A Multi‐Proxy Approach Using Zircon (U‐Th)/He Thermochronometry and Biomarker Thermal Maturity to Robustly Capture Earthquake Temperature Rise Along the Punchbowl Fault, California

During an earthquake, work done to overcome fault friction is dissipated as heat. Coseismic temperature rise, critical for identifying and constraining the magnitude of past earthquakes, is difficult to accurately quantify. To address this issue, we compare two temperature‐sensitive geochemical syst...

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Bibliographic Details
Published in:Geochemistry, geophysics, geosystems : G3 geophysics, geosystems : G3, 2022-04, Vol.23 (4), p.n/a
Main Authors: Armstrong, E. M., Ault, A. K., Bradbury, K. K., Savage, H. M., Polissar, P. J., Thomson, S. N.
Format: Article
Language:English
Subjects:
Apatite
Biomarkers
coseismic temperatures
Earth surface
earthquake
Earthquakes
Fault lines
Fault zones
Friction
Geochemistry
Heat
High temperature
Mathematical models
Numerical models
Organic matter
Physics
Punchbowl fault
radiation damage
Seismic activity
Temperature measurement
Temperature rise
Temporal variability
Temporal variations
Zircon
zircon (U‐Th)/He thermochronometry
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Summary:During an earthquake, work done to overcome fault friction is dissipated as heat. Coseismic temperature rise, critical for identifying and constraining the magnitude of past earthquakes, is difficult to accurately quantify. To address this issue, we compare two temperature‐sensitive geochemical systems, zircon (U‐Th)/He (ZHe) thermochronometry and thermal maturity of organic matter (biomarkers), which respond to short‐duration, high temperatures. Models of prior biomarker data from the Punchbowl fault (PF), CA, indicate coseismic temperatures of ∼465–1,065°C in the principal slip zone (PSZ; Savage & Polissar, 2019, https://doi.org/10.1029/2019gc008225) depending on prescribed thickness of the deforming zone. We resampled two PF sample sites and acquired high‐spatial resolution ZHe data (n = 45 individual analyses) from the PSZ and fault core gouge, together with adjacent crystalline basement and Punchbowl Formation rocks. Results define a positive ZHe date‐effective U (eU) trend from ∼10 to 60 Ma and ∼20–700 ppm eU with a plateau at ∼65 Ma at >700 ppm eU. This pattern suggests the PSZ and fault core gouge share a similar thermal history to material outside the PF. Individual apatite (U‐Th)/He dates (n = 5) from an undeformed Punchbowl Formation sample are ∼4 Ma for grains with ∼30–150 ppm eU, implying rapid cooling and exhumation at that time due to PF activity. Zircon damage‐diffusivity relationships inform a suite of numerical models that collectively bracket coseismic temperatures on the PF to
ISSN:1525-2027
1525-2027
DOI:10.1029/2021GC010291