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Hot faults; iridescent slip surfaces with metallic luster document high-temperature ancient seismicity in the Wasatch fault zone, Utah, USA

James P. Evans, Mitchell R. Prante, Susanne U. Janecke, Alexis K. Ault and Dennis L. Newell
Hot faults; iridescent slip surfaces with metallic luster document high-temperature ancient seismicity in the Wasatch fault zone, Utah, USA
Geology (Boulder) (May 2014) 42 (7): 623-626

Abstract

We document new geological indicators of ancient seismicity in the form of highly reflective, iridescent, hematite-coated fault surfaces. Small faults that cut the Paleoproterozoic Farmington Canyon Complex in the footwall damage zone of the Brigham City segment of the Wasatch fault (Utah, USA) are smooth to striated surfaces, tens of square centimeters to 30 m (super 2) in area. The dull-rusty to high-metallic luster and moderate- to high-gloss surfaces exhibit multicolored elliptical iridescent patches approximately 0.5-3 cm across. Preexisting hematite crystals were deformed during slip on 1-200-mm-thick slip surfaces. Textural observations, X-ray diffraction, X-ray photoelectron spectroscopy, electron backscattered diffraction analysis, surface metrology, and similarity to experimentally formed iridescent spots in rocks and metals indicate that iridescence is associated with high-temperature (>300 degrees C) reduction of iron (Fe (super 3+) to Fe (super 2+) ) and associated conversion of hematite to magnetite. We propose that the iridescent slip surfaces in the Wasatch fault damage zone are the result of seismic slip and flash heating at asperities along the small faults. The thousands of these surfaces represent coseismic or aftershock deformation down to magnitude 3 in the exhumed footwall damage zone of the Wasatch fault.


ISSN: 0091-7613
EISSN: 1943-2682
Coden: GLGYBA
Serial Title: Geology (Boulder)
Serial Volume: 42
Serial Issue: 7
Title: Hot faults; iridescent slip surfaces with metallic luster document high-temperature ancient seismicity in the Wasatch fault zone, Utah, USA
Affiliation: Utah State University, Department of Geology, Logan, UT, United States
Pages: 623-626
Published: 20140522
Text Language: English
Publisher: Geological Society of America (GSA), Boulder, CO, United States
References: 51
Accession Number: 2014-104614
Categories: Structural geologyStratigraphy
Document Type: Serial
Bibliographic Level: Analytic
Annotation: GSA Data Repository item 2014231
Illustration Description: illus.
N37°00'00" - N42°00'00", W114°04'60" - W109°04'60"
Secondary Affiliation: University of Arizona, USA, United States
Country of Publication: United States
Secondary Affiliation: GeoRef, Copyright 2017, American Geosciences Institute. Reference includes data from GeoScienceWorld, Alexandria, VA, United States. Reference includes data supplied by the Geological Society of America, Boulder, CO, United States
Update Code: 201452
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