Peer-reviewed publications
Mechanism and Prevention of Irreversible Trapping
of Atmospheric He During Mineral Crushing
Cox, Miller, Hofmann, Farley (2022)
Geochronology
Highlights:
Adsorption of atmospheric He during sample crushing can increase the measured bulk He concentrations and thereby produce incorrect ages
We provide a model for the impact of adsorptive contamination of He for geochronology
Crushing samples under a low-He atmosphere (water, ethanol, N2) can prevent irreversible adsorption of He
Rapid phase identification of apatite and zircon grains
for geochronology using X-ray micro-computed tomography
Cooperdock/Hofmann, Tibbetts, Carrera, Takase, Celestian (2022)
Geochronology (Chron), 4, 501–515
Apatite and zircon are the most widely used minerals for dating rocks, but they can be difficult to identify in crushed rock samples. Incorrect mineral identification results in wasted analytical resources and inaccurate data. We show how X-ray computed tomography can be used to rapidly and accurately distinguish apatite from zircon based on density variations, and provide non-destructive 3D grain-specific size, shape, and inclusion information for improved data quality.
A rusty record of weathering and groundwater movement in the hyperarid Central Andes
Shaw, Evenstar, Cooper, Adams, Boyce, Hofmann, Farley (2021)
Geochemistry, Geophysics, Geosystems
Key Points
Hematite (U-Th-Sm)/He weathering geochronology constrains late Miocene exhumation rates in the Atacama Desert of northern Chile
Hematite records prolonged post-hyperaridity development of weathering profiles in the Atacama Desert
Exhumation is the most important driver of relative water table descent during supergene enrichment of porphyry copper deposits
Exposure dating of detrital magnetite using 3He enabled by microCT
and calibration of the cosmogenic 3He production rate in magnetite
Hofmann, Cooperdock, West, Hildebrandt, Strößner, Farley (2021)
Geochronology (GChron)
Highlights:
Mineral inclusions contribute a significant amount of 3He, which leads to incorrect age estimates
Analyzing only inclusion-free magnetite significantly improves the quality of the data
We calibrate the production rate of 3He in magnetite by comparing our data to a known 10Be exposure age determined in quartz from the same samples
New 26Al/10Be and (U-Th)/He constraints on the age
of the Upland Complex, central Mississippi River Valley
Odom, Hofmann, Van Arsdale, and Granger (2020), Geomorphology
Paper Supplementary Material: A, B
Highlights:
26Al/10Be and (U-Th)/He dates provide a Pliocene minimum age for the Upland Complex.
The Upland Complex is likely mid-Pliocene and is no older than Late Miocene.
Formation of the Upland Complex may be related to widespread Pliocene aggradation.
Odom et al. (2020): Stratigraphic columns and (U-Th)/He age data of iron-oxide cement of the Upland Complex.
Hofmann et al. (2020): Top: Experimental setup to degas iron-oxide aliquots with high O2 partial pressure in order to prevent U-loss. Bottom: Single-aliquot dates from a samples with known age acquired with this method.
U-loss associated with laser-heating of hematite and goethite in vacuum
during (U-Th)/He dating and prevention using high O2 partial pressure
Hofmann, Treffkorn, and Farley (2020), Chemical Geology
Paper Supplementary Material: A B C D E Pre-print
Highlights:
Laser-heating of goethite and hematite samples can lead to loss of U.
U-loss correlates with phase change from hematite to magnetite.
Phase change and U-loss can be prevented by high O2 partial pressure.
Highly retentive samples can be fully extracted with this method.
This method can be automated to yield reproducible and accurate (U–Th)/He ages.
Evidence for >5 Ma paleoexposure of an Eocene-Miocene paleosol
of the Bohnerz Formation, Switzerland
Hofmann, Farley, and Reichenbacher (2017), EPSL
Highlights
We studied ferruginous pisoliths from a paleosol of the Bohnerz Formation, Switzerland.
Goethite (U–Th)/He formation ages are between 50 Ma and 8 Ma.
Cosmogenic 3He concentrations suggest cosmic ray paleo-exposure duration >5 Ma.
Clay soils might be more stable than previously thought.
Fine-grained soil iron-oxides might be rententive to He.
Hofmann et al. (2017): Top: Photograph of red paleosol on weathered Jurassic limestone overlain by Miocene Molasse units (left) and stratigraphic column (right). Bottom: Results of (U-Th)/He ages and 3He concentrations of pisoliths and 3He concentrations of fine-grained iron-oxides in clay.
