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Paleostress-tensor analysis of late deformation events in the Odenwald Crystalline Complex and comparison with other units of the Mid-German Crystalline Rise, Germany

Research paper by T. M. Will

Indexed on: 01 Jun '01Published on: 01 Jun '01Published in: Mineralogy and Petrology



Abstract

Geometric data of fault planes and fault plane lineations, together with the observed sense of shear on the slip planes, were used to calculate paleostress tensors and fields responsible for the post metamorphic peak D3 and D4 deformation events in the four Odenwald units sensu Krohe (1991). The paleostress fields were calculated using the method of Will and Powell (1991). As inferred from the paleostress analysis, the D3 strike-slip deformation west of the Otzberg fault zone was caused by a, ± N-S directed, compressional regional stress field, with shallowly plunging σ1 axes and σ3 directions that plunge at shallow to moderate angles to the E or W; the calculated mean orientations are: σ1 06 → 350, σ2 77 → 234 and σ3 12 → 085. The Böllsteiner Odenwald east of the Otzberg fault zone was not affected by this stress field. This implies that the Bergsträsser and Böllsteiner Odenwald were spatially separated and formed independent crustal blocks during D3. The D4 faulting event is recognised in all areas investigated, even though most prominently in units III and IV, and juxtaposed the Bergsträsser and Böllsteiner Odenwald. This faulting episode was caused by a paleostress field with a steeply westerly plunging σ1 axis and a shallowly southsoutheasterly plunging σ3 axis. The orientations of the principal stresses are: σ1 52 → 270, σ2 38 → 085 and σ3 06 → 174. With continued deformation from D3 to D4, there was a progressive change in the orientation of the stress field indicating a change from a N-S compressional to extensional stress field, accompanied by the progressive development of strike-slip faults and late normal faults. Paleostress field orientations in the Pfalz Forest, SW of the Odenwald, determined by Flöttmann and Oncken (1992) are very similar to those obtained for the Odenwald region and indicate a regionally consistent stress pattern in the southwestern part of the Mid-German Crystalline Rise (MGCR) during strike-slip and normal faulting deformations.