Abstract

Fabrics in amphibolite rocks from the Kuopio area (eastern Finland) are described and compared with results of finite strain analysis. The area consists of mantled gneiss domes, which are deep-seated diapiric structures. Results concern the cover rocks of the domes. Strain ellipsoids range in shape from prolate to oblate (−0.67 ≤ v ≤ 0.52). Strain intensities vary strongly graphic.Preferred orientations of hornblende have been measured by X-ray texture goniometry and corresponding fabric ellipsoids calculated using an eigenvalue method. The same has been done for biotite where present. Fabric ellipsoids obtained for biotite are all oblate (0.04 ≤ vf ≤ 0.76). Those obtained for hornblende range from prolate to oblate (−0.60 ≤ vf ≤ 0.73). Intensities of hornblende fabric graphic are weaker than those of biotite fabric graphic. Local variations of results are induced by grain-scale factors, such as grain size, or original fabrics. No simple correlation is found between intensities of fabric and strain. In general, increasing strains are probably accompanied by an increase of the oblateness of biotite fabric ellipsoids. Hornblende fabrics are found to give a good approximation of the prolateness of the finite strain ellipsoid. The resulting L–S tectonite pattern is consistent with the general strain pattern and with the development of domal structures in the Kuopio area.

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