title: Seismic reflection images of the Moho underlying melt sills at the East Pacific Rise.
abstract: The determination of melt distribution in the crust and the nature of the crust-mantle boundary (the 'Moho') is fundamental to the understanding of crustal accretion processes at oceanic spreading centres. Upper-crustal magma chambers have been imaged beneath fast- and intermediate-spreading centres but it has been difficult to image structures beneath these magma sills. Using three-dimensional seismic reflection images, here we report the presence of Moho reflections beneath a crustal magma chamber at the 9 degrees 03' N overlapping spreading centre, East Pacific Rise. Our observations highlight the formation of the Moho at zero-aged crust. Over a distance of less than 7 km along the ridge crest, a rapid increase in two-way travel time of seismic waves between the magma chamber and Moho reflections is observed, which we suggest is due to a melt anomaly in the lower crust. The amplitude versus offset variation of reflections from the magma chamber shows a coincident region of higher melt fraction overlying this anomalous region, supporting the conclusion of additional melt at depth.
authors.affiliation: Laboratoire de Géosciences Marines, IPG Paris, 75252 Paris cedex 05, France. singh@ipgp.jussieu.fr
authors.forename: S C
authors.initials: SC
authors.lastname: Singh
authors.forename: A J
authors.initials: AJ
authors.lastname: Harding
authors.forename: G M
authors.initials: GM
authors.lastname: Kent
authors.forename: M C
authors.initials: MC
authors.lastname: Sinha
authors.forename: V
authors.initials: V
authors.lastname: Combier
authors.forename: S
authors.initials: S
authors.lastname: Bazin
authors.forename: C H
authors.initials: CH
authors.lastname: Tong
authors.forename: J W
authors.initials: JW
authors.lastname: Pye
authors.forename: P J
authors.initials: PJ
authors.lastname: Barton
authors.forename: R W
authors.initials: RW
authors.lastname: Hobbs
authors.forename: R S
authors.initials: RS
authors.lastname: White
authors.forename: J A
authors.initials: JA
authors.lastname: Orcutt