Flow perturbation folding in shear zones

G. I. Alsop and R. E. Holdsworth
Geological Society, London, Special Publications, 272, 75-101, 1 January 2007, https://doi.org/10.1144/GSL.SP.2007.272.01.06

Abstract

Variable patterns of displacement in shear zones may result in arcuate fold and fault traces as recognized by Mike Coward and co-workers in the early 1980s. Within such deformation zones, localized perturbations in flow may undergo acceleration (surging flow) or deceleration (slackening flow) with respect to the adjacent regions. Such flow cells may govern the orientation and geometries of folds and fabrics and thereby provide evidence of the scale and nature of deformation associated with heterogeneous flow in the high-strain zones. The length/width ratio of individual flow cells (measured in the direction of flow) may vary from <1 to >1 for situations when flow cells are, respectively, dominated by layer-parallel shear (LPS) or layer-normal shear (LNS). Folds initiating at high angles to transport are associated with LPS, whereas LNS may generate folds with slight clockwise (sinistral LNS) or anticlockwise (dextral LNS) trends relative to flow. Continued progressive deformation may subsequently modify and reduce angular relationships between folds and fabrics, but these geometric obliquities are generally preserved. Using examples from the Moine metasediments of northern Scotland, we show that folding displays predictable geometric patterns that can be related to the development of flow perturbation cells associated with Caledonian ductile thrusting under mid-crustal conditions. The differing relative timing of folds and individual ductile thrusts reflects the complexity of flow cells within ductile imbricates and additionally highlights the progressive foreland-directed propagation of ductile thrusting. These geometric relationships developed during contractional shear are compared with those generated in extensional systems, to provide an overall framework for the study of perturbation patterns. The geometric arrangement of mean fold axial planes about the flow direction results in their intersection forming parallel to the transport direction. This relationship permits transport directions to be calculated via the axial-planar intersection method (AIM), and also allows comparison with other techniques devised primarily for the study of soft-sediment deformation and palaeoslope analysis.

References

  1. Allen, M. B., , Alsop, G. I. , & Zhemchuzhnikov, V. G. , 2001. Dome and basin refolding associated with transpressive inversion along the Karatau Fault System, southern Kazakstan. Journal of the Geological Society, London, 158, 83–95.
    OpenUrlAbstract/FREE Full Text
  2. Alsop, G. I. , 1992. Progressive deformation and the rotation of contemporary fold axes in the Ballybofey Nappe, northwest Ireland. Geological Journal, 27, 271–283.
    OpenUrlWeb of Science
  3. Alsop, G. I. , 1994. Relationships between distributed and localised shear in the tectonic evolution of a Caledonian fold and thrust zone, northwest Ireland. Geological Magazine, 131, 123–136.
    OpenUrlAbstract
  4. Alsop, G. I. , & Holdsworth, R. E. , 1993. The distribution, geometry and kinematic significance of Caledonian buckle folds in the western Moine Nappe, northwestern Scotland. Geological Magazine, 130, 353–362.
    OpenUrlAbstract
  5. Alsop, G. I. , & Holdsworth, R. E. , 1999. Vergence and facing patterns in large-scale sheath folds. Journal of Structural Geology, 21, 1335–1349.
    OpenUrlCrossRefWeb of Science
  6. Alsop, G. I. , & Holdsworth, R. E. , 2002. The geometry and kinematics of flow perturbation folds. Tectonophysics, 350, 99–125.
    OpenUrlCrossRefWeb of Science
  7. Alsop, G. I. , & Holdsworth, R. E. , 2004a. Shear zones — an introduction and overview. In: Alsop, G. I., , Holdsworth, R. E., , McCaffrey, K. J. W. , & Hand, M. , (eds) Flow Processes in Faults and Shear Zones. Geological Society, London, Special Publications, 224, 1–9.
