Shear localisation, strain partitioning and frictional melting in a debris avalanche generated by volcanic flank collapse

Amy Hughes, Jackie E. Kendrick, Guido Edgard Salas Álvarez, Paul A. Wallace, François Legros, Giulio Di Toro, Yan Lavallée

Research output: Contribution to journalArticlepeer-review

2 Scopus citations

Abstract

The Arequipa volcanic landslide deposit to the east of Arequipa (Peru) originated from the Pichu Pichu volcanic complex, covering an area ~200 km2. The debris avalanche deposit exhibits internal flow structures and basal pseudotachylytes. We present field, microstructural and chemical observations from slip surfaces below and within the deposit which show varying degrees of strain localisation. At one locality the basal shear zone is localised to a 1–2 cm thick, extremely sheared layer of mixed ultracataclasite and pseudotachylyte containing fragments of earlier frictional melts. Rheological modelling indicates brittle fragmentation of the melt may have occurred due to high strain rates, at velocities of >31 m s−1 and that frictional melting is unlikely to provide a mechanism for basal lubrication. Elsewhere, we observe a ~40 cm thick basal shear zone, overprinted by sub-parallel faults that truncate topological asperities to localise strain. We also observe shear zones within the avalanche deposit, suggesting that strain was partitioned. In conclusion, we find that deformation mechanisms fluctuated between cataclasis and frictional melting during emplacement of the volcanic debris avalanche; exhibiting strain partitioning and variable shear localisation, which, along with underlying topography, changed the resistance to flow and impacted runout distance.

Original languageEnglish
Article number104132
JournalJournal of Structural Geology
Volume140
DOIs
StatePublished - Nov 2020

Bibliographical note

Funding Information:
This work was conducted during a PhD study supported by the Natural Environment Research Council (NERC) EAO Doctoral Training Partnership and is fully funded by NERC whose support is gratefully acknowledged (Grant Number NE/L002469/1). We acknowledge financial support from the European Research Council Starting Grant on Strain Localisation in Magma (SLiM, No. 306488) and Jackie Kendrick was supported by an Early Career Fellowship of the Leverhulme Trust (ECF-2016-325). We also thank Tom Knott (University of Leicester) for XRF measurements and Jonathan Fellowes (University of Manchester) for technical assistance during EPMA analysis. We thank the editor Joao Hippertt and an anonymous reviewer for their well-thought, precise and constructive comments.

Funding Information:
This work was conducted during a PhD study supported by the Natural Environment Research Council (NERC) EAO Doctoral Training Partnership and is fully funded by NERC whose support is gratefully acknowledged (Grant Number NE/L002469/1 ). We acknowledge financial support from the European Research Council Starting Grant on Strain Localisation in Magma (SLiM, No. 306488) and Jackie Kendrick was supported by an Early Career Fellowship of the Leverhulme Trust ( ECF-2016-325 ). We also thank Tom Knott (University of Leicester) for XRF measurements and Jonathan Fellowes (University of Manchester) for technical assistance during EPMA analysis. We thank the editor Joao Hippertt and an anonymous reviewer for their well-thought, precise and constructive comments.

Publisher Copyright:
© 2020 The Authors

Keywords

  • Cataclasis
  • Pseudotachylyte
  • Sector collapse
  • Shear localisation
  • Strain partitioning

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