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 studi ed by the anisotropy of magnetic susceptibility (AMS) technique. As ex pected from the dominantly paramagnetic nature of the rocks, the magne tic susceptibility zonation accurately compares with the lithological zonation. Detailed examination of the linear and planar structural pat terns of the plutons allows the difficult problem of their formation m echanisms to be explored. The sigmoidal pattern of the linear structur es only results from regional tectonics and points unequivocally to a dextral shear component for the responsible tectonic event. The concen tric planar structures, while also affected by regional tectonics, ret ain some imprint of magma emplacement. The microstructures observed in the granitoids point to a continuous deformation from the magmatic st are to the high temperature solid state. In the country rocks, structu res and kinematic criteria underline the transpressive character of th e D-2 Hercynian event of the Pyrenees which resulted in a partitioning between zones where either compression or dextral strike-slip were do minant. All these data constrain a new model of D-2 syn-tee tonic empl acement for the plutons of the Cauterets-Panticosa complex and remarka bly illustrate structural features resulting from a transpressive regi me. (C) 1998 Elsevier Science Ltd. All rights reserved.