Wednesday, November 9, 2016

The Leucite Hills

Boar's Tusk (foreground) and South Table Mesa

Pilot Butte
Or more formally known as the Leucite Hills Volcanic Province, this unique geological setting encompasses a huge area in Southwest Wyoming, including Table Mountain, Pilot Butte, Cross Mesa, Matthews Hill, Boar's Tusk, and more. We'll talk about mesas and buttes another day.

Geologically, it's made of some weird stuff. And that's saying something, for a geologist. Active around 3.4-1.4 million years ago, these rocks have been classified as Diopside-Leucite-Phlogopite Lamporites. Only because, for the most part, no one really understands how they formed or where they come from.

A lamporite is an super high potassium and magnesium composed igneous rock rich in elements that shouldn't naturally like to bond together. It forms from the melting of the mantle deeper than 100 miles down.  It's close cousins to kimberlites, which are magma pipes of mantle rock that can contain diamonds. But while kimberlites are much more common and therefore better studied, lamporites only sometimes have diamonds. And therefore don't get much love from industry, because who wants to spend a bunch on money studying some old rocks that probably won't turn up a profit? Right?

Boar's Tusk is thought to be the remains of a magma chamber that includes lamporite. There are then a number of lava flows around this area that are from this ancient volcanic activity that brought up more of these unusual rocks.


  1. So these are all part of the Yellowstone volcano?

  2. No. The Leucite Volcanic Province is a completely different tectonic environment. Yellowstone is made from a "hot spot". I should write about hot spots....