US EPA

6865025 

Journal Article 

Coexistence of lawsonite-bearing eclogite and blueschist: phase equilibria modelling of Alpine Corsica metabasalts and petrological evolution of subducting slabs 

Brovarone, AV; Groppo, C; Hetenyi, G; Compagnoni, R; Malavieille, J; , 

2011 

Yes 

Journal of Metamorphic Geology
ISSN: 0263-4929
EISSN: 1525-1314 

WILEY 

HOBOKEN 

583-600 

10.1111/j.1525-1314.2011.00931.x 

WOS:000291222900005 

In Alpine Corsica (France), deeply subducted metabasalts are well preserved as lawsonite-bearing eclogite (Law-Ecl), occurrence of which is restricted to similar to 10 localities worldwide. The Corsican Law-Ecl, consisting of omphacite + lawsonite + garnet + phengite + titanite, occurs as both single undeformed metabasaltic pillows surrounded by lawsonite blueschist (Law-Bs), and carbonate-bearing eclogitic veins. Law-Bs are found as variably deformed metabasaltic pillows locally cross-cut by eclogitic veins and consist of glaucophane + actinolite + lawsonite + garnet + phengite + titanite. Field evidence and microstructures reveal that both Law-Ecl and Law-Bs are stable at the metamorphic peak in the lawsonite-eclogite stability field. Isochemical phase diagrams (pseudosections) calculated for representative Law-Ecl and Law-Bs samples indicate that both lithologies equilibrated at the same conditions of similar to 520 +/- 20 degrees C and 2.3 +/- 0.1 GPa. Therefore, the coexistence at the same peak metamorphic conditions of Law-Ecl and Law-Bs implies that different portions of deeply subducted oceanic crust may store significantly different H2O contents, depending on bulk-rock chemical composition. In addition, thermodynamic modelling of phase equilibria indicates that the occurring progressive dehydration reactions, which are significantly depending on bulk-rock chemical composition, strongly influence rock densification and eclogite formation in subducting slabs.