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

Abstract

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.

Titanite composition and SHRIMP U–Pb dating as indicators of post-magmatic tectono-thermal activity: Variscan I-type tonalites to granodiorites, the Western Carpathians

“…Application of the Fe-Ti oxide geothermometry (Sauerzapf et al 2008;Ghiorso & Evans 2008) show ~630 to 780 °C interval for the equilibrium of magnetite-ilmenite pair for the titanitebearing granitic rocks (Tribeč, Čierna Hora; Broska & Petrík 2011). Moreover, this titanite producing reaction indicates the temperature of ~710 °C at 0.4 GPa pressure and aH 2 O = 0.5, calculated using the Thermocalc 3.31 (Holland & Powell 2011) and the AX software for end-member activities (Broska & Petrík 2015). These calculated temperatures are in accordance with our results based on Zr-in-titanite thermometry (Table 6).…”

“…After the formation of subduction-related I-type granites, subsequent Variscan crustal shortening during younger collisional event might have trigger partial melting and intrusion of limited amounts of leucogranitic melts and/or related high-temperature fluids into I-type tonalites to granodiorites, dated at ~ 340 Ma by chemical U-Th-Pb monazite method in the Tribeč Mts. (Broska & Petrík 2015) and Branisko near Čierna Hora (Bónová et al 2005). Almandine garnet from granitic pegmatite near Rimavská Baňa (Veporic Unit) also reveals a Visean Sm-Nd isotopic age of 339.0 ± 7.7 Ma (Thöni et al 2003).…”

Experimental constraints on the relative stabilities of the two systems monazite-(Ce) – allanite-(Ce) – fluorapatite and xenotime-(Y) – (Y,HREE)-rich epidote – (Y,HREE)-rich fluorapatite, in high Ca and Na-Ca environments under P-T conditions of 200–1000 MPa and 450–750 °C

“…Monazite [(LREE,Th,U)PO 4 ], xenotime-(Y) [(Y,HREE)PO 4 ], fluorapatite [(Ca,LREE,Si,Na) 5 (PO 4 ) 3 F], and allanite [(Ca,REE)(Al 2 ,Fe 2+ )(Si 2 O 7 )(SiO 4 )O(OH)] are common accessory minerals in various types of igneous, metamorphic, and sedimentary rocks and represent the principal hosts of rare earth elements (REEs) in the Earth's crust. They are widely used as geochronometers, including U-Pb and Th-U-Pb dating of monazite (Williams et al 2007) and xenotime-(Y) (Hetherington et al 2008), Lu-Hf, U-Pb, fission track and (U-Th)/He dating of apatite (Chew and Spikings 2015), and epidote in granitic rocks (Broska et al 2005;Broska and Petrík 2015) or fluorapatite and hingganite-(Y) in pegmatite (Majka et al 2011). The P-T conditions for such alterations are not well constrained.…”

Drainage evolution in the Polish Sudeten Foreland in the context of European fluvial archives

“…Much later, SE Poland was affected by Late Cenozoic plate motions, involving southward or southwestward subduction of the former Carpathian Ocean (Fig. 3B); as a result, the mosaic of continental fragments affected by the Variscan orogeny in what is now Slovakia (which were formerly located farther southwest) became juxtaposed against SE Poland (e.g., Plašienka et al, 1997; Szafián et al, 1997; Stampfli et al, 2001, 2002; Von Raumer et al, 2002, 2003; Bielik et al, 2004; Schmid et al, 2004; Alasonati-Tašárová et al, 2009; Handy et al, 2014; Broska and Petrík, 2015). Thus, the crustal structure of Poland is highly variable, reflecting the complex tectonic history of the wider region.…”