Conference Presentations
Cassady, V. C., Petryshyn, V. A., Bernhard, J. M., Hofmann, F., Berelson, W. M., Cooperdock, E. H. G., and Corsetti, F. A.: Microbial and mineral impact on texture in incipient dendrolitic microbialites, Little Hot Creek, CA, Geological Society of America Meeting 2023, Pittsburgh, PA, USA.
Hofmann, F., Cooperdock, E.H.G., McDermott, R.: A survey of inclusions and Li concentrations in magnetite for (U-Th)/He and cosmogenic 3He dating, International Conference on Thermochronology 2023, Riva del Garda, Italy.
Rojas, A., Cooperdock, E.H.G., Hofmann, F., Lackey, J. S.: A multichronometer study of a San Andreas Fault piercing point, International Conference on Thermochronology 2023, Riva del Garda, Italy.
Cooperdock, E.H.G., Rojas, A., Hofmann, F., Valliere, L., Hummel, B., Carrera, A., Grabiec, J., Tibbetts, R.M.C.: ZAMO! 3D quantification of inclusions in zircon, apatite, magnetite, and olivine with implications for thermochronology, International Conference on Thermochronology 2023, Riva del Garda, Italy.
Cassady, V. C., Petryshyn, V. A., Bernhard, J. M., Hofmann, F., Berelson, W. M., Cooperdock, E. H. G., Bottjer, D., and Corsetti, F. A.: Spatial Relationships between Microbes and Minerals in Incipient Carbonate Dendrolitic Microbialites, Little Hot Creek, CA, American Geophysical Union Fall Meeting 2022, Chicago, IL.
Hofmann, Florian; Cooperdock, Emily; and McDermott, Robert: Assessing the suitability of magnetite for (U-Th)/He and cosmogenic 3He exposure dating: a survey of inclusions and Li concentrations, Abstract 186-8, Geological Society of America Annual Meeting 2022, Denver, CO.
Regan, Sean; Marble, Sean; Williams, Michael; Roeske, Sarah, and Hofmann, Florian: Compositional diversification in Eocene arc plutonic rocks along the Denali fault: Implications for arc magma sources and evolution, Abstract 44-10, Geological Society of America Annual Meeting 2022, Denver, CO.
Cooperdock, Emily; Hofmann, Florian; Collins, Ryley; Carrera, Anahi; Takase, Aya; and Celestian, Aaron: Rapid phase identification of apatite and zircon grains for geochronology using micro-computed tomography, Abstract #10225, Goldschmidt 2022, Hawai’i.
Hofmann, Florian; Cooperdock, Emily H.G.; West, A. Joshua; Hildebrandt, Dominic; Strößner, Kathrin; Farley, Kenneth A.: MicroCT as a tool to improve the accuracy of cosmogenic 3He exposure dating in magnetite, American Geophysical Union Fall Meeting 2021, online.
Hildebrandt, Dominic; Hofmann, Florian; Merchel, Silke; Rugel, Georg; Lachner, Johannes; Martschini, Martin; Friedrich, Anke: Using in-situ 36Cl exposure dating of glacial erratics to establish a retreat chronology of the Iller Piedmont Glacier (Southern Germany), The 15th International Conference on Accelerator Mass Spectrometry (AMS-15), Sydney/online.
Hofmann, Florian; Cooperdock, Emily H.G.; West, A. Joshua; Hildebrandt, Dominic; Strößner, Kathrin; Farley, Kenneth A.: Cosmogenic 3He exposure dating of alluvial surfaces using detrital magnetite enabled by microCT scanning, 2021 Southern California Earthquake Center Annual Meeting, online.
Hofmann, Florian; Treffkorn, Jonathan; Farley, Kenneth A.: The high-pO2 method to prevent U-loss during single-aliquot hematite (U-Th)/He measurement: Development, implementation, and automation, 17th International Conference on Thermochronology, Santa Fe, New Mexico.
Hildebrandt, Dominic; Hofmann, Florian; Merchel, Silke; Rugel, Georg; Strößner, Kathrin; Akber, Sami; Friedrich, Anke M.: Timing of the post-LGM retreat of the Iller Piedmont Glacier (Southern Germany) based on in-situ 36Cl exposure dating of glacial erratics, GeoKarlsruhe 2021.
Hofmann, Florian; Hildebrandt, Dominic; Friedrich, Anke M.: Timing and correlation of glacial and glaciofluvial sediments in the German Alpine Foreland, American Geophysical Union Fall Meeting, Online, December 2020.
