OREGON STATE UNIVERSITY

Stop 1: Laguna Colorada Ignimbrite

Laguna Colorada Ignimbrite 22°13'20.17"S  67°24'49 .03"W

The Laguna Colorada ignimbrite defines the boundaries of the ignimbrite shield and can be observed in many places.  The best outcrops, however, are along the northern road from Laguna Colorada to Quetena at 22°13'20.17"S  67°24'49 .03"W and just off the southern road west of Quetena Grande near  22°21'27.29"S  67°23'53.27"W.

Driving through the Laguna Colorada ignimbrite

 

 

 

The Laguna Colorada ignimbrite is a fairly typical ignimbrite for the APVC.  The dominant mineralogy consists of plagioclase, quartz, biotite, and amphibole.  Small lithic and pumice  fragments are common throughout the ignimbrite, although their concentrations vary depending on location.

 

 

 


Lithic rich ignimbrite

 

 

Lithic fragments—mostly consisting of juvenile material—are common throughout the ignimbrite and are incredibly abundant in some facies such as this one.  Pumice fragments are small for the most part, with some larger pumice concentrated near the base of the ignimbrite. 

 

 

 

 

Laguna Colorada Welded Facies

 

 

 

 

The ignimbrite is highly welded near the domes.  Welding often occurs due to high temperatures and large volumes of ignimbrite erupted near the vent.  The welded blocks in this picture contain small fiamme, indicating compaction. You can see the welded ignimbrite in several locations on the northern road, particularly on one of several sharp curves near  22°13'5.09"S  67°26'6.72"W.