Late-Variscan fayalite-bearing granites in Sardinia: The lower crust connection

"The Variscan [340 – 260 Ma, 1] Corsica-Sardinia. Batholith (C-SB) emplaced discordantly across the orogenic. structure, from the roots zone to the Gondwana foreland.. Despite the scarcity (< 5%) of mafic rocks, most pre-300 Ma. plutons are peraluminous biotite granites derived from. dehydration melting of pre-Variscan granitoids and. subordinate metasediments [2]. Lower crustal granulites. observed in the deeply exhumed section of the chain [3] are. thought to have developed in consequence of extensive melt. extraction. The post-300 Ma granites in south Sardinia [4],. instead, display the following crustal characters: $Nd from -6. to -12, "O18 between 7 and 12%, and Sri (290) between 0.703. and 0.715. The rare but systematic occurrence of fayalite or. pyroxene as Fe-buffering phase indicates that these A-type. melts derived by partial melting of anhydrous, poorly evolved. crustal material under high-T (> 900°C), low fH2O and fO2. conditions [5].. NdDM model ages of post-300 Ma granites in south. Sardinia are in the range 1600 - 1700 Ma, about 1 Ga older. than those calculated in Corsica [6]. This implies a older. lithosphere, probably accreted at the northern margin of. Gondwana (S Sardinia) in early Paleozoic. The observation. that this part of the chain never reached a significant crustal. thickness during the Variscan event (i.e., > 40 km) support the. hypothesis that granulites formed before the Carboniferous."