Thermochronologic evidence for timing of denudation and rate of crustal extension of the south mountains metamorphic core complex and sierra estrella, Arizona

P. G. Fitzgerald, S. J. Reynolds, E. Stump, D. A. Foster, A. J W Gleadow

Research output: Contribution to journalArticle

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Apatite fission-track analysis of samples collected along the length of theSouth Mountains metamorphic core complex and in a vertical profile from the adjacent Sierra Estrella reveal rapid cooling during regional crustal extension. Fission-track ages of 17 samples from South Mountains overlap at the 2σ level and have a weighted mean of 17.5 ± 1.0 Ma. Mean fission-track lengths are all greater than 14 μm, indicating rapid cooling at about this time. Integrating these data with K-Ar and 40Ar/39Ar cooling ages of hornblende and biotite yields an average cooling rate of approximately 190°;C/my between 21 and 17 Ma for lower-plate rocks in the South Mountains. Four samples collected over 600 m of relief from the adjacent Sierra Estrella yield apatite ages with a weighted mean of 24.7 ± 0.4 Ma and mean track lengths greater than 14 μm, which also reflect rapid cooling. Geologic constraints suggest that the Sierra Estrella is most likely lower-plate with respect to the South Mountains detachment fault and that its uplift/cooling history is linked to the detachment-style denudation of the South Mountains core complex. If cooling simply reflects tectonic denudation of upper-plate rocks, the calculated rate of extension for the core complex is ≈ 0.3 cm/yr, a rate comparable to those estimated for other core complexes.

Original languageEnglish (US)
Pages (from-to)555-563
Number of pages9
JournalInternational Journal of Radiation Applications and Instrumentation. Part
Issue number4
StatePublished - 1993
Externally publishedYes


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