Cretaceous evolution of a metamorphic core complex, the Veporic unit, Western Carpathians (Slovakia): P–T conditions and in situ⁴⁰Ar/³⁹Ar UV laser probe dating of metapelites

Abstract

Alpine metamorphism, related to the development of a metamorphic core complex during Cretaceous orogenic events, has been recognized in the Veporic unit, Western Carpathians (Slovakia). Three metamorphic zones have been distinguished in the metapelites: 1, chloritoid + chlorite + garnet; 2, garnet + staurolite + chlorite; 3, staurolite + biotite + kyanite. The isograds separating the metamorphic zones have been modelled by discontinuous reactions in the system K2O–FeO–MgO–Al2O3–SiO2–H2O (KFMASH). The isograds are roughly parallel to the north‐east‐dipping foliation related to extensional updoming along low‐angle normal faults. Thermobarometric data document increasing P–T conditions from c. 500 °C and 7–8 kbar to c. 620 °C and 9–10 kbar, reflecting a coherent metamorphic field gradient from greenschist to middle amphibolite facies. 40Ar/39Ar data obtained by high spatial resolution in situ ultraviolet (UV) laser ablation of white micas from the rock slabs constrain the timing of cooling and exhumation in the Late Cretaceous. Mean dates are between 77 and 72 Ma; however, individual white mica grains record a range of apparent 40Ar/39Ar ages indicating that cooling below the blocking temperature for argon diffusion was not instantaneous. The reconstructed metamorphic P–T–t path is ‘clockwise’, reflecting post‐burial decompression and cooling during a single Alpine orogenic cycle. The presented data suggest that the Veporic unit evolved as a metamorphic core complex during the Cretaceous growth of the Western Carpathian orogenic wedge. Metamorphism was related to collisional crustal shortening and stacking, following closure of the Meliata Ocean. Exhumation was accomplished by synorogenic (orogen‐parallel) extension and unroofing in an overall compressive regime.

Fluid-driven destabilization of REE-bearing accessory minerals in the granitic orthogneisses of North Veporic basement (Western Carpathians, Slovakia)

“…This relatively long interval comprised collisional burial to approximately 30 km depth (6-10 kbar at ca. 500-620°C, Putiš et al 1997;Lupták et al 2000;Janák et al 2001) and transpression exhumation enhanced by structural unroofing (Putiš 1994).…”

Apatite fission track and (U-Th)/He thermochronology of the Rochovce granite (Slovakia) – implications for the thermal evolution of the Western Carpathian-Pannonian region

“…the Veporic unit, occupying the footwall position, consists of Variscan crystalline basement together with an Upper Palaeozoic-triassic sedimentary cover, overprinted by low-to medium-grade regional metamorphism in Eoalpine time (Vrána 1964;Vozárová 1990;Plašienka et al 1999;Lupták et al 2000;Janák et al 2001). the Gemeric unit, occupying the hangingwall position, consists of Palaeozoic mostly low-grade metamorphic rocks intruded by Permian granites that underwent an Eoalpine overprint under very low-to low-grade conditions (Hovorka & Méres 1997;Korikovsky et al 1997 and references therein).…”

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

“…In these early convergent stages, the Veporic Unit suffered an internal shortening and thickening documented by upright folding. These early structures were mostly obliterated by the subsequent major deformation associated with the development of subhorizontal mylonitic foliation and the W-E orogen-parallel extension (Hók et al 1993;Plašienka 1993;Janák et al 2001;Jeřábek et al 2007Jeřábek et al , 2008a. In the study area, the Alpine metamorphism shows the greenschist facies conditions of 450 °C at 400-450 MPa (Jeřábek et al 2008a).…”

“…Much progress has been made in recent years towards understanding the processes of Alpine metamorphism during the nappe stacking (e.g., Vrána 1964;Janák et al 2001;Finger et al 2003;Lupták et al 2004;Jeřábek et al 2008aJeřábek et al ,b, 2012, but the Late Cretaceous to Cenozoic evolution is still not well Brought to you by | MIT Libraries Authenticated Download Date | 5/12/18 9:41 PM phase followed by the Late Cretaceous/Palaeocene collapse and the Eocene-Quaternary post-collisional evolution of this part of the Western Carpathians.…”