Extensional tectonic origin of gneissosity and related structures of the Feiran-Solaf metamorphic belt, Sinai, Egypt

A. Fowler, I. Hassan

Research output: Contribution to journalArticlepeer-review

27 Citations (Scopus)


The Feiran-Solaf metamorphic belt consists of low-P high-T amphibolite facies, partly migmatized gneisses, schists, amphibolites and minor calc-silicate rocks of metasedimentary origin. There are also thick concordant synkinematic sheets of diorite, tonalite and granodiorite orthogneiss and foliated granite and pegmatite dykelets. The gneissosity (or schistosity) is referred to as S1, and is almost everywhere parallel to lithological layering, S0. This parallelism is not due to transposition. The gneissosity formed during an extensional tectonic event (termed D1), before folding of S0. S1 formed by coaxial pure shear flattening strain (Z normal to S0, i.e. vertical; with X and Y both extensional and lying in S1). This strain also produced chocolate tablet boudinage of some layers and S1-concordant sills and veins. S1 has a strong stretching lineation L1 with rodding characteristics. Within-plane plastic anisotropy (lower ductility along Y compared to along X) resulted in L1-parallel extensional ductile shears and melt filled cracks. Continued shortening of these veins, and back-rotation of foliations on the shears produced intrafolial F1 folds with hinges parallel to the stretching lineation. F1 fold asymmetry variations do not support previous models involving macroscopic F1 folds or syn-gneissosity compressional tectonics. The sedimentary protoliths of the Feiran-Solaf gneisses were probably deposited in a pre-800 Ma actively extending intracratonic rift characterizing an early stage of the break-up of Rodinia.

Original languageEnglish
Pages (from-to)119-136
Number of pages18
JournalPrecambrian Research
Issue number3-4
Publication statusPublished - Jul 30 2008


  • Extensional tectonic origin of gneissosity
  • Feiran-Solaf
  • Folding during layer-normal shortening
  • Pan-African gneisses and migmatites
  • Sinai

ASJC Scopus subject areas

  • Geology
  • Geochemistry and Petrology


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