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Os, Sr, Nd, Pb, O isotope and trace element data from the Ferrar flood basalts, antarctica: evidence for an enriched subcontinental lithospheric source

Abstract : OS, Sr, Nd, Pb and 0 isotopes and trace element data are reported for basaltic andesite and andesite whole rocks and, in part, for selected mineral separates from the Jurassic Ferrar flood basalt province. Radiogenic Sr (> 0.709), unradiogenic Nd (e Nd =-3 to-5), and radiogenic Pb isotopes, as well as low Nb/La ratios of 0.4-0.6 and Nb/La ratios between 0.45 and 0.6 are found for all rocks including our most primitive sample (Mg# = 7 1.9). This indicates involvement of either continental crust or enriched lithospheric mantle in magma genesis. 's'Re/ '*sOs correlates strongly with '*'OS/ 'ssOs, with an age of 172 + 5 Ma, in agreement with published Ar-Ar data. Initial '*'OS/ '**OS of 0.194 + 0.023 is close to the range of typical mantle values for MORB, OIB and lithospheric mantle and much lower than that of continental crust. 6 "0 values between 5%a and 7%~ were obtained on fresh bulk samples, separated plagioclases and clinopyroxenes. Sr-0 and Sr-0s isotope mixing calculations between depleted mantle peridotite or mantle melts and crustal material rule out assimilation involving basalts with low OS concentrations, and simple binary mixing or pure AFC processes involving pi&es. AFC processes, combined with continuous replenishment of picritic magmas, can explain the isotopic data, provided the crustal end-member has high s'Sr/ 86Sr and low S'*O values. However, lower crustal samples displaying these characteristics are absent in the Ferrar region, and are also unlikely to impart the sediment-like trace element patterns observed in the Ferrar data. A more likely explanation is a lithospheric source enriched by subducted sediments. A contribution to Ferrar magmatism from a plume cannot be distinguished.
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https://hal.univ-lorraine.fr/hal-02970609
Contributor : Laurie Reisberg <>
Submitted on : Friday, April 9, 2021 - 11:35:37 AM
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M. Molzahn, L. Reisberg, G. Wörner. Os, Sr, Nd, Pb, O isotope and trace element data from the Ferrar flood basalts, antarctica: evidence for an enriched subcontinental lithospheric source. Earth and Planetary Science Letters, Elsevier, 1996, 144 (3-4), pp.529-545. ⟨10.1016/S0012-821X(96)00178-1⟩. ⟨hal-02970609⟩

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