Geology and geochronology of the southeast border of the Bitterroot dome: implications for the structural evolution of the mylonitic carapace

Thesis/Dissertation · Sat Jan 01 04:00:00 EST 1983

OSTI ID:5926822

Garmezy, L

Geologic and geochronologic study of the southeast corner of the Bitterroot dome has delimited the evolution of the shallow-dipping mylonitic carapace that developed on the granitic rocks of the Bitterroot lobe of the Idaho Batholith. Reset hornblende from the zone of mylonitization, in conjunction with /sup 40/Ar//sup 39/Ar age spectra of hornblende, muscovite, biotite, and K-feldspar from non-mylonitic samples, indicates that mylonitization began approx.45.5 Ma ago at a depth of probably greater than 9 to 10 km, and continued for approx.2 Ma, during a period of rapid uplift of the dome (.1 to .3 cm/y). The process of mylonitization caused shear heating of as much as 200/sup 0/C above ambient conditions. With only two exceptions, detailed kinematic analyses of mylonitic fabric indicate eastward tectonic transport of the hanging wall throughout the 500-1000 m-thick mylonitic zone. The extensional origin of the mylonitic carapace is supported by the /sup 40/Ar//sup 39/Ar data that indicate a contemporaneity between mylonitization and regional Eocene volcanism and extension. The data show that mylonitization was not associated with either the development of thrust faults in the Sapphire tectonic block or initial intrusion and crystallization of the batholith.

• OSTI ID: 5926822
• Country of Publication: United States
• Language: English

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