A Late-Hercynian intrusion of two-mica leucogranite from the Sila (Calabria, Italy) has been examined for petrographic, geochemical, and radiogenic isotope characteristics. The main objective was to analyse leucogranite genesis and its relation to partial melting of the Sila high-grade migmatitic paragneiss, which is affected by low-pressure metamorphism. The studied leucogranite is strongly peraluminous and is characterized by the presence of andalusite and sillimanite. It is very similar in major element composition to experimental melts produced by muscovite dehydration melting reaction from meta-sedimentary rocks. The leucogranite has high Rb and low Sr contents, whereas Zr and LREE concentrations are moderate to low. Variations in Sr, Rb, Zr, and LREE are inversely correlated to corresponding variations in migmatitic paragneiss. Maximum Zr and LREE contents in two leucogranite samples coherently indicate a saturation temperature of ca. 750 degrees C for both zircon and monazite. The estimate is in good agreement with peak temperatures of 740-770 degrees C obtained for high-grade rocks underlying the granite. These observations suggest a melt-restite connection between leucogranite and migmatitic paragneiss. Sr isotopic data are in agreement with this hypothesis whereas differences in the Nd isotopic composition between leucogranite and migmatitic paragneiss are attributed to disequilibrium retention of monazite in the residue. Mass-balance calculations, performed combining average major oxides analyses of leucogranite and migmatitic paragneiss, allow to reconstruct a composition similar to standard shale, except for the higher Na2O/CaO ratio.
Leucogranite genesis connected with low-pressure high-temperature metamorphism in the Sila basement (Calabria, Italy)
CAGGIANELLI, Alfredo;
2003-01-01
Abstract
A Late-Hercynian intrusion of two-mica leucogranite from the Sila (Calabria, Italy) has been examined for petrographic, geochemical, and radiogenic isotope characteristics. The main objective was to analyse leucogranite genesis and its relation to partial melting of the Sila high-grade migmatitic paragneiss, which is affected by low-pressure metamorphism. The studied leucogranite is strongly peraluminous and is characterized by the presence of andalusite and sillimanite. It is very similar in major element composition to experimental melts produced by muscovite dehydration melting reaction from meta-sedimentary rocks. The leucogranite has high Rb and low Sr contents, whereas Zr and LREE concentrations are moderate to low. Variations in Sr, Rb, Zr, and LREE are inversely correlated to corresponding variations in migmatitic paragneiss. Maximum Zr and LREE contents in two leucogranite samples coherently indicate a saturation temperature of ca. 750 degrees C for both zircon and monazite. The estimate is in good agreement with peak temperatures of 740-770 degrees C obtained for high-grade rocks underlying the granite. These observations suggest a melt-restite connection between leucogranite and migmatitic paragneiss. Sr isotopic data are in agreement with this hypothesis whereas differences in the Nd isotopic composition between leucogranite and migmatitic paragneiss are attributed to disequilibrium retention of monazite in the residue. Mass-balance calculations, performed combining average major oxides analyses of leucogranite and migmatitic paragneiss, allow to reconstruct a composition similar to standard shale, except for the higher Na2O/CaO ratio.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
