Wildcat Peak, Kaibito Plateau, Arizona – Prominent N-S trending Miocene dike complex

I was drafting a lecture, ‘StoryMaps – a Communication Tool for the Geosciences’, for an environmental planning class at the University of New Mexico, when I spotted a prominent black smudge on the Kaibito Plateau, 5.5 miles NW of Tonalea, on Navajo Nation lands of northeastern Arizona. The coal-black smudge has a radius of ~ 0.5 mile, elongated along a north-south trend, and mantles the outcropping Navajo Sandstone (Jurassic-age).  Prominent joint structures in the Navajo Sandstone are oriented north-south.

A closer look reveals a small knob, Wildcat Peak, mantled by dark volcanic float (i.e., rock debris). The float occurs at the intersection of several north-south trending intrusive basaltic(?) dikes.  Apparently, as the dikes ascended through Earth’s crust, they exploited the lower stress field provided by the local north-south joint sets.

(For those with the free Google Earth (GE) application, go to 36°22'35.50"N, 111° 2'6.90"W to more closely examine the dikes converging on Wildcat Peak .)

The dike system extents 3.5 miles south of the Wildcat Peak, and another 0.8 miles to the north, for a total length of ~ 4.5 mile. Mostly continuous for its entire length, the dike thickens to a maximum of about 10 feet as it nears Wildcat Peak; measuring small distances on Google Earth imagery may yield substantial error.

Billingsley & others (2012) report the dike complex as Miocene-age with an Ar/Ar age of 19.05 Ma. Wildcat Peak, which I thought was an eroded cinder cone, may simply be the intersection of two or more dikes. Alternatively, erosion may have obliterated the vent structure.

Ref. Billingsley, G.H., Stoffer, P.W. and Priest, S.S., 2012, Geologic map of the Tuba City 30’ x 60’ quadrangle, Coconino County, northern Arizona. US Geological Survey, Scientific Investigations Map 3227.

Posted M. Conway