Coaxial flattening at deep levels of orogenic belts: Evidence from blueschists and eclogites on Syros and Sifnos (Cyclades, Greece)

Gideon Rosenbaum*, Dov Avigad, Mario Sánchez-Gómez

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

57 Scopus citations

Abstract

This work presents new structural data from a high-pressure/low-temperature (HP/LT) metamorphic terrane exposed on the islands of Syros and Sifnos (Cyclades, Greece). The structure and the metamorphism of a relatively coherent HP/LT rock section were studied in order to elucidate how strain was accommodated at deep crustal levels during the formation and exhumation of HP/LT rocks. At least three deformation phases associated with eclogite- and blueschist-facies conditions (P=8-15 kbar; T=400-550 °C) were recognised. The earliest deformation fabric (SI), preserved as inclusion trails within garnet porphyroblasts, is aligned to define a sub-vertical schistosity (at present orientation), which is frequently orthogonal to the flat matrix schistosity (S2), and may indicate that deep crustal thickening involved upright folding. The currently dominant fabric in the HP rock section, S2, is usually moderately dipping and locally contains NW-trending glaucophane lineations, symmetric pressure-shadows and eclogitic boudins. The symmetric structures associated with this fabric seem to indicate coaxial vertical thinning, although the existence of non-coaxial structures out of the study area cannot be excluded. Glaucophane-bearing shear bands (S3), with top-to-NW sense of shearing, locally crosscut the earlier structures. The latest recognised fabric (D4) is scarce and often absent within the HP rocks. It is associated with top-to-NE kinematic criteria that formed at greenschist-facies conditions (P=4-7 kbar; T=400-450 °C). Based on these observations, it is suggested that partitioning of strain occurred at different crustal levels and at different times. Deep crustal deformation was governed by thickening via upright folding followed by coaxial vertical thinning, whereas non-coaxial shearing occurred when the rocks were already exhumed to relatively shallow crustal levels. The earliest fabrics (D1 to D3) pertain to Alpine orogenesis and possibly to syn-orogenic extension, whereas the latest correspond to whole-crust back-arc extension.

Original languageAmerican English
Pages (from-to)1451-1462
Number of pages12
JournalJournal of Structural Geology
Volume24
Issue number9
DOIs
StatePublished - 2002

Bibliographical note

Funding Information:
Andor Lips and John C. Schumacher are greatly acknowledged for providing constructive reviews of the manuscript. Thanks are due to Z. Garfunkel for discussions and advice, M. Pavlidis for grammatical assistance and M. Krabbendam for comments on an earlier version of the manuscript. We acknowledge funding from the United States–Israel Binational Science Foundation (BSF).

Keywords

  • Cyclades
  • Exhumation
  • Extension
  • Sifnos
  • Syros

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