Granitoid emplacement during a thrusting event: structural analysis, microstructure and quartz c-axis patterns. An example from Hercynian plutons in the French Massif Central
In the French Massif Central, the Rouergue-Albigeois area consists of three tectonic units stacked during the Hercynian orogeny. The structural analysis of the units and particularly the quartz < c> axis, textural and structural observations in the syntectonic Pinet-type plutons allow us to determine the deformation history. A first thrusting event, D1, is responsible for a southwestward emplacement of the high-grade Lévézou nappe, above the Lower Gneiss Unit itself overlying the para-autochthonous micaschists. In Late Devonian-Early Carboniferous, this stack of nappes experienced a second event, D2, characterized by a top-to-the-NW emplacement under medium pressure/medium temperature conditions of the para-autochtonous unit upon the Lower Gneiss Unit. During D2, the Pinet-type plutons were deformed by a shearing consistent with the kinematics recorded in the country rocks. In contrast to previous works, which considered the Pinet-type plutons emplacement to be coeval with the D2 event, we argue that the emplacement of the plutons occurred during the top-to-the-SW D1 nappe stacking. This work emphasizes the importance of the quartz < c> axis and microstructure analysis for the identification of the early structural history in polyphase deformed terranes.