Folding (Structural Geology)

2D analog modeling of fold-and-thrust belts: dynamic interactions with syncontractional sedimentation and erosion

by Jonny Wu

Convoluted accommodation structures in folded rocks

by Tim Dodwell

Accepted for publication in Philos. Mag Special Issue : Instabilities across the scales III

Co-authored with Giles Hunt

A simpli ed variational model for the formation of convoluted accommodation structures, as seen in the hinge zones of... more A simplied variational model for the formation of convoluted accommodation structures, as seen in the hinge zones of larger-scale geological folds, is presented. The model encapsulates
some important and intriguing nonlinear features, notably: infinite critical loads, formation of plastic hinges, and buckling on different length scales. An inextensible elastic beam is forced by
uniform overburden pressure and axial load into a V-shaped geometry dictated by formation of a plastic hinge. Using variational methods developed in [1], energy minimization leads to representation as a fourth-order nonlinear dierential equation with free boundary conditions. Equilibrium solutions are found using numerical shooting techniques. Under the Maxwell
stability criterion, it is recognized that global energy minimizers can exist with convoluted physical shapes. For such solutions, parallels can be drawn with some of the accommodation
structures seen in exposed escarpments of real geological folds.

Multilayered folding with voids

by Tim Dodwell

accepted for publication by Phil. Trans A Special Issue on layered structures.

In the deformation of layered materials such as geological strata, or stacks of paper, mechanical properties compete... more In the deformation of layered materials such as geological strata, or stacks of paper, mechanical properties compete with the geometry of layering. Smooth, rounded corners lead to
voids between the layers, while close packing of the layers results in geometrically-induced curvature singularities. When voids are penalized by external pressure, the system is forced
to trade off these competing effects, leading to sometimes striking periodic patterns.

In this paper we construct a simple model of geometrically nonlinear multilayered structures under axial loading and pressure confinement, with non-interpenetration conditions
separating the layers. Energy minimisers are characterized as solutions of a set of fourthorder nonlinear differential equations with contact-force Lagrange multipliers, or equivalently
of a fourth-order free-boundary problem. We numerically investigate the solutions of this free boundary problem, and compare them with the periodic solutions observed experimentally.

3D Analysis of an Ordovician igneous ensemble: A complex magmatic structure hidden in a polydeformed allochthonous Variscan unit

by Ruben Diez Fernandez

Journal of Structural Geology, 2009
"Journal of Structural Geology Student Author of the Year Award 2009"
Díez Fernández, R. and Martínez Catalán, J.R.

The basal units of the allochthonous complexes of NW Iberia represent a fragment of the external edge of Gondwana... more The basal units of the allochthonous complexes of NW Iberia represent a fragment of the external edge of Gondwana subducted and subsequently exhumed during the Variscan collision. The structural analysis carried out in orthogneissic massifs of the southern part of one of these, the Malpica–Tui Unit, reveals the generation of recumbent folds and associated axial planar foliation during their exhumation. These folds nucleated in irregular igneous bodies that were initially deformed during the subduction event and show east to southeast vergence. Down-plunge projection of surface data and a series of regularly spaced cross-sections have been used to build 3D models of the two main bodies of orthogneiss, of calc-alkaline and peralkaline compositions respectively. The first is presently a lens-shaped body folded in a recumbent syncline, whereas the peralkaline gneiss, also affected by a train of asymmetric recumbent folds in the south, exhibits in the north a fold-like structure which is interpreted as inherited from its primary geometry, that of a ring dike pluton.

Variscan recumbent folding of Ordovician plutons in the Malpica-Tui Unit (NW Iberia)

by Ruben Diez Fernandez

Trabajos de Geologia, 2009
Díez Fernández, R. and Martínez Catalán, J.R.

A structural analysis in orthogneissic massifs of a subducted fragment of the external edge of Gondwana during the... more A structural analysis in orthogneissic massifs of a subducted fragment of the external edge of Gondwana during the onset of the Variscan collision has been carried out, and reveals the generation of recumbent folds and associated axial planar foliation formed during its exhumation. These folds nucleated in irregular igneous bodies, which were initially deformed during the subduction event, show east to southeast vergence. Down-plunge projection of surface data and series of regularly spaced crosssections have been used to build 3D models of the two main bodies of orthogneiss and to constrain their original igneous shape.

Neotectonic activity in the Upper Rhine Graben-Jura Mountains junction (North-Western Switzerland and adjacent France)

by Kamil Ustaszewski

Control of preexisting faults on geometry and kinematics in the northernmost part of the Jura fold-and-thrust belt

by Kamil Ustaszewski

Latest Pliocene to recent thick-skinned tectonics at the Upper Rhine Graben-Jura Mountains junction

by Kamil Ustaszewski

Tectonic evolution of a continental subduction-exhumation channel: Variscan structure of the basal allochthonous units in NW Spain

by Ruben Diez Fernandez

Tectonics (2011)
Díez Fernández, R., Martínez Catalán, J.R., Arenas, R. and Abati, J.

A regional study starting from detailed geological mapping has been carried out in the Malpica-Tui Complex of Galicia... more A regional study starting from detailed geological mapping has been carried out in the Malpica-Tui Complex of Galicia in NW Spain. The complex is formed by two units representing pieces of the external edge of Gondwana, subducted and exhumed during the Variscan collision. The study shows that synsubduction and early synexhumation structures in continental subduction channels tends to be obscured and even erased once exhumation is complete. Detailed structural analysis, matched with the knowledge of the history, and available data for other Galician basal units have elucidated the major structures developed during the subduction-exhumation process. The results include evidence of the plate convergence causing early Variscan continental subduction of the Gondwana margin. Subduction was followed by exhumation driven by ductile thrusting within the subduction channel, which, in turn, provoked crustal duplication in the subducted slab and modified the initial tectonometamorphic architecture of the subduction wedge. The next step was accretion to the adjacent continental domains, placing the subduction wedge on top of unsubducted parts of the Gondwana margin via ductile thrusting. Thrusting was preceded by progressive propagation of a train of recumbent folds toward the foreland that affected the previous structural stack. Subsequent transference of oceanic (Rheic) and peri-Gondwanan terranes to the Gondwana margin took place by out-of-sequence thrusting followed by crustal extensional collapse and strike-slip tectonics.

Plegamiento recumbente en la Serra do Galiñeiro (Pontevedra)

by Ruben Diez Fernandez

Geogaceta, 2006
Díez Fernández, R., Martínez Catalán, J.R. and Abati, J.

Three main deformation phases (D1, D2 and D3) have been identified in the Serra do Galiñeiro using macro and... more Three main deformation phases (D1, D2 and D3) have been identified in the Serra do Galiñeiro using macro and microstructural analysis. The geometric characterization of those showing macrostructural elements (D2 and D3), has been made with the down-plunge method, for the folds related to each phase. In order to apply this technique, the fold axis orientation has been calculated from the structural data collected. The results of this research prove the existence of recumbent folds in the southern part of the Malpica-Tui Unit, and the presence of a stretching lineation related to the main foliation and the recumbent folds, and clearly oblique to their axes.