OREGON STATE UNIVERSITY

Stop 15: Caspana Ignimbrite

 

THE CASPANA IGNIMBRITE

22°15'31.86"S, 68°11'32.22"W

This location reveals a great exposure of the Caspana Ignimbrite, the uppermost unit of the Toconce Formation that is unique from the other ignimbrites that comprise the APVC. It has a distinctive orange color that makes it extremely identifiable and explains its name as the “Orange Sillar”. The Caspana contains rhyolitic and andesitic pumice clasts as well as mixed clasts, making it compositionally heterogeneous.

The Caspana plinian deposit contains little pumice and only minor amounts of crystals, specifically quartz and biotite. The plinian and the ignimbrite have the same source, which is likely an ancestral volcano that is now covered by Leon or Tocanao. At this location, lake sediments are exposed underlying the ignimbrite.

The Caspana lies between the Linzor tuff, 5.77 Ma and the Puripicar ignimbrite, 4.18 Ma. The best age estimate of the Caspana is somewhere between these dates. 

The group stopped for a group photo near Castle Rock and the Caspana Ignimbrite