Abstract

The twinned-calcite strain-gage technique allows the determination of strain magnitude and direction in mildly deformed sedimentary rocks. In that the measurements required for the calculation are rather time-consuming, it is important to know the minimum number required to obtain a precision that is comparable with the accuracy of the result. This paper documents a series of tests on three different limestones having different textures and porosities in order to determine the precision and accuracy of the technique as a function of the number of measurements and the number of perpendicular thin sections. The tests show that, for most purposes, the best measurement strategy will be to make 25 measurements on each of two perpendicular thin sections. The best-determined principal strain axis is the one having a magnitude that is opposite in sign from the other two. Over the range of zero to 11% shortening, the magnitude of the odd-signed strain axis will than have a precision and accuracy of about 11% in magnitude and a precision and accuracy of about 6° to 8° in orientation. Differences in texture and porosity do not appear to have significant effects upon precision and accuracy.

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