Petrology and geochronology of metabasites with eclogite facies relics from NE Sardinia: constraints for the Palaeozoic evolution of Southern Europe

Abstract

In the Golfo Aranci high-grade metamorphic basement of NE-Sardinia (Italy), a fragment of the southern part of the Variscan chain, several metabasic rocks with relic eclogitic parageneses are interlayered with a dominant sequence of migmatitic paragneisses and felsic orthogneisses. Petrologic, geochemical and geochronological data on selected samples permitted the reconstruction of a long history starting from pre-Variscan magmatic activity and progressing with a polyphase metamorphism during the Variscan orogenic event. U–Pb LAM-ICPMS dating of zircon domains from two eclogites allowed us to constrain the emplacement of the mafic protolith in Ordovician times (460±5 Ma). The basic rocks were buried in a subduction-related environment with formation of Ky-bearing eclogite parageneses (undated event, ∼650 °C and ∼1.9 GPa). Subsequently, the eclogites underwent a strong reequilibration first under the granulite facies (sapphirine-bearing parageneses: 700–800 °C, ∼1.0 GPa) and then under the amphibolite facies with pervasive growth of brown amphibole and resetting of the U–Pb system in zircon (352±3 Ma). This high-pressure metamorphic basement and its strong analogies with the basement slices of Corsica, Provence, of the Ligurian Alps and the intra-Alpine massifs indicate the presence of a HP migmatite–eclogite belt extending for several hundreds of kilometers at the southern margin of the Variscan realm.