Tertiary structure and thermal history of the Harquahala and Buckskin Mountains, west central Arizona: Implications for denudation by a major detachment fault system

Journal Article · Sat Nov 10 04:00:00 EST 1990 · Journal of Geophysical Research; (United States)

DOI:https://doi.org/10.1029/JB095iB12p19973· OSTI ID:5319667

Richard, S M ^[1]; Fryxell, J E ^[2]; Sutter, J F ^[3]

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1. Univ. of California, Santa Barbara (USA)
2. Geological Survey, Flagstaff, AZ (USA)
3. Geological Survey, Reston, VA (USA)

The Harquahala and Buckskin Mountains lie in the footwall of the Whipple-Buckskin-Bullard detachment system. In the Harquahala Mountains, Mesozoic fabric and structure are progressively more intensely overprinted by penetrative Tertiary deformation toward the northeastern part of the range. Tertiary mylonitic deformation is recognized by the presence of deformed Miocene mafic dikes and characteristic textural features. Evidence of Tertiary plastic deformation is absent southwest of Sunset Pass. In the central and southwestern Harquahala Mountains, {sup 40}Ar-{sup 39}Ar age spectra from K-feldspar, muscovite, and hornblende and total gas ages from biotite indicate Late Cretaceous to early Tertiary cooling to argon closure temperatures. Biotite and K-feldspar from the area northeast of Sunset Pass record rapid early to middle Miocene cooling. Reconstruction of the original geometry of the detachment system indicate that the initial dip of the detachment fault was most probably between 30{degree} and 40{degree}. Thus the Harquahala Mountains are a tilted block exposing of the order of a 10-km section through the pre-Tertiary crust. Heterogeneous Proterozoic gneiss, sparse Paleozoic and Mesozoic metasedimentary rocks, and an Oligocene plutonic complex are extensively overprinted by Tertiary mylonitic fabrics in the Buckskin Mountains Hornblende {sup 40}Ar-{sup 39}Ar cooling ages suggest that most of these rocks were below hornblende closure temperature by early Tertiary time, except in the vicinity of the Oligocene plutonic complex. Feldspar and biotite {sup 40}Ar-{sup 39}Ar cooling ages suggest that the footwall of the Whipple detachment system experienced a more uniform cooling history in the Buckskin Mountains than in the Harquahala Mountains; cooling ages between about 13 and 20 Ma are recorded throughout the range with no consistent spatial pattern of ages.

• OSTI ID: 5319667
• Journal Information: Journal of Geophysical Research; (United States), Journal Name: Journal of Geophysical Research; (United States) Vol. 95:B12; ISSN 0148-0227; ISSN JGREA
• Country of Publication: United States
• Language: English

Related Subjects

58 GEOSCIENCES
580000* -- Geosciences
AGE ESTIMATION
AMPHIBOLE
ARGON 39
ARGON 40
ARGON ISOTOPES
ARIZONA
BETA DECAY RADIOISOTOPES
BETA-MINUS DECAY RADIOISOTOPES
BIOTITE
CENOZOIC ERA
COOLING
CRETACEOUS PERIOD
DEFORMATION
DEVELOPED COUNTRIES
DIKES
EVEN-EVEN NUCLEI
EVEN-ODD NUCLEI
FEDERAL REGION IX
FELDSPARS
GEOLOGIC AGES
GEOLOGIC FAULTS
GEOLOGIC FRACTURES
GEOLOGIC HISTORY
GEOLOGIC STRUCTURES
GEOLOGY
HORNBLENDE
IGNEOUS ROCKS
ISOTOPE DATING
ISOTOPE RATIO
ISOTOPES
LIGHT NUCLEI
MESOZOIC ERA
MICA
MINERALS
MIOCENE EPOCH
MOUNTAINS
MUSCOVITE
NORTH AMERICA
NUCLEI
PLUTONIC ROCKS
PRECAMBRIAN ERA
RADIOISOTOPES
RESERVOIR TEMPERATURE
ROCKS
SILICATE MINERALS
STABLE ISOTOPES
TECTONICS
TERTIARY PERIOD
USA
YEARS LIVING RADIOISOTOPES