HR: 14:10h
AN: V22F-03    [PDF]
TI: Magmatic Cycles at Spreading Centers: Geochemical Study of a Continuous Extrusive Section in the Oman Ophiolite
AU: * Einaudi, F
EM: einaudi@dstu.univ-montp2.fr
AF: Laboratoire de Geophysique et d'Hydrodynamique en Forage,, ISTEEM, cc056, Universite de Montpellier II, Montpellier, 34095 France
AU: Godard, M
EM: margot@dstu.univ-montp2.fr
AF: Laboratoire de Tectonophysique, ISTEEM, Universite de Montpellier II,, Montpellier, 34095 France
AU: Pezard, P A
EM: pezard@dstu.univ-montp2.fr
AF: Laboratoire de Geophysique et d'Hydrodynamique en Forage,, ISTEEM, cc056, Universite de Montpellier II, Montpellier, 34095 France
AU: Pezard, P A
EM: pezard@dstu.univ-montp2.fr
AF: Laboratoire de Tectonophysique, ISTEEM, Universite de Montpellier II,, Montpellier, 34095 France
AU: Cocheme, J
EM: jean-jacques.cocheme@univ.u-3mrs.fr
AF: Laboratoire de Petrologie Magmatique, Universite d'Aix Marseille, Faculte des Sciences de St Jerome, Marseille, 13397 France
AU: Brewer, T
EM: tsb5@leicester.ac.uk
AF: Department of Geology, University of Leicester, University Rd.,, Leicester, LE1 7RH United Kingdom
AB: The continuous volcanic stratigraphy of the basaltic crust at mid-ocean ridges is of primary importance to understand magma transport and accretion processes at different spreading rates. In order to provide detailed constraints on the construction of the upper oceanic crust, and on possible temporal variations in the ridge activity, we sampled at high-frequency a continuous volcanic transect (300 m-thick) in the Oman ophiolite along Wadi Shaffan. The Wadi Shaffan section is composed of MORB-type lavas (V1-Geotimes volcanism). It consists mainly of pillow lavas interbedded with abundant massive flows in the lower part of the section, the latter getting more scattered in the upper part of the section. Trace element ratios (e.g. Zr/Nb and La/Yb) allow to distinguish two main sequences with two different parental magmas. This suggest that the Wadi Shaffan transect was built through two main petrological and geochemical sequences of volcanic activity. Within each sequence, variations in trace element abundances (TiO2,Zr, REE) involve differentiation processes prior to emplacement. In the lower sequence, the less differentiated lavas form the upper part of the cycle. Magma mixing is proposed to explain this reversed geochemical evolution through time. The upper sequence consists of multiple events of magma emplacement. Variations in trace element abundance suggest four magmatic cycles. Each magmatic cycle is characterized by primitive lavas evolving to more differentiated lavas with time. The upper sequence lavas appear to be in equilibrium with clinopyroxene sampled in the Mantle-Crust Transition Zone (MTZ) sills, for the most primitive lavas, and with clinopyroxene sampled in the lower gabbros. We propose a model in which the upper sequence lavas were directly derived from the MTZ and lower gabbro and then transported to the surface without interaction with higher crustal levels.
DE: 3035 Midocean ridge processes
DE: 3600 MINERALOGY AND PETROLOGY (replaces
DE: 3670 Minor and trace element composition
SC: Volcanology, Geochemistry, Petrology [V]
MN: 2003 Fall Meeting