Kinematics of the Forcarei Synform (NW Iberian Variscan belt)
Francisco José Fernández, Florentino Díaz-García, Jorge Marquínez, 2011. "Kinematics of the Forcarei Synform (NW Iberian Variscan belt)", Kinematic Evolution and Structural Styles of Fold-and-Thrust Belts, J. Poblet, R. J. Lisle
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The Forcarei Synform is a kilometric fold developed in the hinterland of the NW Iberian Variscan belt. A detailed analysis of the synform, based on quartz fabrics and kinematic markers, shows pervasively deformed rocks that have been continuously deformed during the last two main Variscan deformation phases (D2 and D3).
Variscan D2 minor structures related to the synform were formed under general non-coaxial flow and have a sub-horizontal maximum finite stretching toward the SSE. Later a coaxial D3 produced a sub-vertical crenulation cleavage, and type 2 and 3 refolded folds figures at the meso- and micro-scale. Consequently, the strike of the foliations (S2 and S3) become sub-parallel and lineation (L2 and L3) are sub-horizontal. The geometry of the synform and the related structures can be interpreted in the context of D3. However the dominantly sinistral shear sense indicators, observed in both limbs of the synform (in map view), seem to be most probably developed during D2. A model is proposed involving the progressive clockwise rotation of a sub-horizontal shear, with general top-to-the-south sense, during the simultaneous development of shear zone and foliation in agreement with the kinematic indicators.
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Fold-and-thrust belts occur worldwide, have formed in all eras of geological time, and are widely recognized as the most common mode in which the crust accommodates shortening. Much current research on the structure of fold-and-thrust belts is focused on structural studies of regions or individual structures and on the geometry and evolution of these regions employing kinematic, mechanical and experimental modelling. In keeping with the main trends of current research, this title is devoted to the kinematic evolution and structural styles of a number of fold-and-thrust belts formed from Palaeozoic to Recent times. The papers included in this book cover a broad range of different topics, from modelling approaches to predict internal deformation of single structures, 3D reconstructions to decipher the structural evolution of groups of structures, palaeomagnetic studies of portions of fold-and-thrust belts, geometrical and kinematical aspects of Coulomb thrust wedges and structural analyses of fold-and-thrust belts to unravel their sequence of deformations.