Composition and evolution of the lithospheric mantle in central Spain: inferences from peridotite xenoliths from the Cenozoic Calatrava volcanic field

Abstract

Spinel lherzolite xenoliths from the Cenozoic Calatrava volcanic field provide a
sampling of the lithospheric mantle of central Spain. The xenoliths are estimated to originate
from depths of 35–50 km. Trace element content of clinopyroxene and Cr-number in spinel indicate
low degrees of partial melting (5%) of the xenoliths. Although a major element whole-rock
model suggests wider degrees of melting, the Calatrava peridotite chemistry indicates a moderately
fertile mantle beneath central Spain. Calatrava peridotite xenoliths bear evidence for interaction
with two different metasomatic agents. The enrichment in LREE (light rare earth element), Th,
U and Pb, and the negative anomalies in Nb–Ta in clinopyroxene and amphibole from xenoliths
of El Aprisco, indicate that the metasomatic agent was probably a subduction-related melt, whereas
the enrichment in MREE in clinopyroxene from xenoliths of the Cerro Pelado centre suggests an
alkaline melt similar to the host undersaturated magmas. These metasomatic agents are also consistent
with the chemistry of interstitial glasses found in xenoliths of the two volcanic centres.
Differences in metasomatism but also in mantle composition is supported by Sr–Nd whole-rock
data, which show a more radiogenic nature for Sr isotopes of samples from the El Aprisco centre
(87Sr/86Sr ratios of 0.7035–0.7044 instead of 0.7032–0.7037 for samples from Cerro Pelado).
The timing of the subduction-related metasomatic stage is unconstrained, although the Calatrava
intraplate volcanism intrudes an old Variscan lithospheric section reworked during the converging
plate system affecting SE Iberia in the Tertiary. The presence of wehrlite types within the Calatrava
peridotite xenoliths is here interpreted as a reaction of host lherzolites with silica-undersaturated
silicate melts that could be related to the Calatrava alkaline magmatism. The Sr–Nd isotopic composition
of Calatrava peridotites plot within the European asthenospheric reservoir (EAR) mantle,
these values represent more enriched signatures than those found in the other Spanish Cenozoic
alkaline province of Olot.