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Cretaceous evolution of a metamorphic core complex, the Veporic unit, Western Carpathians (Slovakia): P – T conditions and in situ 40 Ar/ 39 Ar UV laser probe dating of metapelites
Author(s) -
Janák M.,
Plašienka D.,
Frey M.,
Cosca M.,
Schmidt S. TH.,
Lupták B.,
Méres Š.
Publication year - 2001
Publication title -
journal of metamorphic geology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.639
H-Index - 114
eISSN - 1525-1314
pISSN - 0263-4929
DOI - 10.1046/j.0263-4929.2000.00304.x
Subject(s) - geology , metamorphic rock , metamorphism , metamorphic core complex , greenschist , staurolite , metamorphic facies , geochemistry , cretaceous , isograd , kyanite , tectonics , geomorphology , paleontology , facies , extensional definition , structural basin
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 K 2 O–FeO–MgO–Al 2 O 3 –SiO 2 –H 2 O (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. 40 Ar/ 39 Ar 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 40 Ar/ 39 Ar 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.