RELICT SULFIDE FORMATIONS OF TAG HYDROTHE RMAL FIELD, MID-ATLANTIC (26-DEGREES-N, 45-DEGREES-W)

During the 23-th Cruise of the R/V ''Akademik Mstislav Keldysh'' an th e TAG hydrothermal field a huge cone-shaped hydrothermal MIR Mound was descovered. Its dimensions are: diameter near basement is more than 7 00 m, height 50 - 70 m. The total weight of hydrothermal material is a bout 10 million tons. The MIR Mound is divided into two zones: the you ng internal and the old outer. The internal zone diameter is about 400 m. There is a dense ''forest'' of high temperature sulfide chimneys i nside the internal zone. The outer zone width is 150 - 200 m. Low temp erature hydrothermal minerals (hydroxides of Fe and Mn, opal, sometime s - sulfides) are mainly inside the outer zone. The outer zone is part ly covered by sediments. The radiocarbon dating of sediments accumulat ed near the MIR Mound showed that it began to form yearlier that 25 k. y. B. P. The periods of hydrothermal activization were 23 - 25, 12 - 16 and 4 - 8 k. y. B. P. Deep tow photographing, side scan survey and sediment studies have indicated that 2.5 km to the North from MIR Moun d another inactive hydrothermal mound of similar dimensions exists.