Formation and evolution of the basal layer in large landslides has important implications
for processes that reduce frictional resistance to sliding. In this report, we show
that zircon geochronology and tectonic provenance can be used to investigate the
basal layer of the gigantic-scale Markagunt gravity slide of Utah, USA. Basal layer
and clastic injectite samples have unique tectonic chronofacies that identify the rock
units that were broken down during emplacement. Our results show that basal material
from sites on the former land surface is statistically indistinguishable and formed
primarily by the breakdown of upper plate lithologies during sliding. Decapitated injectites
have a different tectonic chronofacies than the local basal layer, with more
abundant lower plate-derived zircons. This suggests clastic dikes formed earlier in
the translation history from a structurally deeper portion of the slide surface and a
compositionally different basal layer before being translated to their current position.
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Structural Relationships Across the Sevier Gravity Slide of Southwest Utah and Implications for Catastrophic Translation and Emplacement Processes of Long Runout Landslides
The physical processes that facilitate long‐distance translation of large‐volume gravity slides remain poorly understood. To better understand these processes and the controls on runout distance, we conducted an outcrop and microstructural characterization of the Sevier gravity slide across the former land surface and summarize findings of four key sites. The Sevier gravity slide is the oldest of three mega‐scale (>1,000 km2) collapse events of the Marysvale volcanic field (Utah, USA). Field observations of intense deformation, clastic dikes, pseudotachylyte, and consistency of kinematic indicators support the interpretation of rapid emplacement during a single event. Furthermore, clastic dikes and characteristics of the slip zone suggest emplacement involved mobilization and pressurized injection of basal material. Across the runout distance, we observe evidence for progressive slip delocalization along the slide base. This manifests as centimeter‐ to decimeter‐thick cataclastic basal zones and abundant clastic dikes in the north and tens of meters thick basal zones characterized by widespread deformation of both slide blocks and underlying rock near the southern distal end of the gravity slide. Superimposed on this transition are variations in basal zone characteristics and slide geometry arising from interactions between slide blocks during dynamic wear and deposition processes and pre‐existing topography of the former land surface. These observations are synthesized into a conceptual model in which the presence of highly pressurized fluids reduced the frictional resistance to sliding during the emplacement of the Sevier gravity slide, and basal zone evolution controlled the effectiveness of dynamic weakening mechanisms across the former land surface.
more » « less- Award ID(s):
- 2113155
- NSF-PAR ID:
- 10420720
- Publisher / Repository:
- DOI PREFIX: 10.1029
- Date Published:
- Journal Name:
- Geochemistry, Geophysics, Geosystems
- Volume:
- 24
- Issue:
- 5
- ISSN:
- 1525-2027
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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