P–T evolution of eclogite-facies metabasite from NE Sardinia, Italy: Insights into the prograde evolution of Variscan eclogites

• Published in: Lithos 2011-01, Vol.121 (1-4), p.135-150
• Main Authors: Cruciani, Gabriele, Franceschelli, Marcello, Groppo, Chiara
• Format: Article
• Language: English
• Subjects: Metabasite; Metamorphic evolution; Pseudosection modelling; P–T path; Sardinia; Variscan Orogeny
• ISSN: 0024-4937; 1872-6143
• DOI: 10.1016/j.lithos.2010.10.010

A petrological study of the Punta Orvili metabasite in NE Sardinia has been carried out, integrating quantitative pseudosection modelling with reaction balancing, with the aim of reconstructing the metamorphic evolution and P–T path. The Punta Orvili metabasite preserves microstructural evidence of: (i) a pre-symplectite polyphase and prograde stage (M1) indicated by the occurrence of amphibole inclusions in garnet, by Na-rich diopside and by compositional zoning in garnet, clinopyroxene and amphibole; (ii) a symplectite stage (M2) represented by the occurrence of Cpx2+Pl1 symplectite; (iii) a corona stage (M3) documented by the formation of micrometre-thick Pl2±Am3±Ilm coronas around garnet; and (iv) a late stage (M4), documented by the growth of epidote and albite and by the replacement of biotite and clinopyroxene by chlorite. The M1 pre-symplectite stage has been modelled by P–T pseudosections calculated in the NCKFMASTH model system at a(H2O)=1 (for a(H2O)=0.5 temperature values are ~50°C lower). Mg and Ca zoning in garnet and Na zoning in clinopyroxene testify to a progressive increase in temperature and pressure during garnet and clinopyroxene growth from 610