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Spinel lherzolite xenoliths from the Sant Corneli volcano (Catalan Volcanic Zone, NE Spain) carry the
geochemical imprint of melt/rock reaction events that have affected the subcontinental lithospheric mantle
(SCLM) beneath the northeastern Iberian margin. Trace element signatures of clinopyroxene indicate that this
volume of the SCLM initially experienced low degrees (F = 8 %) of partial melting, followed by extensive
refertilization by alkaline silicate melts undergoing chromatographic fractionation while percolating through the
mantle peridotites. Furthermore, the presence of interstitial sulphide-bearing silicate glass, as well as secondary
coronitic rims around mantle minerals, records the melt/rock reaction product associated with the infiltration of
the host alkaline basalts while erupting to the surface. Abundant irregular/blocky sulphides located within the
interstitial glass patches are comprised of myrmekitic intergrowths of pentlandite ± bornite ± chalcopyrite,
suggesting their derivation from immiscible droplets of Fe-Ni-Cu sulphide melt transported by the host alkaline
basalts. The variable chondrite-normalized platinum-group element (PGE) systematics and chalcogenes (Se, Te,
As, Bi and Sb) abundances of these sulphides track two distinct transport mechanisms for their parental sulphide
melts: 1) by unmixing of Ni-Cu-rich sulphide liquid in alkaline basalts attaining sulphide-saturation while
interacting with the peridotite xenoliths, and 2) by mechanical transport of immiscible droplets of Ni-Cu-rich
sulphide liquid originally extracted by residual monosulphide solid solution undergoing incongruent melting
in their mantle source. In addition, many sulphides have PGE abundances that cannot be explained solely by
solid-melt chemical partition coefficients but that were likely influenced by the mechanical entrapment, or earlymagmatic
segregation, of pre-existing PGE-rich nanoparticles or nanomelts. The geochemical signal of these
mineral nanoparticles may significantly influence sulphides PGE distribution, sometimes resulting in pronounced
positive anomalies in Ir–Rh, Au, or Ru–Rh, along with negative anomalies in Pt.
Citació
Lithos, vol. 488-489 (2024), p. 1-16, 107820