Very low-grade metamorphism of sedimentary rocks of the Meliata unit, Western Carpathians, Slovakia: Implications of phyllosilicate characteristics

P. Árkai, Shah Wali Faryad, Olivier Vidal, K. Balogh

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56 Citations (Scopus)

Abstract

The Meliata unit represents a mélange-like accretionary wedge, containing blueschist facies tectonic blocks and slices in a Triassic and Jurassic sedimentary matrix. The blueschist facies rocks are tectonic remnants of the subducted parts of the Meliata-Hallstatt branch of the Tethys. The phyllosilicate assemblages in very low-grade metapelites represent metastable disequilibrium stages which the assemblages have reached during reaction progress. Therefore, temperature and pressure values of low-T metamorphism of the sedimentary series and the late stages of decompressional cooling of blueschist facies rocks, obtained by phyllosilicate "crystallinity", chlorite thermometric and white K-mica geobarometric methods, can be regarded as semiquantitative estimates. However, results of chlorite-white mica thermobarometry suggest that local equilibrium was approached at a microscopic scale. For deciphering the age relations of prograde and retrograde events, K-Ar isotope geochronological methods were applied. The sedimentary series and related basalts of the Meliata unit experienced high-T anchizonal prograde regional metamorphism, the temperature and pressure of which can vary between ca. 280 and 350 °C and ca. 2.5 and 5 kbar. White K-mica b geobarometry suggests possible minimal pressures of ca. 1.5 to 3 kbar. The mylonitic retrogression of blueschist facies phyllites is characterised by 340 °C and 4 kbar (minimal P). The low-T prograde metamorphism was synchronous with the retrograde metamorphism of the blueschists. The ages of these two events may be between ca. 150 and 120 Ma, culminating most probably at around 140-145 Ma. Thus, the Upper Jurassic (lower-most Cretaceous) very low-grade metamorphism of the Meliata unit is younger than the subduction-related, 160-155 Ma blueschist facies event, and definitely older than the Cretaceous (100-90 Ma) metamorphism of the footwall Gemer Palaeozoic.

Original languageEnglish
Pages (from-to)68-85
Number of pages18
JournalInternational Journal of Earth Sciences
Volume92
Issue number1
Publication statusPublished - Mar 2003

Fingerprint

blueschist facies
low grade metamorphism
phyllosilicate
sedimentary rock
mica
prograde metamorphism
chlorite
metamorphism
Jurassic
geobarometry
Cretaceous
retrograde metamorphism
tectonics
retrogression
blueschist
metapelite
regional metamorphism
accretionary prism
crystallinity
footwall

Keywords

  • Accretionary metamorphism
  • Chlorite
  • Illite-white mica
  • Very low-grade metamorphism
  • Western Carpathians

ASJC Scopus subject areas

  • Earth and Planetary Sciences (miscellaneous)

Cite this

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title = "Very low-grade metamorphism of sedimentary rocks of the Meliata unit, Western Carpathians, Slovakia: Implications of phyllosilicate characteristics",
abstract = "The Meliata unit represents a m{\'e}lange-like accretionary wedge, containing blueschist facies tectonic blocks and slices in a Triassic and Jurassic sedimentary matrix. The blueschist facies rocks are tectonic remnants of the subducted parts of the Meliata-Hallstatt branch of the Tethys. The phyllosilicate assemblages in very low-grade metapelites represent metastable disequilibrium stages which the assemblages have reached during reaction progress. Therefore, temperature and pressure values of low-T metamorphism of the sedimentary series and the late stages of decompressional cooling of blueschist facies rocks, obtained by phyllosilicate {"}crystallinity{"}, chlorite thermometric and white K-mica geobarometric methods, can be regarded as semiquantitative estimates. However, results of chlorite-white mica thermobarometry suggest that local equilibrium was approached at a microscopic scale. For deciphering the age relations of prograde and retrograde events, K-Ar isotope geochronological methods were applied. The sedimentary series and related basalts of the Meliata unit experienced high-T anchizonal prograde regional metamorphism, the temperature and pressure of which can vary between ca. 280 and 350 °C and ca. 2.5 and 5 kbar. White K-mica b geobarometry suggests possible minimal pressures of ca. 1.5 to 3 kbar. The mylonitic retrogression of blueschist facies phyllites is characterised by 340 °C and 4 kbar (minimal P). The low-T prograde metamorphism was synchronous with the retrograde metamorphism of the blueschists. The ages of these two events may be between ca. 150 and 120 Ma, culminating most probably at around 140-145 Ma. Thus, the Upper Jurassic (lower-most Cretaceous) very low-grade metamorphism of the Meliata unit is younger than the subduction-related, 160-155 Ma blueschist facies event, and definitely older than the Cretaceous (100-90 Ma) metamorphism of the footwall Gemer Palaeozoic.",
keywords = "Accretionary metamorphism, Chlorite, Illite-white mica, Very low-grade metamorphism, Western Carpathians",
author = "P. {\'A}rkai and Faryad, {Shah Wali} and Olivier Vidal and K. Balogh",
year = "2003",
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T1 - Very low-grade metamorphism of sedimentary rocks of the Meliata unit, Western Carpathians, Slovakia

