Linking the P-T evolution of granulites and the geochemistry of ultra-K volcanics from Bohemian Massif and Central Tibet

Stéphane Guillot (1) , Fanny Goussin (1) , Petra Maierova , Carole Cordier (1) , Karel Schulmann (2) , Pierrick Roperch (3) , Guillaume Dupont-Nivet (3) , Anne Replumaz (1)

1 ISTerre - Institut des Sciences de la Terre
2 IPGS-Dylbas - Dynamique de la lithosphère et des bassins sédimentaires (IPGS)
3 GR - Géosciences Rennes

Variscan orogeny is traditionally compared to Himalayan- Tibetan orogeny thanks to two main reasons: 1) Variscan orogen originated through progressive amalgamation of Gondwana derived blocks which formed belt that was subsequently squeezed between two continental plates - Laurussia and Gondwana. Similar sequence of events is characteristic for Tibetan-Himalayan orogeny as well, where previously Gondwana accreted blocks were squeezed between Asian continent and India. Therefore, both orogens result from similar reorganization of plates in Paleozoic and Mesozoic- Cenozoic times, which initiated rapid northward drift of Gondwana derived blocks and their final collision with northern continental masses. 2) This process resulted in both cases in formation orogenic root of double-crust thickness characterized by long lasting (HP) granulite facies metamorphism in lower crust followed by isothermal decompression still at granulite facies conditions. In addition, the granulites in central Tibet were transported by high potassium lavas, with geochemical and isotopical signature corresponding to Mg-K granitoids typically associated to HP granulites in the eastern part of the Variscan belt (the Bohemian Massif in particular). In both cases, the origin of granulitic lower crust and associated high potassium lavas are attributed to relamination and thermal maturation of lower crustal allochthon underthrust below upper plate crust during collision. Based on above similarities we argue that the Devonian - Carboniferous evolution of the Bohemian Massif may be a proxy of Eocene to recent crustal dynamics of the Tibetan system. To better quantify similarities between both orogens, we present a set of numerical models which reproduce the tectonic multistage scenario proposed for the Variscan tectonics of Bohemian Massif. These models are subsequently compared with P-T data acquired from the Himalaya and southernTibetan granulites and xenoliths from central Tibet.

Keywords: Tibet; Boehmia; thickening; granulites; volcanism

Domains: Geochemistry; Tectonics

Stéphane Guillot, Fanny Goussin, Petra Maierova, Carole Cordier, Karel Schulmann, et al.. Linking the P-T evolution of granulites and the geochemistry of ultra-K volcanics from Bohemian Massif and Central Tibet. 25 ème Réunion des sciences de la Terre (RST 2016), Société Géologique de France, Oct 2016, Caen, France. pp.151. ⟨insu-01388146⟩