Zipper junctions: A new approach to the intersections of conjugate strike-slip faults

Abstract

Intersecting pairs of simultaneously active faults with opposing slip sense present geometrical and kinematic problems. Such faults rarely offset each other but usually merge into a single fault, even when they have displacements of many kilometers. The space problems involved are solved by lengthening the merged fault (zippering up the conjugate faults) or splitting it (unzippering). This process can operate in thrust, normal, and strike-slip fault settings. Examples of conjugate pairs of large-scale strike-slip faults that may have zippered up include the Garlock and San Andreas faults in California (USA), the North and East Anatolian faults (Turkey), the Karakoram and Altyn Tagh faults (Tibet), and the Tonale and Giudicarie faults (southern Alps). Intersecting conjugate ductile shear zones behave in the same way on outcrop and micro-scales. Zippering may produce complex and significant patterns of strain and rotation in the surrounding rocks, depending on the angle between the faults and the relative strength of the blocks they bound. A zippered fault will have a slip rate equal to the vector sum of the slip rates on the merging faults, unless that displacement is transferred into or out of the system by distributed strain in the surrounding rocks.

Push-pull driving of the Central America Forearc in the context of the Cocos-Caribbean-North America triple junction

“…The lack of strike-slip activity along the volcanic arc in western Guatemala can be interpreted as a propagation towards the southeast of a tectonic suture on a closing zipper-type triple junction (also called extraction fault) 19,85,86 . In this kind of junctions the strike-slip motion in the closing fault is substituted by a transpressional deformation prior to its definitive suturing 87 .…”

Oblique convergence and strain partitioning in the outer deformation front of NE Himalaya

“…It has been proposed that segments of active faults with opposing slip sense are rarely offsets each other in reality, but often merge into single fault system, resulting in geometrical and kinematic problems 51 , 52 . The space and kinematic problems can be resolved by lengthening the merged faults (zipping) or splitting it (unzipping), named as “Zipper junctions” 51 , 52 . We proposed an opening “Zipper junctions” analogy to explain Shillong Plateau/Assam-Brahmaputra valley sliver and Indo-Burmese wedge interaction process (Fig.…”

Eburnean deformation pattern of Burkina Faso and the tectonic significance of shear zones in the West African craton

“…Shear sense inversion is required along curved lens-bounding shear zones throughout anastomosed shear networks. Kinematic complexities further arise at zipper junctions between shear zones (Hudleston, 1999;Platt and Passchier, 2016) within such networks. Therefore, the protracted convergence period (> 30 My) over which strain field 1 has evolved could result locally in apparently complex kinematic configurations due to shear zones interactions achieving the preservation of the kinematic coherency of the regional structural pattern.…”

“…The third reason is that by favoring a local phase approach, one tends not to consider the spatial kinematic diversity of localities as part of a progressive/bulk deformation pattern that would be coherent on a regional scale (examples of regional kinematic integration are provided, for instance, by Martelat et al, 2000;Gapais et al, 2005;Harris and Bédard, 2014;Cochelin et al, 2017). The last and fourth reason is that one must consider fabrics and shear zones rotation and the zipping/ unzipping of shear zones (Platt and Passchier, 2016) during the deformation history of regional structures (e.g., Bouroum-Goren bend; Fig. 5).…”

“…Kinematic model for the growth of the Bouroum-Goren restraining bend in between the Markoye shear zone (to the East) and the Ouahigouya shear zones (to the west): (a) early bending stage; (b) final configuration. The model implies the closure of zipper junctions(Platt and Passchier, 2016) at both tips of the restraining bend.…”