Décollement folding as a mechanism for thrust-ramp spacing

Douglas F. Goff, David V. Wiltschko, Raymond Charles Fletcher

Research output: Contribution to journalArticle

21 Citations (Scopus)

Abstract

The hypothesis that early formed décollement folds localize thrust ramps, explaining the regular spacing of major thrust ramps observed in many mountain belts, is examined. The model for folding instability consists of a rigid basement, a weak décollement zone, and a stiff thrust sheet. The model incorporates the effects of topographic stresses, and syntectonic erosion and redeposition and uses a linearized power law rheology for the thrust sheet. This approximation is valid for small angles of fold limb dip (<15°) and is appropriate for analysis of the wavelength selection of folds at the onset of deformation. The spacing of major thrust ramps and the stratigraphic thicknesses of the décollement zone and thrust sheet from the Wyoming portion of the Sevier fold-and-thrust belt are used to test the model. The ratio of the fold dominant wavelength to thrust sheet thickness, Ld/h2, increases with the ratio, R, of the viscosity of the stiff layer to that of the décollement zone and decreases with the power law stress exponent, n2. The fold amplification factor increases with both n2 and R. As the topographic decay ratio, script D sign, increases, Ld/h2 increases at fixed n2 and R. Acceptable models for the Absaroka and Darby thrust sheets have n2 ≥ 3. Only when R<1000 and significant erosion and redeposition of sediments accompany the folding of the thrust sheet (script D sign ≥ 103) does the required R fall below a reasonable limit. Thus a model in which décollement folding is accompanied by syntectonic erosion and redeposition precedes thrusting is consistent with the available observational constraints.

Original languageEnglish (US)
Pages (from-to)11341-11352
Number of pages12
JournalJournal of Geophysical Research B: Solid Earth
Volume101
Issue number5
StatePublished - May 10 1996

Fingerprint

ramps
thrust
folding
spacing
spatial distribution
Erosion
redeposition
fold
wavelengths
erosion
Wavelength
rheology
Rheology
power law
Amplification
Sediments
viscosity
wavelength
deterioration
mountains

All Science Journal Classification (ASJC) codes

  • Geophysics
  • Geochemistry and Petrology
  • Earth and Planetary Sciences (miscellaneous)
  • Space and Planetary Science

Cite this

Goff, D. F., Wiltschko, D. V., & Fletcher, R. C. (1996). Décollement folding as a mechanism for thrust-ramp spacing. Journal of Geophysical Research B: Solid Earth, 101(5), 11341-11352.
Goff, Douglas F. ; Wiltschko, David V. ; Fletcher, Raymond Charles. / Décollement folding as a mechanism for thrust-ramp spacing. In: Journal of Geophysical Research B: Solid Earth. 1996 ; Vol. 101, No. 5. pp. 11341-11352.
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Goff, DF, Wiltschko, DV & Fletcher, RC 1996, 'Décollement folding as a mechanism for thrust-ramp spacing', Journal of Geophysical Research B: Solid Earth, vol. 101, no. 5, pp. 11341-11352.

Décollement folding as a mechanism for thrust-ramp spacing. / Goff, Douglas F.; Wiltschko, David V.; Fletcher, Raymond Charles.

In: Journal of Geophysical Research B: Solid Earth, Vol. 101, No. 5, 10.05.1996, p. 11341-11352.

Research output: Contribution to journalArticle

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N2 - The hypothesis that early formed décollement folds localize thrust ramps, explaining the regular spacing of major thrust ramps observed in many mountain belts, is examined. The model for folding instability consists of a rigid basement, a weak décollement zone, and a stiff thrust sheet. The model incorporates the effects of topographic stresses, and syntectonic erosion and redeposition and uses a linearized power law rheology for the thrust sheet. This approximation is valid for small angles of fold limb dip (<15°) and is appropriate for analysis of the wavelength selection of folds at the onset of deformation. The spacing of major thrust ramps and the stratigraphic thicknesses of the décollement zone and thrust sheet from the Wyoming portion of the Sevier fold-and-thrust belt are used to test the model. The ratio of the fold dominant wavelength to thrust sheet thickness, Ld/h2, increases with the ratio, R, of the viscosity of the stiff layer to that of the décollement zone and decreases with the power law stress exponent, n2. The fold amplification factor increases with both n2 and R. As the topographic decay ratio, script D sign, increases, Ld/h2 increases at fixed n2 and R. Acceptable models for the Absaroka and Darby thrust sheets have n2 ≥ 3. Only when R<1000 and significant erosion and redeposition of sediments accompany the folding of the thrust sheet (script D sign ≥ 103) does the required R fall below a reasonable limit. Thus a model in which décollement folding is accompanied by syntectonic erosion and redeposition precedes thrusting is consistent with the available observational constraints.

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Goff DF, Wiltschko DV, Fletcher RC. Décollement folding as a mechanism for thrust-ramp spacing. Journal of Geophysical Research B: Solid Earth. 1996 May 10;101(5):11341-11352.