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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2 Citations (Scopus)

Abstract

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
Volume21
Issue number4
DOIs
StatePublished - 1993

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mountains
time measurement
cooling
fission
apatites
detachment
rocks
biotite
tectonics
histories
profiles

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title = "Thermochronologic evidence for timing of denudation and rate of crustal extension of the south mountains metamorphic core complex and sierra estrella, Arizona",
abstract = "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.",
author = "Fitzgerald, {Paul G} and Reynolds, {S. J.} and E. Stump and Foster, {D. A.} and Gleadow, {A. J W}",
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TY - JOUR

T1 - Thermochronologic evidence for timing of denudation and rate of crustal extension of the south mountains metamorphic core complex and sierra estrella, Arizona

AU - Fitzgerald, Paul G

AU - Reynolds, S. J.

AU - Stump, E.

AU - Foster, D. A.

AU - Gleadow, A. J W

PY - 1993

Y1 - 1993

N2 - 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.

AB - 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.

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