Late Eocene Onset And Progression Of Extension With Exhumation In Southeastern Humboldt Range Nevada
The East Humboldt Range (EHR), located in northeastern Nevada, includes metamorphosed rocks surrounded by sedimentary rocks. Transportation of this metamorphic core complex to its present location includes a dimension of vertical uplift, along with regional extension. The metamorphosed rocks of the EHR include minerals capable of recording temperature histories associated with rising from mid-crustal depths. A recently discovered kyanite-bearing schist in the southeastern EHR requires peak pressures and temperatures above 7 kb and 625oC, implying tectonic burial to depths >22 km. This deep-seated metamorphic terrain lies < 500 m beneath a large scale fault system known as the Ruby-EHR detachment fault inferred to have caused its exhumation.To determine timing and progression of uplift beneath this fault, mineral samples collected along a 20 km WNW-trending transect mimic the direction of gradual exhumation from depth. Sampled minerals, including biotite, muscovite, and K-feldspar, are dated using 40Ar/39Ar thermochronometry. These data record cooling through a temperature unique to each mineral known as its closure temperature. In addition, the diffusive loss of argon from K-feldspar allows modeling of cooling histories over a range extending from 450oC to <150oC. The initial phase of cooling beneath the normal fault system and the onset of uplift on the detachment fault occurred from 42 Ma to 35 Ma. Following initial cooling and extension, K-feldspar modeling reveals a reheating event after 28 Ma, and return to cooling signifying renewed extension (See companion presentation by A. Carte). The second cooling event occurs across a range of dates from 26 Ma to 14 Ma from the southeast to northwest. Comparing cooling ages along the transect, records a westward propagating wave of rapid cooling consistent with rotation of the fault to its current angle. Thus it supports the tectonic process of rolling hinge style exhumation.
Allen J McGrew
Primary Advisor's Department
Stander Symposium poster
"Late Eocene Onset And Progression Of Extension With Exhumation In Southeastern Humboldt Range Nevada" (2019). Stander Symposium Posters. 1607.