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Metaluminous pyroxene-bearing granulite xenoliths from the lower continental crust in central Spain: their role in the genesis of Hercynian I-type granites

¹ Departamento de Petrología y Geoquímica, Universidad Complutense, 28040, Madrid, Spain
² Department of Earth Sciences, University of Bristol, BS8 1RJ, Bristol, UK
³ Swedish Museum of Natural History of Stockholm, Sweden

^* Corresponding author, e-mail: granito{at}geo.ucm.es

Basic and intermediate meta-igneous xenoliths are very scarce within the granulite population transported by the Permian alkaline lamprophyric dyke swarm of the Spanish Central System (SCS). These xenoliths are metaluminous pyroxene-bearing charnockites (sensu lato). They show LREE-poor plagioclase and orthopyroxene-clinopyroxene. Crystallization conditions were estimated at about 850 to 1000 °C and 9 to 11 kbar, a slightly higher range than that estimated for the associated peraluminous granulites, but indicating derivation from the lowermost crust.

Whole-rock geochemistry suggests that the charnockite samples are not a cogenetic suite. The more basic varieties have affinities with cumulates from previous calc-alkaline underplated protoliths, whereas intermediate charnockites have a restitic origin. The similarity in Sr-Nd-Pb isotopic signatures between these restitic charnockites and some SCS I-type granites suggests a genetic relationship. This study, including Pb isotopic data from the whole granulite xenolith suite, reinforces the lower-crustal derivation of the SCS Hercynian granitic batholith.

Key-words: granulite xenoliths, pyroxene mineral chemistry, Hercynian granites, igneous petrology, lower crust, central Spain.

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