1EXPERIMENTAL DEFORMATIONAND FOLDING IN PHYLLITEAND PALEOSTRESS ANALYSISFROM TRIANGULAR PLOTSpeaker : Yu-Sheng Liang
Outline3 Introduction Experimental method and results Stress-strain results Intersections of kink Triangular plot Conclusions
Introduction4 Two main approaches to the study of folding: first,geologic field study; and, second, theoretical andexperimental studies of models. In previous study, they was demonstrated with asuitably scaled model material, such as clay, pitch,rubber, and so on. Use the approach of investigating the folds that canbe produced experimentally in specimens of thestrongly foliated rocks such as phyllite.
Definition of kink band5 These consist ideally of parallel-sided domains withsharp boundaries at which the foliation is bentthrough a large angle.
20mm10mmExperimental method6 Most experiments have been run at 5 kb confining-4pressure. The strain rate was about 4.8 X 10 persecond.7mm10mm30~80% shortening0~30% shortening
Experimental method7(1) Anisotropic material— strongly foliated rockssuch as slates, phyllites, and mica schists.(2) Constrained deformation—a. End friction: friction between the end pieceand the end of the specimen gives rise to aresistance on the end of the specimen when ittends to move nonaxially.b. Jacket constraint: the specimens wereenclosed in thick metal jackets to ensure thatdeformation, such as folding, would bedistributed through the specimen on a smallscale.
8No effect of end frictionand jacket constraintEffect of jacket constraintDeform axially underaxial load and bedistributed throughthe specimen on asmall scale.Effective constraintfrom end frictionEffect of end friction andjacket constraint
Experimental results9 Influence of different angle α and jackets inexperiments with examination in reflected light ormicroscopic study in transmitted light.For examination in reflected lightFor microscopic study in transmitted light.
α=0˚, in Reflected light10Specimens compressed parallel to foliation in different jackets.12% Shortening 13%In rubber jacketIn copper jacket
11α=0˚, large strain in transmitted lightA typical sequence of deformation inspecimens shortened parallel tofoliation in brass jackets.0%5%13%Through a microscope in transmittedlight the change from dark to light isseen to be accompanied by changesthe deformed zone (kink) of thefoliation from the undeformed domainsand change from transparent to frostedin the quartz.20%30%47%
α=10˚1213% 19% 28%
α=45˚, 90˚13Mica-rich layer17.5% 28%α=45˚α=90˚Enlargement of DIn rubber jacketIn brass jacketIn brass jacket
Stress-strain results14Influence of angle α to StressstraincurvesEffect of confining pressure to stressstraincurvesin brass jackets
measurementAngles Φ and Φk of kinks15 k kΦΦkΦΦk60In the mica-richerspecimensSpecimens richer inquartz layersdegree
16I undeformed domainII.III initial kinkIV intersections of kinkTheir axial planes are subperpendicular to theaxis of compression.
Ideal model of kink intersections17With increasing deformation, the kink boundaries becomewidening.10-30% Shortening 30-45% 45-50%50%
Triangular plot for paleostress analysis18 Srivastava et al.(1998) used triangular plots forpaleostress analysis from kink band. 60 90k 30
19, k, kGay and Weiss (1974)The most realistic α value of thedatas near the paleostress lineare projection parallel to the ψ-lines in the graph.Plot 6 α≒11.5˚Plot 8 α≒3.5˚Plot 13 α≒3˚
Conclusions20When the foliation of specimens parallel to the axis ofcompression (α=0˚) in metal jackets will intersect to thenetwork.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 Φand Φk don’t change with the shortening. The degree of theangle is relative to the composition of the rock mineral.
21The intersections of kink form the chevron fold that axial planenormal to the axis of compression .Using of the kink-band triangle is suitable for thedetermination of maximum compressive stress orientation fromkink-band structures. In practice. it is better to measure a largenumber of kink-bands.
22Thank you for your attention!!
α=0˚, large strain in Reflected light23Short specimens compressed parallel to foliation in copper jackets14%30% Shortening 45%70%Enlargement of D
Stress-strain results24The stress-strain curves for phyllite compressed parallel to the foliation in variousconstraining jackets at 5 kb confining pressure.a. Brass (15) b. Copper (11)in rubber jackets
Kink intersections25Classifying the intersection of kink accordingto the width and the form of kink boundaries
26Stress-strain curves for tests in compression at various angles to the foliation at 5 kbconfining pressure :a, in rubber jackets b, in thick brass jackets
Stress-strain results27Stress-strain curves of metals usedfor constraining jacketsThe stress-strain curves for phyllite compressedparallel to the foliation in various constrainingjackets at 5 kb confining pressure.a. Brass (15) b. Copper (11)c. Ni-Cr-Mo steel (2) d. High-C steel (1)
31 The initially circular cross section becomes ellipticalwith the minor diameter always lying in the plane ofthe foliation. in the central part of a specimen with20 per cent over-all shortening there is only about1 per cent increase in the minor diameter, whereasthe major diameter shows an increase of about 30per cent