Differential stress, strain rate, and temperatures of mylonitization in the Ruby Mountains, Nevada: Implications for the rate and duration of uplift

Journal Article · Sun Jun 10 04:00:00 EDT 1990 · Journal of Geophysical Research; (United States)

DOI:https://doi.org/10.1029/JB095iB06p08569· OSTI ID:5009679

Hacker, B R; Yin, An; Christie, J M ^[1]; Snoke, A W ^[2]

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1. Univ. of California, Los Angeles (United States)
2. Univ. of Wyoming, Laramie (United States)

Knowledge of the magnitude of the differential stress during the formation of mylonitic rocks provides constraints on mechanical and thermal models for the exhumation of the metamorphosed footwalls of major low-angle detachment faults. The authors have analyzed the differential flow stress during the mylonitization of quartoze rocks in the Ruby Mountains, Nevada, using grain-size piezometers and kinetic laws for grain growth. Quartzites from mylonitic shear zones in Lamoille Canyon and Secret Creek gorge have grain sizes of 91-151 {mu}m and 42-64 {mu}m, respectively. The peak temperature during mylonitization was 630 {plus minus} 50C, and analysis of grain-growth kinetics indicates that mylonitization continued during cooling to temperatures {le}450C. Quartz grain-size piezometers suggest that the mylonitization occurred under differential stresses of 38-64 MPa, or maximum shear stresses of 19-32 MPa. Extrapolation of quartzite flow laws indicates that the mylonitization occurred at strain rates between 10{sup {minus}10} and 10{sup {minus}13} s{sup {minus}1}; arguments presented in the paper suggest that the likely range of strain rates is 10{sup {minus}11} to 10{sup {minus}12} s{sup {minus}1}. These strain rates are compatible with displacement rates of the order of 23 mm yr{sup {minus}1} along a 1.5-km-thick simple shear zone. Such a shear zone dipping 15{degree} would produce an uplift rate of 5.8 km/m.y. and a horizontal extension rate of 22 km/m.y. This uplift rate indicates that midcrustal mylonitic rocks could have been lifted up along a 1.5-km-thick simple shear zone dipping 15{degree} in 2.6 m.y.

• OSTI ID: 5009679
• Journal Information: Journal of Geophysical Research; (United States), Journal Name: Journal of Geophysical Research; (United States) Vol. 95:B6; ISSN 0148-0227; ISSN JGREA
• Country of Publication: United States
• Language: English

Related Subjects

58 GEOSCIENCES
580000* -- Geosciences
COMPRESSION
CRYSTAL STRUCTURE
DEVELOPED COUNTRIES
FEDERAL REGION IX
GEOLOGIC FORMATIONS
GEOLOGIC HISTORY
GRAIN GROWTH
GRAIN SIZE
GROUND UPLIFT
METAMORPHIC ROCKS
MICROSTRUCTURE
MOUNTAINS
NEVADA
NORTH AMERICA
OROGENESIS
PIEZOMETRY
QUARTZITES
RESERVOIR TEMPERATURE
ROCKS
SCHISTS
SIZE
STRAIN RATE
STRESS ANALYSIS
STRESSES
USA