Выпуск 241
Автор(ы):Peacock D.C.P., Sanderson D.J.
Издание:Journal Tectonophysics, 1995 г., 13 стр.
Pull-aparts, shear fractures and pressure solution

Vein arrays are often composed of pull-aparts which are linked by shear fractures, good examples of which occur in the Lower Jurassic limestones of Somerset, southwestern England. Such pull-apart arrays have displacement-distance characteristics which are similar to fault zones, with maximum displacement (indicated by the largest pull-apart widths) near the centre of the array, and with displacement decreasing towards the tips. Pull-apart arrays usually die out into en echelon or pinnate veins. Evidence for pressure solution along the shear fractures which connect pull-aparts include their dark and braided nature, their obliquity to the displacement direction, the high dihedral angles (often > 90°) between conjugate shear fractures, and the dissolution of earlier structures. A range of geometries occurs, with varying relative amounts of veins and pressure solution being related to varying amounts of transtension or transpression. There is a general trend for an increase in the angle between vein segments and the shear fractures as contraction increases. There is therefore a trend for increased pressure solution on the shear fractures in more contractional arrays. The concentration of insoluble material along shear fractures has important implications for the mechanics and sealing of faults.

ТематикаРегиональная геология
МеткиPressure solution, Pull-aparts, Shear fractures
Выпуск 24
Автор(ы):Keewook Y., Wintsch R.P.
Издание:Journal of Structural Geology, 2002 г., 15 стр.
Dissolution and replacement creep: a significant deformation mechanism in mid-crustal rocks

Zoning patterns and zoning truncations in metamorphic minerals in a granodioritic orthogneiss indicate that strain and S-C fabrics in these rocks were produced by dissolution, precipitation, and replacement processes, even at epidote-amphibolite fades metamorphic conditions. The metamorphic fabric is defined by alternating layers and folia dominated by quartz, feldspars, and biotite + epidote. Zoning patterns in most metamorphic plagioclase, orthoclase, epidote, and sphene are truncated at boundaries normal to the shortening direction, suggesting dissolution. Interfaces of relict igneous orthoclase phenocrysts that face the shortening direction are embayed and replaced by biotite, epidote, and myrmekitic intergrowths of plagioclase and quartz. Metamorphic plagioclase grains are also replaced by epidote. We interpret these microstractures to reflect strain-enhanced dissolution. The cores of many grains show asymmetric overgrowths with at least two generations of beards, all oriented on the ends of grains that face the extension direction. We interpret these textures to reflect precipitation of components dissolved by deformation-enhanced dissolution. While biotite and quartz probably deformed by dislocation creep, the overall deformation was accommodated by dissolution perpendicular to the shortening direction, and precipitation parallel to it. These chemical processes must have been activated at lower stresses than the dislocation creep predicted from extrapolations of data from experiments in dry rocks. Thus wet crust is likely to be weaker than calculated from these experimental studies

ТематикаРегиональная геология
МеткиDissolution, Metamorphic reaction mechanism, Precipitation, Pressure solution, Replacement creep, Деформации, Метаморфизм
Выпуск 280
Автор(ы):Gratier J.P, Ortoleva P., Renard F.
Издание:Journal Tectonophysics, 1997 г., 10 стр.
Pressure solution in sandstones: influence of clays and dependence on temperature and stress

The enhancement of dissolution of quartz under the influence of clays has been recognized in sandstones for many years. It is well known that a grain of quartz in contact with a clay flake dissolves faster than when in contact with another grain of quartz. This phenomenon promotes silica transfer during the diagenesis of sandstones and is responsible of deformation and porosity variations. Here we make an attempt to explain the process of this rock deformation using a pressure solution mechanism.

МеткиClay, Compaction, Diagenesis, Pressure solution, Sandstone, Глина, Диагенез, Песчаники
Выпуск 283
Автор(ы):Canole P., Odonne F., Polve M.
Издание:Journal Tectonophysics, 1997 г., 15 стр.
Heterogeneous strain associated with normal faulting evidence of mass transfer by pressure solution associated with fault displacement

In a well stratified flysch in the French Pyrenees, the offset of layers along a fault zone provide good data of relative displacement. It is shown that the fault surface is composed of three right-stepping fractures that opened tensile bridges along small left-stepping fractures. Translation on the fault zone is parallel to the fault surface. The displacement vector field shows that the movement between the two blocks was not a rigid body translation and that deformation in the hanging wall is greater than that in the foot wall. Volume loss within the rock is compensated by volume increase close to the fault surface.

Calcite dissolution and reprecipitation by pressure solution is indicated by the occurrence of stylolites and numerous calcite-filled veins around the fault. Calcite dissolution is more important in the hanging wall, especially in layers where the calcite content is close to 60%. Both cathodoluminescence observations and rare-earths element patterns are in favour of calcite in veins and dominos coming from units adjacent to the fault. There is no evidence that some calcite coming from farther distance could have entered in the system.

ТематикаРегиональная геология, Структурная геология
МеткиMass transfer, Normal faulting, Pressure solution, Strain, Деформация, Массоперенос, Складкообразование, Условия давления
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