Ductile deformation without localization

insights from numerical modeling

Robyn L. Gardner*, Sandra Piazolo, Nathan R. Daczko, Lynn Evans

*Corresponding author for this work

Research output: Contribution to journalArticle

Abstract

Strain is easily localized in a polyphase rock, especially if the rock undergoes syntectonic weakening processes. However, there is ample field evidence for distributed, rather than localized, deformation at the outcrop to hundreds of square kilometer scale. In these areas, distributed strain is evidenced by the presence of continuous foliations and a lack of distinct high-strain zones. Here, we use numerical modeling of viscous deformation to investigate the conditions that allow distributed rather than localized deformation. We identify three strain localization regimes for a system with rheologically strong and weak phases with or without stress-induced weakening. Regime I is characterized by distributed strain. It forms where either deformation-induced interconnection of the weak phase is not possible or the initial weak phase area is intermediate to high (i.e., > ~40–60% of total depending on weak phase geometry). Their resultant bulk strength is either strong or weak, respectively. Regime II is characterized by variably distributed areas of strain localization and develops if the initial proportion of weak phases is intermediate (i.e., 40–60% weak phase depending on geometry) and syntectonic weakening causes an increase (up to ~12%) of weak phase proportion. Regime III exhibits significant strain localization and only develops if the initial proportion of weak phases is relatively low (<20%) and syntectonic weakening increases the proportion of weak phases by over ~12%. Here, high-strain zones readily form irrespective of the initial distribution of rheologically weak and hard phases, and bulk strength is intermediate.

Original languageEnglish
Pages (from-to)5710-5726
Number of pages17
JournalGeochemistry, Geophysics, Geosystems
Volume20
Issue number12
Early online date11 Nov 2019
DOIs
Publication statusPublished - Dec 2019

Bibliographical note

Copyright 2019 American Geophysical Union.

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