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Journal of the Geological Society

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Palaeomagnetic evidence for rotations and deformation in the Nogueras Zone, Central Southern Pyrenees, Spain

Department of Earth Sciences, University of Leeds, Leeds LS2 9JT, UK

A multicomponent palaeomagnetic remanence from the Lower Triassic Buntsandstein redbeds of the Central Southern Pyrenees has been interpreted as being composed of three components; a low blocking temperature recent viscous magnetization (L), an intermediate blocking temperature Eocene remagnetization (I), and a high blocking temperature Lower Triassic remanence (H).

These palaeomagnetic results can be used in conjunction with structural evidence to identify poles of rotation during the development of the Nogueras Zone antiformal stack. Poles from individual sites reflect local deformation and folding, including vertical rotation due to shearing between adjacent thrust sheets. The I component was sometimes acquired syn-tectonically during thrust motion, and can be used to define intermediate stages of structural development.

Results from sites located on a single thrust sheet (‘No. 7’) indicate that it rotated by 45° clockwise during emplacement. This is reflected in an easterly increase in displacement estimated from the construction of balanced cross-sections. Thrust sheets appear to have been pinned close to the present day location of Pont de Suert during the later stages of structural development. The arcuate path of thrust sheet motions, and the potential movements in and out of cross-section, can lead to over- and under-estimates of minimum displacement when using line-length cross-section balancing techniques.

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