    OpenUrlAbstract/FREE Full Text
  8. Alsop, G. I. , & Holdsworth, R. E. , 2004b. Shear zone folds: records of flow perturbation or structural inheritance? In: Alsop, G. I., , Holdsworth, R. E., , McCaffrey, K. J. W. , & Hand, M. , (eds) Flow Processes in Faults and Shear Zones. Geological Society, London, Special Publications, 224, 177–199.
    OpenUrlAbstract/FREE Full Text
  9. Alsop, G. I. , & Holdsworth, R. E. , 2004c. The geometry and topology of natural sheath folds: a new tool for structural analysis. Journal of Structural Geology, 26, 1561–1589.
    OpenUrlCrossRefWeb of Science
  10. Alsop, G. I. , & Holdsworth, R. E. , 2005. Discussion on evidence for non-plane strain flattening along the Moine Thrust, Loch Strath nan Aisinnin, North-West Scotland by Strine & Wojtal. Journal of Structural Geology, 27, 781–784.
    OpenUrlCrossRefWeb of Science
  11. Alsop, G. I. , & Holdsworth, R. E. , 2006. Sheath folds as discriminators of bulk strain type. Journal of Structural Geology, 28, 1588–1606.
    OpenUrlCrossRefWeb of Science
  12. Alsop, G. I., , Holdsworth, R. E. , & Strachan, R. A. , 1996. Transport-parallel cross folds within a mid-crustal Caledonian thrust stack, northern Scotland. Journal of Structural Geology, 18, 783–790.
    OpenUrlCrossRefWeb of Science
  13. Bell, T. H. , 1978. Progressive deformation and reorientation of fold axes in a ductile mylonite zone: the Woodroffe thrust. Tectonophysics, 44, 285–321.
    OpenUrlCrossRefWeb of Science
  14. Berthé, D. , & Brun, J. P. , 1980. Evolution of folds during progressive shear in the South Amorican Shear Zone, France. Journal of Structural Geology, 2, 127–133.
    OpenUrlCrossRefWeb of Science
  15. British Geological Survey 1997. Tongue, Scotland 114E. Solid Geology, 1:50 000.
  16. British Geological Survey 2002. Loch Eriboll, Scotland 114W. Solid Geology, 1:50 000.
  17. Bryant, B. , & Reed, J. C. , 1969. Significance of lineation and minor folds near major thrust faults in the southern Appalachians and the British and Norwegian Caledonides. Geological Magazine, 106, 412–429.
    OpenUrlAbstract
  18. Carreras, J., , Estrada, A. , & White, S. , 1977. The effect of folding on the c-axis fabrics of a quartz mylonite. Tectonophysics, 39, 3–24.
    OpenUrlCrossRefWeb of Science
  19. Cobbold, P. R. , & Quinquis, H. , 1980. Development of sheath folds in shear regimes. Journal of Structural Geology, 2, 119–126.
    OpenUrlCrossRefWeb of Science
  20. Coward, M. P. , 1982. Surge zones in the Moine thrust zone of NW Scotland. Journal of Structural Geology, 4, 247–256.
    OpenUrlCrossRefWeb of Science
  21. Coward, M. P. , 1983. The thrust and shear zones of the Moine thrust zone and the NW Scottish Caledonides. Journal of the Geological Society, London, 140, 795–811.
    OpenUrlAbstract/FREE Full Text
  22. Coward, M. P. , 1984. The strain and textural history of thin-skinned tectonic zones: examples from the Assynt region of the Moine Thrust zone, NW Scotland. Journal of Structural Geology, 6, 89–99.
    OpenUrlCrossRefWeb of Science
  23. Coward, M. P. , & Kim, J. H. , 1981. Strain within thrust sheets. In: McClay, K. R. , & Price, N. J. , (eds) Thrust and Nappe Tectonics. Geological Society, London, Special Publications, 9, 275–292.
