The nature and development of shear zone junctions
Final Report Abstract
Ductile shear zones are usually imagined as straight disc-shaped high strain domains in rocks with simple gradients of vorticity and strain. Most shear zones, however, have a more complex geometry and are part of a network of interconnected zones of variable orientation that branch in a complex manner. Much is known about branching and interconnection of brittle faults, mainly due to 3D information obtained by the minerals industry. However, little is known about the branching systems of ductile shear zones and the way in which they form and develop. We investigated branching of ductile shear zones with a geometrical model, numerical modelling and field examples. The geometrical model predicts two main types of branches, freeway type with three identical branches; and zipper type geometries with two different types of branches. Numerical modelling shows that the rate of weakening within shear ones has a significant influence on their geometry. Shear zone branches gradually develop into junctions, and these change in character with increasing strain and complexity of branching. In most numerical and field examples, freeway shear zone junctions develop first, while zipper shear zone junctions form later. The geometric types of junctions formed in numerical models are similar to those in small scale field examples in simple tectonic settings, but differ significantly from those in large, lithosphere scale examples, where predating lithological elements largely determine the final geometry. An understanding of shear zone branches and their geometry can be important for fluid circulation in shear zone networks and the formation of ore deposits, and also for the storage of radioactive waste in basement rocks.
Publications
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2014. A strike-slip core complex from the Najd fault system, Arabian Shield. Terra Nova 26, 387-394
Meyer, S. E., Passchier, C, Abu-Alam, T, Stüwe, K
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2014. Exhumation of Mid-Crustal Rocks in the Arabian-Nubian Shield. The Baladaya Complex of Saudi Arabia. Journal of Petrology, 55,1941-1964
Abu-Alam, T., Hassan, M., Stüwe, K., Meyer, S., Passchier, C.
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2015. “Branching shear zones in the Arabian –Nubian shield” PhD thesis, Uni Mainz
Meyer, S. E.
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2016. How to make a transverse triple junction—New evidence for the assemblage of Gondwana along the Kaoko-Damara belts, Namibia. Geology 44, 843-846
Passchier, C, Trouw, R, Schmitt, R
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2016. Shear zone junctions: Of zippers and freeways. Journal of Structural Geology 95,188-202
Passchier, C W, Platt, J P
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2016. Zipper junctions: A new approach to the intersections of conjugate strike-slip faults. Geology 44, 795-798
Platt, J P, Passchier, C W.
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2017. Development of branching brittle and ductile shear zones: A numerical study. Geochemistry, Geophysics, Geosystems 18
Meyer, S E, Kaus, B, Passchier, C
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2017. Mimicking shear zones: An example from Wadi Filk, Jordan. Journal of Structural Geology 98, 1-12
Meyer, S. E., Passchier, C, Jarrar, G. H., Ghanem, H, Yaseen, N
