Western Old Woman Mountains shear zone: Evidence for late ductile extension in the Cordilleran orogenic belt

Journal Article · Sun Sep 01 00:00:00 EDT 1991 · Geology; (United States)

DOI:https://doi.org/10.1130/0091-7613(1991)019<0893:WOWMSZ>2.3.CO;2· OSTI ID:5942150

Carl, B S; Miller, C F ^[1]; Foster, D A ^[2]

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1. Vanderbilt Univ., Nashville, TN (United States)
2. State Univ. of New York, Albany (United States)

Rocks within the 1-km-thick Western Old Woman Mountains shear zone (WSZ) contain ductilely deformed quartz and ductilely and brittlely deformed feldspars, indicating greenschist to lower amphibolite facies mylonitization. Foliation measured in 73 Ma mid-crustal granitoids within the zone generally dips west-southwest, and sense-of-shear indicators demonstrate top-to-the-west sense of movement parallel to gently southwest plunging lineation. The tip of the shear zone is not exposed, but 10 km to the west unmetamorphosed Late Cretaceous-age upper crust is present. The WSZ is thus most simply interpreted as a normal-sense low-angle shear zone. Timing of deformation is constrained to the interval 73 to ca. 65 Ma by the age of deformed granitoids and {sup 40}Ar/{sup 39}Ar chronology. This interval coincides with a period of rapid cooling of rocks now exposed in the Old Woman Mountains that probably resulted from 4 to 8 km of unroofing. The authors suggest that movement along the WSZ is responsible for at least some of this unroofing. The proposed history involves tectonic denudation along a low-angle ductile shear zone and is similar to that demonstrated for Tertiary Cordilleran metamorphic core complexes.

• OSTI ID: 5942150
• Journal Information: Geology; (United States), Vol. 19:9; ISSN 0091-7613
• Country of Publication: United States
• Language: English

Related Subjects

58 GEOSCIENCES
CALIFORNIA
MOUNTAINS
TECTONICS
AGE ESTIMATION
ARGON 39
ARGON 40
COMPACTING
CONTINENTAL CRUST
CRETACEOUS PERIOD
DEFORMATION
GEOLOGIC HISTORY
GEOLOGY
ISOTOPE DATING
ISOTOPE RATIO
METAMORPHIC ROCKS
RESERVOIR ROCK
SHEAR
ARGON ISOTOPES
BETA DECAY RADIOISOTOPES
BETA-MINUS DECAY RADIOISOTOPES
DEVELOPED COUNTRIES
EARTH CRUST
EVEN-EVEN NUCLEI
EVEN-ODD NUCLEI
GEOLOGIC AGES
ISOTOPES
LIGHT NUCLEI
MESOZOIC ERA
NORTH AMERICA
NUCLEI
RADIOISOTOPES
ROCKS
STABLE ISOTOPES
USA
YEARS LIVING RADIOISOTOPES
580000* - Geosciences