Among the large number of granitic intrusions within the Dora-Maira
massif, several main types can be distinguished. In this study we report
field, petrographic and geochemical investigations as well as zircon
typology and conventional U-Pb zircon dating of plutons representing
these types. The main results are as follows: the Punta Muret
augengneiss is a polymetamorphosed peraluminous granite of anatectic
origin. It is 457 +/- 2 Ma old and represents one of the numerous
Caledonian orthogneisses of the Alpine basement. All other dated
granites are of Late Variscan age. The Cavour leucogranite is an evolved
granite of probably calc-alkaline affiliation, dated at 304 +/- 2 Ma.
The dioritic and granodioritic facies of the Malanaggio diorite (auct.)
are typical calc-alkaline rocks, whose respective age of 290 +/- 2 and
288 +/- 2 Ma overlap within errors. The Sangone and Freidour granite
types have very similar alkali-calcic characteristics; their ages are
poorly constrained between 267-279 and 268-283 Ma, respectively.
The new data for the Dora-Maira granites are in keeping with models of
the overall evolution of the Late- to Post-Variscan magmatism in the
Alpine area in terms of age distribution and progressive geochemical
evolution towards alkaline melts. In a first approximation, granitic
rocks across the Variscan belt seem to be increasingly younger towards
the internal (southern) parts of the orogen. A Carboniferous, distensive
Basin and Range situation is thought to be responsible for the magmatic
activity. This tectonic context is comparable to the back-are opening of
an active continental margin. The observed southward migration of the
magmatism could be linked to the roll-back of the subducting
Paleotethyan oceanic plate along the Variscan cordillera.