Trondhjemitic leucosomes in paragneisses from NE Sardinia: Geochemistry and P-T conditions of melting and crystallization

摘要: Abstract The sedimentary-derived migmatites from Porto Ottiolu consist of mesosomes and tonalitic to trondhjemitic leucosomes. These rocks contain quartz + plagioclase + muscovite + biotite in different proportions locally fibrolite, K-feldspar kyanite relicts. contact between leucosomes is commonly marked by mm- cm-thick melanosomes mainly formed oriented biotite muscovite, variable amounts quartz plagioclase. Pressure-temperature (P-T) modeling using pseudosections their contouring isopleths for modal abundances minerals melt Si/Al Na/K ratios the suggests that anatexis occurred at ~700 °C 1.1 GPa with contribution ~2 wt% free water. complete crystallization leucosome was finalized P-T conditions 640–690 °C 0.40–0.55 GPa. are folded or parallel S 2 schistosity indicating pre syn-D formation. enriched SiO , CaO, Na O, Sr depleted Fe O 3 MgO, TiO K Rb, Ba, Cr, V, Zr, Nb, REE, except Eu, compared surrounding mesosomes. high CaO contents up 3.3 wt%, low (mean 0.57 wt%) Rb/Sr (