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Publisher
Springer, Berlin, Heidelberg
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Authors: M S Paterson F J Turner
Publish Date: 1970
Volume: , Issue: , Pages: 109-141
Abstract
Calcite crystals were enclosed in strong metal jackets in order to introduce constraints additional to those normally present in tests on single crystals The composite specimens were elongated by various amounts under a confining pressure of 5 kilobars and a temperature in most cases of 300 °C A detailed microscopic study was made of the effects of the constraints on the mechanisms of deformation and the patterns of distribution of strain within the calcite crystalsFour orientations were studied two favourable and two unfavourable to twinning In the former normal to e and 30° to 0001 75° to r the deformation was still mainly by e twinning In extension normal to m it was mainly by r translation In extension parallel to the zone r2 r3 deformation appeared to begin by r translation but as it continued translation gliding on two a planes became prominent and there was some evidence also for f glideTwo main effects of the constraint were evident First domains of heterogeneous deformation on the scale of the crystal such as kinks were no longer sharply defined their boundaries being gradational in nature Second there was a tendency for glide to occur on more than one plane this appeared in the simultaneous activity of equally favoured planes and in the appearance of other glide systems not normally seen in simple tests notably a translation in the r 2 r 3 orientation Calculations of the changes in stresses due to the extra constraints show how the latter development is favoured The work has relevance to the problems of deformation of mineral grains in rocks since the boundary conditions employed here approach more realistically those imposed on a crystal in an aggregate under metamorphic conditions
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