Strain Partitioning Within Bending Orogens, New Insights From the Variscan Belt (Chiroulet‐Lesponne Domes, Pyrenees)

Abstract

AbstractThis study investigates how strain is partitioned within hot orogenic belts in a context of plate reorganization. We document crustal‐scale strike‐slip shear zones, plate‐scale oroclinal bending, and widespread exhumation of deep crustal domains in the core of nascent Pangea plate during late‐Variscan times (ca. 310–290 Ma). The role of strain partitioning in the finite strain patterns is first highlighted at regional scale by a new detailed structural, kinematic, and petrologic analysis of the Chiroulet and Lesponne gneiss domes in the Pyrenees. Vertical strain partitioning in response to N‐S shortening‐dominated dextral transpression is secondly documented at the scale of the Variscan domains of the Pyrenees, based on a synthesis of recent geochronological, thermobarometrical, and structural data. We show that the mid‐lower crust is affected by eastward lateral flow and the upper crust by penetrative thickening and localized thrusting. Local transverse extension in the mid‐lower crust illustrates gravity‐driven instability favored by the accumulation of anatectic melts in gneiss domes. Finally, we highlight the respective position of extended and shortened area within the Variscan belt during late‐Carboniferous/early‐Permian that suggests large‐scale lateral strain partitioning and reorganization of the weak continental crust in the core of the Pangea. This distribution appears significantly different from other orogens in a similar context of oroclinal bending, resulting in localization of the shortened zones in the core of the belt. This highlights the influence of the initial and boundary conditions, such as the obliquity of the belt to the applied stress field and the location of free‐boundaries, on finite strain patterns.