Trace element constraints on the evolution and genesis of the Monte Pulchiana leucogranites, Northern Sardinia, Italy

The Monte Pulchiana leucogranites belong to the Sardinia-Corsica batholith and were emplaced during the post-collisional phase of the Hercynian orogeny. They consist of multiple coalescent intrusions cut by numerous aplitic dikes and outcrop along a surface of about 40 Km2. At least two different parental magmas have been distinguished on the basis of their geochemical characteristics. The evolution of main group of the Monte <pulchiana leucogranites (MGL) can be accounted for by crystal fractionation process of two extreme mineral assemblages. The discrimination between evolutive and genetic processes allows to set constraints on the geochemistry of the source(s) of the Monte Pulchiana leucogranites. Geochemical andphysical arguments provide evidence for a heterogeneous, andesitic-like composition source for the Monte Pulchiana leucogranites. The origin of this andesitic crust be found in the magmatic activity which took place in the Sardinia and Corsica islands in the Ordovician, prior to the onset of the Hercynian orogeny. The source heterogeities could have developed because of either intrinsic or extrinsic processes. The former concern differentiation of the andesitic magmas, whereas the latter concern the percolation of the huge amount of the late-tectonic monzogranitic melts en route to the sourface, throughout the upper portion of the andesitic crust. This resulted in the formation of a mixed, net-veined crustal source which subsequently experienced a partial melting process during the adiabatic upwelling of the Sardinia-Corsica basement occurred in the post-collisional phase of the Hercynian orogeny.