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| Titel |
Origins of Mt. St. Helens Cataclasites: Experimental Insights |
| VerfasserIn |
L. A. Kennedy, J. K. Russell |
| Konferenz |
EGU General Assembly 2009
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 11 (2009) |
| Datensatznummer |
250028993
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| Zusammenfassung |
| Thick (1-3 m) layers of fault rocks that formed during the 2004-2006 dome building
events are interpreted to be linked to the "drumbeat" microseismicity associated
with dome building (Iverson et al. 2006). We experimentally deformed Mt. St.
Helen’s dacite with the intent of reproducing the fault textures observed in nature and
placing further constraints on their conditions of formation. Experiments were run at
confining pressures of 0, 25, 50, and 75MPa, at room temperature and strain rate of
~ 1 x 10-4 s-1. The dacite starting material has low porosity (7.3 and 7.7%), a
uniform bulk composition (65 wt% SiO2), is highly crystalline, containing 41-45%
euhedral to subhedral phenocrsyts and microphenocrysts of plagioclase, hypersthene
and amphibole set in a microcrystalline matrix. The experimental run products
show a progressive increase in peak strength with increasing confining pressure
and all show brittle behavior, characterized by a rapid stress drop. Run products
contain macroscopic fractures with deformation extremely localized around the shear
fractures. Natural and experimentally deformed dacites show extreme grain size
reduction. Total grain size distribution plots (wt%) show that natural gouge sieved
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