Stop 25: Aspero

Leaving Cerro Purico we headed West to Cerro Aspero. Cerro Aspero is a post-glacial (<0.5 My) dome erupted after the Purico ignimbrites (1.3-1.0 My). Hawkesworth et al. (1982) found that mafic enclaves at Cerro Aspero were basaltic-andesite in composition, and therefore represent the most primitive compositions found in the Purico Complex.

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The host rock at Cerro Aspero, similar to the other domes of the Purico Complex is a crystal-rich dacite. Multiple mafic enclaves were collected at this location. The enclaves are fine grained, dark gray, and porphyritic. Crystals include quartz, plagioclase, and hornblende. Quartz crystals are relatively large (~10 mm) and have green reaction rims of clinopyroxene. The quartz crystals along with some of the plagioclase may not be primary. The crystals are sitting in a groundmass of glass, plagioclase, and hornblende.

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Rocks from Aspero also have large megacrysts of plagioclase that may represent the granitic basement beneath the Purico Complex.