A unique blueschist facies metapelite with Mg-rich chloritoid from the Badajoz-Cordoba Unit (SW Iberian Massif): correlation of Late Devonian high-pressure belts along the Variscan Orogen

The Badajoz-Cordoba Unit (BCU, SW Iberian Massif) is a Variscan high-P unit mainly constituted by metapelites, metagreywackes, orthogneisses, Grt-amphibolites, and retrogressed eclogites (high-P metamorphism at c. 377 Ma). Discovery of rare metapelites with well-preserved high-P mineral assemblages, including large garnets up to 1 cm in diameter with abundant inclusions, chloritoid (up to X-Mg = 0.32), kyanite, staurolite, chlorite, phengite (up to Si = 3.16 apfu), paragonite, margarite, and rutile, allows detailed determination of the tectonothermal evolution of the unit. Pseudosection modelling of representative samples indicates that this mineral assemblage formed in blueschist facies (near eclogite facies transition) at P conditions higher than 20 kbar at c. 525 degrees C and that it underwent a subsequent severe exhumation and moderate heating. The lithological composition of the BCU, the age of high-P metamorphism and the characteristics of the high-P mineral assemblages are similar to those found in other high-P and low to intermediate-T units of the Variscan Orogen. All these units form part of a single blueschist-eclogite facies metamorphic belt formed during Late Devonian subduction of the external margin of Gondwana.

Automated summary

The Badajoz-Cordoba Unit is a Variscan high-P unit mainly composed of metapelites, metagreywackes, orthogneisses, Grt-amphibolites, and retrogressed eclogites. The unit underwent high-P metamorphism at around 377 Ma, forming rare metapelites with well-preserved high-P mineral assemblages. Pseudosection modelling suggests formation in blueschist facies under high pressure conditions, followed by exhumation and moderate heating, similar to other units in the Variscan Orogen.