OREGON STATE UNIVERSITY

Stop 2: Cerro Chuhuilla

Stop 2: Cerro Chuhuilla [21˚27’53.9”S, 67˚40’36.0”W]

The second goal was very similar to the first.  It is known that Cerro Chuhuilla is of roughly the same age as the Chuhuilla Ignimbrite.  However, was all of Cerro Chuhuilla erupted at the same time?  Was activity here continuous from the time of the Chuhuilla Ignimbrite to the eruption of the Pastos Grandes Ignimbrite?  Again, contact relationships were determined in the field, with precise dating of the lavas to be done back in the lab.  Multiple lavas were discovered on Cerro Chuhuilla; it was decided that much more detailed mapping will be needed in future field seasons.

In the Chuhuilla Ignimbrite, the pumice is crystal rich with large purple quartz (>5mm) and smaller (≤5mm) biotite.  The pumice also contains dense crystal rich enclaves of euhedral plagioclase, quartz, biotite, and amphibole (Salisbury et al., 2010.)

 

Cerro Chuhuilla and Cerro Chulucani

From the eastern moat of the caldera, Cerro Chuhuilla (right) and Cerro Chulucani (left) can be seen to the North.

Chuhuilla ignimbrite from Cerro Chuhuilla

From the eastern flanks of Cerro Chuhuilla, the Chuhuilla ignimbrite can be seen sprawling out towards the town of Alota, nearly due East of the dome.  Cerro Chuhuilla is not the source of the Chuhuilla Ignimbrite, rather it is part of the collapse scarp of the caldera that may date back to the eruption of the ignimbrite at 5.45Ma.