Compressive strength data for pure plagioclase and pure epidote aggregates deformed at high-pressure, high-temperature conditions

Published: 3 October 2023| Version 1 | DOI: 10.17632/3bytt6b8sp.1


Despite their abundance in crustal rocks at elevated pressure and temperature conditions, the deformation behavior of epidote-group minerals is poorly studied. We experimentally investigated the relative strength of pure epidote and pure plagioclase aggregates at a confining pressure of 1 GPa, two different temperatures (550 and 650 °C) and two different strain rates (5.10^-5 and 5.10^-6 s^-1) using a Griggs apparatus. Furthermore, we investigated potential strength differences due to differences in grain size by deforming aggregates with grain-size ranges of either 90-135 μm or <25 μm. The chemical composition of the starting material is 64 % anorthite, 35 % albite, and 1 % orthoclase for plagioclase, and 69 % epidote. During deformation, most aggregates underwent buckling, i.e., the top part of the sample was sheared relative to its bottom part, which had a strong influence on the mechanical data. The mechanical data of the successful runs shows that epidote aggregates are either as strong as their plagioclase counterparts or moderately stronger, assuming an uncertainty in stress of 100 to 200 MPa.


Steps to reproduce

We provide a MATLAB code (stress_strain.txt), with which we plotted the mechanical data. The load data is smoothed using the MATLAB function movmean (averaging over a window length of 500 samples; sampling rate = 1Hz) and corrected for machine stiffness and friction. The first column in the file represents the axial strain and the second column is the differential stress (sigma1-sigma3) in MPa. The file name is composed in a way to provide all the necessary information seperated by underscores. The first position indicates the material used (Pl for plagioclase; Ep for epidote), the second position shows the initial grain size of the aggregate (either 90-135 µm or <25 µm), the third position marks the confining pressure (1 GPa), the forth position highlights the temperature (550 or 650 ˚C), the fith position reflects the applied strain rate (5.10^-5 and 5.10^-6 s^-1), the sixth position is a number x ranging from 2 to 4 indicating the xth repetition of the test at the same experimental conditions, and an added 'b' at the end highlights that the aggregate underwent buckling.


Ruhr-Universitat Bochum


Experimental Rock Deformation


Alexander von Humboldt-Stiftung