Elsevier

Tectonophysics

Volume 205, Issue 4, 15 May 1992, Pages 357-386
Tectonophysics

Structural evolution of intermediate-crustal rocks in a strike-slip and extensional setting (Variscan Odenwald, SW Germany): differential upward transport of metamorphic complexes and changing deformation mechanisms

https://doi.org/10.1016/0040-1951(92)90443-AGet rights and content

Abstract

The Variscan basement exposed in the Odenwald Mountains, southwest Germany, is composed of several allochthonous metamorphic complexes, showing low pressure metamorphism with varying PT-conditions, and of syntectonic plutons (I-and S-type). During the Late Devonian-Early Carboniferous times, rapid uplift of these rocks caused rapid cooling. Before (and during) the thermal peak of metamorphism, the metamorphic rocks experienced penetrative strain (D1, D2) which was probably generated by crustal shortening and stacking. The resulting (micro-) structures infer distributed strain, activation of [c]-slip in quartz and postkinematic annealing. During and after the thermal peak of metamorphism, NE-SW trending zones of normal oblique sinistral strike shearing (D3) and NNE-SSW trending zones of normal shearing (D4) developed. These episodes of deformation are characterized by strong localization of strain. Strain softening was caused by reorientation of the lattice of quartz toward an orientation more favorable for easy glide along 〈a〉 and by a change in deformation mechanisms of feldspar from dislocation creep to grain size sensitive creep. Normal oblique strike shearing and normal shearing caused juxtaposition of mid-crustal slivers of dissimilar PT- and structural histories and provided mechanisms for their denudation. Detachment of rocks occurred along domains in which strain softening was operative. Further, transtension and extension facilitated uplift and emplacement of syntectonic plutons which experienced also D3 and D4 strain. In the plutonic rocks, strain was broadly distributed in the initial (hot) stages, and became increasingly localized, as the deformation continued through cooling.

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