Gardner, RL, Piazolo, S and Daczko, NR (2016) Shape of pinch and swell structures as a viscosity indicator: Application to lower crustal polyphase rocks. Journal of Structural Geology, 88. pp. 32-45. ISSN 0191-8141
Abstract
Pinch and swell structures occur where a more competent layer in a weaker matrix is subjected to layer-parallel extension. In this contribution, we use numerical models to explore the use of pinch and swell structure shape symmetry and asymmetry as a determinant of relative viscosity between layers. Maximum asymmetry is attained when the matrix viscosity on one side is subtly weaker than the competent layer, while the other side is significantly weaker. Our numerical results are directly applied to asymmetrically developed pinch and swell structures in exposed lower continental crust. Here, shape geometries observed in a shear zone comprised of plagioclase-dominated, garnet-dominated and mixed amphibole-plagioclase-dominated bands, reveals that the plagioclase-dominated band is the most competent band and is marginally stronger (2×) and significantly stronger (10–40×) than the fine grained garnet-dominated and mixed amphibole-plagioclase-dominated band, respectively. Based on the experimentally determined viscosity of a plagioclase-dominated material and quantitative microstructural analysis, the viscosity range of the natural rock bands is 2.8 × 1015 to 1.1 × 1017 Pa s. Consequently, the assumption that the experimentally-derived plagioclase flow law is an appropriate proxy for the middle to lower continental crust may lead to a viscosity over-estimation by up to forty times.
Metadata
Item Type: | Article |
---|---|
Authors/Creators: |
|
Keywords: | Pinch and swell; Boudin; Shape asymmetry; Viscosity; Polyphase rocks; Lower crust |
Dates: |
|
Institution: | The University of Leeds |
Academic Units: | The University of Leeds > Faculty of Environment (Leeds) > School of Earth and Environment (Leeds) > Inst of Geophysics and Tectonics (IGT) (Leeds) |
Depositing User: | Symplectic Publications |
Date Deposited: | 01 Feb 2017 12:16 |
Last Modified: | 11 Jan 2023 14:13 |
Published Version: | https://doi.org/10.1016/j.jsg.2016.04.012 |
Status: | Published |
Publisher: | Elsevier |
Identification Number: | 10.1016/j.jsg.2016.04.012 |
Open Archives Initiative ID (OAI ID): | oai:eprints.whiterose.ac.uk:111451 |