OREGON STATE UNIVERSITY

Stop 2: The Lower Rio San Pedro Ignimbrite

 

THE LOWER RIO SAN PEDRO IGNIMBRITE

21°56'28.36"S, 68°31'50.38"W

A nice outcrop of the Lower Rio San Pedro Ignimbrite is on the road between the San Pedro area and Turi/Chao. 

 

Extracting Pumice from the Lower Rio San Pedro Ig. 

 

The Lower Rio San Pedro Ignimbrite, 9.66 Ma is a dense-micro vesicular dacite with abundant lithics and juvenile pumice. The ignimbrite contains quartz, plagioclase, copper-colored biotite, titanite/sphene, but the pumice is crystal-poor (~ 25%) in relation to the other ignimbrites in the area. The Lower Rio San Pedro is a simple cooling unit of two distinct flow units with an average thickness of 20 m along the Rio San Pedro.