Geochemical Signature of Basalts of the MAR Rift Valley at 20°31′ N: Origin Conditions of the Anomalous Volcanic Center of Puy des Folles in the Axial Zone of the Mid-Atlantic Ridge

The results of a study of chilled glasses sampled during the 45th cruise of the R/V Professor Logachev at the top of the submarine volcano Puy des Folles are presented. The Puy des Folles volcano is located in the axial part of the rift valley of the Mid-Atlantic Ridge (MAR) at 20°31′ N. Unlike typical volcanic axial highs which usually does not exceed several hundred meters the summit of the Puy des Folles volcano is located a depth of 1950 m and rises 1800 m above the bottom of the rift valley. The data on geochemistry and isotope composition of chilled glasses examined allow us to come to a number of conclusions that expanded existing ideas about magmatic and tectonic processes conducted in the rift valley of the slow spreading ridges. Chilled glasses sampled at the top of the Puy des Folles volcano are originated from a very depleted melt formed by partial melting of the DM reservoir. Puy des Folles volcano was formed as result of the activity of a long-lived magma chamber located below the rift valley axis. It is possible that, in addition to the DM reservoir, a mantle source enriched in incompatible elements may have participated in the formation of the parental melts for the studied chilled glasses. A weak geochemical signal of contamination of the parental melt with a hydrothermal component in chilled glasses was established. Signs of stagnation in the spreading of the oceanic crust in the rift valley segment studied in this work have been established.