind the Ryukyu trench-arc system and located along the eastern margin of the Eurasian continent. Based on geophysical and geological studies, the Okinawa Trough is considered a back-arc basin in the rifting stage. Such a tectonic setting is characterized by development of normal faulting in brittle continental crust and frequent intrusion of a magma, which can be expected to provide favorable environment for development of a hydrothermal system.

The Australian-Antarctic Ridge (AAR) has been remained uncharted until 2011 because of its remoteness and harsh weather conditions. From 2011, the multidisciplinary ridge program initiated by the Korea Polar Research Institute (KOPRI) surveyed the little explored eastern segments of the Australian-Antarctic Ridge (AAR) to characterize the tectonics, geochemistry, and hydrothermal activity of this intermediate spreading system.

During R/V Zhukezhen Cruise DY33, Leg 1 (February 09 to March 29 2015, chief scientist: Dr. Xiqiu Han), we conducted comprehensive geophysical mapping, hydrothermal plume surveying, video sled observing and geological sampling along the slow-spreading Carlsberg Ridge. The most significant result of this leg is the discovery of a new ultramafic-hosted hydrothermal sulfide deposit which named Tianxiu Field at 63.82°E, 3.69°N in water depths of around 3450 m, on the southern rift-valley wall, ~5 km from the adjacent rift axis.

The mafic-hosted and inactive Wocan hydrothermal field, located on an axial volcanic ridge at a depth of ~3000 m at 6°21′N along the slow-spreading Carlsberg Ridge, was discovered and sampled by TV-grab at five stations in 2013 on the DY28 cruise. Preliminary investigations show that the field consists of two mineralization mounds called Wocan-1 which located on the east, and Wocan-2 which ~1.7 km away from Wocan-1 on the west.

In 2010, we conducted an ocean bottom seismometer (OBS) experiment surveying the fossil spreading center in the Southwest Sub-basin of the South China Sea. The detailed velocity model, simulated by two-dimensional ray tracing, shows a strong lateral variation in velocity structure across the spreading ridge.

Title: Saldanha hydrothermal field: the role of the sediment-cover in the preservation of ore-forming minerals

Authors: Ágata Sofia C. M. Alveirinho Dias and Fernando J. A. S. Barriga

E-mail: ascdias@fc.ul.pt or agata.dias@usj.edu.mo

Structure and dynamics of the Southeast Indian Ridge and off-axis volcanism, 129°E to 140°E: Preliminary results of the STORM cruise

Hydrothermal Exploration of Mid Ocean Ridges: Where Might the Largest Sulfide Deposits Occur?

C.R.German         S.Petersen            M.D.Hannington

Review of Japanese Taiga project 3:

Geodynamics of the Southern Mariana Trough Back-Arc Basin

Nobukazu Seama