The relationship between deformation and mineral composition in some fold structures

• An attempt is made to correlate the chemical compositions of certain minerals from different parts of fold structures with the theoretical stress pattern. A partial analysis was made on amphibole, plagioclase, garnet, diopside, sphalerite and biotite with a microprobe and the theoretical stress pattern was calculated by means of the finite-element method (FEM). Two of the four fold structures investigated show a systematic variation in the chemistry of some minerals, but there is no simple relationship to the theoretical stress model. The Fe-Mg silicates from the hinge zones often show lower values of iron, compared with the rest of the structure. A systematic variation between co-existing minerals indicates that chemical equilibrium has been attained. In many cases, the studied minerals from a folded layer are quite constant, which may be due either to small pressure gradients or to the fact that we have chosen minerals and elements which are not very sensitive to pressure. Though stress-induced diffusion may create some chemical variations, small fluctuations in partial pressures and local chemistry will very soon mask this pattern.

Ämnesord

NATURVETENSKAP  -- Geovetenskap och miljövetenskap -- Geologi (hsv//swe)

NATURAL SCIENCES  -- Earth and Related Environmental Sciences -- Geology (hsv//eng)

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