The geochemical structure of the mid-Atlantic Ridge axis from Iceland to Bouvet, a GIS approach

A geochemical database of MORB and a geophysical database have been assembled for the entire Mid-Atlantic Ridge (MAR). Using Geographic Information System (GIS), an integrative study of geochemical variations has been conducted at (a) the entire MAR scale; (b) a regional scale (∼3000 km); (c) an anomaly scale; (d) an individual ridge segment scale. Because MORB provide a window into the Earth's mantle, this comprehensive database provides the first look at regional compositional boundaries and widespread geochemical anomalies in the subaxial mantle along the entire MAR.; The MAR can be divided into five mantle regions. Region I (MAR south of Cox FZ) has higher 87Sr/86Sr and lower Pb isotope ratios than the average (average for the MAR excluding anomalies: 87Sr/86Sr: 0.7027, 143Nd/144 Nd: 0.51312, 206Pb/204Pb: 18.46, 207Pb/204Pb: 15.14, 208Pb/204 Pb: 38.03). Region II (MAR between Cox FZ and Doldrums FZ) has lower 87Sr/86Sr but higher Pb isotope ratios than the average. Region III (segments between Doldrums FZ and Hays FZ) has lower 87 Sr/86Sr, higher 143Nd/144Nd and lower Pb isotope ratios than the average. Region IV (the Azores area from Hayes FZ to Charlie Gibbs FZ) has higher 87Sr/86Sr and Pb isotope ratios, but lower 143Nd/144Nd. Region V (segments north of Charlie Gibbs FZ) has isotope ratios close to the average. Regional variations are also observable from satellite altimetry.; Superimposed on these mantle regions are depleted and enriched anomalies. The depleted anomalies are observed at the segment between Chain FZ and Ascension FZ, the segment just south of Charlie Gibbs FZ, and the segment between Kane FZ and 15°20' FZ. Among enriched anomalies, Iceland may be the only anomaly having a truly deep mantle plume source. The Azores are formed by broad upwelling of the upper mantle. Most other anomalies originate from “wet” enriched lumps embedded in the upper mantle or from small-scale upper mantle plumes.; The MAR is formed by active upwelling of many sub-segment size melting diapirs embedded within a spreading-induced passive upwelling upper mantle.