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New method for geometrical classification of large data sets of folds
GEOMECHANICS ABSTRACTS
935004 High amplitude folding of linear-viscous multilayers Cruikshank, K M; Johnson, A M J Struct Geol V15, NI, 1993, P79-94
Geology Tectonic processes and structural geology
Multilayer viscous folding theory of Johnson and Pfaff (1989) is extended to higher amplitudes. The method developed leads to approximate solutions and uses as many terms as necessary to adequately match conditions at boundaries. The theory and solution method are outlined and results presented from single layer and simple repetitive multilayer systems. The ability of the model to simulate fold structures of the Huasna (California) and Berry-Buffalo (Pennsylvania) synclines is examined.
See also: 935207
935001 3-D subsurface displacement and strain fields for faults and fault arrays in a layered elastic half-space Ma, X Q; Kuznir, N J Geophys J VIII, N3, Dec 1992, P542-558 Near-field subsurface displacement associated with faults or fault arrays has been modelled using elastic dislocation theory, with the fault represented as a surface across which there is a discontinuity in prescribed displacement. Oblique or dip-slip faults which may or may not intersect the surface can be considered. 3D surface and subsurface displacement fields have been evaluated for a rectangular fault with constant slip and an elliptical fault with variable slip. The 3D displacement field and associated strain tensor can be determined for individual slip events or cumulative fault displacement.
935O02 Strain and kinematic analysis in general shear zones Simpson, C; De Paor, D G J Struct Geol V15, N1, 1993, P1-20
935005 Superposed buckling in multilayers Ghosh, S K; Mandal, L; Sengupta, S; Deb, S K; Khan, D J Struct Geol V15, NI, 1993, P95-111 The mode of superposed buckling is essentially controlled by the shapes of the early folds. Four standard modes are observed in single layers. A fifth mode is found only in the multilayer case, and here the geometry of the other modes may be modified during refolding. The interference pattern of smaller folds may be distorted by that of larger disharmonic folds. Consequences of this are described. Model simulations using clay layers are illustrated to show the possible geometries.
Environmental effects, weathering and soil formation
A unified theory is presented for the development of distribution of strain markers and kinematic indicators in zones of general shear. The shapes and distributions of rigid and deformable porphyroclast systems are used to distinguish amongst different tectonic regimes. Sub-simple shear and super-simple shear, where rotational components are respectively less than and greater than for simple shear, are introduced. Polar Mohr constructions are useful to analyse general shear in theory. The hyperbolic net is used for practical plotting of real data and derivation of kinematic vorticity number.
935003 New method for geometrical classification of large data sets of folds Bastida, F J Struct Geol VI5, N1, 1993, P69-78 Knowledge of fold geometry is required for interpretation of folding mechanisms. A classification is proposed for folded layers based on the use of two parameters which are related to variation in slope of the curves which describe orthogonal thickness vs dip. The classification is simple to use and has many advantages over geometrical analysis for large sets of folds. It has applications to theoretical analysis, comparison of regional structures, and analysis of folded multilayers.
935006 Quantitative approach to physical and chemical gold mobility in equatorial rainforest iateritic environment Colin, F; Vieillard, P; Ambrosi, J P Earth Planet Sci Lett VI14, N2/3, Jan 1993, P269-285 Mobility of gold from the Dondo Mobi deposits in subtropical south Gabon has been investigated. Calculations have been made of gold mass transfer during lateritic weathering of the auriferous lisvenite, Archaen gneiss, and Proterozoic gneiss, and a new thermodynamic approach to gold solubility under equatorial rainforest conditions is proposed. Both chemical and short distance translocation processes govern the mobility of dissolved and particulate gold. Combined interaction of rock, meteoric water, and biological agents affects long-term evolution of the collapsed open weathering systems.
