Multistage Variscan magmatism in the central Tauern Window (Austria) unveiled by U/Pb SHRIMP zircon data

U/Pb SHRIMP ages of nine Variscan leucocratic orthogneisses from the centra l Tauern Window (Austria) reveal three distinct pulses of magmatism in Earl y Carboniferous (Visean), Late Carboniferous (Stephanian) and Early Permian , each involving granitold intrusions and a contemporaneous opening of volc ano-sedimentary basins. A similar relationship has been reported for the Ca rboniferous parts of the basement of the Alps further to the west? e.g. the ''External massifs" in Switzerland. After the intrusion of subduction-rela ted, volcanic-are granitoids (374 +/- 10 Ma, Zwolferkogel gneiss), collisio nal intrusive-granitic, anatectic and extrusive-rhyolitic/dacitic rocks wer e produced over a short interval at ca. 340 Ma (Augengneiss of Felbertauern : 340 +/- 4 Ma, Hochweissenfeld gneiss: 342 +/- 5 Ma, Falkenbachlappen gnei ss: 343 +/- 6 Ma). This Early Carboniferous magmatism, which produced relat ively small volumes of melt, can be attributed to the amalgamation of the G ondwana-derived "Tauern Window" terrane with Laurussia-Avalonia. Probably d ue to the oblique nature of the collision, transtensional phenomena (i.e. v olcano-sedimentary troughs and high-level intrusives) and transpressional r egimes (i.e. regional metamorphism and stacked nappes with anatexis next to thrust planes) evolved contemporaneously. The magmas are mainly of the hig h-K I-type and may have been generated during a short phase of decompressio nal melting of lithospheric mantle and lower crustal sources. In the Late C arboniferous? a second pulse of magmatism occurred, producing batholiths of calc-alkaline I-type granitoids (e.g. Venediger tonalite: 296 +/- 4 Ma) an d minor coeval bodies of felsic and intermediate volcanics (Heuschartenkopf gneiss: 299 +/- 4 Ma, Peitingalm gneiss: 300 +/- 5 Ma). Prior to this magm atism, several kilometres of upper crust must have been eroded, because vol cano-sedimentary sequences hosting the Heuschartenkopf and Peitingalm gneis ses rest unconformably on 340-Ma-old granitoids. The youngest (Permian) per iod of magma generation contains the intrusion of the S-type Granatspitz Ce ntral Gneiss at 271 +/- 4 Ma and the extrusion of the rhyolitic Schonbachwa ld gneiss protolith at 279 +/- 9 Ma. These magmatic reeks may have been ass ociated with local extension along continental wrench zones through the Var iscan orogenic crust or with a Permian rifting event. The Permian and the a bove-mentioned Late Carboniferous volcano-sedimentary sequences were probab ly deposited in intra-continental graben structures, which survived post-Va riscan uplift and Alpine compressional tectonics.