Conditions and timing of high-pressure Variscan metamorphism in the South Carpathians, Romania

Gordon Medaris, Mihai Ducea, Ed Ghent, Viorica Iancu

Research output: Contribution to journalArticle

55 Scopus citations

Abstract

High-pressure (HP) metamorphic rocks, including garnet peridotite, eclogite, HP granulite, and HP amphibolite, are important constituents of several tectonostratigraphic units in the pre-Alpine nappe stack of the Getic-Supragetic (GS) basement in the South Carpathians. A Variscan age for HP metamorphism is firmly established by Sm-Nd mineral-whole-rock isochrons for garnet amphibolite, 358±10 Ma, two samples of eclogite, 341±8 and 344±7 Ma, and garnet peridotite, 316±4 Ma.A prograde history for many HP metamorphic rocks is documented by the presence of lower pressure mineral inclusions and compositional zoning in garnet. Application of commonly accepted thermobarometers to eclogite (grt+cpx±ky±phn±pg±zo) yields a range in "peak" pressures and temperatures of 10.8-22.3 kbar and 545-745 °C, depending on tectonostratigraphic unit and locality. Zoisite equilibria indicate that activity of H2O in some samples was substantially reduced, ca. 0.1-0.4. HP granulite (grt+cpx+hb+pl) and HP amphibolite (grt+hbl+pl) may have formed by retrogression of eclogites during high-temperature decompression. Two types of garnet peridotite have been recognized, one forming from spinel peridotite at ca. 1150-1300 °C, 25.8-29.0 kbar, and another from plagioclase peridotite at 560 °C, 16.1 kbar.The Variscan evolution of the pre-Mesozoic basement in the South Carpathians is similar to that in other segments of the European Variscides, including widespread HP metamorphism, in which P - T - t characteristics are specific to individual tectonostratigraphic units, the presence of diverse types of garnet peridotite, diachronous subduction and accretion, nappe assembly in pre-Westphalian time due to collision of Laurussia, Gondwana, and amalgamated terranes, and finally, rapid exhumation, cooling, and deposition of eroded debris in Westphalian to Permian sedimentary basins.

Original languageEnglish (US)
Pages (from-to)141-161
Number of pages21
JournalLithos
Volume70
Issue number3-4
DOIs
StatePublished - Oct 2003

Keywords

  • Eclogite
  • Garnet peridotite
  • Sm-Nd geochronology
  • South Carpathians
  • Variscan

ASJC Scopus subject areas

  • Geology
  • Geochemistry and Petrology

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