Rapid Miocene Extensional Unroofing of the Southwestern East Humboldt Range Metamorphic Core Complex, Nevada
The Ruby Mountains and East Humboldt Range of northeastern Nevada expose exceptionally high grade metamorphosed rocks, the tectonic history of which has been hotly debated for decades. To resolve this debate, we collected a WNW-trending transect spanning 20 km of muscovite, biotite, and/or potassium-feldspar bearing samples for dating by the 40Ar/39Ar method. This method allows us to model the timing and progression of cooling, and therefore the uplift history of these rocks. The results from the southernmost transect indicate an early phase of cooling prior to 35Ma (See companion presentation by J. Jeruc). Here, I present results from the western flank of the range that record a later phase in the cooling history. A series of five samples from this transect imply that cooling below 200°C began prior to 30 Ma. The samples then cooled slowly until about 20-24Ma, when they experienced a reheating event to above 250°C. Following reheating, the samples cooled rapidly to below 100°C between 20 and 14Ma, with cooling occuring progressively later towards the WNW. The termination of cooling at 14 Ma is in excellent agreement with fault gouge dating results reported by Haines and van der Pluijm (2010). The progression of cooling ages implies that unroofing proceeded at a rate of 1.8 - 2.4 km/m.y. Although some researchers suggest that the chief trigger of this phase of extension was the drifting of western North America over the Yellowstone hotspot, these results indicate that the onset of extension predated hotspot related volcanism by at least 3 m.y.
Allen J McGrew
Primary Advisor's Department
Stander Symposium poster
"Rapid Miocene Extensional Unroofing of the Southwestern East Humboldt Range Metamorphic Core Complex, Nevada" (2019). Stander Symposium Posters. 1717.