Chemical composition of minerals and rocks from the Sierra Leone segment of the Mid-Atlantic Ridge and from the Markov depression, Central Atlantic

Silicic Fe-Ti-oxide magmatic series was the first recognized in the Sierra Leone axial segment of the Mid-Atlantic Ridge near 6°N. The series consists of intrusive rocks (harzburgites, lherzolites, bronzitites, norites, gabbronorites, hornblende Fe-Ti-oxide gabbronorites and gabbronorite-diorites, quartz diorites, and trondhjemites) and their subvolcanic (ilmenite-hornblende dolerites) and, possibly, volcanic analogues (ilmenite-bearing basalts). Deficit of most incompatible elements in the rocks of the series suggests that parental melts derived from a source that had already been melted. Correspondingly, these melts could not be MORB derivatives. Origin of the series is thought to be related to melting of the hydrated oceanic lithosphere during emplacement of an asthenospheric plume (protuberance on the surface of large asthenospheric lens beneath MAR). Genesis of different melts was supposedly controlled by ascent of a chamber of hot mantle magmas thought this lithosphere in compliance with the zone melting mechanism. Melt acquired fluid components from heated rocks at peripheries of the plume and became enriched in Fe, Ti, Pb, Cu, Zn, and other components mobile in fluids.

Age determination of sediments from Kilkeel and sediment core Y69-71P

Evidence from the Irish Sea basin supports the existence of an abrupt rise in sea level (meltwater pulse) at 19,000 years before the present (B.P.). Climate records indicate a large reduction in the strength of North Atlantic Deep Water formation and attendant cooling of the North Atlantic at this time, indicating a source of the meltwater pulse from one or more Northern Hemisphere ice sheets.Warming of the tropical Atlantic and Pacific oceans and the Southern Hemisphere also began at 19,000 years B.P. These responses identify mechanisms responsible for the propagation of deglacial climate signals to the Southern Hemisphere and tropics while maintaining a cold climate in the Northern Hemisphere.