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Xenolites éclogitiques cratoniques - Origine et évolution du manteau lithosphérique sous-continental

Abstract : This study is based on the most complete existing collection of cratonic eclogites (> 180 nodules), from the Siberian and South African cratons. Non-metasomatized Type IIA eclogites are typically more magnesian, LREE-enriched, with δ18O values of 3.7-7.5 ‰, positive Sr anomalies and corresponding to a low pressure-temperature (PT) layer. The whole-rock composition is consistent with a basaltic protolith. Type IIB eclogites are morsodic and aluminous, LREE-depleted, with δ18O values of 2.3-3.6‰, corresponding to equilibrium at high-PT. The whole-rock trace element composition is consistent with a pyroxenitic protolith. Coesite, kyanite and corundum-bearing eclogites ypically have jadeite-rich clinopyroxenes witlpositive Eu and Sr anomalies and grossular-rich gamets with corresponding positive Eu and negative Sr anomalies. PT-estimates indicate coe-kycor-bearing eclogites equilibrated in the lowermost part of the cratonic keel and reconstructed whole-rock trace element composition corresponds to a very depleted gabbroic protolith. This is consistent with the subduction of a hydrothermally altered, basaltic to websteritic sequence of an incompatible-element-depleted oceanic crust.Calculated water content of omphacite is a minmum estima te of ~930-1410 ppm by weight H2O and reconstructed estimates for whole-rock watercontent ~310-890 ppm HO) for the Obnazhennaya eclogites are significantly higher than those of the surrounding peridotites. Thus, mantle eclogite may be an important water reservoir at the base of the cratonic root, with major consequences for cratonic keel, longevity mantle rheology and global water cvcle
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Ioana Bogdana Radu. Xenolites éclogitiques cratoniques - Origine et évolution du manteau lithosphérique sous-continental. Sciences de la Terre. Université de Lyon, 2018. Français. ⟨NNT : 2018LYSES004⟩. ⟨tel-02292886⟩



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