JOHN R. KLEIST Department of Geological Sciences, University of , Austin, Texas 78712

Kink Bands along the Fault,

ABSTRACT more recently Donath (1972) has developed kink bands in slate at angles up to 45°. The The possible application of kink bands in most favorable angles for kink-band develop- dynamic structural analysis is shown by a ment seem to lie between zero and 15 degrees. recent study along a short segment of the These favorable angles allow kink-band incep- Denali fault, Alaska. In laboratory experi- tion parallel to a shear zone. Growth usually ments, kink-band planes form at measured involves flexural slip in which gliding occurs on angles of 45° to 60° with the maximum princi- the foliation. pal stress (

Geological Society of America Bulletin, v. 83, p. 3487-3490, 3 figs., November 1972 3487

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EXPLANATION

| | Alluvial-glacial deposits, t——I Granodiorite, tlL-ii Rainbow Mtn. Sequence, Quaternary Cretaceous Permian !•* >l Quartz diorite, II11 H Graywacke, tuff, phyllite. Cretaceous? Early Paleozoic RJi^ Porphyritic andesite, ^1 Birch Creek Schist, Trias-'-' Precambrian ?

where approx.

Figure 1. General geologic map of the Canwell Glacier area with inset location map. presence of shear failure subparallel to the Of the seven rock units that comprise the boundaries, or the presence of secondary slip bedrock of the study area (Fig. 1), the Birch surfaces within the kink band, are evidence for Creek Schist (Precambrian?) covers the most brittle behavior. area, directly borders the fault, and contains a The observations discussed earlier suggest variety of structural features such as intrafolial that kink bands can be expected to form at an folds, slip cleavage, fracture cleavage, crinkles, angle of 45° to 60° with cri, and that the obtuse joints, en echelon extension gash fractures, and angles of conjugate sets face the direction of kink bands. For these reasons this paper treats maximum shortening (<7i, or within a small primarily the structural features in the Birch angle of it). Despite these experimental and Creek Schist. naturally occurring variations, the approximate direction of

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N

Figure 3. Contoured equal-area hemispheric dia- Figure 2. Contoured equal-area, lower hemispheric gram of 61 poles to kink planes in the Birch Creek diagram of poles to kink planes in the Birch Creek Schist, with superimposed strikes of kink-band families Schist. Sixty-one measurements are represented; con- represented (hatchline). The arrows outside the circle tours are at 1, 2, 3,4, 5, and 6 points per 1 percent area. represent the probable direction of &i responsible for the kink bands. The indicated direction of

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quently, the cri subparallel to the fault as in- Borg, I., and Handin, J., 1966, Experimental defor- ferred from the kink-band orientations may mation of crystalline rocks: Tectonophysics, reflect the local reorientation of a regional a\ v. 3, no. 4, p. 249-368. that was oriented at a substantial angle to the Donath, F. A., 1964, Kink banding as a mechanism of faulting in anisotropic rock [abs.]: Am. fault. However, offset geomorphic features and Geophys. Union Trans., v. 45, p. 103-104. first-motion studies indicate that the Denali 1968, The development of kink bands in fault is currently acting as a right-lateral strike- brittle anisotropic rock, in Larsen, L. H., ed., slip fault. This suggests a regional cri that is Igneous and metamorphic geology: Geol. Soc. probably oriented other than normal to the America Mem. 115, p. 453-493. fault. The local cri inferred from the kink bands —— 1972, Effects of cohesion and granularity on may be a reflection of the later regional <7i deformational behavior of anisotropic rock, orientation compatible with this recent strike- in Doe, B. R., and Smith, D. K., eds., Studies slip movement. in mineralogy and Precambrian geology: Geol. Soc. America Mem. 135 (in press). Because they are planar and unaffected by Handin, J., 1969, On the Coulomb-Mohr failure the other structural features, the kink bands criterion: Jour. Geophys. Research, v. 74, p. are considered to be the youngest structural 5343-5348. element present in the Birch Creek Schist Kleist, J. R., 1971, The Denali fault in the Canwell along the Canwell Glacier. Although the age of Glacier area, east-central Alaska Range [M.S. the kink bands is unknown, they may indicate thesis]: Madison, Wisconsin Univ.,'Ill p. a change in the stress pattern and the nature of Paterson, M. S., and Weiss, L. E., 1964, Experi- movement along the Denali fault. mental folding in phyllite [abs.]: Am. Geophys. Union Trans., v. 45, p. 104. ACKNOWLEDGMENTS 1966, Experimental deformation 'and folding in phyllite: Geol. Soc. America Bull., v. 77, The above discussion is drawn from a gradu- p. 343-374. ate thesis prepared by this writer at the Uni- Ramsay, J. G., 1967, Folding and fracturing of versity of Wisconsin under the direction of rocks: New York, McGraw-Hill Book Co., Campbell Craddock, whom I wish to thank for p. 436-456. his help in this work. Rondeel, H. E., 1969, On the formation of kink bands: Koninkl. Nederlandse Akad. Wetensch. Proc., Ser. B, v. 72, no. 5, p. 317-329. REFERENCES CITED Anderson, T. B., 1964, Kink-bands and related MANUSCRIPT RECEIVED BY THE SOCIETY JANUARY geological structures: Nature, v. 202, p. 272- 26, 1972 274. REVISED MANUSCRIPT RECEIVED MAY 25, 1972

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