Abstract
In multiply deformed terrains, multiphase boudinage should be common, but identification and analysis of these is difficult. Here we present an analysis of multiphase boudinage and fold structures in deformed amphibolite layers in marble from the migmatitic center of the Naxos metamorphic core complex. Reconstruction of multiple boudinage generations is possible due to the exceptional 3D outcrop conditions. We identify five distinct generations of boudinage, reflecting the transition from high-strain – high-temperature ductile deformation to medium to low strain brittle boudins on the retrograde path during cooling and exhumation. All boudin generations indicate E-W horizontal shortening and variable directions of bedding parallel extension, evolving from subvertical extension in the earliest boudins to subhorizontal N-S extension during exhumation. Two phases of E-W shortening can be inferred, indicating E-W shortening in the Aegean before activity of the brittle North Anatolian Fault. This study highlights the wealth of information that can be gained from detailed analysis of multiphase boudinage structures.
Highlights
Boudins are periodic deformation structures that form in mechanically layered rocks under layer normal shortening and layer parallel extension (Marques et al, 2012; Ramberg, 1955)
We have identified six types of outcrop-scale deformation structures in the study area (Figs. 3, 4): two generations of pinch-and-swell structures (Fig. 5), folds (Fig. 6), and three generations of boudins
In addition to boudinage and folding, the marbles are affected by late deformation structures such as rare mylonitic shear zones and brittle normal- to oblique-slip faults (Fig. 5c) that have been described by Schenk et al (2005), Buick (1991), Cao et al (2017) and Vanderhaeghe (2004)
Summary
Boudins are periodic deformation structures that form in mechanically layered rocks under layer normal shortening and layer parallel extension (Marques et al, 2012; Ramberg, 1955). Considering the number of studies that have utilized crosscutting shear zones, veins or superimposed folds for the reconstruction of multiply deformed domains, the use of polyphase boudinage for this purpose has not yet been used to its full potential. We propose that their ubiquity and rich structure
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