    OpenUrlAbstract/FREE Full Text
  24. Coward, M. P. , & Potts, G. J. , 1983. Complex strain patterns developed at the frontal and lateral tips to shear zones and thrust zones. Journal of Structural Geology, 5, 383–399.
    OpenUrlCrossRefWeb of Science
  25. Downing, K. N. , & Coward, M. P. , 1981. The Okahandja Lineament and its significance for Damaran tectonics in Namibia. Geologische Rundshau, 70, 972–1000.
    OpenUrlCrossRef
  26. Dubey, A. K. , & Cobbold, P. R. , 1977. Noncylindrical flexural slip folds in nature and experiment. Tectonophysics, 38, 223–239.
    OpenUrlCrossRefWeb of Science
  27. Elliot, D. , 1976. The energy balance and deformation mechanisms of thrust sheets. Philosophical Transactions of the Royal Society of London, 283, 289–312.
    OpenUrlCrossRef
  28. Escher, A. , & Watterson, J. , 1974. Stretching fabrics, folds and crustal shortening. Tectonophysics, 22, 223–231.
    OpenUrlCrossRefWeb of Science
  29. Evans, D. J. , & White, S. H. , 1984. Microstructural and fabric studies from the rocks of the Moine Nappe, Eriboll, NW Scotland. Journal of Structural Geology, 6, 369–389.
    OpenUrlCrossRefWeb of Science
  30. Farrell, S. G. , 1984. A dislocation model applied to slump structures, Ainsa Basin, South Central Pyrenees. Journal of Structural Geology, 6, 727–736.
    OpenUrlCrossRefWeb of Science
  31. Fink, J. , 1980. Surface folding and viscosity of rhyolite flows. Geology, 8, 250–254.
    OpenUrlAbstract/FREE Full Text
  32. Fossen, H. , & Rykkelid, E. , 1990. Shear zone structures in the Øygarden area, West Norway. Tectonophysics, 174, 385–397.
    OpenUrlCrossRefWeb of Science
  33. Ghosh, S. K. , & Ramberg, H. , 1968. Buckling experiments on intersecting fold patterns. Tectonophysics, 5, 89–105.
    OpenUrlCrossRefWeb of Science
  34. Ghosh, S. K. , & Sengupta, S. , 1984. Successive development of plane noncylindrical folds in progressive deformation. Journal of Structural Geology, 6, 703–709.
    OpenUrlCrossRefWeb of Science
  35. Ghosh, S. K. , & Sengupta, S. , 1987. Progressive development of structures in a ductile shear zone. Journal of Structural Geology, 9, 277–287.
    OpenUrlCrossRefWeb of Science
  36. Goscombe, B. , 1991. Intense non-coaxial shear and the development of mega-scale sheath folds in the Arunta Block, Central Australia. Journal of Structural Geology, 13, 299–318.
    OpenUrlCrossRefWeb of Science
  37. Hambrey, M. J. , & Lawson, W. , 2000. Structural styles and deformation fields in glaciers: a review. In: Maltman, A. J., , Hubbard, B. , & Hambrey, M. J. , (eds) Deformation of Glacial Materials. Geological Society, London, Special Publications, 176, 59–83.
    OpenUrlAbstract/FREE Full Text
  38. Hansen, E. , 1965. Methods of deducing slip-line orientations from the geometry of folds. Carnegie Institution of Washington Yearbook, 65, 387–405.
    OpenUrl
  39. Hansen, E. , 1967. Natural slip folds in which the fold axes nearly parallel the slip lines. Carnegie Institution of Washington Yearbook, 66, 536–538.
    OpenUrl
  40. Hansen, E. , 1971. Strain Facies. Springer, New York.
  41. Holdsworth, R. E. , 1988. The stereographic analysis of facing. Journal of Structural Geology, 10, 219–223.
    OpenUrlCrossRefWeb of Science
  42. Holdsworth, R. E. , 1989. The geology and structural evolution of a Caledonian fold and ductile thrust zone, Kyle of Tongue region, Sutherland, N. Scotland. Journal of the Geological Society, London, 146, 809–823.
