The Chascon dome is another post-glacial dome (<0.5 My) erupted after the Purico ignimbrites (1.3-1.0 My). The bulk of Chascon is crystal-rich dacite. However, mafic enclaves are very prevalent (up to 20%).
The Chascon dome is dominated by porphyritc crystal-rich (30-35% xls) dacite containing plagioclase (<1-15 mm), quartz (<1-4 mm), hornblende (2-15 mm), and biotite (<1-5 mm) in a glassy groundmass. Rocks from Chascon also contain plagioclase megacrysts (>25 mm), andesitic enclaves, crystal-rich enclaves, and rhyolite. Plagioclase megacrysts may represent basement rocks which have interacted with the APMB. Samples CH09013-DHB (mafic enclave) and CH014-DHB (host) collected at this location.