Fission track thermochronologic constraints on the timing and nature of major Middle Tertiary extension, Ruby Mountains - East Humboldt Range, Nevada

Conference · Tue Jan 01 04:00:00 EST 1985 · Geol. Soc. Am., Abstr. Programs; (United States)

OSTI ID:6643497

Dokka, R K; Mahaffie, M J; Snoke, A W

Fission Track (FT) apatite, zircon, and sphene ages were determined from both mylonitic and non-mylonitic rocks of the Ruby Mountains-East Humboldt Range metamorphic core complex. The analyzed sample suite included various mylonitic orthogneisses as well as amphibolitic orthogneisses from the non-mylonitic infrastructural core. Porphyritic biotite granodiorite of the Oligocene Harrison Pass pluton was also dated. FT ages are concordant and range in age from 27 - 24 Ma. These dates reflect rapid cooling of the lower plate from temperatures above 250/sup 0/C to below 100/sup 0/C during the early Miocene. The general concordance of the FT dates with /sup 40/Ar//sup 39/Ar biotite and hornblende plateau ages from the same sample suite suggest an even more pronounced cooling history. This rapid cooling history is considered to reflect large-scale tectonic denudation (intracrustal thinning), a manifestation of intense crustal extension. Mylonitic rocks that originally formed along ductile shear zones in the middle crust (10-15 km) were quickly brought near the surface and juxtaposed against brittly distended rocks deformed under upper crustal conditions. FT data firmly establish the upper age limit on the timing of mylonitization during the shear zone deformation. This rapid cooling interval also coincides with the inferred age of extensive landscape disruption and the development of an alluvial fan-lacustrine system which included the periodic emplacement of landslide deposits (megabreccias).

• Research Organization: Louisiana State Univ., Baton Rouge (USA)
• OSTI ID: 6643497
• Report Number(s): CONF-8510489-
• Conference Information: Journal Name: Geol. Soc. Am., Abstr. Programs; (United States) Journal Volume: 17
• Country of Publication: United States
• Language: English

Related Subjects

58 GEOSCIENCES
580100 -- Geology & Hydrology-- (-1989)
580400* -- Geochemistry-- (-1989)
AGE ESTIMATION
AMPHIBOLITES
APATITES
CENOZOIC ERA
CHEMISTRY
DEFORMATION
FEDERAL REGION IX
FISSION TRACKS
GEOCHEMISTRY
GEOLOGIC AGES
GEOLOGIC FAULTS
GEOLOGIC FRACTURES
GEOLOGIC HISTORY
GEOLOGIC STRUCTURES
GNEISSES
GRANITES
GRANODIORITES
IGNEOUS ROCKS
METAMORPHIC ROCKS
MINERALS
NEVADA
NORTH AMERICA
OXYGEN COMPOUNDS
PARTICLE TRACKS
PETROGENESIS
PHOSPHATE MINERALS
PLUTONIC ROCKS
ROCKS
SILICATE MINERALS
SILICATES
SILICON COMPOUNDS
TECTONICS
TEMPERATURE MEASUREMENT
TERTIARY PERIOD
TITANITE
TRANSITION ELEMENT COMPOUNDS
USA
ZIRCON
ZIRCONIUM COMPOUNDS
ZIRCONIUM SILICATES