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Mobile-hinge kinking in layered rocks and models
GEOMECHANICS ABSTRACTS
916004 Significance of low symmetry fabrics in magmatic rocks Fernandez, A; Laporte, D J Struct Geol V13, N3, 1991, P337-347
General 916001 New triangular raise cribbing technique for rockburst prone baekfllled stopes. Technical note Archibald, J H CIM Bull V84, N948, April 1991, P55-56 In mines using cut and fill stoping with sandfill, ore passes are built as mining proceeds upwards. These raises are generally made from timber and are square in section. Where mining conditions are such that high horizontal stresses are built up, the rectangular crib may pivot to give a rhombic shape, which supports very little load. A simple practical solution to this problem, using a triangular section raise, is illustrated.
Geology
Low symmetry (monoclinic and triclinic) fabrics have long been recognised in magmatic rocks. Their significance has been studied by simulating the motion of rigid markers in slowly deforming ductile matrices. In agreement with Curie's Symmetry Principle, a non-coaxial strain path is required for the fabric development. Factors influencing the fabric characteristics are evaluated. Analysis of natural monoclinic fabrics can provide information on the type of strain regime, orientation of the axis,and sense of shear. Magnitude of finite strain can be estimated if marker shapes are precisely known.
916005 Rotation, offset and separation of oblique-fraetm'e (rhombic), boudins: theory and experiments under layer-normni compression Mandal, N; Khan, D J Struet Geol V13, N3, 1991, P349-356
Tectonic processes and structural geology See also: 916035, 916063 9160O2 Mobile-hinge kinking in layered rocks and models Stewart, K G; Alvarez, W J Struct Geol V13, N3, 1991, P243-259 The mechanism of the growth of kink folds is one unresolved question for structural geologists. The importance of mobile hinge kinking for multilayered materials with alternate competent and incompetent layers was demonstrated in the laboratory using an analogue material of lead sheets separated by wax-impregnated cloth. Nucleation and expansion of kink bands with mobile hinges was observed, rather than a fixed hinge folding mechanism. The experimental structures are correlated with those in a pelagic limestone of the UmbriaMarche Appenines. 916003 Strain analysis method using the maximum frequency of unimodai deformed orientation distributions: applications to gueissic rocks Soto, J I J Struet Geol V13, N3, 1991, P329-335 A two dimensional strain analysis method is developed using the maximum frequency of the unimodal distributions of the passive lines. Theoretical work of Sanderson (1977) forms the basis of the analysis. It is demonstrated applied to samples of gneiss, using the orientation of feldspar and tourmaline lying in the sehistosity plane, with respect to the stretch lineation.
One method of formation of boudin-like structures is by shear fracturing of competent rocks oblique to their layering. Boudins of rhomboid shape are rotated and offset with respect to each other. Experiments on model materials under layernormal compression and theoretical analysis suggest the segments produced may rotate with separation or rotate with interfacial slip, depending on their geometry. Parameters which can control the rate of rotation versus rate of displacement of layer segments are aspect ratio of the segments and orientation of the fractures.
916006 Experiments on shortening of a &layer model of the continental fithosphere Davy, P; Cobbold, P R Tectonophysics V188, NI/2, March 1991, PI-25 Using analogue materials it was possible to develop simplified models of a layered lithosphere. Gravity effects can be included without the need for a centrifuge. Only four layers were considered: brittle crust, ductile crust, brittle mantle, and ductile mantle. During lithospberic shortening, style of deformation depends on the relative properties of these layers, in particular on the presence of or absence of the brittle mantle. In the initial stages of compression, flexure or buckling often occur without local isostatic compensation. Thrust faults form at the location of these buckles. Results were obtained for 2, 3, and 4 layer models.
© 1991 Pergamon Press plc. Reproduction not permitted 331A
916004 Significance of low symmetry fabrics in magmatic rocks Fernandez, A; Laporte, D J Struct Geol V13, N3, 1991, P337-347
General 916001 New triangular raise cribbing technique for rockburst prone baekfllled stopes. Technical note Archibald, J H CIM Bull V84, N948, April 1991, P55-56 In mines using cut and fill stoping with sandfill, ore passes are built as mining proceeds upwards. These raises are generally made from timber and are square in section. Where mining conditions are such that high horizontal stresses are built up, the rectangular crib may pivot to give a rhombic shape, which supports very little load. A simple practical solution to this problem, using a triangular section raise, is illustrated.
Geology
Low symmetry (monoclinic and triclinic) fabrics have long been recognised in magmatic rocks. Their significance has been studied by simulating the motion of rigid markers in slowly deforming ductile matrices. In agreement with Curie's Symmetry Principle, a non-coaxial strain path is required for the fabric development. Factors influencing the fabric characteristics are evaluated. Analysis of natural monoclinic fabrics can provide information on the type of strain regime, orientation of the axis,and sense of shear. Magnitude of finite strain can be estimated if marker shapes are precisely known.
916005 Rotation, offset and separation of oblique-fraetm'e (rhombic), boudins: theory and experiments under layer-normni compression Mandal, N; Khan, D J Struet Geol V13, N3, 1991, P349-356
Tectonic processes and structural geology See also: 916035, 916063 9160O2 Mobile-hinge kinking in layered rocks and models Stewart, K G; Alvarez, W J Struct Geol V13, N3, 1991, P243-259 The mechanism of the growth of kink folds is one unresolved question for structural geologists. The importance of mobile hinge kinking for multilayered materials with alternate competent and incompetent layers was demonstrated in the laboratory using an analogue material of lead sheets separated by wax-impregnated cloth. Nucleation and expansion of kink bands with mobile hinges was observed, rather than a fixed hinge folding mechanism. The experimental structures are correlated with those in a pelagic limestone of the UmbriaMarche Appenines. 916003 Strain analysis method using the maximum frequency of unimodai deformed orientation distributions: applications to gueissic rocks Soto, J I J Struet Geol V13, N3, 1991, P329-335 A two dimensional strain analysis method is developed using the maximum frequency of the unimodal distributions of the passive lines. Theoretical work of Sanderson (1977) forms the basis of the analysis. It is demonstrated applied to samples of gneiss, using the orientation of feldspar and tourmaline lying in the sehistosity plane, with respect to the stretch lineation.
One method of formation of boudin-like structures is by shear fracturing of competent rocks oblique to their layering. Boudins of rhomboid shape are rotated and offset with respect to each other. Experiments on model materials under layernormal compression and theoretical analysis suggest the segments produced may rotate with separation or rotate with interfacial slip, depending on their geometry. Parameters which can control the rate of rotation versus rate of displacement of layer segments are aspect ratio of the segments and orientation of the fractures.
916006 Experiments on shortening of a &layer model of the continental fithosphere Davy, P; Cobbold, P R Tectonophysics V188, NI/2, March 1991, PI-25 Using analogue materials it was possible to develop simplified models of a layered lithosphere. Gravity effects can be included without the need for a centrifuge. Only four layers were considered: brittle crust, ductile crust, brittle mantle, and ductile mantle. During lithospberic shortening, style of deformation depends on the relative properties of these layers, in particular on the presence of or absence of the brittle mantle. In the initial stages of compression, flexure or buckling often occur without local isostatic compensation. Thrust faults form at the location of these buckles. Results were obtained for 2, 3, and 4 layer models.
© 1991 Pergamon Press plc. Reproduction not permitted 331A