A New Type of Vent Field in the Mid-Atlantic Ridge (Lost City Vent Field, 30°N)

摘要

In the last 25 years, researchers have been engaged in an intense study of deep-water hydrothermal activity in oceanic rifts with the help of manned submersi-bles. However, an active vent field with unusual chemical compositions of solutions was discovered in the Mid-Atlantic Ridge (30°N) in December 2000. In contrast to the majority of deep-water vent fields with sulfate-sulfide mineralization, this field is characterized by carbonate (+ brucite) mineralization. Russian scientists explored this unique vent field in summer 2002 within the framework of the research program of Cruise 47 of the R/V Akademik Mstislav Keldysh. The Lost City vent field, ～100 m in diameter, was discovered approximately 15 km from the intersection of the MAR with transform fracture zone at a depth of 700―850 m on the upper southern slope of the Atlantis Massif. The basal section includes fragments of black and weakly altered ultramafic rocks with brownish gray lithified carbonate cement. The overlying section is composed of thick continuous carbonate plates. About 30 hydrothermal columns are observed above the carbonate plates. Some columns, up to 20 cm across and 3-5 m high, resemble spires. Large columns, up to 10 m across and 60 m high, represent columnar structures commonly with a flat stop. One can see shimmering warm waters on the walls, terraces, and flat stops of active columns. We scrutinized a large column about 60 m high.