The igneous plumbing system of the Early Permian Bolzano/Bozen supervolcano (North-eastern Italy)

<p>Early Permian Post-Variscan magmatism is widespread throughout the Alps and consists mainly of felsic to mafic plutonic and volcanic bodies emplaced between ca. 285 and 275 Ma. This study focuses on the acidic to intermediate intrusions in the areas of Trento and Bolzano/Bozen (North-eastern Italy) like the Cima d’Asta gabbrodiorite/granite, the Pergine granodiorite, the Monte Sabion and the Bressanone (Brixen) granites. New U-Pb zircon data along with ages for the Ivigna (Ifinger) and Monte Croce (Kreuzberg) granites and the Bressanone (Brixen) gabbro constrain the age of the Permian intrusions and Hf isotopic data highlight the interaction between mantle-derived melts and crustal rocks during ascent of the former through the crust. Moreover, the studied intrusions represent the shallow crustal plumbing system of the coeval widespread volcanics of the Athesian Volcanic Group and the mega-caldera of the Bolzano/Bozen supervolcano. This acid intrusive-extrusive magmatism, which identified an elliptic structure of more than 4200 square kilometers, represents the biggest magmatic event outcropping in the Southern Alps and likely influenced the ecosystems of the Athesian Volcanic District and of the dolomitic area l.s. during the Permian.</p>

Late- to post-Variscan magmatism in the Lusatian Block occurred during two short episodes: Evidence from zircon dating

<p>In the Late Carboniferous to Early Permian, post-orogenic processes led to the intrusion of compositionally diverse granitoids and to intense silicic volcanism in Central Europe. In the Lusatian Block, which is situated in the eastern part of the Saxothuringian Zone of the Variscan orogen, the late- to post-Variscan granitoids are subordinate in comparison to the Cadomian basement and late- to post-Variscan volcanic rocks are almost absent. The Lusatian Block is bound towards the NE and the SW by major deep reaching fault zones. Both the granitoid and the volcanic rocks are situated near the boundaries of the block and probably associated with the major NW trending faults of the Elbe Fault Zone (e.g. Hammer et al., 1999, Lisowiec et al., 2014, Oberc-Dziezic et al., 2015). The Elbe Fault Zone is a continental scale zone of crustal weakness that was reactivated with different kinematics at different times (Scheck et al., 2002). </p><p>We acquired new precise CA-ID-TIMS U-Pb zircon ages of the Koenigshain and the Stolpen granites and the volcanics of the Weissig Basin. Our new data show that the Variscan magmatism of the Lusatian Block occurred at two distinct periods, depending on the structures on which they are bound. The age difference between the two groups (12 Myr) is clearly evident in both CA-ID-TIMS and evaporation analyses. Consequently, zircon evaporation data of other granitoid and volcanic rocks that were not dated with CA-ID-TIMS can be assigned to one of the two groups in the Lusatian Block. The new age dating allows comparison of the evolution of the investigated rocks to adjacent Variscan magmatic rocks.</p><p> </p><p>References:</p><p>Hammer et al. (1999), Z. geol. Wiss 27, 401-415.</p><p>Lisowiec et al. (2014), Acta Geologica Polonica 64 (4), 457-472.</p><p>Oberc-Dziezic et al. (2015), Int. J. Earth. Sci. 104, 1139-1166.</p><p>Scheck et al. (2002), Tectonophysics 360, 281-299.</p>