Preliminary Geochemical Results from the Mozambique Ridge, SW Indian Ocean

Gabriele.Uenzelmann-Neben [ at ]


The Mozambique Ridge (120-140 Ma old) is a submarine plateau located in the southwest Indian Ocean. The relationship between plateau formation and the break-up of the Gondwana supercontinent is still unclear. Different models for the origin of this plateau include: 1) a continental fragment split off of Africa or Antarctica during Gondwana break-up and 2) an oceanic Large Igneous Province (LIP) formed by a mantle plume involved in Gondwana break-up. On the R/V SONNE (cruise SO232), we carried out bathymetric mapping, seismic reflection studies and rock sampling of the plateau basement, which confirmed the volcanic nature of at least the upper parts of the plateau. By reconstructing the spatial and temporal evolution in geochemistry of volcanic samples, we hope to gain new insights into the origin of the plateau. The recovered samples are mainly basaltic (SiO2 = 47-52 wt. %). On the Nb/Yb versus Th/Yb diagram, the samples overlap the field for enriched-mid-ocean-ridge basalts (EMORB) and extend towards the field for ocean island basalts (OIB). Most of the samples have relatively flat REE patterns, similar to EMORB or LIP type lavas. Initial Sr-Nd-Hf isotope ratios form tight correlations, excluding late alteration effects. The samples overlap and extend to slightly more radiogenic values than age-corrected SW Indian and South Atlantic MORB and OIB, indicating a two-component mixing between depleted (NMORB source) and enriched (OIB-type) mantle. Similar to some early Kerguelen plateau basalts, some of our samples have low Nd isotope and (Nb/La)n (< 1) ratios suggesting involvement of continental lithosphere and/or lower crust. On the 206Pb/204Pb versus 207Pb/204Pb isotope diagram, the samples extend to higher Δ7/4 than the South West Indian array, overlapping with Kerguelen lavas. Bathymetric data show numerous small cones scattered on the plateau, which are thought to represent a reactivation of volcanism after formation of the plateau basement. Moreover, seismic refraction data show evidence for a thick oceanic lower crust. Together with our new geochemical data, it favors a LIP origin for the Mozambique Ridge.

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Conference (Poster)
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AGU Fall meeting, 12 Dec 2015 - 18 Dec 2015, San Francisco, USA.
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Jacques, G. , Werner, R. , Hauff, F. , Uenzelmann-Neben, G. and Hoernle, K. (2015): Preliminary Geochemical Results from the Mozambique Ridge, SW Indian Ocean , AGU Fall meeting, San Francisco, USA, 12 December 2015 - 18 December 2015 .

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