Melt-rock interactions in south armorican peridotites
Abstract
Five occurrences (four from Champtoceaux; one from Audierne) of South Armorican (SA) serpentinized peridotites were studied using optical microscopy, EMP, ICP-OES, solution ICPMS and laser ablation-ICPMS. Their whole-rock major and trace element contents are characteristic of mantle-derived peridotites. All but one Champtoceaux lherzolite occurrence are harzburgites that have experienced 12 to 25% partial melting (0.57900°C with small-volume HIE-enriched melt/fluids that produced 10-15 vol. % of colourless, sometimes twinned, Ti-poor pargasites from clinopyroxene and spinel. The Audierne samples were pervasively refertilized by water-rich alkali-rich melts that precipitated K- and Cr-richer, low-Ti pargasite. Our new data identify SA peridotites as pieces of residual mantle that were processed with slab-derived melt/fluids in supra-subduction zone settings.
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