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Laxfordian structure, strain distribution and kinematic interpretation of the Kenmore Inlier, Loch Torridon: anatomy of a major Lewisian shear zone

Published online by Cambridge University Press:  03 November 2011

M. Niamatullah  and
R. G. Park
M. Niamatullah
Affiliation:
M. Niamatullah, Department of Geology, University of Baluchistan, Quetta, Pakistan
R. G. Park
Affiliation:
R. G. Park, Department of Geology, University of Keel, Staffordshire ST5 5BG, U.K.
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Abstract

The Kenmore inlier exposes the most intensely deformed part of a major Laxfordian shear zone whose NE margin occurs at Diabaig, N of Loch Torridon. The Laxfordian (post-Scourie dyke) deformation commences with two very intense deformations D1 and D2, producing LS fabrics in dykes and gneisses associated with heterogeneous, locally very large, and typically prolate strains under amphibolite-facies metamorphism. D2 also produced widespread mesoscopic folds. The finite strain was measured at 135 localities using grain-aggregate shapes in Scourie dykes. The combined D1-D2 elongation lineation plunges gently to NW or SE, and the planar fabric appears to have been sub-horizontal before the D3 deformation, which produced NW-SE upright folds under retrogressive metamorphism.

The D1-D2 structure is attributed to a major sub-horizontal shear zone with a top-to-NW movement, a minimum vertical width of 2·5 km and estimated minimum displacement of c. 19 km. The upper (NE) wall of the shear zone at Diabaig exhibits dextral-normal (NE-down) D1 movements. The D2 structures are attributed to superimposition of sub-horizontal movements on earlier inclined D1 fabrics as the shear zone evolves. The D3 refolding reflects a change to a dextral transpressive regime.

Keywords

deformationdextral transpressiveDiabaigelongation lineationfoldsgrainaggregate shapesLS fabricprolate strainScourie dykessuperimposition.
Type
Research Article
Information
Earth and Environmental Science Transactions of The Royal Society of Edinburgh , Volume 81 , Issue 3 , 1990 , pp. 195 - 207
Copyright
Copyright © Royal Society of Edinburgh 1990

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References

Breemen, O. Van, Aftalion, N. & Pidgeon, R. T. 1971. The age of the granitic injection complex of Harris, outer Hebrides. SCOTT J GEOL 7, 130–152.Google Scholar
Bridgwater, D., Escher, A. & Watterson, J. 1973. Tectonic displacements and thermal activity in two contrasting Proterozoic mobile belts from Greenland. PHIL TRANS R SOC LONDON A273, 513–533.Google Scholar
Chapman, H. J. 1979. 2390 Ma Rb-Sr whole-rock age for the Scourie dykes of north-west Scotland. NATURE, LONDON 277, 642–643.CrossRefGoogle Scholar
Coward, M. P. 1976. Strain within ductile shear zones. TECTONOPHYSICS 34, 181–197.CrossRefGoogle Scholar
Coward, M. P. & Park, R. G. 1987. The role of mid-crustal shear zones in the Early Proterozoic evolution of the Lewisian. In Park, R. G. & Tarney, J. (eds) Evolution of the Lewisian and comparable Precambrian high-grade terrains. SPEC PUBL GEOL SOC LONDON 27, 127–138.Google Scholar
Cresswell, D. 1969. The geology of the Lewisian rocks north of Loch Torridon, Ross-shire, Scotland. Unpublished Ph.D. Thesis, University of Keele.Google Scholar
Cresswell, D. 1972. The structural development of the Lewisian rocks on the north shore of Loch Torridon, Ross-shire. SCOTT J GEOL 8, 293–308.CrossRefGoogle Scholar
Evans, C. R. & Tarney, J. 1964. Isotopic ages of Assynt dykes. NATURE LONDON 204, 368–641.CrossRefGoogle Scholar
Flinn, D. 1962. On folding during three-dimensional progressive deformation. Q J GEOL SOC LONDON 118, 385–433.CrossRefGoogle Scholar
Hudleston, P. J. 1973. Fold morphology and some geometric implications of theories of fold development. TEC- TONOPHYSICS 16, 1–46.Google Scholar
Lyon, T. D. B., Pidgeon, R. T., Bowes, D. R. & Hopgood, A. M. 1973. Geochronological investigation of the quartzofeldspathic rocks of the Lewisian of Rona, Inner Hebrides. J GEOL SOC LONDON 129, 389–402.CrossRefGoogle Scholar
Moorbath, S. & Park, R. G. 1971. The Lewisian chronology of the southern region of the Scottish Mainland. SCOTT J GEOL 8, 51–74.CrossRefGoogle Scholar
Park, R. G., Crane, A. & Niamatullah, M. 1987. Early Proterozoic structure and kinematic evolution of the southern mainland Lewisian. In Park, R. G. & Tarney, J. (eds) Evolution of the Lewisian and comparable Precambrian high-grade terrains. SPEC PUBL GEOL SOC LONDON 27, 139–151.Google Scholar
Park, R. G. & Cresswell, D. 1973. The dykes of the Laxfordian belts. In Park, R. G. & Tarney, J. (eds) The early Precambrian of Scotland and related rocks of Greenland, pp. 119–130: University of Keele.Google Scholar
Park, R. G. & Tarney, J. 1987. The Lewisian complex: a typical Precambrian high-grade terrain? In Park, R. G. & Tarney, J. (eds) Evolution of the Lewisian and comparable Precambrian high-grade terrains. SPEC PUBL GEOL SOC LONDON 27, 13–25.Google Scholar
Peach, B. N. J.,Gunn, W., Clough, C. T., Hinxman, L. W. & Teall, J. J. H. 1907. The geological structure of the North West Highlands of Scotland. MEM GEOL SURV GB.Google Scholar
Ramsay, J. G. 1962. The geometry and mechanism of formation off ‘similar’ type folding. J GEOL 70, 309–327.CrossRefGoogle Scholar
Ramsay, J. G. 1967. Folding and fracturing of rocks. New York: McGraw-Hill.Google Scholar
Ramsay, J. G. & Wood, D. S. 1973. The geometric effects of volume change during deformational processes. TEC-TONOPHYSICS 16, 263–277.Google Scholar
Sutton, J. & Watson, J. 1951. The pre-Torridonian metamorphic history of the Loch Torridon and Scourie areas in the Northwest Highlands, and its bearing on the chronological classification of the Lewisian. Q J GEOL SOC LONDON 106,Google Scholar
Watterson, J. 1968. Homogeneous deformation of the gneisses of Vesterland, southwest Greenland. Meddelelser om Grønland, Copenhagen 175 (6).Google Scholar
Wheeler, J., Windley, B. F. & Davies, F. B. 1987. Internal evolution of the major Precambrian shear belt at Torridon, NW Scotland. In Park, R. G. & Tarney, J. (eds) Evolution of the Lewisian and comparable Precambrian high-grade terrains, GEOL SOC LONDON, SPEC PUBL 27, 153–163.Google Scholar