The development of a single cleavage in an area of repeated folding

In the Variscan foreland of SW-Sardinia\ud (Western Mediterranean sea), close to the leading edge of\ud the nappe zone, nappe emplacement caused folding and\ud repetition of stratigraphic successions, km-scale offset of\ud stratigraphic boundaries and an extensive brittle-ductile\ud shear zone. Thrusts assumed a significant role, accommodating\ud a progressive change of shortening direction and\ud forming complicated thrust triangle zones. During thrust\ud emplacement of the nappes, strong penetrative deformation\ud affected rocks beneath the basal thrust of the nappe stack\ud and produced coeval structures with both foreland-directed\ud and hinterland-directed (backthrusting) shear sense. Crosscutting\ud and overprinting relationships clearly show that the\ud shortening direction changed progressively from N–S to E–\ud W, producing in sequence: (1) E–W trending open folds\ud contemporaneous with early nappe emplacement in the\ud nearby nappe zone; (2) recumbent, quasi-isoclinal folds\ud with axial plane foliation and widespread, ‘‘top-towardsthe-\ud SW’’, penetrative shearing; (3) N–S trending folds with\ud axial plane foliation, contemporaneous with late nappe\ud emplacement; (4) backthrusts and related asymmetrical\ud folds developed during the final stages of shortening,\ud postdating foreland-verging structures. Structures at (3)\ud and (4) occurred during the same tectonic transport ‘‘toptowards-\ud the-E’’ of the nappe zone over the foreland. The\ud several generations of folds, thrusts, and foliations with\ud different orientations developed, result in a complex finite\ud structural architecture, not completely explicable by the\ud theoretical model proposed up to date

Section: Kinematic Evolutionsupporting

confidence: 76%

Section: Previous Workmentioning

confidence: 99%

Section: Kinematic Evolutionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

See 2 more Smart Citations

Foreland- and hinterland-verging structures in fold-and-thrust belt: an example from the Variscan foreland of Sardinia

Funedda

2008

“…In contrast to the above interpretations, other studies emphasized that the correlation of superposed fabrics and inferred succession of deformation phases in multiply deformed regions may be rather problematic in general (e.g., Burg 1999;Luneburg and Lebit 1998;Miller et al 2005;Tobisch and Paterson 1988;Williams 1985). The correlations, which traditionally rely on fabric orientation, styles of superposed folding and outcrop-scale overprinting relationships, assume constant boundary conditions, isotropic materials, and homogeneity and synchroneity of regional deformation.…”

Section: Implications For the Interpretation Of Orogenic Fabrics In Tmentioning

confidence: 99%

Magmatic fabrics and emplacement of the cone-sheet-bearing Knížecí Stolec durbachitic pluton (Moldanubian Unit, Bohemian Massif): implications for mid-crustal reworking of granulitic lower crust in the Central European Variscides

Verner

Žák

Nahodilová

et al. 2007

The~340 Ma Knížecí Stolec durbachitic pluton was emplaced as a deep-seated cone-sheetbearing ring complex into the Křišt'anov granulite body (Moldanubian Unit, Bohemian Massif). Prior to the emplacement of the durbachitic magma, the steep sub-concentric metamorphic foliation in the granulite formed due to intense ductile folding during highgrade retrograde metamorphism. Subsequently, the durbachitic pluton intruded discordantly into the granulite at around~340 Ma. The steep margin-parallel magmatic fabric in the durbachitic rocks may have recorded intrusive strain during emplacement. After the emplacement, but prior to the final solidification, the pluton was overprinted by the regional flat-lying fabric under lower pressure-temperature conditions (T = 765 ± 53°C; P = 0.76 ± 0.15 GPa). Based on this study and comparison with other ultrapotassic plutons, we suggest that the flat-lying fabrics, widespread throughout the exhumed lower to middle crust (Moldanubian Unit), exhibit major variations in character, intensity, kinematics, and shape of the fabric ellipsoid. These fabrics may have formed at different structural levels and in different parts of the root prior to~337Ma. Therefore, we suggest that this apparently ''single'' orogenic fabric recorded multiple deformation events and heterogenous finite deformation rather than reflecting a single displacement field within the orogenic root.

Deciphering the Variscan tectonothermal overprint and deformation partitioning in the Cadomian basement of the Teplá–Barrandian unit, Bohemian Massif

Hajná

Žák

Kachlík

et al. 2012

The Teplá-Barrandian unit (TBU) has long been considered as a simply bivergent supracrustal 'median massif' above the Saxothuringian subduction zone in the Variscan orogenic belt. This contribution reveals a much more complex style of the Variscan tectonometamorphic overprint and resulting architecture of the Neoproterozoic basement of the TBU. For the first time, we describe the crustal-scale NE-SW-trending dextral transpressional Krakovec shear zone (KSZ) that intersects the TBU and thrusts its higher grade northwestern portion severely reworked by Variscan deformation over a southeastern very low grade portion with well-preserved Cadomian structures and only brittle Variscan deformation. The age of movements along the KSZ is inferred as Late Devonian (*380-370 Ma). On the basis of structural, microstructural, and anisotropy of magnetic susceptibility data from the KSZ, we propose a new synthetic model for the deformation partitioning in the Teplá-Barrandian upper crust in response to the Late Devonian to early Carboniferous subduction and underthrusting of the Saxothuringan lithosphere. We conclude that the Saxothuringian/Teplá-Barrandian convergence was nearly frontal during *380-346 Ma and was partitioned into pure shear dominated domains that accommodated orogen-perpendicular shortening alternating with orogen-parallel high-strain domains that accommodated dextral transpression or bilateral extrusion. The synconvergent shortening of the TBU was terminated by a rapid gravity-driven collapse of the thickened lithosphere at *346-337 Ma followed by, or partly simultaneous with, dextral strike-slip along the Baltica margin-parallel zones, driven by the westward movement of Gondwana from approximately 345 Ma onwards.