Intrusive Igneous Dike in Northwestern Arizona

January 10, 2019

Dike pair

Photographer: Stan Celestian 
Summary Author: Stan Celestian 

Along U.S. Route 93 in northwestern Arizona, just a bit south of Milepost 8, is a wonderful example of an intrusive igneous dike. The rock is of basaltic composition and has been classified as a camptonite. It was intruded into Pleistocene fanglomerate. The texture of the rocks of this dike shows a narrow chill margin that's only a few inches thick. Beyond this is a faint baked zone.

This outcrop has been a stop for many geology class field trips over the years. Unfortunately, the larger dike outcrop was removed when the highway was widened a few years ago. The image on the right has been color enhanced to bring out the baked zone around the dike (red saturation increased with Photoshop). However, the image on the left is untouched.

To see a hand specimen of a rock from this dike that also shows phenocrysts of kaersutite, click here. Photo taken on November 16, 2018.