935007 Enhanced bedrock weathering in association with late-lying snowpatches: evidence from Livingston Island, Antarctica Hall, K Earth Surf Process Land V18, N2, March 1993, P121-129 Weathering degree on different aspects of rock outcrops on Livingston Island was assessed using a Schmidt hammer, a cone indenter, and measurement of weathering rind thickness. Chemical weathering is enhanced where snow accumulates, as
© 1993 Pergamon Press Ltd. Reproduction not permitted 269A
935004 High amplitude folding of linear-viscous multilayers Cruikshank, K M; Johnson, A M J Struct Geol V15, NI, 1993, P79-94
Geology Tectonic processes and structural geology
Multilayer viscous folding theory of Johnson and Pfaff (1989) is extended to higher amplitudes. The method developed leads to approximate solutions and uses as many terms as necessary to adequately match conditions at boundaries. The theory and solution method are outlined and results presented from single layer and simple repetitive multilayer systems. The ability of the model to simulate fold structures of the Huasna (California) and Berry-Buffalo (Pennsylvania) synclines is examined.
See also: 935207
935001 3-D subsurface displacement and strain fields for faults and fault arrays in a layered elastic half-space Ma, X Q; Kuznir, N J Geophys J VIII, N3, Dec 1992, P542-558 Near-field subsurface displacement associated with faults or fault arrays has been modelled using elastic dislocation theory, with the fault represented as a surface across which there is a discontinuity in prescribed displacement. Oblique or dip-slip faults which may or may not intersect the surface can be considered. 3D surface and subsurface displacement fields have been evaluated for a rectangular fault with constant slip and an elliptical fault with variable slip. The 3D displacement field and associated strain tensor can be determined for individual slip events or cumulative fault displacement.
935O02 Strain and kinematic analysis in general shear zones Simpson, C; De Paor, D G J Struct Geol V15, N1, 1993, P1-20
935005 Superposed buckling in multilayers Ghosh, S K; Mandal, L; Sengupta, S; Deb, S K; Khan, D J Struct Geol V15, NI, 1993, P95-111 The mode of superposed buckling is essentially controlled by the shapes of the early folds. Four standard modes are observed in single layers. A fifth mode is found only in the multilayer case, and here the geometry of the other modes may be modified during refolding. The interference pattern of smaller folds may be distorted by that of larger disharmonic folds. Consequences of this are described. Model simulations using clay layers are illustrated to show the possible geometries.
Environmental effects, weathering and soil formation
A unified theory is presented for the development of distribution of strain markers and kinematic indicators in zones of general shear. The shapes and distributions of rigid and deformable porphyroclast systems are used to distinguish amongst different tectonic regimes. Sub-simple shear and super-simple shear, where rotational components are respectively less than and greater than for simple shear, are introduced. Polar Mohr constructions are useful to analyse general shear in theory. The hyperbolic net is used for practical plotting of real data and derivation of kinematic vorticity number.
935003 New method for geometrical classification of large data sets of folds Bastida, F J Struct Geol VI5, N1, 1993, P69-78 Knowledge of fold geometry is required for interpretation of folding mechanisms. A classification is proposed for folded layers based on the use of two parameters which are related to variation in slope of the curves which describe orthogonal thickness vs dip. The classification is simple to use and has many advantages over geometrical analysis for large sets of folds. It has applications to theoretical analysis, comparison of regional structures, and analysis of folded multilayers.
935006 Quantitative approach to physical and chemical gold mobility in equatorial rainforest iateritic environment Colin, F; Vieillard, P; Ambrosi, J P Earth Planet Sci Lett VI14, N2/3, Jan 1993, P269-285 Mobility of gold from the Dondo Mobi deposits in subtropical south Gabon has been investigated. Calculations have been made of gold mass transfer during lateritic weathering of the auriferous lisvenite, Archaen gneiss, and Proterozoic gneiss, and a new thermodynamic approach to gold solubility under equatorial rainforest conditions is proposed. Both chemical and short distance translocation processes govern the mobility of dissolved and particulate gold. Combined interaction of rock, meteoric water, and biological agents affects long-term evolution of the collapsed open weathering systems.
935007 Enhanced bedrock weathering in association with late-lying snowpatches: evidence from Livingston Island, Antarctica Hall, K Earth Surf Process Land V18, N2, March 1993, P121-129 Weathering degree on different aspects of rock outcrops on Livingston Island was assessed using a Schmidt hammer, a cone indenter, and measurement of weathering rind thickness. Chemical weathering is enhanced where snow accumulates, as
© 1993 Pergamon Press Ltd. Reproduction not permitted 269A