Analysis of Kinematical Folding Mechanisms under Analogue Modelling of Plane Strain

Mehrdad Madani Kivi* and Gernold Zulauf
Johann Wolfgang Goethe, Frankfurt University, Germany
*[email protected]

The purpose of this presentation is to discuss the analysis of kinematical folding mechanisms using analogue modeling of plane strain. We studied mathematical functions that represent the geometry of folded surface profiles under analogue modeling. This analysis can be made by attempting to find theoretical folds that fit natural or experimental folds by the use of the point transformation equations for the basic mechanism. To demonstrate the impact of strain rate on the growth of varying folds under plane strain, we investigated a stiff layer consisting of non-linear viscous Kolb grey plasticine that was embedded in a weak matrix. The matrix consisted of non-linear viscous Beck’s green plasticine, with the layer trending parallel to the X-axis of the constrictional strain ellipsoid. The invariable strain rate was c. 3.5 x 10^-4. The viscosity ratio between the non-linear viscous layer and the upper matrix was set at c. 7.9, with the lower matrix ranging from 7.9 to 20.6. Additional experiments were conducted in which a stiff layer was embedded in a weak matrix, and the matrix parameters were varied up-and-down for the stiff layer (for example density and viscosity); these experiments are similar to nature. Different runs were carried-out in which the layer (S) was oriented perpendicular to the principal strain axes (X>Y>Z). Our results suggest that the strain rate has a considerable influence on the geometry of the deformed stiff layer, including its thickness. The change in arc length and geometry of folds was obvious at a strain rate, which corresponded to a viscosity ratio. The new results might be interesting for those workers who are dealing with deformed rock salt or melt-lubricated shear zones.

AAPG Search and Discovery Article #90077©2008 GEO 2008 Middle East Conference and Exhibition, Manama, Bahrain