Low- and high-angle, normal-sense faults present along the northern margin of the East Humboldt-Wood Hills metamorphic complex record a protracted history of episodic extensional unroofing. The earliest extension associatd with the exhumation of the metamorphic complex occurred in the mid-Eocene (about 50 Ma) during slip along the west-rooted Wells Peak fault. Subsequent extension developed during movement along the east-rooted Black Mountain fault system in the late Eocene (about 35 Ma). Continued exhumation of the high-grade metamorphic rocks, occurred during the late Oligocene to early Miocene (about 29--23 Ma) along a west-rooted, normal-sense, plastic-to-brittle shear zone exposed along the length of the East Humboldt Range and much of the Ruby Mountains. The mylonitic shear zone, Wells Peak fault, and Black Mountain fault system were all overprinted by the west-rooted, low- to high-angle Mary's River fault system which was active from mid-Miocene to Holocene. Broadly coeval extension in the Windermere Hills was also accommodated by the development of high-angle, north and east dipping normal faults between approximately 35-12 Ma and 12-10 Ma. ¿ American Geophysical Union 1993 |