Hydrothermal mineral associations on 71° n of Mid-Atlantic ridge (first results)

Abstract

We discuss the preliminary results of the plume and bottom sediments studies of the Trollveggen hydrothermal vent field based on data from the 68th cruise of the RV Akademik Mstislav Keldysh. The hydrothermal vent field is located to the east of the axial zone of the slow-spreading Mohn Ridge close to the Jan Mayen hotspot at a depth of about 550 m (7118 'N, Norwegian-Greenland Basin). The plume of the hydrothermal vent field was characterized by a weak distribution in the water column, anomalies of temperature, density and salinity, a moderate concentration of methane and a low concentration of suspended particulate matter near the bottom. The enrichment of bottom sediments with barium, strontium and some sulfide forming elements (zinc, lead, copper, molybdenum) was shown. Two mineral associations of hydrothermally modified bottom sediments were revealed: pyrite and barite-marcasite. The temperature of hydrothermal fluids was established by the method of thermal and cryometric studies of gas-liquid fluid inclusions in barite (128260C) and using the FeSZnS equilibrium diagram of sulfide minerals (130290C). Our data were close to the data of direct measurements of fluid temperature [28]. We made a comparison of the hydrothermal mineralization of the Trollveggen vent field and the previously studied fields of the Mid-Atlantic Ridge located near the Azores hotspot. As a result we confirmed the influence of ocean depth and PT-conditions on the formation of hydrothermal deposits.