    OpenUrlAbstract/FREE Full Text
  43. Holdsworth, R. E. , 1990. Progressive deformation structures associated with ductile thrusts in the Moine Nappe, Sutherland, N. Scotland. Journal of Structural Geology, 12, 443–452.
    OpenUrlCrossRefWeb of Science
  44. Holdsworth, R. E. , & Grant, C. J. , 1990. Convergence-related ‘dynamic spreading’ in a mid-crustal ductile thrust zone: a possible orogenic wedge model. In: Knipe, R. J. , & Rutter, E. H. , (eds) Deformation Mechanisms, Rheology and Tectonics. Geological Society, London, Special Publications, 54, 491–500.
    OpenUrlAbstract/FREE Full Text
  45. Holdsworth, R. E. , & Roberts, A. M. , 1984. A study of early curvilinear fold structures and strain in the Moine of the Glen Garry region, Inverness-shire. Journal of the Geological Society, London, 141, 327–338.
    OpenUrlAbstract/FREE Full Text
  46. Holdsworth, R. E., , Strachan, R. A. , & Alsop, G. I. , 2001. Geology of the Tongue District. Memoirs of the British Geological Survey, Sheet 114E (Scotland).
  47. Holdsworth, R. E., , Alsop, G. I. , & Strachan, R. A. , 2007. Tectonic stratigraphy and structural continuity of the northernmost Moine Thrust Zone and Moine Nappe, Scottish Caledonides. In: Ries, A. C., , Butler, R. W. H. , & Graham, R. H. , (eds) Deformation of the Continental Crust: The Legacy of Mike Coward. Geological Society, London, Special Publications, 272, 121–142.
    OpenUrlAbstract/FREE Full Text
  48. Jones, O. T. , 1940. The geology of the Colwyn Bay district: study of submarine slumping during the Salopian Period. Quarterly Journal of the Geological Society of London, 95, 335–382.
    OpenUrl
  49. Lacassin, R. , & Mattauer, M. , 1985. Kilometre-scale sheath fold at Mattmark and implications for transport directions in the Alps. Nature, 315, 739–742.
    OpenUrlCrossRef
  50. Lajoie, J. , 1972. Slump fold axis orientations: an indication of paleoslope? Journal of Sedimentary Petrology, 42, 584–586.
    OpenUrlAbstract/FREE Full Text
  51. Lawson, W. J., , Sharp, M. J. , & Hambray, M. J. , 1994. The structural geology of a surge-type glacier. Journal of Structural Geology, 16, 1447–1462.
    OpenUrlCrossRefWeb of Science
  52. McClay, K. R. , 1987. The Mapping of Geological Structures. Geological Society, London, Handbook.
  53. Mies, J. W. , 1991. Planar dispersion of folds in ductile shear zones and kinematic interpretation of fold hinge girdles. Journal of Structural Geology, 13, 281–297.
    OpenUrlCrossRefWeb of Science
  54. Minnigh, L. D. , 1979. Structural analysis of sheath-folds in a meta-chert from the Western Italian Alps. Journal of Structural Geology, 1, 275–282.
    OpenUrlCrossRefWeb of Science
  55. Platt, J. P. , 1983. Progressive refolding in ductile shear zones. Journal of Structural Geology, 5, 619–622.
    OpenUrlCrossRefWeb of Science
  56. Quinquis, H., , Audren, C., , Brun, J. P. , & Cobbold, P. R. , 1978. Intense progressive shear in Ile de Groix blueschists and compatibility with subduction or obduction. Nature, 273, 43–45.
    OpenUrlCrossRefWeb of Science
  57. Ramsay, J. G. , 1980. Shear zone geometry: a review. Journal of Structural Geology, 2, 83–99.
    OpenUrlCrossRefWeb of Science
  58. Ramsay, J. G. , & Lisle, R. , 2000. The Techniques of Modern Structural Geology. Volume 3: Applications of continuum Mechanics in Structural Geology. Academic Press, London.
