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Intercalibration of multiple thermochonometric systems at the Little Devil's Postpile contact aureole
  • +2
  • David L Shuster,
  • Peter W Reiners,
  • Leif Karlstrom,
  • Jennifer L Schmidt,
  • Peter K Zeitler
David L Shuster
Dept. Earth and Planetary Science, Dept. Geosciences, Dept. Geophysics, Dept. Earth and Environmental Sciences, Dept. Earth and Environmental Sciences, Dept. Geological Sciences, UC Berkeley, University of Arizona, Stanford University, Lehigh University, Lehigh University Richard A Ketcham, University of Texas

Corresponding Author:

Peter W Reiners
Dept. Earth and Planetary Science, Dept. Geosciences, Dept. Geophysics, Dept. Earth and Environmental Sciences, Dept. Earth and Environmental Sciences, Dept. Geological Sciences, UC Berkeley, University of Arizona, Stanford University, Lehigh University, Lehigh University Richard A Ketcham, University of Texas
Leif Karlstrom
Dept. Earth and Planetary Science, Dept. Geosciences, Dept. Geophysics, Dept. Earth and Environmental Sciences, Dept. Earth and Environmental Sciences, Dept. Geological Sciences, UC Berkeley, University of Arizona, Stanford University, Lehigh University, Lehigh University Richard A Ketcham, University of Texas
Jennifer L Schmidt
Dept. Earth and Planetary Science, Dept. Geosciences, Dept. Geophysics, Dept. Earth and Environmental Sciences, Dept. Earth and Environmental Sciences, Dept. Geological Sciences, UC Berkeley, University of Arizona, Stanford University, Lehigh University, Lehigh University Richard A Ketcham, University of Texas
Peter K Zeitler
Dept. Earth and Planetary Science, Dept. Geosciences, Dept. Geophysics, Dept. Earth and Environmental Sciences, Dept. Earth and Environmental Sciences, Dept. Geological Sciences, UC Berkeley, University of Arizona, Stanford University, Lehigh University, Lehigh University Richard A Ketcham, University of Texas

Abstract

A fundamental assumption in thermochronology is extrapolation of kinetic parameters over geologic timescales, temperatures, and mineral compositions that often differ significantly from the laboratory conditions used to quantify them. In this study, we aim to test and intercalibrate kinetic parametersof multiple thermochronometric systems using a tractable, natural thermal perturbation associated with the emplacement of a small, young basalt intrusion into granite in the Sierra Nevada, the site of the classic study of Calk and Naeser (1973). We collected a suite of samples along a linear transect orthogonal to the contact, from which the minerals apatite, zircon, titanite, epidote, magnetite, biotite, horneblende, K-feldspar, and plagioclase were separated. Our results to date reveal that the (U-Th)/He system in apatite was completely reset within ~7 m of the contact during basalt emplacement ~8 Ma. At distances >16 m from the contact, the apatite He ages are uniformly ~58 Ma, which likely represents the background (i.e., unperturbed) cooling ages of the granite. Apatite 4 He/ 3 He thermochronometry and an observed transition from background-to rest-ages of these samples are quantitatively consistent with a higher degree of thermal perturbation nearer to the contact. As predicted by our current quantification of radiation damage accumulation influence on He diffusion kinetics (Flowers et al, 2009), we observe correlation between the "effective uranium" concentration and He ages of individual apatite crystals, particularly within this transition zone. In contrast, the (U-Th)/He system in zircon is only partially reset ~7 m from the contact, and the background cooling ages at distances >10 m are ~78 Ma, consistent with a 40 Ar/ 39 Ar age-spectrum from a distal K-feldspar that rises from ~70 to ~80 Ma; both observations are consistent with the relative, experimentally determined temperature sensitivities of these minerals. We present ongoing numerical modeling that provides a framework with which to quantitatively compare and assess these results with forthcoming 40 Ar/ 39 Ar and fission track results in various mineral systems. Inversion of data using these multi-material conductive models will be used to assess the sensitivity of results to assumptions about geometry (1D, 2D, 3D), duration of basalt emplacement, and pre-intrusion cooling rate.
28 Sep 2023Submitted to ESS Open Archive
28 Sep 2023Published in ESS Open Archive