Sigmoidal structures featuring dextral shear during emplacement of the Hercynian granite complex of Cauterets-Panticosa (Pyrenees)

The three plutons of the Cauterets-Panticosa granite complex are studied by the anisotropy of magnetic susceptibility (AMS) technique. As expected from the dominantly paramagnetic nature of the rocks, the magnetic susceptibility zonation accurately compares with the lithological zonation. Detailed examination of the linear and planar structural patterns of the plutons allows the difficult problem of their formation mechanisms to be explored. The sigmoidal pattern of the linear structures only results from regional tectonics and points unequivocally to a dextral shear component for the responsible tectonic event. The concentric planar structures, while also affected by regional tectonics, retain some imprint of magma emplacement. The microstructures observed in the granitoids point to a continuous deformation from the magmatic stare to the high temperature solid state. In the country rocks, structures and kinematic criteria underline the transpressive character of the D-2 Hercynian event of the Pyrenees which resulted in a partitioning between zones where either compression or dextral strike-slip were dominant. All these data constrain a new model of D-2 syn-tee tonic emplacement for the plutons of the Cauterets-Panticosa complex and remarkably illustrate structural features resulting from a transpressive regime. (C) 1998 Elsevier Science Ltd. All rights reserved.