Duggen, Svend

Geldmacher, Jörg

Hauff, Folkmar

Hoernle, Kaj

Park, S.

English

OceanRep

Geophysical Research Abstracts,Vol. 10, EGU2008-A-05981, 2008SRef-ID: 1607-7962/gra/EGU2008-A-05981EGU General Assembly 2008© Author(s) 2008Pb (double spike)-Nd-isotopic variation of ∼15 Maoceanic crust basalts drilled at IODP Site 1256 in theEastern Pacific: Constraints on mantle processesduring a phase of superfast spreading at the EastPacific Rise and the timing of subsequent alterationS. Duggen (1), K. Hoernle (1), F. Hauff (1), Sung-Hyun Park (2), J. Geldmacher (3)(1) IFM-GEOMAR, Leibniz-Institute of Marine Sciences, Research Division Dynamics of theOcean Floor, Kiel, Germany, (2) Korea Polar Research Institute, South Korea, (3) IntegratedOcean Drilling Program, Texas A&M University, USAContinuous formation of oceanic crust records the geochemical signature of mid-ocean ridge magma sources through time. The radiogenic isotopic variation of drilledyoung oceanic crust - once corrected for alteration processes - can thus provide newconstraints on temporal changes of mantle processes at mid-ocean ridges. We examinethe Pb (double spike, DS)-Nd-isotopic and trace element variation of ∼15 Ma youngoceanic crust drilled at Cocos Plate IODP Site 1256. The basalts were formed dur-ing a phase of superfast spreading ∼11-20 Ma ago at the East Pacific Rise (EPR) ina near-equatorial position and were subsequently variably affected by low- to high-temperature alteration1. Corrections for radiogenic ingrowth, following perturbationof the U-Th-Pb system involving seawater cycling, indicate that alteration was gen-erally completed several million years after the formation of the basalts at the EPR.Most Pb-isotope data currently available for Site 1256 plot along an array above andparallel to the Northern Hemisphere Reference Line in the Pb-isotope diagrams sug-gesting that all basalts, prior to alteration, plotted along a common array inherited frommagma source heterogeneity. The measured and alteration-corrected Nd-Pb-isotopicdata of Site 1256 lavas have hybrid radiogenic isotopic characteristics between moredepleted EPR and enriched Galápagos lavas and Nd- and Pb DS-isotope data showcorrelations along the co-variations formed by these endmembers. Comparison of∼15Ma old Site 1256 data with Recent equatorial EPR glass compositions (6 ˚S to 6˚N)point to higher Pb- but lower Nd-isotopic compositions of basalts formed during thephase of superfast spreading ∼11-20 Ma ago. This suggests temporal variations inthe EPR magma source involving mantle heterogeneity, eventually associated with aperiod of more vigorous upper mantle convection. Magma source heterogeneity mayeither arise from upwelling of more fertile ambient upper mantle material beneath theEPR or pollution of the equatorial EPR magma source with material from the nearbyGalápagos mantle plume.1 Teagle et al. (2007) Proc. ODP, Sci. Results, 206.

Pb (double spike)-Nd-isotopic variation of ~15 Ma oceanic crust basalts drilled at IODP Site 1256 in the eastern Pacific: constraints on mantle processes during a phase of superfast spreading at the East Pacific Rise and the timing of subsequent alteration

Pb (double spike)-Nd-isotopic variation of ~15 Ma oceanic crust basalts drilled at IODP Site 1256 in the eastern Pacific: constraints on mantle processes during a phase of superfast spreading at the East Pacific Rise and the timing of subsequent alteration

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