Showing papers in "Journal of Structural Geology in 1980"

TL;DR: In this article, the authors classified brittle, brittle-ductile, and ductile shear zones into three classes: brittle, ductile and polygonal shear regions, and established the geometry and displacement boundary conditions of these zones.

TL;DR: In this paper, the development of mylonite microstructures and fabrics are discussed from this point of view and seven possible softening processes are discussed: superplasticity, geometrical softening, continual recrystallization, reaction softening and chemical softening.

TL;DR: Extensional crenulation cleavage is defined by sets of small-scale ductile shear-bands along the limbs of very open microfolds in the foliation as mentioned in this paper.

TL;DR: In this paper, the development of three-dimensional fold shapes in shear regimes is studied using theoretical and experimental methods and with reference to natural examples, and three models are presented for their development, two invoking flow with steady stream lines, the third involving unsteadiness accompanying boudinage.

TL;DR: In this article, the effect of deformation history on the development of crystallographic preferred orientation in quartzities has been simulated using a computer program based on the Taylor-Bishop-Hill analysis.

TL;DR: A measure of the non-coaxiality involved in progressive deformation histories is proposed in the form of the kinematical vorticity number, Wk as mentioned in this paper, which measures the relative effects of rotation of material lines (relative to the instantaneous stretching axes) and of stretching of these material lines.

TL;DR: In this paper, the authors reviewed the mechanics and physics of unstable, localized flow in simple shear with special reference to experimental results on materials, taking into account strain hardening or softening, strain-rate sensitivity and shear heating.

TL;DR: In the Outer Hebrides Thrust zone, NW Scotland, textures suggest that pseudotachylyte friction-melt has been produced intermittently by seismic slip on discrete planes within an otherwise ductilely deforming shear zone as discussed by the authors.

TL;DR: In this article, the effect of water on deformation in the brittle-ductile transition region of crustal rocks has been investigated using optical and transmission electron microscopy (TEM).

TL;DR: Strain heating is an important crustal phenomenon which should be incorporated in models of large-scale tectonic processes and may even contribute to local partial melting in some shear zones.

TL;DR: In this article, physical models of geological shear zones are computed taking into account heating by deformation and consequent softening of the rock, showing that initiation of a ductile shear zone proceeds by the rapid build up of a thermal peak and by concentration of the strain.

TL;DR: The main lithological features and structural relations of the South Armorican Shear Zone (S.A.S.Z) are described and the evolution of physical conditions during deformation is outlined in this paper.

TL;DR: Metamorphic reaction was broadly coeval with strong deformation in the shear zones and resulted in the transformations pyx→hbl, hbl→biot, hBL→chl, and fsp→musc as mentioned in this paper.

TL;DR: The South Armorican Shear Zone (S.A.S.Z) as discussed by the authors is composed of several ductile shear zones, which may be followed for more than 300 km in southern Brittany (France).

TL;DR: In this paper, a modification of Ramsay's (1967) classification of fold interference patterns is proposed, based upon angular parameters in part different from those used by Ramsay, using the angle between the axes of the first folds and the pole to the axial planes of the second folds as one of their parameters (gamma).

TL;DR: In this article, a mathematical solution of how randomly oriented planes and lines are rotated and deformed during progressive homogeneous simple shear is presented, and the results are used to predict the redistribution and modification of pre-shear folds.

TL;DR: In this article, a sandbox experiment is described in which conjugate normal faults cut each other in an X configuration and their mutual offset leads to generation of new fault segments, and finally to a complex but systematic interference structure.

TL;DR: The La Gonzalez pull-apart basin this article suggests that Pliocene-Quaternary right-lateral slip on the Bocono fault zone was of the order of 7-9 km.

TL;DR: S1 cleavage in the Hawick Rocks of the Galloway area is non-axial planar, cutting obliquely across the F1 folds in a predominantly clockwise sense.

TL;DR: Variations in mineral chemistry with increasing shear strain have been observed in a shear zone developed in a phlogopite peridotite, and these variations are attributed to re-equilibration of the system towards changing rock composition and the physical conditions prevailing during the formation of the shear zones as discussed by the authors.

TL;DR: In this paper, the authors applied models of thrust tectonics derived from studies in the Rocky Mountains and the Appalachians to the deeper level Caledonian thrusts of the northern part of the Moine thrust zone at Eriboll, N. W. Scotland and also to the Caledian thrusts as a whole.

TL;DR: In this article, the deformation mechanisms within the plagioclase and clinopyroxene of the diabase have been compared to those within monomineralic aggregates of these phases deformed at the same conditions.

TL;DR: In this paper, it is assumed that rocks have linear isotropic viscous or elastic deformational properties, but their moduli may vary with mean stress, and it is argued that the rock in shear zones should be weaker than the surrounding rock.

TL;DR: In this paper, the Griffith maximum tensile stress criterion is used to predict fracture initiation and fracture initiation is associated with a decrease in the strain energy of the crack, and a gradual drop in crack fluid pressure once the threshold for fracture initiation has been passed may promote the extent of spontaneous crack growth.

TL;DR: In this paper, the evolution of structures has been studied in mylonitic quartzo-feldspathic rocks across a shear zone in Adrar des Iforas (Republic of Mali).

TL;DR: In this article, the main features of the shear zones of southern Africa, their size, shape, orientation, state of strain and displacement, and their state of deformation are reviewed.

TL;DR: In this paper, the permanence of dextral shearing along the WMSZ through Middle to Late Palaeozoic time is described, which determined the development of the sedimentary basins and then controlled Hercynian folding and metamorphism.

TL;DR: In this article, a general model based on observations from the modern circum-Pacific and the Palaeozoic Tasman Geosyncline is proposed to explain the evolution of fore-arc regions.

TL;DR: In this paper, microstructural and chemical variations accompanying the mylonitisation of the Roneval anorthosites were studied, and it was shown that mylonites developed by syntectonic recrystallization with grains containing two sets of lamellae recrystizing preferentially.