EXPERIMENTAL DEFORMATION AND FOLDING IN PHYLLITE AND PALEOSTRESS ANALYSIS FROM TRIANGULAR PLOT. Speaker : Yu-Sheng Liang

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1 1 EXPERIMENTAL DEFORMATION AND FOLDING IN PHYLLITE AND PALEOSTRESS ANALYSIS FROM TRIANGULAR PLOT Speaker : Yu-Sheng Liang

2 References 2 Paterson, M.S. and Weiss, L.E. (1966) Experimental deformation and folding in phyllite. Geological Society of America Bulletin 77, Srivastava, D.C.,Lisle, R.J.,Imran, M. and Kandpal, R. (1998) The kink-band triangle: a triangular plot for paleostress analysis from kink-bands. Journal of Structural Geology 20,

3 Outline 3 Introduction Experimental method and results Stress-strain results Intersections of kink Triangular plot Conclusions

4 Introduction 4 Two main approaches to the study of folding: first, geologic field study; and, second, theoretical and experimental studies of models. In previous study, they was demonstrated with a suitably scaled model material, such as clay, pitch, rubber, and so on. Use the approach of investigating the folds that can be produced experimentally in specimens of the strongly foliated rocks such as phyllite.

5 Definition of kink band 5 These consist ideally of parallel-sided domains with sharp boundaries at which the foliation is bent through a large angle.

6 20mm 10mm Experimental method 6 Most experiments have been run at 5 kb confining -4 pressure. The strain rate was about 4.8 X 10 per second. 7mm 10mm 30~80% shortening 0~30% shortening

7 Experimental method 7 (1) Anisotropic material strongly foliated rocks such as slates, phyllites, and mica schists. (2) Constrained deformation a. End friction: friction between the end piece and the end of the specimen gives rise to a resistance on the end of the specimen when it tends to move nonaxially. b. Jacket constraint: the specimens were enclosed in thick metal jackets to ensure that deformation, such as folding, would be distributed through the specimen on a small scale.

8 8 No effect of end friction and jacket constraint Effect of jacket constraint Deform axially under axial load and be distributed through the specimen on a small scale. Effective constraint from end friction Effect of end friction and jacket constraint

or microscopic study in transmitted light.

9 Experimental results 9 Influence of different angle α and jackets in experiments with examination in reflected light or microscopic study in transmitted light. For examination in reflected light For microscopic study in transmitted light.

10 α=0, in Reflected light 10 Specimens compressed parallel to foliation in different jackets. 12% Shortening 13% In rubber jacket In copper jacket

11 α=0, large strain in transmitted light A typical sequence of

from dark to light is seen to be accompanied by changes the

11 11 α=0, large strain in transmitted light A typical sequence of deformation in specimens shortened parallel to foliation in brass jackets. 0% 5% 13% Through a microscope in transmitted light the change from dark to light is seen to be accompanied by changes the deformed zone (kink) of the foliation from the undeformed domains and change from transparent to frosted in the quartz. 20% 30% 47%

12 α= % 19% 28%

13 α=45, Mica-rich layer 17.5% 28% α=45 α=90 Enlargement of D In rubber jacket In brass jacket In brass jacket

14 Stress-strain results 14 Influence of angle α to Stressstrain curves Effect of confining pressure to stressstrain curves in brass jackets

15 measurement Angles Φ and Φk of kinks 15 k k Φ Φk Φ Φk 60 In the mica-richer specimens Specimens richer in quartz layers degree

16 16 I undeformed domain II.III initial kink IV intersections of kink Their axial planes are subperpendicular to the axis of compression.

17 Ideal model of kink intersections 17 With increasing deformation, the kink boundaries become widening % Shortening 30-45% 45-50% 50%

18 Triangular plot for paleostress analysis 18 Srivastava et al.(1998) used triangular plots for paleostress analysis from kink band k 30

19 19, k, k Gay and Weiss (1974) The most realistic α value of the datas near the paleostress line are projection parallel to the ψ- lines in the graph. Plot 6 α 11.5 Plot 8 α 3.5 Plot 13 α 3

20 Conclusions 20 When the foliation of specimens parallel to the axis of compression (α=0 ) in metal jackets will intersect to the network. 1. α=10, the intersections of kink are rare. 2. α=45, the sliding along the foliation replace the kinking. 3. α=90, failure is largely by rupture. The width of kink increase with the shortening, but the angle Φ and Φk don t change with the shortening. The degree of the angle is relative to the composition of the rock mineral.

21 21 The intersections of kink form the chevron fold that axial plane normal to the axis of compression. Using of the kink-band triangle is suitable for the determination of maximum compressive stress orientation from kink-band structures. In practice. it is better to measure a large number of kink-bands.

22 22 Thank you for your attention!!

23 α=0, large strain in Reflected light 23 Short specimens compressed parallel to foliation in copper jackets 14% 30% Shortening 45% 70% Enlargement of D

24 Stress-strain results 24 The stress-strain curves for phyllite compressed parallel to the foliation in various constraining jackets at 5 kb confining pressure. a. Brass (15) b. Copper (11) in rubber jackets

25 Kink intersections 25 Classifying the intersection of kink according to the width and the form of kink boundaries

26 26 Stress-strain curves for tests in compression at various angles to the foliation at 5 kb confining pressure : a, in rubber jackets b, in thick brass jackets

27 Stress-strain results 27 Stress-strain curves of metals used for constraining jackets The stress-strain curves for phyllite compressed parallel to the foliation in various constraining jackets at 5 kb confining pressure. a. Brass (15) b. Copper (11) c. Ni-Cr-Mo steel (2) d. High-C steel (1)

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31 31 The initially circular cross section becomes elliptical with the minor diameter always lying in the plane of the foliation. in the central part of a specimen with 20 per cent over-all shortening there is only about 1 per cent increase in the minor diameter, whereas the major diameter shows an increase of about 30 per cent

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Strength variation and deformational behavior in anisotropic granitic mylonites under high-temperature and -pressure conditions An experimental study

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