title: Mantle thermal pulses below the Mid-Atlantic Ridge and temporal variations in the formation of oceanic lithosphere.
abstract: A 20-Myr record of creation of oceanic lithosphere is exposed along a segment of the central Mid-Atlantic Ridge on an uplifted sliver of lithosphere. The degree of melting of the mantle that is upwelling below the ridge, estimated from the chemistry of the exposed mantle rocks, as well as crustal thickness inferred from gravity measurements, show oscillations of approximately 3-4 Myr superimposed on a longer-term steady increase with time. The time lag between oscillations of mantle melting and crustal thickness indicates that the mantle is upwelling at an average rate of approximately 25 mm x yr(-1), but this appears to vary through time. Slow-spreading lithosphere seems to form through dynamic pulses of mantle upwelling and melting, leading not only to along-axis segmentation but also to across-axis structural variability. Also, the central Mid-Atlantic Ridge appears to have become steadily hotter over the past 20 Myr, possibly owing to north-south mantle flow.
authors.affiliation: Istituto Scienze del Mare, Geologia Marina, CNR, Via Gobetti 101, 40129, Bologna, Italy. bonatti@igm.bo.cnr.it
authors.forename: Enrico
authors.initials: E
authors.lastname: Bonatti
authors.forename: Marco
authors.initials: M
authors.lastname: Ligi
authors.forename: Daniele
authors.initials: D
authors.lastname: Brunelli
authors.forename: Anna
authors.initials: A
authors.lastname: Cipriani
authors.forename: Paola
authors.initials: P
authors.lastname: Fabretti
authors.forename: Valentina
authors.initials: V
authors.lastname: Ferrante
authors.forename: Luca
authors.initials: L
authors.lastname: Gasperini
authors.forename: Luisa
authors.initials: L
authors.lastname: Ottolini