  59. Rhodes, S. , & Gayer, R. A. , 1977. Non-cylindrical folds, linear structures in the X-direction and mylonite developed during translation of the Caledonian Kalak Nappe Complex of Finnmark. Geological Magazine, 114, 329–341.
    OpenUrlAbstract
  60. Ridley, J. , 1986. Parallel stretching lineations and fold axes oblique to displacement direction — a model and observations. Journal of Structural Geology, 8, 647–654.
    OpenUrlCrossRefWeb of Science
  61. Roberts, A. , 1989. Fold and thrust structures in the Kintradwell ‘Boulder beds’, Moray Firth. Scottish Journal of Geology, 25, 173–186.
    OpenUrlAbstract/FREE Full Text
  62. Sanderson, D. J. , 1973. The development of fold axes oblique to the regional trend. Tectonophysics, 16, 55–70.
    OpenUrlCrossRefWeb of Science
  63. Shackleton, R. M. , 1958. Downward-facing structures of the Highland Border. Quarterly Journal of the Geological Society of London, 113, 361–392.
    OpenUrl
  64. Skjernaa, L. , 1980. Rotation and deformation of randomly oriented planar and linear structures in progressive simple shear. Journal of Structural Geology, 2, 101–109.
    OpenUrlCrossRefWeb of Science
  65. Skjernaa, L. , 1989. Tubular folds and sheath folds: definitions and conceptual models for their development with examples from the Grapesvare area, northern Sweden. Journal of Structural Geology, 11, 689–703.
    OpenUrlCrossRefWeb of Science
  66. Strachan, L. J. , 2002. Slump-initiated and controlled syndepositional sandstone remobilization: an example from the Namurian of County Clare, Ireland. Sedimentology, 49, 25–41.
    OpenUrlCrossRefWeb of Science
  67. Strachan, R. A., , Smith, M., , Harris, A. L. , & Fettes, D. J. , 2002. The Northern Highland and Grampian Terranes. In: Trewin, N. , (ed.) Geology of Scotland. Geological Society, London, 81–147.
  68. Strachan, L. J. , & Alsop, G. I. , 2006. Slump folds as estimators of palaeoslope: a case study from the Fisherstreet slump of County Clare, Ireland. Basin Research, 18, 451–470.
    OpenUrlCrossRefWeb of Science
  69. Talbot, C. J. , 1979. Fold trains in a glacier of salt in southern Iran. Journal of Structural Geology, 1, 5–18.
    OpenUrlCrossRefWeb of Science
  70. Talbot, C. J. , & Aftabi, P. , 2004. Geology and models of salt extrusion at Qum Kuh, central Iran. Journal of the Geological Society, London, 161, 321–334.
    OpenUrlAbstract/FREE Full Text
  71. Talbot, C. J. , & Jarvis, R. J. , 1984. Age, budget and dynamics of an active salt extrusion in Iran. Journal of Structural Geology, 6, 521–533.
    OpenUrlCrossRefWeb of Science
  72. Watkinson, A. J. , & Cobbold, P. R. , 1981. Axial directions of folds in rocks with linear/planar fabrics. Journal of Structural Geology, 3, 211–217.
    OpenUrlCrossRefWeb of Science
  73. Williams, G. D. , 1978. Rotation of contemporary folds into the X direction during overthrust processes in Laksefjord, Finnmark. Tectonophysics, 48, 29–40.
    OpenUrlCrossRefWeb of Science
  74. Woodcock, N. H. , 1979. The use of slump structures as palaeoslope orientation estimators. Sedimentology, 26, 83–99.
    OpenUrlCrossRefWeb of Science
Back to top
Alerts
Citation tools
Permissions
View PDF
Email to

Related Articles

Similar Articles

Cited By...