Progressive deformation and the rotation of contemporary fold axes in the Ballybofey Nappe, northwest Ireland

Geoffrey Ian Alsop

Research output: Contribution to journalArticlepeer-review

37 Citations (Scopus)

Abstract

Internal regions of orogenic belts may be characterized by an alignment of fold axes with mineral elongation lineations. This relationship is commonly interpreted as representing progressive tightening and rotation towards the shear direction of early buckle folds, the hinges of which were initiated orthogonal to this direction. Detailed structural analysis of lower amphibolite facies Dalradian metasediments of the Ballybofey (fold) Nappe, north-west Ireland, shows that an intense S3 schistosity is developed axial planar to mesoscopic and minor F3 folds. In areas of low D3 strain, F3 fold axes plunge gently towards the north-east, whereas in regions of greater strain plunges are towards the south-east subparallel to the constant mineral lineation. Minor folds which initiated at angles of 70 - 80-degrees from the mineral lineation subsequently rotated towards the shear direction in a consistent clockwise sense. Progressive and variable non-coaxial deformation oblique to the original mean F3 orientation has resulted in a unimodal distribution pattern of fold axes. Analysis of the angular rotation of fold axes enables estimates of the bulk shear strain to be evaluated and models of progressive deformation to be assessed.

Original languageEnglish
Pages (from-to)271-283
Number of pages13
JournalGeological Journal
Volume27
Issue number3
DOIs
Publication statusPublished - Jul 1992

Keywords

  • PROGRESSIVE DEFORMATION
  • FOLD AXIS ROTATION
  • DONEGAL DALRADIAN
  • X-DIRECTION
  • FINNMARK
  • OBLIQUE
  • THRUST

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