Bas van den Eeckhout, Hendrik J. Zwart; Hercynian crustal-scale extensional shear zone in the Pyrenees. Geology ; 16 (2): 135–138. doi: https://doi.org/10.1130/0091-7613(1988)016<0135:HCSESZ>2.3.CO;2
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Detailed structural analysis of metasedimentary rocks and gneisses in the Hospitalet massif (Pyrenees) has revealed that upright structures in low-grade rocks are in a structurally higher position and older than gently inclined to flat-lying structures in higher grade rocks. The steep structures were (sub)vertically flattened during formation of the flat-lying structures, indicating that the higher grade rocks formed as part of a shear-zone system. A similar conclusion can be drawn from the relation between deformation and metamorphism in the higher grade rocks. We suggest that the shear zone may have accommodated crustal extension.