The Analysis of Strain in the Barberton Mountain Land, Eastern Transvaal, Using Deformed Pebbles

Abstract

Deformed pebbles from the Moodies conglomerate were collected at ten localities in the Barberton Mountain Land. The axial ratios and orientations of these pebbles were used to calculate the total finite strains experienced by the pebbles at each locality. A technique described by Ramsay (1967, p. 209-211) was used to remove the effect of initial pebble shape. Viscosity ratios between the different pebble types were calculated and used to convert pebble strains into the total finite strains experienced by the rocks. The results showed that the amounts of strain varied over the Barberton Mountain Land from low strain localities in the center of the region to areas of high strain in the north and northwest. Generally, the strains were of a flattening type, though at two localities adjacent to granite contacts the strains approximate to pure shear. An attempt is made to relate this variation in strain to the regional structural geology.