Abstract: Understanding the nature and evolution of mantle sequences exhumed along modern magma-poor ocean-continent transition zones (OCTs) is essential for deciphering the complex interplay of tectonic and magmatic processes from rifting to oceanization. However, the data on these specific tectonic settings remain limited. In this study, we revisit peridotites from the West Iberian margin (WIM) through a petrological and geochemical investigation of mantle exposures sampled in the Iberia Abyssal Plain (IAP). We focus on three ODP sites constituting an east-to-west transect, from Hole 1068A to Holes 899B and the westernmost Hole 1070A, to capture the full spectrum of mantle variability from the continental to the most oceanward domains. The analysed samples consist of variably serpentinized, coarse-grained peridotites preserving evidence of melt-rock interactions. In Hole 1068A, strongly serpentinized plagioclase lherzolites are found. Mineral chemistry, i.e., high Cr# and TiO2 in spinel, along with Na2O- and Al2O3-enriched clinopyroxene, indicate that these samples are akin to impregnated peridotites from the sub-continental lithospheric mantle (SCLM). Geochemical modelling based on clinopyroxene REE compositions points to refertilization processes driven by MORB-type melts. In contrast, Hole 899B displays more pronounced variability and apparently contrasting geochemical features. Spinel harzburgites (cpx ~ 2-3 vol.%) exhibit evidence of olivine-forming, pyroxene-dissolving microstructures. Their slightly depleted clinopyroxene compositions (Na2O= 0.23-0.60 wt. %), combined with atypical chondrite-normalized V-shaped REE patterns, suggest that these rocks experienced partial melting followed by interaction with LREE-enriched melts. These peridotites may represent inherited SCLM, or a refractory peridotite modified by rifting-related melts. One sample however, plagioclase harzburgite 899-1 (cpx ~ 8 vol.%), is distinguished by peculiar microtextures—such as opx2±pl aggregates replacing olivine porphyroclasts— and spinel ...
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