Quartz and calcite microfabric transitions in a pressure and temperature gradient, Sivrihisar, Turkey

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Abstract

Interlayered quartzite and marble in the southern Sivrihisar Massif, Turkey, record metamorphic conditions ranging from high-pressure/low-temperature through a Barrovian overprint from chlorite-to sillimanite-zone conditions. This sequence was exhumed under transtension, producing macroscopic constrictional fabrics (L-tectonites) during crustal thinning. Quartz microstructures consist of dynamically recrystallized aggregates in the dislocation creep regime dominated by grain boundary migration. Quartz microstructures are relatively constant across the high metamorphic gradient, and crystallographic fabric patterns transition from plane strain to constriction strain. Calcite fabrics are characterized by progressive overprinting of a columnar texture inherited from the high-pressure polymorph aragonite. In the low-temperature Barrovian domain (<400°C), shearing of calcite rods produced a very strong c-axis point maximum. At moderate temperature, calcite rods were partially to totally recrystallized and the strong preferred orientation maintained. At temperature >500°C and high constriction strain, marble has no crystallographic fabric, likely reflecting a transition from dislocation creep to diffusion creep. Phengite in high-pressure/low-temperature marble and quartzite yields relatively simple age spectra with Late Cretaceous (88-82 Ma) 40Ar/39Ar ages. Barrovian muscovite records significantly younger ages (63-55 Ma). The transtension system and associated metamorphism may have occurred above a subduction zone in Paleocene-Eocene time as a precursor to intrusion of Eocene (~53 Ma) arc plutons.

Original languageEnglish (US)
Pages (from-to)191-206
Number of pages16
JournalGeodinamica Acta
Volume26
Issue number3-4
DOIs
StatePublished - Dec 1 2013

Bibliographical note

Funding Information:
This project was supported by NSF grant EAR-0711263 to Whitney and Teyssier. Parts of this work were carried out in the Characterization Facility, University of Minnesota, which receives partial support from NSF through the MRSEC program.

Keywords

  • Sivrihisar
  • Turkey
  • argon-argon dates
  • calcite
  • constriction
  • crystallographic fabrics
  • microstructure
  • quartz

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