THE POLYCYCLIC EVOLUTION OF THE PENNINIC MAGGIA-NAPPE, CENTRAL ALPS -A SUMMARY REPORT

The Maggia nappe mainly consists of a series of fine-grained hornblend e-free psammitic (arkosic), psephitic, and pelitic gneisses and schist s of Archeaen to early Paleozoic origin, as well as of pre-Alpine laye rs of amphibolites, hornblende gneisses and -schists. These series for m the country rock of a group of coarse-grained peraluminous S-type me tagranitoids called Matorello Gneiss, that were generated by Hercynian ultrametamorphism. Isochemical transitions between Matorello Gneiss a nd the surrounding arkosic gneisses confirm their origin within the co untry rocks by in situ anatexis. Several generations of pre- and post- granitic aplites, pegmatites and newly discovered tonalite porphyrites as well as hornblende-bearing dikes, stocks and sills can be observed , and are of pre-Alpine origin as they show a strong Alpine schistosit y. All hornblende-bearing rocks are of pre-Alpine igneous origin and r eveal a normal calc-alkaline basalt trend; a second rather abnormal tr end of the newly discovered contaminated basaltic rocks is probably th e result of pre-Alpine assimilation. The Maggia nappe underwent Alpine amphibolite facies metamorphism, during which all the rocks were stro ngly recrystallized. Pre-Alpine ages of the zircon U-Pb and Rb-Sr whol e-rock systems were not affected during the Alpine orogeny.