THOLEIITIC MELT FRACTIONATION CONDITIONS IN DIFFERENT TECTONIC SEGMENTS OF THE SOUTHERN PROVINCE OF MID OCEANIC RIDGE

Main magmatic evolutionary trends and crystallization conditions were estimated within separate tectonic segments of the Southern province o f Middle Atlantic oceanic ridge. The study was based on the comparison of quenched glass compositions with the computer modeling data of bas altic melt fractionation. Within all studied area excluding the segmen t corresponding to 1-7-degrees-S the crystallisation depth of magmatic melts was estimated in the interval of 12-15 km. The crystallisation conditions of higher depth melts (6-8 kbar) were suggested to the sout h of the Chain fault (1-7-degrees-S) being in contrast to the regions of the Central and near-Equatorial Atlantics. The primary melts within all segments studied were generated at pressures below 9.5 kbar besid es the segment corresponding to 7-12-degrees-S. The latter was charact erised by the extrusions of higher depth primary melts. This segment c ontoured in terms of petrochemical features coincides with the distinc t geochemical anomaly.