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, P. G.
AU - Reynolds, Stephen
AU - Stump, E.
AU - Foster, D. A.
AU - Gleadow, A. J W
N1 - Funding Information:
Acknowledgements--We thank Kerry Hegarty for collecting an early suite of samples, Kevin Hill for counting two of the apatite mounts, and Ed DeWitt for access to unpublished age data. Suzanne Baldwin and Gordon Lister are thanked for discussions on metamorphic core complexes in general and the South Mountains in particular. PGF and ES acknowledge support from National Science Foundation grant DPP8612938 and DPP8816655. We thank the Neeley Nuclear Research Center at the Georgia Institute of Tech- nology for irradiation of samples dated at ASU. Sue Selkirk kindly drafted the maps. Support for AJWG and DAF came from the Australian Research Council. Irradiation of LTU samples at the HIFAR Reactor was supported by a grant from the Australian Institute of Nuclear Science and Engineering. Trevor Dumitru, Charles Naeser, Gordon Haxel and Ray Donelick are thanked for reviews on various versions of the manuscript.
PY - 1993/10
Y1 - 1993/10
N2 - 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.
AB - 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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M3 - Conference article
AN - SCOPUS:0027672766
SN - 0191-278X
VL - 21
SP - 555
EP - 563
JO - Nuclear Tracks and Radiation Measurements
JF - Nuclear Tracks and Radiation Measurements
IS - 4
T2 - Proceedings of the 7th International Workshop on Fission-Track Thermochronology
Y2 - 13 July 1992 through 17 July 1992
ER -