T2 - Implications of phyllosilicate characteristics

AU - Árkai, P.

AU - Faryad, Shah Wali

AU - Vidal, Olivier

AU - Balogh, K.

PY - 2003/3

Y1 - 2003/3

N2 - The Meliata unit represents a mélange-like accretionary wedge, containing blueschist facies tectonic blocks and slices in a Triassic and Jurassic sedimentary matrix. The blueschist facies rocks are tectonic remnants of the subducted parts of the Meliata-Hallstatt branch of the Tethys. The phyllosilicate assemblages in very low-grade metapelites represent metastable disequilibrium stages which the assemblages have reached during reaction progress. Therefore, temperature and pressure values of low-T metamorphism of the sedimentary series and the late stages of decompressional cooling of blueschist facies rocks, obtained by phyllosilicate "crystallinity", chlorite thermometric and white K-mica geobarometric methods, can be regarded as semiquantitative estimates. However, results of chlorite-white mica thermobarometry suggest that local equilibrium was approached at a microscopic scale. For deciphering the age relations of prograde and retrograde events, K-Ar isotope geochronological methods were applied. The sedimentary series and related basalts of the Meliata unit experienced high-T anchizonal prograde regional metamorphism, the temperature and pressure of which can vary between ca. 280 and 350 °C and ca. 2.5 and 5 kbar. White K-mica b geobarometry suggests possible minimal pressures of ca. 1.5 to 3 kbar. The mylonitic retrogression of blueschist facies phyllites is characterised by 340 °C and 4 kbar (minimal P). The low-T prograde metamorphism was synchronous with the retrograde metamorphism of the blueschists. The ages of these two events may be between ca. 150 and 120 Ma, culminating most probably at around 140-145 Ma. Thus, the Upper Jurassic (lower-most Cretaceous) very low-grade metamorphism of the Meliata unit is younger than the subduction-related, 160-155 Ma blueschist facies event, and definitely older than the Cretaceous (100-90 Ma) metamorphism of the footwall Gemer Palaeozoic.

AB - The Meliata unit represents a mélange-like accretionary wedge, containing blueschist facies tectonic blocks and slices in a Triassic and Jurassic sedimentary matrix. The blueschist facies rocks are tectonic remnants of the subducted parts of the Meliata-Hallstatt branch of the Tethys. The phyllosilicate assemblages in very low-grade metapelites represent metastable disequilibrium stages which the assemblages have reached during reaction progress. Therefore, temperature and pressure values of low-T metamorphism of the sedimentary series and the late stages of decompressional cooling of blueschist facies rocks, obtained by phyllosilicate "crystallinity", chlorite thermometric and white K-mica geobarometric methods, can be regarded as semiquantitative estimates. However, results of chlorite-white mica thermobarometry suggest that local equilibrium was approached at a microscopic scale. For deciphering the age relations of prograde and retrograde events, K-Ar isotope geochronological methods were applied. The sedimentary series and related basalts of the Meliata unit experienced high-T anchizonal prograde regional metamorphism, the temperature and pressure of which can vary between ca. 280 and 350 °C and ca. 2.5 and 5 kbar. White K-mica b geobarometry suggests possible minimal pressures of ca. 1.5 to 3 kbar. The mylonitic retrogression of blueschist facies phyllites is characterised by 340 °C and 4 kbar (minimal P). The low-T prograde metamorphism was synchronous with the retrograde metamorphism of the blueschists. The ages of these two events may be between ca. 150 and 120 Ma, culminating most probably at around 140-145 Ma. Thus, the Upper Jurassic (lower-most Cretaceous) very low-grade metamorphism of the Meliata unit is younger than the subduction-related, 160-155 Ma blueschist facies event, and definitely older than the Cretaceous (100-90 Ma) metamorphism of the footwall Gemer Palaeozoic.

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