The Central Aar Granite: Highly differentiated calc-alkaline magmatism in the Aar Massif (Central Alps, Switzerland)
European Journal of Mineralogy Volume 2 Number 2 (1990), p. 245 - 260
published: Apr 17, 1990
manuscript accepted: Nov 20, 1989
manuscript received: Dec 27, 1988
ArtNo. ESP147050202011, Price: 29.00 €
Abstract The Central Aar Granite is a calc-alkaline batholith of late Westphalian age forming the core of the Aar Massif (Central Alps). These highly differentiated rocks, ranging from granodiorites to leucogranites, have been investigated in three profiles through the massif: the Grimsel, Goscheneralp and Reuss valley cross sections, respectively. The granites are overprinted by Alpine low-grade metamorphism, but still exhibit primary geochemical compositions. The granite suite is characterized by enrichment of the incompatible trace elements Rb, U, Th, Y and Nb and by considerable depletion of Sr, Ba, La, Zr, P and the transition elements during differentiation. The trace element patterns suggest fractional crystallization of plagioclase, K-feldspar, biotite, apatite and allanite, but show some characteristics that cannot be explained by any combination of fractionating minerals. Other processes (mixing, assimilation, assimilation-fractional crystallization) may therefore contribute to the observed trace element trends. The granites display predominantly mantle characteristics with a minor degree of crustal contamination. They are believed to represent deep-seated crustal melts, which were intruded into the Hercynian orogen after the peak of metamorphism and compressional deformation.