Techniques directly dating fault slip are few, limiting the ability to interpret the rock record of seismicity. Hematite is commonly found in fault zones, amenable to (U-Th)/He dating, and slip surface hematite may be reset by shear heating events and/or recrystallization. Glossy hematite-coated fault surfaces in the Wasatch fault footwall damage zone, Utah (USA), exhibit evidence of hematite cataclasis and preserve Pliocene hematite (U-Th)/He dates. Apatite (U-Th)/He and fission track data from the host gneiss indicate footwall unroofing through ∼2 km by ca. 4.5 Ma. Internally reproducible but disparate hematite (U-Th)/He dates 4.5 Ma and younger from isolated locations on a single fault surface do not reflect ambient cooling. We hypothesize that these dates, and associated iridescence and annealed crystal texture, document rapid cooling from friction-generated heat during small seismic slip events between ca. 4.5 and 2.5 Ma. Thus, hematite (U-Th)/He dating offers the potential to decipher thermal anomalies in the rock record associated with slip on 105–106 yr time scales.
Article
Linking hematite (UTh)/He dating with the microtextural record of seismicity in the Wasatch fault damagezone, Utah, USA
Geology
Document Type
Article
Publisher
Geological Society of America
Publication Date
4-15-2015
Disciplines
Abstract
Citation Information
Ault, A.K., Reiners, P.W., Evans, J.P., and Thomson, S.N., 2015, Linking hematite (UTh)/
He dating with the microtextural record of seismicity in the Wasatch fault damage
zone, Utah, Geology, v. 43, p. 771-774, doi:10.1130/G36897.1.