Postcumulus processes in oceanic-type olivine-rich cumulates: the role of trapped melt crystallization versus melt/rock interaction |
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| Authors: | G Borghini E Rampone |
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| Institution: | (1) Dipartimento per lo Studio del Territorio e delle sue Risorse, Università degli Studi di Genova, Corso Europa 26, 16132 Genova, Italy |
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| Abstract: | Combined microstructural and geochemical investigations on MORB-type primitive olivine-rich cumulates intruded in the Erro–Tobbio
(ET) mantle peridotites (Voltri Massif, Ligurian Alps, Italy) revealed that significant chemical changes in minerals were
caused by postcumulus crystallization. This is indicated by the occurrence of accessory interstitial minerals (Ti-pargasite,
orthopyroxene and Fe–Ti oxides) and by systematic chemical zoning in intercumulus clinopyroxene, resulting in marked trace
element (e.g. REE, Ti and Zr) enrichment at constant high Mg-numbers (0.88–0.91) and LREE depletion. Geochemical modelling
shows that low trapped melt amounts (<5%) are sufficient to produce the observed trace element enrichments. Chemical zoning
in large (mm-size) clinopyroxenes was dominantly caused by in situ fractional crystallization of trapped interstitial liquid
rather then porous flow migration of externally derived evolved melts. Zr enrichment relative to REEs in vermicular clinopyroxene
and pargasitic amphibole point to small-scale migration and interaction between residual evolved low melt fractions and the
olivine cumulus matrix at final stage of crystallization.
Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users. |
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| Keywords: | Olivine cumulates Trapped melt Melt/rock interaction In situ trace element analyses |
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