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The Mont Collon mafic complex (Austroalpine Dent Blanche nappe). Permian evolution of the Western European mantle.

Abstract : The complex of the Mot Collon (Austroalpine Dent Blanche nappe) consists of 95% of cumulative mafic rocks crosscut by acid and late mafic dikes (Fe-Ti melanocratic dikes), emplaced in the middle crust. U / Pb zircons crystallization ages (284.2 ± 0.6 and 282.9 ± 0.6 Ma) were obtained on a gabbro and a quartz pegmatite. The 40Ar/39Ar dating on amphiboles of the melanocratic dikes (260.2 ± 0.7 Ma) indicates a second magmatic event. The compositions of cumulates show few variations with the lithology and reveal systematic negative Nb, Ta, Zr, Hf and Ti anomalies. The lack of variation in trace elements in cpx and positive correlation between whole-rock trace elements and the modal percentage of late amphibole are characteristic of a process of crystallization in situ (Langmuir, on 1989) implying 0 to 35 % of interstitial liquid (L) between the cumulus minerals. The calculated parental melt of the cumulates of the Mont Collon present transitional affinity and a strong negative Nb-Ta anomalies. 2 groups of cumulative rocks are discriminated according to their Nd-Sr signatures, supposing possible magmatic reinjections. Pb ratios indicate a subcontinental lithospheric mantle source, contaminated by oceanic sediments. Melanocratic dikes have eNdi of +7, 87Sr/86Sri of 0.703 and Pb ratios indicating an asthenospheric mantle source.
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Submitted on : Monday, July 12, 2004 - 12:27:21 PM
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Philippe Monjoie. The Mont Collon mafic complex (Austroalpine Dent Blanche nappe). Permian evolution of the Western European mantle.. Geochemistry. Université de Lausanne, 2004. English. ⟨tel-00006439⟩

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