Hofmann, Florian; McPhillips, Devin; Kendrick, Katherine J; Farley, Kenneth A: Utilizing Pedogenic Iron-oxides for Cosmogenic 3He Geochronology of Soils, American Geophysical Union Fall Meeting, San Francisco, December 2019.
Hofmann, Florian; Farley, Kenneth A.; Treffkorn, Jonathan: Single-aliquot hematite (U-Th)/He dating: Preventing U loss during laser heating by increased O2 partial pressure, American Geophysical Union Fall Meeting, Washington DC, December 2018.
Hofmann, Florian; Farley, Kenneth A.: Loss of U during laser-heated single-aliquot hematite (U-Th)/He dating, Goldschmidt 2018, Boston, MA, August 2018.
Cox, Stephen E.; Miller, Hayden; Farley, Kenneth A.; Hofmann, Florian: Anomalous trapping of noble gases during sample crushing, American Geophysical Union, Fall Meeting 2017, New Orleans, LA, December 2017.
Hofmann, Florian; McPhillips, Devin; Kendrick, Katherine; Farley, Kenneth A.: The potential of fine-grained pedogenic iron-oxide for cosmogenic 3He dating, Geological Society of America Annual Meeting 2017, Seattle, WA, October 2017.
Hofmann, Florian: Evidence for >5 Ma paleo-exposure of an Eocene–Miocene paleosol of the Bohnerz Formation, Switzerland, 10th Annual Los Angeles Basin Earth and Planetary Sciences Student Research Symposium, University of California, Los Angeles, California, April 2017.
Hofmann, Florian; Farley, Kenneth A: Eocene-Pleistocene goethite precipitation and exposure history of the Bohnerz Formation, Germany and Switzerland, Geological Society of America Annual Meeting 2016, Denver, Colorado, September 2016.
Hofmann, Florian; Farley, Kenneth A: Evidence for >5 Ma paleo-exposure of a paleosol in the Bohnerz Formation, Switzerland, Geological Society of America Annual Meeting 2015, Baltimore, Maryland, November 2015.
Hofmann, Florian; Rosenau, Matthias; Schreurs, Guido, und Friedrich, Anke M.: Quantifying the effects of material properties on analog models of critical taper wedges, European Geosciences Meeting - EGU2012, Vienna, April 2012.
Hofmann, Florian; Rosenau, Matthias; Schreurs, Guido, und Friedrich, Anke M.: The Effect of Material Properties on the Structural Development of Analogue Coulomb Wedges, GeoMunich2011, Munich, September 2011.
Hofmann, Florian; Carena, Sara und Friedrich, Anke M.: Organizing Field Trips for Large Groups of Undergraduate Students: Our Experience from the Berliner Hütte Field Exercise, Zillertal, Austria, GeoMunich2011, Munich, September 2011.
Evers, Serjoscha; Engelmann, Oliver und Hofmann, Florian: "Heureka" in Geological Education? Scientific Research by Undergraduate Students - Learning through Analogue Modeling; GeoMunich2011, Munich, September 2011.
Hofmann, Florian; Rosenau, Matthias und Schreurs, Guido: Critical Taper in Sandbox Experiments? Investigations into the Differences between Pushed and Pulled Wedge Experiments, International Geological Modelling Conference - GeoMod 2010, Lisbon, September 2010.
Buiter, S.; Schreurs, G. M. Albertz, C. Beaumont, C. Burberry, J.-P. Callot, C. Cavozzi, M. Cerca, J.-H. Chen, E. Cristallini, A. Cruden, L. Cruz, M. Cooke, T. Crook, J.-M. Daniel, D. Egholm, S. Ellis, T. Gerya, L. Hodkinson, F. Hofmann, V Garcia, C. Gomes, C. Grall, Y. Guillot, C. Guzmán, T. Nur Hidayah, G. Hilley, B. Kaus, M. Klinkmüller, H. Koyi, W. Landry, C.-Y. Lu, J. Macauley, B. Maillot, C. Meriaux, Y. Mishin, F. Nilfouroushan, C.-C. Pan, C. Pascal, D. Pillot, R. Portillo, M.Rosenau, W. Schellart, R. Schlische, P. Souloumiac, A. Take, B. Vendeville, M. Vettori, M. Vergnaud, S.-H. Wang, M. Withjack, D. Yagupsky, Y. Yamada: Benchmarking the Sandbox: Quantitative Comparisons of Numerical and Analogue Models of Brittle Wedge Dynamics, American Geophysical Union, Fall Meeting 2010, Abstract #T52A-01