Anatomy of a transitional brittle-ductile shear zone developed in a low-T meta-andesite tuff: A microstructural, petrological and geochronological case study from the Bükk Mts. (NE Hungary)

B. Koroknai, P. Árkai, Péter Horváth, K. Balogh

Research output: Contribution to journalArticle

10 Citations (Scopus)

Abstract

Microstructures of the low-T metavolcanites deriving from the transitional brittle-ductile Lillafüred Shear Zone (LSZ, Eastern Bükk Mts., NE Hungary) reveal that the prominent mylonitic rock-structure observed at hand-specimen scale was predominantly achieved at the grain scale by (1) intense microfracturing of rigid minerals (feldspar, opaque phases), and (2) intergranular sliding associated with solution mass transfer within the prevailing, fine-grained, phyllosilicate-rich matrix. Fluid migration during shearing-indicated by widespread growth of syntectonic, secondary calcite and pervasive retrograde alteration of feldspar into "weak", fine-grained mica aggregates-led to substantial weakening and localization of deformation into narrow zones. This is accompanied microstructurally by an evolution from a cataclasis-dominated regime towards a more ductile, mylonitic deformation. Various metamorphic petrological and geochronological parameters (illite Kübler index, chlorite "crystallinity" indices, crystallite thickness, mean lattice strain, chlorite-AlIV thermometry, K-Ar ages on

Original languageEnglish
Pages (from-to)159-176
Number of pages18
JournalJournal of Structural Geology
Volume30
Issue number2
DOIs
Publication statusPublished - Feb 2008

Fingerprint

tuff
anatomy
andesite
chlorite
shear zone
feldspar
ductile deformation
phyllosilicate
crystallinity
mica
illite
sliding
mass transfer
microstructure
calcite
matrix
fluid
mineral
rock
index

Keywords

  • Brittle-ductile
  • Bükk Mts.
  • Chlorite "crystallinity"
  • Illite Kübler index
  • K-Ar Geochronology
  • Low-T shear zone

ASJC Scopus subject areas

  • Geology

Cite this

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abstract = "Microstructures of the low-T metavolcanites deriving from the transitional brittle-ductile Lillaf{\"u}red Shear Zone (LSZ, Eastern B{\"u}kk Mts., NE Hungary) reveal that the prominent mylonitic rock-structure observed at hand-specimen scale was predominantly achieved at the grain scale by (1) intense microfracturing of rigid minerals (feldspar, opaque phases), and (2) intergranular sliding associated with solution mass transfer within the prevailing, fine-grained, phyllosilicate-rich matrix. Fluid migration during shearing-indicated by widespread growth of syntectonic, secondary calcite and pervasive retrograde alteration of feldspar into {"}weak{"}, fine-grained mica aggregates-led to substantial weakening and localization of deformation into narrow zones. This is accompanied microstructurally by an evolution from a cataclasis-dominated regime towards a more ductile, mylonitic deformation. Various metamorphic petrological and geochronological parameters (illite K{\"u}bler index, chlorite {"}crystallinity{"} indices, crystallite thickness, mean lattice strain, chlorite-AlIV thermometry, K-Ar ages on",
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