Hematite is common in fault zones. Iron is the 4th most abundant element in Earth’s crust and hematite grows in a range of shallow fault rocks due to the redox potential of diverse Fe-bearing minerals.
Hematite is amenable to (U-Th)/He thermochronometry because it incorporates trace but measurable amounts of U and Th, negligible He, and retains He over geologic timescales. Our group integrates textural, geochemical, and thermochronometric data from fault zones to document the timing, temperature, and slip rates - ranging from seismic to aseismic - of hematite-coated slip surfaces But hematite (U-Th)/He thermochronometry can not be interpreted in a vacuum (!!!). Accurate interpretation of hematite He data requires independent constraints on hematite aliquot grain size distribution and textural characterization from multi-scale microscopy, as well as data on the ambient thermal conditions during and after hematite formation from conventional thermochronometry and numerical modeling (Ault, 2020; Cooperdock and Ault, 2020). FONTTTS team members have and are applying this approach in a diverse suite of fault systems including the Wasatch fault zone, UT; eastern Denali fault zone, Yukon, Canada; southern San Andreas fault system in Mecca Hills, CA; central Front Range, CO; central Iran; and the Rio Grande rift, NM. This work was initially supported by NSF grant (EAR-1419828) with co-PIs P. Reiners (UA), J. Evans (USU), and D. Shuster (BGC) and collaborators J. Caine (USGS), S. Thomson (UA). |
Publications (denotes * graduate, ** undergraduate, *** postdoctoral mentee)
Cooperdock, E.H.G., and Ault, A.K., in press, Fe-oxide (U-Th)/He thermochronology: new perspectives on faults, fluids, and heat, invited review article, Elements.
Ault, A.K., 2020, Hematite fault rock thermochronometry and textures inform fault zone processes, invited review article, Journal of Structural Geology, v. 133, p. 104002, doi: 10.1016/j.jsg.2020.1004002.
Ault, A.K., Gautheron, C., King, G., 2019, Innovations in (U-Th)/He, fission track, and trapped charge thermochronometry with applications to earthquakes, weathering, surface-mantle connections, and growth and decay of mountains, invited review article for AGU Centennial, Tectonics, v. 38, p. 3705-3739, doi: 10.1029/2018TC005312.
**Jensen, J.L., Siddoway, C.S., Reiners, P.W., Ault, A.K., Thomson, S.N., Steele-MacInnis, M., 2018, Single-crystal hematite (U-Th)/He dates and fluid inclusions document widespread Cryogenian sand injection in crystalline basement, Earth and Planetary Science Letters, v. 500, p. 145-155, doi: 10.1016/j.epsl.2018.08.021.
¨Calzolari, G., Rossetti, F., Ault, A.K., Lucci, F., Olivetti, V., Nozaem, R., 2018, Hematite (U-Th)/He thermochronometry constrains strike-slip faulting on the Kuh-e-Faghan fault, central Iran, Tectonophysics, v. 728-729, p. 41-54, doi: 10.1016/j.tecto.2018.01.023.
*Moser, A.C, Evans, J.P., Ault, A.K., Janecke, S.U., Bradbury, K.K., 2017, (U-Th)/He thermochronometry reveals Pleistocene punctuated deformation and synkinematic hematite mineralization in the Mecca Hills, southernmost San Andreas Fault zone, Earth and Planetary Science Letters, v. 476, p. 87-99, doi: 10.1016:/j.epsl.2017.07.039.
*McDermott, R.G., Ault, A.K., Evans, J.P., Reiners, P.W., 2017, Thermochronometric and textural evidence for seismicity via asperity flash heating on exhumed hematite fault mirrors, Wasatch fault zone, UT, USA, Earth and Planetary Science Letters, v. 471, p. 85-93, doi:10.1016/j.epsl.2017.04.020.
Ault, A.K., Frenzel, M., Reiners, P.W., Woodcock, N.H., and Thomson, S.N., 2016, Record of paleofluid circulation in faults revealed by hematite (U-Th)/He and apatite fission-track dating: an example from Gower Peninsula fault fissures, Wales, Lithosphere, v. 8, p. 379-385, doi: 10.1130/L522.1.
Ault, A.K., Reiners, P.W., Evans, J.P., and Thomson, S.N., 2015, Linking hematite (U-Th)/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.
Cooperdock, E.H.G., and Ault, A.K., in press, Fe-oxide (U-Th)/He thermochronology: new perspectives on faults, fluids, and heat, invited review article, Elements.
Ault, A.K., 2020, Hematite fault rock thermochronometry and textures inform fault zone processes, invited review article, Journal of Structural Geology, v. 133, p. 104002, doi: 10.1016/j.jsg.2020.1004002.
Ault, A.K., Gautheron, C., King, G., 2019, Innovations in (U-Th)/He, fission track, and trapped charge thermochronometry with applications to earthquakes, weathering, surface-mantle connections, and growth and decay of mountains, invited review article for AGU Centennial, Tectonics, v. 38, p. 3705-3739, doi: 10.1029/2018TC005312.
**Jensen, J.L., Siddoway, C.S., Reiners, P.W., Ault, A.K., Thomson, S.N., Steele-MacInnis, M., 2018, Single-crystal hematite (U-Th)/He dates and fluid inclusions document widespread Cryogenian sand injection in crystalline basement, Earth and Planetary Science Letters, v. 500, p. 145-155, doi: 10.1016/j.epsl.2018.08.021.
¨Calzolari, G., Rossetti, F., Ault, A.K., Lucci, F., Olivetti, V., Nozaem, R., 2018, Hematite (U-Th)/He thermochronometry constrains strike-slip faulting on the Kuh-e-Faghan fault, central Iran, Tectonophysics, v. 728-729, p. 41-54, doi: 10.1016/j.tecto.2018.01.023.
*Moser, A.C, Evans, J.P., Ault, A.K., Janecke, S.U., Bradbury, K.K., 2017, (U-Th)/He thermochronometry reveals Pleistocene punctuated deformation and synkinematic hematite mineralization in the Mecca Hills, southernmost San Andreas Fault zone, Earth and Planetary Science Letters, v. 476, p. 87-99, doi: 10.1016:/j.epsl.2017.07.039.
*McDermott, R.G., Ault, A.K., Evans, J.P., Reiners, P.W., 2017, Thermochronometric and textural evidence for seismicity via asperity flash heating on exhumed hematite fault mirrors, Wasatch fault zone, UT, USA, Earth and Planetary Science Letters, v. 471, p. 85-93, doi:10.1016/j.epsl.2017.04.020.
Ault, A.K., Frenzel, M., Reiners, P.W., Woodcock, N.H., and Thomson, S.N., 2016, Record of paleofluid circulation in faults revealed by hematite (U-Th)/He and apatite fission-track dating: an example from Gower Peninsula fault fissures, Wales, Lithosphere, v. 8, p. 379-385, doi: 10.1130/L522.1.
Ault, A.K., Reiners, P.W., Evans, J.P., and Thomson, S.N., 2015, Linking hematite (U-Th)/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.