Devonian/Mississippian I-type granitoids in the Western Carpathians: A subduction-related hybrid magmatism

Self Cite

Abstract:The Tribeč granitic core (Tatric Superunit, Western Carpathians, Slovakia) is formed by Devonian/Lower Carboniferous, calc-alkaline I-and S-type granitic rocks and their altered equivalents, which provide a rare opportunity to study the Variscan magmatic, post-magmatic and tectonic evolution. The calculated P-T-X path of I-type granitic rocks, based on Fe-Ti oxides, hornblende, titanite and mica-bearing equilibria, illustrates changes in redox evolution. There is a transition from magmatic stage at T ca. 800-850 °C and moderate oxygen fugacity (FMQ buffer) to an oxidation event at 600 °C between HM and NNO up to the oxidation peak at 480 °C and HM buffer, to the final reduction at ca. 470 °C at ∆NN = 3.3. Thus, the post-magmatic Variscan history recorded in I-type tonalites shows at early stage pronounced oxidation and low temperature shift back to reduction. The S-type granites originated at temperature 700-750 °C at lower water activity and temperature. The P-T conditions of mineral reactions in altered granitoids at Variscan time (both I and S-types) correspond to greenschist facies involving formation of secondary biotite. The Tribeč granite pluton recently shows horizontal and vertical zoning: from the west side toward the east S-type granodiorites replace I-type tonalites and these medium/coarse-grained granitoids are vertically overlain by their altered equivalents in greenschist facies. Along the Tribeč mountain ridge, younger undeformed leucocratic granite dykes in age 342 ±4.4 Ma cut these metasomatically altered granitic rocks and thus post-date the alteration process. The overlaying sheet of the altered granites is in a low-angle superposition on undeformed granitoids and forms "a granite duplex" within Alpine Tatric Superunit, which resulted from a syn-collisional Variscan thrusting event and melt formation ~340 Ma. The process of alteration may have been responsible for shifting the oxidation trend to the observed partial reduction.

Section: Syn-collisional Granitesupporting

confidence: 76%

“…The S-type granitoids appear younger than 358-367 Ma I-type tonalites (ion microprobe zircon dating, Broska et al 2013).…”

Section: Syn-collisional Granitementioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

See 1 more Smart Citation

Variscan thrusting in I- and S-type granitic rocks of the Tribeč Mountains, Western Carpathians (Slovakia): evidence from mineral compositions and monazite dating

Broska¹,

Petrík²

2015

Self Cite

“…It is post-collisional with respect to the Late Devonian-Mississippian collision, that led to the accretion of the NGU orogenic belt to the Prototatricum crust (the term Prototatricum is coined by Broska et al 2013 for the common Variscan basement of the Tatricum and the Veporicum Units) which was the part of the Galatian Superterrane (von Raumer & Stampfli 2008;von Raumer et al 2009;Stampfli et al 2011), with the oceanic crust of the Prototethys. Radvanec et al (2009) argued that the crustal extension above the Late Variscan subduction zone was the origin of the Gemeric granites, as well as the Permian volcanics.…”

Section: Discussionmentioning

confidence: 99%

First evidence for Permian-Triassic boundary volcanism in the Northern Gemericum: geochemistry and U-Pb zircon geochronology

Vozárová¹,

Presnyakov²,

Šarinová³

et al. 2015

Several magmatic events based on U-Pb zircon geochronology were recognized in the Permian sedimentary succession of the Northern Gemeric Unit (NGU). The Kungurian magmatic event is dominant. The later magmatism stage was documented at the Permian-Triassic boundary. The detrital zircon assemblages from surrounding sediments documented the Sakmarian magmatic age. The post-orogenic extensional/transtensional faulting controlled the magma ascent and its emplacement. The magmatic products are represented by the calc-alkaline volcanic rocks, ranging from basaltic metaandesite to metarhyolite, associated with subordinate metabasalt. The whole group of the studied NGU Permian metavolcanics has values for the Nb/La ratio at (0.44-0.27) and for the Nb/U ratio at (9.55-4.18), which suggests that they represent mainly crustal melts. Magma derivation from continental crust or underplated crust is also indicated by high values of Y/Nb ratios, ranging from 1.63 to 4.01. The new 206 U-238 Pb zircon ages (concordia age at 269 ± 7 Ma) confirm the dominant Kungurian volcanic event in the NGU Permian sedimentary basin. Simultaneously, the Permian-Triassic boundary volcanism at 251 ± 4 Ma has been found for the first time. The NGU Permian volcanic activity was related to a polyphase extensional tectonic regime. Based on the new and previous U-Pb zircon ages, the bulk of the NGU Permian magmatic activity occurred during the Sakmarian and Kungurian. It was linked to the post-orogenic transpression/transtension tectonic movements that reflected the consolidation of the Variscan orogenic belt. The Permian-Triassic boundary magmatism was accompanied by extension, connected with the beginning of the Alpine Wilson cycle.

“…The Veporic crystalline basement is composed of Palaeozoic volcano-sedimentary rocks characterised by medium-grade Variscan metamorphic overprint (Vrána 1964;Méres & Hovorka 1991;Kováčik et al 1996;Putiš et al 1997;Jeřábek et al 2008a), which are located in the footwall of high-grade Variscan migmatites and Upper Devonian-Lower Carboniferous I-and S-type granite rocks (~ 370-350 Ma;Siman et al 1996;Michalko et al 1998;Broska et al 2013). …”

Section: Veporic Unitmentioning

confidence: 99%

Geological evolution of the southwestern part of the Veporic Unit (Western Carpathians): based on fission track and morphotectonic data

Vojtko

Králiková

Andriessen³

et al. 2017