Details

Autor(en) / Beteiligte

• Franceschelli, M.
• Eltrudis, A.
• Memmi, I.
• Palmeri, R.
• Carcangiu, G.

Titel

Multi-stage metamorphic re-equilibration in eclogitic rocks from the Hercynian basement of NE Sardinia (Italy)

Ist Teil von

• Mineralogy and petrology, 1998-01, Vol.62 (3-4), p.167-193

Ort / Verlag

Wien: Springer Nature B.V

Erscheinungsjahr

1998

Quelle

Springer Journals

Beschreibungen/Notizen

• Eclogitic rocks are hosted within gneisses and migmatites of the Hercynian basement of NE Sardinia. They are characterized by two compositional layers: garnet-pyroxene rich-layers and amphibole-plagioclase layers. The former contain structural, mineralogical and compositional relics of eclogite facies re-equilibration. Four stages of evolution have been identified: an eclogite stage, a granulite stage and a retrograde amphibolite to greenschist stage. A possible pre(?)-eclogite stage is documented by inclusions of euhedral tschermakitic amphibole + zoisite within the core of garnet. This early stage was followed by an increase in pressure under which the eclogite climax developed (T up to 700 °C, P =13-15 kbar), as documented by omphacite inclusions towards the rim of garnet. Characteristic mineral reactions after the eclogitic stage are: omphacite [arrow right] diopside + plagioclase (symplectite) and garnet [arrow right] orthopyroxene + plagioclase. These reactions testify the presence of a granulite stage during which the peak of metamorphism was reached (T up to 870'C, P [asymptotically =] 10 kbar). The orthopyroxene [arrow right] cummingtonite + quartz and garnet + diopside [arrow right] hornblende + plagioclase (kelyphite) transformations indicate extensive amphibolite retrogression (T = 550650 °C, P = 3-7 kbar). Finally, actinolite and chlorite developed (greenschist stage) at falling temperature and pressure (T = 300-400 °C, P < 2-3 kbar).[PUBLICATION ABSTRACT]