Mineralogy and Petrology

, Volume 63, Issue 3–4, pp 173–198 | Cite as

High-grade metamorphic rocks in the pre-Alpine nappe stack of the Getic-Supragetic basement (Median Dacides, South Carpathians, Romania)

  • V. Iancu
  • M. Màruntiu
  • V. Johan
  • P. Ledru
Article

Summary

Metamorphic rocks in the pre-Alpine basement of the Getic-Supragetic units (Median Dacides of the Carpathian belt) are spatially related to different lithotectonic units, some of which contain high-pressure relicts reflecting an early stage of oceanic and continental subduction, locally synchronous with mylonitic shear zones. Kyaniteamphibole ± quartz-bearing eclogites preserve a complete metamorphic clockwise loop; the estimated peak conditions within the outer part of the Cumpana unit were at least 20 kb at 780–860 °C. Pre-eclogite-stage magmatic phases occur in some units with true equilibrated eclogites. Clinopyroxene-plagioclase inclusions in garnet of a garnet-clinopyroxene assemblage within a metagabbro indicate a temperature around 760–790 °C at a maximum pressure of about 19 kb. The units finally evolved together during stages of exhumation under metamorphic conditions ranging from the Barrovian-type (minimum age of 330 Ma) to the high-temperature/low-pressure type. The absolute age of the high-pressure stage and the eclogite protoliths is unknown. In comparison with other collision belts, it is likely that the gneiss units of the Median Dacides underwent a complete cycle of underthrusting and exhumation similar to other segments of the European Variscides, and that the formation of the eclogite occurred during the early stages of subduction.

Résumé

Les roches métamorphiques du socle pré-alpin des domaines Gétiques et Supragétiques (Dacides médianes de la chaîne des Carpathes) appartiennent à des unités lithotectoniques différentes dont certaines contiennent des reliques de métamorphisme haute pression reflétant un stade précoce de subduction continentale et océanique, localement synchrone de zones de cisaillement mylonitiques. Des éclogites é disthène-amphibole ± quartz permettent de reconstituer un trajet PT horaire complet. Les conditions paroxysmales sont estimées au sein de l'unité de Cumpana é plus de 20 kb pour 780–860 °C. Des phases magmatiques pré-éclogitiques coexistent avec des phases de haute pression dans les éclogites de certaines unités et des inclusions de clinopyroxene-plagioclase dans les grenats d'un métagabbro indiquent une température de 760–790 °C pour une pression maximale de 19 kb. L'ensemble des unités évolue finalement durant les stades d'exhumation sous les mêmes conditions de métamorphisme barrovien (âge minimum de 330 Ma) puis de haute température-basse pression. L'âge du stade de haute pression et des protholithes reste inconnu. En comparaison avec d'autres chaînes de collision, il est vraisemblable que les Dacides médianes ont subi un cycle d'enfouissement et d'exhumation similaire é celui décrit dans d'autres segments de la chaîne varisque européenne, la formation des éclogites étant attribuée aux premiers stades de la subduction.

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Copyright information

© Springer-Verlag 1998

Authors and Affiliations

  • V. Iancu
    • 1
  • M. Màruntiu
    • 1
  • V. Johan
    • 2
  • P. Ledru
    • 3
  1. 1.Geological Survey of RomaniaBucharestRomania
  2. 2.OrléansFrance
  3. 3.BRGMOrléansFrance

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