Thermochronologic evidence for timing of denudation and rate of crustal extension of the South Mountains metamorphic core complex and Sierra Estrella, Arizona

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

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17 Citations (Scopus)

Abstract

Apatite fission-track analysis of samples collected along the length of the South 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 approximately 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
JournalNuclear Tracks and Radiation Measurements
Volume21
Issue number4
StatePublished - Oct 1993

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Apatites
Cooling
History
Apatite
Rocks
Tectonics
biotite

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Thermochronologic evidence for timing of denudation and rate of crustal extension of the South Mountains metamorphic core complex and Sierra Estrella, Arizona. / Fitzgerald, Paul G; Reynolds, S. J.; Stump, E.; Foster, D. A.; Gleadow, A. J W.

In: Nuclear Tracks and Radiation Measurements, Vol. 21, No. 4, 10.1993, p. 555-563.

Research output: Contribution to journalArticle

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abstract = "Apatite fission-track analysis of samples collected along the length of the South 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 approximately 0.3 cm/yr, a rate comparable to those estimated for other core complexes.",
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