OREGON STATE UNIVERSITY

Stop 5: Carcote Ignimbrite

 

CARCOTE IGNIMBRITE

21°53'41.91"S, 68°34'44.01"W

The Carcoté Ignimbrite, 5.6 Ma is a high silica rhyolite that is visible from the road. The ignimbrite flowed from the Aucanquilcha area and overlies the Sifon Ignimbrite, 8.1 Ma. The Carcoté is a pumice-rich rhyolite, typically 5-6 m thick and has a white-gray color.

The pumice clasts show a sillar texture, indicative of vapor phase alteration. The post-depositional texture is created when the matrix recrystallizes and welds together as bubbles are stretched as they ascend up the conduit. This process results in silky pumice clasts. Lithic fragments are small (~ 2 cm) and rare and the matrix is fine-grained, crystal-poor (10-15%) and contains abundant plagioclase and biotite

Baker and Francis, 1978